Enhanced local viscosity around colloidal nanoparticles probed by equilibrium molecular dynamics simulations.

Area of Science:

• Materials Science
• Fluid Dynamics
• Nanotechnology

Background:

• Nanofluids, dispersions of nanoparticles in liquids, are promising for thermal management.
• A nanolayer around nanoparticles can act as a thermal bridge.
• The impact of this nanolayer on nanofluid viscosity remains unclear.

Purpose of the Study:

• To compute the local viscosity of the nanolayer surrounding nanoparticles.
• To investigate the relationship between solid-liquid interaction strength and nanolayer viscosity.
• To elucidate the origins of viscosity enhancement in the nanolayer.

Main Methods:

• Equilibrium molecular dynamics simulations.
• Application of the Green-Kubo formula for local viscosity calculation.
• Analysis of nanolayer properties for varying solid-liquid interaction strengths.

Main Results:

• The nanolayer viscosity is higher than the bulk liquid viscosity.
• Nanolayer viscosity increases with stronger solid-liquid interactions.
• Liquid density alone does not explain the viscosity enhancement; liquid structure is a key factor.
• The Stokes-Einstein relation fails near the nanoparticle surface.

Conclusions:

• The solid-like structure of the nanolayer significantly contributes to its enhanced viscosity.
• Understanding nanolayer viscosity is critical for optimizing nanofluid thermal performance.
• Hydrodynamic slip influences the relationship between viscosity and diffusion near interfaces.