Spontaneous exfoliation and self-assembly phenomena in polyvinylpyrrolidone/synthetic layered silicate nanocomposites

Nanocomposites of polyvinylpyrrolidone (PVP) and unmodified synthetic montmorillonite (MMT) were prepared by solution-intercalation method using water as solvent. Structure of systems was investigated extensively by wide- and small angle X-ray diffraction techniques (WAXS and SAXS, respectively) including methods involving two-dimensional (2D) detection of scattered radiation. Results of this study, supplemented by transmission electron micrographs, clearly suggest that the nanocomposites are exfoliated up to 20 wt% of MMT in the polymer. Structural investigations revealed also that in 0.25 mm films, clay particles spontaneously orient parallel to the film's surface. Statistical analysis of TEM images showed that in nanocomposites containing 5 wt% of MMT, the average distance between montmorillonite platelets is equal to approximately 10 nm. In addition to structural investigations, thermal properties and optical transparency of the nanocomposites were investigated. DSC and TGA results indicate that incorporation of clay in PVP matrix causes no significant changes in glass transition temperatures (Tg) and thermal stability of the systems. UV–vis spectroscopy revealed lower UV-transmittance of nanocomposites in comparison to neat polyvinylpyrrolidone. However, PVP/MMT has similar transparency of the visible light.