title: Nonlinear rheology of aqueous solutions of hydrophobically modified hydroxyethyl cellulose with nonionic surfactant.
abstract: Shear thickening and strain hardening behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) aqueous solutions was experimentally examined. We focused on the effects of polymer concentration, temperature, and addition of nonionic surfactant. It is found that HMHEC shows stronger shear thickening at intermediate shear rates in a certain concentration range. In this range, the zero-shear viscosity scales with polymer concentration as eta(0) approximately c(5.7), showing a stronger concentration dependence than for more concentrated solutions. The critical shear stress for complete disruption of the transient network follows tau(c) approximately c(1.62) in the concentrated regime. Dynamic tests of the transient network on addition of surfactants show that the enhanced zero-shear viscosity is due to an increase in network junction strength, rather than their number, which in fact decreases. The reduction in the junction number could partly explain the weak variation of strain hardening extent for low surfactant concentrations, because of longer and looser bridging chain segments, and hence lesser nonlinear chain stretching.
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117576, Republic of Singapore.
authors.forename: Guangqiang
authors.initials: G
authors.lastname: Zhao
authors.forename: Shing Bor
authors.initials: SB
authors.lastname: Chen
mesh_terms: D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D012212:Rheology; D012996:Solutions / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D013501:Surface-Active Agents; D014867:Water; D002482:Cellulose