Surface orientational order at liquid-vapor interfaces induced by dipole-image-dipole interactions.
Highly dipolar molecules become orientationally ordered in the vicinity of a surface due to the electrostatic interaction with their image dipoles. We study this orientational order alpha(2) at the noncritical liquid-vapor interface of critical dipolar+nonpolar mixtures using ellipsometry. The dipolar molecules, which are strongly desorbed from the interface, possess an orientational order which is well described by alpha(2) approximately -t(2beta)D(+/-)(z/xi), where t=|T-T(c)|/T(c) is the reduced temperature relative to the critical temperature T(c), D(+/-) is a universal function of the distance z and the surface correlation length xi=xi(s)(o+)t(-nu), while beta=0.328 and nu=0.632 are standard critical exponents. The dipoles, which are preferentially oriented parallel to the surface, are repelled by their image dipoles, where xi(s)(o+)>xi(b)(o+) (the bulk correlation length amplitude).
Cho
Jae-Hie J
JH
Condensed Matter Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601, USA.
Law
Bruce M
BM