Liquid crystal elastomer smart adhesive structures and electric field-induced shaping methods thereof

Abstract

The application discloses a liquid crystal elastomer smart adhesion structure and an electric field induced forming method thereof. The structure comprises a lower electrode plate, a second electrode layer prepared on the lower electrode plate, and a liquid crystal elastomer film prepared on the second electrode layer. The liquid crystal elastomer film is in a mushroom-shaped adhesion shape with an arrayed end and an end bulging feature. The liquid crystal elastomer film has a flat end and good adhesion performance at room temperature. Heating the lower electrode plate causes the liquid crystal elastomer film to shrink, rapidly reduce the contact area, realize in-situ detachment with near zero external force, and restore the appearance and adhesion performance after cooling. The electric field induced forming method comprises the following steps: synthesizing the liquid crystal elastomer, processing the electrode plate, then performing electric field induced liquid crystal elastomer rheological forming, and finally performing liquid crystal elastomer solidification and demolding. The application realizes high-strength adhesion to materials with different materials and roughness surfaces, and simultaneously realizes precise release of super-light materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of bionic adhesion functional structure in micro-nano engineering, and particularly relates to a liquid crystal elastomer intelligent adhesion structure and an electric field-induced forming method thereof. BACKGROUND

[0002] The operation technology capable of stably and flexibly picking and placing various materials is of great significance to the development of Internet of Things and industrial automation, and how to establish reversible adhesion on surfaces with different materials and roughness is a key problem to improve the adaptability and flexibility of the operation technology. The ability of geckos to establish reversible adhesion on surfaces with a wide range of materials and roughness by van der Waals force has attracted widespread attention. This adhesion mechanism has a more extensive surface adaptability than negative pressure and magnetic force adsorption, and does not have the problem of leaving marks on the target surface and poor repeatability caused by chemical adhesives, and is an important part of the new generation of operation technology. The microstructure array with the end swelling feature at the end of the gecko toe can improve the interface contact state and uniform interface stress distribution, thereby maximizing the effect of intermolecular force. Inspired by the structure of gecko setae, the "mushroom-shaped" adhesion structure with the end swelling has been proved to be the optimal structure form to enhance the van der Waals force between interfaces, and a large number of works have studied the forming process of the "mushroom" shaped adhesion structure. For example, Professor Metin Sitti's team of Carnegie Mellon University proposed a method of first preparing a micro-column array through photolithography, and then dipping to integrate the swelling end to prepare the mushroom-shaped adhesion structure; Professor Dai Zhendong's research group of Nanjing University of Aeronautics and Astronautics proposed a process of preparing a metal mold through limited electroplating, and then molding the mushroom-shaped adhesion structure.

[0003] However, the single passive adhesion force limits the release ability of the operation technology for the material. For example, the team of Professor Sameoto of the University of Alberta used photolithography and etching process to manufacture mushroom-shaped adhesion structure, but the passive working mode makes the adhesion force only change with the pre-pressure, and cannot realize the adhesion force regulation in the pick-up and release process (Dan S, Brendan F. Robust large-area synthetic dry adhesives [J]. J Adhes Sci Technol, 2012, 693802: 1-17.). The maximum adhesion force when picking up the material and the minimum adhesion force that can be achieved when releasing the material (i.e. the adhesion-to-detachment ratio) directly affects the pick-up and release efficiency of the operation technology for the material, and at the same time, realizing stable pick-up for high-quality materials and rapid release for ultra-light materials poses a huge challenge to the operation technology. Traditional release strategies usually use complex mechanisms for control, increasing the redundancy of the operation system, and cannot realize compatible operation for materials with cross-scale topography and mass. For example, the team of Professor Mark R. Cutkosky of Stanford University reported in the journal Science Robotics a dry adhesion gripper for microgravity environment, which uses multiple adhesion units and mechanical elements such as ropes, springs, pulleys and bearings to realize the conversion of adhesion and detachment, and its mechanical structure is huge and complex (Jiang H, Hawkes E W, Fuller C, et al. A robotic device using gecko-inspired adhesives can grasp and manipulate large objects in microgravity [J]. Science Robotics, 2017, 2(7): eaan4545.). In-situ control of the adhesion end is an effective solution to solve the problem of cross-scale material operation. For example, Professor Qingsong He's team of Nanjing University of Aeronautics and Astronautics reported a magnetic control deformation columnar array structure, which realizes controllable adhesion and detachment of unmanned aerial vehicles, but the maximum adhesion strength of this columnar array is limited by the geometric structure (Qingsong H E, Zefang Z, Zhong Q, et al. Switchable shape memory polymer bio-inspired adhesive and its application for unmanned aerial vehicle landing [J]. Chinese Journal of Aeronautics, 2024, 37(3): 380-390.). However, how to realize the manufacturing of adhesion structure that can deform in-situ still faces major challenges. SUMMARY

