Foam stabilized by dispersed surfactant solid and lamellar liquid crystal in aqueous systems of diglycerol fatty acid esters

Foaming properties of dilute aqueous systems of diglycerol fatty acid esters (Qn-D, n = 10, 12, and 14, where n represents the carbon number in the hydrocarbon chain length of the surfactant) has been studied at 25 °C. The aqueous Q14-D system formed highly stable foams, and the foams are stable for several days. The foam stability in the Q10-D and Q12-D systems are significantly low compared to the Q14-D system. However, unlike the foam stability, foamability of the aqueous Q14-D system is low compared to the short chain surfactants Q10-D and Q12-D/H2O systems. Both the foamability and the foam stability were increased on increasing the surfactant concentration in the studied systems. Phase behavior study of the Qn-Ds systems showed the dispersion of Lα in the Q10-D, and Q12-D systems and the dispersion of α-solid in the Q14-D system in water rich region at 25 °C. Stable foam in the Q14-D/H2O system was mainly caused by the finely dispersed small α-solid particles. The average particles diameter of the α-solid and the Lα dispersion from the laser diffraction technique is found less than 4.5 and 3 μm, respectively. The particles diameter of the dispersed phases showed the decreasing tendency with the surfactant concentration. Foam stabilized by the lamellar liquid crystal dispersion in the aqueous solutions of the Q10-D and Q12-D systems are less stable compared to the foam stabilized by the α-solid dispersion in the Q14-D system. Thus it can be said that α-solid dispersion can cause more stable foam compared to the Lα dispersion. The foaming properties of the present systems showed a good correlation with the dynamic interfacial properties such as dynamic surface tension and dynamic surface dilatational elasticity.