Eur. Phys. J. E (2015) 38: 17
https://doi.org/10.1140/epje/i2015-15017-4

Regular Article

Direct imaging of long-range concentration fluctuations in a ternary mixture

Direct imaging of ternary mixtures

¹ Department of Physics and Astronomy, College of Charleston, 29424, Charleston, SC, USA
² Department of Physics, University of New Orleans, 70148, New Orleans, LA, USA
³ CNRS, ICMCB, ESEME, UPR 9048, F-33600, Pessac, France
⁶ Univ. Bordeaux, ICMCB, UPR 9048, F-33600, Pessac, France
⁴ Service des Basses Températures, UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble, France
⁵ Physique et Mécanique des Milieux Hétérogènes, UMR 7636 CNRS - ESPCI - Université Pierre et Marie Curie - Université Paris Diderot, 10 rue Vauquelin, 75005, Paris, France

^* e-mail: oprisana@cofc.edu

Received: 3 July 2014
Revised: 10 November 2014
Accepted: 4 February 2015
Published online: 20 March 2015

Abstract

We used a direct imaging technique to investigate concentration fluctuations enhanced by thermal fluctuations in a ternary mixture of methanol (Me), cyclohexane (C), and partially deuterated cyclohexane (C*) within 1mK above its consolute critical point. The experimental setup used a low-coherence white-light source and a red filter to visualize fluctuation images. The red-filtered images were analyzed off-line using a differential dynamic microscopy algorithm that allowed us to determine the correlation time, τ, of concentration fluctuations. From τ, we determined the mutual mass diffusion coefficient, D, very near and above the critical point of Me-CC* mixtures. We also numerically estimated both the background and critical contributions to D and compared the results against our experimental values determined from τ. We found that the experimental value of D is close to the prediction based on Stokes-Einstein diffusion law with Kawasaki’s correction.