Dual-network acrylate dielectric elastomer as well as preparation method and application thereof

Abstract

The invention relates to a dual-network acrylate dielectric elastomer as well as a preparation method and application thereof, an acrylate dielectric elastomer precursor solution is subjected to ultraviolet irradiation to initiate polymerization reaction, and the dual-network acrylate dielectric elastomer is obtained. The acrylate dielectric elastomer precursor solution is prepared from the following components in parts by weight: 35 to 45 parts of acrylate flexible monomer, 5 to 15 parts of acrylate functional monomer, 55 to 65 parts of long-chain acrylate cross-linking agent, 0.5 to 1.5 parts of short-chain acrylate cross-linking agent and 0.1 to 0.5 part of photoinitiator. Compared with the prior art, low-voltage driving and quick response of the dielectric elastomer can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of dielectric elastomer materials and relates to a double network acrylic ester dielectric elastomer and a preparation method and application thereof. Background Art

[0002] Soft robots are an emerging branch of the field of robotics. Due to their high flexibility, biocompatibility and environmental adaptability, they have shown broad application prospects in minimally invasive surgery, environmental monitoring, search and rescue, human-computer interaction, etc. Artificial muscles are the core driving components of soft robots. They can deform when stimulated by external stimuli (such as heat, light, electricity, magnetism, pressure and chemical energy), thereby generating the required motion force or torque.

[0003] As one of the electroactive polymers, dielectric elastomer (DE) stands out among many artificial muscle materials due to its advantages such as large deformation, high energy density, fast reaction speed and low cost. Its working principle is that when a dielectric elastomer coated with flexible electrodes is placed in an electric field, strong electrostatic effects will be generated on the upper and lower electrode surfaces, and the resulting Maxwell force will cause the dielectric elastomer to deform significantly. The area strain (S z ) can be expressed as S z =-ε0ε r E 2 / Y, where ε0 is the dielectric constant of vacuum, ε r is the relative permittivity of the dielectric elastomer, Y is the Young's modulus of the dielectric elastomer, and E is the applied electric field.

[0004] At present, a variety of commercial elastomer materials such as silicone rubber, polyurethane and acrylate elastomers have been widely used in dielectric elastomer actuators. Compared with other types of dielectric elastomer materials, acrylate dielectric elastomers show excellent economic benefits due to their light weight and low cost. In addition, acrylate dielectric elastomers also perform better in terms of driving ability and energy density, and can more effectively simulate the movement of biological muscles, so they have received extensive research and attention. However, acrylate dielectric elastomers represented by commercial VHB4910 require a higher driving electric field to provide energy for their driving due to their high stiffness and low dielectric constant. In addition, this type of dielectric elastomer material has significant viscoelastic properties, and often has a series of problems such as large energy loss, long response time, and poor high-frequency response.

[0005] Researchers have made great efforts to develop acrylate-based dielectric elastomers with higher performance. The best way to increase the area strain of dielectric elastomers is to reduce the elastic modulus or increase the dielectric constant. Traditional strategies often focus on improving a specific property, but this may also lead to a decrease in other properties. Therefore, it remains a challenging task to develop dielectric elastomers with stronger comprehensive performance, such as large strain, high energy density and low loss under low fields.

[0006] Patent CN118930753A discloses a method for preparing a broadband fast-response acrylate dielectric elastomer, its products and applications, including the following steps: uniformly mixing an acrylate crosslinker, an acrylate flexible monomer, an acrylate functional monomer and a photoinitiator to form an acrylate dielectric elastomer precursor solution; vacuuming the acrylate dielectric elastomer precursor solution to remove bubbles, and injecting it into a dielectric elastomer mold with a groove; and UV curing to obtain the acrylate dielectric elastomer. However, the dielectric elastomer driving voltage proposed in the patent is too high, which is not conducive to the safety and stability of the driving device.

