CN111282528B - Micro-reactor and method based on liquid drop tweezers - Google Patents

Micro-reactor and method based on liquid drop tweezers Download PDF

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CN111282528B
CN111282528B CN202010131463.7A CN202010131463A CN111282528B CN 111282528 B CN111282528 B CN 111282528B CN 202010131463 A CN202010131463 A CN 202010131463A CN 111282528 B CN111282528 B CN 111282528B
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droplet
tweezers
reaction
liquid drop
hydrophobic
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CN111282528A (en
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黄海波
卞雄恒
陈立国
朱易辰
申浩
顾鸣伟
马友文
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Suzhou University
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Suzhou University
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/0093—Microreactors, e.g. miniaturised or microfabricated reactors

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Abstract

The invention discloses a micro-reactor based on droplet tweezers, which comprises a supporting piece and droplet tweezers, wherein the supporting piece comprises two supporting arms, the droplet tweezers comprise two clamping plates, each clamping plate comprises a hydrophobic plate and a flexible metal elastic sheet connected with the hydrophobic plate, each hydrophobic plate comprises a base plate, a hydrophobic layer arranged at the upper end of the base plate and a super-hydrophobic layer arranged at the lower end of the base plate, and the two flexible metal elastic sheets are respectively connected with one end of the two supporting arms. The invention also discloses a micro-reaction method. The flexible metal elastic sheet is arranged, the function that the included angle between the two hydrophobic plates is reduced is realized by small extrusion force, so that the liquid drops move to the upper end inside the liquid drop tweezers, the position of the liquid drops is quickly reset, the hydrophobic plates are provided with the hydrophobic layers at the upper ends, and the super-hydrophobic layers at the lower ends, so that the liquid drop tweezers can be ensured to absorb the first reaction liquid drops and the second reaction liquid drops, and controllable micro-reaction operation can be realized without additional electric fields or magnetic fields and the like.

Description

Micro-reactor and method based on liquid drop tweezers
Technical Field
The invention relates to a microreactor, in particular to a microreactor based on liquid drop tweezers and a method.
Background
With the development of chemical and biological technologies, various fluid-based microreaction technologies are receiving increasing attention due to their low consumption and good controllability. The earliest fluid-based microreaction was mainly based on microchannel technology driving droplets by a micropump pump, which served as reaction sites in individual independent "rooms", but this method was very wasteful of reagents; for the requirement of reducing reagent consumption, one starts to use individual droplets as reaction sites in the microchannel, but this method is difficult to control due to the restriction of the channel; then, the students do not use the traditional micro-channel technology, but drive the liquid drop by external driving methods such as an electric field (a dielectric wetting method), a magnetic field (a method of driving the liquid drop by a magnetic bead), a surface acoustic wave (a method of driving the liquid drop by using acoustic wave vibration) and the like, so that the current micro-fluidic technology based on the liquid drop is gradually formed.
However, droplet-based microreactors have certain disadvantages. The most prominent of these problems are: additional forces or electromagnetic fields need to be applied in the droplets due to the applied driving forces which may interfere with the progress of some reactions, especially in certain biological reactions where biological activity may be affected. Therefore, a micro-reactor which can perform micro-reaction without additional driving is urgently needed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a micro-reactor based on liquid drop tweezers and a method.
In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:
the utility model provides a micro-reactor based on liquid drop tweezers, includes support piece, liquid drop tweezers, support piece includes two support arms, liquid drop tweezers include two splint, every splint include the hydrophobic board, with the flexible metal shell fragment that the hydrophobic board is connected, every the hydrophobic board includes the base plate, sets up hydrophobic layer and setting of base plate upper end are in the super hydrophobic layer of base plate lower extreme, two flexible metal shell fragment respectively with two the one end of support arm is connected.
As a further improvement of the invention, the other ends of the two supporting arms are connected into a whole.
As a further improvement of the invention, the substrate and the flexible metal elastic sheet are connected through an adhesive tape.
As a further improvement of the present invention, the hydrophobic layer is a teflon layer.
As a further improvement of the present invention, the hydrophobic layer has a contact angle of 120 degrees.
As a further improvement of the present invention, the super-hydrophobic layer is a nanoparticle coating.
As a further improvement of the invention, the contact angle of the super-hydrophobic layer is 150 degrees.
