A Reversible Adhesion Surface Based on LCEs and a Method for Manipulating Fine Particles

Abstract

The present invention belongs to the technical field of manipulation of fine particle adhesion, and specifically discloses a reversible adhesion surface based on LCEs and a method for manipulating fine particles, which includes an electrothermal film and a solid adhesion layer disposed on the electrothermal film. The solid adhesion layer is constructed by using thermotropic liquid crystal elastomer LCEs. An array of cylindrical microstructures is arranged on the surface of the solid adhesion layer. The cylindrical microstructures include a first microstructure in an upright intermediate state and a second microstructure in a bent intermediate state that can be mutually converted. By adopting the above-mentioned reversible adhesion surface based on LCEs and the method for manipulating fine particles, the present invention realizes effective desorption of fine particles deeply embedded in the gaps of the microstructures, broadens the particle size range for reversible adhesion manipulation of fine particles, and improves the desorption efficiency of fine particles.

Description

Technical Field

[0001] The present invention relates to the technical field of manipulation of fine particle adhesion, and particularly to a reversible adhesion surface based on LCEs and a method for manipulating fine particles. Background Art

[0002] Reversible adhesion surfaces can reversibly regulate the adhesion force and have broad application prospects in fields such as climbing robots and drug release. Existing reversible adhesion surfaces with surface microstructures are vulnerable to fine particle contamination, resulting in a decline in adhesion performance, and require removing the adhered particles to restore the adhesion force. At the same time, there is also a wide demand for reversible adhesion manipulation of fine particles in fields such as drug delivery and micro-object manipulation.

[0003] The adhesion manipulation of fine particles is mainly achieved through contact manipulation, that is, using external stresses such as shear to drive the relative sliding / rolling of fine particles and the microstructures to achieve the de-adhesion of fine particles. Such contact manipulation methods are prone to damaging the surface microstructures and are difficult to remove fine particles deeply embedded in the gaps of the microstructures. The non-contact manipulation method by controlling the spontaneous change of the surface microstructure morphology is expected to achieve the de-adhesion of embedded fine particles. Shape memory materials can convert between different morphologies, which is an effective way to realize the change of microstructures.

[0004] In the prior art, most studies focus on unidirectional shape memory polymers. For example, the patent application with publication number CN115831768A discloses a method for curved surface transfer based on a shape memory polymer stamp, and the patent with publication number CN116376460B discloses a reversible solid-solid-solid liquid adhesion integrated material based on the shape memory effect and its preparation and adhesion regulation method. Such materials still require external force drive when cyclically changing morphologies, which may exacerbate the deep embedding of fine particles in the gaps of the microstructures, resulting in low de-adhesion efficiency.

[0005] Liquid crystal elastomers (LCEs) have a bidirectional shape memory effect and can cyclically and reversibly convert the surface microstructures between different morphologies without external stress drive. For example, the patent application with publication number CN114804009A discloses a temperature-controlled time-varying bionic adhesion structure and regulation method for rapid switching of adhesion / desorption. However, its stretching and deformation mode is only applicable to the adhesion regulation between two surfaces, and it is difficult to achieve the rolling / sliding of fine particles relative to the microstructure surface and cannot be used for the adhesion manipulation of fine particles. Summary of the Invention

[0006] The purpose of the present invention is to provide a reversible adhesion surface based on LCEs and a method for manipulating fine particles, which can effectively desorb fine particles deeply embedded in the gaps of the microstructures, broaden the particle size range of reversible adhesion manipulation of fine particles, and improve the de-adhesion efficiency of fine particles.

[0007] To achieve the above object, the present invention provides a reversible adhesion surface based on LCEs, comprising an electrothermal film and a solid adhesion layer disposed on the electrothermal film. The solid adhesion layer is constructed by a thermotropic liquid crystal elastomer LCEs. The surface of the solid adhesion layer is provided with columnar microstructures arranged in an array. The columnar microstructures include a first microstructure in an upright intermediate state and a second microstructure in a bent intermediate state that can be mutually converted. Under the temperature control of the electrothermal film, the columnar microstructures can reversibly convert between the first microstructure in an upright intermediate state and the second microstructure in a bent intermediate state.

[0008] Preferably, the method for constructing the solid adhesion layer by a thermotropic liquid crystal elastomer LCEs is as follows:

[0009] S1. Prepare a convex hard mold with a columnar array by 3D printing technology, pour a polymer material on the convex hard mold, and prepare a polymer concave mold with a columnar array on the surface.

