Tuning Anisotropic Swelling in a Liquid Crystalline Polyester–Polyethylene Glycol Hydrogel via Large Strain and Annealing

Abstract

The anisotropic swelling behavior of hydrogels can be controlled by the alignment of their molecular chains. In this work, we report a strategy to precisely control the anisotropic swelling direction of hydrogels by leveraging a rationally designed liquid crystalline polymer in combination with large strain and annealing. A liquid crystalline polyester–polyethylene glycol random block copolymer (LCP-b-PEG) is synthesized via one-pot polycondensation. The LCP block serves three key roles: a physical network, anisotropic skeleton, and nucleation agent. Under large strain, the molecular chains of the LCP block orient and extend, losing their nucleating capacity. Consequently, the PEG molecular chains align under strain and form lamellae perpendicular to the stretching direction. Following annealing, the extended LCP molecular chains refold, with the stacked pendant phenyl groups acting as row nuclei, inducing the PEG chains to form lamellae parallel to the stretching direction. This strategy not only enables precise control over swelling behavior but also facilitates versatile actuation modes, allowing the liquid crystalline hydrogel actuator to perform tasks such as grabbing, hugging, crawling, and climbing.