Abstract
The mechanical motion of materials has been increasingly explored in terms of bending and expansion/contraction. However, the locomotion of materials has been limited. Here, we report walking and rolling locomotion of chiral azobenzene crystals, induced thermally by a reversible single-crystal-to-single-crystal phase transition. Long plate-like crystals with thickness gradient in the longitudinal direction walk slowly, like an inchworm, by repeated bending and straightening under heating and cooling cycles near the transition temperature. Furthermore, thinner, longer plate-like crystals with width gradient roll much faster by tilted bending and then flipping under only one process of heating or cooling. The length of the crystal is shortened above the transition temperature, which induces bending due to the temperature gradient to the thickness direction. The bending motion is necessarily converted to the walking and rolling locomotion due to the unsymmetrical shape of the crystal. This finding of the crystal locomotion can lead to a field of crystal robotics.
Highlights
The mechanical motion of materials has been increasingly explored in terms of bending and expansion/contraction
We have recently reported that the chiral azobenzene derivative N-[[4-p-dimethylaminophenylazo]benzoyl]-1-phenylethylamine [trans-(S)-1] shown in Fig. 1 is crystallized to form two polymorphs—an α phase and a β phase—and thin, plate-like crystals of the β phase bend with twisting under ultraviolet (UV) light irradiation[15]
This walking and rolling crystal can be a beginning to the research and development of crystal robotics
Summary
The mechanical motion of materials has been increasingly explored in terms of bending and expansion/contraction. Long plate-like crystals with thickness gradient in the longitudinal direction walk slowly, like an inchworm, by repeated bending and straightening under heating and cooling cycles near the transition temperature. The bending motion is necessarily converted to the walking and rolling locomotion due to the unsymmetrical shape of the crystal This finding of the crystal locomotion can lead to a field of crystal robotics. Materials that can respond to external stimuli, such as light, heat, electricity, humidity, pH, and concentration gradients, have attracted much attention in chemistry, materials science, and engineering fields Such materials are important for future applications in sensors, switches, actuators, artificial muscles, and soft robots. The driving force of the both directional locomotion is generated from the unsymmetrical shape of the crystal This walking and rolling crystal can be a beginning to the research and development of crystal robotics
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