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. 2024 Jun 7;10(23):eadk6452.
doi: 10.1126/sciadv.adk6452. Epub 2024 Jun 5.

Monodisperse nanosheet mesophases

Nobuyoshi Miyamoto  1   2 , Momoka Miyoshi  2 , Riki Kato  2   3 , Yuji Nakashima  2 , Hiroyuki Iwano  2 , Takashi Kato  3   4
Affiliations

Monodisperse nanosheet mesophases

Nobuyoshi Miyamoto et al. Sci Adv. .

Abstract

Self-assemblies of anisotropic colloidal particles into colloidal liquid crystals and well-defined superlattices are of great interest for hierarchical nanofabrications that are applicable for various functional materials. Inorganic nanosheets obtained by exfoliation of layered crystals have been highlighted as the intriguing colloidal units; however, the size polydispersity of the nanosheets has been preventing precise design of the assembled structures and their functions. Here, we demonstrate that the anionic titanate nanosheets with monodisperse size reversibly form very unusual superstructured mesophases through finely tunable weak attractive interactions between the nanosheets. Transmission electron microscopy, polarizing optical microscopy, small-angle x-ray scattering, and confocal laser scanning microscopy clarified the reversible formation of the mesophases (columnar nanofibers, columnar nematic liquid crystals, and columnar nanofiber bundles) as controlled by counter cations, nanosheet concentration, solvent, and temperature.

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Figures

Fig. 1.
Fig. 1.. Formation of ColNFs, ColNF-Nem, and ColNF-Buns of the mNSs controlled by ionic strength and nanosheet concentration.
(A) Schematic structure of the mNS and (B) its TEM image. (C) The phase diagram, POM images, and schematic structures of the mNS aqueous dispersions as the function of [mNS] and [TMA+]. The labels I and Ic represent isotropic dispersions of the mNS and ColNF, respectively. (D) SAXS patterns of the mNS dispersions with varied [mNS] and [TMA+], which are also indicated as black filled triangle plots in the phase diagram. The dashed lines are the simulated SAXS curves for the ColNFs with n layers (figs. S4 and S5 for details). a.u., arbitrary units. (E) TEM and (F) cryo-TEM images of the ColNFs. (G) The observation under crossed polarizers of the ColNF-Nem sample ([mNS] = 3.1 vol % and [TMA+] = 2.2 M) in a glass vial and (H) its POM image at the interface between the colloidal sample and the spacer (silicone rubber sheet with the thickness of 0.5 mm). The arrows A and P show the directions of analyzer and polarizer, respectively. The line R is the direction of the λ plate with the retardation of 530 nm.
Fig. 2.
Fig. 2.. EtOH concentration dependence of the mesophases of the mNS/water/EtOH colloidal sols.
(A) Photographs under crossed polarizers and CLSM images of the colloidal sols ([TMA+] = 0.08 M and [mNS] = 0.15 vol %) and (B) their SAXS profiles.
Fig. 3.
Fig. 3.. Intercalation of various cationic species into the ColNFs.
(A) SAXS profiles of the aqueous dispersions of the ColNFs intercalated with TMA+, TEA+, TPA+, TBA+, C10TMA+, and Ru(bpy)32+ and (B) their schematic structures. (C) The photograph under crossed polarizers and (D) fluorescence microscopy image of ColNF-Buns intercalated with Ru(bpy)32+ ([mNS] = 0.26 vol %, [TMA+] = 0.13 M, Ru/CEC = 1.0) and (E) TEM image of Ru(bpy)32+ intercalated ColNFs (Ru/CEC = 0.8). CEC represents the cation exchange capacity of the mNSs.
Fig. 4.
Fig. 4.. Temperature-controlled mesophase formation of the TBA+/mNS aqueous colloid.
(A) SAXS patterns in the heating process, (B) photographs under crossed polarizers, (C) POM image at 60°C, and (D) schematic structure of the supercrystalline ColNF-Bun. [mNS] = 0.52 vol % and [TBA+] = 0.27 M.
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