Interfacial Interaction in EVA-Carbon Nanotube and Eva-Clay Nanocomposites

Proper filler-matrix compatibility is a key factor in view of obtaining nanocomposites with well-dispersed nanofillers displaying enhanced properties. In this respect, polymer-filler interaction can be improved by a proper combination of matrix and nanofiller polarities. This is explored for matrices ranging from nonpolar high density poly(ethylene) to ethylene-vinyl acetate (EVA) copolymers with varying vinyl acetate contents, in combination with several types of organoclay or carbon nanotubes. A novel in situ characterization methodology using modulated temperature differential scanning calorimetry is presented to evaluate the matrix-filler interaction. During quasi-isothermal crystallization of the matrix, an 'excess' contribution is observed in the recorded heat capacity signal because of reversible melting and crystallization. Its magnitude considerably decreases upon addition of nanofiller in case of strong interfacial interaction, whereas the influence is moderate in case of a less interacting matrix-filler combination. It is suggested that the 'excess heat capacity' can be used to quantify the segmental mobility of polymer chains in the vicinity of the nanofiller. Hence it provides valuable information on the strength of interaction, governed by the physical and chemical nature of matrix and filler. Heating experiments subsequent to quasi-isothermal crystallization point at a certain degree of molecular ordering, responsible for crystal nucleation in EVA copolymers.