The hydrophilic-lipophilic balance of carboxylate and carbonate modified nonionic surfactants

Abstract

The shift of the phase inversion temperature (PIT) of n-octane/water nonionic surfactant (C13EO5) emulsions was studied as a function of increasing amounts of an additional second surfactant in order to rank them according to their hydrophilic-lipophilic-balance. Two different groups of modified nonionic surfactants were investigated with the objective to quantify the contribution of the modified groups to the HLB value of the surfactants. One modification was obtained by copolymerization of ethylene oxide and CO2 for the synthesis of the hydrophilic head group. The second was the capping of the head group with a −CH2−COOH group. Well-defined polyethoxylated alkyl surfactants (CiEj) show a linear variation of the PIT with their mole fraction X2 and can be used as standards to calibrate a scale in terms of dPIT/dX2. With this method, it can be shown that the −CH2−COOH decreases the HLB value in comparison to an unmodified version of the same surfactant when measured at acidic pH values. The modification with CO2 increases the HLB value almost in the same way as the addition of the same number of EO units. This observation reveals the potential of a replacement of EO by CO2 to a certain extent, saving fossil resources, reducing the carbon footprint of the products and introduces a new tuning parameter for chemical and physical properties of the new group of surfactants.