Electrophoretic co-deposition of biomimetic nanoplatelet–polyelectrolyte composites

Bio-inspired assembly of platelet particles and polyelectrolytes into ordered layered composites is of great technological importance in developing light-weight reinforced materials, separation membranes, and gas-barrier coatings. Unfortunately, the broadly applied layer-by-layer self-assembly technology is tedious in generating thick multilayered coatings. Here, we report a rapid and scalable cathodic electrophoretic co-deposition technology that enables simultaneous assembly of positively charged gibbsite nanoplatelets and cationic polyelectrolytes into ordered multilayers in a single step. The resulting nanocomposites have similar organic/inorganic weight ratio and ordered brick-and-mortar nanostructure as natural nacres. Nanoindentation tests show that the electrodeposited nanocomposites exhibit similar hardness and reduced modulus as those of pure gibbsite coatings.     

CdSe/CdTe II型胶态量子阱中长寿命的单激子、带电激子和双激子

Light-harvesters with long-lived excited states are desired for efficient solar energy conversion systems. Many solar-to-fuel conversion reactions, such as H₂ evolution and CO₂ reduction, require multiple sequential electron transfer processes, which leads to a complicated situation that excited states involves not only excitons (electron-hole pairs) but also multi-excitons and charged excitons. While long-lived excitons can be obtained in various systems (e.g., semiconductor nanocrystals), multi-excitons and charged excitons are typically shorted-lived due to nonradiative Auger recombination pathways whereby the recombination energy of an exciton is quickly transferred to the third carrier on a few to hundreds of picoseconds timescale. In this work, we report a study of excitons, trions (an exciton plus an additional charge), and biexcitons in CdSe/CdTe colloidal quantum wells or nanoplatelets. The typeⅡ band alignment effectively separates electrons and holes in space, leading to a single exciton lifetime of 340 ns which is ~2 order of magnitudes longer than that in plane CdSe nanoplatelets. More importantly, the electron-hole separation also dramatically slows down Auger decay, giving rise to a trion lifetime of 70 ns and a biexciton lifetime of 11 ns, among the longest values ever reported for colloidal nanocrystals. The long-lived exciton, trion, and biexciton states, combined with the intrinsically strong light-absorption capability of two-dimensional systems, enable the CdSe/CdTe type-Ⅱ nanoplatelets as promising light harvesters for efficient solar-to-fuel conversion reactions.     

Oriented array of polyethylene-block-poly(ethylene oxide) nanoplatelets in unsaturated polyesters cross-linked coatings

Transparent coatings of cross-linked unsaturated polyester (UP) containing staggered platelets of polyethylene-block-poly(ethylene oxide) with their normal perpendicular to the substrate have been readily prepared by a solvent assisted spin-coating method. For this purpose, homogeneous liquid dispersions of block copolymer platelets in liquid UP resin have been prepared using a selective solvent, deposited onto flat substrates by spin-coating and converted into a transparent solid layer by photochemical cross-linking. Although such stratified morphology has been already reported for inorganic nanoplatelets (typically clay particles), we report for the fist time the formation of such stratified morphology in fully organic system. The shear-induced origin of this organization has been confirmed by the rheological properties of the uncured systems where a pronounced non-Newtonian behavior has been observed.     

Facile synthesis and optical properties of Co3O4 nanostructures by the microwave route

Cobalt oxide (Co₃O₄) nanoplatelet shape like nanostructures have been successfully synthesized through a simple microwave route for the first time using cobalt acetate, NaOH and citric acid at 200 °C for 30 min. The structure and morphology of as-prepared Co₃O₄ nanoplatelets are characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), and scanning electron microscope (SEM). XRD measurements indicate that the product has a perfect crystalline cubic phase of Co₃O₄ with a lattice constant a=8.082 Å. The SEM images show that the obtained Co₃O₄ nanopowder consists of nanoplatelets with diameter 125 nm and thickness 20 nm. Energy-dispersive X-ray spectroscopy (EDS) show that the composition of Co₃O₄ is stoichiometric. Room temperature photoluminescence measurement is exhibited by a strong UV emission and a suppressed green emission, confirming the good optical properties for the as-prepared Co₃O₄ nanoplatelets.     