[0007] Patent CN114181417A discloses a thermosetting dielectric elastomer film and a dielectric driver thereof, wherein the preparation method comprises the following steps: blending an acrylate monomer, an olefin functional monomer having at least one inactive carbon-carbon double bond, an initiator and a cross-linking agent which may be optionally added, and performing bulk free radical copolymerization to obtain a thermosetting film; using an organic solvent soaking and swelling method to simultaneously and uniformly compound a cross-linking agent containing a polythiol group and a photoinitiator into the thermosetting film, and vacuum drying to obtain a thermosetting dielectric elastomer film which can be further cross-linked by ultraviolet light; the cross-linking agent refers to a monomer molecule having two or more free radical polymerization-capable cross-linking agents. The active carbon-carbon double bond at the end includes one or more of 1,3-butadiene, triethylene glycol dimethacrylate, myrcene, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate; the cross-linking agent containing a multi-thiol group is selected from one or more of 1,3-propanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,10-decanedithiol, 3,6-dioxa-1,8-octanedithiol, 1,4-butanediol di(thioglycolate), pentaerythritol tetrathioglycolate, di(2-mercaptoethyl) adipate, 1,4-butanedithiol, and 1,2-butanedithiol. However, the electric area strain of the dielectric elastomer proposed in the patent is relatively small, resulting in a limited range of motion of the actuator and insufficient driving ability.

[0008] Patent CN115160233A discloses an adaptive deformation elastomer electrolyte, electrode and battery, wherein the preparation method is: unsaturated ester monomer, bifunctional ionic liquid, alkali metal salt, initiator and crosslinking agent are mixed, the obtained precursor solution is cured under ultraviolet light irradiation, and the film is dried in a vacuum oven to obtain an adaptive deformation elastomer electrolyte. However, the elastomer preparation method proposed in the patent is complicated and not conducive to large-scale production. Summary of the invention

[0009] The purpose of the present invention is to provide a double network acrylic dielectric elastomer and its preparation method and application in order to overcome at least one of the defects of the above-mentioned prior art, such as high driving electric field, stress relaxation and deformation hysteresis. The present invention can realize low-voltage driving and rapid response of the dielectric elastomer.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] One of the technical solutions of the present invention is to provide a double network acrylate dielectric elastomer, wherein an acrylate dielectric elastomer precursor solution is irradiated with ultraviolet (UV) light to initiate a polymerization reaction to obtain a double network acrylate dielectric elastomer, wherein the acrylate dielectric elastomer precursor solution comprises the following components in parts by weight:

[0012] 35-45 parts of acrylate flexible monomer, 5-15 parts of acrylate functional monomer, 55-65 parts of long-chain acrylate crosslinking agent, 0.5-1.5 parts of short-chain acrylate crosslinking agent and 0.1-0.5 parts of photoinitiator.

[0013] Furthermore, the acrylic ester flexible monomer is selected from one or more of ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate and heptyl acrylate.

[0014] Furthermore, the acrylate functional monomer is selected from one or more of hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, isobornyl acrylate, and acrylic acid.

[0015] Furthermore, the long-chain acrylate crosslinking agent is selected from one or more of polyester acrylate oligomers, polyether acrylate oligomers, and polyurethane acrylate oligomers.

[0016] As a preferred technical solution, the average molecular weight of the long-chain acrylate crosslinking agent is 10 4 ~10 5 of magnitude.

[0017] Furthermore, the short-chain acrylate crosslinking agent is selected from one or more of polyethylene glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, 1,4-butanediol diacrylate, and 1,6-hexanediol diacrylate.

[0018] As a preferred technical solution, the average molecular weight of the polyethylene glycol diacrylate is 400-2000.

[0019] Furthermore, the photoinitiator is selected from one or more of benzil, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzophenone, 1-hydroxy-cyclohexyl benzophenone, and 2,2-dimethoxy-phenyl acetophenone.

