How a polymer chain translocates through a cylindrical pore with its pore size smaller than the chain size (ultrafiltration behavior) is a fundamental question in polymer physics. Answering this question can provide broader implications and lead to potential applications for many applicable processes, such as gene transfection, protein transportation, and separation of a mixture of polymer chains. In the process of an electroneutral polymer chain passing through a nanopore, generally, an external flow with a sufficient high shear stress is needed to apply at the entrance of pore to induce a conformation change from a coil-like to a rod-like shape which is referred to as the “coil-to-stretch” transition, to squeeze into the pore. Up to last decade, many theoretical models have been built and carried out to predict how polymer chains pass through a nanopore. By contrast, rather limited experimental investigations have been performed to validate these theoretical predications, which is mainly because this kind of experimental study demands polymer chains with explicit topologies and nanopores with well-defined structures. Namely, 1) the polymer samples with narrow molecular-weight distributions, well-defined chain configurations, as well as hydrodynamic sizes larger than the pore radii; and 2) membranes with well-defined pore structure and isolated pore channels to prevent possible interaction between neighboring shearing flows.

This paper was originally published in Polymer 67 (2015) Pages A1–A13.

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