Compared study of cooperativity in PMMA nanocomposites and thin films

Strong deviations from the bulk concerning chains dynamics and glass transition have been reported. Different behaviour was observed for s-PMMA and i-PMMA according to the nature of the substrate and the technique used. One appealing approach developed by Donth consists in associating to dynamic heterogeneity measured by NMR a spatial length scale. This length scale has rapidly been identified with cooperatively rearranging regions (CRR) whose size increases near the glass transition. Thus, on an experimental level it is interesting to measure the size of CRR. A convenient way to do it is to confine the polymer chains in geometries with size of the order of the CRR. For instance, clays seem to be an interesting system as it is possible to vary the chemical nature of the surface and the interlayer spacing. Organophilic montmorillonite (OMMT) was used as well as bare clay such as bentonite (BT). In a first step, we determine the size of CRR for s-PMMA and discuss the obtained values. Then in a second step, we compare the evolution of T-g(h) in two different systems e.g. thin films and BT nanocomposites in order to prove that the same mechanisms are at stake. (c) 2004 Elsevier Ltd. All rights reserved.