title: Molecular mixture as an effective single-component system.
abstract: Colloidal systems exhibit a dramatic slowdown in particle dynamics at high concentrations. The study of the concentration-induced glass transition in these systems has been greatly simplified by treating the colloidal phase as an effective single component in a viscous continuum. We seek to apply an effective single-component approach to molecular systems by investigating a material that also exhibits a dramatic slowdown as the relative concentration of two components change. Our system is a binary mixture of ethanol and citric acid, in which the size ratio of the particles is 0.7. We measure the temperature and concentration dependence of the self-diffusivity of both components using pulse-gradient NMR. We model our data with an elementary free volume model and show that the self-diffusivity of both components depends on the properties of an effective single component. The particle size of the effective single component is the number-averaged size of the two components. Our results demonstrate that mixtures can be used to study the effect of particle size on glassy dynamics and are therefore useful for understanding systems that are intermediate between molecular and colloidal.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 114 Roger Adams Laboratory, 600 South Mathews Avenue, Urbana, Illinois 61801, USA. larsen@illinois.edu
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Larsen
authors.forename: Charles F
authors.initials: CF
authors.lastname: Zukoski