Electrostatic theory on the formation of monodispersed two-dimensional nanosize clusters of partially fluorinated surfactants

The electric repulsive energy of circular disks of charged surfactants in t he monolayer on an aqueous solvent was calculated. Because charged surfacta nts of a two-dimensional monolayer in a homogeneous configuration would exh ibit high electrical repulsion energy, they tend to segregate into heteroge neous clusters if it is possible. On the other hand, the line tension energ y of the peripheries of the small clusters antagonizes the cluster formatio n. The screening of the electric repulsion by added ions in the aqueous sol vent bed also affects the size of the cluster. The sum of the screened elec tric repulsive energy and the line tension energy was minimized to predict a circular disk. The theory is applied to-explain the observed monodisperse d, nanometer-sized clusters of partially fluorinated long-chain acids on La ngmuir monolayers as shown in the atomic force microscopy images by Kato an d co-workers (Kata, T.; Kameyama, M.; Ehara, M.; Iimura, K. Langmuir 1998, 14, 1786).