Investigation of Crowding Effect on the Flow-Driven\nCompression-Induced Fractionation (CIF) of Polymer Chains through\nNanochannels by Experimental Observation and Computational Simulation

By\nusing a series of mixed solutions composed of styrene oligomers\n(PS<sub><i>N</i></sub>, 10 < <i>N</i> <\n550) and toluene, this work explores how the macromolecule crowding\neffects, including viscosity effect and conformational compression,\nregulates the flow-driven translocation, i.e., compression-induced\nfractionation (CIF), of polystyrene long chains (PS-1100k, 1.10 ×\n10<sup>6</sup> g/mol) through nanochannels (average pore radius <i>r</i><sub>0</sub> ≈ 10 nm). The correlation between the\nmacroscopic critical flow rate (<i>Q</i><sub>c</sub>) and\napparent viscosity (η<sub>app</sub>) has been tested. Specifically,\nwe have found the following: (1) η<sub>app</sub> of PS<sub><i>N</i></sub>–toluene mixed solutions is found to be easily\nregulated in a broad range (0.52 ≤ η<sub>app</sub> ≤\n5.02 mPa·s) by the oligomer strategy, which is beyond the window\nachieved by the small-molecule solvent system; (2) the translocation\nexperiments in mixed solutions support the relation of <i>Q</i><sub>c</sub> ∼ 1/η<sub>app</sub> predicted by de Gennes\ntheory in the range of 0.52 mPa·s ≤ η<sub>app</sub> ≤ 1.53 mPa·s, but a deviation is observed when 1.53\n< η<sub>app</sub> ≤ 5.02 mPa·s, implying the\npotential influence from the conformational compression of chains\nfor CIF; (3) through a coarse-grained simulation on the blend system\ncomposed of a long chain (<i>N</i><sub><i>l</i></sub> = 100) and oligomer short chains (1 ≤ <i>N</i><sub>s</sub> ≤ 20) with varied volume fraction (φ<sub>s</sub>) from 0.1 to 0.4, the simulation result shows that the degree\nof compression of the long chain increases with <i>N</i><sub>s</sub> and φ<sub>s</sub> of oligomer short chains. Overall,\nthe present study has preliminarily explored how the macromolecule\ncrowding effects (viscosity effect and conformational compression)\nplay the dominant role in regulating translocation behavior during\nthe CIF process, which paves the foundation for understanding the\ntransmembrane transport of biological macromolecules in the natural\ncrowding cell environments.