A soft robot for realizing three-dimensional motion of a gas-liquid interface and a preparation method thereof

Abstract

The present invention relates to a soft robot for realizing three-dimensional motion of a gas-liquid interface and a preparation method thereof. The robot preparation method includes: mixing liquid crystal units and CNTs with high photothermal conversion efficiency, stirring and reacting above the liquid crystal transition temperature to obtain a liquid crystal prepolymer ink, and then obtaining a customizable-oriented soft robot through 3D printing and ultraviolet light curing. The interface soft robot prepared by this method has a series of advantageous features such as programmable orientation, precise spatio-temporal control, and continuous energy supply. And for the first time, three-dimensional motion of a two-phase (gas-liquid) interface is realized by changing the angle of the interface three-phase line (liquid-gas-solid). The method proposed by the present invention will provide a method for the development of a new generation of soft robots at the gas-liquid interface.

Description

Technical Field

[0001] The present invention belongs to the field of robots, and particularly relates to a soft robot capable of realizing three-dimensional motion at the gas-liquid interface and a preparation method thereof. Background Art

[0002] The rapid development of intelligent robots is bringing a revolution to our lives. However, traditional robot technologies usually require rigid motor pumps to provide energy and greatly limit the degrees of freedom, thus restricting their adaptability to the environment. Therefore, there is a great need for soft robots with high degrees of freedom. However, the motion of existing soft robots is usually limited to specific solid or fluid media. Due to the unbalanced mechanical environment, high-degree-of-freedom motion at the two-phase (air-water) interface remains a formidable challenge. Despite great efforts, it is still limited to two-dimensional motion (X and Y axes) at the two-phase interface, and three-dimensional motion (X, Y, and Z axes) has not been achieved. Summary of the Invention

[0003] Aiming at the defects of the prior art, the technical problem to be solved by the present invention is to provide a soft robot capable of realizing three-dimensional motion at the gas-liquid interface and a preparation method thereof, so as to overcome the technical problem that the soft robot in the prior art cannot realize three-dimensional motion at the gas-liquid interface.

[0004] A fully flexible soft robot of the present invention is obtained by 3D printing and ultraviolet light curing of an ink containing liquid crystal units and carbon nanotubes.

[0005] A soft robot capable of realizing three-dimensional motion at the gas-liquid interface of the present invention, the composition of the soft robot includes: a liquid crystal elastomer / carbon nanotube composite with controllable orientation;

[0006] Wherein the structural formula of the liquid crystal elastomer is:

[0007]

[0008] Where n is an integer greater than or equal to 1.

[0009] Furthermore, the soft robot is prepared by the following method:

[0010] Heat the liquid crystal units and carbon nanotubes above the liquid crystal transition temperature, heat and stir to obtain a liquid crystal prepolymer ink; load the ink into the printer cartridge, orient the ink by direct ink writing, and then obtain a liquid crystal elastomer carbon nanotube composite with controllable orientation through ultraviolet light curing.

[0011] A preparation method of a soft robot capable of realizing three-dimensional motion at the gas-liquid interface of the present invention includes:

[0012] (1) Mix 1,4-bis-[4-(6-acryloyloxy)benzoyloxy]-2-methylbenzene (RM82), n-butylamine, a photoinitiator, and carbon nanotubes, heat, stir well, and react to obtain a liquid crystal / carbon nanotube prepolymer printing ink;

[0013] (2) Program the liquid crystal / carbon nanotube printing ink in step (1) using a 3D printer, extrude while orienting the ink and cure it with ultraviolet light to obtain a soft robot that realizes three-dimensional movement at the gas-liquid interface.

[0014] The carbon nanotubes in step (1) are single-walled or multi-walled carbon nanotubes; the photoinitiator is benzoin diethyl ether.

[0015] In step (1), the molar ratio of 1,4-bis-[4-(6-acryloyloxy)benzoyloxy]-2-methylbenzene (RM82) to n-butylamine is 1-1.5:1-1.5; the photoinitiator accounts for 1-5 wt% of the total mass of the reaction monomers; the carbon nanotubes account for 0.5-2 wt% of the total mass of the reaction monomers.

[0016] The heating in step (1) is to heat to the liquid crystal transition temperature of 100-110 °C; the reaction is to heat and stir at 100-110 °C for 18-22 h.

[0017] The 3D printing in step (2) is specifically as follows:

[0018] Before the printing process using a direct ink writing 3D printer, the system is maintained at a printing temperature of 50-65 °C for 20-60 min; during the printing process, the printing speed is 5-12 mm / s, and the extruded ink is exposed to ultraviolet light; after printing is completed, it is exposed to ultraviolet light for another 20-40 min to obtain a cross-linked liquid crystal elastomer.

