Thermodynamics Of Thin Films Research Articles

On Thermodynamics of Thin Films. J Potential

This work acquaints readers with the contemporary apparatus of chemical thermodynamics in the surface and colloid science. The J potential is a new parameter, which represents a series of thermodynamic potentials and is determined for fluid systems as a grand thermodynamic potential in combination with the product of a system volume and some pressure $$p{\kern 1pt} '.$$ A classification has been given with discrimination of the classical J potential (when $$p{\kern 1pt} '$$ is an external pressure) and special J potentials (at other values of $$p{\kern 1pt} '$$). For both classes, hybrid types of the potentials have been considered, when chemical potentials are chosen as variables for one group of components, while the number of molecules or moles is selected as such for another group. The main attention has been focused on the application of all considered types of the J potential to a system containing a planar thin film. In particular, a case has been analyzed in which the pressure in the mother phase of a thin film plays the role of $$p{\kern 1pt} '$$. Resulting fundamental equations have been formulated in terms of the disjoining pressure.

On the Thermodynamics of Thin Films. The Frumkin–Derjaguin Equation

The Frumkin–Derjaguin equation, which is a fundamental relationship in the theory of thin films, relates all surface tensions associated with a wetting film to its disjoining pressure and contact angle. The published ways of proving this relationship have been reviewed and their thermodynamic drawbacks have been analyzed in this work. The relationship has been rigorously derived on the basis of two approaches. The first entails the use of a new thermodynamic potential (J potential), which is defined for fluid systems as the grand thermodynamic potential combined with the product of the system volume and some pressure $$p{\kern 1pt} '$$ (here, the pressure in the mother phase of the thin film is used as $$p{\kern 1pt} '$$). The second approach is based on the Gibbs adsorption equation and entails the use of two dividing surfaces. These approaches yield identical results and suggest that not only temperature, but also all chemical potentials of the film must be fixed when calculating the work of film thinning. The dependence of the contact angle on the disjoining pressure has been considered on the basis of the Young equation. It has been shown that, as the disjoining pressure rises, the thermodynamic surface tension of the film-containing interface increases, while the contact angle decreases. The problems encountered when calculating the contact angles via the disjoining pressure isotherms have been noted.

Chemical and mechanical properties of redox polymer-modified electrodes: Part II. Redox thermodynamics of plasma-polymerized vinylferrocene electrodes

The thermodynamics of thin films (< 200 nm) of plasma-polymerized vinylferrocene (PPVF) deposited on various substrates have been examined in aqueous and non-aqueous electrolytes by controlled potential coulometry. The Nerst plots ( E vs log[ c Fc +/ c F c 0 ]) of these data give slopes in the range of 120–150 mV/decade. Scanning electron microscopy of thicker films (> 400 nm) shows that significant physical damage can occur during electrolysis. These and related observations suggest that the super-Nersntian behavior may be related to stress induced by the forced incorporation of the anion of the supporting electrolyte, as is required to maintain electroneutrality within the films. A mechanical/electrochemical model is employed to explain the origin of the excess free energy required to convert ferrocene sites to ferrocenium sites within the PPVF films.