Rheological properties of concentrated latex suspensions of poly(styrene-butadiene)

Concentrated suspensions of charged latex particles of poly(styrene-butadiene) have been used as model systems to investigate the influence of surface charges on the rheology of colloidal suspensions. The suspensions were found to behave as elastic solids at small strains and to require a finite stress to flow. This was related to an ordered structure of the suspensions at rest, resulting from electrostatic and van der Waals forces. Important shear-thinning effects were observed as a consequence of structure rearrangements under shear. At a fixed shear rate, the steady-shear viscosity as a function of the ionic strength exhibits a minimum. Under oscillatory shear flow, the behavior of the concentrated suspensions was found to be non-linear above a very small strain amplitude. The non-linear output signal from dynamic experiments was analyzed using a fast Fourier transform algorithm. A maximum in the third harmonic intensity as a function of the strain amplitude was observed and the intensity of higher harmonics decreased with increasing ionic strength. The behavior of the suspensions could be adequately described using the structural model of Yziquel et al. (Yziquel F, Carreau PJ, Moan M, Tanguy PA (1999) Rheological modeling of concentrated colloidal suspensions. J Non-Newtonian Fluid Mech 86:133–155).