Riichi Nishimura

Large-scale self-assembled zirconium phosphate smectic layers via a simple spray-coating process

The large-scale assembly of asymmetric colloidal particles is used in creating high-performance fibres. A similar concept is extended to the manufacturing of thin films of self-assembled two-dimensional crystal-type materials with enhanced and tunable properties. Here we present a spray-coating method to manufacture thin, flexible and transparent epoxy films containing zirconium phosphate nanoplatelets self-assembled into a lamellar arrangement aligned parallel to the substrate. The self-assembled mesophase of zirconium phosphate nanoplatelets is stabilized by epoxy pre-polymer and exhibits rheology favourable towards large-scale manufacturing. The thermally cured film forms a mechanically robust coating and shows excellent gas barrier properties at both low- and high humidity levels as a result of the highly aligned and overlapping arrangement of nanoplatelets. This work shows that the large-scale ordering of high aspect ratio nanoplatelets is easier to achieve than previously thought and may have implications in the technological applications for similar materials.

Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order.

Epoxy films containing self-assembled 2D colloidal α-zirconium phosphate nanoplatelets (ZrP) in smectic order were prepared using a simple, energy-efficient fabrication process suitable to industrial processing. The ZrP nanoplatelets form a chiral smectic mesophase with simultaneous lamellar order and helical arrangements in epoxy. The epoxy nanocomposite films are transparent and flexible and exhibit exceptionally high tensile modulus and strength. The findings have broad implications for development of multifunctional materials for engineering applications.

Facile decoration of Au nanoparticles on reduced graphene oxide surfaces via a one-step chemical functionalization approach

A facile way to fabricate functionalized and reduced graphene oxide (RGO) was reported by introducing the dual-function reagent N1-(3-trimethoxysilylpropyl) diethylenetriamine (TSPD), in which (i) the amine functional groups of the organosilane can effectively restore the π bonds of the GO; and (ii) the silanol parts react with the hydroxyl groups of GO and subsequently cross-link to form a monolayer on the graphene surface. The exposed amine groups of the functionalized GO could effectively template the Au nanoparticles (AuNPs) assembly on the graphene surface with high density and good dispersity. TEM images indicate that AuNPs retained their original size and were well-anchored on the graphene surfaces with an average inter-particle distance of 15 nm. The resultant graphene sheets decorated by AuNPs has the capability of sensing single molecules on its surface, e.g., Rhodamine 6G (Rh6G), through the surface-enhanced Raman spectroscopy (SERS).

Highly effective anti-corrosion epoxy spray coatings containing self-assembled clay in smectic order

Epoxy nanocomposite coatings containing self-assembled α-zirconium phosphate nanoplatelets (ZrP) in smectic order were successfully prepared by spray-coating on an aluminum substrate using a simple, energy-efficient fabrication process that is suitable for industrial practices. Aluminium substrates with smectic epoxy/ZrP coatings showed a substantial improvement in corrosion resistance compared to the metal surface coating with unfilled epoxy alone. Lyotropic liquid crystal behaviour of ZrP nanoplatelets was observed in a number of different solvents, which suggests the phenomena are largely entropically driven and would be suitable for various coating systems. The results show that the epoxy coatings containing highly aligned ZrP nanoplatelets in smectic order may be used to effectively protect metal surfaces from corrosion using a scalable and simple approach.

Effect of surface modifier on flow properties of epoxy suspensions containing model plate-like nanoparticles

The influence of inter-particle interaction on the rheology of an uncured epoxy containing model α-zirconium phosphate (ZrP) nanoplatelets with aspect ratio of 160 is reported. Epoxy suspensions containing nanoplatelets exfoliated with tetra-n-butyl ammonium hydroxide (TBA), a low molecular weight quaternary ammonium cation, show short-range repulsive potential with weak elastic response at low concentration. At semi-dilute concentrations, the suspensions are solid-like at intermediate frequency and transition to viscous flow for time scales longer than the rotary diffusion process. The weak elasticity at intermediate frequency is attributed to the effect of Brownian motion on the rotational motion of the isolated plates. Suspensions containing nanoplatelets exfoliated with hydrophilic polyetheramine oligomers show similar behaviour to the ZrP-TBA system, but shifted to lower concentration. The rheological behaviour is attributed to steric stabilization of the nanoplatelets by extended oligomer brushes with short-range repulsive interactions. For suspensions containing nanoplatelets exfoliated with hydrophobic polyetheramines with shorter length, there is evidence for elastic response on local length scales and the flow behaviour shows strong history and temperature dependence. Rheological signatures associated with equilibrium nanoplatelet dispersions with repulsive interactions are discussed.

Electrostatically controlled isolation of debundled single-walled carbon nanotubes from nanoplatelet dispersant

Individually dispersed single-walled carbon nanotubes (SWCNTs) were isolated and stabilized from electrostatically tethered nanoplatelets in aqueous solution, following nanoplatelet-assisted exfoliation. SWCNT isolation was achieved by precipitating nanoplatelets with cations and by concurrent usage of appropriate surfactants to stabilize SWCNTs. It was found that the precipitation of nanoplatelets induced by monovalent cations was due to the ionic screening effect, whereas ion exchange was the main cause for nanoplatelet aggregation when divalent cations were used. When the above processes are optimized, isolation of pure SWCNTs with yield greater than 90% can be achieved. Effects of ion valency, ion size, reaction time, concentration of SWCNTs and surfactant type for the separation process are discussed. The structure and composition of the exfoliated SWCNTs were characterized using various microscopy and spectroscopy tools. The above exfoliation and separation approach does not noticeably affect the electronic state of the SWCNTs, and is thus highly attractive for applications where optimal SWCNT properties are desired.

Spray-coated epoxy barrier films containing high aspect ratio functionalized graphene nanosheets

Epoxy nanocomposite spray-coatings containing large aspect ratio modified graphene (MG) were successfully prepared in a facile manner. The individually exfoliated MG nanosheets form liquid crystalline mesophases in the epoxy precursor at low loadings. The epoxy/MG nanocomposite films exhibit significantly improved gas barrier properties even in humid conditions. The spray-coating method allows for the preparation of high MG content nanocomposites in large scale without compromising processability. Implication of the present finding for fabrication of high-performance graphene-based packaging films with multi-functionality is discussed.