Shear-thickening in aqueous surfactant-associative thickener mixtures

• Published in: Journal of Coatings Technology and Research 2011-05, Vol.8 (3), p.299-309
• Main Authors: Manion, Sean J., Johnson, Laura L., Fernando, Raymond H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemistry and Materials Science; Coatings; Coatings industry; Coatings. Paints, varnishes and inks; Components, formulation; Corrosion and Coatings; Exact sciences and technology; Industrial Chemistry/Chemical Engineering; Materials Science; Polymer industry, paints, wood; Polymer Sciences; Surface active agents; Surfaces and Interfaces; Thin Films; Tribology
• ISSN: 1547-0091; 1945-9645; 1935-3804
• DOI: 10.1007/s11998-011-9320-7

Associative thickeners represent an important class of rheology modifiers used in waterborne coatings. Understanding molecular level interactions between associative thickeners and surfactants has been the subject of a number of prior studies. Our recent studies focused on the behavior of a hydrophobically modified, aminoplast ether (HEAT) associative thickener and a highly hydrophobic ethoxylated octylphenol surfactant in aqueous solution. Aqueous blends of these two materials exhibit shear-thinning, as well as rarely reported, transient, shear-induced thickening behavior. In addition, the same compositions exhibit both thixotropy and antithixotropy. The shear-induced thickening is shown to be the result of transient aggregated structures formed under shear. Addition of a third component, β-cyclodextrin—a molecule known to disrupt hydrophobic associations—to the mixture helped us advance the understanding of the nature of associative thickener–surfactant interactions that cause the transient shear-thickening behavior. Results indicate that, while overall viscosity of the HEAT/surfactant mixtures is decreased by β-cyclodextrin, the shear-induced thickening is unaffected. An intermolecular interaction model to describe the transient thickening mechanism is presented.