[0020] One of the technical solutions of the present invention is to provide a method for preparing the double network acrylic dielectric elastomer, the method comprising the following steps:

[0021] S1, mixing acrylate flexible monomer, acrylate functional monomer, long-chain acrylate cross-linking agent, short-chain acrylate cross-linking agent and photoinitiator to obtain acrylate dielectric elastomer precursor solution;

[0022] S2, evacuating the acrylate dielectric elastomer precursor solution to remove bubbles in the solution; injecting the acrylate dielectric elastomer precursor solution into the mold by solution casting;

[0023] S3, subjecting the acrylate dielectric elastomer precursor solution to ultraviolet light to initiate a polymerization reaction, thereby obtaining a double network acrylate dielectric elastomer;

[0024] S4. The double network acrylic dielectric elastomer is vacuum dried to remove unreacted monomers.

[0025] As a preferred technical solution, the mixing temperature in step S1 is 15-40° C., the stirring rate is 500-1000 r / min, and the mixing time is 6-24 h.

[0026] Furthermore, the vacuum degree of the vacuum pumping in step S2 is 80 to 150 kPa, and the time is 10 to 30 minutes;

[0027] The UV curing power of the polymerization reaction in step S3 is 500-1000 W·cm -1 , the wavelength of ultraviolet light is 300~420nm, and the time is 1~10min.

[0028] As a preferred technical solution, the temperature of the vacuuming and polymerization reaction in steps S2 and S3 is 15-40°C.

[0029] Furthermore, in step S4, the vacuum drying temperature is 40-70° C., the vacuum degree is 80-150 kPa, and the time is 12-48 h.

[0030] One of the technical solutions of the present invention is to provide an application of the double network acrylic dielectric elastomer in a soft robot actuator.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention constructs a double cross-linked network structure by using two cross-linking agents of different lengths, so that the material simultaneously exhibits a low Young's modulus, a large elongation at break, and significant strain hardening behavior;

[0033] (2) The present invention introduces multiple hydrogen bonds by adding acrylate functional monomers to achieve multiple segment effects, thereby achieving a faster dynamic response speed, thereby solving the problems of energy loss, stress relaxation and deformation hysteresis caused by the inherent viscoelasticity of traditional acrylate dielectric elastomer materials;

[0034] (3) The dual-network dielectric elastomer prepared by the present invention can achieve a large actuation strain under a low electric field and has an ultra-high energy density due to the structural design of the polymer molecules formed by the combination of the above factors. The preparation method adopted is simple to operate and easy to prepare on a large scale. It is a strong candidate material for artificial muscles and is suitable for soft robots in various scenarios. It is of great significance for the preparation of high-performance soft robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a tensile curve diagram of the acrylic dielectric elastomer in the examples of the present invention and the comparative examples;

[0036] Figure 2 It is a static area strain diagram of the acrylic dielectric elastomer in the embodiments of the present invention and the comparative examples;

[0037] Figure 3 The dynamic cyclic area strain diagram of the double network acrylic dielectric elastomer in Example 2 of the present invention;

[0038] Figure 4 It is a time-dependent area strain diagram of the acrylic dielectric elastomer in Example 2 of the present invention and the comparative example;

[0039] Figure 5 The frequency-dependent area strain diagram of the acrylic dielectric elastomer in Example 2 of the present invention and the comparative example;

[0040] Figure 6 Graph showing the energy density of the acrylic dielectric elastomer in Example 2 of the present invention and the comparative example. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0042] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0043] Embodiment 1:

[0044] A double network acrylic dielectric elastomer and a preparation method thereof, the specific steps are as follows:

[0045] S1. Weigh and mix butyl acrylate, hydroxyethyl acrylate, polyurethane acrylate oligomer CN9021 with an average molecular weight of 28,000 produced by Sartomer, polyethylene glycol diacrylate with an average molecular weight of 1,000, and 2-hydroxy-2-methyl-1-phenyl-1-propanone in proportion, and stir at room temperature at a stirring rate of 800 r / min overnight to obtain a uniform acrylate dielectric elastomer precursor solution;

