Sigmoidal temporal increase in shear viscosity of titania–toluene–ethanol colloidal suspensions

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2023-10, Vol.675, p.132047, Article 132047
• Main Author: Yamamura, Masato
• Format: Article
• Language: English
• Subjects: Aggregation; Kinetic model; Nanoparticle suspension; Rheology; Wetting
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2023.132047

The shear viscosity of toluene-based TiO2 nanoparticle/poly(vinyl acetate) suspensions initially increased gradually, then increased steeply, and finally levelled off under shearing in the presence of ethanol as a polar additive. This non-linear response followed a sigmoidal function with a characteristic rate constant for a given composition. The rate constant reached a maximum at a critical ethanol concentration, resulting in maxima of the final viscosity and storage modulus that have not been previously reported for non-aqueous macroscopically miscible systems. This viscosity anomaly was attributed to the preferential adsorption of the polar solvent and the resulting alcohol-clustering-induced particle networking in the non-polar medium. The temporal variations in viscosity were reproduced using a proposed kinetic model that newly considered inter-particle bonding assisted by ethanol adsorption. These results elucidate the transient rheological responses of suspensions containing polar/non-polar solvents for coating applications. [Display omitted] •Rheological measurements revealed maxima in shear viscosity at a critical ethanol content, indicating a viscosity anomaly.•The viscosity exhibited a time-dependent increase that could be fitted well using sigmoid curves.•The temporal variations in viscosity were reproduced using a model assuming alcohol-clustering-induced particle networks.