Abstract
Surface-tension induced flows may have a significant impact on the surface topography of thin films or small printed structures derived from polymer solution processing. Despite a century of research on Marangoni convection, the community lacks quantitative experimental flow field data, especially from within drying solutions. We utilize multifocal micro particle tracking velocimetry (µPTV) to obtain these data and show a calibration routine based on point spread function (PSF) simulations as well as experimental data. The results account for a varying sample refractive index, beneficial cover-glass correction collar settings as well as a multifocal lens system. Finally, the calibration procedure is utilized exemplarily to reconstruct a three-dimensional, transient flow field within a poly(vinyl acetate)-methanol solution dried with inhomogeneous boundary conditions.
Highlights
Creating homogeneous thin polymer films from solution is a key processing step in the production of coatings, adhesive tapes, displays, and printed organic electronic devices, such as OLEDs, solar cells, or biosensors
Surface-tension induced flows may have a significant impact on the surface topography of thin films or small printed structures derived from polymer solution processing
We utilize multifocal micro particle tracking velocimetry to obtain these data and show a calibration routine based on point spread function (PSF) simulations as well as experimental data
Summary
Creating homogeneous thin polymer films from solution is a key processing step in the production of coatings, adhesive tapes, displays, and printed organic electronic devices, such as OLEDs, solar cells, or biosensors. Besides well-established slot die coating processes for large area deposition, in the recent decade, inkjet printing for the selective application of small structures evolved from pure graphics application towards the deposition of functional materials [1]. During the subsequent drying of small sessile structures, a hydrodynamic effect occurs, which transports the solute preferably towards the contact line, resulting in elevated edges of the deposit. Either lateral variations of the heat conductivity of the substrate [3] or lateral variations of the solvent mass transport in the gas phase above the drying film cause the liquid-gas interface to deform [4]
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