Abstract
Abstract LogP values for several nonionic surfactants were measured by the slow stirring/surface tension method. Aqueous surfactant solution is equilibrated with octanol. A surface tension technique is used to determine the concentration in the aqueous phase. Interference from octanol, which is surface active, is prevented by evaporation and re-dissolution of the sample. The effect of initial concentration on the observed logP value is discussed. Above a certain concentration the amount of surfactant in the aqueous phase exceeds the critical micelle concentration (cmc). In this region logP appears to decrease markedly with initial concentration. Using a simple model, which includes the effect of octanol on the cmc, the apparent logP can be corrected for this micellisation effect. With a tristyrylphenol ethoxylate the concentrations in aqueous and octanol phases were determined by UV absorption, giving a logP value in good agreement with the surface tension method. For a series of commercial undecyl ethoxylates, the logP value was found to decrease with increasing length of the EO chain. Products with more than 4 EO have a logP less than 3, indicating that they are unlikely to bioaccumulate.
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