[0019] Furthermore, the 3D printing in step (2) is specifically as follows:

[0020] The liquid crystal / carbon nanotube prepolymer printing ink is oriented in the liquid crystal domains using a direct ink writing 3D printer. Direct ink writing is designed for extrusion using a three-axis motion control platform (Aerotech Inc.). The ink is extruded by pressure driving using an Ultimus V pressure cell (Nordson EFD) according to the programmed G-code (Mecode). The extrusion head of the 3D printer consists of a steel barrel surrounded by a heating coil with a thermocouple (type K). To bring the system to steady-state operating conditions, the system is held at the printing temperature of 50 - 65 °C for approximately 30 minutes prior to the printing process. During the printing process, the printing speed is set at 5 - 12 mm / s, and the extruded ink is exposed to ultraviolet light. Additionally, the G-code design can be modified to model and control the printing parameters. After printing, the LCE is further exposed to ultraviolet light of higher intensity for 20 - 40 min (10 - 20 min for the top and bottom respectively) to achieve uniform cross-linking and facilitate the release of the soft robot from the substrate.

[0021] The ultraviolet light irradiation power during printing is 5 - 20 mW / cm 2 ; after printing is completed, the ultraviolet light irradiation power is 20 - 40 mW / cm 2 .

[0022] A soft robot with three-dimensional motion at the gas-liquid interface is prepared by the method of the present invention.

[0023] An application of the soft robot with three-dimensional motion at the gas-liquid interface of the present invention, such as drug transportation, closed pipeline transportation, intelligent transportation, etc.

[0024] The liquid crystal elastomer ink of the present invention is mainly synthesized from a bisacrylate-based liquid crystal unit and n-butylamine through an aza-Michael addition reaction. To avoid volume changes and residual stresses caused by solvent loss during the drying process, a solvent-free reaction method is used to increase the molecular weight of the liquid crystal elastomer, which can maximize the potential driving strain. Under ultraviolet light irradiation, the reactive acrylate end groups react and cross-link to form liquid crystal elastomers (LCEs)( Figure 6 ).

[0025] In the present invention, liquid crystal elastomers are used as matrices to provide high degrees of freedom and repeatable deformation. Liquid crystal mesogens are oriented by direct ink writing to achieve programmable deformation. The addition of carbon nanotubes (CNTs) enables near-infrared light response, remote control, and continuous energy supply for soft robots. Therefore, a bionic leaf beetle larva soft robot composed of liquid crystal elastomer-carbon nanotube composite ink (LCE / CNTs) can exhibit asymmetric geometric shape changes under near-infrared (NIR) irradiation, can change the inclination angle of the liquid-solid-gas three-phase line, and successfully achieve multimodal motion (forward, backward, rotation) while realizing three-dimensional flipping of the two-phase interface and motion inside a closed glass tube (such as Figure 1 D, Figure 4 as shown in H). This opens up a new path for the development of soft robots at the two-phase interface.

[0026] Inspired by leaf beetle larvae, the present invention adopts the mechanism of the three-phase contact line along the water surface and solid surface. A fully flexible soft robot is 3D printed using a composite material of a light-responsive liquid crystal elastomer / carbon nanotube to simulate the movement of leaf beetle larvae on the water surface. The complex three-dimensional motion of the bionic leaf beetle larva soft robot, including flipping and rolling at the gas-liquid interface, is realized for the first time. In addition, the soft robot uses light remote driving to achieve precise spatio-temporal control, which provides great advantages for applications. As an example, we demonstrate the controllable motion of the soft robot inside a closed pipeline, which will be used for drug delivery and intelligent transportation.

[0027] Beneficial effects

[0028] The present invention realizes the three-dimensional motion of a fully flexible soft robot at the gas-liquid interface. The soft robot constructed by combining the LCE / CNTs composite material with 3D printing technology realizes high degrees of freedom and programmability of motion, including forward, backward, rotation, and three-dimensional flipping at the gas-liquid interface. In addition, the soft robot based on a photo-heatable material can achieve remote controllability and continuous energy supply under infrared light irradiation. Moreover, the motion can be further changed by combining various functional fillers or programming directions. The design principle and materials developed in this work will inspire the development of the next generation of functional soft robots. Description of the Drawings

[0029] Figure 1Schematic diagram of the design of a 3D-printed bionic leaf beetle larva soft robot and its three-dimensional flipping at the gas-liquid interface; (A) Schematic diagram of 3D printing of the soft robot based on LCE / CNTs, (i) the morphology of the disordered ink during heating, (ii) the orientation of the LCE / CNTs ink induced by the printer, (iii) the morphology of LCE / CNTs after ultraviolet cross-linking; (B) Molecular structure of the LCE / CNTs composite ink; (C) Schematic diagram of the motion mechanism: the spline surface is heated above the liquid crystal deformation temperature after being irradiated by infrared light, while the bottom of the spline remains non-deformed at a lower temperature due to the poor light penetration; (D) Three-dimensional motion of the bionic leaf beetle larva soft robot at the two-phase interface under near-infrared light (808 nm) irradiation.

