DYNAMIC LIGHT-SCATTERING OF SUSPENSIONS OF PEO-COATED LATEX-PARTICLES

Photon correlation spectroscopy has been used in conjunction with elec trophoresis to determine the hydrodynamic layer thickness (HLT) and su rface properties of poly(ethylene oxide) (PEO) adsorbed onto carboxyla ted poly(styrene) and poly(styrene-butadiene) latexes from water. The effects of the surface charge density of the latex particle, the surfa ce roughness of the latex particle, PEO molecular weight and concentra tion, the presence of PEO clusters in solution, and the manner in whic h PEO is added to the latex suspension on the HLT were studied. The pr operties and stability of brominated latex suspensions were also studi ed. The results indicate that the adsorption of PEO onto latex particl es is kinetically controlled and that increased surface roughness and polarity of the latex particles decreases PEO adsorption. The molar ma ss exponent, a, was found to increase with decreasing surface roughnes s and surface charge density. The manner in which PEO is added to the latex suspension was found to be the most important factor affecting t he value of a. A molar mass exponent of a = 0.36 +/- 0.02 for all the latexes, regardless of surface roughness and surface charge density, w as found for two-step PEO additions. PEO clusters in solution were fou nd to increase the value of the effective diffusion constant, D(eff), and thus decrease the calculated HLT. Bromination of the latexes allow ed for an estimation of the ''hairy'' layer thickness of the latex par ticles.