Equilibrium thin liquid films

The latest results are reviewed and a number of new concepts of the thermodynamics of thin films are formulated. Current definitions of disjoining pressure and their applications for introducing disjoining pressure into thermodynamics of phase equilibria, as well as the new thermodynamic definition of the thickness of thin film, are considered. New approaches to the rigorous definition of disjoining pressure in curved films and films with nonuniform thickness, including transition zones of wetting films, are analyzed. The modulus of Gibbs’ elasticity is derived for the case of a thin film. The role of the elasticity of this type in thin films and its correlation with traditional transverse (Derjaguin) elasticity related to the disjoining pressure are explained.     

Characterization of rhenium-silicon thin films

Rhenium-silicon thin films have been characterized as promising compounds of thermoelectric applications by means of analytical transmission electron microscopy and X-ray diffraction referring to composition, morphology, short-range order and phase formation. Beyond the discussion of the results some methodical aspects and problems are presented.     

Review of CdO thin films

Cadmium Oxide (CdO) thin film is one of the first transparent conducting oxide semiconductors. Its excellent optical and electronic properties have made CdO a promising material for flat panel displays. In this article, we provide a comprehensive review of the state-of-the-art research activities related to the ‘preparation-property-application’ triangle of CdO thin films.     

Birefringence of thin liquid films

Birefringences of oriented aggregates of Na-montmorillonite expanded in sodium chloride solutions were measured and compared with birefringences calculated from Wiener's equation. The difference between the calculated and the observed values is nearly constant in the region of swelling values 10–20 X. It is inferred that the difference comes from the birefringence of the polymolecular water layers and that it is evidence for a specific anisotropic structure. Anisotropy is also shown in some intercalated organic polymolecular films.     

Self-supporting isotopic chromium thin films

Chromium is a shiny, hard and malleable metal, which can be cold rolled in good quality to a thickness below a micrometer. Thinner foils can be obtained by electron-beam gun evaporation or by electroplating. Isotopically enriched material typically has not the quality for cold rolling processes. As ⁵⁰Cr has a natural abundance of only 4.5 % the enriched material is rather expensive so electron-beam deposition is not a good option because of the inherently low yield of the method. In this contribution we present the preparation of self-supporting ⁵⁰Cr thin films by thermal evaporation out of a tantalum crucible as an alternative to electrodeposition. With the described method we obtained self-supporting films with a thickness between 250 and 620 μg/cm².     

Chromatography in thin polyamide films

Summary The applicability of Russian-made samples of polyamide for use as sorbents for the separation of some amino acid derivatives has been shown.M. M. Shemyakin Institute of the Chemistry of Natural Compounds, Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 66–68, January, 1971.     

Membrane proteins in thin films

Molecular functions and structural changes of membrane proteins in an aqueous environment can be elucidated by reaction-induced FTIR difference spectroscopy upon photolysis of caged compounds. The achieved detection of IR band changes even due to single amino acid residues is, however, only possible in the presence of very high protein concentrations, implying that a low water content must be present. In general, the films are formed by controlled dehydration of membrane protein suspensions at reduced pressure and low temperature. For the retention of enzymatic activity of Na,K-ATPase, for example, a cosolvent such as glycerol is required. In order to interprete the results obtained by FTIR spectroscopy, it is important to know whether essential properties of the proteins such as hydration are changed upon film formation. Therefore, a differential scanning calorimetry (DSC) study has been carried out with purified Na,K-ATPase and Ca-ATPase in suspension, in form of pellets obtained by high-speed ultracentrifugation and in thin films. As relevant thermoanalytical properties, the endothermic denaturation transitions of the proteins have been studied. For Na,K-ATPase in the presence of 20% glycerol as cosolvent, a single, comparatively narrow endothermic and irreversible denaturation transition with a denaturation enthalpy of about 1.7 MJ mol⁻¹ and transition temperatures of about 65 and 70°C is found in concentrated suspension and in the state of the pellet, respectively. In the case of thin films suitable for IR spectroscopy, a characteristic change is observed in a reproducible manner. The enthalpy change of the remaining transition around 70°C is reduced but an additional transition at about 77°C is observed. Based on control experiments, the new high temperature transition is attributed to a partially dehydrated state of the protein. Furthermore, a comparatively broad endothermic transition around 20°C is found under conditions of high protein concentrations (film), which is tentatively assigned to a transition of the lipid environment of this integral membrane protein. Similar results are found for Ca-ATPase films. In the absence of glycerol, the deoxycholate treated enzyme in suspension exhibits a narrow endothermic main transition at 52°C with a denaturation enthalpy around 0.9 MJ mol⁻¹. For the film of this protein, two almost equally large endothermic transitions are found at 59 and 77°C. Also here, the data are characteristic of partial protein dehydration. These results show clearly that DSC can easily be applied in a sensitive manner to control and characterize the integrity and hydration properties of concentrated protein samples in thin films.     

Mesoporous silicon oxynitride thin films

Highly-ordered, pore-modified with amine groups, and glass-like mesoporous silicon oxynitride thin films were prepared by heat treatment of as-synthesized mesoporous silica thin films in a flowing ammonia environment at high temperatures.     

Fluorescence in thin liquid films

The fluorescence properties of Rhodamine B in thin liquid films, formed from a number of anionic, cationic and non-ionic surfactant solutions, were investigated. Laser excitation was used and the emission was monitored over a period of time. Drainage profiles with light and dark fluorescence fringes were recorded with plane-polarized radiation. Change of polarization caused profound changes in the appearance of the profiles. The distribution of dye molecules between surfaces of the film and its interior was assessed and found to be related to the speed of film drainage. Expressions were established for the relation between fluorescence fringes and film thickness at different orientations of the film surface to the emission measurement direction.     

Magnetic cobalt nanowire thin films

Two-dimensional (2D) and three-dimensional (3D) magnetic cobalt nanowire thin films with tunable 3-10 nm wire diameters have been electrodeposited using mesoporous silica templates containing 2D hexagonal or 3D cubic pore channels. As compared to bulk cobalt films, the cobalt nanowire thin films exhibit enhanced coercivities and controllable magnetic anisotropy through tuning of the mesostructure and dimension of the nanowires. Such novel magnetic nanowire thin films may provide a new platform for high-density information storage applications.     

Polyelectrolytes in thin liquid films

The review addresses the influence of polyelectrolytes on the statics and dynamics of thin liquid films. Both, changes of interfacial and bulk properties, contribute to the overall behaviour of thin films formed from aqueous polyelectrolyte solutions. Therefore, the chapter is separated into two parts: polyelectrolytes at film interfaces and polymers in film bulk.     

Photoluminescence study of sexithiophene thin films

To determine the exciton diffusion length of sexithiophene (6T) thin films, quenching of the photoluminescence (PL) of vacuum-deposited 6T films on TiO2 and on quartz has been investigated. For films with a thickness of more than 22 nm and at temperatures below 100 K, additional PL lines appear in luminescence spectra. This feature is related to the structural properties of 6T films. The PL intensity is thermally activated with an activation energy of 18 meV on TiO2 and 6 meV on quartz. When 6T is applied on TiO2, exciton quenching occurs for films up to 120 nm. For 6T on quartz this value is reduced to 60 nm. By comparing the relative luminescence intensities of 6T on quartz and on TiO2 substrates, an exciton diffusion length of 60 +/- 5 nm is derived.