Development of highly stable paraffin wax/water phase change material nano-emulsions as potential coolants for thermal management

This study was to explore the hydrophilic surfactant/Brij L4 mixture scheme for fabrication of highly stable paraffinic nano-emulsions melting at 55 °C by the low-energy phase inversion temperature method that has not been reported previously. Two commercial paraffin waxes were chosen as the PCM agents, Sasolwax 5203 with a higher onset T_m of 54 °C in the initial development and OP44E with a lower onset T_m of 44 °C for further assessment and fabrication. At accelerated stability testing by thermal approach, the rate of droplet size increase was mainly attributed to Ostwald ripening destabilization mechanism, and decreased by about 5 times for every 5 °C drop. Only a moderate increase in the particle size was observed, from 47.7 nm to 120.6 nm, over a period of 9 months at 45 °C. The exciting results in the accelerated stability evaluation greatly outperformed than those previous results only obtained from the regular stability testing including room temperature storage and heating-cooling cycles in a container, and hence this experimental result can offer a more meaningful reference in terms of service life of nano-emulsions flowing in pipelines. With the optimized surfactant mixtures, a series of highly stable paraffinic nano-emulsions in the working temperature range of 30–50 °C were successfully formulated as promising coolants in the active thermal management system.