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Activity-crowding coupling effect on diffusion dynamics of a self-propelled particle in polymer solutions

Abstract

The anomalous diffusion dynamics of an active particle in polymer solutions is studied based on a Langevin Brownian dynamics simulation. Firstly, the mean-square displacement (MSD) is investigated under various system parameters of active force $F_a$, probe size $\sigma_a$, polymer volume fraction $\phi$ and polymer chain length $N$. A very novel transition between superdiffusion and subdiffusion is observed with varying $F_a$ and $\phi$, owing to the activity and crowding competition effect. Diagram of the two anomalous diffusive regimes are identified in the parameter space. The increment of MSD under activity is examined in the intermediate time scales, which manifests a power law relation with the particle's dynamical persistence length $L$, i.e., $\Delta \mbox{MSD}=2L^m$ where the exponent $m$ decreases with $\phi$. Secondly, we explicitly evaluate the long-time diffusion coefficients $D_a^0$ in pure solvent and $D_a$ in polymer solutions. The dependence of relative diffusivity $D_a/D_a^0$ on volume fraction $\phi$ reproduces the well-known Phillies' equation $\exp(-\kappa \phi^{\mu})$. The fitting parameters show $\mu\simeq 1$, but $\kappa$ apparently increases with activity. More importantly, our simulation justifies a multi-length scaling relation in a very similar form to that for passive probes, depending on simple structural parameters of the probe-polymer system. By the aid of activation energy model, we find out a counterintuitive activity-crowding coupling effect: activity enhances effective viscosity experienced by the probe and thus strengthens the crowding-induced retardation to diffusion.

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Publication details

The article was received on 14 Aug 2019, accepted on 09 Oct 2019 and first published on 10 Oct 2019


Article type: Paper
DOI: 10.1039/C9CP04498A
Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Activity-crowding coupling effect on diffusion dynamics of a self-propelled particle in polymer solutions

    C. Yuan, A. Chen, B. Zhang and N. Zhao, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP04498A

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