Reversible adhesion surface based on LCEs and fine particle control method

Abstract

The invention belongs to the technical field of fine particle adhesion control, and particularly discloses an LCEs-based reversible adhesion surface and a fine particle control method, the LCEs-based reversible adhesion surface comprises an electrothermal film and a solid adhesion layer arranged on the electrothermal film, the solid adhesion layer is constructed by adopting a thermotropic liquid crystal elastic polymer LCEs, and the solid adhesion layer is formed by adopting the thermotropic liquid crystal elastic polymer LCEs. Cylindrical microstructures arranged in an array are arranged on the surface of the solid adhesion layer, and each cylindrical microstructure comprises a vertical intermediate of a first microstructure and a bent intermediate of a second microstructure, which can be mutually converted. By the adoption of the reversible adhesion surface based on the LCEs and the fine particle control method, effective desorption of fine particles deeply embedded into micro-structure gaps is achieved, the particle size range of reversible adhesion control over the fine particles is widened, and the fine particle deadhesion efficiency is improved.

Description

Technical Field

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

[0002] Reversible adhesion surfaces can achieve reversible regulation of adhesion force and have broad application prospects in fields such as climbing robots and drug release. Existing reversible adhesion surfaces with surface microstructures are easily contaminated by fine particles, resulting in a decrease in adhesion performance, and need to remove the adhered particles to restore the adhesion force. At the same time, the need for reversible adhesion control of fine particles also widely exists in fields such as drug delivery and micro-object manipulation.

[0003] The adhesion control of fine particles is mainly achieved through contact control, 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 control methods are prone to damage the surface microstructures and are difficult to remove fine particles deeply embedded in the gaps of the microstructures. The non-contact control 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 mutually transform 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 invention patent application with the publication number CN115831768A discloses a method for curved surface transfer based on a shape memory polymer stamp, and the invention patent with the publication number CN116376460B discloses a reversible solid-solid-solid liquid adhesion integrated material based on 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 transform the surface microstructures between different morphologies without external stress drive. For example, the invention patent application with the 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 control 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 controlling fine particles, which can effectively desorb fine particles deeply embedded in the gaps of the microstructures, broaden the particle size range of reversible adhesion control 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, which includes 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 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 on the convex hard mold, and prepare a polymer concave mold with a columnar array on the surface; S2. After adding a liquid crystal monomer, a chain extender, and a crosslinking agent to a solvent and mixing them evenly, a liquid crystal elastomer mixture is obtained. 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 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; S4. Fix the second microstructure in a bent intermediate state obtained in S3 on the electrothermal film to obtain a reversible adhesion surface.

[0009] Preferably, in S1, the polymer material is one of polydimethylsiloxane (PDMS), silica gel, and polytetrafluoroethylene (PTFE).

[0010] 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 column centers is 50 - 1250 μm.

[0011] 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.

[0012] 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.

[0013] 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).

[0014] Preferably, the dithiol monomers include 3,6-dioxa-1,8-octanedithiol (EDDET), 1,2-ethanedithiol, 1,3-propanedithiol, and 1,6-hexanedithiol.

[0015] Preferably, the monomers containing both a silicon-oxygen bond and an amino group 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).

[0016] Preferably, in S2, the solvent is one or more of toluene, acetone, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide.

[0017] Preferably, in S2, the degree of vacuum for evacuation is 0.6 - 1 MPa, and the holding time is 5 - 30 min.

[0018] Preferably, in S2, the temperature for heat curing is 20 - 120 °C, and the time is 0.5 - 48 h.

[0019] Preferably, in S3, the applied pressure is 0.98 - 98 N.

[0020] Preferably, in S3, the temperature for heating is 80 - 250 °C, and the holding time is 1 - 3 h.

[0021] 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 rapidly heat up at a low voltage.

[0022] 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 microstructures in an upright intermediate state, causing the fine particles to adhere; After removing the electric field, the reversible adhesion surface naturally cools, and the cylindrical microstructures transform into the second microstructures in a bent intermediate state; the morphology of the cylindrical microstructures changes cyclically multiple times, causing the fine particles to roll or slide relative to the cylindrical microstructures until they are de-adhered from the surface.

[0023] Preferably, the particle size of the fine particles is 100 - 800 μm.

