Dynamics of a liquid crystal molecule at a solid-liquid interface detected by the time-resolved transient grating method

Dynamics of MBBA (N-(4-methoxybenzylidene)-4-n-butylaniline) in ethanol at a liquid-solid interface is selectively detected using the transient grating method with total internal reflection for probe light. The thermal grating signal decays much faster than that in bulk liquid. This faster decay is explained by the thermal conduction from the liquid to solid phase. Species grating signal from the interface also decays faster than that from the bulk liquid. The fringe length dependence of the rate constant reveals that the diffusion constant at the interface region (49 nm) is similar to that in the bulk liquid. The faster decay of the species grating is mainly attributed to the enhanced cis-trans back isomerization of MBBA at the interface.