[0010] S2. Add a liquid crystal monomer, a chain extender, and a crosslinking agent to a solvent and mix evenly to obtain a liquid crystal elastomer mixture. Fill the liquid crystal elastomer mixture into the polymer concave mold, evacuate to promote the liquid crystal elastomer mixture to enter the polymer concave mold, and heat and cure to obtain a first microstructure in an upright intermediate state.

[0011] S3. Apply pressure to the surface of the first microstructure in an upright intermediate state obtained in S2 and fix it, and heat to obtain a second microstructure in a bent intermediate state.

[0012] S4. Fix the second microstructure in a bent intermediate state obtained in S3 on the electrothermal film to obtain a reversible adhesion surface.

[0013] Preferably, in S1, the polymer material is one of polydimethylsiloxane (PDMS), silica gel, and polytetrafluoroethylene (PTFE).

[0014] Preferably, in S1, the column diameter of the convex hard mold is 50 - 250 μm, the aspect ratio is 0.5 - 5, and the center distance between adjacent columns is 50 - 1250 μm.

[0015] Preferably, in S2, the liquid crystal monomer is one or more of benzoate liquid crystal monomers, the chain extender is one or more of dithiol monomers, the addition amount of the chain extender is 50% - 150% of the molar amount of the liquid crystal monomer, the crosslinking agent is one or more of monomers containing both a silicon-oxygen bond and an amino group, which has both a crosslinking effect and a catalytic effect, and the addition amount of the crosslinking agent is 50% - 150% of the molar amount of the liquid crystal monomer.

[0016] Preferably, the liquid crystal elastomer is a thermotropic liquid crystal based on orthogonal click chemistry, the liquid crystal order depends on temperature changes, and its shape memory effect is realized by dynamic silicon-oxygen bonds.

[0017] Preferably, the benzoate liquid crystal monomers include 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) and 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82).

[0018] Preferably, the dithiol monomers include 3,6-dioxa-1,8-octanedithiol (EDDET), 1,2-ethanedithiol, 1,3-propanedithiol, and 1,6-hexanedithiol.

[0019] Preferably, the monomers containing both silicon-oxygen bonds and amino groups include 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (BATS) and N1,N1'-((1,1,3,3-tetramethyldioxadisiloxane-1,3-diyl)bis(propane-3,1-diyl))bis(propane-1,3-diamine) (BEATS).

[0020] Preferably, in S2, the solvent is one or more of toluene, acetone, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide.

[0021] Preferably, in S2, the vacuum degree of vacuum pumping is 0.6 - 1 MPa, and the holding time is 5 - 30 min.

[0022] Preferably, in S2, the temperature for heat curing is 20 - 120 °C, and the time is 0.5 - 48 h.

[0023] Preferably, in S3, the applied pressure is 0.98 - 98 N.

[0024] Preferably, in S3, the heating temperature is 80 - 250 °C, and the holding time is 1 - 3 h.

[0025] Preferably, in S4, the electrothermal film is one of a polyimide electrothermal film, a graphene electrothermal film, and a carbon nanotube electrothermal film. The electrothermal film has a good Joule heating effect and can quickly heat up at a low voltage.

[0026] The present invention also provides a method for manipulating fine particles. Using the above reversible adhesion surface, a direct current of 2 - 12 V is applied for 30 - 90 s, and the cylindrical microstructures of the reversible adhesion surface are in the form of the first upright intermediate microstructure, so that the fine particles adhere.

[0027] After the electric field is removed, the reversible adhesion surface cools naturally, and the cylindrical microstructures are transformed into the second microstructures which are curved intermediates; the morphology of the cylindrical microstructures changes cyclically many times, causing the fine particles to roll or slide relative to the cylindrical microstructures until they are de-adhered from the surface.

[0028] Preferably, the particle size of the fine particles is 100 - 800 μm.

[0029] Therefore, the present invention adopts the above-mentioned reversible adhesion surface based on LCEs and the method for manipulating fine particles, and the beneficial effects are as follows:

[0030] (1) For the reversible adhesion surface prepared by the present invention, the surface microstructures are beneficial to the adhesion of fine particles at rest. By utilizing the bidirectional shape memory effect of the liquid crystal elastomer, the morphology of the surface microstructures can be reversibly changed precisely and directly by temperature, and non-contact de-adhesion of fine particles can be achieved without external force intervention. This reversible adhesion mechanism coupling the bidirectional shape memory effect promotes the rolling / sliding of fine particles relative to the microstructures until they are de-adhered from the surface, which is beneficial to improving the problems in the traditional technology that the de-adhesion of fine particles depends on the manipulation of shear external force and it is difficult to de-adhere fine particles deeply embedded, avoids the damage to the surface structure caused by traditional contact de-adhesion, improves the adaptability of the reversible adhesion surface, and provides new ideas for the development of the adhesion manipulation field.

