A Glassy Bending-Mode Polymeric Actuator Which Deforms in Response to Solvent Polarity Kenneth D. Harris,* 1,2 Cees W. M. Bastiaansen, 1,2 Dirk J. Broer 1,3 1 Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Postbus 513, 5600 MB, Eindhoven, The Netherlands E-mail: k.harris@tue.nl 2 Dutch Polymer Institute, 5600 AX, Eindhoven, The Netherlands 3 Philips Research Laboratories, High Tech Campus 4, 5656 AE, Eindhoven, The Netherlands Received: May 15, 2006; Accepted: June 14, 2006; DOI: 10.1002/marc.200600342 Keywords: anisotropic swelling; liquid crystalline polymers; hydrogels; hydrogen bonding Introduction In many polymeric gel systems, networks expand enor- mously in one solvent, but contract when transferred to another less favorable solvent. [1–3] The composition of the gel, its chemical surroundings (including the pH and salt concentration), and external ﬁelds (mechanical, electrical, or magnetic) all have a signiﬁcant inﬂuence over the swel- ling and collapse of the network, and a large body of work has been developed to describe these effects and their applications. [4–10] In most cases, however, the gels that are described swell and collapse in an isotropic manner, while a much smaller body of research describes the anisotropic swelling observed in liquid crystal (LC) gels and elasto- mers. [11–14] These anisotropic systems, however, are of signiﬁcant interest due to perceived applications as artiﬁcial muscles, [15,16] contact lens materials, [17,18] or active micro- ﬂuidics components. [19,20] In this communication, we investigate an LC polymer network incorporating reversible hydrogen bonds in the nematic structure. The material anisotropically deforms in response to variations in the composition of the surrounding medium, and because it is stiff and glassy, the network is well-suited to applications requiring mechanical elements. We use a bending-mode deformation, yet our system is monolithic and does not require a bilayer construction. Because the elastic moduli are large (>2 GPa in the dry state, and 200 MPa when swollen), [21] and only moderate quantities of solvent are admitted to the network under equilibrium conditions, it is not fully accurate to describe the material as an ‘‘LC elastomer’’ or hydrogel. The material differentiates itself from these existing systems in that it is Summary: We investigate a series of glassy polymer actuators which are found to bend rapidly and reversibly in response to changes in the solvent environment. The actuators are based on hydrogen-bonded liquid crystal networks, and bending motion is created using director proﬁles engineered to take advantage of the network swelling anisotropy. Strongly polar solvents easily swell the network, forcing bending in one direction, while the less polar solvents extract water to force bending in the opposite direction. Shape variation of twisted conﬁguration liquid crystal polymer ﬁlms in acetone and water. Macromol. Rapid Commun. 2006, 27, 1323–1329 ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Communication DOI: 10.1002/marc.200600342 1323