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

By using a series of mixed solutions composed of styrene oligomers (PSN, 10 < N < 550) and toluene, this work explores how the macromolecule crowding effects, including viscosity effect and conformational compression, regulates the flow-driven translocation, i.e., compression-induced fractionation (CIF), of polystyrene long chains (PS-1100k, 1.10 × 106 g/mol) through nanochannels (average pore radius r0 ≈ 10 nm). The correlation between the macroscopic critical flow rate (Qc) and apparent viscosity (ηapp) has been tested. Specifically, we have found the following: (1) ηapp of PSN–toluene mixed solutions is found to be easily regulated in a broad range (0.52 ≤ ηapp ≤ 5.02 mPa·s) by the oligomer strategy, which is beyond the window achieved by the small-molecule solvent system; (2) the translocation experiments in mixed solutions support the relation of Qc ∼ 1/ηapp predicted by de Gennes theory in the range of 0.52 mPa·s ≤ ηapp ≤ 1.53 mPa·s, but a deviation is observed when 1.53 < ηapp ≤ 5.02 mPa·s, implying the potential influence from the conformational compression of chains for CIF; (3) through a coarse-grained simulation on the blend system composed of a long chain (Nl = 100) and oligomer short chains (1 ≤ Ns ≤ 20) with varied volume fraction (φs) from 0.1 to 0.4, the simulation result shows that the degree of compression of the long chain increases with Ns and φs of oligomer short chains. Overall, the present study has preliminarily explored how the macromolecule crowding effects (viscosity effect and conformational compression) play the dominant role in regulating translocation behavior during the CIF process, which paves the foundation for understanding the transmembrane transport of biological macromolecules in the natural crowding cell environments.