EP4644590A1 - Method for manufacturing a fiber - Google Patents

Method for manufacturing a fiber

Info

Publication number
EP4644590A1
EP4644590A1 EP24305701.5A EP24305701A EP4644590A1 EP 4644590 A1 EP4644590 A1 EP 4644590A1 EP 24305701 A EP24305701 A EP 24305701A EP 4644590 A1 EP4644590 A1 EP 4644590A1
Authority
EP
European Patent Office
Prior art keywords
droplet
channel
equal
fiber
inferior
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24305701.5A
Other languages
German (de)
French (fr)
Inventor
Matthieu LABOUSSE
Joshua MCGRAW
Samuel HIDALGO-CABALLERO
Grégoire CLEMENT
Mathieu OLERON
Finn BOX
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Centre National de la Recherche Scientifique CNRS
Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI
Universite Paris Sciences et Lettres
Original Assignee
Centre National de la Recherche Scientifique CNRS
Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI
Universite Paris Sciences et Lettres
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Centre National de la Recherche Scientifique CNRS, Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI, Universite Paris Sciences et Lettres filed Critical Centre National de la Recherche Scientifique CNRS
Priority to EP24305701.5A priority Critical patent/EP4644590A1/en
Priority to PCT/EP2025/061827 priority patent/WO2025229057A1/en
Publication of EP4644590A1 publication Critical patent/EP4644590A1/en
Pending legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/38—Formation of filaments, threads, or the like during polymerisation
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/12—Stretch-spinning methods
    • D01D5/14—Stretch-spinning methods with flowing liquid or gaseous stretching media, e.g. solution-blowing

Definitions

  • the presentation relates to the field of manufacturing fibers and in particular polymer-based fibers that present a width inferior or equal to 10 ⁇ m.
  • a fiber presents an elongated shape along a main extension direction X.
  • the fiber presents a length L along the main extension direction X and a width W along a Y direction orthogonal to X, and a height H along a Z-direction orthogonal to both X et Y directions.
  • the width corresponds to a diameter of the fiber.
  • a fiber presents an elongated shape along the main extension direction X means that a first aspect ratio L/W and a second aspect ratio L/H are significantly superior to 1.
  • the dimension of an elongated fiber along its main extension direction is much larger than the dimension of the fiber in a transverse plane orthogonal to the main extension direction.
  • a third aspect ratio, H/W is also variable and can be much larger or much less than 1. When the third aspect ratio H/W is significantly different from 1, the fiber presents a ribbon shape.
  • Polymer-based fibers presenting a width or diameter inferior or equal to 10 ⁇ m are complex to manufacture.
  • a method for manufacturing a fiber comprising the following steps:
  • a device for manufacturing a fiber comprising:
  • a device 1 for manufacturing a fiber comprises a droplet generator 2 and a fluidic channel 3.
  • the device 1 comprises a microfluidic circuit 5 that includes both the droplet generator 2 and the fluidic channel 3.
  • the droplet generator 2 comprises a microfluidic pathway 29 that comprises two inlets 30 and 32 and one outlet 34.
  • the microfluidic pathway 29 extends in a plane defined by orthogonal directions Xa and Ya.
  • a first inlet 30 of the droplet generator is configured to receive a continuous phase 40 that comprises advantageously Krytox oil and 1% of surfactant.
  • Krytox oil can be used in place of Krytox oil, such as mineral oils or hydrocarbon derivatives.
  • the surfactant may be advantageously PFPE- COOH.
  • Other types of surfactants such as polysorbate 20, sorbitan monooleate, Sodium dodecyl sulfate (SDS), etc... may also used.
  • the droplet generator 2 comprises a continuous phase reservoir that is fluidically connected to the first inlet 30.
  • a second inlet 32 of the droplet generator is configured to receive a polymer phase 42 or, also generally called dispersed phase that comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and a proportion of water superior or equal to 10% and inferior or equal to 30%.
  • PEGDA Polyethylene glycol diacrylate
  • Other types of photopolymerisable polymer formulation may be used instead of PEGDA such as PVA, PEGDVE, PEGDMA, etc....
  • the polymer phase comprises light-curing polymers such as UV-curing polymers.
  • the polymer phase may advantageously comprise a photo-initiator 2-hydroxy-2-methylpropiophenone
  • photo-initiators such as Ethylanthraquinone, Ferrocene, Hydroxybenzophenone, acetophenone, etc., can also be used.
  • the polymer phase and the continuous phase correspond to non-miscible fluids.
  • the droplet generator 2 comprises a polymer phase reservoir that is fluidically connected to the second inlet 32.
  • the droplet generator 2 comprises a second pressure actuator 57 fluidically connected to the second inlet 32 through a second provider channel 59.
  • the second pressure actuator 57 is configured to apply a pressure Pd to the continuous phase contained in the second inlet 32.
  • the second pressure actuator 57 is fluidically connected to the polymer phase reservoir so as to provide the polymer phase to the second inlet 32.
  • the droplet generator 2 comprises a command unit 64 that is configured to control the pressure actuators 56 and 57.
  • the first pressure actuator 56 and the second pressure actuator 57 may be syringe pumps, pressure controllers or any device which is either pressure-controlled or flow-controlled....
  • the microfluic pathway presents a height measured in an orthogonal to directions Xa and Ya that is superior or equal to 10 ⁇ m and inferior or equal to 50 ⁇ m, for instance the height is equal to 28.5 ⁇ m.
  • the height of the microfluic pathway corresponds to the height of each channel comprised in the microfluic pathway, such as the first inlet channel 39.
  • the first inlet channel 39 extends up to an upper channel 43 and a lower channel 44 of the microfluidic pathway 29 and opens into both the upper channel 43 and the lower channel 44.
  • the upper channel 43 comprises :
  • the third portion 44C of the lower channel 44 and the third portion 43C of the upper channel 43 presents the same width 49 measured along the Xa direction.
  • the length 33 is advantageously comprised between 100 ⁇ m and 4000 ⁇ m, for instance equal to 1700 ⁇ m
  • the length 35 is advantageously comprised between 2000 ⁇ m and 20000 ⁇ m, for instance equal to 7665 ⁇ m
  • the width 49 is advantageously comprised between 50 ⁇ m and 500 ⁇ m, for instance equal to 150 ⁇ m.
  • the upper channel 43 and the lower channel 44 are arranged symmetrically with respect to the direction Xa.
  • the upper channel 43 and the lower channel 44 define between them a rectangular area 45.
  • the second inlet 32 is located in the rectangular area 45.
  • the second inlet 32 is located in the center of the rectangular area 45 with respect to the Ya direction.
  • the microfluidic pathway 29 comprises a second inlet channel 46 that connects fluidically the second inlet 32 to the rest of the microfluidic pathway 29.
  • the second inlet channel 46 extends from the second inlet 32 along the direction Xa.
  • the second inlet channel may alternatively comprise a central part that presents a sinuous shape, the central part being located between two straight parts that both extend along a main extension direction parallel to Xa.
  • the second inlet channel 46 presents a length 36 along this main extension direction which is the direction Xa or alternatively a variable direction in the case of sinuous central part.
  • the second inlet channel 46 presents a width 47 measured along the Ya direction.
  • the length 36 is advantageously comprised between 1000 ⁇ m and 20000 ⁇ m, for instance equal to 9225 ⁇ m.
  • the width 47 is advantageously comprised between 50 ⁇ m and 500 ⁇ m, for instance equal to 150 ⁇ m.
  • the first inlet channel 39 and the second inlet channel 46 have the same main extension direction so that the first inlet channel 39 and the second inlet channel 46 are aligned.
  • the second inlet channel 46 extends from the second inlet 32 along the direction Xa up to the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • the second inlet channel 46 opens into both the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • the microfluidic pathway 29 comprises an outlet channel 53 that connects fluidically the outlet 34 to the rest of the microfluidic pathway 29.
  • the outlet channel 53 extends from the outlet 32 in the opposite direction to Xa and presents a length 37 along this main extension direction.
  • the first inlet channel 39, the second inlet channel 46 and the outlet channel 53 have the same main extension direction so that they are all aligned.
  • the outlet channel 53 extends from the outlet 32 in the opposite direction to Xa up to the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • the outlet channel 53 opens into both the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • the outlet channel 53 comprises a collar 51 that connects the third portion 43C and the third portion 44C to the rest of the outlet channel.
  • the collar 51 presents a width 54 along the direction Ya that is smaller than a width 55 of the rest of the outlet channel 53 along the direction Ya.
  • the length 37 is advantageously comprised between 5000 ⁇ m and 20000 ⁇ m, for instance equal to 8000 ⁇ m.
  • the width 55 is advantageously comprised between 50 ⁇ m and 300 ⁇ m, for instance equal to 200 ⁇ m.
  • the width 54 is advantageously comprised between 20 ⁇ m and 70 ⁇ m, for instance equal to 50 ⁇ m.
  • the microfluidic pathway 29 defines a cross junction 80 where the second inlet channel 46, the third portion 43C of the upper channel 43, the third portion 44C of the upper channel 44 and the collar 51 of the outlet channel 53 meet.
  • the third portion 43C and the third portion 44C are facing each other and aligned on the Ya direction, and the second inlet channel 46 and the collar 51 of the outlet channel 53 are facing each other and aligned on the Xa direction.
  • the first inlet 30 is provided with the continuous phase 40 and the second inlet 32 is provided with the polymer phase 42
  • the droplet generator 2 is configured to create an interface 60 between the continuous phase and the polymer at the cross junction 80. More specifically, the interface 60 is located within the second inlet channel 46 so as to define a flow focusing junction.
  • the droplet generator 2 comprises a sensor 62 located close to the cross junction 80, the sensor 62 being configured to monitor the interface 60.
  • the sensor 62 is a camera configured to image the interface 60 and the cross junction 80.
  • the sensor 62 is a conductivity sensor configured to perform a conductivity measurement across the microchannel in the Ya direction at the meniscus 60.
  • a capacitance sensor configured to perform a capacitance measurement along the same direction.
  • an optical sensor configured to perform a local measurement of the optical density. Such an optical sensor may be different from a camera.
  • the sensor 62 is connected to the command unit 64.
  • the command unit 64 is configured to control the pressure actuators 56 and 57 possibly based on a signal provided by the sensor 62.
  • the dispersed phase When Pd is above this equilibrium value and below a second threshold, the dispersed phase is squeezed by the flow of continuous phase and breaks into droplets.
  • Different regimes exist in the microfluidic literature dripping, squeezing, jetting...) depending on the mechanism responsible for the pinch-off of the neck.
  • droplet production occurs in the squeezing regime.
  • the dispersed phase clogs the channel which gives rise to a pressure gradient inside the film of continuous phase in between the wall and the dispersed phase. When the latter fills the exit channel over a sufficient length, the pressure gradient becomes strong enough to deform and break the dispersed phase.
  • the dispersed phase forms a jet inside the outlet channel 53: this is commonly referred to as the jetting regime in microfluidic literature Note that in the illustrated configuration of figure 3 , the jet remains stable over the whole length of the exit channel.
  • the droplet generator 2 as described above can be used to implement a step S2 of generating a single droplet.
  • the step S2 is a step of a fiber generation process P which is described further in the description.
