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

Foaming properties of dilute aqueous solutions of pentaglycerol monostearate (C18G5) and pentaglycerol monooleate (C18:1G5) have been studied at 25 °C. The aqueous C18G5 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 C18G5 and C18:1G5 systems. The C18:1G5/water system showed lower foam stability compared to the C18G5/water system. Aqueous phase behavior of the C18G5 and C18:1G5 systems showed the dispersion of α-solid and Lα phase respectively in water rich region at 25 °C. Stable foam in the C18G5/water system was mainly due to the finely dispersed small surfactant solid particles. The average particles diameter of α-solid and Lα 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 Lα dispersion; however, the foam stability differs largely. Foam stabilized by lamellar liquid crystal dispersion in C18:1G5/water system, is less stable compared to the foam stabilized by the surfactant solid dispersion in C18G5/water system. The foamability and foam stability of the surfactant systems show poor correlation with the dynamic surface tension properties.

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