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ABSTRACT:
Phase diagrams of α-sulfonate methyl ester derived from palm stearin (α-SMEPS)/alcohol/water systems were mapped at 30 ± 0.1°C. Two main regions-an isotropic and a lamellar liquid crystalline-were the focal points in this system. An increase in alcohol chain length decreased the isotropic region and increased the lamellar liquid crystal region. In the isotropic region, self-assembly of α-SMEPS at different alcohol chain lengths was determined by using conductivity and viscosity measurements. The phase boundaries of micelle to bicontinuous structure and bicontinuous structure to inverse micelle transitions in the isotropic regions are proposed from these analytical methods. The increase in alcohol chain length shifted the micelle [Lef-right arrow] bicontinuous structure to the water-rich corner, and the bicontinuous structure [Lef-right arrow] inverse micelle transition moved toward the alcohol-rich corner.
Paper no. S1399 in JSD 7, 263-270 (July 2004).
KEY WORDS: Bicontinuous, conductivity, inverse micelle, L phase, micelle, phase diagram, viscosity.
Abbreviations: CMC, critical micelle concentration; α-SME, α-sulfonate methyl ester; α-SMEPS, α-sulfonate methyl esters derived from palm stearin.
Applications of α-sulfonate methyl ester (α-SME), a relatively new anionic surfactant, have been widely studied, especially in the detergent industry (1-3). The main driving force to produce this surfactant commercially has been its superior detergency (4-6) and biodegradability (7-10). The physicochemical properties, such as critical micelle concentration (CMC), interfacial tension, surface tension, Krafft point, and water hardness tolerance of different chain lengths of the hydrophobic portion, have been well documented (5,10-13). Various formulations have been developed for different detergent purposes, i.e., heavy-duty laundry detergent, light-duty laundry detergent, and dishwashing. Although much work on α-SME in dilute solutions has been done, only a few studies have focused on their phase behavior (self-assembly of the surfactant) (14-16).
α-SME consists of both hydrophilic and hydrophobic portions; therefore, it has the ability to self-assemble into various structures (i.e., micelle and liquid crystalline) owing to the hydrophilicity of the α-SME molecule. In the binary system of α-SME and water, micellar, lamellar, and hexagonal liquid crystalline structures are formed at different water contents (14). The presence of a foreign compound will disrupt the association structure of the α-SME molecule. However, when suitable proportions of a surfactant, co-surfactant (e.g., alcohol), and solvent (e.g., water) are mixed together, a micellar solution is formed. By varying the...