[0030] Figure 2 Characterization of the LCE / CNTs composite ink, where (A) is the variation diagram of the viscosity of the liquid crystal composite ink with the shear rate between Tg and T N-I ; Diagram (B) of the polarized light image shows the birefringence phenomenon of the uniaxially printed LCEs (scale bar = 20 μm); (C) Orientation degree of the LCE strips printed at different speeds (6, 9, 12, 15 mm / s); (D) Diagram of the relationship between the near-infrared irradiation time and temperature of LCE / CNTs.

[0031] Figure 3 Programmable spatial motion of the fully flexible soft robot based on LCE / CNTs; (A - B) Bar-shaped soft robot, printed with the upper and lower parts at ±45° relative to the long axis to achieve local motion control; (C - D) Flower-shaped soft robot consists of six ellipses with Archimedean spiral orientation, and different petals can be opened as needed; (E - F) Boy-shaped soft robot dances under irradiation; (G - H) Network-shaped soft robot consists of two network structures, which are rotated 90° compared with the previous layer. When the two layers of the network are irradiated, different deformations occur at the bottom and the top (the white arrows indicate the direction of the liquid crystal polymer).

[0032] Figure 4Mechanical analysis of the bionic leaf beetle larva soft robot; (A) The bionic leaf beetle larva soft robot is restricted by the contact line at the two-phase interface. When illuminated, it arches its back like a leaf beetle larva to produce a meniscus deformation and thus generates movement; (B) The motion model of the bionic leaf beetle larva soft robot; (C) The bionic leaf beetle larva soft robot rotates clockwise and counterclockwise in a closed tube (scale = 5 mm); (D) Force analysis of the bionic leaf beetle larva soft robot floating on the gas-liquid interface; (E) Force analysis of the bionic leaf beetle larva soft robot at the equilibrium state (i) 0 < α < 90°, (ii) 90 < α < 180°, (iii) α = 180°; (F) Statistical curve of the repeatable deformation of the bionic leaf beetle larva soft robot (20 mm × 4 mm) under periodic light irradiation; (G) Displacement under near-infrared light and (H) Angular velocity change with time; Contact angle of the bionic leaf beetle larva soft robot with different solutions; (I) Motion control of the spider-shaped soft robot driven by near-infrared light (scale = 10 mm);

[0033] Figure 5 Kinematics analysis of the bionic leaf beetle larva soft robot and finite element simulation of three-dimensional motion at the two-phase interface. (A) Mechanical analysis of the bionic leaf beetle larva soft robot during (i) falling, (ii-iii) swimming, and (iv) leaving the gas-liquid interface; (B) Motion forms of the bionic leaf beetle larva soft robot at different stages: including (i) bending, (ii) torsion, (iii) curling and flipping, and (iv) recovery; (C) Velocity nephogram and (D) Velocity vector diagram of the soft robot during the recovery stage; (E) Lateral capillary force distribution of the soft robot along the tangential direction of the body side. (ii) The force distribution at the top of the body tends to concentrate in the swimming direction.

[0034] Figure 6 FTIR spectra of the pre-crosslinked LCE / CNTs ink and the crosslinked LCE / CNTs elastomer. After the uncrosslinked composite ink and the liquid crystal elastomer are irradiated with 365 nm ultraviolet light, the C-H bond with a stretching vibration peak at 2360 cm -1 changes from unsaturated to saturated.

[0035] Figure 7 Example of the actual printed pattern. After preheating at 50 °C for 30 min, melt extrusion printing is carried out, which has good extrudability and shape retention.

[0036] Figure 8 DSC schematic diagram of the composite ink. Thermal analysis is carried out by a differential scanning calorimeter to obtain its glass transition temperature T g which is 14.0 °C and TN-I is 91.1 °C.

[0037] Figure 9 Examples of bionic leaf beetle larva soft robots immersed in different solvents. In KMnO4 (10 mg / ml), glycerol (0.63 g / ml), H 2 SO 4 in solutions of HCl (pH = 2) and NaOH (pH = 12) for 48 h.

[0038] Figure 10 is the change in the weight fraction of the bionic leaf beetle larva soft robot within 48 h of soaking, and the weight loss within 48 h does not exceed 2% (water as the reference solvent).

[0039] Figure 11 is for the establishment of the geometric model and mesh generation. The initial model of the larva is established using DEFINE_GRID_MOTION (DM) software. The computational domain is divided into two parts. One part is the external fluid domain, which is a cylinder with a diameter of 50 mm and a height of 10 mm. The other part is the larva body, with a length of 20 mm, a width of 3 mm, and a height of 0.6 mm, laid on the two-phase interface. Specific implementation mode

[0040] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0041] Materials: 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (98%) was purchased from Sdyano Fine Chemical. n-Butylamine (99.5%) and glycerol (≥99%) were purchased from Sigma-Aldrich Chemical. Benzoin diethyl ether (>98%) was purchased from TCI Chemical, and carbon nanotubes (MWCNT>98%, O.D.×I.D.×L, 10 nm ± 1 nm×4.5 nm ± 0.5 nm×3 - 6 μm) were from J&K Chemical Co., Ltd. HCl, NaOH, and KMnO4 were purchased from Sinopharm Chemical Reagent. Unless otherwise specified, all reagents were used directly without further purification.

