Understanding Nanoparticle Diffusion and Exploring Interfacial Nanorheology using Molecular Dynamics Simulations

Abstract

We have studied the dynamics of nanoparticles at polydimethylsiloxane (PDMS) oil-water interfaces using molecular dynamics (MD) simulations. The diffusion of nanoparticles in pure water and low-viscosity PDMS oil is found to be reasonably consistent with the prediction by the Stokes-Einstein equation. In addition, we have calculated the shear moduli and viscosities of bulk oil and water, as well as oil-water interfaces from single nanoparticle tracking and demonstrated the potential of probing nanorheology from an MD simulation approach. Surprisingly, we found that the lateral diffusion of nanoparticles as well as apparent interfacial nanorheology at the PDMS oil (low viscosity)-water interface are independent of the position of the nanoparticle at the interface.

Molecular simulation of nanoparticle diffusion at fluid interfaces

“…, in good agreement with previous simulations [22]. The present results are also in good agreement with experimental measurements, with D t ≈ 0.2 cm 2 s −1 for 1 nm dye particles [32].…”

“…These are in good agreement with previous simulations [22] and find that the in-plane diffusion coefficients are larger that the nanoparticle diffusion coefficient in bulk solvent. This increased diffusion may arise due to the lower viscosity of the interfacial region; from RNEMD simulations [28,36] the viscosity in the interfacial region is found to be approximately four times smaller that in the bulk (η I ≈ 0.25mσ…”

“…Previous simulations have addressed the stability of nanoparticles at interfaces [13][14][15][16][17], interactions between nanoparticles [18], orientational behaviour of anisotropic nanoparticles [17,19], and the self-assembly of nanoparticles at fluid interfaces [20,21]. These simulations have largely focused on the static properties of nanoparticles at interfaces, while only recently has simulation be turned to the dynamic properties of nanoparticles at liquid interfaces [22].…”

Complex Molecules at Liquid Interfaces: Insights from Molecular Simulation

“…Once the two-dimensional confinement of the particles was accounted for, it was found that the particle diffusion was increased relative to bulk solution, which may be understood due to the lower effective viscosity of the interfacial region. The results of this work differed from those of Song et al [47], studying carbon nanoparticles at a water-PDMS interface. This difference may be due to the larger particles used in that work or the difference in viscosity between the water and polymer components in that work; the diffusion of particles on a fluid interface increases when the viscosity difference between the two fluid components is small [48].…”

Molecular dynamics study of nanoparticle stability at liquid interfaces: Effect of nanoparticle-solvent interaction and capillary waves

“…More recently the interaction potential between a nanoparticle and a liquid interface was determined using Monte Carlo or molecular dynamics simulations, for uniform 18 , Janus (amphiphilic) 19 , and polymer-grafted nanoparticles 20 . Simulations have also been used to study the interactions between adsorbed nanoparticles 21 , self-assembly of nanoparticles at liquid-liquid interfaces 22 , and nanoparticle diffusion at interfaces 23,24 .…”