  • step S2 To realize this step S2 and generate a single droplet, the following substeps can be implemented :
  • the process P can comprise the optional steps :
  • Such monitoring and adjustment greatly improve the stability of the interface 60 and enable to generate single droplet in a much more efficient way.
  • Figure 4 illustrates this temporal sequence wherein curve 66 corresponds to the pressure applied to the continuous phase and curve 68 corresponds to the pressure applied to the polymer phase.
  • Figure 6 illustrates the generation of a single droplet obtained thanks to such a pressure pulse application.
  • Image 71 of figure 5 corresponds to the situation before the application of the pulse: the polymer phase is located inside the second input channel 46 and the interface 60 is stable.
  • Image 72 of figure 5 corresponds to the situation during the application of the pulse: the polymer phase is projected out of the second input channel 46 up to the outlet channel 53.
  • the polymer phase forms a liquid neck between the second inlet channel 46 and the collar 51 and further in the outlet channel the polymer phase forms a curved volume.
  • the curved volume, the liquid neck and the rest of the polymer phase inside the second input channel 46 form a continuous polymer phase.
  • the liquid neck stops and is compressed by the continuous phase, the curved volume is separated from the rest of the polymer phase inside the second input channel 46 so as to generate a single droplet 38.
  • the step T6 leads to a step T7 of extracting a single droplet from the polymer phase.
  • the volume of the droplet is controlled by the pulse amplitude ⁇ P, its duration ⁇ t and the pressures Pc and Pd.
  • the microfluidic droplet generator may first be calibrated.
  • a basic calibration method C may be implemented before the implementation of the step S2.
  • the basic calibration method C comprises the following steps:
  • Step C2 may be achieved by a balance of pressures based on the following equality: the difference in pressure between the first inlet 30 and the pressure at junction 48 is equal to the difference in pressure between the second inlet 32 and the Laplace pressure at the meniscus 60.
  • the Laplace pressure Pl depends on the surface tension between the continuous phase 42 and the dispersed phase 42, the channel height and the width 47 of the second inlet channel 46.
  • Step C5 may be achieved by optical observation.
  • the sensor 62 may advantageously comprise a camera.
  • the basic calibration method may advantageously be implemented for a plurality of different values of the pulse amplitude ⁇ P.
  • microfluidic droplet generator may be further calibrated by :
  • phase diagrams may be built.
  • a phase diagram may be associated with each candidate value of Pc, and represent schematically the determined values of the pulse amplitude ⁇ P and of determined values of the pulse length ⁇ t that lead to the generation of a single droplet of the polymer phase.
  • figure 9 An example of a phase diagram is given in figure 9 , for four different sets of values of pressure of the continuous phase Pc and pulse amplitude ⁇ P, figure 9 illustrates values of pulse length ⁇ t (x-axis) for which a single droplet is generated. The volume of the droplet is given on the y-axis. This diagram shows additionally that the volume increases when the pulse amplitude ⁇ P increases and/or when the pulse length ⁇ t increases.
  • the control of the pressure actuators so as to stabilize the interface is stopped during the pressure pulse.
  • microfluidic droplet generating devices may be used, for instance a device based on a T-junction. Pressure pulses as previously described may be used to generate a single droplet in these alternative microfluidic droplet generating devices. Analogous calibration methods may also be implemented to identify pressure pulse parameters that lead to a single droplet generation.
  • the polymer phase may be generated during a first step S1 of the process P.
  • the polymer phase 42 comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and 10% of water. Other types of photopolymers may be used instead of PEGDA such as PVA, PEGDVE, PEGDMA, etc ...
  • the polymer phase comprises light-curing polymers such as UV-curing polymers.
  • the polymer phase may advantageously comprise a photo-initiator 2-hydroxy-2-methylpropiophenone.
  • Other photo-initiators such as Ethylanthraquinone, Ferrocene, Hydroxybenzophenone, acetophenone, etc., can also be used. In the case of 2-hydroxy-2-methylpropiophenone, 5% is placed in the mixture.
  • the polymer phase may comprise, in addition to light-curing polymers and water, functional material configured to modify physical-chemical properties of the polymer phase.
  • Such functional material are in particular conductive material, magnetic material, catalytic material, piezoelectric material, fluorophore, or electrets....
  • the functional material is mixed with light-curing polymers.
  • the conductive material may comprise carbon nanotubes, Silver Nanoparticles, reduced graphene oxide or PEDOT:PSS (polymer mixture of polystyrene sulfonate and poly(3,4-ethylenedioxythiophene)).
  • Carbon nanotubes (CNT) may be single walled CNT or multiwalled CNTs.
  • the generation of the polymer phase may comprise:
  • an optional previous step of adding a polar solvent to the liquid phase can be implemented.
  • a further step after the ultrasonication step of removing the polar solvent by evaporation is necessary to obtain a liquid phase that fulfills the initial polymer solution conditions.
  • the fluidic channel 3 extends along a transport axis 9 from an inlet 6 of the fluidic channel 3 to an outlet 15 of the fluidic channel 3.
  • the fluidic channel comprises advantageously walls in PDMS (Polydimethylsiloxane).
  • the fluidic channel 3 extends in a main plane defined by orthogonal directions Xb and Yb.
  • the transport axis 9 is parallel to the direction Xb.
  • the fluidic channel 3 presents a height measured in an orthogonal to directions Xb and Yb that is superior or equal to 10 ⁇ m and inferior or equal to 200 ⁇ m, for instance the height is equal to 28.5 ⁇ m.
  • the height of the fluidic channel is the same as channel 3 and it is superior or equal to 10 ⁇ m and inferior or equal to 200 ⁇ m.
  • the inlet 6 of the fluidic channel may be advantageously fluidically connected to the outlet 34 of the droplet generating device 2.
  • the fluidic channel 3 presents a width (or more generally a dimension) measured along the direction Yb and orthogonally to the transport axis 9.
  • the width (or dimension) of the fluidic channel is variable along the transport axis 9.
  • the inlet 6 and the outlet 15 of the channel correspond to straight channel so that in the main plane walls of the inlet 6 and the outlet 15 of the fluidic channel 3 are parallel to the transport axis 9.
  • the width of the fluidic channel 3 is constant in the inlet 6 and the outlet 15.
  • the width of the fluidic channel 3 in the inlet 6 and the outlet 15 is inferior or equal to 500 ⁇ m.
  • the fluidic channel 3 comprises three different portions located along the direction defined by the transport axis between the inlet 6 and the outlet 15.
  • the fluidic channel 3 comprises a first portion 7 that is contiguous to the inlet 6.
  • the first portion 7 is contiguous to the inlet 6 means that the wall of the fluidic channel is continuous from the inlet 6 to the first portion 7.
  • the same meaning of the term "contiguous" is used further in the description.
  • the first portion 7 has a funnel shape so that the dimension 8 of the channel in the first portion continuously decreases along the transport axis 9.
  • the first portion 7 extends on a length 20 superior or equal to 200 ⁇ m and inferior or equal to 1000 ⁇ m measured along the transport axis 9.
  • the fluidic channel 3 comprises a second portion 10 that is contiguous to the first portion 7.
  • the second portion 10 has a straight shape so that the dimension 11 of the channel in the second portion 10 is constant along the transport axis 9.
  • the second portion 10 extends on a length 22 superior or equal to 400 ⁇ m and inferior or equal to 4000 ⁇ m measured along the transport axis 9.
  • the dimension 11 is superior or equal to 2 ⁇ m and inferior or equal to 100 ⁇ m.
  • the dimension may take any value between 2 ⁇ m and 100 ⁇ m, for instance 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m.
  • the dimension 11 may take any value between 2 ⁇ m and 12 ⁇ m, for instance 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m and 11 ⁇ m.
  • the fluidic channel 3 comprises a third portion 12 that is contiguous to the second portion 10.
  • the third portion 12 has a funnel shape, the dimension 13 of the channel continuously increasing along the transport axis 9.
  • the third portion 12 extends on a length 24 superior or equal to 200 ⁇ m and inferior or equal to 1000 ⁇ m measured along the transport axis 9.
  • the fluidic channel may be centered on the transport axis 9.
  • the first portion 7 presents a funnel shape so that an angle 16 of a wall of the first portion 7 with respect to the transport axis 9 is inferior or equal to 30°, and advantageously inferior or equal to 7°.
  • a ratio (R1) of a decrease ( ⁇ w1) of the dimension (width) of the channel in the first portion over a distance ( ⁇ L1) along the transport axis so that R1 ⁇ w1/ ⁇ L1 is inferior or equal to 1 and advantageously inferior or equal to 0.24.
  • R1 is equal to twice the tangent of the angle 16.
  • the decrease ( ⁇ w1) of the dimension (width) of the channel is determined between two points of the wall of the fluidic channel in the first portion before entering the zone of constant dimension 11.
  • the two points are separated along the transport axis 9 by a distance ⁇ L1.
  • the fluidic channel presents a first width wA and at the second point the fluidic channel presents a second width wB. If the second point is closer to the outlet 15 and the first point closer to the inlet 6, then wB ⁇ wA and R is equal to the ratio (wA-wB)/ ⁇ L1.
  • the angle 16 of a wall of the first portion 7 with respect to the transport axis 9 can be superior or equal to 2° and advantageously superior or equal to 4°.
  • the ratio (R1) of the decrease ( ⁇ w1) of the dimension (width) of the channel in the first portion over the distance ( ⁇ L1) along the transport axis is superior or equal to 0.07 and advantageously superior or equal to 0.14.
  • the third portion 12 presents a funnel shape so that an angle 18 of a wall of the third portion 12 with respect to the transport axis 9 is inferior or equal to 32°.
  • a ratio (R2) of an increase ( ⁇ w2) of the dimension (width) of the channel in the third portion 12 over a distance ( ⁇ L2) along the transport axis so that R2 ⁇ w2/ ⁇ L2 is inferior or equal to 1 and advantageously inferior or equal to 1.2.
  • R2 is equal to twice the tangent of the angle 18.
  • the increase ( ⁇ w2) of the dimension (width) of the channel is determined between two points of the wall of the fluidic channel in the third portion.
  • the two points are separated along the transport axis 9 by a distance ⁇ L2.
  • the fluidic channel presents a first width wC and at the second point the fluidic channel presents a second width wD. If the second point is closer to the outlet 15 and the first point closer to the inlet 6, then wD>wC and R2 is equal to the ratio (wD-wC)/ ⁇ L2.
  • the angle 18 of a wall of the third portion 12 with respect to the transport axis 9 can be superior or equal to 2° and advantageously superior or equal to 4°.
  • the ratio (R2) of the increase ( ⁇ w2) of the dimension (width) of the channel in the third portion 12 over the distance ( ⁇ L2) along the transport axis is superior or equal to 0.07 and advantageously superior or equal to 0.14.
  • the angle of a wall of the second portion 10 with respect to the transport axis 9 is equal to zero as the second portion is a straight portion.
  • the angle presents a continuous variation in the first portion 7, the second portion 10 and the third portion 12.
  • the angle of a wall of the fluidic channel with respect to the transport axis 9 is equal to zero in the second portion 10 and takes continuously positive values from the second portion to the first portion or from the second portion to the third portion.
  • the device 1 for manufacturing a fiber comprises also a light source 14 configured to expose the second portion to a light radiation.
