Physics (Internal)

Ultrafiltration of macromolecules through nanopores

This event is part of the Biophysics/Condensed Matter Seminar Series.

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.