[0046] S2. The acrylate dielectric elastomer precursor solution is evacuated at room temperature at a vacuum degree of 100 kPa for 15 minutes to remove bubbles in the solution; in order to ensure an oxygen-free environment during the photocuring process, the acrylate dielectric elastomer precursor solution is slowly injected into a special container by a solution casting method. The special container is composed of two pieces of transparent glass and a polytetrafluoroethylene frame sandwiched in the middle. A space for accommodating the acrylate dielectric elastomer precursor solution is formed between the polytetrafluoroethylene frame and the two pieces of transparent glass. This special container can effectively isolate the air and ensure the smooth progress of the curing process;

[0047] S3, the acrylate dielectric elastomer precursor solution was heated at room temperature and a power of 678 W·cm -1 , initiate polymerization reaction under ultraviolet light with a wavelength of 365nm for 5min;

[0048] S4. After the polymerization is completed, the obtained double network acrylate dielectric elastomer film is placed in a vacuum oven at a temperature of 50° C. and a vacuum degree of 100 kPa for vacuum drying for 24 hours to remove unreacted monomers.

[0049] The composition of the acrylate dielectric elastomer precursor solution in this embodiment is shown in Table 1.

[0050] Table 1 Composition of the acrylic dielectric elastomer precursor solution in Example 1

[0051]

[0052] Embodiment 2:

[0053] A double network acrylate dielectric elastomer and a preparation method thereof are basically the same as Example 1, except that the short-chain acrylate crosslinker polyethylene glycol diacrylate is replaced by polyethylene glycol diacrylate. The composition of the acrylate dielectric elastomer precursor solution in this example is shown in Table 2.

[0054] Table 2 Composition of the acrylic dielectric elastomer precursor solution in Example 2

[0055]

[0056] Embodiment 3:

[0057] A double network acrylate dielectric elastomer and a preparation method thereof are basically the same as those in Example 1, except that the short-chain acrylate crosslinker polyethylene glycol diacrylate is replaced by neopentyl glycol diacrylate. The composition of the acrylate dielectric elastomer precursor solution in this example is shown in Table 3.

[0058] Table 3 Composition of the acrylic dielectric elastomer precursor solution in Example 3

[0059]

[0060] Comparative Example:

[0061] The invention discloses an acrylic dielectric elastomer, which is a commercial acrylic dielectric elastomer VHB4910 sold by 3M Company.

[0062] The above-mentioned acrylic dielectric elastomer is subjected to the following tests or experiments, and then the test or experiment results are analyzed.

[0063] Test Example 1:

[0064] The mechanical properties of the above-mentioned acrylic dielectric elastomer were tested at room temperature using a microcomputer-controlled electronic universal testing machine. The specific steps are as follows:

[0065] The thickness of the acrylic dielectric elastomer film sample was fixed at 1 mm and was cut into a standard dumbbell shape to facilitate stress application and deformation measurement;

[0066] During the test, the film was stretched at a constant stretching rate of 100 mm / min until the film broke;

[0067] According to the stress-strain curve obtained from the test, the ratio of stress to strain at 5% strain is defined as the Young's modulus of the film.

[0068] like Figure 1 As shown, it can be seen that compared with the comparative example, Examples 1 to 3 all have lower Young's modulus; at the same time, due to the selection of appropriate short-chain acrylate crosslinking agents, Example 2 also exhibits low Young's modulus, large elongation at break and significant strain hardening behavior, and is an ideal material for dielectric elastomers.

