Impact of compositional gradients on the dynamics of solid-liquid-vapor contact lines

by Olinka Johani Ramírez Soto
Doctoral thesis
Date of Examination:2022-02-24
Date of issue:2022-03-28
Advisor:Dr. Stefan Karpitschka
Referee:Stefan Karpitschka
Referee:Prof. Dr. Marcus Müller
Persistent Address: http://dx.doi.org/10.53846/goediss-9144

 

 

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Abstract

English

The motion of a liquid over a solid surface is a process that happens in natural phenomena and everyday life situations, therefore its understanding is of great importance. The motion of the liquid is limited by the dynamics of the solid-liquid-vapor contact line. In this thesis, the effect that the liquid composition has over moving contact lines is studied, in particular when surface tension gradients, driven by compositional gradients, are present. The objective is to get insights of the governing mechanisms. The model system is Marangoni-contracted drops. The wetting behavior is investigated by experiments that allow for a control of the ambient conditions, macroscopic observations, and micro-PIV, simultaneously. A quantitative description of the shape and the internal flows of the drops is obtained and used to build a theoretical understanding of the governing mechanisms. First, a system where two wetting mechanisms compete is presented. These mechanisms are: Marangoni contraction and autophobing. The regimes where the mechanisms dominate are presented. Then, it is shown that Taylor-Aris dispersion dominates the evolution of the compositional field of Marangoni-contracted drops. The theoretical model, based on thin film theory and accounts for Taylor-Aris dispersion, is proposed. Then, it is shown that in systems were liquid-liquid phase separation is induced, Marangoni-contraction is lost. The responsible of this are surface forces causing an earlier phase separation in the precursor film. The previous studies where done on smooth high energy surfaces. In the last part of this thesis, the behavior of Marangoni contracted drops on porous substrates is explored and preliminary results are given.
Keywords: Fluid dynamics; Drops; Thin liquid films; Wetting; Contact line dynamics; Evaporation/condensation; Binary fluids; Complex fluids; Contact angle; Surface tension; Marangoni convection; Diffusion; Taylor-Aris dispersion; Lubrication approximation; Autophobing; Phase separation; Porous media; Drop spreading; Imbibition
 
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