  • the light source 14 may be a UV light source.
  • the light source emits light in a specific band width and provides a light energy density in the second portion 10.
  • the light source is configured to not emit light towards the first portion or the third portion.
  • the device 1 for manufacturing a fiber may comprise complementary channels 80 and 82 that open into the fluidic channel at a transition between the second portion 10 and the third portion 13.
  • the complementary channels are parallelly disposed with respect to the transport axis 9.
  • the complementary channels are curved so that the main direction of extension of each complementary is variable in the plane defined by directions Xb and Yb.
  • the main direction of extension of each complementary channel becomes more and more parallel to the transport axis 9 as the complementary channel approaches the fluidic channel 3.
  • an angle between the transport axis 9 and the main direction of extension of a complementary channel at the transition of the complementary channel and the fluidic channel 3 is inferior or equal to 5° and preferably between 0° and 4°.
  • complementary channels are configured to be filled with continuous phase and to carry complementary flows 81, 83.
  • the complementary flow 81, 83 is directed along the main direction of extension of the complementary channel and directed to enter the fluidic channel and flow from the second portion towards the third portion.
  • the device 1 for manufacturing a fiber can be used to implement a process P to manufacture a fiber.
  • a process P to manufacture a fiber.
  • the first step S1 and the second step S2 of the process P are evoked previsously in the description and correspond respectively to the generation of the polymer phase and the generation of a single droplet.
  • the first step S1 may be preceded by the steps of the calibration method C of the droplet generator.
  • a third step S3 of the process P comprises moving the single droplet 38 containing light-curing polymers from the outlet 34 of the droplet generator 2 to the inlet 6 of the fluidic channel 3, for instance through the microfluidic circuit 5 that may include both the droplet generator 2 and the fluidic channel 3.
  • a main flow 70 can be provided, during a sub-step S3A, along the transport axis 9 in the continuous phase through the fluidic channel 3 which is filled with the continuous phase 40.
  • the third step S3 may be preceded by the steps of the calibration method F of the fluidic channel which is presented further in the description.
  • a fourth step S4 of the process P comprises moving the single droplet 38 in the first portion 7 of the fluidic channel 3 along the transport axis.
  • the width of the fluidic channel continuously decreases and the shape of the droplet continuously changes.
  • the width of the droplet decreases in the direction Yb and the length of the droplet expands in the direction Xb.
  • Moving the single droplet 38 in the first portion 7 leads to the sub-step S4A of decreasing continuously a dimension of the droplet measured along a transverse direction orthogonal to the transport axis.
  • a main flow 70 can be provided along the transport axis 9 in the continuous phase through the fluidic channel 3 which is filled with the continuous phase 40.
  • Step S5 the droplet 38 is transported in the second portion 10 of the channel 3. As the single droplet 38 progresses in the second portion the width of the fluidic channel reaches a minimum value. The width of the droplet decreases and reaches a minimum value. Steps S4 and S5 are schematically illustrated in parts 74 and 75 of figure 6 .
  • the wavelength of the light source and the density of light energy provided in the second junction are adapted to the type of light-curing polymers contained in the droplet and the density of light-curing polymers contained in the droplet, so as to cure the droplet.
  • the wavelength of the light source can be in the UV range, for example around 365 nm.
  • the polymer solution reticulates and solidifies when exposed to the light of the light source 14.
  • the polymer solution retains the shape of the second portion 10.
  • the size and shape of the droplet are controlled by the geometry of the channel. As the droplet is cured in the second portion, the size and shape of the droplet in the second section is retained. By controlling the size and shape of the second section, it is thus possible to manufacture fibers presenting a width inferior or equal to 10 ⁇ m and/or a rectangular cross-section.
  • the droplet 38 is surrounded in the second portion by a thin, continuous-phase layer of that facilitates the movement of the droplet and once cured, the movement of the fiber.
  • the walls of the fluidic channel 3 are made of PDMS, the presence of the thin continuous-phase layer is promoted by a molecular oxygen diffusion through the PDMS. This diffusion leaves around the droplet/fiber an unpolymerized oxygen inhibition layer.
  • Adding 10% of deionized water to the polymer solution prevents further wetting. 10% of deionized water was used for the experiments. 5% of deionized water corresponds to a minimum amount of water to prevent wetting issues. 30% of deionized water corresponds to a maximum value above which no polymerization is achievable.
  • the fiber does not stop in the second portion and keeps moving along the transport axis 9.
  • Exposing the droplet to the light radiation may comprise advantageously providing a light energy density to the droplet superior or equal to a predetermined energy density threshold, and maintaining the droplet in the second portion during a duration superior or equal to a predetermined duration threshold.
  • the elastic properties thus depend on the speed at which the droplet crosses the light-illuminated zone.
  • the speed can be controlled by the pressures applied to the continuous phase.
  • the fluidic channel 3 can be calibrated previously to implement the method P.
  • phase diagrams as a function of the width of the second portion, the power of the light source, the pressures applied to the continuous phase and polymer phase during the droplet generation.
  • a seventh step S7 one can move the droplet 38 from the second portion 10 to the third portion 12.
  • This fifth step corresponds to the extraction of the fiber from the thin second portion.
  • the funnel shape of the third portion enables to prevent clogging of the fluidic channel 5 and breakage of the fiber. To the contrary, an abrupt transition will lead to a sudden deceleration of the head of the fiber when it exits the second portion, so that the rest of the fiber is also slowed down. The rest of the fiber will consequently spend more time in the light-exposed second portion. The rest of the fiber may reach a level of curation significantly higher than the head of the fiber, leading to an inhomogeneous fiber and possibly to a clogging of the second portion.
  • the funnel shape of the third portion enables a more progressive deceleration that prevents clogging and the production of more homogeneous fibers.
  • the fiber exits the second section it experiences slower velocities that can lead to channel clogging, especially in the case of a thin fiber.
  • the funnel shape of the third portion prevents clogging as it limits this slowdown and simplifies the extraction of the rest of the fiber out of the second section.
  • the step S7 of the process P comprises a substep S7A of adding complementary continuous-phase flows in the third portion so as to align the fiber with the transport axis.
  • the complementary continuous phase flows 81 and 83 help the soft fiber to exit the second portion 10 without deforming and speed up the step S7 of moving the single droplet 38 in the third portion 12, that is extracting the fiber from the second portion 10.
  • active molecules may include enzymes, conductive dispersions of nanoparticles, magnetic materials, piezoelectric materials, catalytic materials, electrets, fluorophore etc., ... Covering the fiber with active molecules can be realized thanks to the initial mixture preparation.
  • a homogeneous dispersion of the initial mixture preparation helps to locate the active molecules at the surface of the extruded fiber.
  • a homogeneous dispersion may be obtained using an ultrasonication of the mixture in the dispersed phase 42, or using surface chemical modifications of the conductive phase. This latter can be, for example, grafted polymer chains.
  • a method F for calibrating the fiber channel may comprise the following steps.
  • a first step F1 the operator selects a set of pressure pulse parameters (values of Pc, corresponding equilibrium value of Pd, pulse amplitude ⁇ P and pulse duration ⁇ t), for which a single droplet is obtained using the droplet generator 2.
  • a second step F2 the operator selects a set of candidate values of the width 11 of the second portion 10. The operator will thus need to dispose of different fluidic channels that each presents one of the candidate values of the width 11. Each fluidic channel may be fluidically connected to the droplet generator as previously mentioned.
  • a third step F3 the operator selects a set of candidate values of power of the light source.
  • the operator will thus need to dispose means to modify the power of the light source so as to be able to provide the second portion of the channel with each candidate value.
  • the light source may be naturally controlled in power thanks to a variator, or alternatively calibrated attenuator windows may be disposed between the light source and the second portion.
  • Other means to modify the power of the light source may include pulse width modulation via an electronic trigger and spectral filters.
  • the operator implements a droplet generation and a fiber generation by connecting the outlet of the droplet generator to the inlet of the fluidic channel, generating in the droplet generator a single droplet based on the set of pressure pulse parameters, moving the single droplet through the fluidic channel from the first portion to the second portion, exposing the droplet in the second portion to a candidate power of the light source, and evaluating if a fiber is efficiently manufactured at the output of the fluidic channel.
  • a fifth step F5 the operator may repeat steps F4 for different sets of pressure pulse parameters.
  • a sixth step F6 the operator determines each case an exposure time of the droplet to the light source and a light energy density at which the droplet was exposed to the light source.
  • the exposure time depends on the velocity of the droplet inside the second portion, this velocity depending itself on the pressure Pc and the geometry of the fluidic channel.
  • the light energy density depends on the power of the light source and the geometry of the second portion of the fluidic channel.
  • a seventh step F7 the operator determines a minimum exposure time above which fibers can be obtained. This determination may be limited to a specific geometry of the fluidic channel, for instance to a specific width of the second portion.
  • a seventh step F8 the operator determines a minimum light energy density above which fibers can be obtained. This determination may be limited to a specific geometry of the fluidic channel, for instance to a specific width of the second portion.
  • This calibration enables also to identify a minimum light energy density above which fibers can be obtained. This minimum light energy density can then be used in the process to provide a light energy density superior or equal to this minimum light energy density corresponding then to a predetermined energy density threshold.
  • substeps S6A and S6B may be advantageously to step S6 of exposing the droplet to the curing light provide by the light source.
  • the light source provides a light energy density to the droplet superior or equal to the predetermined energy density threshold.
  • the manufacturing device 1 and the manufacturing method P enables to manufacture fibers comprising curing polymers and in particular light-curing material.
  • larger widths may also be manufactured, for instance fibers presenting a width superior or equal to 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 50 ⁇ m and even 100 ⁇ m can be manufactured.
  • the fiber presents a length L along the main extension direction X and a width W along a Y direction orthogonal to X, and a height H along a Z-direction orthogonal to both X and Y directions.
  • the fiber has a rectangular cross-section when the shape of the fiber is rectangular in a plane Y Z orthogonal to the main extension direction X.
  • the transverse aspect ratio of the fiber corresponds to the ratio H/W. When the third aspect ratio H/W is different from 1, the fiber presents a ribbon shape.
  • the fiber presents a transverse rectangular cross-section when the second portion 10 presents a rectangular cross-section.
  • the cross section of the second portion is given by the ratio of the width 11 of the second portion 10 by the height of the second portion 10.
  • the height of the second portion 10 corresponds to the height of the fluidic channel and is measured in the direction orthogonal to both directions Xb and Yb.
  • the second portion 10 presents a height superior or equal to 10 ⁇ m and inferior or equal to 200 ⁇ m, for instance the height is equal to 28.5 ⁇ m.
  • the height of the second portion 10 may be equal to 20 ⁇ m, 30 ⁇ m, 40 ⁇ m, 50 ⁇ m, 60 ⁇ m, 80 ⁇ m, 100 ⁇ m, 120 ⁇ m,
  • the aspect ratio of the rectangular cross-section of the second portion 10 may be comprised between 1.25 and 20.
  • the aspect ratio H/W is equal to 1.5, 2, 3, 3.5, 4, 4.5, 5, 7, 10, 15, 20, 25 or 30.
  • the aspect ratio of the rectangular cross-section of the second portion 10 gives the aspect ratio H/W of the fiber.
