Slowing Down of the Mutual Diffusion Process Approaching the Liquid/Liquid Coexistence Curve of a Nonionic Surfactant/Deuterium Oxide System:  Study of the System C₁₂E₅/D₂O

Abstract

In the "large aggregates" region of the phase diagram of the system C 12 E 5 /D 2 O the mutual diffusion coefficient of mixtures with critical and noncritical composition is determined by dynamic light scattering (compositions: 0.23 × 10 -2 e y e 10.01 × 10 -2 ; y c ) 1.08 × 10 -2 ; y, mass fraction of C 12 E 5 ). In all experiments the diffusion coefficient decreases with increasing temperatures, approaching the liquid/liquid coexistence curve at fixed values of y. This is a system independent property observed in "simple" as well as in "complex" binary mixtures with a miscibility gap. The change of size and shape of C 12 E 5 micelles with composition and temperature in aqueous solutions reported for the "large aggregates" region appears to be the result of concentration fluctuations existing in a wide temperature and composition region below the binodal curve. Approaching T p (T c ) the diffusive property of the mixtures is dominated by the dynamics of concentration fluctuations.

Study of the Viscosity of Nonionic Surfactant/Deuterium Oxide Mixtures and of the Self-Diffusion Coefficient of the Surfactant Approaching the Liquid/Liquid Coexistence Curve

“…C 12 E 5 was purchased from Nikko Chemical Co. (Japan). It was the same material as used recently. , Details of the preparation of the C 12 E 5 /D 2 O mixtures and the handling of the mixtures are given in ref .…”

“…The mutual diffusion coefficient decreased with increasing temperatures approaching the binodal curve. This information was obtained from static and dynamic light scattering experiments as well as from small angle neutron scattering experiments. − …”

“…This information was obtained from static and dynamic light scattering experiments as well as from small angle neutron scattering experiments. [1][2][3] The term "complex" draws attention to the fact that the system has a more complicated phase diagram than "simple" binary mixtures with a miscibility gap (e.g., methanol/cyclohexane). 4 The critical micelle concentration (cmc) of C 12 E 5 in water is considerably smaller than the critical concentration (y cmc ≈ 10 -5 ).…”

Pressure Dependence of the Critical Micelle Concentration of a Nonionic Surfactant in Water Studied by 1H-NMR

“…Nonionic surfactants of the type C i E j ( n -alkyl polyoxyethylene ether) form a variety of microstructures in water, ranging from simple micelles at low surfactant concentrations to complex mesophases, such as hexagonal and lamellar phases, at high concentrations. , Two key features of the temperature−composition phase diagram at low surfactant concentrations are the critical micelle concentration (cmc), above which surfactant molecules self-assemble into micelles, and an upper miscibility gap indicating the coexistence of two micellar phases at temperatures above a concentration-dependent cloud-point temperature. This two-phase region influences microstructure in that concentration fluctuations occurring in the one-phase region close to the cloud point promote the mobility of surfactant molecules and their exchange between micelles. − …”

“…This two-phase region influences microstructure in that concentration fluctuations occurring in the one-phase region close to the cloud point promote the mobility of surfactant molecules and their exchange between micelles. [3][4][5][6] The cmc, its temperature dependence, and the upper miscibility gap have been determined for many C i E j /water mixtures at ambient pressure. However, much less is known about the effect of pressure on the cmc or the coexistence region for nonionic surfactant solutions.…”