title: Dipole orientational order at the critical interface.
abstract: We present experimental evidence that dipoles exhibit orientational order at the critical interface of mixtures of polar plus nonpolar liquids using the technique of ellipsometry. In this technique the ellipticity rho; at the critical interface for all nonpolar or weakly polar fluids or fluid mixtures diverges as t(beta-nu) where t=(Tc-T)/Tc is the reduced temperature relative to the critical temperature Tc and beta=0.328, nu=0.632 are critical exponents. For polar fluids, however, the dipole-image dipole interaction at the interface can cause long-range orientational order resulting in deviations from this power-law divergence. Theoretical results predict that the surface orientational order parameter alpha2(z) approximately m(*4)[d2v(z)/dz2], where m(*) is the reduced dipole moment and v(z) is the local composition at position z within the interface. We find quantitative agreement with these predictions for two different critical binary liquid mixtures composed of a highly polar plus nonpolar component.
authors: Condensed Matter Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601, USA.
authors: A
authors: A
authors: Mukhopadhyay
authors: B M
authors: BM
authors: Law