STRUCTURAL AND DYNAMIC PROPERTIES OF PARTIALLY CHARGED POLY(ACRYLIC ACID) GELS - NONERGODICITY AND INHOMOGENEITIES

Small-angle neutron scattering (SANS) and light scattering experiments have been performed on partially neutralized poly(acrylic acid) (PAA) solutions and swollen networks with various cross-link densities. The ensemble-averaged intensity of light scattered from gels was measured by a procedure that allows the scanning of many independent speckles across the detector. For all investigated samples, the scattered light intensity was found to be independent of the scattering wave vector q in contrast with the behavior observed in neutral gels. SANS shows a peak in the structure factor, revealing the existence of microstructure at a small scale (approximately 100 angstrom). The dynamic structure factors were obtained by using a method based on a recent theory of dynamic light scattering by nonergodic media. The PAA gels showed an increasingly nonergodic behavior upon an increase of cross-link content and/or a decrease of ionization degree. Light scattering and SANS results can be explained by assuming a liquid-like structure of densified clusters.