[0042] The changes in the liquid crystal prepolymer and the crosslinked structure of the reaction were evaluated by attenuated total reflection FTIR (Nicolet 6700, Nicolet Inc., USA).

[0043] The stress-temperature curves of the strips (ca. 1 mm (T)×4 mm (W)×20 mm (L)) were obtained by dynamic thermomechanical analysis on DMA (METTLER TOLEDO). At least three samples were tested for each sample and the average value was taken.

[0044] Thermogravimetric analysis (TGA) tests were carried out on a Discovery TGA from 40 °C to 530 °C at a heating rate of 10 °C / min.

[0045] DSC tests were performed on a NETZSCH DSC 204F1 Phoenix at a temperature range of -50 °C to 150 °C, with a heating rate of 10 °C / min, under a nitrogen atmosphere.

[0046] A hot stage polarized light microscope (BX51-P) was used to observe the birefringence of uniaxially printed LCE and the dispersion of carbon nanotubes in the liquid crystal matrix.

[0047] A field emission scanning electron microscope (Hitachi SU8010) was used to study the morphology of CNTs embedded in the LCE matrix. X-ray diffraction (XRD) experiments were carried out using a D / max-2550PC X-ray diffractometer (Rigaku Corporation, Japan).

[0048] A fully automatic solid-liquid dual-purpose densitometer (FK-120S) was used to measure the density of the liquid crystal elastomer / carbon nanotube composite. The density of the 3D printed strip was obtained as 1.1945 g / cm 3

[0049] Example 1

[0050] Synthesis and printing of LCE / CNTs ink: A liquid crystal composite ink was prepared by a catalyst-free Michael addition method. The molar ratio of RM82 to n-butylamine was 1:1, 2 wt% photoinitiator benzoin diethyl ether, 1 wt% carbon nanotubes were added to the reaction flask in one pot, and the reaction was stirred thoroughly at 110 °C for 20 h to finally obtain a homogeneous 3D printable liquid crystal polymer ink. The LCE / CNTs composite was printed using a direct ink writing 3D printer at a liquid crystal phase temperature between the glass transition temperature (T g =-14 °C) and the nematic-isotropic transition point (T N-I =91 °C) (see the phase transition temperature in Figure 8 ). Direct ink writing was carried out using a three-axis motion control platform (Aerotech Inc.) for extrusion design ( Figure 1 A). According to the programmed G-code (Mecode), the ink was extruded by pressure using an Ultimus V pressure cartridge (Nordson EFD). The extrusion head of the 3D printer consisted of a steel barrel surrounded by a heating coil with a thermocouple (Type K). To bring the system to steady-state operating conditions, the system was held at the printing temperature of 50 °C for about 30 minutes before the printing process. During the printing process, the printing speed was set at 12 mm / s, and the extruded ink was exposed to ultraviolet light at 20 mW / cm 2In addition, the G-code design modeling and printing parameters can be modified. After printing, the LCE is then exposed to ultraviolet light with a higher intensity of 31 mW / cm 2 , for 30 min (15 min for the top and bottom respectively) to achieve uniform cross-linking and facilitate the release of the soft robot from the substrate.

[0051] As the temperature rises to T N-I , the ink viscosity decreases sharply from 25 °C to 90 °C and exhibits shear thinning with the change of shear rate. When the temperature rises from 50 °C to 60 °C, the viscosity of the ink shows a sharp drop (about one order of magnitude decrease), and the viscosity remains at 10 2 ~10 3 Pa·s. As shown in Figure 2 Figure A. To ensure the shape retention of the printing orientation and the extrudability of printing, 50 °C is selected for printing.

[0052] The uniaxially printed LCE / CNTs splines show typical anisotropic optical properties, that is, the birefringence properties related to the oriented nematic LCE observed under crossed polarizers, as shown in Figure 2 Figure B.

[0053] Meanwhile, X-ray diffraction was used to characterize the degree of orientation ( 2 Figure C) of LCE strips with different printing speeds (6, 9, 12, and 15 mm / s) cured by ultraviolet light (31 mW / cm Figure 2 ) at a printing temperature of 50 °C for 30 min. This shows that at a printing speed of 12 mm / s, the strips can maintain a good shape and a high degree of orientation (the degree of orientation is about ~0.73).

[0054] Meanwhile, due to the addition of 1 wt% CNTs in the LCEs, melt extrusion at 50 °C, printing at 12 mm / s, and ultraviolet light curing (31 mW / cm 2 , 30 min), the surface temperature of the oriented LCE / CNTs strips exceeds its liquid crystal transition temperature T N-I (~91 °C) within 0.69 s, and can rise from 25 °C to ~260 °C in less than 8 s, while for the pure LCE without CNTs as a control, the temperature change only increases by less than 10 °C. In addition to the high photothermal conversion efficiency, CNTs can also provide continuous energy supply and remote precise control for the fully flexible soft robot ( Figure 2 Figure D).

