Rheology and Nanostructure of Shear-banding Tallowtrimonium Chloride Wormlike Micelles by Constitutive Modelling and Rheo-optical Characterization
Date
2017-05
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Publisher
The Ohio State University
Abstract
With appropriate counterion and concentrations, surfactant molecules in aqueous solution form wormlike micelle structure that entangles and undergoes reversible breakage, resulting in viscoelastic behavior. In this study, micellar solutions of tallowalkyltrimethyl ammonium chloride (TTAC) and sodium salicylate are investigated by rheology and rheo-optical characterizations. The shear rheology of model solutions can be captured by Giesekus-diffusion model, which provides a criterion to quantify the extent of shear-banding. It is shown that G-D model gives reasonable agreement with experimental data except at very high shear rates where viscous/solvent effect becomes pronounced. To account for this solvent effect, modification to the G-D model is suggested. In addition, model solutions exhibit non-Maxwellian pattern with varying degree specific to time scales of elasticity and relaxation. Deviation from Maxwellian behavior is quantified by a Cole-Cole representation and a viscosity-Weissenberg profile in reference to a constructed Maxwell curve. It is shown that a micellar solution at 0.04M TTAC/0.04M NaSal can be well approximated by a Maxwell fluid, and fitting of Maxwell model to SAOS and G-D model to stress-rate curve gives reasonable agreement. Flow birefringence experiments are conducted to characterize solutions’ structural properties. Using stress-optic rules, structural parameters such as persistence length can be estimated structural modeling. The relationship between the nanostructure and micellar fluid’s rheology and optical behaviors is also discussed.
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Keywords
Rheology, micelle, nano, rheo-optic, wormlike, Giesekus, Maxwell, persistence length, Tallow