Structure and Dynamics of Dilute Polymer Solutions under Shear Flow via Nonequilibrium Molecular Dynamics

Abstract

We present and discuss results obtained by an extensive nonequilibrium molecular dynamics computer simulation study of polymer solutions under shear, where the chain consists of N beads connected by a finitely extendable nonlinear elastic (FENE) spring force and the solvent is explicitly taken into account. Various scaling laws are extracted from the data which allow one to predict the qualitatives and to certain extent also quantitativesstructural and rheological behavior of polymer solutions under good solvent conditions. For most quantities, the results drawn from simulation are compared with experimental data and theoretical predictions which are based on similar models (e.g., harmonic bond potentials or Brownian dynamics methods). Specifically, and in contrast to common theoretical approaches, the simulation yield information about a set of different but characteristic relaxation times, which determine the rheological and structural behavior (for example, flow birefringence, structure factor, rotational dynamics) separately, the difference either resulting from the underlying static or dynamic nature or from relaxation processes which act on different length scales.

Semidilute Polymer Solutions at Equilibrium and under Shear Flow

“…At sufficiently large shear rates, the polymers are aligned and deformed, which implies shear thinning [11,14,80,88]. Figure 13 shows the polymer contribution η p to the shear viscosity.…”

“…However, an even stronger decay of the viscosity is observed in simulations at larger shear rates in Refs. [9,14]. Experiments of dilute polymer solutions reported exponents ranging from −0.4 to −0.85 [9,88].…”

Multi-Particle Collision Dynamics: A Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids

“…For self-avoiding linear polymers, a somewhat smaller exponent µ = 0.54 ± 0.03 was obtained in Refs. [87,146], whereas theoretical calculations predict ∼ Wi 2/3 in the limit of large Weissenberg numbers [147].…”

“…One possibility for investigating complex fluids is the straightforward application of molecular dynamics simulations (MD), in which the fluid is course-grained and represented by Lennard-Jones particles. Such simulations provide valuable insight into polymer dynamics [83][84][85][86][87]. Similarly, mesoscale algorithms such as Lattice-Boltzmann and dissipative particle dynamics have been widely used for modeling of colloidal and polymeric systems [88][89][90][91][92].…”

Propriedades dinâmicas de fluidos por simulação computacional: métodos híbridos atomístico-contínuo

“…Simulações NEMD de polímeros em solução revelam deformação e alongamento da cadeia em situações de fluxo, a dependência da viscosidade com a taxa de deformação, as diferentes escalas dinâmicas de processos de relaxação etc. [31][32][33] Nesses casos, o esforço computacional pode estar mais localizado no tratamento de um número elevado de moléculas de solvente do que no próprio modelo do polímero, que é o interesse central do estudo. Portanto, o desenvolvimento de metodologias híbridas NEMD/CFD é particularmente interessante, uma vez que o sistema pode ser aumentado tratando parte do mesmo como um meio contínuo.…”