Role of Surface Forces in the Stability of Evaporating Thin Liquid Films That Contain Surfactant Micelles
✍ Scribed by Theodor Gurkov; Krassimir Danov; Norbert Alleborn; Hans Raszillier; Franz Durst
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 449 KB
- Volume
- 198
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
human eye, in which the conditions for film rupture represent We consider an evaporating liquid film which lies on a planar the main objective of investigation. Numerous studies have heated solid substrate. The film contains a dissolved surfactant at been devoted to this problem, either in the geometry of free a high concentration, so that micellar aggregates exist in the bulk. films or for liquid layers on solid substrates. Scheludko (1) Linear stability analysis of this system is performed by investigatsuggested the idea that rupture instability results from ampliing the time evolution of the amplitude of fluctuation waves. The fication of spontaneous fluctuations in the shape of the fluid liquid-vapor interface is regarded as a two-dimensional continuum interfaces, under the action of long-range attractive van der characterized by intrinsic viscosity, specific adsorption, and sur-Waals forces. The latter are always operative at small thickface tension. The latter quantities depend on the instantaneous nesses, below Ç100 nm. subsurface concentration of surfactant monomers (subject to fluctuation) and upon the temperature. At small Reynolds and large
A surfactant monolayer, spread on the liquid interface, is Peclet numbers, and for thin films, the lubrication approximation well known to damp the wave motion ( ). The phenomenon model can be applied to solve the hydrodynamic problem. In the is due to the fact that as the monolayer is compressed and balance of normal stress at the fluid interface, we account for the expanded, the local variations of the adsorption lead to contribution of intermolecular forces. There are van der Waals, changes in the interfacial tension. The combination of the electrostatic, steric, and oscillatory structural interactions, which resulting tension gradients (Marangoni effect) with the inare described in terms of separate components of disjoining presterfacial viscous friction brings about suppression of the sursure. The oscillatory structural forces are due to the presence of face waves. surfactant micelles or other colloidal particles in the film. These Linear stability analysis for an isothermal nondraining forces turn out to have the highest magnitude, and are of great film on a horizontal plate was carried out by Ruckenstein and importance for the stability. We solve numerically the evolution equation for the fluctuation, thus finding the critical thickness of Jain (3), who accounted for the van der Waals interactions in film rupture and the critical lateral wave number. The influence the context of the so-called ''body force'' approach. A gradiof the surfactant type and concentration and the relative signifient of appropriate potential energy was added to the Naviercance of the particular interactions under different conditions are Stokes equations in the liquid film. Williams and Davis (4) discussed in detail. ᭧ 1998 Academic Press proposed a nonlinear theory for the same system. The treat-Key Words: evaporating thin liquid films; linear stability analysis; ment was based on the fact that the unstable fluctuation oscillatory structural forces; surfactant at a high concentration; indisturbances had wavelengths much larger than the film terfacial viscosity; Marangoni temperature and adsorption effects. thickness. Constant interfacial tension was assumed by Williams and Davis (4); i.e., the Marangoni effects were discarded. The nonlinear analysis of de Wit et al. (5) included