Light-induced crawling of crystals on a glass surface

Abstract

Motion is an essential process for many living organisms and for artificial robots and machines. To date, creating self-propelled motion in nano-to-macroscopic-sized objects has been a challenging issue for scientists. Herein, we report the directional and continuous motion of crystals on a glass surface when irradiated simultaneously with two different wavelengths, using simple azobenzenes as a photoresponsive organic compound. The direction of the motion can be controlled by the position of the light sources, and the crystals can even climb vertical surfaces. The motion is driven by crystallization and melting at the front and rear edges of the crystal, respectively, via photochemical conversion between the crystal and liquid phases induced by the trans–cis isomerization of azobenzenes. This finding could lead to remote-controlled micrometre-sized vehicles and valves on solid substrates.

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

“…Clearly, for every energy distribution, there always exists a wavelength with a comparatively large response in which the dynamic effect can be exploited: choosing near-UV light, emitting at the largest intensity, and letting the other wavelength be close to the effective cis absorbance range, which leads to a relatively high cis conversion and simultaneously a large, effective trans-cis-trans cycling rate. This result quantitatively matches the light-induced motion of azobenzene crystal plates [28], in which a mixed 200 mW=cm 2 365 nm and 60 mW=cm 2 465 nm exposure yields the most favorable deformation. The above single-and double-wavelength approaches can be extended to multiple sources, such as LC actuators containing azo derivatives exposed to light sources emitting multiple wavelength peaks, like mercury light [29,30] and actinic light [9,31,32].…”

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

“…Instead of uniformly illuminating a complex, carefullyengineered device 13 or focusing the light onto a single spot [37][38][39] , our approach is to use structured dynamic light fields to excite sophisticated intra-body deformations within LCE microrobots with very simple and agnostic designs. In this scheme the microrobot is regarded as a continuously addressable body that acts as an extended array of many infinitesimally small actuators, each of which can be independently triggered by the local light field.…”

Photomotility of polymers

“…Photomechanical effects in crystalline materials have also been subject to recent research, including demonstrations of bending, jumping and twisting56. Photomechanical effects in polymers and crystalline materials have been subject to a number of recent reviews7891011.…”