WO2019078784A1

WO2019078784A1 - Transfer patterning on fibrous material

Info

Publication number: WO2019078784A1
Application number: PCT/SG2018/050519
Authority: WO
Inventors: Chee Keong Benjamin TEE; Sen Wai Kwok
Original assignee: Agency For Science, Technology And Research
Priority date: 2017-10-17
Filing date: 2018-10-17
Publication date: 2019-04-25

Abstract

The present disclosure relates to a method of forming a patterned fibrous material comprising the steps of providing a patterned sacrificial film having a pattern-forming material thereon; disposing a fibrous material onto said patterned sacrificial film; and subjecting said disposed fibrous material to an elastomeric substrate under strain to thereby transfer said pattern-forming material onto said fibrous material upon removal of said sacrificial film and upon release of the strain from said elastomeric substrate. The present disclosure also relates to an assembly of a three-dimensional (3D) array of a plurality of patterned fibrous material on an elastomeric substrate.

Description

Title of Invention: Transfer Patterning on Fibrous

Material References To Related Applications

This application claims priority to Singapore application number 10201708563Y filed on 17 October 2017, the disclosure of which is hereby incorporated by reference. Technical Field

The present invention relates to a method of forming a patterned fibrous material and an assembly of a three-dimensional (3D) array of a plurality of patterned fibrous material on an elastomeric substrate.

Background Art

Wearable electronic devices have attracted widespread and intensive research attention due to its role to integrate functionality into people' s daily lives in a convenient and accessible way and such devices play an important part in the integration of Internet of Things (IoT). A great number of wearable electronic devices have been developed based on flexible, stretchable, and bendable films, or based on miniaturization of devices such as smart watches, wearable sensors, etc. Current wearable devices remain bulky, hard, or semi-rigid. These physical characteristics make them unsuitable for long-term continuous use or limit their use and integration as wearable devices. Textile based devices remain another important category of wearable electronics as they have the potential to be better integrated into clothes, hats or shoes. Layer by layer coating can be used to build functionality into fibrous material, which is the component of making a textile. Direct patterning onto the fibrous material can also be performed, but is often limited by the dimension of the material and associated with higher cost.

It has been a topic of broad and increasing interest for controlled formation of three-dimensional functional structures, particularly in the near decade, due to important application in different fields of micro/nanosystem technology, from biomedical devices to microelectromechanical components, metamaterials, sensors, electronics and others. Although volumetric optical exposures, colloidal self-assembly, residual stress induced bending and bio-templated growth can be used to fabricate different kinds of structures in certain types of materials, techniques that are based on rastering of fluid nozzles or focused beams of light, ions or electrons provide the greatest versatility in design. Applicability of these methods, however, only extends directly to materials that can be formulated as inks or patterned by exposure to light/energetic particles, and indirectly to those that can be deposited onto or into sacrificial three-dimensional structures formed with these materials. Compressive buckling method has also been developed based on the strain restoration of a pre-strained substrate to transform a patterned two-dimensional material into three-dimensional structure. However, it has not been applied to the field of textile based wearable electronic devices.

There is therefore a need to provide a method for patterning a fibrous material that overcomes or ameliorates one or more of the disadvantages mentioned above.

Summary

In one aspect, there is provided a method of forming a patterned fibrous material comprising the steps of:

a) providing a patterned sacrificial film having a pattern-forming material thereon;

b) disposing a fibrous material onto said patterned sacrificial film; and

c) subjecting said disposed fibrous material to an elastomeric substrate under strain to thereby transfer said pattern-forming material onto said fibrous material upon removal of said sacrificial film and upon release of the strain from said elastomeric substrate.

Advantageously, different and complex two-dimensional patterns can be pre -fabricated on the sacrificial film, and then transferred onto the fibrous material through a compressive buckling process. This may eliminate the need for direct patterning on the fibrous material, which is often associated with low throughput and high cost. This also enables an array of patterns to be formed and the array of patterns can be designed to be transferred to the fibrous material instead of via layer-by-layer coating only, which serves as an important foundation for more electronic functions to be built in.

