Measurement of coherence-length anisotropy in the isotropic phase of nematics

A phase-sensitive, differential, light-scattering method is used to measure the shape of correlated regions in the isotropic phase of nematics. In MBBA (p-methoxybenzylidene p-n-butylaniline) these regions are elongated along the molecular-axis direction and the critical behavior is close to that predicted by mean-field theory; de Gennes's parameter L2A is positive. In the isotropic phase of the smectic OBBA (p-octoxybenzylidene p-n-butylaniline) the correlated regions are flat and cannot be described by a constant L2. © 1975 The American Physical Society.