Shape memory investigation of alpha-keratin fibers as multi-coupled stimuli of responsive smart materials

Abstract

Like the water responsive shape memory (SM) effect of beta-keratin bird feathers, alpha-keratin hairs either existing broadly in nature are found responsive to many types of coupled stimuli in SM behaviors. In this article, alpha-keratin hairs were investigated for the combined stimuli of thermo-solvent, solvent-solvent, and UV (radiation)-reductant sensitive SM abilities. The related netpoints and switches from the hair molecular networks were identified. The experimental results showed that alpha-keratin hairs manifested a higher ability of shape fixation under thermal stimulus followed with the stimuli of solvent and UV-radiation. Shape recovery from the hair with a temporarily fixed shape showed a higher recovery ability using solvent than the stimuli of heat and UV-radiation. The effects of coupled stimuli on hair's shape fixation and recovery and on variations of the crystal, disulfide, and hydrogen bonds were studied systematically. A structural network model was thereafter proposed to interpret the multi-coupled stimuli sensitive SM of alpha-keratin hair. This original study is expected to provide inspiration for exploring other natural fibers to reveal related smart functions and for making more types of remarkable adapted synthetic materials.