Clay dispersion and aspect ratios in polymer-clay nanocomposites

It has clearly been shown in the literature that the properties achieved by polymer clay nanocomposites are often related to their structures and to the states of dispersion of the silicate platelets in the polymer matrices. Unfortunately, up to date most techniques used in a standard procedure do not allow a correct interpretation of polymer-clay nanocomposite structure and dispersion. In a recent work, we proposed an image analysis procedure (I.A.P.) based on TEM/OM observations to characterize the clay dispersion in polymer clay nanocomposites. The I.A.P. allows a very fine description of the nanocomposites microstructure. Nevertheless this analysis method shows some limits like the representativity of the sample analyzed volume. The purpose of this work is to discuss about the accuracy of the parameters extracted from the I.A.P. We propose SAXS experimental developments for evaluating the thickness distribution of the clay tactoids. The good agreement between the results of the two techniques confirms the validity of the I.A.P. methodology. Moreover, other experiments were performed in order to understand the abnormally low platelet lengths and aspect ratios determined from TEM micrographs. Wet-STEM observations revealed that clay platelets were not broken during the extrusion process. And, low platelet lengths and aspect ratios were shown to originate from the preparation of the ultramicrotomed sections and from TEM projection effects induced by the clay platelet wavy shape.