2002 Volume 51 Issue 6 Pages 379-386
Effect of additives (inorganic salts and polyols) on the cloud point of water-polyglycerol didodecanoate ((C11)2Gn) system was investigated as a function of the weight fraction of polyglycerol chain in whole surfactant, WH/WS, which is directly related to Griffin’s HLB number (=20×WH/WS). The average number of dodecanoic acid residues attached to polyglycerol, m, is in the range of 1.6-2.3. Unlike an ordinary commercial polyglycerol surfactant, the surfactants used in this study contain a very small amount of unreacted polyglycerol. Compared with poly(oxyethylene)-type nonionic surfactant aqueous solutions, NaCl and Na2SO4 largely decrease the cloud point, whereas NaSCN and 1,3-butanediol abruptly increase it with increasing the salt concentration at a fixed WH/WS. However, in the absence of additive, the cloud point drastically increases with a small increase in the hydrophilic chain length or WH/WS. It means that the solubility of polyglycerol surfactant in water is not largely influenced by temperature but is highly dependent on WH/WS. The apparent large effect of additive on the cloud point is mainly attributed to the temperature-insensitiveness of the phase behavior of (C11)2Gn. Single-phase or three-phase microemulsions are formed at the water/oil ratio=1 in water/(C11)2Gn/hydrocarbon(heptane, decane, hexadecane, and m-xylene) systems. As well as the cloud point, the three-phase temperature or HLB temperature is abruptly increased with a small increase in WH/WS. However, both WH/WS for the HLB temperatures are coincident around 25°C, since the hydrophilicity of polyglycerol chain per weight is almost similar to that of poly (oxyethylene) chain at room temperature.
