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Influence of Solutocapillary Convection on Macrovoid Defect Formation in Polymeric MembranesMacrovoids (MVs) are large (10-50 micrometers) pores often found in polymeric membranes prepared via phase-inversion techniques. They are generally considered undesirable, as they adversely affect the permeability properties and performance of polymeric membranes for microfiltration, ultrafiltration, and reverse osmosis. However, MVs can be useful in certain thin-film applications in which vapor transmission is necessary, or for use as reservoirs for enzymes or liquid membrane material. If more could be learned about the nature and causes of MV formation, it might be possible to devise techniques to control and/or prevent MV formation that are more effective than those currently employed. Two hypotheses for the MV growth mechanism have been advanced. Reuvers proposed that once initiated, MV growth can be attributed to diffusion of (primarily) solvent to the MV nuclei. Because this mechanism does not involve gross movement of the MV, the presence or absence of body forces such as buoyancy should not significantly affect MV growth. On the other hand, Shojaie et al. proposed that solutocapillary convection induced by a steep surface-tension gradient along the MV/bulk solution interface enhances mass transfer to the growing MV. This interfacial convection exerts a force that pulls the growing MV downward into the casting solution. Both buoyancy and viscous drag hinder MV growth by inhibiting this motion. Thus, removing the buoyancy force by casting in microgravity should augment MV growth according to this hypothesis. Whereas neither surface tension nor gravity has a significant effect on MV growth according to the first hypothesis, buoyancy forces should be important if the second hypothesis is correct. The overall goal of this research is to test these two hypotheses in order to improve our understanding of the MV growth processing solvent-cast polymeric membranes. Studying MV growth in low-gravity conditions is pivotal to our ability to discriminate between these two hypotheses.
Document ID
20010057252
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Pekny, M. R.
(INTEL Corp. Santa Clara, CA United States)
Zartman, J.
(Colorado Univ. Boulder, CO United States)
Greenberg, A. R.
(Colorado Univ. Boulder, CO United States)
Todd, P.
(Space Hardware Optimization Technology, Inc. Greenville, IN United States)
Krantz, W. B.
(Cincinnati Univ. OH United States)
Date Acquired
August 20, 2013
Publication Date
March 1, 2001
Publication Information
Publication: Microgravity Materials Science Conference 2000
Volume: 1
Subject Category
Nonmetallic Materials
Funding Number(s)
CONTRACT_GRANT: NAG8-1475
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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