Katarzyna Kita

Molecular interaction in mixed monolayers at the air/water interface

Abstract Different approaches used to characterize molecular interaction in mixed monolayers, formed either by adsorption or by spreading at the air/water interface, are reviewed in this paper.

Properties of anionic–cationic adsorption films

Abstract The regular solution model for mixed monolayers was used to calculate the composition of the anionic–cationic adsorption films and parameters characterizing the mutual interactions between their components. The surfactants forming the mixed monolayers were decylpyridinium chloride and sodium hexylsulfonate. The monolayers under investigation were all adsorbed from equimolar solutions of surfactants. The results obtained show that the composition of the anionic–cationic adsorption films is dependent on the concentration and the kind of inorganic electrolyte present in the solution. The values of surface interaction parameter β , being all negative, show that the adsorbed components attract mutually. It has been observed that the strength of the attraction mentioned is also dependent on the factors given above for the composition of mixed adsorption films. It has also been established that the system examined here behaves, both qualitatively and quantitatively, in very similar manner to the previously investigated mixture of decylpyridinium chloride and sodium octylsulfonate, i.e. of surfactants with the same difference in length of the hydrocarbon chains as examined in this work.

Influence of apolar group structure on the properties of Langmuir monolayers of polyphenyl carboxylic acids

Abstract Langmuir monolayers of purely aromatic carboxylic acids are investigated through surface pressure ( π ), surface potential (Δ V )–area ( A ) isotherms and Brewster angle microscopic studies. The monolayer characteristic of the basic compound, namely 5′-phenyl-1,1′:3′,1″-terphenyl-4-carboxylic acid, abbreviated as PTCA, is compared with its derivatives containing hydrophilic (nitro) or hydrophobic (phenyl) substituents attached to the symmetrical triphenylbenzene core. The nature of the substituent as well as its position (2′ or 4′) has profound influence on the monolayer organization. Also, chemical modification leading to rotation restrictions of the hydrophobic moiety of PTCA was found to alter significantly its characteristic as Langmuir monolayer. The results are discussed in view of different orientation and different molecular packing arrangements.

Langmuir monolayers formed by a novel group of aromatic amphiphiles

Langmuir films formed by a group of polyphenyl carboxylic acids, derivatives of symmetrical triphenylbenzene, were investigated at the air/water interface. Surface pressure and electric surface potential measurements were supplemented by Brewster angle microscope images. The two-fold decrease in area per molecule, observed within the plateau region of the pressure/area isotherms, is tentatively attributed to conformational changes of the triphenylbenzene ring system upon compression.

Langmuir monolayers from substituted aromatic carboxylic acids

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 moment calculated using semiempirical quantum methods. The local dielectric permittivity in the vicinity of hydrophobic groups was calculated to be 4.8. By adopting a dielectric constant of 7.6 in the vicinity 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.