Sign inversion of the spontaneous polarization in ferroelectric liquid crystals: a thickness dependence study in freely suspended films

¹ Fachbereich Physikalische Chemie, Philipps-Universität Marburg - D-35032 Marburg, Germany
² Iwan-N.-Stranski-Institut für Physikalische und Theoretische Chemie Technische Universität Berlin - D-10623 Berlin, Germany
³ School of Chemistry, The University, Hull HU6 7RX, UK

Received: 29 January 1996
Accepted: 15 April 1996

Abstract

A smectic ferroelectric liquid crystal, which is known to exhibit as a bulk sample at a certain temperature a spontaneous inversion of the direction of the spontaneous electric polarization with respect to the direction of the molecular tilt, is studied in freely suspended films with thicknesses between nearly one hundred and only three molecular layers. The spontaneous polarization inversion is observed in all films regardless of their thickness, and the inversion occurs simultaneously, at the same temperature, in all layers of a given film. The inversion temperature is found to decrease linearly with the reciprocal film thickness indicating the influence of the reduced dimensionality. Our results support the competing-conformers model rather than the dipolar-quadrupolar-coupling model.