Intelligent liquid crystal elastomer adhesion structure and electric field induced forming method thereof

Abstract

The invention relates to a liquid crystal elastomer intelligent adhesion structure and an electric field induction forming method thereof, the structure comprises a lower electrode plate, a second electrode layer is prepared on the lower electrode plate, a liquid crystal elastomer film is prepared on the second electrode layer, and the tail end of the liquid crystal elastomer film is arrayed and has a mushroom-shaped adhesion shape with a tail end expansion characteristic; the liquid crystal elastomer film has a flat tail end at normal temperature and has good adhesion performance; when the lower electrode plate is heated, the liquid crystal elastomer film shrinks, the contact area is rapidly reduced, in-situ desorption close to zero external force is achieved, and the morphology and the adhesion performance can be recovered after cooling; the electric field induction forming method comprises the following steps: synthesizing a liquid crystal elastomer, and then treating an electrode plate; then electric field induction liquid crystal elastomer rheological forming is carried out, and finally liquid crystal elastomer curing and demolding are carried out. According to the invention, high-strength adhesion of materials with different materials and roughness surfaces is realized; and meanwhile, precise release of ultralight materials is achieved.

Description

Technical Field

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

[0002] The operation technology capable of stably and flexibly picking and placing various materials is of great significance for the development of the Internet of Things and industrial automation. How to establish reversible adhesion on surfaces with different materials and roughnesses is the key issue 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 roughnesses by relying on van der Waals forces has received extensive attention. This adhesion mechanism has a wider surface adaptation ability compared to negative pressure and magnetic adsorption, and there is no problem that chemical adhesives will leave marks on the target surface and have poor repeatability. It is an important part of the new generation of operation technology. The microstructural array with enlarged ends at the tips of gecko toes can improve the contact state between interfaces and evenly distribute the stress between interfaces, thereby maximizing the effect of intermolecular forces. Inspired by the gecko setae structure, the "mushroom-shaped" adhesion structure with enlarged ends has been proven to be the optimal structure form for enhancing the van der Waals force between interfaces. At the same time, a large amount of work has studied the forming process of the "mushroom-shaped" adhesion structure. For example, the team of Professor Metin Sitti at Carnegie Mellon University proposed a method to prepare a mushroom-shaped adhesion structure by first fabricating a microcolumn array through lithography and then integrating enlarged ends by dipping; the research group of Professor Daizhen Dong at Nanjing University of Aeronautics and Astronautics proposed a process to prepare a metal mold by a confined electroplating method and then mold and manufacture a mushroom-shaped adhesion structure.

[0003] However, a single passive adhesion force limits the release ability of the operation technology for materials. For example, the team of Professor Sameoto at the University of Alberta fabricated mushroom-shaped adhesion structures using lithography and etching processes. However, the passive working mode makes its adhesion force only vary with the pre-pressure, and it is impossible to achieve the regulation of the adhesion force during the pick-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 materials and the minimum adhesion force that can be achieved when releasing materials (i.e., the adhesion-to-release ratio) directly affect the picking and releasing efficiency of the operation technology for materials. At the same time, achieving stable picking of high-quality materials and rapid release of 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 operating system and unable to achieve compatible operation for materials with cross-scale topographies and qualities. For example, the team of Professor Mark R. Cutkosky at Stanford University reported a dry adhesion gripper for the microgravity environment in the journal Science Robotics. It uses multiple adhesion units and mechanical components such as ropes, springs, pulleys, and bearings to achieve the conversion between 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, the team of Researcher He Qingsong at Nanjing University of Aeronautics and Astronautics reported a magnetically controlled deformed columnar array structure, achieving controllable attachment and detachment of unmanned aerial vehicles. However, 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, there are still major challenges in manufacturing an adhesion structure that can deform in-situ. Summary of the Invention

[0004] To overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a liquid crystal elastomer intelligent adhesion structure and its electric field-induced forming method. The micron-scale "mushroom"-shaped structure array can achieve high-strength adhesion to materials with different materials and roughness surfaces through uniform interfacial contact stress and separation stress; at the same time, the liquid crystal elastomer microstructures can change the interfacial contact area through reversible in-situ deformation regulated by temperature, so as to achieve precise release of ultra-light materials.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A liquid crystal elastomer intelligent adhesion structure includes a lower electrode plate 6. A second electrode layer 5 is prepared on the lower electrode plate 6. A liquid crystal elastomer film 4 is prepared on the second electrode layer 5. The end of the liquid crystal elastomer film 4 forms an array and has a mushroom-shaped adhesion shape with an enlarged end. At room temperature, the liquid crystal elastomer film 4 has a flat end and has good adhesion performance; heating the lower electrode plate 6 will cause the liquid crystal elastomer film 4 to shrink, rapidly reduce the contact area, and achieve in-situ desorption with almost zero external force. After cooling, it will recover its morphology and adhesion performance.