The invention also discloses a micro-reaction method, which uses the micro-reactor and comprises the following steps:
(1) the liquid drop tweezers are close to the first reaction liquid drop and are in contact with the first reaction liquid drop to form a liquid bridge, the opening and closing of the liquid drop tweezers are reduced to suck the first reaction liquid drop, and the first reaction liquid drop enters the liquid drop tweezers;
(2) performing at least one cyclic opening and closing step, wherein the opening and closing step comprises reducing the opening and closing of the droplet tweezers and then increasing the opening and closing of the droplet tweezers until the first reaction droplet moves to the upper end position of the droplet tweezers;
(3) the liquid drop tweezers are close to the second reaction liquid drop and are in contact with the second reaction liquid drop to form a liquid bridge, the opening and closing of the liquid drop tweezers are reduced to suck the second reaction liquid drop, and the second reaction liquid drop enters the liquid drop tweezers;
(4) and increasing the opening and closing of the liquid drop tweezers, so that the first reaction liquid drop at the upper end falls down, and the first reaction liquid drop and the second reaction liquid drop are mixed to carry out micro reaction.
As a further improvement of the present invention, in the step (2), the lower ends of the droplet tweezers are folded, and then at least one cycle of opening and closing steps is performed, where the opening and closing step includes first rotating and squeezing the droplet tweezers inwards, and then rotating and stretching the droplet tweezers outwards until the first reaction droplet moves to the upper end position of the droplet tweezers, and opening the lower ends of the droplet tweezers.
As a further improvement of the present invention, in the step (4), the lower ends of the droplet tweezers are folded, and then the droplet tweezers are rotated outwards to stretch the droplet tweezers to increase the opening and closing of the droplet tweezers, so that the first reaction droplet at the upper end falls down, and the first reaction droplet and the second reaction droplet are mixed to perform a micro reaction.
The invention has the beneficial effects that:
(1) the support is arranged as a backbone of the liquid drop tweezers, and the hydrophobic unparallel plate structure can be supported to realize the hydrophobic unparallel plate structure, namely the extrusion and stretching operation of the two hydrophobic plates.
(2) According to the hydrophobic plate, the hydrophobic layer is arranged at the upper end, the super-hydrophobic layer is arranged at the lower end, so that when the droplet tweezers absorb the second reaction droplets, the first reaction droplets at the upper end are relatively more hydrophilic and cannot fall down, but are fixed at the upper end, the second reaction droplets are prevented from entering the droplet tweezers to be influenced, the first reaction droplets and the second reaction droplets can enter the droplet tweezers, meanwhile, the droplets are prevented from being retained on the side surfaces of the droplet tweezers by the aid of the characteristic that the hydrophobic layer cannot be adhered to the droplets, the first reaction droplets fall down and are mixed with the second reaction droplets, and micro-reaction is realized.
(3) Through setting up flexible metal shrapnel, utilize its characteristic of being easily buckled, can make liquid droplet tweezers in extrusion process to less extrusion force realizes the function that the contained angle diminishes between two hydrophobic boards, thereby makes the liquid droplet move to the inside upper end of liquid droplet tweezers, realizes resetting fast of liquid droplet position.
(4) The invention adopts the liquid drop tweezers, can change the direction and the size of the capillary force applied to the liquid drop through the change of the hydrophobic non-parallel plate structure, can realize the upward movement and the downward movement of the liquid drop, thereby realizing the absorption/release of the liquid drop, realizing the controllable micro-reaction operation without an extra electric field or a magnetic field and the like, and ensuring the biological activity in some specific biological reactions.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a microreactor in accordance with a preferred embodiment of the present invention;
FIG. 2 is a schematic structural view of a hydrophobic plate according to a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of a microreactor controlling droplet placement in accordance with a preferred embodiment of the present invention;
FIG. 4 is a schematic diagram of the process of droplet pickup into droplet tweezers in accordance with a preferred embodiment of the present invention;
FIG. 5 is a flow chart of a microreactor according to a preferred embodiment of the present invention controlling a first reaction droplet and a second reaction droplet to achieve a microreaction;
FIG. 6 is a schematic diagram of a change of state of a microreactor with a first reaction droplet position reset according to a preferred embodiment of the present invention;
FIG. 7 is a diagram for analyzing the force and motion trend of the liquid drop in the non-parallel plate and a diagram for experimental results under the condition of the opposite/far translational motion of the hydrophobic non-parallel plate according to the preferred embodiment of the invention;
FIG. 8 is a graph of analysis of the force and movement tendency of a droplet in a non-parallel plate with the hydrophobic non-parallel plate closed/open and experimental results for a preferred embodiment of the present invention;
FIG. 9 shows the difference between the droplets
Figure BDA0002395876280000041
And a motion trend plot at θ;
FIG. 10 is a schematic view of a droplet entering a droplet tweezer to form a liquid bridge according to a preferred embodiment of the present invention;
FIG. 11 shows the difference between the droplets
Figure BDA0002395876280000042
And a motion trend plot at θ;
FIG. 12 shows the difference between the droplets
Figure BDA0002395876280000043
And a motion trend plot at θ.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The inventors of the present invention have found that a change in the configuration of the hydrophobic non-parallel plate can change not only the magnitude of the tensile force exerted by the droplet, but also the direction of the tensile force exerted by the droplet.