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a liquid crystal elastomer smart adhesion structure and an electric field-induced shaping method thereof, and a micrometer-scale "mushroom" structure array can realize high-strength adhesion to materials with different materials and roughness surfaces through uniform interfacial contact stress and separation stress; meanwhile, the liquid crystal elastomer microstructure can change the interfacial contact area through reversible in-situ deformation regulated by temperature, so as to realize precise release of ultra-light materials.

[0005] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0006] A liquid crystal elastomer smart adhesion structure, comprising a lower electrode plate 6, a second electrode layer 5 prepared on the lower electrode plate 6, and a liquid crystal elastomer film 4 prepared on the second electrode layer 5, wherein the liquid crystal elastomer film 4 has an array of mushroom-shaped adhesion shapes with an end swelling feature, and the liquid crystal elastomer film 4 has a flat end at room temperature and has good adhesion performance; heating 10 the lower electrode plate 6 will cause the liquid crystal elastomer film 4 to shrink, rapidly reduce the contact area, realize in-situ detachment with near-zero external force, and restore the morphology and adhesion performance after cooling.

[0007] An electric field-induced shaping method of a liquid crystal elastomer smart adhesion structure, comprising the following steps:

[0008] 1) Synthesis of liquid crystal elastomer: adding a photoinitiator to an oligomer and stirring until the two are completely mixed to obtain a primary cross-linked liquid crystal elastomer; the mass ratio of the photoinitiator to the oligomer is 1:1.06;

[0009] 2) Processing of electrode plate: preparing a first electrode layer 2 on the lower surface of an upper electrode plate 1, and preparing a dielectric layer 3 with a nanometer thickness on the first electrode layer 2; preparing a second electrode layer 5 on the upper surface of a lower electrode plate 6, and coating and spin-coating the primary cross-linked liquid crystal elastomer synthesized in step 1) on the second electrode layer 5 after air extraction to obtain a liquid crystal elastomer film 4;

[0010] 3) Electric field-induced rheological shaping of liquid crystal elastomer: contacting the upper electrode plate 1 and the lower electrode plate 6 through a dielectric support bracket 7 under an external pressure, applying an external direct current power source to the first electrode layer 2 and the second electrode layer 5, adjusting the voltage, so that the electric field force acting on the liquid crystal elastomer film 4 overcomes the surface tension and viscous resistance and flows in a direction perpendicular to the electrode layer; after contacting the dielectric layer 3 on the surface of the upper electrode plate 1, expanding along the upper electrode plate 1 under the action of the electrowetting effect, and flowing into a mushroom-shaped adhesion shape with an end swelling feature;

[0011] 4) Curing and demolding of the liquid crystal elastomer: after the liquid crystal elastomer is cured by irradiation with a UV lamp while keeping the voltage unchanged, the upper electrode plate 1 is removed, and a mushroom-shaped liquid crystal elastomer adhesion structure, i.e., a liquid crystal elastomer smart adhesion structure, is obtained.

[0012] The first electrode layer in step 2) is prepared by a magnetron sputtering plating process.

[0013] The dielectric layer in step 2) is prepared by a spin coating and curing process.

[0014] The thickness of the support 7 in step 3) is 2-3 times the thickness of the liquid crystal elastomer film 4.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] Compared with the conventional passive adhesion structure, the present application can realize reversible in-situ deformation by controlling the temperature, so as to regulate the contact state between interfaces and realize the adhesion and detachment conversion. Compared with the mechanical and magnetic detachment means, the present application has a light structure and can realize detachment with nearly zero external force. In addition, the liquid crystal elastomer is rheologically formed into a mushroom-shaped microstructure with an enlarged end by electric field induction, which can solve the problems of difficult demolding and insufficient filling in the conventional mold pressing method, and can realize more obvious molecular orientation, thereby enhancing the thermal deformation of the adhesion structure. The liquid crystal elastomer adhesion structure prepared by the present application can realize stable picking and precise release of various materials and mass materials, and has important application potential in high-precision material transfer, mechanical hand gripping and the like. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 1 is a sectional view of the upper electrode plate of the present application.

