Effects of additives on the rheology and phase behavior of lamellar-structured concentrated surfactant solutions.
basic_science · Level V
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- Record sourced from PubMed, PMID 40785543.
- Also identified by DOI 10.1039/d5sm00597c.
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Abstract
Structure-property-processing relationships for model lamellar structured 70 wt% SLE<sub><i>n</i></sub>S solutions were developed with a combination of rheometry, cross-polarized optical microscopy, calorimetry, small angle X-ray scattering, and rheo-ultrasonic speckle velocimetry. Additives were utilized to maintain high surfactant activity, reduce bulk viscosity and simplify processing. While the bulk flow behavior of neat SLE<sub><i>n</i></sub>S solutions was similar, the effect of some additives was sensitive to the degree of ethoxylation. Linear-chain alcohols (C<sub>2</sub>-C<sub>5</sub>) partitioned into inter-bilayer water layers, dehydrating surfactant headgroups and inducing lamellar-to-micellar transitions. Short-chain polyols formed higher-viscosity hexagonal and mixed phases at room temperature through hydrogen bonding with surfactant headgroups. Heating beyond the upper temperature limit weakened these interactions, resulting in low-viscosity solutions. Within the lamellar phase, common salt promoted shear-induced crystallization above the equilibrium temperature range. Propylene glycol suppressed shear-induced crystallization and promoted wall-slip under shear, forming lubrication layers near the wall. These strategies offer practical levers to tune rheology and microstructure of concentrated surfactant systems, with the datasets developed providing a foundation for future modeling. Outcomes from this study inform the sustainable design and efficient processing of concentrated surfactant-based products.