[0024] 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: (1) For the reversible adhesion surface prepared by the present invention, the surface microstructure is beneficial to the adhesion of fine particles at rest. By utilizing the bidirectional shape memory effect of the liquid crystal elastomer, the morphological reversible change of the surface microstructure is accurately and directly driven by temperature, and the non-contact de-adhesion of fine particles can be realized without external force intervention. This reversible adhesion mechanism coupling the bidirectional shape memory effect promotes the rolling / sliding of fine particles relative to the microstructure 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 shear external force manipulation and it is difficult to de-adhere fine particles deeply embedded, avoiding the damage to the surface structure caused by traditional contact de-adhesion, enhancing the adaptability of the reversible adhesion surface, and providing new ideas for the development of the adhesion manipulation field.

[0025] (2) The present invention can effectively desorb fine particles deeply embedded in the gaps of the microstructure, broaden the particle size range of reversible adhesion manipulation of fine particles, as small as 100 μm, and improve the de-adhesion efficiency of fine particles, reaching 70% - 90%.

[0026] 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

[0027] 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; Figure 2 is a schematic diagram of the preparation process of the reversible adhesion surface solid adhesion layer of a reversible adhesion surface based on LCEs of the present invention; Figure 3 is a microscopic image of the change of the surface microstructure under temperature control of a reversible adhesion surface based on LCEs of the present invention, where (a) is the cooling state and the cylindrical microstructure is in a bent form, and (b) is the heating state and the cylindrical microstructure is in an upright form; Figure 4 is an optical micrograph of the de-adhesion of fine particles deeply embedded in the microstructure when the reversible adhesion surface prepared in Example 1 of the present invention undergoes cyclic temperature changes.

[0028] Reference Signs 1. Protruding hard mold; 2. Concave mold; 3. Intermediate body with the first microstructure in an upright state; 4. Weight; 5. Thin glass; 6. Intermediate body with the second microstructure in a bent state; 7. Electric heating film; 8. Reversible adhesion surface. Detailed Embodiments

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0031] Embodiment 1 As Figure 1 shown, a reversible adhesion surface based on LCEs includes an electrothermal film 7 and a solid adhesion layer disposed on the electrothermal film 7. The solid adhesion layer is constructed of a thermotropic liquid crystal elastomer LCEs having a bidirectional shape memory effect. The surface microstructure undergoes a reversible conversion between a bent state and an upright state under the temperature control of the electrothermal film 7. That is, 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 3 and a second microstructure in a bent intermediate state 6 that are mutually convertible. When the bent 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 are de-adhered from the surface. The de-adhesion efficiency can reach 70%-90%, realizing the reversible adhesion control of the fine particles. The columnar microstructures of the solid adhesion layer can adhere to and de-adhere fine particles with a particle size of 100-800 μm.

[0032] As Figure 2 shown, a preparation method of a reversible adhesion surface 8 based on LCEs and a method for controlling fine particles thereof include the following steps: (1) A convex hard mold 1 with a cylindrical array is prepared by 3D printing technology. The cylinder diameter is 50-150 μm, the height is 100-300 μm, and the center distance between adjacent cylinder centers is 50-200 μm. Silicone is poured on the surface of the convex hard mold 1 and cured to obtain a silicone concave mold 2.

[0033] (2) At 25°C, 0.8 mol of liquid crystal monomer RM82, 1.2 mol of chain extender 3,6-dioxa-1,8-octanedithiol (EDDET), crosslinking agent 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (BATS), and 0.2 mol of N1,N1'-((1,1,3,3-tetramethyldioxasilane-1,3-diyl)bis(propane-3,1-diyl))bis(propane-1,3-diamine) (BEATS) are added to dichloromethane to obtain a liquid crystal elastomer mixed solution. The liquid crystal elastomer mixed solution is filled into the silicone concave mold 2, and a vacuum of 0.8 MPa is maintained for 15 min, and a polymerization reaction is carried out at 25°C for 36 h. After the reaction is completed, demolding is carried out to obtain the first microstructure in an upright intermediate state 3.

[0034] (3) Place a thin glass 5 and a weight 4 on the upright intermediate 3 of the first microstructure in sequence and then fix them. Apply a pressure of 9.8 N and heat at 200 °C for 1 h to form a bent intermediate 6 with the second microstructure.

