A review of humidity-Responsive Actuation in Liquid Crystal elastomer films: Controlling reversibility and irreversibility through hydrogen bonding

Abstract

Humidity-responsive actuation refers to the phenomenon where certain materials alter their shape, size, or color in response to fluctuations in humidity levels. This behavior is reminiscent of natural processes observed in plants, where seeds and flowers react to moisture. The potential applications of humidity-responsive materials span various fields, including soft robotics, smart sensors, biomimetic devices, and anti-counterfeiting measures. Liquid Crystal Elastomers (LCEs)are particularly noteworthy in this context, as they possess a unique combination of properties derived from both liquid crystals and elastomers. These materials exhibit significant changes in shape in response to external stimuli such as temperature, light, electric fields, and humidity. As a result, this paper focuses on the humidity-responsive properties of Liquid Crystal Elastomer (LCE) films, with a specific emphasis on the role of hydrogen bonding in this process. And this review covers the synthesis methods, underlying mechanisms, performance characteristics, challenges, and future prospects of humidity-responsive Liquid Crystal Elastomer (LCE) films.