Super‐Stable Nonaqueous Foams in Diglycerol Fatty Acid Esters—Non Polar Oil Systems

Abstract

Foamability and foam stability of diglycerol fatty acid esters (designated as Qn‐D, where, n represents the carbon number in the alkyl chain of the amphiphile) were studied in different nonaqueous solvents, namely, liquid paraffin (LP70), squalane, squalene, and glycerol tris (2‐ethylhexanoic) ester (TIO) at 25°C. Five per cent by weight of diglycerol monomyristate (Q14‐D) in LP 70 gave super‐stable foam among all oils; not ruptured for more than 12 hours. Q14‐D/squalene also formed very stable foam, whereas there was no foam in a Q14‐D/squalane system. Diglycerol monolaurate (Q12‐D) in LP 70, squalene and squalane gave foams, which coarsened quickly, leading to the progressive destruction of the foam within few minutes.

The above systems are essentially dispersions in which surfactant solid or liquid crystal is finely divided. After phase separation took place or the surfactant was precipitated at the bottom of vial, no foaming was observed from the supernatant phase, which is almost pure solvent. Hence, the stability of the foams was caused by the dispersed solid or liquid crystal. In nonfoaming and unstable foam systems, surfactant solid and/or liquid crystal coagulated, precipitated very fast and did not stabilize foams. When particle size (∼20 µm) of solid and liquid crystal was small enough, super‐stable foam was produced in systems like in Q14‐D/LP 70. Judging from the SAXS and foaming tests, it is concluded that surfactant solid (L_β or α‐gel phase) mainly was responsible for the super‐stable nonaqueous foams in these systems instead of lamellar liquid crystalline phase.

Keywords:

• Nonaqueous foams
• diglycerol fatty acid esters
• non polar oils
• α‐solid
• lamellar liquid crystal