Porous internal phase emulsion

If a high internal phase emulsion is prepared in which the continuous phase contains one or more monomeric species, and polymerisation is initiated, a novel type of highly porous material is produced. Polymers of this type are referred to as PolyHIPE, using the nomenclature devised by Unilever scientists [128],... 

The idea of the preparation of porous polymers from high internal phase emulsions had been reported prior to the publication of the PolyHIPE patent [128]. About twenty years previously, Bartl and von Bonin [148,149] described the polymerisation of water-insoluble vinyl monomers, such as styrene and methyl methacrylate, in w/o HIPEs, stabilised by styrene-ethyleneoxide graft copolymers. In this way, HIPEs of approximately 85% internal phase volume could be prepared. On polymerisation, solid, closed-cell monolithic polymers were obtained. Similarly, Riess and coworkers [150] had described the preparation of closed-cell porous polystyrene from HIPEs of water in styrene, stabilised by poly(styrene-ethyleneoxide) block copolymer surfactants, with internal phase volumes of up to 80%. 

PolyHIPE materials have also been prepared by polycondensation in high internal phase emulsions [153]. Thus, a resorcinol-formaldehyde (RF) porous copolymer was synthesised from an o/w HIPE of cyclohexane in an aqueous solution of resorcinol, formaldehyde and surfactant. Addition of an acid catalyst to the emulsion, followed by heating, resulted in copolymerisation. Other systems prepared included urea-formaldehyde, phenol-formaldehyde, melamine-formaldehyde and a polysiloxane-based elastomeric species. 

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). 

In this study, after a brief introduction to PI we provide the bases of a technique for the preparation of polymeric micro-porous materials, known as polyHIPE polymers (PHPs) which are now used extensively in PIM, and micro-reactor technology. These polymers are prepared through the high internal phase emulsion (HIPE) polymerization route. In order to control the pore size, the flow-induced phase inversion phenomenon is applied to the emulsification technique. The metalization of these polymers and formation of nano-structured micro-porous metals for intensified catalysis are also discussed. Finally, we illustrate the applications of these materials in chemical- and bioprocess intensifications and tissue engineering while examining the existence of several size-dependent phenomena. 

A highly porous polymeric foam can be prepared through emulsion templating by polymerizing the continuous phase of high internal phase emulsions [150], A maleimide-terminated aryl ether sulfone oligomer was copolymerized with divinylbenzene in the continuous phase, using a mixed surfactants system, cetyltrimethylammonium bromide, dodecylbenzene-sulfonic acid sodium salt, and a peroxide initiator. The polymers show a CO2 adsorption and improved mechanical properties. The materials exhibit an open cell and a secondary pore structure with surface areas of a 400 m g ... 

Emulsion-templated highly porous PolyHIPE monoliths These are initiated from high internal phase liquid emulsions and polymerized (see the review by Silber-stein [42]). In general, the main porosity of High Internal Phase Emulsions (HIRES) lies in the micrometer size range, but HIRES may show a multiscale porosity with one distribution down to some tens of nanometers. 

Cameron, N.R., 2005. High internal phase emulsion templating as a route to well-defined porous polymers. Polymer 46,1439-1449. 

In order to produce highly porous materials, a certain class of emulsion, known as high internal phase emulsion, or HIPE, is used. HIPEs are defined as having an internal, or droplet, volume phase ratio, (f>, of 0.74 or greater. A volume fraction of 0.74 represents the maximum volume ratio at which the droplet phase will pack as uniform non-deformable spheres. Values of 0 up to 0.99 can be observed, indicating that the droplet phase in a HIPE is either non-uniform or that the droplets are deformed into polyhedral ones. ... 

C02 as the internal phase are strictly emulsions, which led Wellington (5) to coin the phrase foamulsion . The term foam is retained here. Some nonaqueous foams in porous media have been studied primarily for use as barriers against gas coning through thin oil zones (11, 12) and well stimulation (13, 14). However, because the basic principles appear similar, the discussion is limited to aqueous foams. 

Finally, w/c and c/w PFPE based emulsions have been used for the synthesis of porous materials, which are the skeletal replica of the emulsions after removal of the internal phase. W/c microemulsions allowed for macroporous polyacrylate monoliths to be produced (80-82). Conversely, c/w emulsions may be used for the preparation of well-defined porous hydrophilic polymers (83). 

Invivition adsorption is encountered in porous solid panicles that are wet by the continuous phase. The latter diffuses into the pores, thereby increasing 0,. Osmotic diffusion occurs in multiple emulsions, in which there is an electrolytic unbalance between the innermost internal phase and the continuous phase. Thi.s condition induces migration of liquid from the region of high osmotic pressure to low osmotic pressure. Transference of continuous phase into the droplets pro-duce.s an increase of 0. whereas transference from the droplets to the continuous phase produces a decrease of ( ),. Both effects account for an increase or decrease of viscosity, respectively. Invivition and osmotic diffusion are of great importance in concentrated systems in which a relatively small increase of leads to large increases of viscosity and on the complexity of the rheological behavior. 

Clearly, wettability will affect the flow of OAV emulsions in porous media. Many surface-active compounds (which are normally needed for stable emulsions) will alter wettability, which will then affect the flow of the oil and water phases inside the reservoir. No studies have addressed the effect of wettability on the flow of emulsions in porous media. However, some effects of wettability appear to be obvious from simple intuitive reasoning. The nature of interactions between the internal surfaces of the... 

---