Enhanced colloidal stabilization via adsorption of diblock copolymer from a nonselective Theta solvent

Experimental measurements, interpreted with mean field theories, provide qu antitative understanding of the stability of colloidal particles coated wit h a highly asymmetric diblock copolymer. Adsorption of poly((dimethylamino) ethyl methacrylate)/poly(n-butyl methacrylate) onto colloidal silica partic les from 2-propanol, which is nonselective and a Theta solvent for poly(n-b utyl methacrylate), yields a very high surface coverage and a highly stretc hed brush. With increasing temperature, the adsorbed chains swell more than those in the bulk. Upon cooling, the dispersions exhibit thermodynamic sta bility well below the Theta temperature of the nonadsorbed block. A simple mean-field theory rationalizes the stability as a consequence of the high s urface coverage, which is attributed in turn to strong segmental adsorption of the short anchor block and negligible excluded volume interactions amon g the stabilizing chains.