Critical point and effective field of binary ferroelectric smectic materials at freely suspended film

Ferroelectric smectic material C7 showing the first order transition exhibits the critical point in an electric field. The critical point of the binary mixture of C7 and 10.O.4, showing the second order transition, shifts depending on concentration of 10.O.4, and disappears at certain critical concentration, i.e., the transition changes to the second order. A freely suspended film of the mixture without the field is studied, and it is found that non-uniformity due to surface layers works as the external field in the bulk. By introducing a concept of an effective field to describe the non-uniformity of the system, similarity between effects due to the surface layers in the film and those due to the field in the bulk is proved at the concentration dependence of the critical point.