Conformational effects of adsorbed polymer on the swelling behavior of engineered clay minerals

The conformational behavior of polymers in clay-polymer nanocomposites (CPN) is not fully understood because of the many factors involved. The purpose of the present study was to investigate the conformational behavior of a polymer at the micro- and meso-scales in order to predict the behavior of tunable CPN. The study used a pH-responsive polymer, polyacrylamide, which has time-dependent hydrolysis response properties, to examine micro-scale conformational behavior of the polymer adsorbed on representative clay-mineral surfaces, SiO (sub 2) and Al (sub 2) O (sub 3) . A nanocomposite and a microcomposite were used to link meso-scale CPN behavior to micro-scale polymer conformation. The conformational behavior was characterized using in situ, real-time spectroscopic ellipsometry. The contracted coil conformation of polyacrylamide was observed at pH=3, while extended conformation was observed at pH=11.5 on both SiO (sub 2) and Al (sub 2) O (sub 3) surfaces. At pH=11.5, the polymer conformation changed from expanded coil to extended conformation over time. The polymer conformation changed more rapidly with the Al (sub 2) O (sub 3) surface due to mineral dissolution at pH=3 and 11.5. Swelling tests were conducted as functions of pH and time to link the micro-scale phenomena to meso-scale CPN behavior. The results indicated that the swelling potential of CPN corresponded to the conformation of adsorbed polyacrylamide, which varied with pH and time. The swelling potential of CPN was maximized at pH=11.5 and decreased with decreasing pH, corresponding to the observed micro-scale conformational behavior.