Interactions between polystyrene latex spheres and a semiflexible polymer, hydroxypropylcellulose

Abstract

Shear viscosity has been measured for aqueous solutions of hydroxypropylcellulose (HPC) having molecular weight 292,000 in the concentration range 0–4% by weight. Additionally, the diffusivities, D. of latex spheres with diameters of 794 and 1814 Å suspended in these solutions were measured by dynamic light scattering. As HPC concentration was increased, the initial effect on D was a decrease of about 50% due to adsorption of HPC and “bridging” of the latex spheres by the HPC to form clusters. At higher HPC concentrations, the cluster diffusivities approximately follow a stretched exponential form, D = e − αw v , where w is the HPC weight fraction, but the significance of this result is limited in the present case. The diffusivities were essentially independent of scattering vector over the measured range. The microviscosities calculated from η μ = kT 6πDR exceeded the shear viscosities, η, from cone and plate and capillary measurements. However, this appears to be the result of the initial absorption/bridging to form clusters. If the cluster sizes are used to recalculate the microviscosities, then agreement between the micro- and the macroviscosities is found, within error, over almost three decades of viscosity. The clustering process was defeated by the addition of small amounts of a nonionic surfactant, regardless of the order of mixture of HPC, latex, and surfactant. The diffusivities of these bare spheres in solutions containing up to 0.1% HPC were measured and the microviscosities agreed reasonably well with the macroscopic viscosities, the maximum deviation being about − 12%.