Foaming Properties of Monoglycerol Fatty Acid Esters in Nonpolar Oil Systems

Abstract

Foaming properties of monoglycerol fatty acid esters that have different alkyl chain lengths were studied in different nonpolar oils, namely liquid paraffin (LP 70), squalane, and squalene. The effect of the hydrocarbon chain length of the surfactant, the concentration, the nature of the oil, and the temperature on the nonaqueous foam stability was mainly studied. Five weight percent of glycerol alpha-monododecanoate (monolaurin) formed highly stable foams in squalane at 25 degrees C, and the foams were stable for more than 14 h. Foam stability of the monolaurin/LP 70 and the monolaurin/squalene systems are almost similar, and the foams were stable for more than 12 h. Foam stability was decreased as the hydrocarbon chain length of the monoglyceride decreased. In the glycerol alpha-monodecanoate (monocaprin)-oil systems, the foams were stable only for 3-4 h, depending on the nature of the oil. However, the foams formed in the glycerol alpha-monooctanoate (monocaprylin)-oil systems coarsened very quickly, leading to the progressive destruction of foam films, and all of the foams collapsed within a few minutes. Foam stability decreased when the oil was changed from squalane to squalene, in both monocaprin and monolaurin systems. It was observed that, in the dilute regions, these monoglycerides form fine solid dispersions in the aforementioned oils at 25 degrees C. At higher temperatures, the solid melts to isotropic single-liquid or two-liquid phases and the foams formed collapsed within 5 min. Judging from the wide-angle X-ray scattering (WAXS) and the foaming test, it is concluded that the stable foams are mainly caused by the dispersion of the surfactant solids (beta-crystal) and foam stability is largely influenced by the shape and size of the dispersed solid particles.

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

“…Besides, the adsorption behavior of the particles depends on several factors such as structure, size, shape and hydrophobicity. Previously, we have found stable nonaqueous foams from the dispersion of monoglycerides solids in liquid paraffin, squalene, and squalane [38]. Similarly, highly stable nonaqueous foams have been achieved with the solid dispersions in diglyceride/oil systems [39].…”

Photoresponsive self-assemblies based on fatty acids

“…When self-assembled structures and particles are blocked inside the foam liquid channels, they can lead to an increase of the foam stability. [22][23][24] Fatty acids are surfactants known to easily produce aqueous foams. 25 The foam stability depends mainly on the size of the self-assembled structures present in the foam liquid channels between the bubbles.…”

Non-Aqueous and Crude Oil Foams

“…This work suggests that the surfactants essentially precipitate at the surface and act as solid stabilizers. Along these lines, Shrestha et al [22][23][24] have shown that fatty acid esters act as surfactants in different non polar and vegetable oil systems, and that the ester particles can stabilize the foam showing higher stability as their concentration is increased. They note that the particle size plays an important role on the stability -smaller sizes are more effective.…”

“…In their work, liquid crystals are adsorbed onto the surface and change the rheological properties of the lamellar and foam stability increases with the concentration of crystals. Furthermore, Shrestha et al [23,24] have shown that the stability of non-aqueous foams depends on the surfactant size with smaller sizes producing higher foam stability. Specifically, Friberg and Greene [34] have studied the system triethanolammonium oleate/p-xylene showing that if the concentration of p-xylene is lower than 3% weight, it behaves as lamellar liquid crystals and if it is higher than 13%, the system is an isotropic liquid.…”