HYDROPHILE-LIPOPHILE BALANCE AND CLOUD POINTS OF NONIONIC SURFACTANTS

The comparison of the cloud points of 165 nonionic surfactants was based on their calculated hydrophile‐lipophile balance (HLB) values. The surfactants were classified according to structure and width of molecular weight distribution. Increasing length of the polyoxyethylene moiety increased the HLB and cloud points. At constant HLB, the following features were found to lower the cloud point: decreasing molecular weight, broader molecular weight distribution (probably due to the presence of fractions of such low degree of polyoxyzthylation that they were insoluble in water at all temperatures), branching or greater symmetry of the surfactant molecule, the introduction of olefinic unsaturation, replacement of the terminal hydroxyl by a methoxyl group, and replacement of an ether by an ester bond. The equations for calculating the HLB, which had been derived from emulsification experiments with only a limited number of surfactants, contain the weight‐percentage of polyoxyethylene as the sole variable characterizing the surfactant. Therefore, the calculated HLB is not affected by the surfactant characteristics listed above, which largely govern the values of cloud point, CMC, and interfacial tension. Additional HLB measurements are needed to determine whether the equations used to calculate HLB fully describe the emulsifying characteristics of all nonionic surfactants, i.e., whether all experimental HLB values are really independent of the structure of the surfactant molecules. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company