Referring to fig. 7-9, the force and motion of the droplets in the hydrophobic non-parallel plate structure were analyzed. Droplet motion is affected primarily by two forces. The first is the asymmetric Rayleigh force caused by the structure, which causes droplet motion, determining the direction of droplet motion. The second is the hysteresis force caused by Contact Angle Hysteresis (CAH), which hinders the movement of the liquid drop and determines whether the liquid drop can move under the action of the pulling force.
These two points were analyzed one by one as follows:
first, the structure generates a Rayleigh force, the magnitude and direction of which are determined by two factors, the first being the width L of the liquid bridge bottom ends in the hydrophobic non-parallel plate structurenHere, to eliminate the influence of the droplet size, at the microscale, use
Figure BDA0002395876280000051
To replace LnAnd more precisely. The second is the angle theta between the hydrophobic plate and the vertical. The influence of these two factors on the direction of droplet motion was analyzed by geometry and laplace's equation. A model of a hydrophobic non-parallel plate structure is shown in fig. 7. Assuming that the Contact Angle (CA) at the bottom of the liquid bridge is alpha1The upper contact angle is alpha2The length of the liquid bridge is D, the distance of the intersection point between the bottom end of the liquid bridge and the non-parallel plate is S, and the volume of the liquid drop in the liquid bridge can be expressed as:
V≈2π·D2·(D+2S)·sinθ (0-1)
in addition, according to the geometric relationship, LnCan use equation LnAnd ≈ 2S · sin θ. Because the droplets are in equilibrium, equation 5-2 needs to be satisfied according to the Laplace equation:
Figure BDA0002395876280000052
if the nanoparticle coating is used as the interface material, a hydrophobic nonparallel plate structure is constructed, assuming alpha1＝α2Approximately 150 deg., a theoretical curve of the trend of the droplet movement can be obtained according to equations 5-1 and 5-2, as shown in fig. 9, the solid line is the pressure equilibrium curve of the droplet, above the solid line is the downward movement trend, below the solid line is the upward movement trend. The inventors have found a larger
Figure BDA0002395876280000053
Or theta will encourage downward movement.
Second, the inventors analyzed the hysteresis force caused by CAH. The upper limit of the contact angle is assumed to be the advancing angle (subscript 'a'), and the lower limit is the receding angle (subscript 'r'). According to the definition of CAH, when the drop moves upwards, α1＝αr，α2＝αa(ii) a When the droplet moves downward, α1＝αa，α2＝αr. Therefore, a curve that the liquid drop can overcome different CAHs and realize upward/downward movement is obtained. As shown in fig. 9, the dotted/dashed line represents a critical curve of downward/upward movement of the droplet when CAH is 10 °, and the two-dotted/dashed line represents a critical curve of downward/upward movement of the droplet when CAH is 20 °. We can then get the motion state of the droplets under different CAHs. For example, due to point A
Figure BDA0002395876280000061
And θ is 5 °) below the solid line, the droplet tends to move upward. Furthermore, since point A is located between the dotted and dashed lines, it is shown that point A can still move upward when CAH ≦ 10, but cannot move upward when CAH ≧ 20. As can be seen from fig. 9, the larger the CAH, the stronger the resistance to droplet movement, but the CAH has no effect on the droplet movement tendency.
Based on the experiments carried out in the prior art,
Figure BDA0002395876280000062
and the effect of theta on this motion was also verified. Experiments As shown in FIG. 7, when the non-parallel plate structures move in translation (translationally), that is, decrease/increase
Figure BDA0002395876280000063
Will produce a corresponding droplet up/down motion; as shown in fig. 8, when the non-parallel plate structure is opened/closed, i.e., theta is decreased/increased, the droplet moves up/down. These results are in full agreement with theoretical and simulation results. All the above shows that the direction and the size of the pull force of the liquid drop can be changed along with the change of the hydrophobic non-parallel plate structure, and the direction is provided for the subsequent absorption/release of the liquid drop.
In addition, the inventors of the present invention found that a change in the configuration of the hydrophobic non-parallel plate enables a repositioning of the position of the droplet, a schematic of which is shown in fig. 3.
