Investigation of peo-coated polystyrene latex by phase analysis light scattering and photon correlation spectroscopy

Abstract

Colloidal particles are encountered in many industrial and technological processes because the small particle size amplifies their interfacial properties. The characteristics of these suspensions can be modified by adsorbing macromolecules from solution onto the particles. The degree of change in the particles' interfacial attributes is highly sensitive to the conformation and adsorbed amount of the polymer on the surface. The primary goal of this research was to study the effect of adsorbed polyethylene oxide (PEO) upon the interfacial properties of two different colloidal polystyrene (PS) particles in aqueous suspensions. The two particles possessed different surface compositions. One PS sample (D305) was believed to have adsorbed anionic surfactant on the surface while the other (PSPP10) was surfactant free. Interfacial properties were characterized by photon correlation spectroscopy, phase analysis light scattering, dielectric spectroscopy, and direct polymer adsorption measurements. PCS measurements were performed on PEO-coated PSPP10 suspended in electrolyte solution of varying pH. Measurements show a molecular weight dependence of layer thickness on PEO for both PSPP10 and D305 particles. The results also indicate an increase in layer thickness of PSPP10 as the pH becomes alkaline. The increase in layer thickness also corresponded to a reduction in particle mobility. It is believed that the conformation of the adsorbed PEO becomes extended due to the removal of hydronium ions which hydrogen bond to the PEO chains. At acidic pH values. the layer thickness increases due to aggregation of the particles caused by a decrease in zeta potential. This corresponds to a drop in mobility. Supplemental dielectric spectroscopy experiments were performed to examine the effects of adsorbed PEO on the polarizability of the suspensions. The adsorbed PEO reduced the dielectric response for both D305 and PSPP10. However, the reduction was much more significant for D305 particles. This was attributed to desorption of weakly adsorbed surfactants on the D305 particles which reduced the surface potential and hence the polarizability. This conclusion was also supported by mobility measurements which showed a reduction in particle mobility after the suspensions were ion exchanged.