Multi-wavelength actuation of dual-dye-doped liquid crystal network thin films: experiments and simulations

Photoabsorbers have been incorporated into inherently thermo-responsive liquid crystal polymers to impart photoresponsivity. We studied the effect of adding two azobenzene chromophores simultaneously into a liquid crystal polymer network (LCN) thin film through experiments and simulations. The chromophores are chosen such that one exhibits a photo-thermal effect, while the other exhibits both photo-thermal and photo-chemo-mechanical effects. The azobenzene dyes used are A3MA and DR1A with maximum absorbance at 365 nm and 483 nm, respectively. The photo-actuation experiments are performed at their respective absorption wavelengths, <i>i.e.</i>, 365 nm and 455 nm. In addition, an intermediate wavelength of 395 nm is employed to study the actuation. It is observed that the dual dye films exhibit comparable tip displacements with lower maximum surface temperatures in comparison to single dye films with equal dye mole fractions. A comprehensive finite element model for simulating the combined photo-chemo and photo-thermal responses of dual dye LCN films is implemented. The attenuation depths of the individual dyes from the dual-dye films are determined and used for calculating the through-thickness intensity variation and steady state <i>cis</i>-mass fraction for respective illumination wavelengths. The simulations demonstrate good quantitative correlation with experimental observations.