Flow-Induced Translocation and Conformational Transition of Polymer Chains through Nanochannels: Recent Advances and Future Perspectives

How polymer chains with different architectures translocate through narrow nanochannels with the channel size much smaller than the chain size in flow fields remains a fundamental question in polymer physics. In the flow-induced channel translocation process, the chain conformation successively undergoes three states, i.e., initial free state, intermediate transporting state, and final confinement state. Accordingly, focusing on the three conformational states, extensive experimental and computational works have been performed in the past decades to investigate the interactive relationships between fundamental parameter (chain architecture, solution concentration, etc.) and translocation behavior to understand the flow-induced conformational transitions. In this Perspective, we aim to present the current status, highlight the key issues and existing controversies, and discuss further directions in the field. By focusing on the three conformational states during the translocation process, we intentionally organized the Perspective as follows: (i) First, we started with the presentation of the classical results of conformational properties of free polymer chains in bulk solutions, and meanwhile, we summarized recent experimental progress. (ii) Then, we moved to discuss the conformational properties of polymer chains under channel confinements or in free flows. (iii) Afterward, we discussed the classical theoretical predictions for the flow-induced “coil-to-stretch” conformational transition under channel confinement. (iv) On the basis of the above three sections, we put emphasis on discussing recent experimental progress in flow-induced translocation and conformational transition through nanochannels; in particular, we discussed the influence from the most essential variables in polymer solutions, i.e., chain length, chain architecture, and solution concentration, on the translocation behavior. (v) Further, some exciting application results were introduced. (vi) Finally, several important unresolved questions were enumerated for future studies. We hope that the present Perspective can afford useful information for understanding related phenomena, regulating (bio)macromolecule translocation processes, and promoting technological development.