Nobuyuki Tsubaki

Solution properties of mixed surfactant system. VI: The effect of oxyethylene groups in nonionic surfactant on surface tension of anionic-nonionic surfactant systems

The effect of oxyethylene groups in a nonionic surfactant on the surface tension of anionic-nonionic systems is described; these systems are sodium 3,6,9-trioxaicosanoate (ECL)-alkyl polyoxyethylene ethers (POEn, n = 10, 20, 30, and 40). The surface tension of each mixed surfactant solution decreases with increasing mole fraction of anionic surfactant. However, these surface tension vs mole fraction curves are shifted from specific curves to monotonous curve with increasing polyoxyethylene chain length in nonionic surfactant. Moreover, in the case of the mixed systems including a nonionic surfactant which has shorter polyoxyethylene chain length, the surface tension vs total concentration curve shows only one breakpoint. In the case of systems including the nonionic surfactant which has longer polyoxyethylene chain length, that curve shows two breakpoints in the vicinity of the CMC for ECL alone and that for POEn alone. This may be attributed to the fact that the mixed micelle is formed more easily by a nonionic surfactant including shorter polyoxyethylene chain length than by one having long. Then, in the mixed surfactant systems, there are two kinds of micelles coexisting (one rich in nonionic surfactant and the other rich in nonionic one).

Solution properties of mixed surfactant system (II): Electric properties of anionic-nonionic surfactants in aqueous solutions

Electric properties of mixed anionic-nonionic surfactant systems in aqueous solutions above the CMC have been studied in terms of pNa values, electrical conductivities, and dielectric constants; these systems are sodium 3, 6, 9-trioxaicosanoate (ECL) — alkyl polyoxyethylene ethers (CmPOE; m=12, 14, 16, and 18). The degree of ionic dissociation of mixed micelle increases with increasing the number of carbon atoms of the alkyl group in the nonionic surfactant. The electrical conductivity increases with increasing the alkyl chain length in the nonionic surfactant, in spite of the increase of the activation energy for conduction. The size of mixed micelles also increases with increasing alkyl chain length. This may be attributed to the fact that the mixed micelle is formed more easily by a nonionic surfactant including long alkyl chains than for one having shorter alkyl chains.

PREPARATION AND PROPERTIES OF MULTIPHASE MICROEMULSIONS WITH SOME PHOSPHATIDYLCHOLINES HAVING DIFFERENT ALKYL CHAINS

Abstract The phase behavior and physicochemical properties (dynamic light scattering, electrical conductivity, interfacial tension, heats of transition, etc.) of various phosphatidylcholine (PC)/ n -alkane/1-alcohol/water systems are investigated. When the concentration of 1-butanol increases, the phase behavior changes from lower-phase microemulsion (O/W-type) to upper-phase microemulsion (W/O-type) by way of the middle-phase microemulsion; this transition is not observed with higher or lower 1-alcohols; we propose, therefore, that 1-butanol just balances the hydrophilic-lipophilic interactions of PC with water and alkanes and thereby weakens the molecular interaction between the phosphatidylcholine molecules. Both the hydrodynamic diameter ( HD ) and solubilization parameter ( SP ) of the middle-phase microemulsion increase with a decrease in alkyl carbon number ( ACN ) of n -alkane, but interfacial tension (γ) decreases with decreasing ACN . Furthermore, the hydrophilic-lipophilic properties of the PC microemulsions are found to be just balanced by the addition of an n -alkane whose melting point is close to the chainmelting transition temperature ( Tc ) of the respective PC.