Accelerating tetrahydrofuran hydrate nucleation under static conditions: synergistic effects of metal substrates and surfactant chemistry

Rapid nucleation is critical for deploying hydrate-based technologies in cold energy storage and thermal management. This study systematically investigated the promotion of heterogeneous nucleation for tetrahydrofuran (THF) hydrate through combined metal substrate and surfactant intervention under static (non-agitated) conditions. Experimental results on 180 parallel samples per condition revealed that metal surfaces dramatically enhanced nucleation kinetics following the order: Zn > Cu > Al, while no hydrate nucleation was observed in any of the 180 parallel samples in the system without any solid substrate within 30 h. The optimal Zn-DTAC combination achieved a nucleation rate of 1.12 h−1, representing a 283-fold acceleration over the Al-pure water baseline and a two-fold increase over the Zn-pure water system. Mechanistic analysis using classical nucleation theory revealed divergent surfactant mechanisms: anionic surfactants (SDS, SDBS) inhibited nucleation through surface adsorption that passivates the metal surface and increases the contact angle, raising the heterogeneous nucleation barrier, whereas cationic DTAC promoted nucleation by lowering the hydrate-liquid interfacial tension via bulk micellization, without inducing metal surface passivation. Temperature-dependent studies confirmed consistent promotion rankings across the subcooling regime relevant to air-conditioning applications. These findings provide both mechanistic insight into heterogeneous nucleation pathways and a practical, energy-efficient strategy for accelerating hydrate formation in cold-storage systems without external mechanical input or energy-intensive additives.