Surfactant-mediated gelation of hydrophobically modified hydroxyethyl cellulose: effects of polymer and surfactant structure

Abstract

We have investigated the effects of polymer structure, surfactant structure, and system composition on the phase behavior of a nonionic hydrophobically modified cellulose ether (HMHEC) and the rheological properties of selected hydrogels. Specific conditions under which strong hydrogels phase separate out of these systems have been identified. Gel formation is favored when the side chain level on the polymer is ∼210 side chains/backbone. In general, gel strength increases with increasing polymer molecular weight but does not scale with side chain content on the polymer. A mechanism for this is proposed. Stronger gels formed in sodium dodecyl sulfate (SDS) than in sodium octyl sulfate (SOS) or sodium octyl sulfonate (SS), suggesting that the surface activity of a surfactant, which is proportional to the length of its tail group and inversely proportional to its critical micelle concentration (cmc), governs the extent of surfactant binding to the polymer as well as the extent of polymer/polymer hydrophobic association.