Stability of thin films

Even this short list of examples - aqueous, polymer, and metal films - shows that we deal with very different situations. Polymer and metal films are usually Uquid only above room temperature when the material is heated above the melting temperature. In addition, the polymer or metal is usually not in contact with a reservoir. The thermodynamic condition for equilibrium is therefore not a constant chemical potential but a constant amount of material. We now focus on the case that the liquid is practically nonvolatile and its amount is supposed to be constant. 

Let us start with macroscopic films. In macroscopic films, which are thicker than 100nm, interfacial forces between the solid-liquid and the liquid-gas interfaces are usually negligible. A liquid film is stable, if the free energy of creating a solid-liquid and a liquid-gas interface is less than the free energy of the bare solid surface Yl + Yls Ys- Here, Yl. Yls Ys surface tensions 

The last term represents the gravitational work required to form a film of thickness ho. It represents the hydrostatic pressure. The height is 

With the capillary constant Xc = Yr/eg (Eq. (5.7)) and applying Young s equation, we can write 

A liquid film of actual thickness h is stable if H ho- If the film prepared is thinner, h ho, it will eventually form holes and dry patches until the patches have a thickness h = ho given by Eq. (7.30). 

---

Thomas, R. E. Gaines, B. G. "Methodology for Designing Accelerated Aging Tests for Predicting Life of Photovoltaic Arrays" Department of Energy/National Bureau of Standards Workshop on Stability of Thin Film Solar Cells and Materials, Washington, D.C., May 1-3, 1978. 

V Brusic, J. Horkans, and D. J. Barklay offer an authoritative review of the electrochemical aspects of fabrication and of evalution of the stability of thin film storage media. Recent developments have led to improved thermodynamic stability, thereby rendering thin film disks suitable for high density storage applications. 

Pitts, R.R., Smith, D., Lee, S., and Tracy, E. Interfacial Stability of Thin Film Hydrogen Sensors, FY 2004 Annual Progress Report, VI.3, DOE Hydrogen Program, 2004. 

Gao, T. Gao, J. Sailor, M. J., Tuning the response and stability of thin film mesoporous silicon vapor sensors by surface modification, Langmuir. 2002, 18, 9953 9957... 

Bibette has used this method to study the effect of osmotic pressure on the stability of thin films in concentrated o/w emulsions [96], by means of an osmotic stress technique. The emulsion is contained in a dialysis bag, which is immersed in an aqueous solution of surfactant and dextran, a water-soluble polymer. The bag is permeable to water and surfactant, but impermeable to oil and polymer. The presence of the polymer causes water to be drawn out of the emulsion, increasing the phase volume ratio and the deformation of the dispersed droplets (Fig. 10). 

Zaitsev (Zl), 1960 Theoretical treatment of stability of thin film of viscous liquid (with surface tension) on wall in the presence of a cocurrent gas stream. 

Van der Waals forces The case pex = 0 is purely academic, since van der Waals interactions are omnipresent and are known to affect the stability of thin films. In the non-retarded case, the van der Waals disjoining pressure is... 

Maldarelli, Ch. and Jain, R.K., The hydrodynamic stability of thin films, in Thin Liquid Films, Ivanov, I.B., Ed., Marcel Dekker, New York, 1988, p. 497. 

Danov, K.D. et al., Bancroft rule and hydrodynamic stability of thin films and emulsions, in Proc. First World Congress on Emulsion, 19-22 Oct., Paris, 1993, p. 125. 

Tait, Properties of Matter, 1899, 256 for forms of films on frames, etc., see Searle, Proc. Cambr. PhiL Soc.9 1913, 17, 285 Michl, Phys. Z.9 1913, 14, 1218. For stability of thin films, Phillips and Rose-Innes, Proc. Phys. Soc., 1915, 27, 328. For pressure in a soap bubble, Kuenen, Proc. K. Akad. Wetens. Amsterdam, 1915,17, 946 Comm. Leiden, 1914,154 a). On the effect of evaporation on the stability of liquid films and froths, see Talmud and Suchowolskaja, Z. phys. Chem.9 1931, 154, 277 Neville and Hazlehurst, J. Phys. Chem.91937,41, 545. 

The stability of thin films against rupture (Section 13.4.1). 

The stability of thin films and the catastrophes of film systems may play a crucial role in the case of chemical reactions proceeding at the boundary of a liquid phase and another phase. Phase transitions are of a great significance in physical chemistry. The diffraction phenomena for the... 

The electrostatic components of disjoining pressure and free energy of interaction in the film, given by eqs. (VII.21) and (VII.22), are positive, i.e. represent repulsion. These quantities may be compared with corresponding molecular components that are negative and describe attraction. This allows one to analyze according to the DLVO theory the stability of thin films, and consequently of disperse systems stabilized by adsorption layers. Carrying out summation of eqs. (VII.21) and (VII.22) with expressions (VII.9) and (VII. 10) one obtains ... 

Role of Adsorbed Surfactant Layer. Foams, irrespective of the nature of liquid and gas involved, require a third component for stabilization of thin films (lamellae) of the liquid. In the familiar case of aqueous soap films, this third component is the soap, a surface-active chemical that adsorbs at the gas—liquid interface and lowers the surface tension of water. The two effects, adsorption at the liquid surface and the depression of surface tension, are intimately linked and occur concomitantly. The adsorption is defined as the excess moles of solute per unit area of the liquid surface. In a binary system, this surface excess can be directly related to the lowering of surface tension by Gibbs adsorption equation ... 

VI.A.2 Interfacial Stability of Thin Film Hydrogen Sensors... 

PROBABLE FATE photolysis, no information is available, may not be an important fate process based on the stability of thin films exposed to light >300 nm, if released to the atmosphere, it will react with hydroxyl radicals, with a half-life of 1.23 hr oxidation probably not important hydrolysis probably an important process, hydrolysis half-lives of endosulfan isomers 35.4-37.5 days at pH 7 and 150.6-187.3 days at pH 5.5 volatilization no information available, evaporation from water is probably an important fate process based on an estimated half-life of 43 hr from a river Im deep, flowing 1 m/s and a wind velocity of 3 m/s, evaporation from lakes and deeper streams and rivers will be slower sorption no information available, if released to soil, it will be expected to bind to the soil, if released to water, it will be expected to bind to the sediment biological processes no information available... 

In order to consider the linear stability of thin film wavy motions governed by the B-M problem, we must first determine the steady-state solutions of the evolution equations presented. Then we can perturb about the steady-states using the normal modes. Assuming that the perturbing quantities are small, we linearize the evolution equations about the steady-state solutions to obtain an eigenvalue system for the considered B-M problem. 

Danov, K.D., Velev, O.D., Ivanov, I.B., and Borwankar, R.P., Bancroft rule and hydrodynamic stability of thin films and emulsions, in First World Congress on Emulsion, October 19-22, Paris, France, 1993, p. 125. Kunieda, H., Evans, D.F., Solans, C., and Yoshida, Colloids Surf., 47, 35, 1990. 

---