Further advantageously, the pattern forming material can be selected from the group consisting of a conductor, a semiconductor, an insulator and a mixture thereof. Different fabrication techniques (e.g. photolithography, inkjet printing, laser cutting or mechanical cutting) can be utilized based on the type of pattern forming material and the dimension of patterns desired to be patterned onto the fibrous material. The conformity of the pattern forming material with the fibrous material can be achieved by the fastening effect from the pre -strained elastomeric substrate after the strain is removed and the elastomeric substrate shrinks.

In another aspect, there is provided an assembly of a three-dimensional (3D) array of a plurality of patterned fibrous material on an elastomeric substrate.

Advantageously, different layers of patterns can also be pre -fabricated on the two-dimensional sacrificial film, which can be transferred to the fibrous material in a one-step manner. The three dimensional structures formed on the fibrous material are compatible with textile based wearable electronics, which enables them for long term use, more integration and lighter weight.

Definitions

The following words and terms used herein shall have the meaning indicated:

The term "patterned fibrous material" as used herein refers to a fibrous material that has another type of material with a designed shape forming a pattern on the surface of the fibrous material. The material making up the pattern can be in conformal contact with the surface of the fibrous material or a gap may exist that can be minimized by fastening or stabilizing by encapsulation. The term "sacrificial" as used herein refers to a film that is used as an intermediate for a specific purpose, which can later be removed by physical or chemical means such as dissolving in a certain solvent. The term "elastomeric substrate" as used herein refers to a material that can be stretched to a certain amount of strain by an external force in one or multiple specific directions, which can return or be restored to its original shape after the force is removed.

The term "strain" as used herein refers to a deformation caused by an external force relative to the original shape or size of a body. The term "strain" as used herein specifically refers to an elastic deformation of a body that can return or be restored to its original shape after the external force is removed.

The term "two-dimensional (2D)" as used herein refers to a shape with only two dimensions (such as width and height) but no thickness or the thickness is not significant (e.g. ratio of the width along x and y plane to the thickness along z-axis of the pattern forming material is at least 20: 1).

The term "three-dimensional (3D)" as used herein refers to a structure having the three dimensions of length, width and height. It can be formed by an out-of-plane bending or buckling of a two- dimensional pattern or material.

The term "buckling" as used herein refers to a deformation that occurs due to axial compressive loading. If the fabricated pattern is on a two-dimensional plane (e.g. on the surface of a substrate), the buckling process can force the patterned material to transform into a three-dimensional structure in a controlled manner by the design of the extent of buckling.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub- ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Detailed Disclosure of Embodiments

Exemplary, non-limiting embodiments of a method of forming a patterned fibrous material will now be disclosed.

The method of forming a patterned fibrous material may comprise the steps of:

b) disposing a fibrous material onto said patterned sacrificial film; and

The pattern forming material may be a conductor, a semiconductor, an insulator or a mixture thereof.

The pattern forming material may be patterned on a substrate by methods comprising photolithography, inkjet printing, 3D printing, laser cutting or mechanical cutting.

The ratio of the width (along xy plane) to the thickness (along z-axis) of the pattern forming material may be in the range of about 20 to about 50, about 25 to about 50, about 30 to about 50, about 35 to about 50, about 40 to about 50, about 45 to about 50, about 20 to about 45, about 20 to about 40, about 20 to about 35, about 20 to about 30, about 20 to about 25, or sub-ranges there between.

The pattern forming material may be masked with a coating that has a low adhesion attraction force to the surface of the elastomeric substrate as compared to the regions of the pattern forming material without coating. The selected regions without coating are termed as "adhesion pad(s)" or "bonding site(s)". The mask coating may be removed or etched chemically by exposure to suitable chemicals without damaging the pattern forming material. The mask coating is used to define the regions of adhesion pads to be attached to the pre-stretched elastomeric substrate.

The pattern forming material may be formed on the sacrificial film by transfer from a substrate. The material of the sacrificial film may be any suitable material. Exemplary material for the sacrificial film may be selected from the group consisting of polyvinylalcohol or polyvinylacetate.

The fibrous material may be selected from the group consisting of wire, filament, thread, yarn, polyester, nylon, spandex, cotton, aramide, wool, hydrogel fibers, other synthetic fibers, or combinations of them. The fibrous material may be partially immobilized to the sacrificial film mechanically or chemically.

