Capillary filling of star polymer melts in nanopores

TL;DR

This study uses molecular dynamics simulations to explore how star polymer topology affects capillary filling in nanopores, revealing complex dynamics influenced by arm length, functionality, and confinement.

Contribution

It provides new insights into the imbibition behavior of star polymers, highlighting the effects of topology on flow dynamics, entanglement, and configuration changes during nanopore filling.

Findings

Star polymers with short arms penetrate slower than predicted by Lucas-Washburn.

Long-arm star polymers penetrate faster than the Lucas-Washburn prediction.

Higher functionality increases entanglement points and affects flow behavior.

Abstract

Topology of polymer profoundly influences on its behavior. However, its effect on imbibition dynamics remains poorly understood. In the present work, capillary filling (during imbibition and following full imbibition) of star polymer melts was investigated by molecular dynamics simulations with a coarse-grained model. The reversal of imbibition dynamics observed for linear-chain systems was also present for star polymers. Star polymers with short arms penetrate slower than the prediction of the Lucas-Washburn equation, while systems with long arms penetrate faster. The radius of gyration increases during confined flow, indicating the orientation and disentanglement of arms. In addition, the higher the functionality of the star polymer, the more entanglement points are retained. Besides, a stiff region near the core segments of the stars is observed, which increases in size with functionality. The proportion of different configurations of the arms (e.g. loops, trains, tails) changes dramatically with the arm length and degree of confinement, but is only influenced by the functionality when the arms are short. Following full imbibition, the different decay rates of the self-correlation function of the core-to-end vector illustrate that arms take a longer time to reach the equilibrium state as the functionality, arm length, and degree of confinement increases, in agreement with recent experimental findings. Furthermore, the star topology induces a stronger effect of adsorption and friction, which becomes more pronounced with increasing functionality.