Effect of spherical geometry on the dynamics of the photostimulated nematic-isotropic transition

Abstract

A flow-focusing microfluidic system was used to create photoresponsive nematic liquid crystal (NLC) spherical droplets of uniform size in the micrometer range. Using transmitted intensity as a probe, we investigated the quantitative comparison of photoinduced phase transition activity and switching kinetics in flat geometry and spherical microdroplets under UV light irradiation (365 nm) at different intensities (7, 14, and 20 mW/cm2). Due to the trans-cis isomerization of photoresponsive molecules in flat and curved geometry, UV (7 mW/cm2) irradiation induced a 7 °C change in the N–I transition temperature. Furthermore, the observed shift ΔT in relation to incident UV intensity was qualitatively consistent with the molecular mean field model. The dynamic response time was calculated by specifying two response times for UV ON and OFF states in the N–I shift region at different temperatures. Given the nature of the thermal back relaxation mechanism, the second case can be divided into two processes: delay and off time. While τON for droplets is slightly lower than for flat samples, both are affected by UV irradiation intensity and temperature. τOFF, on the other hand, has a quicker response for droplets over the entire temperature range investigated. As a result, when compared to flat geometry samples, the results show a significant improvement in dynamic response times in the microdroplets, resulting in a significantly faster thermal back relaxation process has practical applications in optical devices.