[0055] Example 2

[0056] The bionic leaf beetle larva soft robot composed of double-layer LCE / CNTs splines (length * width * depth, 20 mm x 4 mm x 0.5 mm) shows good cyclic repeatability in air. The splines are formed by direct ink writing 3D printing to orient the LCE / CNTs ink in the liquid crystal domain. By modifying the G code, a rectangular spline with dimensions of 20 mm x 4 mm x 0.5 mm is designed. Before printing, the system is maintained at a printing temperature of 50 °C for about 30 minutes, and then extruded at an extrusion rate of 12 mm / s while being exposed to ultraviolet light at 20 mW / cm 2 . After printing, the printed model of the bionic leaf beetle larva soft robot is further exposed to higher-intensity ultraviolet light at 31 mW / cm 2 , for 30 min (15 min for the top and bottom respectively) to achieve uniform crosslinking and release the printed model from the substrate.

[0057] Place it in air to test its actuation performance. When infrared light (808 nm) irradiates the LCE / CNTs strip, since the LCE strip is deliberately designed to have a much thicker thickness (600 μm) than most light-responsive LCE films (usually less than 30 μm), as the film thickness increases, a temperature gradient is generated. The temperature of the irradiated area reaches the liquid crystal transition temperature T N-I or above, and the LC molecules change from the nematic phase (ordered) to the isotropic phase (disordered) on the irradiated surface. The entropy and free volume of the exposed area both increase, enhancing the movement of the molecular chains. At the same time, the temperature of the bottom area of the exposed part may still be lower than T N-I , and the LC molecules and the crosslinked network remain in good alignment. The internal stress is released from the exposed part of the top surface and drives the LCE / CNTs strip to bend towards the light. When the near-infrared light is turned off, the temperature drops below T N-I or below. As the entropy and free volume of the exposed area decrease, the LC molecules reorient along the y-axis, so the LCE / CNTs strip returns to its initial state ( Figure 1 C). By turning the near-infrared lamp on and off, the initially flat spline instantaneously bends and has good repeatability. Five consecutive light-responsive deformation cycles are performed, and the shape fixation rate for each cycle is 95%, and the shape recovery rate is 100% ( Figure 4 F).

[0058] Example 3

[0059] As Figure 3The specific preparation method of the soft robot shown is as follows: Prepare a liquid crystal composite ink using the catalyst-free Michael addition method. RM82 and n-butylamine with a molar ratio of 1:1, 2 wt% photoinitiator benzoin diethyl ether, and 1 wt% carbon nanotubes are added to the reaction flask in one pot and stirred vigorously at 110 °C for 20 h to finally obtain a homogeneous 3D printable liquid crystal polymer ink. The LCE / CNTs composite is printed using a direct ink writing 3D printer at a liquid crystal phase temperature of 50 °C. Direct ink writing is performed by extrusion design using a three-axis motion control platform (Aerotech Inc.). Soft robot models with different orientations, such as strip-shaped, flower-shaped, child-shaped, and cross-net-shaped, are programmed according to the programmed G-code (Mecode), and the ink is extruded by pressure using an Ultimus V pressure cell (Nordson EFD). The extrusion head of the 3D printer consists of a steel barrel surrounded by a heating coil with a thermocouple (Type K). To bring the system to steady-state operating conditions, the system is maintained at the printing temperature of 50 °C for approximately 30 minutes before the printing process. During the printing process, the printing speed is set at 12 mm / s, and the extruded ink is exposed to ultraviolet light at 20 mW / cm 2 . After printing, the LCE is further exposed to higher-intensity ultraviolet light at 31 mW / cm 2 for 30 min (15 min on the top and bottom each) to achieve uniform cross-linking and facilitate the release of the soft robot from the substrate. (See the printing diagram in Figure 7 )

[0060] In addition to the single-orientation strip-shaped soft robot, more complex orientation structures are designed through G-code programming to demonstrate the control of liquid crystal orientation in direct ink writing 3D printing. First, an LCE / CNTs soft robot composed of four different orientation parts is printed on the same plane. The upper and lower parts are inclined at ±45°. When the +45° cross-section is irradiated with near-infrared light, the LCE / CNTs actuator rotates to the right, and vice versa for the left rotation ( Figure 3 A). Secondly, a flower-shaped soft robot with an Archimedean spiral orientation, consisting of six petals, is printed and can be controllably bloomed under infrared light irradiation ( Figure 3 C). A child-like LCE / CNTs fully flexible soft robot with an Archimedean curve orientation head and a specific body orientation is printed, and these printing directions dance with the control of near-infrared light ( Figure 3 E). Figure 3G shows a reticular LCE / CNTs fully flexible soft robot with locally controlled molecular orientation processed by direct ink writing. The reticular soft robot (L x W, 10 mm x 10 mm) consists of a bilayer fiber filament, where the direction of one layer is perpendicular to the other layer. Different from the rotation or bending of the entire film, this reticular fully soft robot can control the fixed-point contraction in the X-Y plane through near-infrared light.

