Photomechanical

Photomechanical refers to processes and materials in which light induces mechanical motion, deformation, or stress. The term covers mechanisms that convert optical energy into mechanical work, typically via photochemical or photothermal effects.

Photochemical photomechanical responses arise from light-induced chemical changes in molecular building blocks embedded in a solid matrix. For example, azobenzene groups undergo reversible trans-cis isomerization under specific wavelengths, causing molecular shape changes that propagate to macroscopic bending or twisting in polymer films.

Photothermal mechanisms rely on light-absorbing components that convert photons into heat, creating temperature gradients that drive expansion, contraction, or bending, often in bilayer or composite structures where differential thermal expansion yields motion.

Materials that demonstrate photomechanical actuation include azobenzene-containing polymers, spiropyrans and diarylethenes, photo-crosslinkable networks, and liquid crystal elastomers augmented with light-absorbers. Actuators commonly take the form of thin films, cantilever-like beams, fibers, or microstructures that bend, curl, twist, or contract in response to illumination.

Applications span soft robotics, adaptive optics, microfluidics, and haptics, where remote, wireless light control can operate small, low-power devices. Photomechanical systems aim for fast response, high efficiency, and good fatigue resistance, but challenges remain in cycle stability, photodegradation, and spectral selectivity.

See also: photomechanics, optical actuation, light-responsive polymers.