Three-Dimensional Shape Transformation of Eu3+-Containing Polymer Films through Modulating Dynamic Eu3+-Iminodiacetate Coordination

Shape-transformative materials that can autonomously adopt three-dimensional (3D) shapes in response to environmental stimuli are of interest for the development of sensors and soft robotics. We herein report a new synthetic strategy to fabricate shape-transformable Eu3+-containing interpenetrating polymer films consisting of poly(vinyl alcohol) (PVA) and poly(3-iminodiacetate-2-hydroxypropylmethacrylate-co-acrylic acid) (P-(IDHPMA-co-AA)). Given the dynamic nature of Eu3+-iminodiacetate (IDA) coordination, ink patterning and water/Fe3+ diffusion are used to generate the in-plane or z-directional heterogeneities of Eu-IDA dynamic coordination in the polymer film, respectively. The heterogeneities can be visualized by the distribution of fluorescence emission of Eu3+. When subjected to high humidity, the differences in the swelling ratio and modulus as a result of chemical inhomogeneity further drive various 3D shape morphings, including rolling, helixing, twisting, surface buckling, and folding. Shape transformation is reversible upon the removal of moisture from the polymer films. The ink concentration and environmental humidity are demonstrated to impact the shape transformation kinetics and the final 3D shape along with other geometric parameters. Our work illustrates a novel way to fabricate new-generation biomimetic actuators and sensors.