Fig. 3
From: Mechanical adaptability of artificial muscles from nanoscale molecular action
Active modulation of stiffness in response to light. a Photo-tensile experiments on flat ribbons. The polymer is stretched parallel to the molecular alignment, as indicated by a black double-headed arrow. The stiffness of the material adapts to illumination. b Ex situ stress–strain curves for a R = 1 material, in room-light condition (black squares) and under irradiation (blue circles). We define R as the molar ratio between the free liquid crystal and the molecular photo-switch. c In situ stress–strain curve for material with R = 1. The film is initially strained in ambiant conditions (black squares) and then exposed to UV light (blue circles). When the light is switched on, the material requires time to adjust to the new illumination conditions, which is visible in in situ tensile measurements. d Contact angle of free liquid crystal on a fully polymerized, unswollen polymer network, before and after activation with UV light. The contact angle increases upon light activation. e Ex situ stress–strain curves for material with R = 9.6 in room-light condition (black squares) and under irradiation (red circles). f In situ stress–strain curves: the material is first strained (black squares) and then exposed to UV light (red circles). g Average Young modulus before (black squares) and after irradiation (red circles), for increasing proportions of free liquid crystal in the material. Error bars correspond to standard deviation. h Photo-induced variation of the Young modulus, for increasing proportions of free liquid crystal in the material. Error bars correspond to standard deviation
