The mech. 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 temp. 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 temp., which induces bending due to the temp. gradient to the thickness direction. The bending motion is necessarily converted to the walking and rolling locomotion due to the unsym. shape of the crystal. This finding of the crystal locomotion can lead to a field of crystal robotics. [on SciFinder(R)]
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