Density and Phase State of a Confined Nonpolar Fluid (Editors' suggestion of a PRL paper with only one figure)

Density and Phase State of a Confined Nonpolar Fluid

Daniel F. Kienle and Tonya L. Kuhl

Department of Chemical Engineering and Materials Science, University of California Davis, Davis, California 95616, USA

Phys. Rev. Lett. 117, 036101 – Published 14 July 2016

Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.036101

Abstract

Measurements of the mean refractive index of a spherelike nonpolar fluid, octamethytetracylclosiloxane (OMCTS), confined between mica sheets, demonstrate direct and conclusive experimental evidence of the absence of a first-order liquid-to-solid phase transition in the fluid when confined, which has been suggested to occur from previous experimental and simulation results. The results also show that the density remains constant throughout confinement, and that the fluid is incompressible. This, along with the observation of very large increases (many orders of magnitude) in viscosity during confinement from the literature, demonstrate that the molecular motion is limited by the confining wall and not the molecular packing. In addition, the recently developed refractive index profile correction method, which enables the structural perturbation inherent at a solid-liquid interface and that of a liquid in confinement to be determined independently, was used to show that there was no measurable excess or depleted mass of OMCTS near the mica surface in bulk films or confined films of only two molecular layers.

Editors' suggestion

"Does it freeze or go glassy? Experiments show that a nonpolar fluid undergoes a glass transition, rather than a freezing transition, when it is confined in very thin channels."