[0061] Example 4

[0062] By placing a 3D printed oriented spline (biomimetic leaf beetle larva soft robot) on the gas-liquid interface, the mechanism of direction control and propulsion was explored, and a mechanical analysis was established. Generally, the fluid exerts an upward buoyancy force (F b ) on an object with a density lower than its own. However, the density of the biomimetic leaf beetle larva soft robot is 1.1945 g / cm 3 which is higher than the water density of 1.0 g / cm 3 , but it can still maintain balance on the liquid surface. Therefore, when the biomimetic leaf beetle larva soft robot contacts the interface, it is not only affected by F b , but also affected by the surface tension of water (F T ). According to Archimedes' principle, F b is calculated from the weight of the water in the submerged area A and the deformed pit area B ( Figure 4 D). F b and F T can be determined by the following equations.

[0063]

[0064] F T = γL (2)

[0065] where ρ is the density of water, d and l are the width and length of the contact surface between the biomimetic leaf beetle larva soft robot and water respectively; H 1 and H are the underwater depth of the biomimetic leaf beetle larva soft robot and the depth from the bottom of the biomimetic leaf beetle larva soft robot to the top of the water surface respectively; g is the gravitational constant, and X is the two-dimensional contour equation of the gas-liquid interface. In equation (2), γ is the surface tension coefficient and L is the length of the biomimetic leaf beetle larva soft robot affected by the surface tension.

[0066] The vertically upward force on the biomimetic leaf beetle larva soft robot in the static state:

[0067]

[0068] where α is the inclination angle of the gas-liquid interface to the horizontal plane at the three-phase (liquid-gas-solid) contact line.

[0069] The spider-inspired soft robot is in a balanced state when floating statically. According to the Young-Laplace equation, the two-dimensional contour curve equation X of its water-air interface can be derived as follows: When the bionic spider soft robot floats on the water surface, in the balanced state, the radius of curvature of the deformed water surface and the pressure difference on both sides satisfy the Young-Laplace equation:

[0070]

[0071] where R 1 , R 2 are the two radii of curvature at any point on the surface formed by the deformed water surface; h is the distance between any point on the surface formed by the deformed water surface and the horizontal plane, and it is positive above the horizontal plane.

[0072] For Figure 4 the two-dimensional schematic diagram shown in E, the Young-Laplace equation is:

[0073]

[0074] where R is the radius of curvature, and the curvature formula is as follows:

[0075]

[0076] By combining formulas (5) and (6), the differential form of the two-dimensional plane Young-Laplace equation can be obtained:

[0077]

[0078] Let h' = y, Substituting into formula (7) gives:

[0079]

[0080] Integrating both ends respectively, the relationship between the coordinate h at any point on the two-dimensional deformation curve of the water surface and the curvature at that point can be obtained:

[0081]

[0082] As Figure 4 shown in E, the rectangular support leg can be divided into three processes from contacting the water surface to submerging into the water surface. The fully submerged state is a critical state and will not be studied here.

[0083] When α = 0°, the water-air interface contour is a straight line, h = 0, which is a critical state and will not be studied here

[0084] When 0° < α ≤ 90°, its schematic diagram is as Figure 4(i), when below the water surface, h ≤ 0, the equal sign holds when x → ∞, h' ≥ 0; h'|h = 0, let Substituting into formula 9 gives

[0085]

[0086] At the starting point of the two-dimensional curve, h' = tanα 0 , substituting into formula (10) gives:

[0087]

[0088] Using trigonometric identity transformation, the ordinate h0 at the starting point of the two-dimensional curve can be obtained:

[0089]

[0090] From formula (10), we have: Integrating and solving for dx gives:

[0091]

[0092] where atanh represents the inverse hyperbolic tangent function,

[0093] Simplifying gives:

[0094]

[0095] Substituting into the above formula gives:

[0096]

[0097] Therefore, when 0° < θ ≤ 90°, the two-dimensional contour curve equation of the water-air interface can be obtained:

[0098]

[0099] When 90° < α ≤ 180°, the two-dimensional contour of the water-air interface is as shown in Figure 4 E(ii). This two-dimensional curve can be divided into two parts: h' ≥ 0 and h' < 0. The part where h' ≥ 0 is the same as the Figure 4 case of E(i), and the derivation process is as follows:

[0100] For the curve part where h' ≥ 0, the included angle between the starting point and the horizontal line is known Since this part is the same as the two-dimensional contour curve of the water-air interface when 90° < α ≤ 180°, the equation of the curve part where h' ≥ 0 can be obtained according to formula (14):

[0101]

