Phase Separation in Binary Fluid Mixtures with Continuously Ramped Temperature

TL;DR

This paper investigates the complex phase separation behavior of binary fluid mixtures under gradually increasing temperature, highlighting the interplay of density-driven fluid motion and diffusive instabilities, supported by experimental observations.

Contribution

It introduces a simplified model assuming isothermal conditions to analyze competing nonlinear effects during temperature ramping in binary fluids.

Findings

Observation of oscillations in heat capacity and optical properties

Identification of conditions where nonlinear effects interact

Experimental evidence supporting the theoretical analysis

Abstract

We consider the demixing of a binary fluid mixture, under gravity, which is steadily driven into a two phase region by slowly ramping the temperature. We assume, as a first approximation, that the system remains spatially isothermal, and examine the interplay of two competing nonlinearities. One of these arises because the supersaturation is greatest far from the meniscus, creating inversion of the density which can lead to fluid motion; although isothermal, this is somewhat like the Benard problem (a single-phase fluid heated from below). The other is the intrinsic diffusive instability which results either in nucleation or in spinodal decomposition at large supersaturations. Experimental results on a simple binary mixture show interesting oscillations in heat capacity and optical properties for a wide range of ramp parameters. We argue that these oscillations arise under conditions where both nonlinearities are important.