Tunable Thermal Transport in Phase Change Materials Using Inverse Micellar Templating and Nanofillers

We report extremely large tunable thermal conductivity (k) in alkanes using inverse micellar templating and nanofillers. The thermal properties of n-hexadecane containing inverse micelles of different volume fractions (phi) have been studied during freezing and melting. The k enhancement between the solid and liquid phase in the presence of oleic acid, dioctyl sodium sulfosuccinate, and sorbitan oleate inverse micelles (size similar to 1.5-6 nm) are found to be 185, 119, and 111%, respectively. Unlike the conventional nanofluids, the k enhancement in micellar templated alkanes is perfectly reversible under repeated thermal cycling owing to the monodispersity and nonaggregating nature of micelles. Our results suggest that during the first-order phase transition, the inverse micelles with highly packed linear chain surfactant are pushed to the intercrystal boundaries of alkanes, thereby reducing the interfacial thermal resistance. The k contrasts in surface modified graphite nanofibers and multiwalled carbon nanotube in n-hexadecane at 15 degrees C for a phi similar to 0.0039 are found to be 161 and 157%, respectively. The surface modified nanofillers dispersed in alkanes showed a higher thermal contrast compared to bare ones, owing to their uniform dispersibility in intercrystal regions. Our findings of the large thermal contrast using inexpensive surfactant micelles in alkane should have interesting applications in heat management.