Simple triple-state polymer actuators with controllable folding characteristics

Abstract

Driven by the interests in self-folding, there have been studies developing artificial self-folding structures at different length scales based on various polymer actuators that can realize dual-state actuation. However, their unidirectional nature limits the applicability of the actuators for a wide range of multi-state self-folding behaviors. In addition, complex fabrication and programming procedures hinder broad applications of existing polymer actuators. Moreover, few of the existing polymer actuators are able to show the self-folding behaviors with the precise control of curvature and force. To address these issues, we report an easy-to-fabricate triple-state actuator with controllable folding behaviors based on bilayer polymer composites with different glass transition temperatures. Initially, the fabricated actuator is in the flat state, and it can sequentially self-fold to angled folding states of opposite directions as it is heated up. Based on an analytical model and measured partial recovery behaviors of polymers, we can accurately control the folding characteristics (curvature and force) for the rational design. To demonstrate an application of our triple-state actuator, we have developed a self-folding transformer robot which self-folds from a two-dimensional sheet into a three-dimensional boat-like configuration and transforms from the boat shape to a car shape with the increase in the temperature applied to the actuator. Our findings offer a simple approach to generate multiple configurations from a single system by harnessing behaviors of polymers with the rational design.

Light-Assisted Reconfiguration of Thermosetting Polyurethane Enabled by Gradient Plasticity

“…Light-induced self-folding materials are mainly composed of a shape-memory polymeric flat and a light-responsive layer. One valid approach to prepare such self-folding materials is to focus an external stimulus to a local region of the materials or to prepare a heterogeneous material that can be partially responsive. − To meet these design requirements, PEGU and MWCNTS doped PU samples were spatially organized to obtain different light-responsive species by the simple hot-pressing method (Figure a). The thickness of the PEGU film and MWCNTS doped PU film was 1.5 mm and 150 μm, respectively.…”

A theoretical model for two‐way bending behavior of bilayer shape memory polymer plate

“…Ge et al proposed a constitutive model of a two‐way poly(cyclooctene) SMP laminate by embedding pre‐stretched SMP into an acrylate‐based polymer matrix eccentrically from the center position, in which the stress and strain in the processes of crystallization (in the cooling step) and melting (in the heating step) were considered individually 26 . In addition to the above‐mentioned theoretical model, Chen et al fabricated a UV‐cured two‐way SMP bilayer with a curved permanent shape, predicting the critical bending curvature based on the Timoshenko bilayer beam theory with different thermal expansion coefficients 27,28 . Furthermore, Chen et al also proposed a theoretical model to predict the two‐way critical bending curvature based on the strain energy balance theory.…”

“…26 In addition to the above-mentioned theoretical model, Chen et al fabricated a UV-cured two-way SMP bilayer with a curved permanent shape, predicting the critical bending curvature based on the Timoshenko bilayer beam theory with different thermal expansion coefficients. 27,28 Furthermore, Chen et al also proposed a theoretical model to predict the two-way critical bending curvature based on the strain energy balance theory. The predicted results were clearly higher than the experimental ones with ignoring the releasing process of strain-energy during the heating recovery step.…”