PIV measurements of flow in drying polymer solutions during solvent casting |
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Authors: | Iman Mansoor Boris Stoeber |
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Institution: | (1) Department of Electrical and Computer Engineering, The University of British Columbia, 5500–2332 Main Mall, Vancouver, BC, V6T 1Z4, Canada;(2) Department of Mechanical Engineering, The University of British Columbia, Vancouver, BC, Canada |
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Abstract: | An experimental method based on confocal microscopy and particle image velocimetry (PIV) is used to characterize the flow
in a polymer solution during solvent casting. The flow inside a 200-μm-thick film of a poly(vinyl alcohol) (PVA) solution
is visualized near a vertical wall of a mold using confocal microscopy of seed particles during solvent evaporation at 25,
35, and 45°C, and the corresponding velocity vector fields are determined from projections of the confocal images. Flow toward
the vertical wall is observed inside the film as well as a slower Marangoni-type counter flow at the film surface during the
initial phase of solvent evaporation, resulting from a polymer concentration gradient along the film due to a local variation
in evaporation rate. Total volume of the polymer solution in the observation volume as well as solvent evaporation rate are
determined as a function of time, both revealing close correlation to average horizontal velocity data from PIV. The PIV measurements
show significant differences in the flow velocity fields at different temperatures. The PIV measurements correlate with the
solvent evaporation rates as well as the final polymer thicknesses on the vertical wall of the mold. Surface tension and viscosity
measurements are taken for different concentrations of PVA solution. |
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