Concentration, salt and temperature dependence of strain hardening of step shear in CTAB/NaSal surfactant solutions

Abstract

By measuring stress relaxation following a step strain, we find that strain hardening is prevalent over a temperature range of 15–25 °C for a solution of cetyl trimethylammonium bromide (CTAB) with the added hydrotrope sodium salicylate (NaSal) at hydrotrope-to-surfactant concentration ratios (CS/CD) between 0.5 and 3.0. The extent of strain hardening upon nonlinear deformation varies nonmonotonically as a function of salt-to-surfactant ratio for different temperatures. As the strain amplitude is progressively increased, a transition from strain hardening to softening or linear response is observed at strains that are dependent on temperature and concentration. Strain hardening was also found in CTAB when using sodium 3-Hydroxy-2-naphthoate as a hydrotrope with CTAB, but solutions of anionic sodium lauryl sulfate surfactants in salt with no hydrotrope showed no strain hardening, indicating that the hydrotrope is critical to obtaining strain hardening in step strains. The results indicate a stress relaxation mechanism that is more complex than that of simple disentanglement and micelle breakage and rejoining, possibly involving strain-induced associations between micelles facilitated by hydrotropes that may act as linkers.

Ternary diffusion in aqueous sodium salicylate + sodium dodecyl sulfate solutions

“…The interaction between NaSal and surfactants leads to a change in micellization properties of the latter [14,15]. This can be justified by the occurrence of the screening effect due to an increase in the ionic strength -the salicylate anion decreases the electrostatic repulsion between surfactant's head-groups-favoring the micelle formation and forming mixed micelles, once the aromatic ring interacts with the hydrophobic tails of surfactants [16][17]. This also induces the occurrence of wormlike micelles.…”

Flow of gluten with tunable protein composition: From stress undershoot to stress overshoot and strain hardening

“…3e). The hardening is understood as the ability of the flow to induce a nonlinear stretching of the stress bearing chains due to the finite extensibility of the network strand [60][61][62] . The large value of the deformation at which strainhardening is measured (around 10) is consistent with a loosely connected polymer-like gel sample.…”

Higher Salt Hydrophobicity Lengthens Ionic Wormlike Micelles and Stabilizes Them upon Heating

“…The impact of temperature on the features of WLM solutions was studied by several authors. ,,− One example is adding methyl salicylic acid to CTAB solutions at concentrations slightly larger than the equimolar one. This system forms unilamellar vesicles, which transform into WLMs above a critical temperature, switching from a Newtonian fluid to a viscoelastic shear-thinning behavior .…”