Surfactant Rheology and Processing for Concentrated Formulations

Surfactants are the key cleaning agents in shampoos, detergents, and many household products. Conventional formulations contain large amounts of water, increasing packaging waste and transportation costs. The industry is therefore moving toward low-water, high-active products, which reduce environmental impact and enable new ingredients—but are much more challenging to process because they become highly viscous and sensitive to temperature, shear, and mixing conditions.

Prof. Erk’s group develops the structure–property–processing relationships needed to manufacture these concentrated surfactant feedstocks efficiently and reliably. Click here to watch Prof. Erk’s recent lecture in the JNNFM + JoR + RA 2024 seminar series.

In collaboration with engineers at The Procter & Gamble Company (P&G), we studied a model concentrated surfactant system containing 70% sodium laureth sulfate and 30% water, with and without industrial additives. The group developed a new dynamic-diffusive interfacial transport (D-DIT) instrument to rapidly map phase behavior and local water content across an entire isotherm in a single experiment.

Kelkar, Erk and Lindberg, “Dynamic diffusive interfacial transport (D-DIT): A novel quantitative swelling technique for developing binary phase diagrams of aqueous surfactant systems,” *Review of Scientific Instruments* 2024

Connecting Lab-Scale Rheophysical Measurements to the Industrial Scale

Lab-scale measurements at Purdue—using rheometry and custom velocimetry—were validated at P&G using an MRI-instrumented pilot-scale pipe loop, bridging the gap between fundamental characterization and industrial processing. These studies provide a robust experimental foundation for future predictive models of concentrated surfactant flow and phase behavior. Key outcomes include the following:

Phase behavior & kinetics: D-DIT enabled fast, time-resolved mapping of phase evolution (RSI 2024). Confined environments showed phase transitions that differed from bulk behavior, including shifts in the micellar-to-hexagonal transition concentration. The method was also applied to track droplet dissolution and polymer film drying (Langmuir 2025)

Processing challenges & formulation strategies: Low temperatures produced shear-induced crystallization and peaks in complex viscosity (Soft Matter 2024). Three classes of additives improved processability (Soft Matter 2025). (1) Linear-chain alcohols dehydrated headgroups and shifted lamellar systems toward micellar phases. (2) Short-chain polyols promoted higher-viscosity hexagonal/mixed phases at low temperature but thinned upon heating. (3) Within lamellar phases, salt promoted shear-induced crystallization, while propylene glycol suppressed crystallization and enhanced wall slip.

Multiscale flow measurements: Bench rheometry and ultrasound velocimetry (USV) were compared to pressure-based viscosity estimates and 2D MRI velocity profiles. Viscosity correlations were robust above shear rates of 1 s⁻¹. MRI captured bulk flow, while USV resolved near-wall behavior (Rheo Acta 2019). Alcohols produced simple-shear profiles; propylene glycol increased wall slip—both reducing pressure drop and enabling higher flow rates.

This research advances the efficient processing of concentrated, sustainable surfactant formulations, providing new tools, validated workflows, and mechanistic insights that support the development of next-generation consumer cleaning products. Currently, we are studying the formation and evolution of defect structures in confined surfactant bilayers.