Polymer–filler interaction. Thermodynamic calculations and a proposed model

From a study of the sorption of water vapor by epoxy polymers filled with titanium dioxide, the differences in enthalpy and entropy of the filled and the unfilled polymers are calculated. The enthalpy and the entropy of the filled polymer are smaller than those of the unfilled polymer by about 2 cal./g. and 6 × 10 −3 e.u., respectively. These differences may be explained by the existence of a higher degree of local ordering of the polymer segments. A model is proposed to describe the interaction between the polymer and the filler as a function of the distance from the interface. It appears that polymer segments at a distance less than 1500 A. from the surface of the filler particle are within the sphere of influence of the filler. The effects of filler incorporation of the thermal expansion coefficient, heat capacity, and partial molar heat of solution of the polymer are discussed in terms of the model.