The elastomeric substrate may be stretched to a pre-determined strain in specific directions. The amount of applied strain (such as tensile strain) should always be lower than the elastic limit of the elastomeric substrate so that the elastomeric substrate recovers its original dimension after the applied strain is removed. The elastomeric substrate may be selected from the group consisting of silicon elastomer or polyurethane elastomer. The amount of pre-determined strain based on the original dimension of the elastomeric substrate can be in the range of about 50% to about 120%, about 60% to about 120%, about 70% to about 120%, about 80% to about 120%, about 90% to about 120%, about 100% to about 120%, about 110% to about 120%, about 50% to about 110%, about 50% to about 100%, about 50% to about 90%, about 50% to about 80%, about 50% to about 70%, or about 50% to about 60%o. The elastomeric substrate may be pretreated with ultraviolet radiation, oxygen, ozone plasma, or application of a thin layer of adhesive coating. Bonding may be performed such that the direction of applied strain on the pre-stretched elastomeric substrate is aligned with the intended directions of buckling of pattern forming material. Such bonding is utilized to attach the adhesion pads of the pattern forming material to the elastomeric substrate.

The assembly of patterned fibrous material with the sacrificial film on the elastomeric substrate may be exposed to a suitable solvent that will remove the sacrificial film, but will not remove the low- adhesion coating on the pattern forming material. Where the sacrificial film used in PVA, water may be used as the solvent. The removal of the sacrificial film can be performed by immersion in a bath of the solvent, or the solvent can be sprayed repeatedly onto the assembly to remove the sacrificial film.

When the tensile strain force is applied on the fibrous material, this causes the fibrous material to straighten so that the fibrous material resides along the longitudinal axis and interior of the pattern forming material after the appropriate tensile strain is applied, and remain interior to the pattern forming material after the tensile force on both ends is removed. The direction and the magnitude of tensile force applied may be adjusted to minimize damages to the pattern forming material. This tensile strain is applied on the fibrous material as compared to the previous strain that is applied on the elastomeric substrate.

The elastomeric substrate may be re-stretched along the longitudinal axis of the assembly of patterned fibrous material with the sacrificial film on the elastomeric substrate. The amount of re-stretched strain can be in the range of about 50% to about 120%, about 60% to about 120%, about 70% to about 120%, about 80% to about 120%, about 90% to about 120%, about 100% to about 120%, about 110% to about 120%, about 50% to about 110%, about 50% to about 100%, about 50% to about 90%, about 50% to about 80%, about 50% to about 70%, or about 50% to about 60%. A minimal amount of strain may be applied so that the interior of the three-dimensional (3D) array of the pattern forming material is in conformal contact with the surface of the fibrous material.

The method as defined herein may further comprise a step of sealing the 3D array of pattern forming material and the fibrous material together by applying a suitable encapsulating material. The encapsulating material can be selected from different types of epoxy, thermoplastic or thermosetting polymers, that can then be cured to encapsulate the pattern forming material onto the fibrous material. The curing of the encapsulating material may be via heat or ultraviolet light.

The method as defined herein may further comprise a step of detaching the encapsulated 3D array of patterned fibrous material from the elastomeric substrate. The detaching can be done mechanically or by applying a suitable chemical or mixture of chemicals to dissociate bonding between the elastomeric substrate and the adhesion pads of the pattern forming material.

There is provided a three-dimensional (3D) array of a plurality of patterned fibrous material on an elastomeric substrate. The three-dimensional (3D) array may further comprise a suitable encapsulating material. The elastomeric substrate may be detached from the encapsulated 3D array of a plurality of patterned fibrous material.

Brief Description of Drawings

The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention. Fig.l

[Fig. 1] is a schematic diagram showing a process of forming a patterned fibrous material, whereby the fibrous material is a straight fiber.