[0031] (2) The present invention can effectively desorb fine particles deeply embedded in the gaps of the microstructures, broadens the particle size range for reversible adhesion manipulation of fine particles, as small as 100 μm, and improves the de-adhesion efficiency of fine particles, reaching 70% - 90%.

[0032] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0033] Figure 1 is a process schematic diagram of the method for manipulating fine particles by a reversible adhesion surface based on LCEs of the present invention;

[0034] Figure 2 is a process schematic diagram for preparing the reversible adhesion surface solid adhesion layer of the reversible adhesion surface based on LCEs of the present invention;

[0035] Figure 3 is a microscopic image of the change of the surface microstructures under temperature control of the reversible adhesion surface based on LCEs of the present invention, where (a) is the cooling state and the cylindrical microstructures are in the curved morphology, and (b) is the heating state and the cylindrical microstructures are in the upright morphology;

[0036] Figure 4Optical micrograph of the detachment of fine particles deeply embedded in the microstructure when the reversibly adhesive surface prepared in Example 1 of the present invention undergoes temperature cycling changes.

[0037] Reference numerals

[0038] 1. Raised hard mold; 2. Concave mold; 3. First microstructure upright intermediate; 4. Weight; 5. Thin glass; 6. Second microstructure curved intermediate; 7. Electric heating film; 8. Reversibly adhesive surface. Detailed implementation manners

[0039] The technical solutions of the present invention will be further described below with reference to the drawings and examples.

[0040] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meanings understood by those with ordinary skills in the field to which the present invention belongs.

[0041] Example 1

[0042] As Figure 1 shown, a reversibly adhesive surface based on LCEs includes an electric heating film 7 and a solid adhesive layer provided on the electric heating film 7. The solid adhesive layer is constructed of a thermotropic liquid crystal elastomer LCEs with a bidirectional shape memory effect. The surface microstructure undergoes reversible conversion between a curved state and an upright state under the temperature control of the electric heating film 7. That is, cylindrical microstructures are arranged in an array on the surface of the solid adhesive layer. The cylindrical microstructures include a first microstructure upright intermediate 3 and a second microstructure curved intermediate 6 that are convertible with each other. When the curved state and the upright state of the surface microstructure change continuously, it causes the fine particles to roll / slide relative to the microstructure until they detach from the surface. The detachment efficiency can reach 70%-90%, realizing the reversible adhesion control of the fine particles. The cylindrical microstructures of the solid adhesive layer can adhere to and detach fine particles with a particle size of 100-800 μm.

[0043] As Figure 2 shown, a preparation method of a reversibly adhesive surface 8 based on LCEs and a control method for fine particles include the following steps:

[0044] (1) Use 3D printing technology to prepare a raised hard mold 1 with a cylindrical array, with a cylinder diameter of 50-150 μm, a height of 100-300 μm, and a center distance between adjacent cylinder centers of 50-200 μm. Pour silicone on the surface of the raised hard mold 1 and cure it to obtain a silicone concave mold 2.

[0045] (2) At 25 °C, 0.8 mol of liquid crystal monomer RM82, 1.2 mol of chain extender 3,6-dioxo-1,8-octanedithiol (EDDET), 0.2 mol each of crosslinking agent 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (BATS) and N1,N1'-((1,1,3,3-tetramethyldisiloxane-1,3-diyl)bis(propane-3,1-diyl))bis(propane-1,3-diamine) (BEATS) were added to dichloromethane to obtain a liquid crystal elastomer mixed solution. The liquid crystal elastomer mixture was filled into the silica gel concave mold 2, and a vacuum of 0.8 MPa was maintained for 15 min, and a polymerization reaction was carried out at 25 °C for 36 h. After the reaction was completed, the mold was demolded to obtain the first microstructure upright intermediate 3.

[0046] (3) After sequentially placing the thin glass 5 and the weight 4 on the first microstructure upright intermediate 3 and fixing them, a pressure of 9.8 N was applied, and heating was carried out at 200 °C for 1 h to form the second microstructure bent intermediate 6.

[0047] (4) Using a carbon nanotube heating film 7 with a rated voltage of 2 V and a power of 4 W, the second microstructure bent intermediate 6 was fixed on the heating film 7 to form a reversible adhesion surface 8.

[0048] (5) After heating for 60 s at 2 V, fine particles with a surface adhesion particle size of 400 - 600 μm were controlled; after removing the electric field, the material was naturally cooled, and the microstructure was bent to form the second microstructure bent intermediate 6; then the microstructure was heated upright to form the first microstructure upright intermediate 3. After the microstructure cycled and deformed dynamically 3 times, the de-adhesion efficiency of the fine particles reached 80% - 85%.

