Abstract:Emulsion liquid membranes (ELMs) are extensively utilized for the extraction and separation of target substances due to their large contact area, rapid reaction kinetics, and capacity for simultaneous extraction and stripping. However, industrial implementation is hindered by membrane instability resulting from phenomena such as coalescence, swelling, or leakage during separation and enrichment processes. This review systematically examines the critical factors influencing ELM stability, their microscopic mechanisms, and future research directions. Carrier concentration exhibits a distinct threshold: low concentrations promote metal-carrier complex formation to enhance mass transfer, while high concentrations induce a sharp increase in membrane-phase viscosity, triggering droplet coalescence and osmotic swelling (water migration into the membrane diluting the internal phase), thereby reducing both stability and separation efficiency. In surfactant systems, Span 80 forms elastic monomolecular films via robust interfacial adsorption; β-cyclodextrin polymers establish high-mechanical-strength interfacial barriers against coalescence; and blended systems (e.g., Span 80/Tween 80) improve stability through HLB synergy. Surfactant concentrations exceeding the critical micelle concentration (CMC) compromise stability due to increased micellar viscosity and mass transfer resistance. Membrane additives (e.g., iso-octanol, amphiphilic polymer P(LM-AA), polymer HPAM) significantly reinforce interfacial films by adjusting HLB values, providing steric hindrance, and forming viscous networks. Destabilization mechanisms in operational parameters manifest as follows: emulsification beyond critical energy thresholds causes excessively small droplets and membrane thinning; prolonged extraction exacerbates osmotic swelling, leading to internal phase osmotic pressure accumulation and rupture; elevated temperatures reduce membrane-phase viscosity and interfacial film strength, accelerating coalescence. Microscopic analyses reveal stability originates from dynamic interfacial behavior: dilatational rheology shows the elastic modulus directly characterizing deformation resistance (high-modulus films formed by Span 80 saturation, with D2EHPA blending reducing rigidity via enhanced hydrophilicity of phosphate groups); shear rheology demonstrates that high interfacial viscosity suppresses droplet rupture through shear-thinning energy dissipation. Future research must focus on two advances: developing green, efficient stabilizers combining high interfacial strength, low environmental impact, and minimal mass transfer resistance; and fundamentally elucidating microscopic mechanisms through in situmolecular-level interfacial characterization to enable rational design of specialized stabilizers. This review provides critical insights for addressing ELM instability and advancing industrial applications.
