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The surface morphology of polystyrene thin films formed from various molecular weight polystyrene and solvent conditions is studied. When spin-cast from tetrahydrofuran (THF) wrinkles are formed at the extremities that have periodicity with wavelengths in the μm range and amplitudes in the nm range but varies with molecular weight. A mixed solvent system consisting of THF and dimethylformamide (DMF) leads to periodic structures only with THF-rich compositions. THF and DMF have similar properties relevant to spin-casting: density, surface tension, molecular weight, and viscosity but different boiling points and room temperature vapor pressures, demonstrating that formation periodicity requires a volatile solvent. The formation of the surface structures is attributed to the Marangoni effect and the film thicknesses and wave parameters are shown to be consistent with literature models.
Chunyi Tang, Matthew Mullen, William B. Euler. Influence of solvent and molecular weight in wrinkle formation in spin-cast polystyrene thin films[J]. AIMS Materials Science, 2020, 7(1): 60-74. doi: 10.3934/matersci.2020.1.60
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