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    Dynamic Properties of Supercritical C14TEMPO Monolayers at the Air/Water Interface

    Year: 2001

    Journal: J. Phys. Chem. B 2001, 105, 514-519, 20111221

    Authors: Michael J. Johnson, David J. Anvar, Janusz J. Skolimowski, and Marcin Majda

    Organizations: Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460 Department of Organic Chemistry, University of Narutowicza 68, 90-136, Poland

    Monolayers of 4-tetradecaneamido-2,2,6,6-tetramethyl-1-piperidinyloxy (C14TEMPO) were investigated at the air/water interface. Pressure-area diagrams and Brewster angle microscopy provided evidence of supercritical state of this monolayer at temperatures as low as 2 °C. The supercritical character of C14TEMPO Langmuir monolayers allowed the 2-D voltammetric measurements of its lateral diffusion constant, D, to be extended into a previously inaccessible region of low surface densities with mean molecular areas A ~ 600 Å2/molecule. At A > 250 Å2/molecule, D becomes independent of the C14TEMPO surface concentration and depends solely on the hydrodynamic coupling of the polar headgroup to the aqueous subphase. These measurements and the supercritical state of C14TEMPO monolayer open a possibility to probe the viscoelastic properties of the water liquid-vapor interfacial region.