Directionally asymmetric self-assembly of cadmium sulfide nanotubes using porous alumina nanoreactors: Need for chemohydrodynamic instability at the nanoscale

TL;DR

This paper investigates the asymmetric self-assembly of cadmium sulfide nanotubes within porous alumina nanoreactors, emphasizing the role of chemohydrodynamic instabilities at the nanoscale, which classical hydrodynamics cannot explain.

Contribution

It demonstrates the necessity of chemohydrodynamic convective instabilities for nanotube nucleation at the nanoscale, highlighting the need for further study of fluid dynamics in nanoconfined systems.

Findings

Uneven precursor flow causes asymmetric nanotube growth

Classical hydrodynamics cannot explain nanoscale instabilities

Chemohydrodynamic effects are essential for nanotube nucleation

Abstract

We explore nanoscale hydrodynamical effects on synthesis and self-assembly of cadmium sulfide nanotubes oriented along one direction. These nanotubes are synthesized by horizontal capillary flow of two different chemical reagents from opposite directions through nanochannels of porous anodic alumina which are used primarily as nanoreactors. We show that uneven flow of different chemical precursors is responsible for directionally asymmetric growth of these nanotubes. On the basis of structural observations using scanning electron microscopy, we argue that chemohydrodynamic convective interfacial instability of multicomponent liquid-liquid reactive interface is necessary for sustained nucleation of these CdS nanotubes at the edges of these porous nanochannels over several hours. However, our estimates clearly suggest that classical hydrodynamics cannot account for the occurrence of such instabilities at these small length scales. Therefore, we present a case which necessitates further investigation and understanding of chemohydrodynamic fluid flow through nanoconfined channels in order to explain the occurrence of such interfacial instabilities at nanometer length scales.