1 research outputs found
Photochemically Induced Marangoni Patterning of Polymer Bilayers
Surface-tension gradients created along a polymer film
by patterned
photochemical reactions are a powerful tool for creating surface topography.
Here, we use mathematical modeling to explore a strategy for patterning
photochemically inactive polymers by coupling a light-sensitive and
light-insensitive polymer to form a polymer bilayer. The light-sensitive
polymer forms the top layer, and the most dominant surface-tension
gradients are introduced at the interface between this layer and air.
Lubrication
theory is used to derive nonlinear partial differential equations
describing the heights of each layer, and linear analysis and nonlinear
simulations are performed to characterize interface dynamics. Patterns
form at both the polymer–air and polymer–polymer interfaces
at early thermal annealing times as a result of Marangoni stresses
but decay on prolonged thermal annealing as a result of the dissipative
mechanisms of capillary leveling and photoproduct diffusion, thus
setting a limit to the maximum individual layer deformation. Simulations
also show that the bottom-layer features can remain “trapped”,
i.e., exhibit no significant decay, even while the top layer topography
has dissipated. We study the effects of two key parameters, the initial
thickness ratio and the viscosity ratio of the two polymers, on the
maximum deformation attained in the bottom layer and the time taken
to attain this deformation. We identify regions of parameter space
where the maximum bottom-layer deformation is enhanced and the attainment
time is reduced. Overall, our study provides guidelines for designing
processes to pattern photochemically inactive polymers and create
interfacial topography in polymer bilayers