[0035] (4) Use a carbon nanotube electrothermal film 7 with a rated voltage of 2 V and a power of 4 W to fix the bent intermediate 6 with the second microstructure on the electrothermal film 7 to form a reversible adhesion surface 8.

[0036] (5) Heat for 60 s under a voltage of 2 V and then control the surface to adhere to fine particles with a particle size of 400 - 600 μm; after removing the electric field, the material cools naturally, the microstructure bends to form a bent intermediate 6 with the second microstructure; then heat the microstructure to be upright to form an upright intermediate 3 with the first microstructure. After the microstructure undergoes cyclic dynamic deformation 3 times, the de-adhesion efficiency of the fine particles reaches 80% - 85%.

[0037] Example 2 A preparation method of a reversible adhesion surface based on LCEs and a method for manipulating fine particles thereof, comprising the following steps: (1) Use 3D printing technology to prepare a convex hard mold 1 with a cylindrical array, with a cylinder diameter of 50 - 80 μm, a height of 50 - 80 μm, and a center distance of 80 - 120 μm between adjacent cylinder centers. Pour PDMS on the surface of the convex hard mold 1 and cure it to obtain a PDMS concave mold 2.

[0038] (2) At 25 °C, add 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 cross - linker N1,N1’ - ((1,1,3,3 - tetramethyldisiloxane - 1,3 - diyl)bis(propane - 3,1 - diyl))bis(propane - 1,3 - diamine) (BEATS) into acetone to obtain a liquid crystal elastomer mixed solution. Fill the liquid crystal elastomer mixed solution into the PDMS concave mold 2, maintain a vacuum degree of 0.6 MPa for 25 min, and carry out a polymerization reaction at 35 °C for 12 h. After the reaction ends, demold to obtain an upright intermediate 3 with the first microstructure.

[0039] (3) Place a thin glass 5 and a weight 4 on the upright intermediate 3 of the first microstructure in sequence and then fix them. Apply a pressure of 49 N and heat at 180 °C for 2 h to form a bent intermediate 6 with the second microstructure.

[0040] (4) Use a graphene electrothermal film 7 with a rated voltage of 2 V and a power of 6 W to fix the bent intermediate 6 with the second microstructure on the electrothermal film 7 to form a reversible adhesion surface 8.

[0041] After heating for 90 s at 5 V, fine particles with a surface adhesion particle size of 100 - 250 μm are controlled; after removing the electric field, the material is naturally cooled, and the microstructure bends to form a second microstructure in the shape of a bent intermediate 6; after reheating, the microstructure stands upright to form a first microstructure in the shape of an upright intermediate 3. After the microstructure undergoes cyclic dynamic deformation 3 times, the de-adhesion efficiency of the fine particles reaches 70% - 75%.

[0042] Example 3 A preparation method of a reversible adhesion surface based on LCEs and a method for manipulating fine particles thereof, comprising the following steps: (1) A convex hard mold 1 in a cylindrical array is prepared by using 3D printing technology. The diameter of the cylinder is 80 - 100 μm, the height is 60 - 80 μm, and the center distance between adjacent cylinder centers is 200 - 250 μm. Polytetrafluoroethylene is poured on the surface of the convex hard mold 1 and cured to obtain a polytetrafluoroethylene concave mold 2.

[0043] (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) are added to toluene to obtain a liquid crystal elastomer mixed solution. The liquid crystal elastomer mixed solution is filled into the polytetrafluoroethylene concave mold 2, and a vacuum of 1 MPa is maintained for 8 min, and a polymerization reaction is carried out at 80 °C for 6 h. After the reaction is completed, the mold is demolded to obtain a first microstructure in the shape of an upright intermediate 3.

[0044] (3) A thin glass 5 and a weight 4 are sequentially placed on the first microstructure in the shape of an upright intermediate 3 and then fixed, and a pressure of 98 N is applied and heated at 150 °C for 3 h to form a second microstructure in the shape of a bent intermediate 6.

[0045] (4) A polyimide electrothermal film 7 with a rated voltage of 12 V and a power of 5 W is used to fix the second microstructure in the shape of a bent intermediate 6 on the electrothermal film 7 to form a reversible adhesion surface 8.

