Flow-visualization during macrovoid pore formation in dry-cast cellulose acetate membranes |
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| Affiliation: | 1. Department of Chemical Engineering, University of Colorado, Boulder, CO 80309-0424, USA;2. Department of Chemical Engineering, University of Cincinnati, Cincinnati, OH 45221-0171, USA;3. Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, USA;4. Space Hardware Optimization Technology Inc., Greenville, IN 47124-9515, USA;1. Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 133-791, Republic of Korea;2. R&D Center for Membrane Technology, Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan;3. National Research Council – Institute on Membrane Technology (ITM–CNR), Via Pietro BUCCI, c/o The University of Calabria, cubo 17C, 87036 Rende CS, Italy;1. Centre for Technology in Water and Wastewater, School of Civil and Environmental Engineering, University of Technology Sydney (UTS), P. O. Box 123, 15 Broadway, NSW 2007, Australia;2. Department of Land, Water, and Environment Research, Korea Institute of Civil Engineering and Building Technology (KICT), 283 Goyang-Daero, Ilsanseo-Gu, Goyang-Si, Gyeonggi-Do, 10223, Republic of Korea;3. Civil Engineering Department, Kyungnam University, Wolyoung-dong, Changwon, 631-701, Republic of Korea;1. Faculty of Chemical Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Iran;2. Faculty of Chemical Engineering, Babol University of Technology, P.O. Box 484, Babol, Iran;1. Research Center for High Performance Polymer and Composite Systems (CREPEC), Chemical Engineering Department, Polytechnique Montreal, PO Box 6079, Stn Centre-Ville, Montreal, QC H3C 3A7, Canada;2. Département des Sciences du bois et de la forêt, Faculté de foresterie, géographie et géomatique, Université Laval, Quebec, QC G1V 0A6, Canada |
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| Abstract: | Video-microscopy flow-visualization (VMFV) is adapted to study the development of macrovoid (MV) pores in the dry-casting of cellulose acetate (CA)/acetone/water solutions. Particle tracer velocities provide the first direct evidence for the presence of solutocapillary-driven convection that can enhance mass-transfer to a MV. Three phases of MV development are observed: fast initial growth, slow growth, and collapse. During the latter, MVs were observed on occasion to initiate far from the demixing front. These studies have led to a significantly modified hypothesis for MV development. Extremely rapid initial MV growth is thought to occur owing to coalescence of dispersed phase microdroplets. To ensure net mass-transfer to a growing MV, it is postulated that a homogeneous supersaturated solution layer must exist between the demixed fluid layer and the homogeneous stable solution layer. Fast growth also involves convective mass-transfer to the MV whose surface is initially entirely immersed in this homogeneous supersaturated solution layer. Slow growth involves net transport that results from both convective mass-transfer to the MV across the portion of its surface in contact with the homogeneous supersaturated solution layer, and convective mass-transfer from the portion of its surface that extends into the homogeneous stable solution layer. Active collapse is thought to occur owing to skin formation at the MV surface. Passive collapse occurs when the convective mass-transfer from the MV in the homogeneous stable solution layer exceeds that entering the MV in the homogeneous supersaturated solution layer. |
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