Nanowerk July 30, 2021
Only very thin crystals (up to 20 microns) can show appreciable mechanical response. Researchers in Japan accidentally discovered that the photothermal effect causes a crystal to bend fast. To create a new, faster bending crystal and clarify the underlying mechanism, they exposed a thin salicylideneaniline derivative crystal to UV light and obtained substantial bending within approximately 1 second. However, the bend angle dropped rapidly with increasing crystal thickness, revealing that the bending was caused by photoisomerization. When they illuminated a thick (>40 microns) crystal with UV light, they observed an extremely rapid bending within several milliseconds, a distinct signature of the photothermal effect. By using a pulsed UV laser light, they could make the crystals bend at a frequency of 500 Hz (cycles/second). By calculating the temperature gradient numerically, they simulated the bending motion to validate the proposed mechanism. As the photothermal effect occurs in almost all crystals that absorb light, any light may move any crystal at high speeds. The phenomenon can be used to create light-driven actuators and novel soft robotic structures that ensure safe human-robot interaction…read more. TECHNICAL ARTICLEÂ