Microencapsulated Alkane Wax Melting: Measured by 1 H NMR Relaxometry and Diffusometry

ABSTRACT Phase change materials (PCMs) are useful for energy storage. Large latent heats make n ‐alkane waxes effective PCMs. Octadecane and eicosane were studied as both unencapsulated and microencapsulated with NMR relaxometry and diffusometry throughout melting. Each wax was stepped degree‐wise through its melting point. At each temperature point, NMR relaxation, correlated relaxation, and PGStE measurements as a function of molecular migration time were acquired. These measurements detected molecular‐level disordering due to microencapsulation. NMR relaxometry measurements on the solid waxes measured a major intermediate mobility domain in the microencapsulated waxes. This pseudo interface domain in the solid microencapsulated waxes is consistent with the disruption of long‐range order, increasing heterogeneity and extending the melting point range. NMR diffusometry measured diffusion coefficients in the unencapsulated wax melts, matching values established in the literature. as a function of was fit for Arrhenius activation energies as a function of for each stage of melting. values are reported for each solid wax sample, which are not measurements of only molecular diffusion but are consistent with magnetization transport via spin diffusion.