title: Chemical potential of a nonionic surfactant in solution.
abstract: The chemical potential of a surfactant in solution can be calculated from the Gibbs adsorption equation when the surface excess of the surfactant and the surface tension of the solution as a function of surfactant concentration are known. We have investigated a solution of the nonionic surfactant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the polar solvent 3-hydroxypropionitrile at concentrations below and above the critical micelle concentration (cmc). Neutral impact collision ion scattering spectroscopy was applied for the direct measurement of the surface excess of POPC as a function of concentration. The Gibbs adsorption equation was applied in conjunction with surface tension measurements to evaluate the chemical potential and the activity coefficients of POPC, respectively. We find that the solution shows ideal behavior up to the cmc and that the chemical potential remains constant at concentrations larger than the cmc.
authors.affiliation: University of Leipzig, Wilhelm-Ostwald-Institute of Physical and Theoretical Chemistry, Linnéstrasse 2, 04103 Leipzig, Germany. thomaskrebs@gmx.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Krebs
authors.forename: Gunther
authors.initials: G
authors.lastname: Andersson
authors.forename: Harald
authors.initials: H
authors.lastname: Morgner