Quantifying nematic order in evaporation-driven self-assembly of Halloysite nanotubes: Nematic islands and critical aspect ratio

Abstract

Halloysite nanotubes (HNTs) are naturally occurring clay minerals found in Earth's crust that typically exist in the form of high aspect-ratio nanometers-long rods. Here, we investigate the evaporation-driven self-assembly process of HNTs and show that a highly polydisperse collection of HNTs self-sort into a spatially inhomogeneous structure, displaying a systematic variation in the resulting nematic order. Through detailed quantification using nematic order parameter $S$ and nematic correlation functions, we show the existence of well-defined isotropic-nematic transitions in the emerging structures. We also show that the onset of these transitions gives rise to the formation of nematic islands - phase coexisting ordered nematic domains surrounded by isotropic phase - which grow in size with $S$. Detailed image analysis indicates a strong correlation between local $S$ and the local aspect ratio, $L/D$, with nematic order possible only for rods with $L/D\ge 6.5\pm 1$. Finally, we conclude that observed phenomena directly result from aspect ratio-based sorting in our system. Altogether, our results provide a unique method of tuning the local microscopic structure in self-assembled HNTs using $L/D$ as an external parameter.

9 pages, 4 figures

References in corpus (2)

• Minimal model for active nematics: quasi-long-range order and giant fluctuations
• Catapulting of topological defects through elasticity bands in active nematics

Cited by in corpus (3)

• Phases and correlations in active nematic granular systems
• Role of Fluid Forces and Depletion Interactions in Directing Assembly of Aqueous Gold Nanorods on Hydrophobic Surfaces
• Nematic ordering via vertical stratification in drying clay nanotube suspensions