A positive and energy stable numerical scheme for the Poisson-Nernst-Planck-Cahn-Hilliard equations with steric interactions

JOURNAL OF COMPUTATIONAL PHYSICS

卷:426

Article

Qian, Yiran^1,2  Wang, Cheng³  zhou, Shenggao^4,5 

[1] Soochow Univ, Dept Math, 1 Shizi St, Suzhou 215006, Jiangsu, Peoples R China

[2] Soochow Univ, Math Ctr Interdiscipline Res, 1 Shizi St, Suzhou 215006, Jiangsu, Peoples R China

[3] Univ Massachusetts Dartmouth, Dept Math, N Dartmouth, MA 02747 USA

[4] Shanghai Jiao Tong Univ, Sch Math Sci, Shanghai 200240, Peoples R China

[5] Shanghai Jiao Tong Univ, MOE LSC, Shanghai 200240, Peoples R China

关键词: Poisson-Nernst-Planck-Cahn-Hilliard equations;    Positivity;    Energy stability;    Electric double layer;    Self-assembly pattern;   

DOI  :  10.1016/j.jcp.2020.109908

来源: Elsevier

【 摘 要 】

In this work, we consider numerical methods for the Poisson-Nernst-Planck-Cahn-Hilliard (PNPCH) equations with steric interactions, which correspond to a non-constant mobility H-1 gradient flow of a free-energy functional that consists of electrostatic free energies, steric interaction energies of short range, entropic contribution of ions, and concentration gradient energies. We propose a novel energy stable numerical scheme that respects mass conservation and positivity at the discrete level. Existence and uniqueness of the solution to the proposed nonlinear scheme are established by showing that the solution is a unique minimizer of a convex functional over a closed, convex domain. The positivity of numerical solutions is further theoretically justified by the singularity of the entropy terms, which prevents the minimizer from approaching zero concentrations. A further numerical analysis proves discrete free-energy dissipation. Extensive numerical tests are performed to validate that the numerical scheme is first-order accurate in time and second-order accurate in space, and is capable of preserving the desired properties, such as mass conservation, positivity, and free energy dissipation, at the discrete level. Moreover, the PNPCH equations and the proposed scheme are applied to study charge dynamics and self-assembled nanopatterns in highly concentrated electrolytes that are widely used in electrochemical energy devices. Numerical results demonstrate that the PNPCH equations and our numerical scheme are able to capture nanostructures, such as lamellar patterns and labyrinthine patterns in electric double layers and the bulk, and multiple time relaxation with multiple time scales. The multiple time relaxation dynamics with metastability take long time to reach an equilibrium, highlighting the need for robust, energy stable numerical schemes that allow large time stepping. In addition, we numerically characterize the interplay between cross steric interactions of short range and the concentration gradient regularization, and their impact on the development of nanostructures in the equilibrium state. (C) 2020 Elsevier Inc. All rights reserved.

【 授权许可】

Free