Small Angle Neutron Scattering, X-ray Diffraction, Differential Scanning Calorimetry, and Thermogravimetry Studies to Characterize the Properties of Clay Nanocomposites

Abstract

Nanocomposites based on laponite RD and (ethylene oxide)98(propylene oxide)67(ethylene oxide)98 (F127)triblock copolymer or poly(ethylene) glycol 2000 (PEG2000) were prepared by using the melting method. Small-angle neutron scattering and the X-ray diffraction experiments provided insights into the organization of the laponite RD dispersed in the macromolecular matrix over a wide length scale. SANS data analysis by means of a fractal law evidenced the formation of clusters of laponite RD at long correlation distance. The single laponite RD particles and the lamellar structure of F127 were described in the shorter length scale. Finally, the crystalline structure of the macromolecule was observed for very short length scales. Differential scanning calorimetry measurements confirm that the macromolecule anchored to the laponite RD surface is amorphous, in agreement with the XRD findings, and allowed to determine amount and thickness of the adsorbed macromolecule layer. The mesoscopic structure of the nanocomposites is straightforwardly correlated with the macroscopic properties (thermal stability, crystallization), which are crucial in the application areas. Namely, the different effect played by the nanofiller on the thermal stability of F127 and PEG2000 was correlated to the laponite RD cluster size. Accordingly, the thermal stability of the nanocomposites is enhanced if the clusters have a smaller size. As concerns the crystallization, the clusters were invoked as responsible for the observed retardation of the growth of the crystalline domains due to an increased diffusion energy barrier that slows down the macromolecule mobility.