Dimensionality of hexatic melting in liquid crystals by in situ electron diffraction

Abstract

The theory of melting in two dimensions indicates that it is very different from the melting in three dimensions. An intermediate hexatic phase, with long range orientational but short range translational order, is proposed to exist between two dimensional solid and fluid phases. Because the long range order is limited experimentally by the domain or “grain” size, which is expected to be of sub-millimeter size, selected area electron diffraction is the method of choice for observing orientational order. Free-standing smectic liquid crystal films prove to be a most attractive system in which to verify this theory. However, multilayered liquid crystal samples are not strictly two dimensional systems because of interlayer interaction, their melting characteristics are expected to deviate from that of two dimensional systems. Furthermore, the outer layers may behave differently from the inner ones due to interfacial tension. We have applied low dose electron diffraction to study the effect of dimensionality, or number of layers, on the melting of multilayer organic liquid crystals.