Self-assembly and thermal conductivity of amphiphilic Janus nanoparticles under nanoslit confinement

Abstract

The interplay between nanoparticle (NP) interaction anisotropy and nanoscale confinement gives rise to diverse self-assembly behaviors and the resulting macroscopic thermal properties. In this study, we use molecular dynamics (MD) simulations to explore the relationship between the structural and thermal properties of nanofluids confined in nanoscale channels. The chemical surface design of NPs alters the dependence of thermal conductivity on channel width: homogeneous hydrophilic (HI) NPs maintain thermal conductivity by forming a stable adsorption layer around dispersed NPs, whereas diblock Janus NPs exhibit clustering effects due to interaction anisotropy. This clustering weakens adsorption layers, reducing thermal conductivity even under weak confinement. Under strong confinement, solvent molecules form more pronounced structured layers near the walls; however, NPs disrupt this ordering, resulting in lower thermal conductivity than in a confined purely solvent system. Diblock Janus NPs, in particular, disrupt these layers more due to their clustering, further hindering thermal conductivity. Although both NP types exhibit reduced Brownian motion as channel width decreases, we conclude that it does not significantly affect the thermal conductivity of nanofluids. For instance, Janus NPs, which exhibit greater Brownian motion in wider channels, still show lower thermal conductivity than HI NPs. While HI NPs form stable adsorption layers that enhance thermal transport, Janus NPs tend to self-assemble into micelles, weakening the adsorption layer and further reducing thermal conductivity. Our study provides molecular insight into the relationship between NP dynamics, surface properties, and adsorption layers in determining the thermal conductivity of confined nanofluids.