Water‐in‐Oil Phase Change Emulsions for Subzero Cold Transport and Storage With Reduced Supercooling

Ice slurries effectively utilize latent heat, but are generally restricted to temperatures around 0°C. Below this threshold, oil‐based cooling is often used, yet oil alone offers limited sensible heat capacity and is expensive compared to water. To overcome these limitations, this study aims to create a water‐in‐oil (W/O) phase change emulsion that combines the benefits of the high latent heat of (salt) water with an oil‐based matrix to maintain flowability at subzero temperatures. The freezing temperature of an aqueous ammonium sulfate solution is reduced to −18°C and shows additional supercooling when dispersed in oil, pushing the solidification temperature below −48°C. Adding polyethylene glycol (PEG‐600) as a nucleation agent mitigates supercooling from over 30 to about 3 K as proven by thermal analysis. A tailored surfactant system based on Tween 80 (T80) and Span 85 (S85) with a hydrophilic–lipophilic balance (HLB) near 7 stabilizes a 30 wt% water phase in thermal oil, thus, harnessing the latent heat of water without compromising pumpability. Measured enthalpy values reach about half the theoretical maximum of 116 J g −1 in a 10 K wide phase change region, offering more than three times the storage capacity of pure oil. Thermomechanical investigations show the emulsions’ capability to withstand repeated freeze–thaw cycles, ensuring kinetic stability for cold transport applications. This study demonstrates how W/O emulsions provide outstanding thermal performance and remain flowable below 0°C. Thereby, key shortcomings of both ice slurries and oil‐based coolants are resolved, unlocking the potential for future high‐performance solutions in cold storage and transport.