Effect of a strong electric field on the reentrant nematic to smectic A_d phase transition

Abstract

We report experimental studies on the effect of a strong electric field on the nematic-smectic A_d (N-A_d ) and A -reentrant nematic (A_d -N_R ) phase transitions in a binary mixture. Both the transition temperatures increase with field. The A -N transition point changes much more rapidly than that of A_d -N transition, indicating that the A_d phase will get bounded at a sufficiently high field. We have included the effect of the electric field in our molecular model of reentrant phases in highly polar compounds, in which the mutual orientation of near neighbour molecules changes from an antiparallel to a parallel configuration as the temperature is lowered. It is argued that the cross-over temperature increases with field which accounts for the observed trends. For suitable parameters, it is also predicted that either a nematic-nematic transition line can branch off from the A_d -N_R line or a smectic A-smectic A transition line can meet the A_d -N_R line at an appropriate field. In the latter case, the A_d -N_R line has an associated slope change which is consistent with the experimental data.