ABSTRACT
A technique for measuring the difference between the splay and bend flexoelectric coefficients in a nematic liquid crystal is demonstrated. The method uses the flexoelectric-optic effect, but instead of a uniform lying helix structure, a TN cell geometry with an in-plane electric field is used. This has the advantage of avoiding difficulties associated with aligning the helix and can be used to measure achiral materials. The effects due to ionic screening are also taken into account.
ABSTRACT
The interaction between the antiferroelectric helix and an electric field applied perpendicular to its axis is investigated, both experimentally and theoretically. A two-stage switching process is observed: (i) in the pretransitional regime the helix distorts and then unwinds to form a nonhelical antiferroelectric state, with the plane of the molecules parallel to the applied field; (ii) at higher fields switching to the ferroelectric state occurs. The mechanism for unwinding is the interaction of the applied field with a polarization that is induced by a change to the anticlinic ordering.
