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    Langmuir monolayers from substituted aromatic carboxylic acids

    Year: 2001

    Journal: Progr Colloid Polym Sci (2001) 118:5-10, 20111221

    Authors: P. Dynarowiczaka, K. Kita, P. Milart, A. Dhanabalan, A. Cavalli, D. A. da Silva Filho, Osvaldo N. Oliveira Jr.

    Organizations: aJagellonian University, Faculty of Chemistry, Ingardena 3, 30-060 Krakow, Poland, bEindhoven University of Technology, Laboratory of Macromolecular and Organic Chemistry, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands cInstituto de Biociancias, Letras e Ciancia Exatas, Universidade de Estado de Sao Paulo, Sao Jose do Rio Preto, SP, Brazil dUniversidade Estadual de Campinas- Instituto de Fisica Gleb Wataghin Campinas, SP, Brazil eInstituto de Fisica de Sao Carlos, Universidade de Sao Paulo, CP 369, CEP, 13560-970, Sao Carlos, SP, Brazil

    A series of 5´-phenyl-m-terphenyl carboxylic acid derivatives with methyl, phenyl, chloro, p-chlorophenyl and fluoro substituents have been characterised as Langmuir monolayers at the air/water interface by measuring the surface pressure and the electric surface potential upon monolayer compression. The three-layer capacitor model proposed by Demchak and Fort [(1974) J Colloid Interface Sci 46:191] is employed to relate the experimental surface potentials of the monolayers investigated to the molecular dipole movement calculated using semi-empirical quantum methods. The local dielectric permittivity in the vincinity of hydrophobic groups was calculated to be 4.8. By adopting a dielectric constant of 7.6 in the vincinity of the hydrophilic groups, the contribution from the water reorientation was found to be 0.15 D, very close to that estimated for small aromatic molecules forming Gibbs monolayers at the air/water interface.