Preparation,Properties And Oriented Electroactuation Of Plant Oil-based DE Films

Dielectricelastomer(DE)is an electroactive polymer that can be deformed under an external electric field,which is the key material for flexible actuators and soft robots.However,conventional DE films are generally mechanically isotropic,and the plane of isotropic DE films would uniformly expand under an eternal electric field.In order to produce oriented deformation in the plane of isotropic DE films for achieving directional energy output.Some efforts have been applied to combine rigid fiber fillers in DE films or fix asymemetrical pre-stretching to DE films by rigid frames.These methods could constrain or guide the deformation direction,but they would bring some problems,such as: stress relaxation and performance degradation,even low electromechanical conversion efficiency of the complex structure using external rigid frames.In contrast,the development of DE films with intrinsically mechanical anisotropy can directly carry out directional output.Here,we report a spatial post-crosslinking strategy to locally modulate the modulus of DE films and thus to achieve stable mechanical anisotropy and oriented actuation.Specifically,an elastomer network with reserved carbon-carbon double bonds is conveniently established by the bulk copolymerization of n-butyl acrylate(BA)and synthesized oil-based methacrylate(OBMA).The double bonds are from the side group of OBMAs,which are inactive in copolymerization but can be post-crosslinked by thiol-ene click reaction under UV irradiation.Therefore,we can modulate the elastic modulus via controlling the irradiated area with a designed mask pattern.By introducing the periodic post-crosslinked strip pattern in the elastomer film,we can fabricate DE actuators with highly oriented actuation.The main research contents are as follows:(1)Synthesis of vegetable oil-based acrylate functional monomers(OBMA)and preparation and characterization of their copolymer modified DE films.OBMA was synthesized from glyceride trioleate by transesterification reaction and copolymerized with n-butyl acrylate(BA)to prepare pristine DE film,P(BA-R-OBMA).It was found that when the initiator(AIBN)was 0.17 mol% of the total molar volume of the copolymer monomer and 20 mol% of OBMA,the DE film had the best overall mechanical properties with an initial modulus of 0.28 MPa,breaking strength of 0.85 MPa and an elongation at break of 420%.(2)Preparation and characterization of UV-crosslinkable plant oil-based composite DE films and study of their actuate properties.The pristine DE films were soaked into a THF solution containing crosslinking agents(3,6-dioxa-1,8-octanedithiol,DODT)and photo-initiators(darocur 2959).After the swelling process,the THF was evaporated at room temperature.Then,the thermosetting DE films with the capability of post-crosslinking under UV irradiation were obtained by vacuum drying.The optimum formulation and curing process was determined as follows: 20 mol% OBMA,0.5 times the molar amount of OBMA for DODT,and a full light time of at least 12 min.The initial modulus of the optimized DE films was continuously controlled from 0.28 MPa to 3.0 MPa by the duration of UV illumination.In addition,circular DE actuators prepared based upon the optimized DE film can achieve a maximum actuating strain of 37%.(3)Study on the preparation and properties of mechanical anisotropic plant oil-based composite DE film.Based on optimized P(BA-r-20 mol% OBMA)composite DE films with parallel symmetrically arranged regions of cross-linked strips by UV irradiated through the mask,thus exhibiting mechanical anisotropy.Along the length direction of parallel strips,the initial modulus of irradiated DE films increases as gradually increasing the strip number,from 0.58 MPa with one strip increases up to 2.5 MPa with five strips.Perpendicular to the length direction of parallel strips,the initial modulus of DE films has little increment,from pristine 0.30 MPa increases up to 0.37 MPa with five strips.The circular actuator was prepared based on the mechanical anisotropic DE films,which exhibited good directional actuate deformation performance,and the same results were obtained by mechanical simulation.To further investigate the pattern of influence of bar distribution on the performance of DE films,mechanical simulations were used to predict the actuate performance of rectangular DE actuators.The simulation results are as follows: Under the same irradiated area ratio(30%),the performance of oriented electroactuation in the length direction of rectangular DE actuators would be primarily increased and then stabilized at around 6.0% as increasing the parallel strip number.Whereas the actuation strain is relatively small in the width direction(below 3.4%),the strain would gradually decrease to near 1.0% as increasing the parallel strip number.Based on the simulation results different DE bending actuators were prepared,which showed the best bending performance at strip number count 12,with tip displacements and block forces of 14 mm and 600 m N respectively,and soft grippers for handling objects were assembled from the three bending actuators.The controllability of oriented electroactuation of DE actuators via manipulating the locally mechanical behavior of DE films expands the technological potential in achieving complicated deformation of DE actuators.