Simulation of charged nanotubes self-assembly during evaporation of a sessile droplet on a substrate

TL;DR

This paper presents a mathematical model to understand how charged nanotubes self-assemble during droplet evaporation, revealing the combined effects of advection, diffusion, and electrostatics on deposit morphology.

Contribution

The study introduces a comprehensive model that explains the formation of complex nanotube deposit structures during evaporation, integrating multiple physical interactions.

Findings

Model confirms electrostatic, advection, and diffusion effects influence deposit morphology.

Qualitative agreement with experimental observations for specific parameters.

Provides insights into controlling nanotube assembly processes.

Abstract

The ability to control the morphology of the nanotube deposit formed during the evaporation of a sessile droplet on a substrate is of theoretical and practical interest. Such deposits are required for various applications including nanotechnology, medicine, biotechnology, and optronics. In the experiment of Zhao et al. [J. Colloid Interface Sci. 440, 68 (2015)], an annular deposit was formed near the contact line. The deposition geometry is caused by the coffee ring effect. This deposit is unusual in its morphology. It changes gradually in space from a disordered structure in the inner part of the ring to an aligned structure of nanotubes close to the periphery. To understand the mechanisms that lead to this, we have developed a mathematical model that takes into account the effects of advection, diffusion, and electrostatic interactions on particle transport. Results of numerical calculations have confirmed that all these factors together have an influence on the formation of such a variable morphology. Qualitative agreement with the experiment is shown for some values of the model parameters.