  • the length of the fiber may be as small as 25 ⁇ m and as large as 1cm.

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Abstract

This invention relates to a method (P) for manufacturing a fiber, the method comprising:
- (S2) generating a single droplet containing light-curing polymers,
- (S4) moving the droplet in a first portion of a fluidic channel, a dimension of the channel in the first portion continuously decreasing along a transport axis of the droplet,
- (S5) moving the droplet in a second portion of the channel, the second portion being contiguous to the first portion, the dimension of the channel being constant in the second portion,
- (S6) exposing in the second portion the droplet to a light radiation so as to at least partially cure the droplet into a fiber, and
- (S7) moving the fiber in a third portion of the channel, the third portion being contiguous to the second portion, the dimension of the channel in the third portion continuously increasing along the transport axis.

Description

    FIELD OF THE INVENTION
  • The presentation relates to the field of manufacturing fibers and in particular polymer-based fibers that present a width inferior or equal to 10 µm.
    • STATE OF THE ART
  • A fiber presents an elongated shape along a main extension direction X. The fiber presents a length L along the main extension direction X and a width W along a Y direction orthogonal to X, and a height H along a Z-direction orthogonal to both X et Y directions. When the fiber has a circular cross-section orthogonally to the main extension direction X, the width corresponds to a diameter of the fiber. A fiber presents an elongated shape along the main extension direction X means that a first aspect ratio L/W and a second aspect ratio L/H are significantly superior to 1. In other words, the dimension of an elongated fiber along its main extension direction is much larger than the dimension of the fiber in a transverse plane orthogonal to the main extension direction. A third aspect ratio, H/W is also variable and can be much larger or much less than 1. When the third aspect ratio H/W is significantly different from 1, the fiber presents a ribbon shape.
  • Most of the fibers have a circular cross-section. Producing filaments with different cross-section, such as ribbons that present a rectangular cross-section, can be of interest for many technological applications.
  • Polymer-based fibers presenting a width or diameter inferior or equal to 10 µm are complex to manufacture.
  • There is a need for a process for manufacturing polymer-based fibers presenting a width inferior or equal to 10 µm, especially fibers with a rectangular cross-section.
    • DISCLOSURE OF THE INVENTION
  • It is an object of this presentation to provide a process for manufacturing polymer-based fibers presenting a width inferior or equal to 10 µm, especially fibers with a rectangular cross-section.
  • To that end, it is provided a method for manufacturing a fiber, the method comprising the following steps:
    • generating a single droplet containing light-curing polymers,
    • moving the droplet in a first portion of a fluidic channel, the first portion having a funnel shape so that a dimension of the channel in the first portion continuously decreases along a transport axis of the droplet,
    • moving the droplet in a second portion of the channel, the second portion being contiguous to the first portion, the dimension of the channel being constant in the second portion,
    • exposing in the second portion the droplet to a light radiation so as to at least partially cure the droplet into a fiber, and
    • moving the fiber in a third portion of the channel, the third portion being contiguous to the second portion, the third portion having a funnel shape so that the dimension of the channel in the third portion continuously increases along the transport axis.
  • Such method is advantageously and optionally completed by the following features taken singly or in combination:
    • a dimension of the droplet measured along a transverse direction orthogonal to the transport axis is inferior or equal to 500 µm, the dimension being inferior or equal to 12 µm in the second portion;
    • moving the droplet in the first portion comprises decreasing continuously a dimension of the droplet measured along a transverse direction orthogonal to the transport axis, a ratio of a decrease of the dimension of the droplet over a transport distance of the droplet being inferior or equal to 1 and advantageously inferior or equal to 0.24;
    • generating the single droplet comprises forming an interface between a polymer phase and a continuous phase in a microfluidic droplet generating device, such as a flow-focusing or T-junction, the polymer phase containing light-curing polymers, and applying a pressure pulse to the polymer phase so as to eject a single droplet from the polymer phase into the continuous phase;
    • generating the single droplet comprises monitoring the interface, and adjusting a pressure of the polymer phase and a pressure of the continuous phase so as to stabilize the interface;
    • moving the droplet in the first portion comprises providing a main flow of a continuous phase along the transport axis in the fluidic channel, moving the fiber in the third portion comprising adding complementary continuous-phase flows in the third portion so as to align the fiber with the transport axis;
    • exposing the droplet to the light radiation comprises providing a light energy density to the droplet superior or equal to a predetermined energy density threshold, and maintaining the droplet in the second portion during a duration superior or equal to a predetermined duration threshold;
    • generating the single droplet comprises extracting the single droplet from a polymer phase, the method further comprising a step of generating the polymer phase that comprises
  • mixing light-curing polymers and a functional material in a liquid phase, the functional material being configured to modify physical-chemical properties of the polymer phase;
    • the functional material is a conductive material;
    • the conductive material comprises carbon nanotubes, the step of generating the polymer phase comprising the following substeps: adding a polar solvent to the liquid phase, the polar solvent preferably being dimethylformamide, exposing the liquid phase to ultrasound waves advantageously for a duration superior or equal to 30 minutes and inferior or equal to 6 hours, and evaporating the polar solvent out of the liquid phase; and
    • a step of covering the fiber with active molecules, such as enzymes and other catalytic materials.
  • It is also provided a device for manufacturing a fiber, the device comprising:
    • a droplet generator configured to generate a single droplet,
    • a fluidic channel comprising:
      • --a first portion having a funnel shape, a dimension of the channel continuously decreasing along a transport axis,
      • -- a second portion contiguous to the first portion, the dimension of the channel being constant in the second portion,
      • -- a third portion contiguous to the second portion, the third portion having a funnel shape, the dimension of the channel continuously increasing along the transport axis, and
    • a light source configured to expose the second portion to a light radiation.
  • Such device is advantageously and optionally completed by the following features taken singly or in combination:
    • a microfluidic circuit including the droplet generator and the fluidic channel, wherein a width of the channel measured along a transverse direction orthogonal to the transport axis is inferior or equal to 500 µm, the width of the channel being inferior or equal to 12 µm in the second portion;
    • the funnel shape of the first portion is centered on the transport axis, an angle of a wall of the first portion with respect to the transport axis being inferior or equal to 30°, and advantageously inferior or equal to 7°, the funnel shape of the third portion being centered on the transport axis, an angle of a wall of the third portion with respect to the transport axis being inferior or equal to 32°; and
    • the droplet generator comprises a microfluidic droplet generating device, such as a flow-focusing or a T-junction, the microfluidic droplet generating device being configured to provide an interface between a polymer phase and a continuous phase, the device comprising a sensor configured to monitor the interface, the droplet generator comprising pressure actuators configured to adjust a pressure of the polymer phase and a pressure of the continuous phase, the device comprising a command unit configured to command the actuators so as to stabilize an image of the interface.
  • It is finally provided a fiber comprising light-cured polymers, the fiber presenting a width inferior or equal to 12 µm.
  • Such fiber is advantageously and optionally completed by the following features taken singly or in combination:
    • the fiber presenting a length along a main extension direction, a width along a first transverse direction orthogonal to the main extension direction and a height along a second transverse direction orthogonal to the main extension direction and the first transverse direction, the length being superior to the height, the height being superior to the width, the fiber having a rectangular cross-section in a plane defined by the first transverse direction and the second transverse direction, a transverse aspect ratio corresponding to a ratio of the height above the width being superior or equal to 1.25 and inferior or equal to 20; and
    • the fiber being manufactured by a method as previously mentioned.
    DESCRIPTION OF THE FIGURES
  • Further features and advantages will be apparent from the following description, which is purely illustrative and non-limiting, and should be read in conjunction with the appended drawings on which :
    • figure 1 is a schematic representation of a device for manufacturing a fiber;
    • figure 2 is a schematic representation of a fluidic channel of the device;
    • figure 3 is a schematic representation of a droplet generator of the device;
    • figure 4 is a schematic representation of a pressure pulse applied to the droplet generator;
    • figure 5 is a schematic representation of a droplet generation;
    • figure 6 is a schematic representation of a fiber generation;
    • figure 7 is a schematic representation of a phase diagram of a fiber generation;
    • figure 8 is a schematic representation of a process for manufacturing a fiber; and
    • figure 9 is a schematic representation of a phase diagram of a droplet generation.
    DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
  • In correspondence with figure 1, a device 1 for manufacturing a fiber comprises a droplet generator 2 and a fluidic channel 3.
  • Advantageously, the device 1 comprises a microfluidic circuit 5 that includes both the droplet generator 2 and the fluidic channel 3.
    • Droplet generator
  • In correspondence with figure 3, the droplet generator 2 comprises a microfluidic pathway 29 that comprises two inlets 30 and 32 and one outlet 34. The microfluidic pathway 29 extends in a plane defined by orthogonal directions Xa and Ya.
  • A first inlet 30 of the droplet generator is configured to receive a continuous phase 40 that comprises advantageously Krytox oil and 1% of surfactant. Other types of oil can be used in place of Krytox oil, such as mineral oils or hydrocarbon derivatives. The surfactant may be advantageously PFPE- COOH. Other types of surfactants such as polysorbate 20, sorbitan monooleate, Sodium dodecyl sulfate (SDS), etc... may also used.
  • The droplet generator 2 comprises a continuous phase reservoir that is fluidically connected to the first inlet 30.
  • The droplet generator 2 comprises a first pressure actuator 56 fluidically connected to the first inlet 30 through a first provider channel 58. The first pressure actuator 56 is configured to apply a pressure Pc to the continuous phase contained in the first inlet 30. The first pressure actuator 56 is fluidically connected to the continuous phase reservoir so as to provide the continuous phase to the first inlet 30.
  • A second inlet 32 of the droplet generator is configured to receive a polymer phase 42 or, also generally called dispersed phase that comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and a proportion of water superior or equal to 10% and inferior or equal to 30%. Other types of photopolymerisable polymer formulation may be used instead of PEGDA such as PVA, PEGDVE, PEGDMA, etc.... The polymer phase comprises light-curing polymers such as UV-curing polymers. In addition to light-curing polymers, the polymer phase may advantageously comprise a photo-initiator 2-hydroxy-2-methylpropiophenone Other photo-initiators such as Ethylanthraquinone, Ferrocene, Hydroxybenzophenone, acetophenone, etc., can also be used.
  • The polymer phase and the continuous phase correspond to non-miscible fluids.
  • The droplet generator 2 comprises a polymer phase reservoir that is fluidically connected to the second inlet 32.
  • The droplet generator 2 comprises a second pressure actuator 57 fluidically connected to the second inlet 32 through a second provider channel 59. The second pressure actuator 57 is configured to apply a pressure Pd to the continuous phase contained in the second inlet 32. The second pressure actuator 57 is fluidically connected to the polymer phase reservoir so as to provide the polymer phase to the second inlet 32.
  • The droplet generator 2 comprises a command unit 64 that is configured to control the pressure actuators 56 and 57.
  • The first pressure actuator 56 and the second pressure actuator 57 may be syringe pumps, pressure controllers or any device which is either pressure-controlled or flow-controlled....