[0046] (5) After heating for 30 s at 12 V, fine particles with a surface adhesion particle size of 600 - 800 μm are controlled; after removing the electric field, the material is naturally cooled, and the microstructure bends to form a second microstructure in the shape of a bent intermediate 6; after reheating, the microstructure stands upright to form a first microstructure in the shape of an upright intermediate 3. After the microstructure undergoes cyclic dynamic deformation 3 times, the de - adhesion efficiency of the fine particles reaches 80% - 90%.

[0047] Test and measurement The deformation of the microstructure of the reversible adhesion surface 8 obtained in Example 1 is tested by using a microscope, as Figure 3As shown, the microstructure of the reversible adhesion surface 8 is in a curved shape at low temperature and in an upright shape at high temperature.

[0048] 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 and high temperatures, the continuous change in the microstructure morphology causes the fine particles to roll / slide relative to the microstructure, resulting in the de-adhesion of the fine particles.

[0049] 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 through 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. It provides a new idea for the development of the adhesion manipulation field.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended 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 replacements, and these modifications or equivalent replacements 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: The invention comprises an electric heating film and a solid adhesion layer arranged on the electric heating film, wherein the solid adhesion layer is constructed by using thermotropic liquid crystal elastic polymers (LCEs), and the surface of the solid adhesion layer is provided with cylindrical microstructures arranged in an array, wherein the cylindrical microstructures comprise a first microstructure in an upright intermediate body and a second microstructure in a curved intermediate body which can be converted into each other.

2. A reversible adhesion surface based on LCEs according to claim 1, characterized in that: The method of constructing the solid adhesion layer using thermotropic liquid crystal elastic polymers LCEs is as follows: S1. Using 3D printing technology to prepare a convex hard mold with a cylindrical array, pouring a polymer material on the convex hard mold to prepare a polymer concave mold with a cylindrical array on the surface; S2, adding a liquid crystal monomer, a chain extender, and a cross-linking agent to a solvent and mixing them evenly to obtain a liquid crystal elastic polymer mixed solution, filling the liquid crystal elastic polymer mixed solution into a polymer concave mold, vacuuming to promote the liquid crystal elastic polymer mixed solution to enter the polymer concave mold, and heating and curing to obtain a first microstructure in an upright intermediate; S3, applying pressure to the surface of the first microstructure upright intermediate obtained in S2, fixing it, and heating it to obtain a second microstructure curved intermediate; S4, fixing the second microstructure obtained in S3 in a curved intermediate on the electric heating film to obtain a reversible adhesion surface.

3. A reversible adhesion surface based on LCEs according to claim 2, characterized in that: In S1, the cylindrical diameter of the raised hard mold is 50-250 μm, the aspect ratio is 0.5-5, and the distance between the centers of adjacent cylinders is 50-1250 μm.

4. The LCEs-based reversible adhesive surface according to claim 2, characterized in that: In S2, the liquid crystal monomer adopts one or more of benzoate liquid crystal monomers, the chain extender adopts one or more of dithiol monomers, the added amount of the chain extender is 50%-150% of the molar amount of the liquid crystal monomer, and the cross-linking agent adopts one or more of monomers containing both silicon-oxygen bonds and amino groups, and the added amount of the cross-linking agent is 50%-150% of the molar amount of the liquid crystal monomer.

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

6. The LCEs-based reversible adhesive surface according to claim 2, characterized in that: In S2, the temperature of the heating curing is 20-120°C and the time is 0.5-48h.

7. The LCEs-based reversible adhesive surface according to claim 2, characterized in that: In S3, the applied pressure is 0.98-98N.

8. The LCEs-based reversible adhesive surface according to claim 2, characterized in that: In S3, the heating temperature is 80-250°C and the holding time is 1-3h.

9. A method for manipulating fine particles, using the reversible adhesion surface according to any one of claims 1 to 8, characterized in that: applying a direct current of 2-12V for 30-90s, wherein the cylindrical microstructure of the reversible adhesion surface is an intermediate of the first microstructure being upright, so that fine particles adhere; After the electric field is removed, the reversibly adhesive surface cools naturally, and the cylindrical microstructure transforms into a curved intermediate of the second microstructure; the morphology of the cylindrical microstructure changes in multiple cycles, causing the fine particles to roll or slide relative to the cylindrical microstructure until they are detached from the surface.

10. A method for controlling fine particles according to claim 9, characterized in that: The particle size of the fine particles is 100-800 μm.

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