Surface electroclinic effect near the first-order smectic-A*–smectic-C*transition

Abstract

We analyze the surface electroclinic effect (SECE) in a material that exhibits a first order bulk smectic-A * (Sm-A * ) -smectic-C * (Sm-C * ) transition. The effect of a continuously varying degree of enantiomeric excess on the SECE is also investigated. We show that due to the first order nature of the bulk Sm-A * -Sm-C * transition, the SECE can be unusually strong and that as enantiomeric excess is varied, a jump in surface induced tilt is expected. A theoretical state map, in enantiomeric excess -temperature space, features a critical point which terminates a line of first order discontinuities in the surface induced tilt. This critical point is analogous to that found for the phase diagram (in electric field -temperature space) for the bulk electroclinic effect. Analysis of the decay of the surface induced tilt, as one moves from surface into bulk shows that for sufficiently high surface tilt the decay will exhibit a well defined spatial kink within which it becomes especially rapid. We also propose that the SECE is additionally enhanced by the de Vries nature (i.e. small layer shrinkage at the bulk Sm-A * -Sm-C * transition) of the material. As such the SECE provides a new means to characterize the de Vries nature of a material. We discuss the implications for using these materials in device applications and propose ways to investigate the predicted features experimentally.

Modeling the field control of the surface electroclinic effect near continuous and first-order smectic-A*to smectic-C*transitions

“…However, despite the discontinuity between surface and bulk tilt, the tilt profile θ(x) can be shown to be continuous. Thus, as in the zero field case [14], θ(x) and α(x) may each display a kink, but not a discontinuity. We still expect the onset of buckling to occur for fields beyond which the surface tilt is reversed, i.e., for fields smaller than −|E 0 | It should be pointed out that the above analysis only considers the effect of the tilt on layer spacing (and thus strain) but not vice versa.…”

“…Recently, we developed a generalized model, which can be used to analyze the SECE near both continuous and first order Sm-A * -Sm-C * transitions [14]. This was motivated in part by the increasing number of compounds exhibiting a first order transition and also by the dramatic nature of the BECE near such a transition.…”