Shear and elongational flow behavior of acrylic thickener solutions

Abstract

We investigate the effect of hydrophobic ag- gregation in alkali-swellable acrylic thickener solutions on shear and extensional flow properties at technically relevant polymer concentrations using the commer- cial thickener Sterocoll FD as model system. Appar- ent molecular weight of aggregates in water is Mw ≈ 10 8 g/mol and decreases by more than an order of magnitude in ethanol. Zero shear viscosity η0 is low and shear thinning is weak compared to the high molecular weight of the aggregates. Linear viscoelastic relaxation is described by the Zimm theory up to frequencies of 10 4 rad/s, demonstrating that no entanglements are present in these solutions. This is further supported by the concentration dependence of η0 and is attributed to strong association within the aggregates. Extensional flow behavior is characterized using the capillary break- up extensional rheometry technique including high- speed imaging. Solutions with φ ≥ 1% undergo uniform deformation and show pronounced strain hardening up to large Hencky strains. Elongational relaxation