Synthesis of porous hydrogel structures by polymerizing the continuous phase of a microemulsion

A series of microemulsions have been formulated, with 2‐hydroxyethyl methacrylate (HEMA) or HEMA/water/propanol mixtures as the continuous phase and methylcyclohexane as the discontinuous phase. The effect of surfactant type was investigated with the utilization of both anionic and nonionic surfactants. The microemulsion continuous phase was polymerized by UV radiation and a thermal post‐cure. The resultant polymers were extracted to remove the discontinuous phase and the surfactant. On swelling, the majority of the polymers became opaque, although transparent PHEMA hydrogels were synthesized with an improved equilibrium water content (EWC). The cause of opacity was shown by field emission scanning electron microscopy (FESEM). The breakdown in the microemulsion on polymerization is caused by unfavourable interactions between the PHEMA and the stabilizing surfactants causing agglomerization of the discontinuous phase. All the hydrogels were found to have higher water retention than PHEMA, with EWCs of up to 70%. The modified polymers also demonstrated an increased rate of water diffusion into the matrix. A preliminary study of oxygen permability revealed that a significant improvement had been made over standard PHEMA membranes. The porous structure of the PHEMA gels has been shown to be dependent on the type of surfactant used during synthesis.