Computer simulation of elongated bipolar nematic droplets - II. External field aligned normal to the droplet axis of symmetry

Numerical results from the modelling and computer simulation of the magneti c-induced director reorientation dynamics in elongated bipolar nematic drop lets are presented in this paper. The magnetic field is applied normally to the droplet axis-of-symmetry direction, which is one possible scenario fou nd in applications of polymer dispersed liquid crystal (PDLC) films. This c ase has not yet been studied numerically, and its understanding is far from complete. The model is composed of the Leslie-Ericksen and Frank continuum theories and is solved in two dimensions since bipolar nematic droplets ex hibit mirror symmetry in certain planes. The numerical results replicate fr equently reported experimental observations on the performance of PDLC film s. These observations include the ubiquitous exponential increase followed by saturation in light transmittance as the external applied field increase s, and the exponential increase (decrease) followed by saturation as time i ncreases in the on (off)-state. Furthermore, in contrast to current underst anding for both the on- and off-states, the model predicts that the directo rs in the centre (surface) region of the droplet exhibit a dead time (no de ad time) before reorientation. The numerical results presented in this pape r provide a better understanding of the director reorientation dynamics in elongated bipolar nematic droplets; this can be used to optimize the design and performance of devices using PDLC films.