When we hold a droplet between hydrophobic non-parallel plates structures, as shown in FIG. 3-a, by rotating inward at a certain angle, the droplet will move upward due to squeezing, assuming that it moves upward by a distance Lup(ii) a Thereafter, if rotated outward at the same angle, as shown in FIG. 3-b, the drop will fall downward, assuming that it has moved downward a distance Ldown. We have found that the distances of upward and downward movement are not equal due to the presence of contact angle hysteresis (L)up≠Ldown) Thus, the resetting of the position of the liquid drop can be realized through a cycle of extrusion and stretching, and the liquid drop is upwards Lup-LdownThe distance of (c). By using the method, the liquid drops can enter the non-parallel plate structure similar to the liquid drop tweezers one by one and react.
Referring to fig. 1 and 2, the invention provides a micro-reactor based on droplet tweezers, which comprises a support member 1 and droplet tweezers 2, wherein the support member 1 comprises two support arms 11, the droplet tweezers 2 comprise two clamping plates, each clamping plate comprises a hydrophobic plate 21 and a flexible metal elastic sheet 22 connected with the hydrophobic plate 21, each hydrophobic plate 21 comprises a base plate 211, a hydrophobic layer 212 arranged at the upper end of the base plate 211 and a super-hydrophobic layer 213 arranged at the lower end of the base plate 211, and the two flexible metal elastic sheets 22 are respectively connected with one end of each of the two support arms 11.
Wherein the support 1 serves as a backbone of the droplet tweezers 2 for supporting the droplet tweezers 2 to perform the squeezing and stretching operations of the two hydrophobic plates 21. The two hydrophobic plates 21 are arranged in an angle, and the two hydrophobic plates 21 are not parallel, namely the two hydrophobic plates 20 form a hydrophobic non-parallel plate structure; the two hydrophobic plates 21 can translate relatively, that is, the two hydrophobic plates 20 can realize opening and closing actions of mutual translation; and the angle between the two hydrophobic plates 21 is adjustable, that is, the two hydrophobic plates 20 can realize the opening and closing action of rotating around the intersection point of the extension lines of the two hydrophobic plates 21. The liquid drops are subjected to different acting forces by means of the opening and closing actions of the two hydrophobic plates 20 in the mutual translation and/or the opening and closing actions of the two hydrophobic plates 20 in the rotation around the intersection point of the extension lines of the two hydrophobic plates 20, and then the liquid drops are sucked or released. When the droplet tweezers suck or release a droplet, the support arm 11 does not contact the droplet, and the hydrophobic plate 21 directly contacts the droplet. Hydrophobic plate 21 sets up hydrophobic layer 212 through the upper end, the lower extreme sets up super hydrophobic layer 213, the upper end surface of hydrophobic plate 21 is hydrophobic nature, the lower extreme surface of hydrophobic plate 21 is super hydrophobic nature, can guarantee like this that droplet tweezers 2 are when absorbing second kind of reaction liquid drop, because the liquid drop of upper end is more hydrophilic relatively, the first kind of reaction liquid drop that is located the upper end position can not down drop, but be fixed in the upper end position, avoid getting into droplet tweezers 2 to the second kind of reaction liquid drop and cause the influence, ensure that first kind of reaction liquid drop and second kind of reaction liquid drop homoenergetic get into in the droplet tweezers. The flexible metal elastic sheet 22 plays a role in the resetting process of the liquid drop position, and the liquid drop tweezers 2 can realize the function of reducing the included angle between the two hydrophobic plates 21 in the extrusion process by utilizing the characteristic that the flexible metal elastic sheet 22 is easy to bend, so that the liquid drops move to the upper end inside the liquid drop tweezers 2.
In order to facilitate the handling of the support 1 and thus the variation of the droplet tweezers 2, it is preferred according to the invention that the other ends of the two support arms 11 are integrally connected.
In the present invention, the substrate 211 is preferably made of a glass material.
In one embodiment, the substrate 211 has a thickness of 150 μm. The length and width of the substrate 211 were 5 cm.
The substrate 211 and the flexible metal dome 22 are preferably connected by an adhesive tape 23.
According to the invention, the hydrophobic layer 212 is preferably a Teflon layer which has good hydrophobic property, so that the application occasions of the liquid droplet tweezers 2 can be further expanded.
In a preferred embodiment, the hydrophobic layer 212 has a contact angle of 120 degrees, which can have good hydrophobic properties and can further expand the application range of the droplet tweezers 2. In order to further expand the range of use of the droplet tweezers 2, the present invention preferably has a Contact Angle Hysteresis (CAH) of the hydrophobic layer 212 of 10 degrees.
Further, the thickness of the water-repellent layer 212 is preferably 100 μm.
