Stabilization of nonaqueous foam with lamellar liquid crystal particles in diglycerol monolaurate/olive oil system

Nonaqueous foams stabilized by lamellar liquid crystal (L α ) dispersion in diglycerol monolaurate (designated as C 12G 2)/olive oil systems are presented. Foamability and foam stability depending on composition and the effects of added water on the nonaqueous foaming behavior were systematically studied. It was found that the foamability increases with increasing C 12G 2 concentration from 1 to 3 wt% and then decreases with further increasing concentration, but the foam stability increases continuously with concentration. Depending on compositions, foams are stable for a few minutes to several hours. Foams produced by 10 wt% C 12G 2/olive oil system are stable for more than 6 h. In the study of effects of added water on the foaming properties of 5 wt% C 12G 2/olive oil system, it was found that the foamability and foam stability of 5 wt% C 12G 2/olive oil decreases upon addition of 1 wt% water, but with further increasing water, both the foamability and foam stability increase. Foams with 10% water added system are stable for ∼4 h. Phase behavior study of the C 12G 2 in olive oil has shown the dispersion of L α particles in the dilute regions at 25 °C. Thus, stable foams in the C 12G 2/olive oil system can be attributed to L α particle, which adsorb at the gas–liquid interface as confirmed by surface tension measurements and optical microscopy. Laser diffraction particle size analyzer has shown that the average particle diameter decreases with increasing the C 12G 2 concentration and, hence, the foams are more stable at higher surfactant concentration. Judging from foaming test, optical micrographs, and particle size, it can be concluded that stable nonaqueous foams in the studied systems are mainly caused by the dispersion of L α particles and depending on the particle size the foam stability largely differs. Nonaqueous foams stabilized by L α particles: Normal view (left) and microscopic view (right).