Hexagonal Superalignment of Nano-Objects with Tunable Separation in a Dilute and Spacer-Free Solution.

Manipulating building-block nanomaterials to form an ordered superstructure in a dilute and spacer-free solution phase challenges the existing 5-nm node lithography and nanorobotics. The cooperative nature of nanocrystals, polymers, and cells can lead to superarrays or colloidal crystals. For known highly ordered systems, the characteristic length of materials, defined as the shortest dimension of objects, is generally larger than their separations. A spacer (small-molecule surfactant or polymer) is typically required to diminish short range van der Waals attraction, which results in a glassy or liquid state. Herein we propose a new concept of achieving highly ordered nano-objects in a dilute and spacer-free system via the synergistic effects of excellent solvation and appropriate constraints on rotational motion. As a proof of concept, this study demonstrates that aluminosilicate nanotubes (AlSiNTs) suspended in water under dilute conditions (e.g., 1.0 wt%) can spontaneously form hexagonal arrays with an intertubular distance as large as tens of nanometers. The separation distance of the ordered superstructure is also tunable via controlling the concentration and length of nanotubes. These superaligned structures are probed using small-angle x-ray scattering and cryo-TEM characterizations, with underlying mechanisms investigated at an atomic level using molecular dynamics simulations. The concept and discovery of this work can open up opportunities to a variety of applications including visible-UV photonics and nanolithography, and may be generalizable to other nano-object systems that fulfill similar requirements.

Properties of Single-Walled Aluminosilicate Nanotube/Poly(vinyl alcohol) Aqueous Dispersions.

The properties of (synthesized) single-walled aluminosilicate nanotube (AlSiNT; light-scattering characterized length ∼2000 ± 230 nm and diameter ∼35 ± 4 nm) dispersed in an aqueous poly(vinyl alcohol) (PVA) solution (10 wt %) are systematically explored using a comprehensive combination of (polarized/depolarized) dynamic light scattering, rheological, rheo-optical, and scanning electron microscopy analysis schemes. The nanotube/polymer dispersions under investigation are promising for their fair nanotube dispersion in pristine aqueous media (e.g., without salt or acid addition), as well as for the optical transparency that greatly facilitates systematic exploration of structural features and dispersion state that are practically inaccessible for many of their (opaque) companions such as carbon nanotube dispersions. We provide the first in-depth analysis revealing excellent dispersion state of (unmodified) AlSiNT in the PVA matrix, giving rise to (critical) gel-like features and substantially promoted elasticity that can be utilized, as a practical assessment, to produce uniform and defect-free electrospun nanofibers. Additionally, there is unambiguous evidence of nematic liquid crystal-like "wagging" (strain-invariant, periodic oscillation) under steady shear flow, a phenomenon previously unreported for nanotube composite materials. Overall, the present findings suggest that AlSiNT/PVA dispersions possess promising rheological, optical, and electrospinning properties that are highly desirable for current nanotechnological applications, and may serve as an ideal model system for establishing structure-performance relationships for like nanotube/polymer composite materials.