Aqueous foam stabilized by dispersed surfactant solid and lamellar liquid crystalline phase

Abstract Foaming properties of dilute aqueous solutions of pentaglycerol monostearate (C 18 G 5 ) and pentaglycerol monooleate (C 18:1 G 5 ) have been studied at 25 °C. The aqueous C 18 G 5 system formed highly persistent foams, which did not rupture for several days. Foamability and foam stability were increased on increasing the surfactant concentration in both C 18 G 5 and C 18:1 G 5 systems. The C 18:1 G 5 /water system showed lower foam stability compared to the C 18 G 5 /water system. Aqueous phase behavior of the C 18 G 5 and C 18:1 G 5 systems showed the dispersion of α -solid and L α phase respectively in water rich region at 25 °C. Stable foam in the C 18 G 5 /water system was mainly due to the finely dispersed small surfactant solid particles. The average particles diameter of α -solid and L α dispersion is found less than 1 μm and it decreases with increasing surfactant concentration. There is no appreciable difference in the particle size of the α -solid and L α dispersion; however, the foam stability differs largely. Foam stabilized by lamellar liquid crystal dispersion in C 18:1 G 5 /water system, is less stable compared to the foam stabilized by the surfactant solid dispersion in C 18 G 5 /water system. The foamability and foam stability of the surfactant systems show poor correlation with the dynamic surface tension properties.