Coating Technology Moves to Next Level with Modeling and Simulation Insights
The challenge becomes greater as we advance engineered devices into ever-diminishing length scales.
This time sequence in a coating simulation shows how wetting constituent (blue) forms a monolayer and spreads out along the surface (red). Then the nonwetting constituent (yellow) spreads on top of the wetting monolayer.
How to ensure that a substrate material
is evenly and securely wetted by a wetting
agent has long been the challenge in coating
technology. Failure to develop a complete
wetting of a substrate often leads to coating
failure. In epoxy systems, for instance, incomplete
wetting of the surfaces to be joined
can lead to sealant failure and, in turn, device
failure. The challenge becomes greater as we
advance engineered devices into ever smaller
scales.
Understanding coating failure requires
molecular-level descriptions of the coating
constituents as well as the interface with
the solid material. This is a level of resolution
unattainable by existing experimental
techniques. Molecular-scale simulations have
been used to study wetting phenomena, but
until recently computational resources did
not exist to study chemically realistic coating
materials.
In this simulation, a polymer nanodroplet (red) spreads across
a chemically patterned surface. The pattern consists of parallel
strips of wetting (blue) and nonwetting (green) regions. The
droplet spreads on the wetting strip by removing material from
on top of the nonwetting (green) region. Understanding the
complex patterns of coating can guide engineers in developing
new nanodevices.
Sandia researchers Gary Grest and
Edmund Webb developed numerical
simulations of multicomponent polymer
nanodroplets being applied to substrates.
The simulations, using high-performance,
large-scale parallel-processing computers,
were done with binary component droplets.
Grest and Webb observed conditions where
a nonwetting coating constituent was made
to wet the substrate by carefully controlling
coating constituents.
With sufficient interaction strength between
the polymer components, the nonwetting
substance spread on top of a molecular
layer of the wetting substance. This effort
revealed previously unavailable molecularscale
information about phenomena controlling
coating behavior.
The model created can address constituents
of arbitrary molecular structure and
interaction strength, which permits broad
applicability across coating engineering
science. In addition, complexities such as
introducing a chemical pattern on the substrate
surface have been studied. Results are
helping coatings scientists develop stable
multicomponent wetting formulations that
allow the use of required wetting agents
even when those substances would not
otherwise coat the substrate.
For more information:
Edmund B. Webb, III, Ph.D., 505-284-6517, ebwebb@sandia.gov
