Abstract
Like the water responsive shape memory (SM) effect of β-keratin bird feathers, α-keratin hairs either existing broadly in nature are found responsive to many types of coupled stimuli in SM behaviors. In this article, α-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 α-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 α-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.
Highlights
A shape memory polymer (SMP) is a material that ‘remembers’ its original shape and that enables the deformed shape to return to its pre-deformed state when stimulated
Most SMPs [6,7,8,9,10] are single stimulus responsive to hybrid or co-block synthetic polymers; for example, moisture-sensitive SMPs that are hybridized with chitosan, cupric sulphate pentahydrate, or poly(vinyl alcohol), respectively, that contain a large amount of hydroxyl groups or co-block synthesizing polyhedral oligomeric silsesquioxane molecules and poly(ethylene glycol), for hard and soft segments separately
Figure demonstrates the results of three of coupled stimuli acting on the shape fixation fixation was applied, all goat hairs showed a curly or spiral shape that was maintained from their and recovery behaviors of a single goat hair fiber
Summary
A shape memory polymer (SMP) is a material that ‘remembers’ its original shape and that enables the deformed shape to return to its pre-deformed state when stimulated. The shape memory effect (SME) of each SMP is disclosed due to the related lock/unlock effect by external stimulus on the reversible switch of polymeric material, varying the flexibility of some parts of the macromolecule chains during shape fixation and recovery [11,12]. In this respect, the reversible switch and invariable structural ingredient sound compulsory in SMP compounds
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