3-PHASE BEHAVIOR AND HLB NUMBERS OF BILE-SALTS AND LECITHIN IN A WATER-OIL SYSTEM

A bile salt forms a surfactant phase (microemulsion) together with a cosurfactant such as monoglyceride. When the hydrophile-lipophile property of a mixed amphiphile (bile salt + monoglyceride) is just balanced to a given brine-oil system, the surfactant phase coexists with excess water and oil phases. According to the method in the previous paper (J. Colloid Interface Sci. 107, 129 (1985)), we calculated the HLB numbers of bile salts, which are in the range 20-25 at 1% NaCl and 30°C. These values are quite large compared to an ordinary ionic surfactant such as sodium dodecyl sulfate (17.2 under the same conditions) and it means that a bile salt is very hydrophilic. The HLB number of a bile salt decreases with the decreasing number of hydroxyl groups in lipophilic moieties whereas the effect of hydrophilic groups (-COONa or -SO3Na) on the HLB number is rather small. The solubilizing power of bile salts decreases significantly with decreasing hydroxyl groups. In comparison with a SDS system, a bile salt serves to break a lamellar liquid crystal. The HLB number of soybean lecithin was also determined to be 9.2-9.5. © 1990.