Preparation And Application Of Actuators Based On Graphene Gradient Composites

Smart actuating materials have wide application prospects in artificial muscles,soft robots,and flexible electronics.As one of them,photo-responsive materials have been attracting much attention,and the photo-responsive actuators prepared by them have great advantages in many aspects such as remote manipulation,response time and spatial accuracy.Among various photoresponsive materials,graphene-based polymer composites have become a good choice for the preparation of photoresponsive actuators due to their low cost,high photothermal conversion efficiency,good mechanical properties and special thermal expansion behavior.However,the response performance of such actuators is largely limited by the graphene content in the composites and the structure of the actuators.On the one hand,polymer composites with high graphene content can better absorb external light energy and promote photothermal conversion,thus exhibiting better actuation performance,but high graphene loading in the polymer matrix usually causes graphene aggregation,resulting in reduced mechanical properties and inhomogeneous deformation under external stimuli.On the other hand,the performance of conventional bilayer photothermal actuators basically depends on the difference of thermal expansion coefficients between different materials,and the search for materials with larger thermal expansion coefficient differences becomes the only way to improve the actuator performance.Therefore,in order to improve the performance of such actuators,more graphene needs to be loaded in a limited polymer matrix.In this work,we designed and prepared a multilayer graphene/polydimethylsiloxane(PDMS)composite gradient material for efficient photoresponsive actuators by a simple in situ stacking and curing method from the perspective of structural optimization.A typical gradient structure material consists of a pure PDMS layer and multiple graphene/PDMS composite layers with monotonically varying graphene concentration.Due to the design of the gradient structure and the high photothermal conversion efficiency of graphene,the prepared actuators show enhanced photoresponse performance with a fast response within 8 s and an improved photothermal conversion efficiency of 40.9%.It was confirmed by theoretical modeling and finite element simulation,respectively,that the actuation performance was significantly improved with increasing the number of stacked layers for the same total thickness of the actuator.In addition,it was found that the thickness of the film and the concentration of graphene also had a significant effect on the actuator performance,and a 180 μm thick four-layer gradient actuator was prepared by tuning to achieve a deflection of more than 90 degrees.The final actuator based on the optimized structure was demonstrated for applications including cantilever beams,soft crawling robots,and smart grippers.This work provides a new design idea for the preparation of highly efficient lightresponsive actuators.