^{1}, Fernando Escobedo

^{1}and Yong Lak Joo

^{1,a)}

### Abstract

Coarse-grained, molecular dynamics (MD) simulations have been conducted to study the effect of shear flow on polymernanocomposite systems. In particular, the interactions between different components have been tuned such that the nanoparticle-nanoparticle attraction is stronger than nanoparticle-polymer interaction, and therefore, the final equilibrium state for such systems is one with clustered nanoparticles. In the current study, we focus on how shear flow affects the kinetics of particle aggregation at the very initial stages in systems with polymers of different chain lengths. The particle volume fraction and size are kept fixed at 0.1 and 1.7 MD units, respectively. Through this work, shear has been shown to significantly slow down nanoparticle aggregation, an effect that was found to be a strong function of both polymer chain length and shear rate. To understand our findings, a systematic study on effect of shear on particle diffusion and an analysis of relative time scales of different mechanisms causing particle aggregation have been conducted. The aggregation rate obtained from the time scale analysis is in good agreement with that determined from the aggregation time derived from the pair correlation function monitored during simulations.

I. INTRODUCTION

II. MODEL AND METHODS

A. Potentials

B. Thermostat

C. Simple shear flow

D. Computational details

III. RESULTS AND DISCUSSION

IV. CONCLUSIONS

### Key Topics

- Diffusion
- 58.0
- Aggregation
- 54.0
- Polymers
- 48.0
- Shear flows
- 25.0
- Nanocomposites
- 14.0

## Figures

Self-attracting NP polymer nanocomposites. (a) Snapshots for , , and 0.1 at (left) and (right), and 3000 MD units. Matrix chain length is and for NP-NP attraction. Polymer chains have been removed for clarity.

Self-attracting NP polymer nanocomposites. (a) Snapshots for , , and 0.1 at (left) and (right), and 3000 MD units. Matrix chain length is and for NP-NP attraction. Polymer chains have been removed for clarity.

Self-attracting NP polymer nanocomposites. Snapshots of system at , , and 0.1 at different elapse MD units, and 3000 MD units. For all figure parts, matrix chain length is and for NP-NP attraction. Polymer chains have been removed for clarity.

Self-attracting NP polymer nanocomposites. Snapshots of system at , , and 0.1 at different elapse MD units, and 3000 MD units. For all figure parts, matrix chain length is and for NP-NP attraction. Polymer chains have been removed for clarity.

NP pair correlation function at (a), 0.05 (b), and 0.1 (c) at different elapsed times. For all figure parts, matrix chain length and for NP-NP attraction. The curves have been normalized with the maximum peak value at (a).

NP pair correlation function at (a), 0.05 (b), and 0.1 (c) at different elapsed times. For all figure parts, matrix chain length and for NP-NP attraction. The curves have been normalized with the maximum peak value at (a).

(a) NP pair correlation function at , (center) 0.1, and (right) 0.15. (b) Nonbonded potential energy between NP pairs at different shear rates as a function of time. Matrix chain length and for NP-NP attraction. The curves have been normalized with the maximum peak value at (a).

(a) NP pair correlation function at , (center) 0.1, and (right) 0.15. (b) Nonbonded potential energy between NP pairs at different shear rates as a function of time. Matrix chain length and for NP-NP attraction. The curves have been normalized with the maximum peak value at (a).

Diffusion measurements for system with and . (a) Unconvected NP mean squared displacement vs time for different shear rates. (b) Diffusion calculated using Eq. (8) as a function of shear rate.

Diffusion measurements for system with and . (a) Unconvected NP mean squared displacement vs time for different shear rates. (b) Diffusion calculated using Eq. (8) as a function of shear rate.

Unconvected NP mean squared displacement for different matrix chain lengths as a function of time (a) , (c) , and (d) . Part (b) shows the diffusion coefficient values for different NP diameters at and .

Unconvected NP mean squared displacement for different matrix chain lengths as a function of time (a) , (c) , and (d) . Part (b) shows the diffusion coefficient values for different NP diameters at and .

Diffusion coefficient as a function of matrix chain length for different shear rates.

Diffusion coefficient as a function of matrix chain length for different shear rates.

(a) Unconvected NP mean squared displacement for a polymer nanocomposites system with and at different shear rates as a function of time. (b) Diffusion coefficient calculated using slope of part (a) using Eq. (8) as a function of shear rate. (c) Diffusion coefficient vs shear rate for different matrix chain lengths.

(a) Unconvected NP mean squared displacement for a polymer nanocomposites system with and at different shear rates as a function of time. (b) Diffusion coefficient calculated using slope of part (a) using Eq. (8) as a function of shear rate. (c) Diffusion coefficient vs shear rate for different matrix chain lengths.

Time scale analysis of various forces and events during aggregation of NPs under shear flow as a function of shear rate, (a) and (b) . In both figure parts, the left curve shows the time scales of shear/deformation and diffusion and the right curve shows the “predicted” and “calculated” normalized nondimensional aggregation rates of NPs. Please see text for explanation of various terms.

Time scale analysis of various forces and events during aggregation of NPs under shear flow as a function of shear rate, (a) and (b) . In both figure parts, the left curve shows the time scales of shear/deformation and diffusion and the right curve shows the “predicted” and “calculated” normalized nondimensional aggregation rates of NPs. Please see text for explanation of various terms.

Time scale analysis of various forces and events during aggregation of NPs under shear flow as a function of matrix chain length (a) , (b) , and (c) . In all figure parts, the left curve shows the time scales of shear/deformation and diffusion and the right curve shows the “predicted” and “calculated” normalized nondimensional aggregation rates of NPs. Please see text for explanation of various terms.

Time scale analysis of various forces and events during aggregation of NPs under shear flow as a function of matrix chain length (a) , (b) , and (c) . In all figure parts, the left curve shows the time scales of shear/deformation and diffusion and the right curve shows the “predicted” and “calculated” normalized nondimensional aggregation rates of NPs. Please see text for explanation of various terms.

## Tables

Simulation parameters.

Simulation parameters.

Simulation details.

Simulation details.

Article metrics loading...

Full text loading...

Commenting has been disabled for this content