Experimental and theoretical study of PEG bulk volume fraction effect on clay/PEG2000 hybrid properties

Abstract

This article focuses on the preparation of hybrids based on a clay matrix intercalated with poly(ethylene glycol) (PEG) molecules. Hybrids obtained by direct mixing in the presence of a solvent, in this case water, are intended mainly for the thermal insulation of buildings. The study highlighted the impact of the PEG bulk volume fraction, (φ), on the structure and properties of composite formulations for a molecular weight M=2000g/mol. Scanning electron microscopy (SEM) results showed that the structure of purified clay is heterogeneous, characterized by the existence of smectite, illite, kaolinite. These clay minerals are associated with spherical particles of average size ranging from 10 to 30μm, which are affected to quartz. Meanwhile, Fourier transform infrared spectroscopy (FTIR) was used to estimate the changes caused by the addition of PEG to the matrix. The results reveal a decrease in the intensities of the vibrational bands assigned to water molecules ν(HOH) at 3440cm-1 and δ(HOH) at 1638cm-1 as φ increases. This decrease is linked to the desorption of water molecules outside the interlayer environment thanks to the adsorption of PEG. On the other hand, the changes detected in the ν(O-H) band recorded at 3621cm-1 confirm the formation of a hydrogen bond between the PEG backbone and the siloxane surface. As for the X-ray diffraction (XRD) results, it is clear that adsorption takes place in two cycles characterizing the adsorption of two polymer layers. Each cycle contains three regimes including the dilute regime, the bidimensional semi-dilute regime and the plateau. Finally, XRD results were used to monitor the variation of d-spacing versus PEG bulk volume fraction. These results show very good agreement with the theory developed using De Gennes scaling laws for the different regimes near the surface.