Turbidimetric evaluation of the solubilization rate: dissolution of dodecane nanodrops in 7.5 mM sodium dodecylsulfate solutions at selected sodium chloride concentrations

TL;DR

This study investigates how salt concentration affects the rate of dodecane nanodrop dissolution in SDS solutions using turbidimetric measurements, revealing salt-dependent variations in solubilization rates.

Contribution

It introduces a turbidimetric method to evaluate nanodrop solubilization rates across different salt concentrations, highlighting the impact of salinity on micelle-mediated dissolution.

Findings

Solubilization rate decreases with increasing salt concentration.

Salt promotes micelle aggregation and precipitation at higher concentrations.

Dissolution rate is halved in saline compared to pure water.

Abstract

The rate of micelle solubilization (SR) can be appraised following the decrease of the radius of a macroscopic drop of oil in contact with a surfactant solution [Todorov, 2002]. Alternatively, the time required for the dissolution of a liquid dispersion can be used for this purpose. Here, the decrease of the turbidity of a dodecane-in-water (d/w) nanoemulsion in 7.5 mM sodium dodecylsulfate (SDS) is studied at sodium chloride concentrations of 100, 300, 500, 700, 900, and 1000 mM NaCl. These salinities correspond to non-aggregating (< 300), aggregation-promoted (500) and surfactant precipitation regimes (> 700). It is found that SR is equal to 2.3 x 10^-11, half the value observed in the absence of salt for a neat aqueous surfactant solution above its critical micelle concentration (7.0 < cmc < 8.7 mM SDS [Deodhar, 2020]).