[0069] Test Example 2:

[0070] The above-mentioned acrylic dielectric elastomer was subjected to a static drive test using a circular thin film actuator. The specific steps are as follows:

[0071] After the acrylic dielectric elastomer film sample was pre-stretched equiaxially by 200%, it was fixed on a polyethylene terephthalate (PET) ring frame, and carbon grease with a diameter of 1 cm was coated on both sides of the film as a flexible electrode, which was applied to the soft robot actuator, and the area coated with the flexible electrode was connected to the AMR10R20 high-voltage power supply with a silver-plated copper wire;

[0072] During the driving process, the area of ​​the electrically active part expands and the thickness decreases. The driving process is recorded by a camera. The high-voltage power supply gradually increases from 0V until the driver undergoes electrical breakdown.

[0073] The area strain was then analyzed using the software IMAGEJ. The area strain was calculated by the area change before and after driving. The final area strain was obtained by the formula S = (a1-a0) / a0×100%, where a1 is the actuation area of ​​the film when an electric field is applied, and a0 is the initial area of ​​the film when no electric field is applied.

[0074] like Figure 2 As shown, it can be seen that Example 1 can -1 The static electric area strain of 107% can be achieved under an electric field of 60V·μm -1 The static electric area strain of 200% can be achieved under an electric field of 77V·μm -1 The static electric area strain of 118% was achieved under an electric field of 60V·μm -1 There is only 26% static electric area strain under an electric field, and the driving capability of Example 2 is about 7.6 times that of the comparative example.

[0075] Test Example 3:

[0076] The above-mentioned acrylic dielectric elastomer is subjected to a dynamic driving test, which is divided into a cycle test, a time response test and a frequency response test. The specific steps are as follows:

[0077] In the cyclic test, the electric field applied to the acrylate dielectric elastomer film sample was fixed at 45 V·μm-1 , the frequency was kept at 1 Hz, and a total of 10,000 actuations were performed to analyze the cyclic characteristics of the film and focus on the deformation stability of the film;

[0078] In the time response test, the electric field applied to the film was fixed at 45 V·μm -1 , and continued to drive for 600s to analyze the time response characteristics of the film and pay attention to the deformation speed of the film;

[0079] In the frequency response test, the voltage applied to the film was fixed at 45V·μm -1 , the frequency gradually increases from 1 Hz to 100 Hz, so as to analyze the frequency response characteristics of the film and pay attention to the deformation stability of the film.

[0080] like Figure 3 As shown, it can be seen that Example 2 can be stably driven for 10,000 cycles at a frequency of 1 Hz under an area strain of 100%, which indicates that Example 2 has excellent durability and stability, can maintain high-efficiency performance during long-term operation, and is suitable for application scenarios with high requirements for reliability and cycle life.

[0081] like Figure 4 As shown, it can be seen that Example 2 only takes 4 seconds to reach 90% of the final strain, which is significantly better than the comparative example, which takes at least 200 seconds to reach 90% of the final strain.

[0082] like Figure 5 As shown, it can be seen that when the driving frequency gradually increases from 1 Hz to 100 Hz, the energy loss of the comparative example under high-frequency conditions increases significantly, and the area strain rapidly drops to 37% of the maximum area strain, while Example 2 shows better dynamic response capability and can still maintain a high strain level of 69% at 100 Hz.

[0083] Test example 4:

[0084] The energy density test of the above-mentioned acrylic dielectric elastomer is carried out in the following steps:

[0085] After the acrylic dielectric elastomer film sample was pre-stretched by 200%, polyethylene terephthalate was adhered to the top and bottom edges of the film to constrain the active film, and the energy density was tested by hanging a weight at the bottom of the film;

[0086] Under a load of 200 g, the voltage was gradually increased from 0 V, and the uniaxial area strain during the film contraction process was recorded with a camera;

[0087] According to the increase of load potential energy during the contraction process, the formula E = m L gh / m aCalculate the energy density of the film under different electric fields, where m L is the mass of the load, m a is the effective mass of the film driving area, and h is the height change of the load.

