## Effective Particle Size From Molecular Dynamics Simulations in Fluids

## Abstract

Here, we report molecular dynamics simulations designed to investigate the effective size of colloidal particles suspended in a fluid in the vicinity of a rigid wall where all interactions are defined by smooth atomic potential functions. These simulations are used to assess how the behavior of this system at the atomistic length scale compares to continuum mechanics models. In order to determine the effective size of the particles, we calculate the solvent forces on spherical particles of different radii as a function of different positions near and overlapping with the atomistically defined wall and compare them to continuum models. This procedure also then determines the effective position of the wall. Our analysis is based solely on forces that the particles sense, ensuring self-consistency of the method. The simulations were carried out using both Weeks–Chandler–Andersen and modified Lennard-Jones (LJ) potentials to identify the different contributions of simple repulsion and van der Waals attractive forces. Upon correction for behavior arising the discreteness of the atomic system, the underlying continuum physics analysis appeared to be correct down to much less than the particle radius. For both particle types, the effective radius was found to be ~0.75σ, where σ defines the length scale ofmore »

- Authors:

- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Mechanical Engineering
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

- Publication Date:

- Research Org.:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

- Sponsoring Org.:
- USDOE

- OSTI Identifier:
- 1411988

- Alternate Identifier(s):
- OSTI ID: 1415366

- Report Number(s):
- LA-UR-14-28035

Journal ID: ISSN 0935-4964; TRN: US1800771

- Grant/Contract Number:
- AC52-06NA25396

- Resource Type:
- Published Article

- Journal Name:
- Theoretical and Computational Fluid Dynamics

- Additional Journal Information:
- Journal Volume: 32; Journal Issue: 2; Journal ID: ISSN 0935-4964

- Publisher:
- Springer

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING; Material Science; molecular dynamics, colloids

### Citation Formats

```
Ju, Jianwei, Welch, Paul Michael Jr., Rasmussen, Kim Orskov, Redondo, Antonio, Vorobieff, Peter, and Kober, Edward Martin. Effective Particle Size From Molecular Dynamics Simulations in Fluids. United States: N. p., 2017.
Web. doi:10.1007/s00162-017-0450-0.
```

```
Ju, Jianwei, Welch, Paul Michael Jr., Rasmussen, Kim Orskov, Redondo, Antonio, Vorobieff, Peter, & Kober, Edward Martin. Effective Particle Size From Molecular Dynamics Simulations in Fluids. United States. doi:10.1007/s00162-017-0450-0.
```

```
Ju, Jianwei, Welch, Paul Michael Jr., Rasmussen, Kim Orskov, Redondo, Antonio, Vorobieff, Peter, and Kober, Edward Martin. Fri .
"Effective Particle Size From Molecular Dynamics Simulations in Fluids". United States. doi:10.1007/s00162-017-0450-0.
```

```
@article{osti_1411988,
```

title = {Effective Particle Size From Molecular Dynamics Simulations in Fluids},

author = {Ju, Jianwei and Welch, Paul Michael Jr. and Rasmussen, Kim Orskov and Redondo, Antonio and Vorobieff, Peter and Kober, Edward Martin},

abstractNote = {Here, we report molecular dynamics simulations designed to investigate the effective size of colloidal particles suspended in a fluid in the vicinity of a rigid wall where all interactions are defined by smooth atomic potential functions. These simulations are used to assess how the behavior of this system at the atomistic length scale compares to continuum mechanics models. In order to determine the effective size of the particles, we calculate the solvent forces on spherical particles of different radii as a function of different positions near and overlapping with the atomistically defined wall and compare them to continuum models. This procedure also then determines the effective position of the wall. Our analysis is based solely on forces that the particles sense, ensuring self-consistency of the method. The simulations were carried out using both Weeks–Chandler–Andersen and modified Lennard-Jones (LJ) potentials to identify the different contributions of simple repulsion and van der Waals attractive forces. Upon correction for behavior arising the discreteness of the atomic system, the underlying continuum physics analysis appeared to be correct down to much less than the particle radius. For both particle types, the effective radius was found to be ~0.75σ, where σ defines the length scale of the force interaction (the LJ diameter). The effective “hydrodynamic” radii determined by this means are distinct from commonly assumed values of 0.5σ and 1.0σ, but agree with a value developed from the atomistic analysis of the viscosity of such systems.},

doi = {10.1007/s00162-017-0450-0},

journal = {Theoretical and Computational Fluid Dynamics},

number = 2,

volume = 32,

place = {United States},

year = {2017},

month = {12}

}

DOI: 10.1007/s00162-017-0450-0