PMSE 80 |
| Phase inversion filtration membranes often display unwanted voids called macrovoids, much larger than surrounding microstructure, which significantly reduce membrane strength and performance. Recent research using time-sectioning cryogenic SEM suggests that macrovoids in phase separating coatings form due to a unique network instability triggered by successive tensile ruptures of the gelled polymer-rich network. In a wet cast process, it is demonstrated how (i) build-up of compressive pressure in pores (polymer-lean) and tensile stress in the network from overall swelling and local syneresis, (ii) vertical rupture (perpendicular to substrate), (iii) stress localization, (iv) post-rupture relaxation and (v) plausible horizontal ruptures may cause this network instability and drive convective flows from adjacent pores into the growing void. Development of this instability resembles splitting failure observed in fracture of oil wells, yet is unique due to syneresis. The hypothesis is applicable to dry cast and other processes, and to cylindrical geometries (hollow fibers, tubes). |
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Tess Award Symposium in Honor of L. E. (Skip) Scriven
8:00 AM-12:05 PM, Monday, August 20, 2007 Westin Boston Waterfront -- Grand Ballroom D, Oral
Division of Polymeric Materials: Science & Engineering |