Catálogo de publicaciones - libros

We present a conclusive overview of the stability conditions and the dewetting scenarios of thin liquid coatings. The stability of thin films is given by the effective interface potential φ () of the system and depends among other parameters on the film thickness . In the case of unstable or metastable films holes will appear in the formerly uniform layer and the film dewets the substrate. We describe the analysis of emerging hole patterns and how to distinguish between different dewetting scenarios. From this analysis we derive the effective interface potential for our particular system, φ(), which agrees quantitatively with what is computed from the optical properties of the system. Our studies on thin polystyrene films on Si wafers of variable Si oxide layer thickness demonstrate that the assumption of additivity of dispersion potentials in multilayer systems yields good results and are also in accordance with recent numerical simulations.

We outline some recent developments in the theoretical description of structure formation in thin liquid films. The main focus is systems involving a single layer of liquid on a solid substrate that can be described using an evolution equation for the film thickness profile. We review the history of the subject and we sketch important experimental and theoretical results and practical applications. After discussing the classification of the different cases, we introduce the common mathematical framework for studies of thin films of soft matter, namely by deriving the generic evolution equation for such films from the Navier-Stokes equations. In the main part we first introduce the different possible geometries and the transitions between them, i.e. from homogeneous to inhomogeneous substrates, or from horizontal to inclined substrates. We then present the physical questions posed by the individual systems and discuss approaches and results for:

Finally, we shortly discuss extensions of thin film studies beyond the case of a single evolution equation. In particular, we introduce two different models based on two coupled evolution equations describing the dynamics of dewetting of a two-layer thin film and the chemically driven self-propelled movement of droplets, respectively.

We discuss the mathematical description of self-similar phenomena. Such phenomena cover many different length or time scales. Self-similarity allows a transformation from one scale to another and final reduction to a system that has only one scale. This is illustrated through a series of examples including diffusion processes, drop pinch-off and nanojets.

We discuss a few situations where a liquid is brough into contact with a solid, with air around. Starting from the very classical Young equation, we present recent developments in the field, such as the possibility of generating spontaneous motions, or the wetting of textured surfaces. Then, we describe a few dynamic situations, in particular wicking, creeping and coating.

A film falling down an inclined plane has been an active topic of fundamental research at the international level for several decades both theoretically and experimentally and is now a classical hydrodynamic instability problem. However, the dynamics of a falling film in the presence of additional complexities, as compared to the classical problem, has largely been ignored by the majority of studies in falling films, even though these complexities are crucial in most situations of practical interest. These additional factors include heated substrates and three-dimensional effects. Here we present very recent and most-up-to-date developments for the problem of a falling film in the presence of these complexities and we outline open questions and issues which have not been resolved.

Analysis is carried out to examine the miscible fingering phenomenon when a fluid with a lower electrolyte concentration advances into one with a higher concentration. Unlike earlier miscible fingering theories, the linear stability analysis is carried out in the self-similar coordinates of the diffusing front. The dominant destabilizing mode is shown to be a localized concentration disturbance within the diffusive layer. However, transverse diffusion is shown to eventually stabilize the instability at time that scales as , where is the breadth of the channel, and lengthen the dominant transverse wavelength as in the interim. With these scaling laws, we arrive at the conclusion that transient fingering is insignificant in sub-millimeter micro-devices which use electrokinetic flow to transport biological and environmental electrolyte samples.