John Howard Hone

Rheology of polystyrene latexes with adsorbed and free gelatin

Abstract The rheology of monodisperse polystyrene latex particles of two different particle radii (26 and 67 nm) has been studied with a range of concentrations of the polyampholyte gelatin. Gelatin contributes to the rheology by adsorption to the particles and by thickening the continuous phase. High viscosities and strong shear thinning are measured for low volume fractions of latex. A procedure is presented to deconvolute the effects of free and bound gelatin by applying simple hard-sphere models. This procedure allows us to estimate the effective size of the gelatin-covered particles as well as the continuous-phase gelatin concentration and viscosity. The layer thicknesses from rheology agree well with those from PCS. The effect of varying particle volume fraction, ionic strength, pH and gelatin and surfactant concentration on the rheology of these suspensions is presented. For the smaller latex, the adsorbed layer occupies a greater fraction of the effective volume. Increasing free polymer concentration reduces the adsorbed-layer thickness. The reduced critical shear stress increases with the suspension viscosity for suspensions of the 26 nm latex but is constant for the 67 nm latex. At very high shear (>2000 s −1 ), the suspensions show excess shear thinning over that expected from a hard-sphere model. This excess thinning is attributed to deformation of the adsorbed gelatin layer under high shear stress and interpreted in terms of an empirical interparticle potential.

Controlling Suspension Rheology with Novel Oligomeric Dispersants

Suspensions of cationic boehmite (Catapal 200) exhibit “challenging” rheological properties—irreversible shear thickening to viscoelastic or jammed states, dependent on the shear history. A range of commercially available dispersants—either small molecules or polymers—were able to reduce viscosity but not able to eliminate shear‐induced jamming. We designed and synthesized oligomeric functional anchor‐buoy dispersants, with a small, strongly adsorbing carboxylic acid based anchor and a simple, inexpensive water‐soluble oligomeric buoy (typically 25–30 acrylamide units). In the presence of the dispersant, the viscosity was reduced and irreversible shear thickening eliminated.