Measurement of the interaction forces between poly(N-isopropylacrylamide-acrylic acid) microgel and silica surfaces by colloid probe microscopy

摘要

The interaction of an immobilized layer of copolymer microgels of poly(N-isopropylacrylamide-acrylic acid) with a silica colloid probe, separated by aqueous solutions, has been studied using atomic force microscopy. The interaction was seen to be repulsive at all separations for all pH and ionic strengths studied. Dejaguin-Landau-Verwey-Overbeek (DLVO) theory (solely electrostatic and van der Waals forces) was not able to satisfactorily describe the interaction between the silica probe and the microgel layer. The magnitude and range of the measured forces were both far greater than DLVO theory would predict. The discrepancy is ascribed to compression/deformation of the microgel and the presence of a "hairy" steric layer, composed of polyelectrolyte chains, at the microgel surface. The forces that result from these phenomena are the major components of the overall interaction observed. The range of the measured interactions varied with solution pH and ionic strength. It is believed that changes in the solution conditions give rise to variation in the dissociation and screening of the sulfate and carboxylate groups present in the microgel. In turn, this causes the microgel "core" and hairy layer to alter their conformations. Hence, electrostatic effects (although not in the DLVO sense) are important in determining the character of the silica-microgel interaction. [References: 49]