Bending actuation of a composite liquid crystal elastomer via direct Joule heating

Abstract

In this work a new bi-layered composite actuator based on a polysiloxane-based monodomain nematic Liquid Crystal Elastomer (LCE) and on a conductive PEDOT:PSS thin layer is proposed. The basic idea is to integrate electroconductive properties in the LCE and to validate the feasibility of direct actuation of the LCE by Joule heating of the conductive (and compliant) PEDOT:PSS layer. The fabrication of the actuator is achieved by depositing a thin conductive polymer layer by drop casting a PEDOT:PSS waterborne solution after having increased the LCE surface wettability with an air plasma treatment. The excellent stability of PEDOT:PSS and its mechanical properties, better matched with LCE ones compared to metals or inorganic nanoparticles used in other approaches, allowed to develop an all-organic reliable actuating composite based on thermoresponsive properties of LCE. Thermal actuation via direct Joule heating of the composite has been verified and prototypes of LCE/PEDOT:PSS bending actuators have been preliminary tested

Nanostructured Composites Based on Liquid-Crystalline Elastomers

“…As reported in several studies of LCE-based composite bilayers [86,87,88,89,90,91,92], if the ratio (d nl )/(d LCE ) is lower than a critical value (which depends on the chemistry of the conductive nanolayers), bending actuation is not observed. Instead, micro- or nanostructured surface wrinkling is obtained with the possibility of fine-tuning their geometrical properties.…”

“…Another field of research related to LCE composites concerns the preparation of bilayered or multilayered systems obtained by coupling monodomain LCE films, mainly prepared according to the “two-step” cross-linking procedure [35], and one or two layers of conductive materials deposited onto the top surface of LCEs. These bilayered (or multilayered) systems were the object of several experimental and theoretical works in the past six years [85,86,87,88,89,90,91,92,93,94,95]. Several new technological applications were explored in detail based on unique phenomena characterizing the LCE-based bilayer composites, such as bending actuation [85,87,89,91,92,93,94,95] and surface wrinkling [85,86,88,90,92,93,94], as described in the sections below.…”

“…The first bilayer LCE-systems were produced by depositing conductive nanostructured thin polymer layers on the top surface of standard polysiloxane-based LCE films (see the general schemes reported in Figure 15). Agrawal et al [90] used nanolayers of poly(styrene) (PS), while Domenici, Greco et al [86,87,88] chose the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) conductive polymer.…”

“…In the case of PEDOT:PSS/LCE bilayers, several strategies were optimized [85,86,87,88,89]. The PEDOT:PSS material was chosen for its excellent properties of conductivity, and mechanical and chemical stability, and for the possibility of fabricating nanolayers with very high control and reproducibility [96,97].…”

“…Deposition of the DMSO-doped PEDOT:PSS nanolayer was done by drop-casting of the solution onto the LCE stripes and the wires, resulting in a good adhesion and electrical contact between the wire and the conductive layer. In all cases [85,86,87,88,89], the PEDOT:PSS material was deposited onto the surface of the LCE films at room temperature, i.e., in the nematic phase (Figure 15b).…”