A scaling theory to approximate the thermal conductivity of the interphase region in polymer nanocomposites

In this study, De Gennes’s scaling theory was developed to evaluate the variation of distance-dependent thermal properties inside the polymer/particle interphase region based on the molecular characteristics of the polymer matrix and surface adsorption energy. Accordingly, the average thermal conduction coefficient of the region was predicted and used to approximate the overall thermal conductivity of the nanocomposite system. The physical characteristics of the nanoparticle clusters (e.g., size and content) were defined using a specific strategy based on the equilibrium between dispersion and cohesion energies during the preparation of the nanocomposite samples, via melt mixing. Maxwell’s model was also developed and used to predict the thermal conduction coefficient of the polymer/nanoparticle system considering the determinative impact of the polymer/particle interphase region and aggregation/agglomeration phenomenon. It was found that the scaling parameter, defining the polymer/particle interaction strength, increased by almost 50% by increasing the compatibility. This also increased the thermal conductivity of the interphase from 1.401 (W.m-1.K-1) to 3.028 (W.m-1.K-1) in the samples containing compatible nanoparticles. The thermal conductivity of nanoparticle clusters decreased exponentially with increasing the number of involved nanoparticles. The maximum prediction error of the proposed model (6.9%) was 12% less than that of the original Maxwell’s model.