[0018] Figure 2 FIG. 2 is a sectional view of the lower electrode plate of the present application.

[0019] Figure 3 FIG. 3 is a schematic view of the present application for applying pressure and an external electric field to a parallel plate capacitor for electrically induced rheological forming.

[0020] Figure 4 FIG. 4 is a schematic view of the present application for the liquid crystal elastomer flowing in a direction perpendicular to the electrode plate.

[0021] Figure 5 FIG. 5 is a schematic view of the present application for the liquid crystal elastomer flowing in a direction along the upper electrode plate after contacting the upper electrode plate.

[0022] Figure 6 FIG. 6 is a schematic view of the present application for curing the liquid crystal elastomer by a UV lamp.

[0023] Figure 7 The schematic diagram of the liquid crystal elastomer adhesive structure obtained after curing and removing the upper plate for the embodiment of the present application.

[0024] Figure 8 The schematic diagram of the liquid crystal elastomer adhesive structure prepared for the embodiment of the present application deforming when heated. DETAILED DESCRIPTION

[0025] The present application will be described in detail below in conjunction with the embodiments and the accompanying drawings.

[0026] Embodiment, the electric field induced forming method of the liquid crystal elastomer intelligent adhesive structure, the electrode layer selects metal Au, and the dielectric layer selects polydimethylsiloxane (PDMS) solution to describe, including the following steps:

[0027] 1) Synthesis of liquid crystal elastomer: first take the appropriate oligomer, generally about 1g, placed in the 80℃ oven heating 2 minutes to oligomer completely transparent, then use the dropper to take the mass ratio of 1:1.06 of the photoinitiator, added to the oligomer, stirred with a glass rod until the two are completely mixed, that is, to get the first cross-linked liquid crystal elastomer;

[0028] 2) Processing of electrode plate: refer to Figure 1 , first adopt the evaporation or sputtering and other plating film process, on the lower surface of the upper electrode plate 1 to prepare a layer of 20nm-100nm of the first electrode layer 2, on the first electrode layer 2 to prepare a layer of nanometer thickness of the dielectric layer 3; this embodiment first PDMS and curing agent mixed with the mass ratio of 10:1, then daubed on the first electrode layer 2 and spin coating, after that in the 80℃ temperature curing 120min, form the dielectric layer 3, convenient wetting to form the brim structure, easy to demould; refer to Figure 2 , on the upper surface of the lower electrode plate 6 to prepare a layer of 20nm-100nm of the second electrode layer 5, after the step 1) to synthesize the first cross-linked liquid crystal elastomer daubed on the second electrode layer 5 and spin coating, to get a layer of 50μm-150μm of the liquid crystal elastomer film 4;

[0029] 3) Electric field induced liquid crystal elastomer adhesive structure forming: refer to Figure 3, the blank area on the second electrode layer 5 without the liquid crystal elastomer film 4 is placed with a polyimide film with good insulation and heat resistance as a support 7, and the upper electrode plate 1 is placed on the support 7, forming a parallel plate capacitor composed of upper electrode / air / LCE / lower electrode from top to bottom; wherein the thickness of the support 7 needs to be greater than the thickness of the liquid crystal elastomer film 4, generally 2-3 times the thickness of the liquid crystal elastomer film 4, thereby reserving space for the rheological flow of the liquid crystal elastomer film 4; a pressure P is applied to the parallel plate capacitor, so that the upper electrode plate 1 is connected to the lower electrode plate 6 through the support 7; the construction method of the parallel plate capacitor is maintained, and a direct current voltage 8 is applied between the upper electrode plate 1 and the lower electrode plate 6, with a regulation range of 200V-2000V, the liquid crystal elastomer film 4 is subjected to the electric field force at the gas / liquid interface, overcoming the surface tension between the self-viscous resistance and the interface to grow upwards, as shown in Figure 4 , the forming height is equal to the distance between the two electrode plates, that is, the height of the support 7; then, when the liquid crystal elastomer film 4 contacts the dielectric layer 3, the electrowetting effect is generated, and the electric field force acting on the three-phase junction (solid / liquid / gas) continues to expand the liquid crystal elastomer film 4 towards the outside, forming a "mushroom-shaped" contact end with a diameter slightly larger than the support column, as shown in Figure 5 ;

