Emulsion-derived (PolyHIPE) foams: optimization of properties and morphology for fluid flow applications

Abstract

The aim of the work described in this thesis is the development of highly porous materials (PolyHIPEs) which could find wide applications in separation science and in solid phase synthesis. Two systems were developed and studied. In the first one, PolyHIPE materials from divinylbenzene were synthesised in the presence of porogens of different chemical structures. These materials possess two levels of porosity: large pores ( 1 - 20 µm) which guarantee the flow of fluids under the application of small pressures and a fine porosity (1 - 100 nm) present in the walls of the foams which confer to the materials high surface areas (up to 700 m(^2)g(^-1)). The chemical nature of the porogens employed has a significant influence on the morphologies of the foams affecting both the dimension of the cavities and the fine porous structure. It was shown that the mechanisms operating at the emulsion stage and thus determining the characteristics of the final foams are the co-adsorption at the oil/water interface of the porogens and/or monomers together with the primary surfactant, and diffusion of the dispersed aqueous phase through the continuous organic phase. The latter phenomenon can be minimized by the appropriate choice of the surfactant system. The second system consisted of styrene/4-vinylbenzylchloride/divinylbenzene foams. The presences of a chloromethyl group render these PolyHIPE foams amenable to functionalization. Also in this case, the morphologies of the resulting foams were studied. It was shown that emulsion composition is the relevant variable affecting via the interfacial tension and viscosity not only foam morphologies but also their mechanical properties