Synthesis and field emission properties of nickel oxide nanoplatelets prepared by simple novel technique

Single crystalline NiO nanoplatelets were successfully synthesized by new facile method at 200 °C. The morphology and microstructure were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD measurement indicated that the prepared sample had typical cubic structures. The SEM investigation confirmed that the product was of the form of nanoplatelets. These nanoplatelets have average width length 250 nm and thickness of 20 nm. The field emission measurements demonstrate that the NiO nanoplatelets show a promising field emission property. The improved field emission is attributed to the local field enhancement factor at the nanoplatelets. The results confirm the importance of the morphology of nanomaterial in field emission.     

Nanoscale structure intercrystalline interactions in fat crystal networks

The functional attributes of fat-structured food products such as butter, margarine, chocolate, and ice cream are strongly influenced by the structure and physical properties of an underlying fat crystal network present in the material. Fat crystal networks are arranged in a hierarchical manner with characteristic and quantifiable nano and mesoscale structures. Recent studies carried out by our group have demonstrated that the formation of such a fat crystal network starts with the association of nanoplatelets at the lowest constitutional level. These nanoplatelets interact and aggregate via van der Waals's forces into larger fractal structures, which eventually form a 3-dimensional network responsible for the solid-like characteristics of the material. The purpose of this review is to summarize recent efforts in the characterization and quantification of these recently discovered crystalline nanoplatelets and to discuss the role of van der Waals interactions between them. In addition a brief discussion of previous fractal model will be presented. The new experimental findings on the nanostructural level will then be used to validate our fractal structural–mechanical model of fats (Marangoni, 2000). These new insights will contribute to our knowledge of the nature of fat crystal network in plastic fats at different length scales and the relationship of these structural characteristics to the function and properties of fats.     

Long-lived Single Excitons,Trions, and Biexcitons in CdSe/CdTe Type-Ⅱ Colloidal Quantum Wells

Light-harvesters with long-lived excited states are desired for efficient solar energy conversion systems. Many solar-to-fuel conversion reactions, such as H₂ evolution and CO₂ reduction, require multiple sequential electron transfer processes, which leads to a complicated situation that excited states involves not only excitons (electron-hole pairs) but also multi-excitons and charged excitons. While long-lived excitons can be obtained in various systems (e.g., semiconductor nanocrystals), multi-excitons and charged excitons are typically shorted-lived due to nonradiative Auger recombination pathways whereby the recombination energy of an exciton is quickly transferred to the third carrier on a few to hundreds of picoseconds timescale. In this work, we report a study of excitons, trions (an exciton plus an additional charge), and biexcitons in CdSe/CdTe colloidal quantum wells or nanoplatelets. The typeⅡ band alignment effectively separates electrons and holes in space, leading to a single exciton lifetime of 340 ns which is ~2 order of magnitudes longer than that in plane CdSe nanoplatelets. More importantly, the electron-hole separation also dramatically slows down Auger decay, giving rise to a trion lifetime of 70 ns and a biexciton lifetime of 11 ns, among the longest values ever reported for colloidal nanocrystals. The long-lived exciton, trion, and biexciton states, combined with the intrinsically strong light-absorption capability of two-dimensional systems, enable the CdSe/CdTe type-Ⅱ nanoplatelets as promising light harvesters for efficient solar-to-fuel conversion reactions.     

Formation of Polyvinyl Alcohol film with graphene nanoplatelets and carbon black for electrostatic discharge protective packaging

This research investigated the synergic effect of graphene nanoplatelets (GNPs) and carbon black (CB) as a blended conductive filler for polymer film used as electrostatic discharge (ESD) packaging materials. Various weight ratios of GNPs/CB and combined filler concentrations were mixed and processed into Polyvinyl Alcohol (PVOH) based film. The surface resistivity and volume resistivity of the resulting film was measured under three different humidity environments. The study found that the composite with GNPs/CB ratios of 10:90 and 30:70 resulted in a sharp drop in surface resistivity by 5–8 orders of magnitude at the filler loading 8-10 wt%. The volume resistivity of the resulting film exhibited steady and consistent ranges within 10⁸–10¹² Ω cm across all loadings. The difference in conductivity between surface and volume made the film possible to be used in protecting equipment against electrostatic discharges inside of a package. The high loading of GNPs in hybrid GNPs/CB had no effect on enhancing both surface and volume conductivity of the composite film.