[0030] 4) Solidification and demolding of liquid crystal elastomer: under the condition of keeping the voltage unchanged, the liquid crystal elastomer is solidified by ultraviolet light 9 with a wavelength of 365nm for 10min, as shown in Figure 6 ; the upper electrode plate 1 is removed, and a mushroom-shaped liquid crystal elastomer adhesion structure, that is, a liquid crystal elastomer intelligent adhesion structure, is obtained, as shown in Figure 7 .

[0031] Referring to Figure 8 , a liquid crystal elastomer intelligent adhesion structure includes a lower electrode plate 6, a second electrode layer 5 prepared on the lower electrode plate 6, and a liquid crystal elastomer film 4 prepared on the second electrode layer 5, wherein the liquid crystal elastomer film 4 has a mushroom-shaped adhesion shape with an arrayed end and an end swelling feature, and has a flat end and good adhesion performance at room temperature; heating the lower electrode plate 6 for 10min will cause the liquid crystal elastomer film 4 to shrink along the rheological direction, rapidly reduce the contact area, and realize in-situ detachment with near-zero external force, and the appearance and adhesion performance will be restored after cooling.

Claims

1. A method for electric field-induced forming of a liquid crystal elastomer smart adhesion structure, characterized in that: A liquid crystal elastomer smart adhesion structure includes a lower electrode plate (6), a second electrode layer (5) prepared on the lower electrode plate (6), and a liquid crystal elastomer film (4) prepared on the second electrode layer (5). The liquid crystal elastomer film (4) has an array of ends and a mushroom-shaped adhesion shape with end swelling characteristics. At room temperature, the liquid crystal elastomer film (4) has flat ends and good adhesion performance. Heating the lower electrode plate (6) (10) will cause the liquid crystal elastomer film (4) to shrink, rapidly reduce the contact area, and achieve in-situ desorption with near-zero external force. After cooling, the morphology and adhesion performance will be restored. The electric field-induced forming method for a liquid crystal elastomer smart adhesion structure includes the following steps: 1) Synthesis of liquid crystal elastomer: The photoinitiator is added to the oligomer and stirred until the two are completely mixed to obtain a one-crosslinked liquid crystal elastomer; the mass ratio of photoinitiator to oligomer is 1:1.06; 2) Electrode plate processing: A first electrode layer (2) is prepared on the lower surface of the upper electrode plate (1), and a dielectric layer (3) with a nanometer thickness is prepared on the first electrode layer (2); a second electrode layer (5) is prepared on the upper surface of the lower electrode plate (6), and the first cross-linked liquid crystal elastomer synthesized in step 1) is degassed and coated on the second electrode layer (5) and spin-coated to obtain a liquid crystal elastomer film (4). 3) Electric field induced liquid crystal elastomer rheoforming: External pressure is applied to make the upper electrode plate (1) and the lower electrode plate (6) contact through the dielectric support bracket (7), and an external DC power supply is applied to the first electrode layer (2) and the second electrode layer (5). The voltage is adjusted so that the electric field force on the liquid crystal elastomer film (4) overcomes the surface tension and viscous resistance and rheoforms in the direction perpendicular to the electrode layer. When it contacts the dielectric layer (3) on the surface of the upper electrode plate (1), it unfolds along the upper electrode plate (1) under the action of electrowetting effect and rheoforms into a mushroom-shaped adhesive shape with end swelling characteristics. 4) Curing and demolding of liquid crystal elastomer: While keeping the voltage constant, the liquid crystal elastomer is cured by irradiation with ultraviolet light and then the upper electrode plate (1) is removed to obtain a mushroom-shaped liquid crystal elastomer adhesion structure, namely, a liquid crystal elastomer smart adhesion structure.

2. The method according to claim 1, characterized in that: In step 2), the first electrode layer (2) is prepared by magnetron sputtering.

3. The method according to claim 1, characterized in that: The preparation of the dielectric layer (3) in step 2) is carried out by spin coating and curing.

4. The method according to claim 1, characterized in that: In step 3), the thickness of the support (7) is 2-3 times the thickness of the liquid crystal elastomer film (4).

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