Morphology and surface area of emulsion-derived (PolyHIPE) solid foams prepared with oil-phase soluble porogenic solvents: Span 80 as surfactant

Poly(divinylbenzene) emulsion-derived (PolyHIPE) solid foams prepared with porogens (toluene, chlorobenzene, (2-chloroethyl)benzene, 1,2-dichlorobenzene, and 1-chloro-3-phenylpropane) in the oil phase have morphologies and surface areas that are strongly influenced by the nature of the porogen. For the case where the surfactant employed is Span 80, we show that the solid foam structure depends on (i) the ability of the solvent to swell the growing network, (ii) the solvent polarity, and (iii) the ability of the solvent to adsorb at the emulsion interface. In particular, relatively polar solvents that are able to transport water through the emulsion continuous phase (Ostwald ripening) are shown to produce much lower surface areas than analogous resins prepared by homogeneous solution polymerization of divinylbenzene in the presence of the solvent in question alone. The influence of Ostwald ripening is further suggested by the observation that surface area decreases with increasing emulsion aqueous phase content for relatively polar solvents whereas little variation in surface area with aqueous phase content is observed for more hydrophobic solvents. All PolyHIPEs prepared were characterized by SEM, TEM, N₂ Sorption analysis, and mercury intrusion porosimetry. The relative merits of TEM and mercury intrusion porosimetry as techniques for the reliable characterization of the solid foams are discussed.