Fig.2

[Fig. 2] is a schematic diagram of a process of forming a patterned fibrous material, whereby the fibrous material is a zigzag fiber. Detailed Description of Drawings

Referring to Fig. 1, there is provided a process 1 for forming a patterned fibrous material, whereby the patterned fibrous material is a straight fiber. In Step 1 , there is a sinusoidal pattern forming material 100 formed on a sacrificial film 102 with adhesion pads 101 defined by a mask coating. A fibrous material 110 is aligned above with its longitudinal axis 111 parallel to the longitudinal axis of the pattern forming material 103. Two ends of the fibrous material are immobilized on the sacrificial film 102. In Step 2, the assembly is transferred and the exposed adhesion pads 120 are attached to a pre- stretched elastomeric substrate 131. The longitudinal axis of the assembly 130 is perpendicular to the tensile strain axis of the elastomeric substrate. In Step 3, the sacrificial film 102 is dissolved with a solvent. In Step 4, the axis strain from the elastomeric substrate is removed; hence the distance between adhesion pads along the direction of tensile strain after the strain release is smaller than that before the strain release.

Referring to Fig. 2, there is provided a process 2 for forming a patterned fibrous material, whereby the patterned fibrous material is a sewed zigzag fiber. In Step 1 , there is a sinusoidal pattern forming material 200 formed on a sacrificial film 202 with adhesion pads 201 defined by a mask coating. The fibrous material 210 is sewed on the sacrificial film in zigzag pattern above 212 and below 211 the pattern forming material and sacrificial film assembly. The zigzag pattern is anti-phase to the sinusoidal pattern forming material. In Step 2, the assembly is transferred and the adhesion pads 222 are attached to a pre-stretched elastomeric substrate 220. In Step 3, the sacrificial film 202 is dissolved with a solvent. In Step 4, the tensile strain is removed from the elastomeric substrate 220. In Step 5, the fibrous material is straightened by applying tensile strain on two ends of fibrous material and along the longitudinal axis of the assembly 230. Examples

Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1: Forming a patterned fibrous material with a straight fiber

A two-dimensional (2D) array of pattern forming material with the pattern as shown in Fig. 1 was firstly made on a selected substrate. There are many available methods for patterning 2D array of pattern forming material. These methods include photolithography, inkjet printing, 3D printing, laser cutting, and mechanical cutting. The ratio of the width (along xy plane) to the thickness (along Z-axis) of the pattern forming material should be at least >20: 1.

Selected region(s) of the pattern forming material were masked with a coating that has very low adhesion attraction force for the surface of pre-treated elastomeric substrate than selected regions of pattern forming material without coating. The selected regions without coating will be termed as "adhesion pads" or "bonding sites" 101. The coating can be removed or etched chemically by exposure to suitable chemicals without damaging the pattern forming material. Patterned pattern forming material 100 was then transferred to a sacrificial film 102. Materials of sacrificial film includes, but not limited to, polyvinylalcohol and polyvinylacetate.

The fibrous material 110 was aligned above and parallel to the longitudinal axis of pattern forming material 103 with the longitudinal axis of the fibrous material 111 and two ends of the fibrous material were immobilized on the sacrificial PVA film (Step 1).

The assembly was transferred and the exposed adhesion pads 120 were attached to the pre- stretched elastomeric substrate 131. The longitudinal axis of the assembly 130 was perpendicular to the tensile strain axis of the elastomeric substrate (Step 2).

The sacrificial film was dissolved with water (Step 3). The axis strain was removed from elastomeric substrate (Step 4).

Example 2: Forming a patterned fibrous material with a sewed zigzag fiber

A two-dimensional (2D) array of pattern forming material with the pattern as shown in Fig. 2 was firstly made on a selected substrate. There are many available methods for patterning 2D array of pattern forming material. These methods include photolithography, inkjet printing, 3D printing, laser cutting, and mechanical cutting. The ratio of the width (along xy plane) to the thickness (along Z-axis) of the pattern forming material should be at least >20: 1.

Selected regions of the pattern forming material were masked with a coating that has very low adhesion attraction force for the surface of pre-treated elastomeric substrate than selected regions of pattern forming material without coating. The selected regions without coating are termed as "adhesion pads" or "bonding sites" 201. The coating can be removed or etched chemically by exposure to suitable chemicals without damaging the pattern forming material.

Patterned pattern forming material 200 was then transferred to a sacrificial film 202. Materials of sacrificial film includes, but not limited to, polyvinylalcohol and polyvinylacetate.

