title: Experimental validation of the Helmoltz equation for the surface potential of Langmuir monolayers.
abstract: We show in this paper that monolayers of the nonhydrophilic F8H18 semifluorinated n -alkane constitute when spread on the hydrophobic top of an alamethicin Langmuir monolayer, a very good experimental system in order to check the validity of Helmoltz equation. This system allows for a good agreement between measured and calculated surface potentials of unionized Langmuir monolayers. We show also that the relative dielectric constant of the F8H18 monolayer does not vary upon compression of the monolayer, the measured 2.9 value is in a very good agreement with literature data. We attribute this behavior to the self-aggregation of F8H18 molecules in nanosized circular domains whose size remains constant upon compression as shown by atomic force microscopy.
authors.affiliation: Laboratoire de Neuro-Physique Cellulaire, Université Paris Descartes, 45 rue des Saints-Pères, 75006 Paris, France. abdel.elabed@parisdescartes.fr
authors.forename: Abdel I
authors.initials: AI
authors.lastname: El Abed
mesh_terms: D000408:Alamethicin / Q000737:chemistry; D000473:Alkanes / Q000737:chemistry; D017097:Electric Impedance; D057927:Hydrophobic and Hydrophilic Interactions; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D011312:Pressure; D015203:Reproducibility of Results; D013499:Surface Properties
chemical_list: D000473:Alkanes; D000408:Alamethicin; C022883:octadecane