Rheology and Pinching Dynamics of Associative Polysaccharide Solutions

Associative polysaccharides, decorated by multiple but short, side-chain hydrophobic stickers (typically 6–20 carbon long) that associate in solution, are used as thickeners for an extensive range of aqueous-based formulations. Characterizing and elucidating the influence of stickers on the response to extensional flows that spontaneously arise in pinching necks formed during spraying, jetting, or coating fluids have remained longstanding experimental and analytical challenges due to relatively low viscosity and elasticity of industrially relevant systems. In this contribution, we contrast the shear rheology as well as extensional rheology and pinching dynamics of hydrophobically modified hydroxyethyl cellulose (hmHEC, Mw = 300 kg/mol) as a sticky polymer with the bare chain of a higher molecular weight (hydroxyethyl cellulose (HEC), Mw = 720 kg/mol) using the recently developed dripping-onto-substrate (DoS) rheometry protocols. We show that sticker associations enhance zero shear viscosity and relaxation time (elasticity), and both quantities display stronger concentration-dependent variation for sticky polymers. Striking differences are observed in neck shapes, radius evolution profiles, and extensional viscosity plotted as a function of strain as well as strain rate. We present a comprehensive analysis of changes in pinching dynamics, concentration-dependent variation in steady, terminal viscosity as well as filament lifespan as a function of the sticky polymer concentration and describe the influence of multiple stickers on the macromolecular strain, relaxation, and dynamics of associative polysaccharides.