[0049] Example 2

[0050] A preparation method of a reversible adhesion surface based on LCEs and a method for manipulating fine particles thereof, comprising the following steps:

[0051] (1) Using 3D printing technology to prepare a convex hard mold 1 with a cylindrical array, the cylinder diameter is 50 - 80 μm, the height is 50 - 80 μm, and the center distance between adjacent cylinders is 80 - 120 μm. PDMS was poured on the surface of the convex hard mold 1 and cured to obtain the PDMS concave mold 2.

[0052] (2) At 25 °C, 0.8 mol of liquid crystal monomer RM257, 0.2 mol of chain extender 1,3-propanedithiol, 0.4 mol of chain extender 1,6-hexanedithiol, and 1.2 mol of crosslinker N1,N1'-((1,1,3,3-tetramethyldisiloxane-1,3-diyl)bis(propane-3,1-diyl))bis(propane-1,3-diamine) (BEATS) were added to acetone to obtain a liquid crystal elastomer mixed solution. The liquid crystal elastomer mixed solution was filled into the PDMS concave mold 2, and a vacuum of 0.6 MPa was maintained for 25 min, followed by a polymerization reaction at 35 °C for 12 h. After the reaction, the mold was demolded to obtain an intermediate 3 with a first microstructure in an upright shape.

[0053] (3) A thin glass 5 and a weight 4 were successively placed on the intermediate 3 with a first microstructure in an upright shape and fixed. A pressure of 49 N was applied, and heating was carried out at 180 °C for 2 h to form an intermediate 6 with a second microstructure in a bent shape.

[0054] (4) Using a graphene heating film 7 with a rated voltage of 2 V and a power of 6 W, the intermediate 6 with a second microstructure in a bent shape was fixed on the heating film 7 to form a reversible adhesion surface 8.

[0055] (5) After heating at 5 V for 90 s, fine particles with a surface adhesion particle size of 100 - 250 μm were controlled; after removing the electric field, the material was naturally cooled, and the microstructure was bent to form the intermediate 6 with a second microstructure in a bent shape; then the microstructure was heated to be upright to form the intermediate 3 with a first microstructure in an upright shape. After the microstructure underwent cyclic dynamic deformation 3 times, the de-adhesion efficiency of the fine particles reached 70% - 75%.

[0056] Example 3

[0057] A preparation method of a reversible adhesion surface based on LCEs and a method for manipulating fine particles thereof, comprising the following steps:

[0058] (1) Using 3D printing technology to prepare a convex hard mold 1 with a cylindrical array, the cylinder diameter is 80 - 100 μm, the height is 60 - 80 μm, and the center distance between adjacent cylinders is 200 - 250 μm. Polytetrafluoroethylene was poured on the surface of the convex hard mold 1 and cured to obtain a polytetrafluoroethylene concave mold 2.

[0059] (2) At 25 °C, 0.8 mol of liquid crystal monomer RM82, 1 mol of chain extender 1,6 - hexanedithiol, and 1.1 mol of cross - linker N1,N1'-((1,1,3,3 - tetramethyldisiloxane - 1,3 - diyl)bis(propane - 3,1 - diyl))bis(propane - 1,3 - diamine) (BEATS) were added to toluene to obtain a liquid crystal elastomer mixed solution. The liquid crystal elastomer mixture was filled into a polytetrafluoroethylene concave mold 2, and a vacuum of 1 MPa was maintained for 8 min, followed by a polymerization reaction at 80 °C for 6 h. After the reaction ended, the mold was demolded to obtain an intermediate 3 with the first microstructure in an upright shape.

[0060] (3) A thin glass 5 and a weight 4 were successively placed on the intermediate 3 with the first microstructure in an upright shape and then fixed. A pressure of 98 N was applied and heated at 150 °C for 3 h to form an intermediate 6 with the second microstructure in a bent shape.

[0061] (4) A polyimide electrothermal film 7 with a rated voltage of 12 V and a power of 5 W was used to fix the intermediate 6 with the second microstructure in a bent shape on the electrothermal film 7 to form a reversible adhesion surface 8.

[0062] (5) After heating for 30 s at 12 V, fine particles with a surface adhesion particle size of 600 - 800 μm were controlled; after removing the electric field, the material cooled naturally, and the microstructure bent to form the intermediate 6 with the second microstructure in a bent shape; then the microstructure was heated to be upright to form the intermediate 3 with the first microstructure in an upright shape. After the microstructure underwent cyclic dynamic deformation 3 times, the de - adhesion efficiency of the fine particles reached 80% - 90%.