[0007] An electric field-induced forming method for a liquid crystal elastomer intelligent adhesion structure includes the following steps:

[0008] 1) Synthesis of liquid crystal elastomer: Add a photoinitiator to the oligomer and stir until the two are completely mixed to obtain a once-crosslinked liquid crystal elastomer; the mass ratio of the photoinitiator to the oligomer is 1:1.06;

[0009] 2) Treatment of electrode plates: Prepare a first electrode layer 2 on the lower surface of the upper electrode plate 1, and prepare a dielectric layer 3 with a nanoscale thickness on the first electrode layer 2; prepare a second electrode layer 5 on the upper surface of the lower electrode plate 6, evacuate the once-crosslinked liquid crystal elastomer synthesized in step 1) and apply it on the second electrode layer 5 and spin-coat to obtain a liquid crystal elastomer film 4;

[0010] 3) Electric field-induced liquid crystal elastomer rheological forming: Apply an external pressure to make the upper electrode plate 1 and the lower electrode plate 6 contact through a dielectric support bracket 7, apply an external DC power supply to the first electrode layer 2 and the second electrode layer 5, adjust the voltage, and make the electric field force received by the liquid crystal elastomer film 4 overcome the surface tension and viscous resistance and rheologically flow 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 the electrowetting effect and rheologically flows into a mushroom-shaped adhesion shape with an enlarged end;

[0011] 4) Curing and demolding of the liquid crystal elastomer: With the voltage kept constant, irradiate with an ultraviolet lamp to cure the liquid crystal elastomer, and then remove the upper electrode plate 1 to obtain a mushroom-shaped liquid crystal elastomer adhesion structure, that is, a liquid crystal elastomer intelligent adhesion structure.

[0012] In step 2) described above, the first electrode layer is prepared by a magnetron sputtering coating process.

[0013] In step 2) described above, the dielectric layer is prepared by a spin-coating and curing process.

[0014] In step 3) described above, the thickness of the bracket 7 is 2 - 3 times the thickness of the liquid crystal elastomer film 4.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] Compared with the traditional passive adhesion structure, the present invention can achieve reversible in-situ deformation by controlling the temperature, thereby regulating the contact state between interfaces and realizing the adhesion and detachment conversion. Compared with mechanical, magnetron and other detachment means, it is not only light in structure, but also can achieve detachment with almost zero external force. In addition, by electric field induction, the liquid crystal elastomer is rheologically formed into a mushroom-shaped microstructure with a swollen end, which can solve the problems of difficult demolding and insufficient filling existing in the traditional molding method, and at the same time can achieve more obvious molecular orientation, thereby enhancing the heat-induced deformation phenomenon of the adhesion structure. The liquid crystal elastomer adhesion structure prepared by the present invention can achieve stable picking and precise release of various materials and quality materials, and has important application potential in high-precision material transfer, robotic arm grasping, etc. Description of the Drawings

[0017] Figure 1 It is a cross-sectional view of the upper electrode plate of the embodiment of the present invention.

[0018] Figure 2 It is a cross-sectional view of the lower electrode plate of the embodiment of the present invention.

[0019] Figure 3 It is a schematic diagram of electro-induced rheological forming by applying pressure and external electric field to a parallel plate capacitor in the embodiment of the present invention.

[0020] Figure 4 It is a schematic diagram of the rheology of the liquid crystal elastomer in the embodiment of the present invention along the direction perpendicular to the electrode plate.

[0021] Figure 5 It is a schematic diagram of the rheology of the liquid crystal elastomer along the upper electrode plate direction after contacting the upper electrode plate in the embodiment of the present invention.

[0022] Figure 6 It is a schematic diagram of curing the liquid crystal elastomer by an ultraviolet lamp in the embodiment of the present invention.

[0023] Figure 7 Schematic diagram of the liquid crystal elastomer adhesion structure obtained after curing and removing the upper electrode plate in the embodiment of the present invention.

[0024] Figure 8 Schematic diagram of the deformation of the liquid crystal elastomer adhesion structure prepared in the embodiment of the present invention when heated. Detailed implementation manners

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

[0026] Embodiment, an electric field-induced forming method for a liquid crystal elastomer intelligent adhesion structure. The electrode layer is selected as metal Au, and the dielectric layer is selected as a polydimethylsiloxane (PDMS) solution for description, including the following steps:

[0027] 1) Liquid crystal elastomer synthesis: First, take an appropriate amount of oligomer, generally about 1 g, place it in an 80 °C oven and heat for about 2 minutes until the oligomer becomes completely transparent. Then, use a dropper to suck a photoinitiator with a mass ratio of 1:1.06 to the oligomer, add it to the oligomer, and stir with a glass rod until the two are completely mixed to obtain a once-crosslinked liquid crystal elastomer.

[0028] 2) Treatment of the electrode plate: Refer to Figure 1 , first, adopt a coating process such as evaporation or sputtering to prepare a first electrode layer 2 with a thickness of 20 nm - 100 nm on the lower surface of the upper electrode plate 1, and prepare a dielectric layer 3 with a nanoscale thickness on the first electrode layer 2. In this embodiment, PDMS and a curing agent are first mixed in a mass ratio of 10:1 and degassed, then applied to the first electrode layer 2 and spin-coated, and then cured at 80 °C for 120 min to form the dielectric layer 3, which is convenient for wetting to form a brim structure and easy to demold; refer to Figure 2 , prepare a second electrode layer 5 with a thickness of 20 nm - 100 nm on the upper surface of the lower electrode plate 6, and apply the once-crosslinked liquid crystal elastomer synthesized in step 1) after degassing on the second electrode layer 5 and spin-coat to obtain a liquid crystal elastomer film 4 with a thickness of 50 μm - 150 μm.

