STABILITY OF DISPERSIONS IN THE PRESENCE OF GRAFT COPOLYMER .1. ADSORPTION OF GRAFT-COPOLYMERS ON LATEX DISPERSIONS AND THE STABILITY AND RHEOLOGY OF THE RESULTING DISPERSIONS

The adsorption of graft copolymers on polystyrene latex dispersions and the stability and theology of the resulting dispersions have been investigated using adsorption isotherms and theological measurements. Two latex particles with diameters of 427 and 867 nm were used and two graft copolymers with poly(methyl methacrylate-methacrylic acid) backbone and poly(ethylene oxide) side chains were studied. It was found that the amount of copolymer adsorbing per unit particle surface area was approximately constant for both latex particles. The adsorption amount increased with increase in temperature as a result of reduction of solvency for the chains. The steric interaction of the particle at saturation adsorption of copolymer was investigated using theological measurements, namely steady-state shear stress-shear rate and oscillatory measurements. The adsorbed layer thickness of copolymers on the latex particle-was estimated as a function of volume fraction of the particles in the dispersion. The adsorbed layer thickness depends on the density of the grafted PEO chains; the higher the density of graft PEO chains, the larger the adsorbed layer thickness. Scaling laws were used to estimate the relationship between particle Volume fraction and the elastic modulus and the compressibility of the particles. The effects of addition of electrolyte and/or change of temperature on the stability of the dispersions were also studied and both the critical flocculation temperature (CFT) and the critical flocculation concentration (CFC) of electrolyte were determined. The flee radius of suspension above CFC was estimated using the elastic flee model.