Effect of additives (inorganic salts and polyols) on the cloud point of water-polyglycerol didodecanoate ((C
11)
2G
n) system was investigated as a function of the weight fraction of polyglycerol chain in whole surfactant, W
H/W
S, which is directly related to Griffin’s HLB number (=20×W
H/W
S). 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 Na
2SO
4 largely decrease the cloud point, whereas NaSCN and 1,3-butanediol abruptly increase it with increasing the salt concentration at a fixed W
H/W
S. However, in the absence of additive, the cloud point drastically increases with a small increase in the hydrophilic chain length or W
H/W
S. It means that the solubility of polyglycerol surfactant in water is not largely influenced by temperature but is highly dependent on W
H/W
S. The apparent large effect of additive on the cloud point is mainly attributed to the temperature-insensitiveness of the phase behavior of (C
11)
2G
n. Single-phase or three-phase microemulsions are formed at the water/oil ratio=1 in water/(C
11)
2G
n/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 W
H/W
S. However, both W
H/W
S 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.
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