Phase Behavior of Diglycerol Fatty Acid Esters−Nonpolar Oil Systems

Abstract

Phase behavior of diglycerol fatty acid esters (Qn-D, where n represents the carbon number in the alkyl chain length of amphiphile, n = 10-16) were investigated in different nonpolar oils, liquid paraffin (LP70), squalane, and squalene. There is surfactant solid at lower temperature, and the surfactant solid does not swell in oil, and the melting temperature is almost constant in a wide range of compositions. In all of the systems, a lamellar liquid crystal (L(alpha)) is formed in a concentrated region at a temperature between the solid melting temperature and the isotropic two- or single-phase regions. In the dilute regions, reverse vesicles are formed in L(alpha) + O regions. There are two liquid-phase regions above the L(alpha) present region. This two-phase boundary corresponds to the cloud-point curve of nonionic surfactant aqueous solutions. However, instead of being less soluble in water at high temperature for the cloud point, the surfactant becomes more soluble in the organic solvents at high temperature. Namely, the effect of temperature on the solubility is opposite to the clouding phenomenon. When the hydrocarbon chain of the diglycerol surfactant decreases, the two-phase region becomes wider. In the case of a fixed surfactant, the surfactant is most miscible with squalene (narrowest two-phase regions) and the order of dissolutions tendency is squalene > LP70 > squalane. These results show that the hydrophilic moiety (diglycerol group) is more insoluble in oil compared with that of a conventional poly(oxyethylene)-type nonionic surfactant. Formation of reversed rodlike micelles was confirmed by SAXS scattering curve. When the hydrocarbon chain of surfactant is short, the micellar size becomes larger. In a fixed surfactant system, the reverse micellar size increases by changing oil from squalene to LP70. A small amount of water induces a dramatic elongation of reverse micelles.

Structure of Diglycerol Polyisostearate Nonionic Surfactant Micelles in Nonpolar Oil Hexadecane: A SAXS Study

“…In the studies of non-aqueous phase behavior of mono-and diglycerol fatty acid esters in a variety of organic solvents we have found evidences on the formation of various self-assembled structures in the latter systems 19 . Although liquid crystalline phases were absent in the temperature-composition diagrams of the monoglycerol fatty acid ester/oil systems, an isotropic solution of micellar aggregates was observed at elevated temperatures 27 .…”

“…Furthermore, they have also been observed in aqueous systems of lipophilic surfactant in surfactant rich regions 14,15 . Only few reports exist that describes the formation of reverse micelles in organic solvents without water addition [16][17][18][19][20] .…”

Structural Investigation of Diglycerol Monolaurate Reverse Micelles in Nonpolar Oils Cyclohexane and Octane

“…Amphiphilic molecules undergo self-aggregation and form a variety of self-assembled structures both in polar and nonpolar solvents [1][2][3][4][5][6][7][8] . Phase behavior and self-assembled structures of a variety of surfactants including conventional poly(oxyethylene)-type nonionic surfactants in aqueous systems were extensively studied in the past [9][10][11][12][13] .…”

Dynamic Surface Tension and Surface Dilatational Elasticity Properties of Mixed Surfactant/Protein Systems

“…The use of polyglycerol fatty acid esters in foods 3,4) , cosmetics 5,6) , detergents 7) and pharmaceutics 8,9) are increasing day-byday due to its low toxicity and ease of biodegradability. Besides, due to their capability of a-solid formation in water 10,11) or oils 12) , they are mostly desired for the efficient foam and emulsion stabilization purposes [13][14][15] . Many attempts have been made to clarify the functions of the polyglycerol fatty acid esters.…”