Spatially selective actuation of liquid-crystalline polymer films through two-photon absorption processes

Abstract

Soft materials that respond to external stimuli are promising candidates for next-generation actuators with human-friendly nature^1,2. Among various stimuli to induce strain, light offers spatial selectivity, which allows versatile motion of a continuous body. However, spatial selectivity of photoactuation has been limited in two dimension due to the predominant absorption of photons by chromophores near a light source in accordance with Beer-Lambert law. Here, we report the deformation of crosslinked liquid-crystalline polymer films triggered by two-photon absorption. The films containing azotolane moieties show photoinduced deformation upon irradiation with fs laser pulses through two-photon absorption. The direction of photoinduced bending is controlled by depth-selective excitation with a focused laser beam. Furthermore, the mode of deformation is transformed from bending to twisting by irradiating spots near an edge of the film. Inhomogeneous photoirradiation with high spatial selectivity allows an infinite variation of three-dimensional motions even apart from preprogrammed behavior, which would be advantageous especially in application to microactuators.

Spatial selectivity of photoactuation in soft material has been limited in two dimension and three-dimensionally selective actuation is an effective approach to control the direction and types of macroscopic motions. Here, the authors report the photoinduced deformation of liquid-crystalline polymer films with high spatial selectivity via a two-photon absorption process.