According to the invention, the super-hydrophobic layer 213 is preferably a nano-particle coating, and the nano-particle coating has good super-hydrophobic performance, so that the application occasions of the liquid drop tweezers 2 can be further expanded.
In one embodiment, the contact angle of the super-hydrophobic layer 213 is 150 degrees, which can have good super-hydrophobic property and can further expand the application range of the droplet tweezers 2. In order to further expand the range of use of the droplet tweezers 2, the super-hydrophobic layer 213 preferably has a Contact Angle Hysteresis (CAH) of 5 degrees.
Further, the thickness of the super-hydrophobic layer 213 is preferably 100 μm.
It is of course understood that the material of the substrate 211 of the present invention is not limited to glass, and other materials may be used as the substrate. Similarly, the hydrophobic layer 212 is not limited to a teflon layer, and may be a hydrophobic layer made of other materials. Similarly, the super-hydrophobic layer 213 is not limited to the nanoparticle coating layer, and may be a super-hydrophobic layer made of other materials. It is further understood that the hydrophobic plate 21 may be a unitary plate, i.e., the hydrophobic plate is directly made of hydrophobic material and super-hydrophobic material, or the surface microstructure of the substrate 211 directly makes the surface hydrophobic and super-hydrophobic.
The invention also provides a micro-reaction method, and the micro-reactor provided by the invention comprises the following steps:
(1) the liquid drop tweezers 2 are close to the first reaction liquid drop 3 and are in contact with the first reaction liquid drop 3 to form a liquid bridge, the opening and closing of the liquid drop tweezers 2 are reduced to suck the first reaction liquid drop 3, and the first reaction liquid drop 3 enters the liquid drop tweezers 2;
(2) at least one cyclic opening and closing step is carried out, wherein the opening and closing step comprises the steps of reducing the opening and closing of the droplet tweezers 2 and then increasing the opening and closing of the droplet tweezers 2 until the first reaction droplet 3 moves to the upper end position of the droplet tweezers 2. As a preferred scheme, the lower ends of the droplet tweezers 2 are folded, and then at least one cyclic opening and closing step is carried out, wherein the opening and closing step comprises the steps of inwards rotating to squeeze the droplet tweezers 2, then outwards rotating to stretch the droplet tweezers 2 until the first reaction droplet 3 moves to the upper end position of the droplet tweezers 2, and opening the lower ends of the droplet tweezers 2;
(3) the droplet tweezers 2 are close to the second reaction droplet 4 and are in contact with the second reaction droplet 4 to form a liquid bridge, the opening and closing of the droplet tweezers 2 are reduced to suck the second reaction droplet 4, and the second reaction droplet 4 enters the droplet tweezers 2;
(4) the opening and closing of the droplet tweezers 2 are increased, so that the first reaction droplet 3 at the upper end falls down, and the first reaction droplet 3 and the second reaction droplet 4 are mixed to carry out micro reaction. Preferably, the lower ends of the droplet tweezers are folded, and then the droplet tweezers are rotated outwards to stretch the droplet tweezers to increase the opening and closing of the droplet tweezers. As a preferable scheme, the lower end of the droplet tweezers 2 is folded, and then the droplet tweezers 2 are rotated and stretched outwards to increase the opening and closing of the droplet tweezers 2, so that the first reaction droplet 3 at the upper end falls down, and the first reaction droplet 3 and the second reaction droplet 4 are mixed to perform a micro-reaction.
The droplet extraction process was analyzed as follows:
first, the droplet tweezers 2 approach the droplet vertically downwards, and then the droplet enters the droplet tweezers 2 partially to form a liquid bridge, as shown in the figure4 a-b. Secondly, continuing to move the droplet tweezer 2 downwards squeezes more droplets into the droplet tweezer 2, which also means that less is done
Figure BDA0002395876280000091
As shown in fig. 4 b-c. Third, by squeezing, the contact area of the droplet with the surface of the base plate is reduced, and the adhesive force is reduced. In addition, the extrusion is also reduced
Figure BDA0002395876280000092
This increases the upward capillary force. Then, an upward movement of the droplets is generated, as in c-d of fig. 4. Finally, by continuing to squeeze the droplet, the droplet can be made to enter the droplet tweezers 2 completely as shown in d-e of fig. 4.
The inventors found that there are four controllable variables in the droplet extraction process; initial droplet tweezer tip width in first step (L)IniI.e. LnInitial value of) and a critical non-parallel plate included angle (θ); the final pressing height (H) of the droplet tweezers in the second step; final width of the drop tip (L) in the third stepFinal，LnFinal value of). Next, the following paragraphs will discuss these four variables separately.
