ABSTRACT
Halloysite nanotubes (HNTs) are naturally occurring clay minerals found in the Earth's crust that typically exist in the form of high aspect-ratio nanometer-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 the 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, a phase resembling ordered nematic domains surrounded by an 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 ≥ 6.5 ± 1. Finally, we conclude that the 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.
ABSTRACT
One-step evaporative jamming of colloidal silica particles in contact-free spray droplets resulted in well-defined powder micro-granules with interstitial nanopores. This paper reports the anomalous freezing behaviour of confined water in the microspheres synthesized using spray drying. It has been revealed that the freezing point of water in these microspheres gets significantly lowered (â¼-45 °C) owing to the confinement effect. Thermoporometry results are corroborated with the structural details obtained using complementary techniques of gas adsorption measurements and small-angle x-ray scattering.