Patrycja Dynarowicz

Electrical properties of some adsorbed films at the water―air interface

Abstract Measurements of surface potential (ΔV) and surface tension (Δσ) of aqueous solutions of acetic acid, chloro-, dichloro-, trichloroacetic acid, and alcohols (methanol, ethanol, 2,2,2-trifluoroethanol) were used for the determination of effective dipole moments (μ) and their separate components. For this purpose, the Helmholtz equation (in the form presented by Demchak and Fort (5)) have been applied. The contributions from the reorientated water molecules ( μ 1 /ϵ 1 ), and from hydrophilic ( μ φ - COOH , μ φ- OH ) and hydrophobic ( μ φ- CH 3 , μ φ- CH 2 Cl , μ φ- CHCl 2 , μ φ- CF 3 ) groups and the local dielectric permittivity in the vicinity of these groups were calculated.

Electrical properties of adsorbed films of some aromatic compounds at the water/air interface

Abstract Surface tension (Δσ) and electric surface potential (ΔV) measurements of aqueous solutions of some aromatic compounds (benzoic, p-toluic and p-fluorobenzoic acid, benzaldehyde, and tolualdehyde) were used to determine effective dipole moments using the Helmholtz equation. Knowing the effective dipole moments the surficial orientations of adsorbed molecules were estimated. Using the latter and applying the formula presented by R. J. Demchak and T. Fort (J. Colloid Interface Sci. 46, 191 (1974) ) the separate components of effective dipole moments connected with reorientation of water molecules ( μ 1 ϵ 1 ), hydrophilic ( μ φ- COOH , μ φ- CHO ) and hydrophobic ( μ φ- CH 3 , μ φ- F ) groups, and local dielectric permittivities in the vicinity of these groups (ϵ2, ϵ3) were calculated.

Stability of dialkyldimethylammonium bromides monolayers spread at the water/air interface

Abstract The pressure/are ( π A ) isotherms of Langmuir monolayers of a series of the dialkyldimethylammonium bromides with alkyl chain lengths of 12, 14, 16 and 18 have been studied in terms of their stability at the water/air interface. Only dihexadecyldimethylammonium bromide (DHAB) and dioctadecyldimethylammonium bromide (DOAB) form stable Langmuir monolayers whereas the other compounds investigated desorb from the interface. The change of the area available for one molecule in the monolayer with time at different temperatures of the subphase (water and 0.1 M KBr aqueous solution) was investigated. The process of desorption was found to be controlled by the mechanism of diffusion. Applying the Ter Minassian-Saraga model [L. Ter Minassian-Saraga, J. Chim. Phys. 52 (1955) 181], the kinetics parameters corresponding to the desorption and diffusion, for DDAB and DTAB, were estimated.

Surface properties of some acetic acid derivatives at the water/air interface

Abstract Electric surface potential (Δ V ) and surface tension (Δ σ ) measurements of aqueous solutions of trifluoro-, trichloro-, tribromo-, and trimethylacetic acid were used to determine the surface activity, orientation of molecules, effective dipole moments (connected with water molecules, hydrophilic and hydrophobic groups), and local dielectric permittivity of the surface layer.

Electrical properties of the mixed films of 2,2,2-trifluoroethanol—ethanol at the water/air interface

Abstract The coadsorption of 2,2,2-trifluoroethanol and ethanol at free water surface was investigated. The effective dipole moment of 2,2,2-trifluoroethanol has been determined using the Helmholtz equation. The calculations have been done on the base of surface excess values, got from surface tension measurements and surface potential changes of aqueous solutions of 2,2,2-trifluoroethanol. Knowing the effective dipole moment and composition of mixed film the surface potential was calculated.

Surface orientation and electrical properties of n-butyl alcohol isomers at the free surface of water solution

Abstract Electric surface potential (Δ V ) and surface tension (γ) measurements of aqueous solutions of n-butyl alcohol, iso-, sec-, tert-butyl alcohol, butandiol, trichloro-tert-butyl alcohol and pivalaldehyde were used for the determination of the monolayer structure parameters, e.g. effective dipole moments connected with the reorientation of water molecules, hydrophilic and hydrophobic groups, local dielectric permittivities in the vicinity of these groups and surface orientation angles of adsorbed molecules at the water/air interface.

Distribution and the energetics of orientation of molecules adsorbed at the water/air interface

Abstract The average orientation of molecules adsorbed at the water/air interface can be determined from the function = μ /μ, where μ is the effective dipole moment of the adsorbed molecule and μ is the dipole moment of the free molecule. The behaviour of molecules adsorbed at the free surface of water was assumed to be similar to that of a system of permanent dipoles in the external field, with the simple interaction given by a cos θ where a=w/kT (w is the energy of orientation of the adsorbed molecule). When calculated from the probability density function parameter, a has the mean value of 0.4 for the carboxylic acids, alcohols, phenol (and its derivatives), amides and amines investigated, which indicates that the distribution of angles is very broad. The energy of orientation of the adsorbed molecule is rather small (average, 0.971 kJ mol−1) which could be expected for molecules that form gaseous films at the water/air interface.

Langmuir-Blodgett manipulation of capped cadmium sulfide quantum dots

Abstract Cadmium sulfide quantum dots, as prepared by the single source approach, have been used as the starting materials for Langmuir–Blodgett deposition on several types of substrates. Conventional procedures, such as isotherms and Brewster angle measurements, were used to investigate the manipulation of organically capped Q-CdS. The optical properties of the films obtained were studied and compared to solutions containing the original dots.

Surface orientation and effective dipole moments of some salicylic acid derivatives at the water/air interface

Abstract Surface tension (δσ) and electric surface potential (δV) measurements of aqueous solutions of salicylic, acetylsalicylic, and sulfosalicylic acid and salicylaldoxime were used for determination of the surface activity, orientation of molecules, the effective dipole moments, and standard free energy of adsorption.

Molecular interaction in mixed spread films at the water/air interface

Abstract The treatment of a two-dimensional system of three components of isomegetic molecules, adapted from statistical thermodynamics, is used to derive parameters which can be related to the interaction between molecules at the collapse pressure in mixed spread films at the water/air interface. The theory is illustrated by the mixed system of stearic acid and 1-octadecanol.