Stress-Free Two-Way Liquid Crystalline–Semicrystalline Shape Memory Copolymer Actuators with Multistimuli-Responsive Actuation Behaviors

Abstract

Stress-free two-way shape memory semicrystalline networks have garnered significant interest due to their ability to undergo reversible shape changes under external stimuli without repeated programming. However, their reversible actuation strain is often limited by the low anisotropy of the skeleton phase and the low crystallization rate and crystallinity of the actuation phase. In this study, we present a novel approach to developing two-way shape memory actuators utilizing liquid crystalline polymers as the skeleton phase, achieving high actuation strain and multistimuli-responsive behaviors. Specifically, we have designed and synthesized multiblock liquid crystalline–semicrystalline copolymers, poly(4,4’-bis(6-hydroxyhexyloxy)biphenyl phenylsuccinate)-poly(ethylene glycol) (PBDPS-PEG), and characterized their reversible shape changes in response to various external stimuli. The PBDPS block, easily stretchable within the liquid crystal phase, induces the epitaxial crystallization of the PEG block, forming microphase-separated ordered lamellar structures that facilitate reversible shape changes and anisotropic swelling behaviors under thermal, water absorption, and humidity stimuli. PBDPS-PEG actuators extend their functionality to grippers capable of manipulating objects across diverse environmental conditions and serve as humidity sensors, reflecting ambient humidity levels through reversible shape changes. This study highlights the potential of liquid crystalline–semicrystalline copolymer actuators in applications such as soft robotics, biomedical devices, and environmental sensors.