[0102] For the curve part where h' ≤ 0, h'| X＝0 = -∞, c 1 = -k, substituting into the above formula (9) gives the formula

[0103]

[0104] h’ at the starting point of the two - dimensional curve 0 = tanα 0 , substituting into formula (16) gives:

[0105]

[0106] Using trigonometric identity transformation, the ordinate of h at the starting point of the two - dimensional curve can be obtained 0 ordinate:

[0107]

[0108] Rearranging and transforming formula (16) gives:

[0109] Substituting h'| X＝0 = -∞, we get:

[0110]

[0111] Combining the above h' ≥ 0 and h' < 0, when 90° < θ ≤ 180°, the two - dimensional contour curve equation of the water - air interface can be obtained:

[0112]

[0113] Obtaining the expression of the two - dimensional contour curve equation X of the water - air interface and substituting it into Equation 3, the force formula when the bionic leaf beetle larva soft robot is in equilibrium can be obtained.

[0114] Example 5

[0115] Under near - infrared light irradiation, the free swimming of the bionic leaf beetle larva soft robot (the preparation process parameters are as in Example 3, only the shape is different, being a rectangular strip in the shape of a leaf beetle larva) is realized. As Figure 4 shown in C, the LCE / CNTs - based body bends in the part exposed to infrared light and pushes the unexposed part along the long axis of the bionic leaf beetle larva soft robot. The actual displacement and angular velocity of the bionic leaf beetle larva soft robot over time are as Figure 4 shown in G and Figure 4 GH. It is worth mentioning that the movement starts immediately after being exposed to infrared light within 1 second, which is consistent with the photothermal drive in air( Figure 4F). In addition to the on / off switch and speed control of the lamp, the control of the moving direction is also essential for maneuvering the moving direction. Under NIR irradiation, the photodynamic clockwise rotation of the body (20 mm × 4 mm × 0.5 mm) can also be achieved. The length of the bionic leaf beetle larva soft robot is at least twice the diameter of the light spot. Therefore, the illumination can be concentrated on half of the body. Unilateral light irradiation provides torque rather than thrust, causing the bionic leaf beetle larva soft robot to swing its body in a rotational motion like a leaf beetle larva. When the infrared irradiation point is changed, the rotational direction of the bionic leaf beetle larva soft robot is reversed. In addition to the fully soft robot of the leaf beetle larva type, other reptilian insects, such as the fully soft spider robot with controllable moving direction, were also prepared to illustrate the generality of this method.

[0116] Figure 4 Figure I shows the movement of the spider-like fully soft robot at the gas-liquid interface under directional light irradiation. When the light irradiates the left part far from the geometric center of the spider-like soft robot, a bend towards the near-infrared light is generated, resulting in a right turn. Similarly, when the near-infrared light irradiates the right side, the spider-like soft robot turns to the left. When irradiated alternately on the left and right, the robot moves straight forward without turning.

[0117] In addition to two-dimensional movement, the bionic leaf beetle larva soft robot based on LCE / CNTs also exhibits the ability to perform three-dimensional movement at the gas-liquid interface. When the near-infrared light irradiates one-third of the bionic leaf beetle larva soft robot, a curling movement of the body appears at the gas-liquid interface. Generally speaking, the aquatic environment is complex and challenging for fully soft robots. Here, the chemical resistance of the bionic leaf beetle larva soft robot in H 2 SO 4 (pH = 2), NaOH (pH = 12), KMnO 4 (10 mg / ml), and glycerol (0.63 g / ml) solutions was studied, and its weight loss did not exceed 2% within 48 hours of immersion ( Figure 9 and 10 ). In addition to the harsh conditions, we also printed a smaller bionic leaf beetle larva soft robot (10 mm × 3 mm), which was placed in a closed glass tube with a diameter of 15 mm. Due to the penetration of light, the body could rotate freely and complete a 360° rotation in 3.5 seconds ( Figure 4 H).

[0118] Example 6

[0119] The triple-phase line contact angle generates a surface tension difference to establish a motion mechanism. During this process, the movement of the bionic leaf beetle larva soft robot is controlled by the buoyancy F b and the surface tension F T . ( Figure 4B). When infrared light irradiates the bionic leaf beetle larva soft robot, the swimming process can be divided into falling, swimming, and leaving. As Figure 5 shown in A(i) and (iv), the force F of the bionic leaf beetle larva soft robot at a certain moment during falling and leaving L is close to equilibrium, which is similar to the Figure 4 analysis in E. During the swimming process ( Figure 5 A(ii and iii)), the bionic leaf beetle larva soft robot will produce different deformations when exposed to NIR light, causing changes in the angle between the surface tension and the horizontal plane and the contact surface length. The three-dimensional motion of the two-phase interface is achieved. ( Figure 5 B). The force expression during the motion process is:

[0120] F r = γL 1 sinα R -γL 2 sinα L

[0121] where L 1 and L 2 are the contact lengths of both sides of the bionic leaf beetle larva soft robot with the gas-liquid interface.

