Poly(HIPE) morphology, crosslink density, and mechanical properties influenced by surfactant concentration and composition

Porous polymer monoliths were prepared by emulsion templating. The relationship between emulsion behavior and cellular morphology and mechanical properties after polymerization of the monomeric continuous phase was investigated. Porous poly(High Internal Phase Emulsion)s were synthesized with the same strut material and relative density but different morphology and mechanical properties, achieved by varying the surfactant system and concentration. The range of morphologies spanned from cellular solids with hierarchical porosity and millimeter-scale voids to highly interconnected, micron-scale voids resembling Kelvin cell structures. The difference in mechanical properties was evaluated as a function of morphology and polymer crosslinking density. According to the Gibson-Ashby relative modulus - density relationship, morphology was not the sole indicator of mechanical properties. Variance in crosslinking density was inferred from swelling and thermal degradation, indicating that the interfacial film in the emulsion stage influences the polymerization reaction and the degree of crosslinking. A mixed surfactant system of cationic and nonionic surfactant showed the best ability to support small droplets and limit coalescence. However, the magnitude of the interfacial tension alone is not an indicator of the final properties.