1. Selecting an appropriate initial droplet tweezer tip width LIniAnd angle theta to ensure that the droplet can partially enter the droplet tweezer (first step)
In the initial state, there is no liquid inside the droplet tweezers. As the droplet tweezers move downward, the droplet will enter the droplet tweezers. However, if the initial droplet tweezer head tip is too small, the droplet will be squeezed to one side of the droplet tweezer. To avoid this, it is necessary to enable the droplets to wet up along the inner side of the non-parallel plates, and then the initial contact angle α needs to satisfy α > αa(αaContact angle of a droplet tweezer). Then, according to the geometrical relationship shown in FIG. 10, the angle thereof is expressed by
Figure BDA0002395876280000101
Can obtain information about LIniAnd the conditional equation of theta, the liquid drop can partially enter the hydrophobic non-parallel plateStructure:
Figure BDA0002395876280000102
wherein R is the spherical radius of the droplet on the open surface, LIniTweezers tip Width for initial droplet, αaThe contact angle of the droplet tweezers. From equation 5-3, L is foundIniAnd R is linearly related, and R is determined by the droplet size
Figure BDA0002395876280000103
And wettability beta of the surface of the soleplateaAnd (6) determining. Thus, if the backplane is assumed to be made of Teflon (β)a120 deg.) coverage, then one can calculate that at different theta the drop enters the drop tweezer
Figure BDA0002395876280000104
The value range of (a). For three different combinations
Figure BDA0002395876280000105
And θ were tested and found to be able to enter the liquid tweezers, consistent with theoretical analysis.
2. Suitable drop tweezers Final pressing height H (second and third steps)
The second step is inevitable and so there is no requirement for control parameters. This conclusion is illustrated from a theoretical point of view, defining the part inside the droplet tweezers as part 1, where the pressure is P1(ii) a The part under the droplet tweezers was part 2, where the pressure was P2. Therefore, P1And P2Can be calculated using the following equation:
Figure BDA0002395876280000111
Figure BDA0002395876280000112
in the formula, LwThe width of the upper end of the liquid bridge of the droplet tweezers, and H the height of the droplet tweezers from the bottom surface. P when the droplet tweezers were moved vertically downwards (H decreased), i.e. part 2 was squeezed2And is increased. Meanwhile, as the droplet enters the droplet tweezer, the droplet in part 1 grows, LwIncrease of P1And decreases. It can be seen that the pressure difference between part 1 and part 2(Δ P ═ P) is seen during the downward movement of the droplet tweezers after the formation of the liquid bridge2-P1) The droplets inevitably move upwards as they grow.
H is mainly limited by the third step. If it is desired to separate the droplet from the floor surface, the adhesion should be overcome. To reduce this adhesion, the droplets are squeezed to reduce the contact area, i.e., to reduce the contact line length of the bottom surface. To accomplish this, leakage should be avoided. Then, whether a droplet leaks depends on two conditions: first, if the motion trend of part 1 is upward, no leakage occurs; second, if part 1 has a tendency to move downward, then the bottom surface "liquid valve" will prevent this leakage. For the first condition, the analysis and equation L for part 1 above is followedw2(S + D) · sin θ, the downward motion can be obtained
Figure BDA0002395876280000113
The value range of (a). For the second condition, then β < β must be satisfieda. The H constraint which can effectively prevent leakage can be obtained by the formulas (5-4) and (5-5):
Figure BDA0002395876280000114
in addition, to
Figure BDA0002395876280000115
And
Figure BDA0002395876280000116
the relationship was analyzed. Assuming the droplet is on the Teflon floor surface, betaa＝120°Its initial radius is R, so its volume
Figure BDA0002395876280000117
Assuming that the droplet height is H before the droplet tweezers are squeezed, part 2 of the droplet is approximately a cylinder. Thus, the volume of the droplet can be approximated by
Figure BDA0002395876280000121
Because L isn< 2R, so Vpart2≤πHR2And is and
Figure BDA0002395876280000122
thereby we obtain
Figure BDA0002395876280000123
And
Figure BDA0002395876280000124
to obtain the approximate transformation relation of
Figure BDA0002395876280000125
The value range of (a).
According to the two conditions, combine
Figure BDA0002395876280000126
And
Figure BDA0002395876280000127
analysis of the relationship obtains the conditions of different theta
Figure BDA0002395876280000128
The value range of (a). As shown in fig. 11, the upper solid line indicates that leakage may occur, and the lower solid line indicates that leakage may not occur.