[0029] 3) Electric field-induced forming of the liquid crystal elastomer adhesion structure: Refer to Figure 3, a polyimide film with good insulation and heat resistance is placed as a support 7 in the blank area of the second electrode layer 5 without the liquid crystal elastomer film 4, and an upper electrode plate 1 is placed on the support 7 to form a parallel plate capacitor composed of an upper electrode / air / LCE / lower electrode from top to bottom; among them, 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, so as to reserve space for the rheology of the liquid crystal elastomer film 4; a pressure P is applied to the parallel plate capacitor to connect the upper electrode plate 1 to the lower electrode plate 6 through the support 7; while maintaining the construction method of the parallel plate capacitor, a DC voltage 8 is applied between the upper electrode plate 1 and the lower electrode plate 6, and the adjustment range is 200V to 2000V. The liquid crystal elastomer film 4 is affected by the electric field force at the gas / liquid interface, overcomes its own viscous resistance and the surface tension at the interface, and thus grows upward, as Figure 4 shown. The forming height is equal to the distance between the two plates, that is, the height of the support 7; subsequently, when the liquid crystal elastomer film 4 contacts the dielectric layer 3, the electrowetting effect occurs, and the electric field force acting at the three-phase boundary (solid / liquid / gas) continues to make the liquid crystal elastomer film 4 expand outward, forming a "mushroom-shaped" contact end with a diameter slightly larger than the support column, as Figure 5 shown;

[0030] 4) Curing and demolding of the liquid crystal elastomer: Under the condition of keeping the voltage unchanged, it is cured with ultraviolet light 9 with a wavelength of 365nm for 10 minutes, as Figure 6 shown; the upper electrode plate 1 is removed to obtain a mushroom-shaped liquid crystal elastomer adhesion structure, that is, a liquid crystal elastomer intelligent adhesion structure, as Figure 7 shown.

[0031] Referring to Figure 8 , a liquid crystal elastomer intelligent adhesion structure includes a lower electrode plate 6. A second electrode layer 5 is prepared on the lower electrode plate 6, and a liquid crystal elastomer film 4 is prepared on the second electrode layer 5. The end of the liquid crystal elastomer film 4 is in an array and has a mushroom-shaped adhesion shape with an enlarged end feature. At room temperature, the liquid crystal elastomer film 4 has a flat end and has good adhesion performance; heating the lower electrode plate 6 will cause the liquid crystal elastomer film 4 to shrink along the rheological direction, rapidly reducing the contact area, realizing in-situ desorption with almost zero external force, and the morphology and adhesion performance will be restored after cooling.

Claims

1. A liquid crystal elastomer intelligent adhesion structure, comprising a lower electrode plate (6), characterized in that: A second electrode layer (5) is prepared on a lower electrode plate (6), and a liquid crystal elastomer film (4) is prepared on the second electrode layer (5). The ends of the liquid crystal elastomer film (4) are arrayed and have a mushroom-shaped adhesion shape with end swelling characteristics. At room temperature, the liquid crystal elastomer film (4) has a flat end and has good adhesion properties. Heating (10) the lower electrode plate (6) causes the liquid crystal elastomer film (4) to shrink, rapidly reducing the contact area and achieving in-situ desorption with close to zero external force. After cooling, the morphology and adhesion properties are restored.

2. The electric field induced forming method of a liquid crystal elastomer intelligent adhesive structure according to claim 1, characterized in that: The following steps are involved: 1) Synthesis of liquid crystal elastomer: Add the photoinitiator to the oligomer and stir 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; 2) Processing of the electrode plate: preparing a first electrode layer (2) on the lower surface of the 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 the lower electrode plate (6), and applying the once cross-linked liquid crystal elastomer synthesized in step 1) on the second electrode layer (5) after degassing and spin coating to obtain a liquid crystal elastomer film (4); 3) Electric field induced liquid crystal elastomer rheological deformation: external pressure is applied to make the upper electrode plate (1) and the lower electrode plate (6) contact each other through the dielectric support bracket (7), an external DC power supply is applied to the first electrode layer (2) and the second electrode layer 5, and 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 flows in a 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 the electrowetting effect and flows into a mushroom-shaped adhesion shape with a terminal swelling feature; 4) Curing and demoulding of the liquid crystal elastomer: while keeping the voltage unchanged, use ultraviolet light to cure the liquid crystal elastomer and then remove the upper electrode plate (1) to obtain a mushroom-shaped liquid crystal elastomer adhesion structure, i.e., a liquid crystal elastomer intelligent adhesion structure.

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

4. The method according to claim 2, characterized in that: The dielectric layer (3) in step 2) is prepared by a spin coating and curing process.

5. The method according to claim 2, characterized in that: In the 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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