Chiral nematic latex–GO composite films with synchronous response of color and actuation

Abstract

We report the preparation of flexible latex/graphene oxide (GO) composite films templated by cellulose nanocrystals (CNCs), which show dual responses with interesting color and morphological changes toward water. First, ternary composite films with chiral nematic order were prepared via evaporation-induced self-assembly (EISA) of an aqueous dispersion containing latex, GO and CNCs. Driven by the difference in gravity and the increase of entropy, uneven distribution of GO occurs with the majority gathering at the top of the film. In the second step, CNCs were selectively etched by alkali treatment, leading to the formation of latex/GO (LG) composite films which retain the chiral nematic order and the asymmetric distribution of GO. Meanwhile, the flexibility of the film has been greatly improved. The asymmetrically-organized LG film has different wettability on the top and bottom surfaces, which induces varying extent of swelling toward water. As a result, the synchronous response of color and actuation was realized. Compared to other two-dimensional actuators, the LG films presented in this work have the advantage of easy preparation and additional color change. In addition, the films are also more robust than those with a bilayer structure, which tend to delaminate during repeated utilization.