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Stability of thin liquid films on chemically patterned surfaces

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					          Stability of thin liquid films on chemically patterned surfaces
                        Berend Brasjen and Prof. Anton Darhuber
            Both experiments and numerical simulations (finite element) possible

Many state-of-the-art industrial processes for the manufacturing of, for instance, organic
electronic devices or biotechnological applications, rely on the behavior of liquid on a chemically
heterogeneous substrate. One of the many industrial techniques is to deposit an initially uniform
film with a typical thickness of 10 microns onto a surface that is periodically hydrophilic (i.e. water
attracting) and hydrophobic (i.e. water repelling). For films this thin, the fluid mechanics contain
contributions from gravity, surface tension, viscosity and surface energies, which makes the
problem complex and challenging.
         Due to the difference in surface energy (i.e. the energy needed to adhere to the
substrate), the liquid will spontaneously move from the hydrophobic regions to the hydrophilic
regions. As can be seen in Fig. 1, this redistribution takes place in two manners: laterally inwards
from the edge of the film (orange arrow) and in the center of the pattern by means of dry-spot
nucleation (red arrow).




Figure 1: Spontaneous liquid redistribution from the edge and from the center of a chemical pattern.

          The redistribution process depends on many parameters (e.g. film thickness, liquid
properties, pattern configuration). Moreover, it has to compete against the solidification of the
liquid, if this is drying solution. The industrial desire is to manufacture uniform films on the
hydrophilic patches, with clean hydrophobic separation regions, at the highest possible speed. It
is therefore of vital importance to understand and control the fluid dynamics of liquid redistribution
as a function of all the above mentioned parameters.

Students interested in this project are invited to contact Berend Brasjen (b.j.brasjen@tue.nl) or
Prof. Anton Darhuber (a.a.darhuber@tue.nl). A cooperation with TNO/Holst Centre at the High-
Tech Campus in Eindhoven is possible.

				
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posted:7/25/2011
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