(318d) Temperature Dependent Self–Exfoliation of Clay Polymer Nanocomposite

Upon mixing organo-clay powder aggregates into end-functionalized polybutadiene, the clay aggregates break up into individual clay particles (stacks of clay sheets) and, finally, separate into individual clay sheets (which consist of three layers: an aluminum rich center interposed between two layers composed of silicon, hydrogen, and oxygen) to form a nanocomposite of randomly oriented clay sheets in a polymeric matrix. The exceptionality of this exfoliation mechanism lies in the observation that it occurs rapidly and without requiring shear or sonication. As the clay exfoliation proceeds and the clay surface accessible to the polymer increases, polymer molecules and clay connect into a sample-spanning network, a physical gel, with increasing modulus and decreasing relaxation times. Thus, small amplitude oscillatory shear (SAOS) is a sensitive probe for the evolving structure and is chosen here for exploring the exfoliation dynamics.  Results from SAXS agreed with results from SAOS in that the clay sheet spacing rapidly increased and a maximum rate of expansion was found at intermediate temperatures. This maximum rate at intermediate temperatures had not been previously reported as earlier work had not been conducted at higher temperatures. The results were analyzed with regard to several previously proposed mechanisms of exfoliation and some inconsistencies were found.