Rheology of dilute and semidilute suspensions of spherical polyelectrolyte brushes
Résumé
The viscosity, eta, of dilute aqueous suspensions of spherical polyelectrolyte brushes is discussed. The spherical polyelectrolyte brushes consist of a solid polystyrene core of 100-nm diameter onto which linear poly(acrylic acid) chains are grafted. The relative viscosity, eta/eta(S) (eta(S) is the viscosity of the solvent) of these suspensions is studied as a function of shear rate in the presence of different amounts of added salt. A marked dependence on shear rate is found, in particular when going to higher concentrations. Extrapolation to zero shear rate leads to the relative zero-shear viscosity, eta(0)/eta(S), which can be described in terms of an effective volume fraction, phi(eff), for all salt concentrations under consideration. Moreover, the hydrodynamic radii derived from phi(eff) coincide with data obtained by dynamic light scattering in the infinitely dilute regime. Data taken at higher concentrations point to a shrinking of the brush layer owing to mutual interaction.