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.