Three-Dimensional Imaging of Emulsion Separation through Liquid-Infused Membranes Using Confocal Laser Scanning Microscopy

The removal of emulsified oils from water has alwaysbeen a challengedue to the kinetic stability resulting from the small droplet sizeand the presence of stabilizing agents. Membrane technology can treatsuch mixtures, but fouling of the membrane leads to dramatic reductionsin the process capacity. Liquid-infused membranes (LIMs) can potentiallyresolve the issue of fouling. However, their low permeate flux comparedwith conventional hydrophilic membranes remains a limitation. To gaininsight into the mechanism of transport, we use 3D images acquiredby confocal laser scanning microscopy (CLSM) to reconstruct the sequenceof events occurring during startup and operation of the LIM for removalof dispersed oil from oil-in-water emulsions. We find evidence forcoalescence of oil droplets on the surface of and formation of oilchannels within the LIM. Using image analysis, we find that the rateat which oil channels are formed within the membrane and the numberof channels ultimately govern the permeate flux of oil through theLIMs. Oil concentration in the feed affects the rate of coalescenceof oil on the surface of the LIM, which, in turn, affects the channelformation dynamics. The channel formation dynamics also depend onthe viscosity of the infused liquid and the operating pressure. Ahigher affinity to the pore wall for infused liquid than permeatingliquid is essential to antifouling behavior. Overall, this work offersinsight into the selective permeation of a dispersed liquid phasethrough a LIM.

Automated summary

Membrane technology is effective for treating emulsified oil-water mixtures, but fouling of the membrane reduces its capacity. Liquid-infused membranes (LIMs) show potential for resolving fouling issues, but their low permeate flux is a limitation. By using confocal laser scanning microscopy (CLSM) to analyze 3D images, we observe the coalescence of oil droplets and formation of oil channels in LIMs, which are influenced by factors such as oil concentration, infused liquid viscosity, and operating pressure. This study provides insights into the selective permeation of dispersed liquid phases through LIMs.