[0063] Experimental Test

[0064] The deformation of the microstructure of the reversible adhesion surface 8 obtained in Example 1 was tested using a microscope. As Figure 3 shown, at low temperature, the microstructure of the reversible adhesion surface 8 was in a bent form, and at high temperature, the microstructure of the reversible adhesion surface 8 was in an upright form.

[0065] The process of manipulating fine particles on the reversible adhesion surface 8 obtained in Example 1 was tested using a microscope. As Figure 4 shown, when cycling between low temperature and high temperature, the continuous change in the microstructure morphology caused the fine particles to roll / slide relative to the microstructure, resulting in the de - adhesion of the fine particles.

[0066] Therefore, the present invention adopts the above - mentioned reversible adhesion surface based on LCEs and the method for manipulating fine particles. By directly driving the reversible change of the microstructure morphology with temperature, non - contact de - adhesion of fine particles can be achieved without external force intervention. This reversible adhesion mechanism coupling the bidirectional shape - memory effect is beneficial to improving the problems in traditional technologies where the de - adhesion of fine particles depends on shear external force manipulation and it is difficult to de - adhere fine particles deeply embedded, providing a new idea for the development of the adhesion manipulation field.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent substitutions, and these modifications or equivalent substitutions cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A reversible adhesion surface based on LCEs, characterized in that, It includes a heating film and a solid adhesion layer disposed on the heating film. The solid adhesion layer is constructed by a thermotropic liquid crystal elastomer (LCEs). The surface of the solid adhesion layer is provided with columnar microstructures arranged in an array. The columnar microstructures include a first microstructure in an upright intermediate state and a second microstructure in a bent intermediate state that can be converted into each other. The method for constructing the solid adhesion layer by using the thermotropic liquid crystal elastomer (LCEs) is as follows: S1. Use 3D printing technology to prepare a convex hard mold with a columnar array, pour a polymer material onto the convex hard mold, and prepare a polymer concave mold with a columnar array on the surface. S2. Add a liquid crystal monomer, a chain extender, and a crosslinking agent into a solvent and mix them evenly to obtain a liquid crystal elastomer mixture. Fill the liquid crystal elastomer mixture into the polymer concave mold, evacuate to promote the liquid crystal elastomer mixture to enter the polymer concave mold, and heat and cure to obtain a first microstructure in an upright intermediate state. S3. Apply pressure on the surface of the first microstructure in an upright intermediate state obtained in S2 and fix it, then heat to obtain a second microstructure in a bent intermediate state. S4. Fix the second microstructure in a bent intermediate state obtained in S3 on the heating film to obtain a reversible adhesion surface. In S1, the column diameter of the convex hard mold is 50 - 250 μm, the aspect ratio is 0.5 - 5, and the center distance between adjacent columns is 50 - 1250 μm. In S2, the liquid crystal monomer is one or more of benzoate liquid crystal monomers, the chain extender is one or more of dithiol monomers, the addition amount of the chain extender is 50% - 150% of the molar amount of the liquid crystal monomer, the crosslinking agent is one or more of monomers containing both a silicon - oxygen bond and an amino group, and the addition amount of the crosslinking agent is 50% - 150% of the molar amount of the liquid crystal monomer.

2. The reversible adhesion surface based on LCEs according to claim 1, characterized in that, In S2, the vacuum degree of the evacuation is 0.6 - 1 MPa, and the holding time is 5 - 30 min.

3. The reversible adhesion surface based on LCEs according to claim 1, wherein, In S2, the temperature of the heat curing is 20 - 120 °C, and the time is 0.5 - 48 h.

4. A reversible adhesion surface based on LCEs according to claim 1, characterized in that, In S3, the applied pressure is 0.98 - 98 N.

5. A reversible adhesion surface based on LCEs according to claim 1, characterized in that, In S3, the temperature of the heating is 80 - 250 °C, and the holding time is 1 - 3 h.

6. A method for manipulating fine particles, using the reversible adhesion surface according to any one of claims 1-5, characterized in that, Apply a direct current of 2 - 12 V for 30 - 90 s. The columnar microstructures of the reversible adhesion surface are in the first microstructure in an upright intermediate state, so that fine particles adhere. After removing the electric field, the reversible adhesion surface cools naturally, and the columnar microstructures are transformed into the second microstructures in a bent intermediate state. The morphology of the columnar microstructures changes cyclically for multiple times, so that the fine particles roll or slide relative to the columnar microstructures until they are detached from the surface.

7. A method for manipulating fine particles according to claim 6, characterized in that, The particle size of the fine particles is 100 - 800 μm.

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