  • The microfluidic pathway 29 comprises a first inlet channel 39 that connects fluidically the inlet 30 to the rest of the microfluidic pathway 29. The first inlet channel 39 has a main extension direction parallel to the direction Xa and presents a length 31 along this main extension direction. The length 31 is advantageously comprised between 900 µm and 1000 µm, for instance equal to 970 µm.
  • The microfluic pathway presents a height measured in an orthogonal to directions Xa and Ya that is superior or equal to 10 µm and inferior or equal to 50 µm, for instance the height is equal to 28.5 µm.
  • The height of the microfluic pathway corresponds to the height of each channel comprised in the microfluic pathway, such as the first inlet channel 39.
  • The first inlet channel 39 extends up to an upper channel 43 and a lower channel 44 of the microfluidic pathway 29 and opens into both the upper channel 43 and the lower channel 44.
  • The upper channel 43 comprises :
    • a first portion 43A extending from the first inlet channel 39 along the direction Ya and presenting a length 33 along the direction Ya,
    • a second portion 43B extending from the first portion 43A along the direction Xa and presenting a length 35 along the direction Xa, and
    • a third portion 43C extending from the second portion 43B in the opposite direction to the direction Ya and presenting a length equal to the length 33 along the direction Ya.
  • The lower channel 44 comprises :
    • a first portion 44A extending from the first inlet channel 39 in the opposite direction of the direction Ya and presenting a length equal to the length 33 along the direction Ya,
    • a second portion 44B extending from the first portion 44A along the direction Xa and presenting a length equal to the length 35 along the direction Xa, and
    • a third portion 44C extending from the second portion 44B along the direction Ya and presenting a length equal to the length 33 along the direction Ya.
  • The third portion 44C of the lower channel 44 and the third portion 43C of the upper channel 43 presents the same width 49 measured along the Xa direction.
  • The length 33 is advantageously comprised between 100 µm and 4000 µm, for instance equal to 1700 µm
  • The length 35 is advantageously comprised between 2000 µm and 20000 µm, for instance equal to 7665 µm
  • The width 49 is advantageously comprised between 50 µm and 500 µm, for instance equal to 150 µm.
  • The upper channel 43 and the lower channel 44 are arranged symmetrically with respect to the direction Xa.
  • The upper channel 43 and the lower channel 44 define between them a rectangular area 45. The second inlet 32 is located in the rectangular area 45. The second inlet 32 is located in the center of the rectangular area 45 with respect to the Ya direction.
  • The microfluidic pathway 29 comprises a second inlet channel 46 that connects fluidically the second inlet 32 to the rest of the microfluidic pathway 29. The second inlet channel 46 extends from the second inlet 32 along the direction Xa. The second inlet channel may alternatively comprise a central part that presents a sinuous shape, the central part being located between two straight parts that both extend along a main extension direction parallel to Xa. The second inlet channel 46 presents a length 36 along this main extension direction which is the direction Xa or alternatively a variable direction in the case of sinuous central part. The second inlet channel 46 presents a width 47 measured along the Ya direction.
  • The length 36 is advantageously comprised between 1000 µm and 20000 µm, for instance equal to 9225 µm.
  • The width 47 is advantageously comprised between 50 µm and 500 µm, for instance equal to 150 µm.
  • The first inlet channel 39 and the second inlet channel 46 have the same main extension direction so that the first inlet channel 39 and the second inlet channel 46 are aligned. The second inlet channel 46 extends from the second inlet 32 along the direction Xa up to the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • The second inlet channel 46 opens into both the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • The microfluidic pathway 29 comprises an outlet channel 53 that connects fluidically the outlet 34 to the rest of the microfluidic pathway 29. The outlet channel 53 extends from the outlet 32 in the opposite direction to Xa and presents a length 37 along this main extension direction.
  • The first inlet channel 39, the second inlet channel 46 and the outlet channel 53 have the same main extension direction so that they are all aligned.
  • The outlet channel 53 extends from the outlet 32 in the opposite direction to Xa up to the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44. The outlet channel 53 opens into both the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
  • The outlet channel 53 comprises a collar 51 that connects the third portion 43C and the third portion 44C to the rest of the outlet channel. The collar 51 presents a width 54 along the direction Ya that is smaller than a width 55 of the rest of the outlet channel 53 along the direction Ya.
  • The length 37 is advantageously comprised between 5000 µm and 20000 µm, for instance equal to 8000 µm.
  • The width 55 is advantageously comprised between 50 µm and 300 µm, for instance equal to 200 µm.
  • The width 54 is advantageously comprised between 20 µm and 70 µm, for instance equal to 50 µm.
    • Cross-junction
  • The microfluidic pathway 29 defines a cross junction 80 where the second inlet channel 46, the third portion 43C of the upper channel 43, the third portion 44C of the upper channel 44 and the collar 51 of the outlet channel 53 meet.
  • In the cross junction the third portion 43C and the third portion 44C are facing each other and aligned on the Ya direction, and the second inlet channel 46 and the collar 51 of the outlet channel 53 are facing each other and aligned on the Xa direction.
  • In operation, the first inlet 30 is provided with the continuous phase 40 and the second inlet 32 is provided with the polymer phase 42, the droplet generator 2 is configured to create an interface 60 between the continuous phase and the polymer at the cross junction 80. More specifically, the interface 60 is located within the second inlet channel 46 so as to define a flow focusing junction.
  • The droplet generator 2 comprises a sensor 62 located close to the cross junction 80, the sensor 62 being configured to monitor the interface 60. For instance, the sensor 62 is a camera configured to image the interface 60 and the cross junction 80. In another instance, the sensor 62 is a conductivity sensor configured to perform a conductivity measurement across the microchannel in the Ya direction at the meniscus 60. Another option is to use a capacitance sensor configured to perform a capacitance measurement along the same direction. Another possible option is to use an optical sensor configured to perform a local measurement of the optical density. Such an optical sensor may be different from a camera. The sensor 62 is connected to the command unit 64. The command unit 64 is configured to control the pressure actuators 56 and 57 possibly based on a signal provided by the sensor 62. An option of control consists in varying a set value of the first pressure actuator 56 while a command signal of the second pressure actuator 57 is maintained constant. Alternatively, the operator may vary a set value of the second pressure actuator 57 while a command signal of the first pressure actuator 56 is maintained constant. In particular, the command unit 64 is configured to control the pressure actuators 56 and 57 so as to stabilize the interface 60. This stabilization may correspond to a constant or a quasi-contant signal provided by the sensor 62.
    • Droplet generation
  • For a given pressure Pc of the continuous phase, there exists a pressure Pd of the dispersed phase or polymer phase at which the interface 60 is at equilibrium close to the cross junction 80. Then, in steady conditions, if Pd is below this value, there is some backflow inside the second inlet channel 46. Conversely, if Pd exceeds this equilibrium value, the dispersed phase is pushed towards the collar 51 of the outlet channel 53.
  • When Pd is above this equilibrium value and below a second threshold, the dispersed phase is squeezed by the flow of continuous phase and breaks into droplets. Different regimes exist in the microfluidic literature (dripping, squeezing, jetting...) depending on the mechanism responsible for the pinch-off of the neck. In the illustrated configuration of figure 3, droplet production occurs in the squeezing regime. In that case, the dispersed phase clogs the channel which gives rise to a pressure gradient inside the film of continuous phase in between the wall and the dispersed phase. When the latter fills the exit channel over a sufficient length, the pressure gradient becomes strong enough to deform and break the dispersed phase. When Pd exceeds the second threshold, the dispersed phase forms a jet inside the outlet channel 53: this is commonly referred to as the jetting regime in microfluidic literature Note that in the illustrated configuration of figure 3, the jet remains stable over the whole length of the exit channel.
  • The droplet generator 2 as described above can be used to implement a step S2 of generating a single droplet. The step S2 is a step of a fiber generation process P which is described further in the description.
  • To realize this step S2 and generate a single droplet, the following substeps can be implemented :
    • T1 : providing the continuous phase 40 from the first inlet 30 of the droplet generator and providing the polymer phase 42 from the second inlet 32,
    • T2 : setting a given pressure Pc to the continuous phase,
    • T3 : forming an interface between a polymer phase and a continuous phase, for instance by setting a given pressure Pd to the polymer phase, the given pressure corresponding to the equilibrium value so as to create an interface 60 in the cross junction 80,
    • T6 : applying a pressure pulse in the polymer (or dispersed) phase so as to increase Pd by an amount ΔP for a duration Δt.
  • Optionally, when the droplet generator 2 comprises the sensor 62, the process P can comprise the optional steps :
    • T4, during which the sensor 62 monitors the interface 60, and
    • T5, during which the command unit 64 controls the pressure actuators to adjust the pressure of the polymer phase and the pressure of the continuous phase and stabilize the interface.
  • Such monitoring and adjustment greatly improve the stability of the interface 60 and enable to generate single droplet in a much more efficient way.
  • Figure 4 illustrates this temporal sequence wherein curve 66 corresponds to the pressure applied to the continuous phase and curve 68 corresponds to the pressure applied to the polymer phase.
  • To generate a single droplet, different pressure pulse parameters corresponding to pressure Pc, pressure Pc, amplitude ΔP and duration Δt, can be applied.
  • Figure 6 illustrates the generation of a single droplet obtained thanks to such a pressure pulse application. Image 71 of figure 5 corresponds to the situation before the application of the pulse: the polymer phase is located inside the second input channel 46 and the interface 60 is stable. Image 72 of figure 5 corresponds to the situation during the application of the pulse: the polymer phase is projected out of the second input channel 46 up to the outlet channel 53. The polymer phase forms a liquid neck between the second inlet channel 46 and the collar 51 and further in the outlet channel the polymer phase forms a curved volume. The curved volume, the liquid neck and the rest of the polymer phase inside the second input channel 46 form a continuous polymer phase.
  • At the end of the pressure pulse, the liquid neck stops and is compressed by the continuous phase, the curved volume is separated from the rest of the polymer phase inside the second input channel 46 so as to generate a single droplet 38.
  • The step T6 leads to a step T7 of extracting a single droplet from the polymer phase.
  • The volume of the droplet is controlled by the pulse amplitude ΔP, its duration Δt and the pressures Pc and Pd.
  • Larger single droplets may be obtained by increasing the amplitude ΔP or the duration Δt. Smaller single droplets may be obtained by decreasing the amplitude ΔP or the duration Δt.
    • Calibration of the droplet generator
  • In order to generate a single droplet, the microfluidic droplet generator may first be calibrated. A basic calibration method C may be implemented before the implementation of the step S2.
  • The basic calibration method C comprises the following steps:
    • C1: selecting a value of the pressure Pc of the continuous phase,
    • C2: determining the corresponding equilibrium value of Pd,
    • C3: selecting a value of the pulse amplitude ΔP and a set of candidate values of the pulse duration Δt,
    • C4: for each candidate value of the pulse duration Δt, applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd, the value of the pulse amplitude ΔP and the candidate value of the pulse duration Δt,
    • C5: for each candidate value of the pulse duration Δt, determining if a single droplet is generated
    • C6: validating a candidate value of the pulse length Δt if a single droplet of polymer phase is generated.
  • Step C2 may be achieved by a balance of pressures based on the following equality: the difference in pressure between the first inlet 30 and the pressure at junction 48 is equal to the difference in pressure between the second inlet 32 and the Laplace pressure at the meniscus 60. The Laplace pressure Pl depends on the surface tension between the continuous phase 42 and the dispersed phase 42, the channel height and the width 47 of the second inlet channel 46.