The fibrous material 210 was sewed on the sacrificial PVA film in zigzag pattern above 212 and below 211 the pattern forming material-PVA assembly. The zigzag pattern was anti-phase to the sinusoidal pattern forming material (Step 1). The assembly was transferred and the exposed adhesion pads 222 were attached to a pre- stretched elastomeric substrate. The longitudinal axis of the assembly 223 was parallel to the tensile strain axis of the elastomeric substrate (Step 2). The sacrificial PVA film as dissolved with water (Step 3). Tensile strain was removed from the elastomeric substrate (Step 4).

The fibrous material was straightened by applying tensile strain on two ends of the fibrous material and along the longitudinal axis of the assembly 230 (Step 5).

In some embodiment, after the fibrous material is straightened, the elastomeric substrate is re- stretched along the longitudinal axis of the assembly of the patterned fibrous material on the elastomeric substrate assembly. As a result of the partial bonding between the 3D array and elastomeric substrate, the 3D array of the pattern forming material was pulled and elongated along with the stretched elastomeric substrate in the direction of the applied tensile stress. This applied strain also resulted in radial shrinkage of the 3D array of the pattern forming material. A minimal amount of strain was applied so that the interior of 3D array of the pattern forming material was in conformal contact with the surface of the fibrous material. The 3D array of pattern forming material and the fibrous material were sealed together by applying a suitable encapsulating material.

The encapsulated 3D array of patterned fibrous material were detached from the elastomeric substrate mechanically or by applying a suitable chemical or mixture of chemicals to dissociate the bonding between the elastomeric substrate and the adhesion pads of the pattern forming material.

Industrial Applicability In the present disclosure, the patterned fibrous material may be applied to electronics on textile, wearable devices, implants and other areas of textile based flexible electronics.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

I. A method of forming a patterned fibrous material comprising the steps of:

b) disposing a fibrous material onto said patterned sacrificial film; and

2. The method according to claim 1, wherein the pattern forming material is a conductor, a semiconductor, an insulator or a mixture thereof.

3. The method according to claim 1 or 2, wherein said providing step (a) comprises the step of forming a pattern on a substrate by photolithography, inkjet printing, 3D printing, laser cutting or mechanical cutting.

4. The method according to any one of the preceding claims, further comprising the step of applying a masked coating onto said pattern forming material.

5. The method according to any one of the preceding claims, comprising the step of selecting the material of said sacrificial film from the group consisting of polyvinylalcohol or polyvinylacetate.

6. The method according to any one of the preceding claims, wherein said disposing step (b) comprises the step of partially immobilizing said fibrous material to said patterned sacrificial film by mechanical or chemical means.

7. The method according to any one of the preceding claims, wherein said subjecting step (c) comprises the step of stretching said elastomeric substrate to obtain said elastomeric substrate under strain, wherein said elastomeric substrate under strain has a pre-determined strain in specific directions.

8. The method according to claim 7, comprising the step of selecting the amount of strain applied, wherein the amount of strain applied is lower than the elastic limit of said elastomeric substrate.

9. The method according to any one of the preceding claims, wherein said elastomeric substrate is a silicon elastomer or a polyurethane elastomer.

10. The method according to any one of the preceding claims, comprising the step of pre-treating the elastomeric substrate with UV, oxygen, ozone plasma, or a thin layer of adhesive coating.

I I. The method according to any one of the preceding claims, comprising the step of exposing the patterned fibrous material with the sacrificial film on said elastomeric substrate to a solvent and removing the sacrificial film.

12. The method according to any one of the preceding claims, further comprising the step of applying a tensile force on the patterned fibrous material to straighten the patterned fibrous material.

13. The method according to claim 12, comprising the step of adjusting the direction and the magnitude of tensile force applied onto said patterned fibrous material.

14. The method according to any one of the preceding claims, further comprising the step of re- stretching the elastomeric substrate along a longitudinal axis of the patterned fibrous material on the elastomeric substrate.

15. The method according to any one of the preceding claims, further comprising the step of sealing the pattern-forming material and the fibrous material together by applying an encapsulating material.

16. The method according to any one of the preceding claims, further comprising the step of detaching the encapsulated patterned fibrous material from the elastomeric substrate

17. An assembly of a three-dimensional array of a plurality of patterned fibrous material on an elastomeric substrate, wherein said assembly is obtained from the method according to any one of claims 1 to 16.