(698b) Molecular-Level Understanding of Phase Behavior in Phase-Change Nano-Emulsions for Thermal Energy Storage
AIChE Annual Meeting
Thursday, November 19, 2020 - 8:15am to 8:30am
To better understand the molecular-level origins of phase stability in PCMs nano-emulsions, multi-dimensional 1H and 13C solution-state nuclear magnetic resonance (NMR) methods have been applied to a molecularly simple octadecane-water-stearic acid system under thermal cycling. Octadecane freezing and melting were readily observed, yielding information on octadecane supercooling effects. 1H pulsed-field-gradient (PFG) NMR methods were applied to measure the diffusion coefficients of the octadecane nano-emulsions, enabling estimates of their average sizes by the Stokes-Einstein equation. Chemical shift, relaxation, and diffusion of the component species were examined as indicators of phase stability as a function of temperature and number of thermal cycles. The results lay the groundwork towards molecular understanding of phase stability under thermal cycling in oil-water-surfactant phase-change nano-emulsions.