Fig. 4 | Nature Communications

Fig. 4

From: Mechanical adaptability of artificial muscles from nanoscale molecular action

Fig. 4

Influence of light intensity on the possibility to produce work and on the magnitude of the stiffness increase. a Actuation stress imposed by the photo-stiffening polymer (R = 4.7), for increasing intensities of light (λ = 365 nm): 1 (17 mW/cm2), 2 (38 mW/cm2), 3 (118 mW/cm2), 4 (307 mW/cm2), and 5 (381 mW/cm2). This curve does not relate to light-induced stiffness changes of the material, instead it is related to its light-induced shape changes, and because of these shape changes the material exerts a force on the cantilever, i.e., in other words this experiments shows the potential for this material to convert light into mechanical work. At low intensities, the response of the polymer, i.e., its tendency to change shape, is regulated by the molecular switch. At higher intensities (2–5), the temperature intervenes. b Infrared images of a photo-stiffening material under different intensities of light irradiation. c Stress exerted by photo-stiffening materials (red squares) and photo-softening materials (blue circles, R = 1) as a function of light intensity. Error bars correspond to standard deviation. d Tensile test on a photo-softening ribbon, reported for three different illumination conditions. Here, the tensile stress is the force causing the deformation of the material, and the strain is the response of the material by ways of elongation. In contrast to the experiment reported in Fig. 4a, here the response of the material relates to changes in the Young Modulus (i.e., tensile elasticity). e Tensile test on a photo-stiffening ribbon, for three different illumination conditions. Photo-stiffening occurs even under harsh illumination, in spite of the increase of temperature that competes with the stiffening

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