Modification of nancomposite gels by irreversible rearrangement of polymer/clay network structure through drying

Nanocomposite gels (NC gels) have a unique organic (polymer)/inorganic (clay) network structure which causes them to exhibit excellent mechanical and swelling properties. It was found that dried and reswollen NC gels showed higher tensile moduli and strengths and low elongations at break as well as lower swelling when compared to those of NC gels as-prepared. The modification in properties brought about by drying was observed in all NC gels, regardless of the type of polymer used and the clay concentration. These changes were attributed to the irreversible rearrangement of the polymer/clay network structure in which additional cross-links are formed due to additional contacts between polymer chains and clay and the strengthening of preformed loose contacts in the concentrated state. The rearranged network structure remained almost unchanged on repeated drying and heating in the dried state. In contrast, conventional chemically cross-linked hydrogels showed no changes in properties in response to drying treatment.