Tuning the Crystallization Properties of Advanced Phase Change Materials

Petroleum-based paraffin waxes are versatile phase change materials (PCMs) with attractive benefits such as high latent heat, chemical inertness, low vapor pressure, and good thermal stability. Nevertheless, a significant drawback of paraffin waxes is low thermal conductivity, making heat storage and release slow. Nanomaterials with high thermal conductivity can be used as dopants in paraffin waxes. However, the PCMs must undergo many heating and cooling cycles (>1000) in a PCM-based energy storage system. The stability and dispersion characteristic of nanomaterials after several thermal cycles also change the phase transition properties of PCMs. Due to the repetitive thermal cycle, little fundamental understanding exists of phase change behavior. We propose to exploit the effect of thermal cycles on the phase transition behavior of carbon nanotube (CNT) doped commercial paraffin. In this study, we take two approaches: 1) a bulk phase measurement of the phase change behavior mechanism (dispersion of nanomaterial, heat of fusion, crystallinity, and weight loss) using SEM-EDS, DSC, XRD, and TGA, respectively, and 2) parallel a phase contrast microscopy methods to directly visualize the stochastic nature of the onset of crystallization and melting of microcapsules of CNT-doped paraffin.