  • Step C5 may be achieved by optical observation. To that end, the sensor 62 may advantageously comprise a camera.
  • This basic calibration method may advantageously comprise the complementary steps :
    • C7: determining a lower threshold of Δt1 so that applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd, the value of the pulse amplitude ΔP and any value of Δt inferior or equal to Δt1 does not generate a single droplet of polymer phase, and
    • C8: determining an upper threshold of Δt2 so that applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd, the value of the pulse amplitude ΔP and any value of Δt superior or equal to Δt2 does not generate multiple droplets of polymer phase; Δt2 can be estimated during the calibration phase by holding the second pressure actuator 57 at the combined value Pd+ΔP and observing the time elapsed between successive droplet formation events.
  • These complementary steps are based on the following trends that have been generally observed. There are a lower threshold Δt1 and an upper threshold Δt2, so that:
    • below Δt1, the pulse is too short to generate a droplet, and
    • above Δt2, either the droplet takes the shape of a plug or the droplet gets separated into a plurality of smaller droplets; a plug corresponds to a droplet that entirely fills the width 55 of the outlet channel 53, the plug being elongated in the direction Xa.
  • The basic calibration method may advantageously be implemented for a plurality of different values of the pulse amplitude ΔP.
  • The microfluidic droplet generator may be further calibrated by :
    • C9: selecting a set of candidate values of Pc and
    • C10: applying the basic calibration method for each candidate value of Pc.
  • Based on these different method steps, phase diagrams may be built. A phase diagram may be associated with each candidate value of Pc, and represent schematically the determined values of the pulse amplitude ΔP and of determined values of the pulse length Δt that lead to the generation of a single droplet of the polymer phase.
  • The following trends have been generally observed. Long pulses (Δt > Δt2) generate plugs at high amplitude ΔPh (that is the set of values Pc and Pd+ ΔPh corresponds to the jet regime ; in other words Pd+ ΔPh is above the second threshold of Pd for which the dispersed phase forms a stable jet inside the outlet channel 53 when the pressure is applied continuously at Pd+ ΔPh) and several drops at low amplitude ΔPl (that is the set of values Pc and Pd+ ΔPl corresponds to the dripping regime ; in other words Pd+ ΔPl is below the second threshold of Pd for which the dispersed phase breaks into droplets inside the outlet channel 53 when the pressure is applied continuously at Pd+ ΔPl).
  • An example of a phase diagram is given in figure 9, for four different sets of values of pressure of the continuous phase Pc and pulse amplitude ΔP, figure 9 illustrates values of pulse length Δt (x-axis) for which a single droplet is generated. The volume of the droplet is given on the y-axis. This diagram shows additionally that the volume increases when the pulse amplitude ΔP increases and/or when the pulse length Δt increases.
  • The control of the pressure actuators so as to stabilize the interface is stopped during the pressure pulse.
  • It is to be noted that alternative microfluidic droplet generating devices may be used, for instance a device based on a T-junction. Pressure pulses as previously described may be used to generate a single droplet in these alternative microfluidic droplet generating devices. Analogous calibration methods may also be implemented to identify pressure pulse parameters that lead to a single droplet generation.
    • Functionalized polymer phase
  • The polymer phase may be generated during a first step S1 of the process P.
  • The polymer phase 42 comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and 10% of water. Other types of photopolymers may be used instead of PEGDA such as PVA, PEGDVE, PEGDMA, etc ... The polymer phase comprises light-curing polymers such as UV-curing polymers. In addition to light-curing polymers, the polymer phase may advantageously comprise a photo-initiator 2-hydroxy-2-methylpropiophenone. Other photo-initiators such as Ethylanthraquinone, Ferrocene, Hydroxybenzophenone, acetophenone, etc., can also be used. In the case of 2-hydroxy-2-methylpropiophenone, 5% is placed in the mixture.
  • The polymer phase may comprise, in addition to light-curing polymers and water, functional material configured to modify physical-chemical properties of the polymer phase.
  • Such functional material are in particular conductive material, magnetic material, catalytic material, piezoelectric material, fluorophore, or electrets....
  • In a first substep G1 of the step S1, the functional material is mixed with light-curing polymers.
  • If the functional material is a conductive material, the conductive material may comprise carbon nanotubes, Silver Nanoparticles, reduced graphene oxide or PEDOT:PSS (polymer mixture of polystyrene sulfonate and poly(3,4-ethylenedioxythiophene)). Carbon nanotubes (CNT) may be single walled CNT or multiwalled CNTs.
  • In the case of carbon nanotubes, graphene oxide or PEDOT:PSS, the generation of the polymer phase may comprise:
    • the first substep G1 that comprises mixing the functional material with light-curing polymers in a liquid phase,
    • a second substep G2 that comprises adding a polar solvent to the liquid phase, the polar solvent preferably being dimethylformamide,
    • a third substep G3 that comprises exposing the liquid phase to ultrasound waves advantageously for a duration superior or equal to 30 minutes and inferior or equal to 6 hours, and
    • a fourth substep G4 that comprises evaporating the polar solvent out of the liquid phase. The substep G3 of exposing the liquid phase to ultrasound, also known as a ultrasonication step, enables to supply mechanical energy to debundle CNTs (or graphene oxide or PEDOT:PSS) and create percolated suspensions in the liquid phase.
  • In order to obtain even more homogeneous dispersions in the liquid phase, an optional previous step of adding a polar solvent to the liquid phase can be implemented. In this case, a further step after the ultrasonication step of removing the polar solvent by evaporation is necessary to obtain a liquid phase that fulfills the initial polymer solution conditions.
    • Fluidic channel
  • In correspondence with figure 2, the fluidic channel 3 extends along a transport axis 9 from an inlet 6 of the fluidic channel 3 to an outlet 15 of the fluidic channel 3.
  • The fluidic channel comprises advantageously walls in PDMS (Polydimethylsiloxane).
  • The fluidic channel 3 extends in a main plane defined by orthogonal directions Xb and Yb. The transport axis 9 is parallel to the direction Xb.
  • The fluidic channel 3 presents a height measured in an orthogonal to directions Xb and Yb that is superior or equal to 10 µm and inferior or equal to 200 µm, for instance the height is equal to 28.5 µm.
  • The height of the fluidic channel is the same as channel 3 and it is superior or equal to 10 µm and inferior or equal to 200 µm.
  • The inlet 6 of the fluidic channel may be advantageously fluidically connected to the outlet 34 of the droplet generating device 2.
  • The fluidic channel 3 presents a width (or more generally a dimension) measured along the direction Yb and orthogonally to the transport axis 9. The width (or dimension) of the fluidic channel is variable along the transport axis 9.
  • The inlet 6 and the outlet 15 of the channel correspond to straight channel so that in the main plane walls of the inlet 6 and the outlet 15 of the fluidic channel 3 are parallel to the transport axis 9. The width of the fluidic channel 3 is constant in the inlet 6 and the outlet 15. For example, the width of the fluidic channel 3 in the inlet 6 and the outlet 15 is inferior or equal to 500µm.
  • The fluidic channel 3 comprises three different portions located along the direction defined by the transport axis between the inlet 6 and the outlet 15.
  • The fluidic channel 3 comprises a first portion 7 that is contiguous to the inlet 6. The first portion 7 is contiguous to the inlet 6 means that the wall of the fluidic channel is continuous from the inlet 6 to the first portion 7. The same meaning of the term "contiguous" is used further in the description.
  • The first portion 7 has a funnel shape so that the dimension 8 of the channel in the first portion continuously decreases along the transport axis 9.
  • The first portion 7 extends on a length 20 superior or equal to 200 µm and inferior or equal to 1000 µm measured along the transport axis 9.
  • The fluidic channel 3 comprises a second portion 10 that is contiguous to the first portion 7. The second portion 10 has a straight shape so that the dimension 11 of the channel in the second portion 10 is constant along the transport axis 9. The second portion 10 extends on a length 22 superior or equal to 400 µm and inferior or equal to 4000 µm measured along the transport axis 9.
  • The dimension 11 is superior or equal to 2 µm and inferior or equal to 100 µm. The dimension may take any value between 2 µm and 100 µm, for instance 15 µm, 20 µm, 25 µm, 30 µm, 35 µm, 40 µm, 45 µm, 50µm. Advantageously the dimension 11 inferior or equal to 12µm and even more advantageously inferior or equal to 10µm. The dimension 11 may take any value between 2 µm and 12 µm, for instance 4 µm, 5µm, 6µm, 7µm, 8 µm, 9µm, 10µm and 11µm. The fluidic channel 3 comprises a third portion 12 that is contiguous to the second portion 10. The third portion 12 has a funnel shape, the dimension 13 of the channel continuously increasing along the transport axis 9. The third portion 12 extends on a length 24 superior or equal to 200 µm and inferior or equal to 1000 µm measured along the transport axis 9.
  • The fluidic channel may be centered on the transport axis 9.
  • In this case, the first portion 7 presents a funnel shape so that an angle 16 of a wall of the first portion 7 with respect to the transport axis 9 is inferior or equal to 30°, and advantageously inferior or equal to 7°. In other words, a ratio (R1) of a decrease (Δw1) of the dimension (width) of the channel in the first portion over a distance (ΔL1) along the transport axis so that R1=Δw1/ΔL1 is inferior or equal to 1 and advantageously inferior or equal to 0.24. R1 is equal to twice the tangent of the angle 16.
  • The decrease (Δw1) of the dimension (width) of the channel is determined between two points of the wall of the fluidic channel in the first portion before entering the zone of constant dimension 11. The two points are separated along the transport axis 9 by a distance ΔL1. At the first point the fluidic channel presents a first width wA and at the second point the fluidic channel presents a second width wB. If the second point is closer to the outlet 15 and the first point closer to the inlet 6, then wB<wA and R is equal to the ratio (wA-wB)/ΔL1. The angle 16 of a wall of the first portion 7 with respect to the transport axis 9 can be superior or equal to 2° and advantageously superior or equal to 4°. In other words, the ratio (R1) of the decrease (Δw1) of the dimension (width) of the channel in the first portion over the distance (ΔL1) along the transport axis is superior or equal to 0.07 and advantageously superior or equal to 0.14.
  • In this same case, the third portion 12 presents a funnel shape so that an angle 18 of a wall of the third portion 12 with respect to the transport axis 9 is inferior or equal to 32°.
  • In other words, a ratio (R2) of an increase (Δw2) of the dimension (width) of the channel in the third portion 12 over a distance (ΔL2) along the transport axis so that R2=Δw2/ΔL2 is inferior or equal to 1 and advantageously inferior or equal to 1.2. R2 is equal to twice the tangent of the angle 18.
  • The increase (Δw2) of the dimension (width) of the channel is determined between two points of the wall of the fluidic channel in the third portion. The two points are separated along the transport axis 9 by a distance ΔL2. At the first point the fluidic channel presents a first width wC and at the second point the fluidic channel presents a second width wD. If the second point is closer to the outlet 15 and the first point closer to the inlet 6, then wD>wC and R2 is equal to the ratio (wD-wC)/ΔL2.
