Ultrafiltration of macromolecules through nanopores
When: August 23, 2007 (Thu), 11:00AM to 12:00PM
Hosted by:
Ophelia Tsui
Speaker: Chi Wu, The Chinese University of Hong Kong
This event is part of the Condensed Matter Seminar Series. All seminars will take place in the Metcalf Science Center, Room 352 at noon, unless otherwise noted
Abstract: Using a special double-layer membrane to avoid interaction among flow fields generated by different pores, we have, for the first time, observed the predicted discontinuous first-order transition in ultra-filtration of flexible linear polymer chains. Namely, the chain could pass through a pore much smaller than its unperturbed radius only when the flow rate is higher than a certain value. When only one chain and one pore considered in theory, such a threshold is surprisingly independent of both the chain length and the pore size. Our results reveals that for a membrane with many pores and at a microscopic flow rate (q) lower than the threshold, the inevitable blocking of some pores by longer non-stretched coiled chains increases q in those non-blocked pores because the macroscopic flow rate (Q) is a constant. Our results reveal that the force to stretch a polymer coil in an athermal solvent is only ~10 fN. Further, using this method, we are able to measure how “soft” a polymer chain is and how strong the inter-chain interaction is when they are collapsed and entangled with each other.