Multiscale Modeling of the Effects of Salt and Perfume Raw Materials on the Rheological Properties of Commercial Threadlike Micellar Solutions

Abstract

We link micellar structures to their rheological properties for two surfactant body-wash formulations at various concentrations of salts and perfume raw materials (PRMs) using molecular simulations and micellar-scale modeling, as well as traditional surfactant packing arguments. The two body washes, namely, BW-1EO and BW-3EO, are composed of sodium lauryl ethylene glycol ether sulfate (SLEnS, where n is the average number of ethylene glycol repeat units), cocamidopropyl betaine (CAPB), ACCORD (which is a mixture of six PRMs), and NaCl salt. BW-3EO is an SLE3S-based body wash, whereas BW-1EO is an SLE1S-based body wash. Additional PRMs are also added into the body washes. The effects of temperature, salt, and added PRMs on micellar lengths, breakage times, end-cap free energies, and other properties are obtained from fits of the rheological data to predictions of the "Pointer Algorithm" [ Zou , W. ; Larson , R.G. J. Rheol. 2014 , 58 , 1 - 41 ], which is a simulation method based on the Cates model of micellar dynamics. Changes in these micellar properties are interpreted using the Israelachvili surfactant packing argument. From coarse-grained molecular simulations, we infer how salt modifies the micellar properties by changing the packing between the surfactant head groups, with the micellar radius remaining nearly constant. PRMs do so by partitioning to different locations within the micelles according to their octanol/water partition coefficient P and chemical structures, adjusting the packing of the head and/or tail groups, and by changing the micelle radius, in the case of a large hydrophobic PRM. We find that relatively hydrophilic PRMs with log P < 2 partition primarily to the head group region and shrink micellar length, decreasing viscosity substantially, whereas more hydrophobic PRMs, with log P between 2 and 4, mix with the hydrophobic surfactant tails within the micellar core and slightly enhance the viscosity and micelle length, which is consistent with the packing argument. Large and very hydrophobic PRMs, with log P > 4, are isolated deep inside the micelle, separating from the tails and swelling the radius of the micelle, leading to shorter micelles and much lower viscosities, leading eventually to swollen-droplet micelles.

Analytical modeling of micelle growth. 2. Molecular thermodynamics of mixed aggregates and scission energy in wormlike micelles

“…Upon variation of solution's composition, peaks in viscosity have been often observed [27][28][29][30][31], which can be explained with the synergistic growth of giant entangled wormlike micelles and their transformations into disklike or multiconnected (branched) aggregates [32][33][34][35][36][37]. The prediction and control of micelle growth and formulation's viscosity are issues of primary importance for various practical applications [38][39][40][41].…”

The Relationship between Wormlike Micelle Scission Free Energy and Micellar Composition: The Case of Sodium Lauryl Ether Sulfate and Cocamidopropyl Betaine

“…WLM form at lower salt concentrations. 50 To ensure the validity of our CAPB model, a simulated salt curve for SLES 1 EO:CAPB at 11wt%, ratio 9.85 to 1.15 wt%, was generated, as in the work of Tang et al 34 All simulations for the salt curve were performed in NVT ensemble using DL MESO mesoscale simulation package 51 and all the systems were simulated in a cubic box with volume of 64 × 10 3 DPD unit length. Slater-type charge smearing was applied to the systems, as in previous works.…”

Rheology of mixed solutions of sulfonated methyl esters and betaine in relation to the growth of giant micelles and shampoo applications

“…Along the abscissa, the total NaCl concentration is plotted, which includes both the added salt and the salt present as an admixture in the surfactants; see Section 2.1. Each experimental dependence has a typical shape of curve with maximum, called the salt curve [37][38][39][40][41][42]. In Fig.…”

“…Second, in systems containing ionic surfactants the dependence of viscosity on the concentration of added salt (the so called salt curve) often exhibits a high peak [28,[37][38][39][40][41][42][43]. In this case, the peak could be explained with a transition from wormlike micelles to branched micelles [44][45][46][47][48].…”