High internal phase emulsion HIPE

Cameron, N.R. and Sherrington, D. C. High Internal Phase Emulsions (HIPEs)-Structure, Properties and Use in Polymer Preparation. Vol. 126, pp. 163-214. 

High Internal Phase Emulsions (HIPEs) - Structure, Properties and Use in Polymer Preparation... 

An important quantity, which characterizes a macroemulsion, is the volume fraction of the disperse phase 4>a (inner phase volume fraction). Intuitively one would assume that the volume fraction should be significantly below 50%. In reality much higher volume fractions are reached. If the inner phase consists of spherical drops all of the same size, then the maximal volume fraction is that of closed packed spheres (fa = 0.74). It is possible to prepare macroemulsions with even higher volume fractions volume fractions of more than 99% have been achieved. Such emulsions are also called high internal phase emulsions (HIPE). Two effects can occur. First, the droplet size distribution is usually inhomogeneous, so that small drops fill the free volume between large drops (see Fig. 12.9). Second, the drops can deform, so that in the end only a thin film of the continuous phase remains between neighboring droplets. 

Polymeric foams, called polyHIPE , has been developed by Unilever researchers5. The production of these porous materials was based on the polymerisation of high internal phase emulsion (HIPE)6. The system is composed of two phases an organic phase -called the continuous phase- containing the monomers and a suitable amount of emulsifier and an aqueous phase -called the dispersed phase- containing the radical initiator (scheme 1). 

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