No abstract

Conformation of polymers at solid/liquid interface is an important property that determines their effectiveness in processes such as dispersion, deposition, adhesion, and wettability. In this work, conformational behavior of pyrene labeled poly(maleic acid-co-propylene), MS-P*, in solution and at the alumina surface and its changes upon perturbation in solution pH or addition of a second oppositely charged polymer than the ones in solution were studied using fluorescence spectroscopy. Conformation of this weak polyanion, both in solution and at the solid/liquid interface was found to be strongly pHdependent. The degree of coiling on alumina depended on the solution state immediately before the adsorption. The conformation of the polymers in solution and on the solid were the same above pH 4, but, interestingly, the adsorbed polymer was more stretched at low pH. When the polymer is in the coiled form, changes in pH caused partial conformational adjustments of the adsorbed species. However, in the stretched form, the adsorbed polymer was unable to adopt the coiled conformation on the surface even with pH perturbation. Addition of polycations, poly(ethyleneimine) and poly(diallyldimethylammonium) chloride, to systems containing the preadsorbed polyanion led to conformational changes due to the formation of complexes between them at the surface. While the polyelectrolyte adsorbed in the stretched form undergoes very little conformational rearrangement, the re-conformation of the polymer adsorbed in the coiled form depends on the charge density of the second polymer and the solid. These results are compared with the behavior of polyelectrolyte complexes in solution and analyzed to elucidate possible conformational dynamics of polymers at interfaces.