Verification of universal surface scaling behavior in critical binary liquid mixtures with neutron and x-ray reflectometry

by Brown, Matthew D.

Abstract (Summary)
We have studied two critical binary liquid mixtures in the mixed phase regime with x-ray

and neutron reflectometry to verify universal critical scaling at a non-critical interface. We

compared our results with previous results obtained with ellipsometry.

At a solid-liquid or liquid-vapor interface of an AB binary liquid mixture the component

with the lower surface tension will dominate that interface. If the surface tension differential between the components of the mixture is large enough the composition of the

surface layer will loose its dependence on. This case is referred to as strong adsorption.

We study the case of strong adsorption for a binary liquid mixture at the critical composition

with respect to the demixing phase transition. Sufficiently close to the critical

temperature Tc the influence of bulk critical behavior is expected to dominate the way

the surface adsorption layer decays with depth z from the surface composition to the bulk

composition. The length scale of the decay profile is expected to be proportional to the composition

correlation length, and is expected to scale with a universal composition scaling


In a neutron reflectometry study of a critical mixture of D2O and 3-methylpyridine

against a quartz substrate we verify universal critical scaling using a scaling function previously

used to describe ellipsometry data. In an x-ray reflectometry study of the liquid-vapor

interface of a critical mixture of n-dodecane and 1,1,2,2 tetrabromoethane, which had previously

been studied with ellipsometry, we find that we are able to describe all data by

using the same scaling function provided that we account for non-critical, system dependent

surface structure as well. We are also able to simulate ellipsometry with our mathematical

profile model and compare the simulation to the previous ellipsometry data.

Bibliographical Information:


School:Kansas State University

School Location:USA - Kansas

Source Type:Master's Thesis

Keywords:reflectometry ellipsometry critical binary neutron scaling physics condensed matter 0611


Date of Publication:01/01/2007

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