Highly concentrated W/O emulsions prepared by the PIT method as templates for solid foams

The main aim of this work was to use highly concentrated W/O (water-in-oil) emulsions, prepared by the PIT (phase inversion temperature) method as templates for solid polystyrene foams with a narrow pore size distribution. The highly concentrated emulsions were prepared by a method based on the PIT principle, which consists of increasing rapidly the temperature across the conditions where the hydrophilic and lipophilic properties of the surfactant in the system are balanced (T-HLB). This method allows one to obtain emulsions with small droplets which are relatively homogeneous. The solid foams were obtained by polymerization, initiated by potassium persulfate, of the continuous phase of the highly concentrated water-in-styrene emulsions, stabilized by nonionic surfactants. Water and surfactant were removed by washing and drying. The pore volume of the obtained monoliths was very high (> 15 mL/g). The mechanical properties of such solid foams were characterized by means of compression tests. The properties were dependent on both composition and emulsification parameters. For comparative purposes, the polymerization was also carried out in highly concentrated emulsions prepared by a conventional method. The strength and the toughness of the solid foams obtained from highly concentrated emulsions prepared by the PIT method were 400 and 50% higher, respectively, than that of solid foams obtained from emulsions prepared by conventional methods.