[0088] like Figure 6 As shown in Figure 2, the energy density of the acrylic dielectric elastomer increases with the increase of the driving electric field; when the driving electric field is 55 V·μm -1 When the energy density of Example 2 is 274 J·kg -1 , while the energy density of the comparative example is only 80 J·kg -1 ; This shows that Example 2 exhibits significantly better energy storage capacity under high driving electric fields, reflecting the advantages of double network acrylic dielectric elastomers in improving energy density, and further proving the potential and value of double network acrylic dielectric elastomers in high-efficiency electric drive applications.

[0089] The reason why the dual network acrylate dielectric elastomer shows excellent driving performance in the embodiment is mainly due to the ingenious combination of the dual cross-linked network structure design and the dynamic hydrogen bond. This dual cross-linked network provides excellent electromechanical properties for the elastomer, so that the elastomer can achieve ultra-large strain under low electric field. At the same time, the presence of dynamic hydrogen bonds greatly improves the viscoelasticity of the elastomer, gives the elastomer low energy loss, and the elastomer has excellent dynamic responsiveness. This combined effect makes the dual network acrylate dielectric elastomer outstanding in driving performance and shows a broad prospect.

[0090] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A double network acrylic dielectric elastomer, characterized in that: The acrylate dielectric elastomer precursor solution is irradiated with ultraviolet light to initiate a polymerization reaction to obtain a double network acrylate dielectric elastomer, wherein the acrylate dielectric elastomer precursor solution comprises the following components in parts by weight: 35-45 parts of acrylate flexible monomer, 5-15 parts of acrylate functional monomer, 55-65 parts of long-chain acrylate crosslinking agent, 0.5-1.5 parts of short-chain acrylate crosslinking agent and 0.1-0.5 parts of photoinitiator.

2. A double network acrylic dielectric elastomer according to claim 1, characterized in that: The acrylic ester flexible monomer is selected from one or more of ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate and heptyl acrylate.

3. The double network acrylic dielectric elastomer according to claim 1, characterized in that: The acrylate functional monomer is selected from one or more of hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, isobornyl acrylate, and acrylic acid.

4. The double network acrylic dielectric elastomer according to claim 1, characterized in that: The long-chain acrylate crosslinking agent is selected from one or more of polyester acrylate oligomers, polyether acrylate oligomers, and polyurethane acrylate oligomers.

5. The double network acrylic dielectric elastomer according to claim 1, characterized in that: The short-chain acrylate crosslinking agent is selected from one or more of polyethylene glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, 1,4-butanediol diacrylate, and 1,6-hexanediol diacrylate.

6. The double network acrylic dielectric elastomer according to claim 1, characterized in that: The photoinitiator is selected from one or more of benzil, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzophenone, 1-hydroxy-cyclohexyl benzophenone, and 2,2-dimethoxy-phenyl acetophenone.

7. A method for preparing a double network acrylic dielectric elastomer according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1, mixing an acrylate flexible monomer, an acrylate functional monomer, a long-chain acrylate cross-linking agent, a short-chain acrylate cross-linking agent and a photoinitiator to obtain an acrylate dielectric elastomer precursor solution; S2, evacuating the acrylate dielectric elastomer precursor solution; S3, subjecting the acrylate dielectric elastomer precursor solution to ultraviolet light to initiate a polymerization reaction, thereby obtaining a double network acrylate dielectric elastomer; S4. vacuum drying the double network acrylic dielectric elastomer.

8. The method for preparing a double network acrylic dielectric elastomer according to claim 7, characterized in that: The vacuum degree of the vacuum pumping in step S2 is 80 to 150 kPa, and the time is 10 to 30 minutes; The UV curing power of the polymerization reaction in step S3 is 500-1000 W·cm -1 , the wavelength of ultraviolet light is 300~420nm, and the time is 1~10min.

9. The method for preparing a double network acrylic dielectric elastomer according to claim 7, characterized in that: The vacuum drying temperature in step S4 is 40-70° C., the vacuum degree is 80-150 kPa, and the time is 12-48 hours.

10. Use of the double network acrylate dielectric elastomer according to any one of claims 1 to 6 in a soft robot actuator.

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