3. Final width range (L) of tip of droplet tweezer capable of successfully sucking droplet in third stepFinal)
In the third step, L is requiredFinalThe value of (c) is small. If the liquid drop of part 1 can overcome the resistance of CAH, the liquid drop is carried upwards after extrusionThe liquid drops can be far away from the bottom plate (at the moment, the contact area of the surface of the bottom plate is small, the adhesive force is small, and V ispart1V). Thus, from previous analysis, it was obtained that when at different θ, the droplet could overcome the CAH and go completely into the droplet tweezer
Figure BDA0002395876280000129
(ii) range (portion under the solid line in fig. 12). By measuring the complete entry of the droplet into the droplet tweezers at different theta
Figure BDA00023958762800001210
The values of (a) to (b) confirm this theoretical result, and it was found that these points are below the solid line, and the experimental results agree well with the theoretical analysis.
Preferably, during aspiration, the droplet tweezer 2 is initially gapped L before the droplet tweezer 2 contacts the dropletnThe following conditions are satisfied:
Figure BDA00023958762800001211
wherein alpha isaThe contact angle of the liquid drop tweezers is theta, the included angle between the hydrophobic plate of the liquid drop tweezers and the vertical direction is theta, and R is the spherical radius of the liquid drop.
Preferably, during aspiration, the following relationship should be satisfied:
Figure BDA00023958762800001212
wherein H is the minimum height of the liquid drop tweezers from the surface of the bottom plate, and L iswWidth of upper end of liquid bridge, alpha, of tweezers for liquid dropsaContact angle of tweezers for liquid droplet, betaaIs the contact angle of the surface of the bottom plate, and theta is the included angle between the hydrophobic plate of the liquid drop tweezers and the vertical direction.
The micro-reaction method of the present invention will be specifically described below.
(1) Firstly, selecting a proper initial gap of the droplet tweezers 2 according to the size of the first reaction droplet 3, and vertically downwards moving the droplet tweezers, as shown in FIG. 4-a, so that the two hydrophobic plates 21 are close to the first reaction droplet 3 and are in contact with the first reaction droplet 3, thereby forming a liquid bridge in the two hydrophobic plates 21, as shown in FIG. 4-b; then, selecting a proper pressing height of the droplet tweezers 2, and continuously moving the two hydrophobic plates 21 downwards to enable the first reaction droplets 3 to enter between the two hydrophobic plates 21 more, as shown in fig. 4-c; then, selecting a proper squeezing distance of the droplet tweezers 2, and squeezing the first reaction droplet 3 inwards at both sides of the two hydrophobic plates 21 to reduce the contact of the first reaction droplet 3 with the bottom plate surface so as to reduce the adhesion force (adhesion force) and simultaneously reduce the width of the bottom end of the liquid bridge so as to obtain a larger upward capillary force, as shown in fig. 4-d; finally, the first reaction liquid drop 3 is sucked up by continuously extruding the first reaction liquid drop 3 to enable the first reaction liquid drop 3 to completely enter between the two hydrophobic plates 21, as shown in FIG. 4-e;
(2) the lower ends of the droplet tweezers 2 are folded, that is, the lower ends of the two hydrophobic plates 21 of the droplet tweezers 2 are abutted together, and meanwhile, the two hydrophobic plates 21 can rotate around the abutted part of the two hydrophobic plates 21, as shown in fig. 5-a, and then at least one cyclic opening and closing step is performed, as shown in fig. 5 b-c and fig. 6, wherein the opening and closing step comprises the steps of rotating inwards to press the droplet tweezers 2, rotating the two hydrophobic plates 21 towards each other, moving the first reaction droplet 3 upwards, rotating outwards to pull the droplet tweezers 2, rotating the two hydrophobic plates 21 back to each other, moving the first reaction droplet 3 downwards until the first reaction droplet 3 moves to the upper end position of the droplet tweezers 2, and simultaneously, because the upper end position surface of the droplet tweezers 2 is the hydrophobic layer 212, the lower end position surface of the droplet tweezers 2 is the super-hydrophobic layer 213, and the upper end of the droplet tweezers 2 is more hydrophilic than the lower end, the first reaction droplet 2 will be fixed at the upper end of the droplet tweezers and will not fall down, and the lower end of the droplet tweezers 2 is opened, as shown in fig. 5-d, to reset the position of the first reaction droplet 3, as shown in fig. 5-e;