  • The angle 18 of a wall of the third portion 12 with respect to the transport axis 9 can be superior or equal to 2° and advantageously superior or equal to 4°. In other words, the ratio (R2) of the increase (Δw2) of the dimension (width) of the channel in the third portion 12 over the distance (ΔL2) along the transport axis is superior or equal to 0.07 and advantageously superior or equal to 0.14.
  • The angle of a wall of the second portion 10 with respect to the transport axis 9 is equal to zero as the second portion is a straight portion. Advantageously, the angle presents a continuous variation in the first portion 7, the second portion 10 and the third portion 12. In other words, the angle of a wall of the fluidic channel with respect to the transport axis 9 is equal to zero in the second portion 10 and takes continuously positive values from the second portion to the first portion or from the second portion to the third portion.
  • The device 1 for manufacturing a fiber comprises also a light source 14 configured to expose the second portion to a light radiation. In particular, the light source 14 may be a UV light source.
  • The light source emits light in a specific band width and provides a light energy density in the second portion 10.
  • The light source is configured to not emit light towards the first portion or the third portion.
  • Optionally, the device 1 for manufacturing a fiber may comprise complementary channels 80 and 82 that open into the fluidic channel at a transition between the second portion 10 and the third portion 13. The complementary channels are parallelly disposed with respect to the transport axis 9. The complementary channels are curved so that the main direction of extension of each complementary is variable in the plane defined by directions Xb and Yb. In particular, the main direction of extension of each complementary channel becomes more and more parallel to the transport axis 9 as the complementary channel approaches the fluidic channel 3. Advantageously an angle between the transport axis 9 and the main direction of extension of a complementary channel at the transition of the complementary channel and the fluidic channel 3 is inferior or equal to 5° and preferably between 0° and 4°.
  • These complementary channels are configured to be filled with continuous phase and to carry complementary flows 81, 83. For each complementary channel 80, 82, the complementary flow 81, 83 is directed along the main direction of extension of the complementary channel and directed to enter the fluidic channel and flow from the second portion towards the third portion.
    • Fiber generation
  • The device 1 for manufacturing a fiber can be used to implement a process P to manufacture a fiber. In correspondence with figure 8, we now present the process P.
  • The first step S1 and the second step S2 of the process P are evoked previsously in the description and correspond respectively to the generation of the polymer phase and the generation of a single droplet. The first step S1 may be preceded by the steps of the calibration method C of the droplet generator.
  • A third step S3 of the process P comprises moving the single droplet 38 containing light-curing polymers from the outlet 34 of the droplet generator 2 to the inlet 6 of the fluidic channel 3, for instance through the microfluidic circuit 5 that may include both the droplet generator 2 and the fluidic channel 3.
  • In order to implement this transport, a main flow 70 can be provided, during a sub-step S3A, along the transport axis 9 in the continuous phase through the fluidic channel 3 which is filled with the continuous phase 40.
  • The third step S3 may be preceded by the steps of the calibration method F of the fluidic channel which is presented further in the description.
  • A fourth step S4 of the process P comprises moving the single droplet 38 in the first portion 7 of the fluidic channel 3 along the transport axis.
  • As the single droplet 38 progresses in the first portion towards the second portion, the width of the fluidic channel continuously decreases and the shape of the droplet continuously changes. In particular, the width of the droplet decreases in the direction Yb and the length of the droplet expands in the direction Xb.
  • Moving the single droplet 38 in the first portion 7 leads to the sub-step S4A of decreasing continuously a dimension of the droplet measured along a transverse direction orthogonal to the transport axis.
  • Thanks to the funnel shape of the first portion, the shape of the droplet is progressively modified when it travels from the first portion towards the second portion along the transport axis 9. The funnel shape enables to avoid fragmentation of the droplet into multiple smaller droplets.
  • In order to implement this transport, a main flow 70 can be provided along the transport axis 9 in the continuous phase through the fluidic channel 3 which is filled with the continuous phase 40.
  • During a fifth step S5, the droplet 38 is transported in the second portion 10 of the channel 3. As the single droplet 38 progresses in the second portion the width of the fluidic channel reaches a minimum value. The width of the droplet decreases and reaches a minimum value. Steps S4 and S5 are schematically illustrated in parts 74 and 75 of figure 6.
  • During a sixth step S6, the light source 14 provides light to the second portion 10 so as to at least partially cure the droplet into a fiber.
  • The wavelength of the light source and the density of light energy provided in the second junction are adapted to the type of light-curing polymers contained in the droplet and the density of light-curing polymers contained in the droplet, so as to cure the droplet.
  • In particular, the wavelength of the light source can be in the UV range, for example around 365 nm.
  • The polymer solution reticulates and solidifies when exposed to the light of the light source 14. The polymer solution retains the shape of the second portion 10.
  • In the second section of the channel, the size and shape of the droplet are controlled by the geometry of the channel. As the droplet is cured in the second portion, the size and shape of the droplet in the second section is retained. By controlling the size and shape of the second section, it is thus possible to manufacture fibers presenting a width inferior or equal to 10 µm and/or a rectangular cross-section.
  • The droplet 38 is surrounded in the second portion by a thin, continuous-phase layer of that facilitates the movement of the droplet and once cured, the movement of the fiber.
  • When the walls of the fluidic channel 3 are made of PDMS, the presence of the thin continuous-phase layer is promoted by a molecular oxygen diffusion through the PDMS. This diffusion leaves around the droplet/fiber an unpolymerized oxygen inhibition layer. Adding 10% of deionized water to the polymer solution prevents further wetting. 10% of deionized water was used for the experiments. 5% of deionized water corresponds to a minimum amount of water to prevent wetting issues. 30% of deionized water corresponds to a maximum value above which no polymerization is achievable.
  • Thanks to the continuous-phase layer, the fiber does not stop in the second portion and keeps moving along the transport axis 9.
  • Exposing the droplet to the light radiation may comprise advantageously providing a light energy density to the droplet superior or equal to a predetermined energy density threshold, and maintaining the droplet in the second portion during a duration superior or equal to a predetermined duration threshold.
  • There is a light exposure threshold for the cross-linking of each polymer solution. The elastic properties of the obtained fiber appear to depend directly on the energy density of the light and the exposure time.
  • The elastic properties thus depend on the speed at which the droplet crosses the light-illuminated zone. The speed can be controlled by the pressures applied to the continuous phase.
  • In order to establish the optimal parameters to generate a fiber, the fluidic channel 3 can be calibrated previously to implement the method P.
  • For instance, one can elaborate phase diagrams as a function of the width of the second portion, the power of the light source, the pressures applied to the continuous phase and polymer phase during the droplet generation.
  • For a set of pressure pulse parameters corresponding to pressure Pc, pressure Pc, amplitude ΔP and duration Δt, one can run a fiber generation process with different values of the width of the second portion and different values of power of the light source and evaluate in each case if a fiber is efficiently manufactured. An optical validation, for instance using a camera, can be implemented to verify the presence of a fiber. A calibration method F of the fluidic channel is presented further in the description.
  • During a seventh step S7, one can move the droplet 38 from the second portion 10 to the third portion 12. This fifth step corresponds to the extraction of the fiber from the thin second portion. The funnel shape of the third portion enables to prevent clogging of the fluidic channel 5 and breakage of the fiber. To the contrary, an abrupt transition will lead to a sudden deceleration of the head of the fiber when it exits the second portion, so that the rest of the fiber is also slowed down. The rest of the fiber will consequently spend more time in the light-exposed second portion. The rest of the fiber may reach a level of curation significantly higher than the head of the fiber, leading to an inhomogeneous fiber and possibly to a clogging of the second portion. The funnel shape of the third portion enables a more progressive deceleration that prevents clogging and the production of more homogeneous fibers.
  • In other words, as the fiber exits the second section, it experiences slower velocities that can lead to channel clogging, especially in the case of a thin fiber. The funnel shape of the third portion prevents clogging as it limits this slowdown and simplifies the extraction of the rest of the fiber out of the second section.
  • Advantageously and when the device for manufacturing a fiber comprises complementary channels 80, 82, the step S7 of the process P comprises a substep S7A of adding complementary continuous-phase flows in the third portion so as to align the fiber with the transport axis. The complementary continuous phase flows 81 and 83 help the soft fiber to exit the second portion 10 without deforming and speed up the step S7 of moving the single droplet 38 in the third portion 12, that is extracting the fiber from the second portion 10.
  • During an optional eighth step S8 implemented once the fiber is reticulated and extracted from the second portion, one can cover the fiber with active molecules. Active molecules may include enzymes, conductive dispersions of nanoparticles, magnetic materials, piezoelectric materials, catalytic materials, electrets, fluorophore etc., ... Covering the fiber with active molecules can be realized thanks to the initial mixture preparation. Preferably, a homogeneous dispersion of the initial mixture preparation helps to locate the active molecules at the surface of the extruded fiber.A homogeneous dispersion may be obtained using an ultrasonication of the mixture in the dispersed phase 42, or using surface chemical modifications of the conductive phase. This latter can be, for example, grafted polymer chains.
    • Calibration method of the fiber channel
  • A method F for calibrating the fiber channel may comprise the following steps.
  • During a first step F1, the operator selects a set of pressure pulse parameters (values of Pc, corresponding equilibrium value of Pd, pulse amplitude ΔP and pulse duration Δt), for which a single droplet is obtained using the droplet generator 2.
  • During a second step F2, the operator selects a set of candidate values of the width 11 of the second portion 10. The operator will thus need to dispose of different fluidic channels that each presents one of the candidate values of the width 11. Each fluidic channel may be fluidically connected to the droplet generator as previously mentioned.
  • During a third step F3, the operator selects a set of candidate values of power of the light source. The operator will thus need to dispose means to modify the power of the light source so as to be able to provide the second portion of the channel with each candidate value. For instance, the light source may be naturally controlled in power thanks to a variator, or alternatively calibrated attenuator windows may be disposed between the light source and the second portion. Other means to modify the power of the light source may include pulse width modulation via an electronic trigger and spectral filters.
  • During a fourth step F4 and for each fluidic channels, the operator implements a droplet generation and a fiber generation by connecting the outlet of the droplet generator to the inlet of the fluidic channel, generating in the droplet generator a single droplet based on the set of pressure pulse parameters, moving the single droplet through the fluidic channel from the first portion to the second portion, exposing the droplet in the second portion to a candidate power of the light source, and evaluating if a fiber is efficiently manufactured at the output of the fluidic channel.
  • During a fifth step F5, the operator may repeat steps F4 for different sets of pressure pulse parameters.
  • During a sixth step F6, the operator determines each case an exposure time of the droplet to the light source and a light energy density at which the droplet was exposed to the light source. The exposure time depends on the velocity of the droplet inside the second portion, this velocity depending itself on the pressure Pc and the geometry of the fluidic channel. The light energy density depends on the power of the light source and the geometry of the second portion of the fluidic channel.
  • During a seventh step F7, the operator determines a minimum exposure time above which fibers can be obtained. This determination may be limited to a specific geometry of the fluidic channel, for instance to a specific width of the second portion.
  • During a seventh step F8, the operator determines a minimum light energy density above which fibers can be obtained. This determination may be limited to a specific geometry of the fluidic channel, for instance to a specific width of the second portion.
