A new differential scheme for the development of thermally conductive polymer-composites with non-dilute filler concentrations

The recent approach for enhancing the thermal conductivity of polymer-composites is to generate an interconnecting network of thermally conductive fillers. However, the existing models for effective thermal conductivity of composites are, generally, based on effective medium theory and valid for dilute filler concentration (low volume fraction), which leads to inaccurate predictions with non-dilute and percolating filler concentrations. In this work, the model is developed focusing on non-dilute filler concentrations, which is more practical for the recent approach towards thermally conductive polymer-composites. The existing model for dilute filler concentrations is modified based on Bruggeman's differential scheme wherein the ‘non-dilute concentrations’ are obtained by integrating the effect of adding ‘dilute concentrations’ in small increments. The proposed model can handle particulate fillers of variable geometry. The proposed model is validated by producing different polymer matrix composite systems with ceramic fillers. Using Al₂O₃ or AlN as filler, and high-density polyethylene or polypropylene as matrix, different binary composite systems were processed with volume fractions up to 0.5. From the parametric studies, conducted to establish the understandings of the model, the aspect ratio of filler particles is found the most critical. The proposed model is expected to be the mathematical ground for the industry and researchers to produce computationally designed polymer composites with tailorable ultrahigh thermal conductivity in corrosive environment-heat transfer applications such as polymeric heat exchangers for seawater desalination.