Emulsification using microporous systems

Emulsions are disperse systems of two immiscible or poorly miscible liquid phases. Examples for emulsions are mayonnaise consisting of small oil droplets dispersed in a continuous water phase (oil-in-water emulsion, o/w) or margarine, which is small water droplets dispersed in a continuous oil phase (water-in-oil emulsion, w/o). With membrane emulsification, Nakashima et al. [T. Nakashima, M. Shimizu, M. Kukizaki, Membrane emulsification by microporous glass, Key Eng. Mater. 61–62 (1991) 513–516] began research on alternative emulsification methods in the early 1990ʹs. One phase is dispersed into the other phase by being pressed through the pores of a membrane. The detachment of the droplets on the membrane surface results in the production of an emulsion with a narrow droplet size distribution at mild process conditions. In the late 1990s, Suzuki et al. [K. Suzuki, I. Shuto, Y. Hagura, Characteristics of the membrane emulsification method with preliminary emulsification for preparing corn oil-in-water emulsions, Food Sci. Technol. Int. 2 (1) (1996) 43–47] used membranes to disrupt droplets of a coarse emulsion by pushing the entire emulsion through the pores. This allows a higher production rate than the above mentioned emulsification method. The fast progress in micro engineering and semi conductor technology enabled the development of custom-designed microchannels, that Nakajima and co-workers [T. Kawakatsu, Y. Kikuchi, M. Nakajima, Regular-sized cell creation in microchannel emulsification by visual microprocessing method, JAOCS 74 (1997) 317–321] applied in emulsification technology. The special geometry of those microchannels causes the formation of unisized droplets by the Laplace instability. Since no additional forces for the droplet detachment are necessary, process conditions in microchannel emulsification are even milder than in membrane emulsification.