Oil-in-Water Emulsions Stabilized by Acylglutamic Acid–Alkylamine Complexes as Noncovalent-Type Double-Chain Amphiphiles

Abstract

We have studied the preparation and stabilization mechanism of oil-in-water-type emulsions in the presence of amphiphilic 1:1 stoichiometric complexes of acylglutamic acids (CnGlu) with tertiary alkylamines (CnDMA). Relatively stable emulsions were obtained when C16Glu-C16DMA (or C18Glu-C18DMA), hexadecane, and water were homogenized at 80 °C and then stored at room temperature. The gel-liquid crystal phase transition temperatures (T) of C16Glu-C16DMA and C18Glu-C18DMA dispersed in water were determined to be ca. 39 and 53 °C, respectively. This indicates that the complexes form an adsorbed layer at the oil/water interface during the homogenization process above the T and then change into a gel during storage at room temperature. The gel phase formed at the oil/water interface prevents the oil droplets from coalescing. In contrast, shorter chain analogues (C10Glu-C10DMA and C12Glu-C12DMA) did not yield stable emulsions because their adsorption layers were not able to prevent coalescence of the oil droplets (i.e., the T of these analogues was below the room temperature). We have also demonstrated that the dispersion stability of these emulsion systems can be controlled by changing the aqueous pH.

Corn Oil–Water Separation: Interactions of Proteins and Surfactants at Corn Oil/Water Interfaces

“…Oil–water separation is a critical industrial process in a variety of fields such as foods, agricultural products, petrochemicals, textile, and pharmaceuticals. − In the corn refining industry, oil–water separation plays a significant role for the treatment and collection of corn oil products. − Generally, the oil–water separation processes can be severely hindered by the presence of an emulsifier in the mixture, for example, protein molecules or surfactants. These molecules can migrate to the oil/water interface and stabilize smaller oil droplets distributed in aqueous solutions to form the relatively homogeneous emulsions. − However, when proteins and other artificial surfactants are both present in such systems, their individual emulsifying mechanisms might be incompatible, leading to competitive destabilization of small oil droplets. − Therefore, the introduction of a surfactant into an oil–water emulsion stabilized by a protein can effectively disrupt the stability of the system, resulting in coalescence of oil droplets, leading to easier oil–water separation. − …”

Physicochemical Properties of Acylglutamic Acid-Alkylamine Complexes in Aqueous Media

“…This means the coexistence of two lyotropic liquid crystals. These complexes have a gelliquid crystal phase transition temperature, and the temperature increases with hydrophobic chain length 13 . This causes a difficulty in preparing a homogenous sample at high concentrations and at low temperatures, under a given homogenization process.…”

“…In our previous work, we reported that acylglutamic acid-alkylamine complexes CnGlu-CnDMA, where n is the number of carbon atoms in the hydrophobic chains form pH-sensitive wormlike micelles and hydrogels 12 . In addition, these complexes can stabilize oil droplets dispersed in water against their coalescence 13 . In this paper, we report the physicochemical property of CnGlu-CnDMA in their dilute aqueous solutions by static surface tensiometry.…”