Role of Oxygenated Oils in n-Alkyl β-d-Monoglucoside Microemulsion Phase Behavior

Abstract

The phase behavior of mixtures of water, alkyl ethylene glycol ethers (CkOC2OCk) and n-alkyl -Dglucopyranosides (CmG1) is systematically reported as a function of temperature and composition. Previous work has shown that CmG1 are nearly insoluble in alkanes, and ternary mixtures of water-alkane-CmG1 produce stable emulsions. Replacing alkanes with more hydrophilic alkyl ethylene glycol ethers increases the solubility of C mG1 in the oil. The well-known 2-3-2 h phase sequence is observed in water-CkOC2-OCk-CmG1 mixtures with increasing temperature, indicating that CmG1's partition into the oil at higher temperatures. This microemulsion phase behavior closely resembles that of mixtures made with water, oil, and other nonionic surfactants, e.g., n-alkyl polyglycol ethers (CiEj), and both tricritical phenomena and general patterns of phase behavior are observed.

The Effect of Anomeric Head Groups, Surfactant Hydrophilicity, and Electrolytes onn-Alkyl Monoglucoside Microemulsions

“…The anomeric nature of the C m G 1 head group provides an additional degree of freedom in these surfactant structures, and substituting the ␣-D anomer (C m ␣G 1 ) for ␤-D anomer (C m ␤G 1 ) produces Krafft boundaries in all water-C m ␣G 1 mixtures studied. This is in contrast to the behavior of water-C m ␤G 1 mixtures, in which Krafft boundaries are observed only for m ϭ 10 (20).…”

“…1), but the two-phase region closes (at cp ␤ ) just before contacting the Krafft boundary. This is in contrast to the water-C 10 ␤G 1 mixture, where the miscibility gap collides with the Krafft boundary, obscuring the lower boundary and critical point of the mixture (20). Therefore, the lower critical point of the water-C 10 G 1 mixture apparently rises by at least 25°C with a change from the ␤-D to ␣-D form.…”

“…Increasing m in either water-C m ␤G 1 (20) or water-C m ␣G 1 mixtures causes the Krafft boundary to rise in temperature, which mimics the trends observed in a number of other surfactant families, including alkyl sulfates (26) and alkyldimethylphosphine oxides (26,27). The anomeric nature of the C m G 1 head group provides an additional degree of freedom in these surfactant structures, and substituting the ␣-D anomer (C m ␣G 1 ) for ␤-D anomer (C m ␤G 1 ) produces Krafft boundaries in all water-C m ␣G 1 mixtures studied.…”

“…The hydrophilic nature of the glucose head group makes these surfactants extremely insoluble in many oils, including alkanes (15,16). So although these compounds exhibit upper miscibility gaps in the binary water-surfactant mixture (4,15,20) that are similar to the family ethoxylated alcohol surfactants (C i E j 's), the ternary phase behavior of water-alkane-C m G n mixtures is drastically different than that of water-alkane-C i E j mixtures.…”

“…Another successful path for making water-oil-C m G n microemulsions without the aid of a cosurfactant involves the use of oxygenated oils, which are more hydrophilic than normal alkanes. We have previously (20) studied microemulsions containing water, n-alkyl ␤-D-monoglucosides (C m ␤G 1 ), and alkyl ethylene glycol ether oils (C k OC 2 OC k , where k is the effective carbon number of the alkyl ether chains). C m ␤G 1 are soluble in C k OC 2 OC k at higher temperatures, and this surfactant solubility in the oil allows for the normal 2-3-2 phase progression with increasing temperature for water-C k OC 2 OC k -C m ␤G 1 mixtures.…”