Transfer of Homologous Alkanols from Water to Fluorocarbon and Hydrocarbon Surfactant Micelles

Abstract

Abstract The critical micelle concentration, cmc, of sodium perfluorooctanoate, SPFO, and sodium dodecyl sulfate, SDS, in the presence of two homologous series of alkanols (l-alkanols and ω-phenyl-l-alkanols) at very low concentrations of the alkanols Ca, was measured by a differential specific conductivity method. The free energy of transfer per CH2 group in the alkanols from water to the respective micelles, ΔG°(CH2), has been estimated from a linear relation of the rate of cmc-decrease, Δcmc/ΔCa, with the number of carbon atoms in the alkyl chain of alkanols. The respective values of ΔG°(CH2) obtained for two series of homologues added to a given surfactant are in good agreement with each other: ΔG°(CH2) is −1.73 kJ mol−1 in the SPFO system and −2.30 kJ mol−1 in the SDS system. The former has been found to be smaller in magnitude than the latter. On the basis of ΔG°(CH2), a thermodynamic parameter has been proposed which characterizes the degree of modification of a medium from its pure liquid state to surfactant micelles or to interfaces composed of a hydrocarbon or a fluorocarbon.