Quantitative treatment of surface potentials in Langmuir films from aromatic amphiphiles

It is shown that the surface potentials of Langmuir monolayers from aromati c compounds can be interpreted using the three-layer capacitor model of Dem chak and Fort, with the same local dielectric constants employed for alipha tic compounds. Based on new data for monolayers from an acid, amine and est er compounds with an aromatic hydrophobic part, we show that the dielectric constant for the monolayer/water interface region is 6 +/-1. Good agreemen t between experiment and theory was obtained by taking the dielectric const ant of the monolayer/interface as 3.0 +/-0.6, which are essentially the sam e as those obtained for long tail aliphatic compounds. (C) 2001 Elsevier Sc ience B.V. All rights reserved.