Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers

• Published in: ACS applied materials & interfaces Vol. 8; no. 19; pp. 12466 - 12472
• Main Authors: Xia, Yu, Lee, Elaine, Hu, Hao, Gharbi, Mohamed Amine, Beller, Daniel A, Fleischmann, Eva-Kristina, Kamien, Randall D, Zentel, Rudolf, Yang, Shu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18.05.2016; American Chemical Society (ACS)
• Subjects: actuator; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; liquid crystal elastomer; monodomain; soft lithography; surface chemistry; actuator; surface chemistry; monodomain; soft lithography; liquid crystal elastomer
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b02789

Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). Here, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau–de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly­(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. Vertically aligned LCMs, a preferred configuration for actuation, are only observed when using a PDMS mold with planar anchoring. Guided by the numerical modeling, we coat the PDMS mold with a thin layer of poly­(2-hydroxyethyl methacrylate) (PHEMA), leading to planar anchoring of LCM. Confirmed by polarized optical microscopy, we observe monodomains of vertically aligned LCMs within the mold, in agreement with modeling. After curing and peeling off the mold, the resulting NLCE micropillars showed a relatively large and reversible radial strain (∼30%) when heated above the nematic to isotropic transition temperature.