Transport of a polymer chain in constriction–expansion microchannels: a dissipative particle dynamics study

With the rapid development of microfluidic technology, understanding polymer-chain migration and conformational evolution in confined flows is important for biomacromolecular transport and separation. In this study, dissipative particle dynamics (DPD) coupled with an improved finitely extensible nonlinear elastic (FENE) model was used to investigate single-polymer transport in constriction–expansion microchannels. The effects of constriction length, chain length, and chain stiffness on polymer conformation and centre-of-mass migration were systematically examined. The results show that polymer chains are predominantly coiled in the expansion region and stretched within the constriction. Increasing the constriction length mainly prolongs the highly stretched state rather than increasing the maximum extension. For (N = 20), increasing (Ld) from 15 to 25 increases the duration of the highly stretched state (Rg ≥ 6.5) by approximately 46.5%, while the maximum (Rg) remains nearly unchanged at about 7.0. Increasing the chain length by 10 beads increases the characteristic (Rg) by approximately 50%, whereas a one-third increase in (Ld) produces only about a 6% increase. Longer chains exhibit stronger centreline focusing and shorter transit times, while shorter or stiffer chains show weaker focusing and greater near-wall migration. These findings provide guidance for the design and parameter selection of constriction–expansion microchannels for biomacromolecular transport and separation.