Escape dynamics of active ring polymers in a cylindrical nanochannel.

We explore the escape dynamics of active ring polymers confined in a cylindrical nanochannel using Brownian dynamics. Our simulation results show that the escape time decreases with the increase of the Péclet number, which is not noticeable between the two stages of the escape process, based on whether the center of mass of the polymer is inside or outside the nanochannel. However, the monomer motion trajectory of the active polymer is very different from that of the passive polymer, similar to the snake-like motion with uniform velocity. The passive polymer, however, is in constant fugitive motion with increased velocity at the tail end of the escape. Our work is vital for understanding the escape dynamics of active ring polymers in the confined nanochannel, which provides new perspectives on their characterization and analysis.

Flow-Driven Translocation of a Diblock Copolymer through a Nanopore.

Using a hybrid molecular dynamic and lattice Boltzmann simulation method, we investigate the flow-driven translocation of a diblock copolymer which is composed of a hydrophilic block and a hydrophobic block through a nanopore. Our results illustrate the nontrivial translocation dynamics of diblock copolymers. We find that the increase in the number of hydrophobic segments requires a larger critical flow rate and a reduced translocation time, which implies that the separation of diblock copolymers with different fractions of hydrophobic segments can be achieved by adjusting the flow rate. Our work deepens the understanding of copolymer translocation through a nanopore and provides an insight into designing related microscaled separation devices.

Effect of Bidispersity on Dynamics of Confined Polymer Films.

Using Monte Carlo simulations, we studied the effect of bidispersity on the dynamics of polymer films capped between two neutral walls, where we chose three representative compositions for bidispersed polymer films. Our results demonstrate that the characteristic entanglement length is an important parameter to clarify the effect of the bidispersity on the dynamics of polymer films. For the short chains, shorter than the characteristic entanglement length, the average number of near-neighboring particles increases with the decrease of the film thickness and limits the diffusivity of the short chains, which is independent of the film compositions. However, the dynamics of the long chains, of which is above the characteristic entanglement length, is determined by the film's composition. In our previous paper, we inferred from the structures and entanglements of the bidisperse system with short and long chains that the constraint release contributes significantly to the relaxation mechanism of long chains. By calculating the self-diffusion coefficient of long chains, we confirmed this prediction that, with a lower weight fraction of long chains, the self-diffusion coefficient of long chains decreases slowly with the decrease of the film thickness, which is similar to that of short chains. With a higher weight fraction of long chains, the competition between the disentanglement and the increased in the local degree of confinement which resulted in the self-diffusion coefficient of long chains varying non-monotonically with the film thickness. Furthermore, for the bidisperse system with long and long chains, the diffusivity of long chains was not affected by the constraint release, which varied nonmonotonically with the decrease of the film thickness due to the competition between the disentanglement and the enhanced confinement. Herein, compared with the previous work, we completely clarified the relationship between the structures and dynamics for three representative compositions of bidisperse polymer films, which contains all possible cases for bidisperse systems. Our work not only establishes a unified understanding of the dependency of dynamics on the bidispersity of polymer films, but also helps to understand the case of polydispersity, which can provide computational supports for various applications for polymer films.

Effects of nanopore size on the flow-induced star polymer translocation.

We study the effects of the nanopore size on the flow-induced capture of the star polymer by a nanopore and the afterward translocation, using a hybrid simulation method that couples point particles into a fluctuating lattice-Boltzmann fluid. Our simulation demonstrates that the optimal forward arm number decreases slowly with the increase of the length of the nanopore. Compared to the minor effect of the length of the nanopore, the optimal forward arm number obviously increases with the increase of the width of the nanopore, which can clarify the current controversial issue for the optimal forward arm number between the theory and experiments. In addition, our results indicate that the critical velocity flux of the star polymer is independent of the nanopore size. Our work bridges the experimental results and the theoretical understanding, which can provide comprehensive insights for the characterization and the purification of the star polymers.

Flow-induced polymer translocation through a nanopore from a confining nanotube.

We study the flow-induced polymer translocation through a nanopore from a confining nanotube, using a hybrid simulation method that couples point particles into a fluctuating lattice-Boltzmann fluid. Our simulation illustrates that the critical velocity flux of the polymer linearly decreases with the decrease in the size of the confining nanotube, which corresponds well with our theoretical analysis based on the blob model of the polymer translocation. Moreover, by decreasing the size of the confining nanotube, we find a significantly favorable capture of the polymer near its ends, as well as a longer translocation time. Our results provide the computational and theoretical support for the development of nanotechnologies based on the ultrafiltration and the single-molecule sequencing.