Molecular simulation of translational and rotational diffusion of Janus nanoparticles at liquid interfaces

TL;DR

This study uses molecular dynamics simulations to analyze how Janus nanoparticles move and rotate at liquid interfaces, revealing how amphiphilicity and fluid interactions influence their diffusion and structure formation.

Contribution

It provides new insights into the effects of amphiphilicity on nanoparticle dynamics and fluid structuring at interfaces, advancing understanding of anisotropic particle behavior.

Findings

Increased amphiphilicity reduces rotational motion.

Higher amphiphilicity slows in-plane diffusion.

Particles induce ordered fluid structures that resist movement.

Abstract

We perform molecular dynamics simulations to understand the translational and rotational diffusion of Janus nanoparticles at the interface between two immiscible fluids. Considering spherical particles with different affinity to fluid phases, both their dynamics as well as the fluid structure around them are evaluated as a function of particle size, amphiphilicity, fluid density, and interfacial tension. We show that as the particle amphiphilicity increases due to enhanced wetting of each side with its favorite fluid, the rotational thermal motion decreases. Moreover, the in-plane diffusion of nanoparticles at the interface becomes slower for more amphiphilic particles, mainly due to formation of a denser adsorption layer. The particles induce an ordered structure in the surrounding fluid that becomes more pronounced for highly amphiphilic nanoparticles, leading to increased resistance against nanoparticle motion. A similar phenomenon is observed for homogeneous particles diffusing in bulk upon increasing their wettability. Our findings can provide fundamental insight into the dynamics of drugs and protein molecules with anisotropic surface properties at biological interfaces including cell membranes.