Enhancing Thermal Transport in Polymeric Composites Via Engineered Noncovalent Filler-Polymer Interactions

Understanding thermal transport mechanisms in polymeric composites allows us to expand the boundaries of thermal conductivity in them, either increasing it for more efficient heat dissipation or decreasing it for better thermal insulation. But, these mechanisms are not fully understood. Systematic experimental investigations remain limited. Practical strategies to tune the interfacial thermal resistance (ITR) between fillers and polymers and the thermal conductivity of composites remain elusive. Here, we studied the thermal transport in representative polymer composites, using polyethylene (PE) or polyaniline (PANI) as matrices and graphite as fillers. PANI, with aromatic rings in its backbone, interacts with graphite through strong noncovalent pi-pi stacking interactions, whereas PE lacks such interactions. We can then quantify how pi-pi stacking interactions between graphite and polymers enhance thermal transport in composites. PE/graphite and PANI/graphite composites with the same 1.5% filler volume fractions show a similar to 22.82% and similar to 34.85% enhancement in thermal conductivity compared to pure polymers, respectively. Calculated ITRs in PE/graphite and PANI/graphite are similar to 6 x 10(-8) m(2)KW(-1) and similar to 1 x 10(-8) m(2)KW(-1), respectively, highlighting how pi-pi stacking interactions reduce ITR. Molecular dynamics (MD) simulations suggest that pi-pi stacking interactions between PANI chains and graphite surfaces enhance alignment of PANI's aromatic rings with graphite surfaces. This allows more carbon atoms from PANI chains to interact with graphite surfaces at a shorter distance compared to PE chains. Our work indicates that tuning the pi-pi stacking interactions between polymers and fillers is an effective approach to reduce the ITR and enhance the thermal conductivity of composites.