  • This calibration may lead to a phase diagram as examplified in figure 7. This phase diagram corresponds to a fixed geometry of the fluidic channel for which the parameters of exposure time (y-axis) and energy density (x-axis) have been scanned. Situations for which a fiber is obtained are illustrated as inclined squares, other situations correspond to right squares.
  • This calibration enables to identify a minimum exposure time above which fibers can be obtained. This minimum exposure time can then be used in the process to maintain the droplet in the second portion during a duration superior or equal to this minimum exposure time, corresponding then to a predetermined duration threshold.
  • This calibration enables also to identify a minimum light energy density above which fibers can be obtained. This minimum light energy density can then be used in the process to provide a light energy density superior or equal to this minimum light energy density corresponding then to a predetermined energy density threshold.
  • If the calibration method is perfomed, substeps S6A and S6B may be advantageously to step S6 of exposing the droplet to the curing light provide by the light source.
  • During the substep S6A, the light source provides a light energy density to the droplet superior or equal to the predetermined energy density threshold.
  • During the substep S6B, the droplet is maintained in the second portion during a duration superior or equal to the predetermined duration threshold.
    • Fiber
  • The manufacturing device 1 and the manufacturing method P enables to manufacture fibers comprising curing polymers and in particular light-curing material.
  • The width of the fiber is given by the width of the second portion 10 of the fluidic channel 3. As the width of the second portion 10 may be as small as 2 microns, thin fibers may be manufactured, and in particular fibers presenting a width inferior or equal to 12 µm, 10 µm, 8 µm, 6 µm and even 4 µm.
  • In addition, larger widths may also be manufactured, for instance fibers presenting a width superior or equal to 15 µm, 20 µm, 25 µm, 50 µm and even 100 µm can be manufactured.
  • Another advantage of the manufacturing device 1 and the manufacturing method P is the possibility to control the shape of the fiber produced. In particular, it is possible to manufacture fibers that present a rectangular cross-section. The fiber is, in this case, a ribbon.
  • The fiber presents a length L along the main extension direction X and a width W along a Y direction orthogonal to X, and a height H along a Z-direction orthogonal to both X and Y directions. The fiber has a rectangular cross-section when the shape of the fiber is rectangular in a plane Y Z orthogonal to the main extension direction X. The transverse aspect ratio of the fiber corresponds to the ratio H/W. When the third aspect ratio H/W is different from 1, the fiber presents a ribbon shape.
  • The fiber presents a transverse rectangular cross-section when the second portion 10 presents a rectangular cross-section.
  • The cross section of the second portion 10 is the section of the second portion 10 in a plane defined by the direction Yb and the direction orthogonal to both directions Xb and Yb.
  • The cross section of the second portion is given by the ratio of the width 11 of the second portion 10 by the height of the second portion 10. The height of the second portion 10 corresponds to the height of the fluidic channel and is measured in the direction orthogonal to both directions Xb and Yb. The second portion 10 presents a height superior or equal to 10 µm and inferior or equal to 200 µm, for instance the height is equal to 28.5 µm.
  • The height of the second portion 10 may be equal to 20 µm, 30 µm, 40 µm, 50 µm, 60µm, 80µm, 100µm, 120µm,
  • The aspect ratio of the rectangular cross-section of the second portion 10 may be comprised between 1.25 and 20. For instance the aspect ratio H/W is equal to 1.5, 2, 3, 3.5, 4, 4.5, 5, 7, 10, 15, 20, 25 or 30.
  • The aspect ratio of the rectangular cross-section of the second portion 10 gives the aspect ratio H/W of the fiber.
  • The aspect ratio H/W of the fiber may be comprised between 1.25 and 20. For instance the aspect ratio H/W is equal to 1.5, 2, 3, 3.5, 4, 4.5, 5, 7, 10, 15, 20, 25 or 30.
  • The manufacturing device 1 and the manufacturing method P enables to manufacture fibers comprising light-curing material that presents a very wide range of lengths and a very wide range of widths. The length of the fiber is given by the volume of the single droplet and the width of the fiber is given by the width of the second portion 10.
  • The length of the fiber may be as small as 25µm and as large as 1cm.
  • An important advantage of the manufacturing device 1 and the manufacturing method P is the high repeatability of the fibers produced. Once a set of manufacturing parameters is chosen (pressure pulse parameters and dimensions of the second portion 10 of the fluidic channel), the manufacturing method leads to single droplets generated that have a very regular volume and to fibers generated that have a very regular length, width and height. Thanks to the precision of microfluidic technologies, the statistic distribution of the length, (respectively the width and the height) of the fibers produced with a fixed set of manufacturing parameters is a very narrow peak so that the distribution can be qualified as monodisperse.
  • Fibers with precise and repeatable geometry can be fabricated based on the manufacturing device 1 and/or the manufacturing method P.

Claims (18)

  1. A method (P) for manufacturing a fiber, the method comprising the following steps:
    - (S2) generating a single droplet (38) containing light-curing polymers,
    - (S4) moving the droplet in a first portion (7) of a fluidic channel (3), the first portion having a funnel shape so that a dimension of the channel in the first portion continuously decreases along a transport axis (9) of the droplet,
    - (S5) moving the droplet in a second portion (10) of the channel, the second portion being contiguous to the first portion, the dimension of the channel being constant in the second portion,
    - (S6) exposing in the second portion the droplet to a light radiation so as to at least partially cure the droplet into a fiber (78), and
    - (S7) moving the fiber in a third portion (12) of the channel, the third portion being contiguous to the second portion, the third portion having a funnel shape so that the dimension of the channel in the third portion continuously increases along the transport axis.
  2. The method according to claim 1, wherein a dimension of the droplet measured along a transverse direction orthogonal to the transport axis is inferior or equal to 500 µm, the dimension being inferior or equal to 12 µm in the second portion.
  3. The method according to claim 2, wherein moving the droplet in the first portion comprises decreasing (S4A) continuously a dimension of the droplet measured along a transverse direction orthogonal to the transport axis, a ratio of a decrease of the dimension of the droplet over a transport distance of the droplet being inferior or equal to 1 and advantageously inferior or equal to 0.24.
  4. The method according to any of claims 1 to 3, wherein generating the single droplet comprises:
    - (T3) forming an interface (60) between a polymer phase (42) and a continuous phase (40) in a microfluidic droplet generating (29) device, such as a flow-focusing or T-junction, the polymer phase containing light-curing polymers, and
    - (T6) applying a pressure pulse to the polymer phase so as to eject a single droplet (38) from the polymer phase into the continuous phase.
  5. The method according to claim 4 wherein generating the single droplet comprises:
    - (T4) monitoring the interface, and
    - (T5) adjusting a pressure of the polymer phase and a pressure of the continuous phase so as to stabilize the interface.
  6. The method according to any of claims 1 to 5, wherein moving the droplet in the first portion comprises (S3A) providing a main flow (70) of a continuous phase along the transport axis in the fluidic channel,
    moving the fiber in the third portion comprising adding (S7A) complementary continuous-phase flows in the third portion so as to align the fiber with the transport axis.
  7. The method according to any of claims 1 to 6, wherein exposing the droplet to the light radiation comprises providing (S6A) a light energy density to the droplet superior or equal to a predetermined energy density threshold, and maintaining (S6B) the droplet in the second portion during a duration superior or equal to a predetermined duration threshold.
  8. The method according to any of claims 1 to 7, wherein generating the single droplet comprises extracting (T7) the single droplet from a polymer phase, the method further comprising a step of generating (S1) the polymer phase that comprises mixing (G1) light-curing polymers and a functional material in a liquid phase, the functional material being configured to modify physical-chemical properties of the polymer phase.
  9. The method according to claim 8, wherein the functional material is a conductive material.
  10. The method according to claim 9, wherein the conductive material comprises carbon nanotubes, the step of generating the polymer phase comprising the following substeps:
    - (G2) adding a polar solvent to the liquid phase, the polar solvent preferably being dimethylformamide,
    - (G3) exposing the liquid phase to ultrasound waves advantageously for a duration superior or equal to 30 minutes and inferior or equal to 6 hours, and
    - (G4) evaporating the polar solvent out of the liquid phase.
  11. The method according to any of claims 1 to 10 further comprising a step of covering (S8) the fiber with active molecules, such as enzymes and other catalytic materials.
  12. A device (1) for manufacturing a fiber, the device comprising:
    - a droplet generator (2) configured to generate a single droplet,
    - a fluidic channel (3) comprising:
    --a first portion (7) having a funnel shape, a dimension of the channel continuously decreasing along a transport axis (9),
    -- a second portion (10) contiguous to the first portion, the dimension of the channel being constant in the second portion,
    -- a third portion (12) contiguous to the second portion, the third portion having a funnel shape, the dimension of the channel continuously increasing along the transport axis, and
    - a light source (14) configured to expose the second portion to a light radiation.
  13. The device according to claim 12 comprising a microfluidic circuit (5) including the droplet generator (2) and the fluidic channel (3), wherein a width (26) of the channel measured along a transverse direction orthogonal to the transport axis is inferior or equal to 500 µm, the width (11) of the channel being inferior or equal to 12 µm in the second portion.
  14. The device according to any of claims 12 and 13, wherein the funnel shape of the first portion is centered on the transport axis, an angle (16) of a wall of the first portion with respect to the transport axis being inferior or equal to 30°, and advantageously inferior or equal to 7°, the funnel shape of the third portion being centered on the transport axis, an angle (18) of a wall of the third portion with respect to the transport axis being inferior or equal to 32°.
  15. The device according to any of claims 12 to 14 wherein the droplet generator comprises a microfluidic droplet generating device (29), such as a flow-focusing or a T-junction, the microfluidic droplet generating device being configured to provide an interface (60) between a polymer phase (42) and a continuous phase (40), the device comprising a sensor (62) configured to monitor the interface (60), the droplet generator comprising pressure (56, 57) actuators configured to adjust a pressure of the polymer phase and a pressure of the continuous phase, the device comprising a command unit (64) configured to command the actuators so as to stabilize an image of the interface.
  16. A fiber (78) comprising light-cured polymers, the fiber presenting a width inferior or equal to 12 µm.
  17. A fiber according to claim 16 presenting a length along a main extension direction, a width along a first transverse direction orthogonal to the main extension direction and a height along a second transverse direction orthogonal to the main extension direction and the first transverse direction, the length being superior to the height, the height being superior to the width, the fiber having a rectangular cross-section in a plane defined by the first transverse direction and the second transverse direction, a transverse aspect ratio corresponding to a ratio of the height above the width being superior or equal to 1.25 and inferior or equal to 20.
  18. The fiber according to any of claims 16 and 17 manufactured by a method according to any of claims 1 to 11.
EP24305701.5A 2024-05-02 2024-05-02 Method for manufacturing a fiber Pending EP4644590A1 (en)

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EP24305701.5A EP4644590A1 (en) 2024-05-02 2024-05-02 Method for manufacturing a fiber
PCT/EP2025/061827 WO2025229057A1 (en) 2024-05-02 2025-04-30 Method for manufacturing a fiber

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Citations (3)

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US20160000886A1 (en) * 2013-02-22 2016-01-07 President And Fellows Of Harvard College Nanostructured active therapeutic vehicles and uses thereof
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