[0122] ABAQUS finite element is used to prove the consistency of the motion principle and mechanical analysis. DEFINE_GRID_MOTION(DM) is used to establish the initial model of the bionic leaf beetle larva soft robot. The computational domain is divided into two parts. One part is the external fluid domain, which is a cylinder with a diameter of 50 mm and a height of 10 mm. The other part is the body of the bionic leaf beetle larva soft robot, with a length, width, and height of 20 mm, 3 mm, and 0.6 mm respectively, laid at the two-phase interface. The establishment of the geometric model and mesh generation are as Figure 11 shown.

[0123] For the bionic leaf beetle larva soft robot based on LCE / CNTs, the temperature on one side rises rapidly after near-infrared light irradiation, and the body rotates upward at the two-phase interface. During the motion of the robot, the contact area with the gas-liquid interface changes, and the inclination angle along the three-phase contact line changes, thus causing a surface tension difference, which leads to the forward or even flipping of the body of the bionic leaf beetle larva soft robot. After the infrared light is turned off, the bionic leaf beetle larva soft robot returns to its initial state. The deformations and free interfaces of the bionic leaf beetle larva soft robot in four states (bending, twisting, upward curling, and recovery) are as Figure 5 shown in B.

[0124] By analyzing the motion of the bionic leaf beetle larva soft robot after the infrared lamp is turned off, the mechanism of the three-phase contact line is further demonstrated. With the change of the inclination angle along the contact line, the F in the motion directionT Increased, which makes the bionic leaf beetle larva soft robot move faster than before. Vector diagrams and velocity contour maps are given in the computational domain ( Figure 5 C and 5D). The lateral capillary force of the bionic leaf beetle larva soft robot is uniformly distributed along the three-phase contact line before being irradiated by light. After irradiation, the force distribution of the bionic leaf beetle larva soft robot is mainly concentrated in the irradiated area ( Figure 5 E). The movement of the bionic leaf beetle larva soft robot at the gas-liquid interface is proven to be caused by the difference in surface tension, which is consistent with the mechanical analysis.

Claims

1. A method for preparing a soft robot that can realize three-dimensional motion at a gas-liquid interface. include: (1) mixing 1,4-bis-[4-(6-acryloyloxy)benzoyloxy]-2-methylbenzene (RM82), n-butylamine, a photoinitiator, and carbon nanotubes, heating, fully stirring, and reacting to obtain a liquid crystal / carbon nanotube prepolymer printing ink; (2) The liquid crystal / carbon nanotube prepolymer printing ink in step (1) is printed using a 3D printer, and the ink is oriented while being extruded and photocured by ultraviolet light to obtain a soft robot that can achieve three-dimensional motion at the gas-liquid interface; wherein the direct ink writing 3D printer is used, and before the printing process, the system is maintained at a printing temperature of 50 to 65°C for 20 to 60 minutes; during the printing process, the printing speed is 12 mm / s, and the extruded ink is exposed to ultraviolet light; after printing, it is exposed to ultraviolet light for 20 to 40 minutes to obtain a liquid crystal elastomer with a cross-linked structure; wherein the direct ink writing is performed using a three-axis motion control platform for extrusion design, and the ink is extruded by pressure-driven extrusion using an Ultimus V pressure box according to the programmed G code, and the extrusion head of the 3D printer consists of a steel barrel surrounded by a heating coil with a thermocouple.

2. The preparation method according to claim 1, It is characterized in that In the step (1), the carbon nanotubes are single-walled or multi-walled carbon nanotubes; and the photoinitiator is benzoin diethyl ether.

3. The preparation method according to claim 1, It is characterized in that In the step (1), the molar ratio of 1,4-bis-[4-(6-acryloyloxy)benzoyloxy]-2-methylbenzene (RM82) to n-butylamine is 1-1.5:1-1.5; The photoinitiator accounts for 1-5 wt% of the total reaction monomer mass; the carbon nanotubes account for 0.5-2 wt% of the total reaction monomer mass.

4. The preparation method according to claim 1, It is characterized in that In the step (1), the heating is performed to a liquid crystal transition temperature of 100-110° C.; and the reaction is performed by heating at 100-110° C. with stirring for 18-22 hours.

5. The preparation method according to claim 1, It is characterized in that The ultraviolet light irradiation power during printing is 5 - 20 mW / cm 2 ; After printing is completed, the ultraviolet light irradiation power is 20 - 40 mW / cm 2 .

6. A soft robot capable of realizing three-dimensional motion at a gas-liquid interface prepared by the method of claim 1, wherein the material component of the soft robot is a liquid crystal elastomer / carbon nanotube composite with controllable orientation; The liquid crystal elastomer structural formula is: where n is an integer with n ≥ 1.

7. Application of a soft robot capable of realizing three-dimensional motion at a gas-liquid interface prepared by the method of claim 1 in transportation.

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