ELECTRIC PROPERTIES AND CONFORMATION OF POLYETHYLENIMINE AT THE HEMATITE-AQUEOUS SOLUTION INTERFACE

The variations of electro-optical behavior and pH of ellipsoidal hemat ite (alpha-Fe2O3) particle suspension are investigated in the presence of polyethylenimine (PEI). Suspension stability and particle electrop horetic mobility are also followed. Considerable shift of pH and the p article isoelectric point are found at extremely low PEI concentration s, indicating that nearly all amino groups of unfolded PEI molecules c ontact with the oxide surface. The small polymer layer thickness in st abilized suspension (from electro-optical data) shows ''flattening'' o f the PEI molecules even at higher polymer adsorption. Similar electro -optical behavior of suspensions with either a positive or a negative oxide particle, saturated with PEI, indicates that the colloid-polymer complex assumes charge characteristics of the polymer. Reduced counte rion mobility, found in both systems, is attributed to counterion cond ensation on the polyion surface and, possibly, to conformational trans ition in adsorbed low-charged polymer molecules. (C) 1997 Academic Pre ss.