(3) selecting a proper initial gap of the droplet tweezers 2 according to the size of the second reaction droplet 4, and vertically placing the droplet tweezers 2 downwards, as shown in FIG. 4-a, so that the two hydrophobic plates 21 are close to the second reaction droplet 4 and contact with the second reaction droplet 4, thereby forming a liquid bridge in the two hydrophobic plates 21, as shown in FIG. 4-b; then, selecting a proper pressing height of the droplet tweezers 2, and continuously moving the two hydrophobic plates 21 downwards to enable the second reaction droplets 4 to enter between the two hydrophobic plates 21 more, as shown in fig. 4-c; then, selecting a proper squeezing distance of the droplet tweezers 2, and squeezing the second reaction droplet 4 inwards at both sides of the two hydrophobic plates 21 to reduce the contact of the second reaction droplet 4 with the bottom plate surface so as to reduce the adhesion force (adhesion force) and simultaneously reduce the width of the bottom end of the liquid bridge so as to obtain a larger upward capillary force, as shown in fig. 4-d; finally, the second reaction liquid drop 4 can completely enter the liquid drop tweezers 2 by continuously extruding the second reaction liquid drop 4, and the second reaction liquid drop 4 is sucked up, as shown in fig. 4-e;
(4) the lower ends of the droplet tweezers 2 are closed, that is, the lower ends of the two hydrophobic plates 21 of the droplet tweezers 2 are abutted together, meanwhile, the two hydrophobic plates 21 can rotate relatively around the abutting surfaces, as shown in fig. 5-f, then the droplet tweezers 2 are rotated outwards to stretch to increase the opening and closing of the droplet tweezers 2, the lower ends of the droplet tweezers 2 are opened, as shown in fig. 5-g, so that the first reaction droplets 3 at the upper ends fall down, as shown in fig. 5-h, and the first reaction droplets 3 and the second reaction droplets 4 are mixed to perform micro-reaction.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims (9)

1. The utility model provides a micro-reactor based on liquid droplet tweezers, its characterized in that includes support piece, liquid droplet tweezers, support piece includes two support arms, liquid droplet tweezers include two splint, every splint include the hydrophobic board, with the flexible metal shrapnel that the hydrophobic board is connected, every the hydrophobic board includes the base plate, sets up hydrophobic layer and setting of base plate upper end are in the super hydrophobic layer of base plate lower extreme, two flexible metal shrapnel respectively with two the one end of support arm is connected, two the other end of support arm links into an organic whole.
2. The droplet tweezers-based microreactor of claim 1, wherein said base plate and said flexible metal dome are connected by adhesive tape.
3. The droplet tweezers-based microreactor of claim 1, wherein said hydrophobic layer is a teflon layer.
4. The droplet tweezers-based microreactor according to claim 1, wherein the contact angle of the hydrophobic layer is 120 degrees.
5. The droplet tweezers-based microreactor according to claim 1, wherein said superhydrophobic layer is a nanoparticle coating.
6. The droplet tweezers-based microreactor according to claim 1, wherein the contact angle of the superhydrophobic layer is 150 degrees.
7. A microreaction method using a microreactor according to any of claims 1 to 6, comprising the steps of:
(1) the liquid drop tweezers are close to the first reaction liquid drop and are in contact with the first reaction liquid drop to form a liquid bridge, the opening and closing of the liquid drop tweezers are reduced to suck the first reaction liquid drop, and the first reaction liquid drop enters the liquid drop tweezers;
(2) performing at least one cyclic opening and closing step, wherein the opening and closing step comprises reducing the opening and closing of the droplet tweezers and then increasing the opening and closing of the droplet tweezers until the first reaction droplet moves to the upper end position of the droplet tweezers;
(3) the liquid drop tweezers are close to the second reaction liquid drop and are in contact with the second reaction liquid drop to form a liquid bridge, the opening and closing of the liquid drop tweezers are reduced to suck the second reaction liquid drop, and the second reaction liquid drop enters the liquid drop tweezers;
(4) and increasing the opening and closing of the liquid drop tweezers, so that the first reaction liquid drop at the upper end falls down, and the first reaction liquid drop and the second reaction liquid drop are mixed to carry out micro reaction.
8. The micro-reaction method according to claim 7, wherein in the step (2), the lower end of the droplet tweezers is closed, and then at least one cycle of opening and closing steps is performed, wherein the opening and closing steps comprise inward rotating to press the droplet tweezers, and outward rotating to stretch the droplet tweezers until the first reaction droplet moves to the upper end position of the droplet tweezers, and the lower end of the droplet tweezers is opened.
9. The micro-reaction method according to claim 7, wherein in the step (4), the lower ends of the droplet tweezers are closed, and then the droplet tweezers are rotated outwards to stretch the droplet tweezers to increase the opening and closing of the droplet tweezers, so that the first reaction droplet at the upper end falls down, and the first reaction droplet and the second reaction droplet are mixed to perform micro-reaction.
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