Synthesis and Thermal Characterization of Polyurethane/Clay Nanocomposites Based on Palm Oil Polyol

Polyurethanes (PUs) are very versatile polymeric materials with a wide range of physical and chemical properties. PUs also have desirable properties, such as high abrasion resistance, tear strength, shock absorption, flexibility, and elasticity. Although they have poor thermal stability, it can be improved by using treated clay.

The objective of the present work is to study the thermal stability of polyurethane, polyurethane/montmorillonite (PU CTAB-mont 3% wt), and polyurethane/montmorillonite containing moca (PU Moca CTAB-mont 3% wt) nanocomposites based on palm oil polyol.

The interest of investigating the synthesis of polyurethane/clay nanocomposites based on palm oil polyol is to explore the use of palm oil polyol to partially replace petrochemical-based polyol.

Polyurethane/clay nanocomposites were prepared by a pre-polymer method and evaluated by Fourier Transform Infrared Spectra (FTIR) to determine micro-domain structures of segmented PU, PU CTAB-mont 3% wt, and PU Moca CTAB-mont 3% wt. The morphology of the nanocomposites was characterized by X-ray diffraction (X-RD), and flame retardant was investigated with thermogravimetric analysis (TGA). The result showed that in comparison with the virgin polyurethane, adding clay and moca demonstrated better thermal stability.     

Heat and Mass Transfer Mechanisms in Drying of a Suspension Droplet: A New Computational Model

A new computational single-droplet drying model is presented. The model considers heat and mass transfer simultaneously together with the receding evaporation front approach. A spherical droplet under constant drying conditions is considered. Computations are performed to predict the drying of colloidal silica-water suspension and skimmed milk. It is shown that the results agree well with those of experimental observations available in the literature.     

Large-Area (over 50 cm × 50 cm) Freestanding Films of Colloidal InP/ZnS Quantum Dots

We propose and demonstrate the fabrication of flexible, freestanding films of InP/ZnS quantum dots (QDs) using fatty acid ligands across very large areas (greater than 50 cm × 50 cm), which have been developed for remote phosphor applications in solid-state lighting. Embedded in a poly(methyl methacrylate) matrix, although the formation of stand-alone films using other QDs commonly capped with trioctylphosphine oxide (TOPO) and oleic acid is not efficient, employing myristic acid as ligand in the synthesis of these QDs, which imparts a strongly hydrophobic character to the thin film, enables film formation and ease of removal even on surprisingly large areas, thereby avoiding the need for ligand exchange. When pumped by a blue LED, these Cd-free QD films allow for high color rendering, warm white light generation with a color rendering index of 89.30 and a correlated color temperature of 2298 K. In the composite film, the temperature-dependent emission kinetics and energy transfer dynamics among different-sized InP/ZnS QDs are investigated and a model is proposed. High levels of energy transfer efficiency (up to 80%) and strong donor lifetime modification (from 18 to 4 ns) are achieved. The suppression of the nonradiative channels is observed when the hybrid film is cooled to cryogenic temperatures. The lifetime changes of the donor and acceptor InP/ZnS QDs in the film as a result of the energy transfer are explained well by our theoretical model based on the exciton-exciton interactions among the dots and are in excellent agreement with the experimental results. The understanding of these excitonic interactions is essential to facilitate improvements in the fabrication of photometrically high quality nanophosphors. The ability to make such large-area, flexible, freestanding Cd-free QD films pave the way for environmentally friendly phosphor applications including flexible, surface-emitting light engines.     

Nanoscopic characterization of two-dimensional (2D) boron nitride nanosheets (BNNSs) produced by microfluidization

A microfluidizer high pressure fluid processor is successfully conducted for the first time to exfoliate few layer two dimensional (2D) boron nitride nanosheets (BNNSs) from micro-sized hexagonal boron nitride (h-BN) precursors of large flakes. The mixture of N,N-dimethylformamide and chloroform is conducted as solvent. In determination of to what extent the high pressure microfluidizer successfully assisted with exfoliation of 2D BNNSs from h-BN precursors of large flakes, secondary electron-scanning electron microscopy (SE-SEM) imaging, bright field-transmission electron microscopy (BF-TEM) imaging, energy filtering (EF)TEM-3 window elemental mapping, electron energy loss spectroscopy (EELS), high resolution (HR)TEM imaging and nano beam electron diffraction (NBED) techniques are carried out. Based on the nanoscopic-scale evidences of few layer 2D BNNSs through various TEM techniques, the sheets are observed to have micrometer dimensions in plane whereas nanometer dimensions through their thicknesses depending on the number of layers stacked together. More specifically, the thickness of 2D BNNSs is calculated to be around between 8 and 12 nm using EELS analysis. This value suggests that BNNSs are composed of approximately between 20 and 30 monatomic 2D graphene-like h-BN layers. We are in the opinion that this study has thrown new light on fabricating large scale of 2D BNNSs, which is cited as a highly promising nanomaterial of the future to be utilized in a variety of potential industrial applications including optoelectronic nanodevices, functional polymer composites, support films, hydrogen accumulators and electrically insulating substrates.     

Vacuum insulation of the high energy negative ion source for fusion application

Vacuum insulation on a large size negative ion accelerator with multiple extraction apertures and acceleration grids for fusion application was experimentally examined and designed. In the experiment, vacuum insulation characteristics were investigated in the JT-60 negative ion source with >1000 apertures on the grid with the surface area of ～2 m(2). The sustainable voltages varied with a square root of the gap lengths between the grids, and decreased with number of the apertures and with the surface area of the grids. Based on the obtained results, the JT-60SA (super advanced) negative ion source is designed to produce 22 A, 500 keV D(-) ion beams for 100 s.     

Nanocrystal Skins with Exciton Funneling for Photosensing

Highly photosensitive nanocrystal (NC) skins based on exciton funneling are proposed and demonstrated using a graded bandgap profile across which no external bias is applied in operation for light‐sensing. Four types of gradient NC skin devices (GNS) made of NC monolayers of distinct sizes with photovoltage readout are fabricated and comparatively studied. In all structures, polyelectrolyte polymers separating CdTe NC monolayers set the interparticle distances between the monolayers of ligand‐free NCs to <1 nm. In this photosensitive GNS platform, excitons funnel along the gradually decreasing bandgap gradient of cascaded NC monolayers, and are finally captured by the NC monolayer with the smallest bandgap interfacing the metal electrode. Time‐resolved measurements of the cascaded NC skins are conducted at the donor and acceptor wavelengths, and the exciton transfer process is confirmed in these active structures. These findings are expected to enable large‐area GNS‐based photosensing with highly efficient full‐spectrum conversion.     

Europium (II)-doped microporous zeolite derivatives with enhanced photoluminescence by isolating active luminescence centers

Solid-state reaction is the most common method for preparing luminescent materials. However, the luminescent dopants in the hosts tend to aggregate in the high-temperature annealing process, which causes adverse effect in photoluminescence. Herein, we report a novel europium (II)-doped zeolite derivative prepared by a combined ion-exchange and solid-state reaction method, in which the europium (II) ions are isolated to a large extent by the micropores of the zeolite. Excited by a broad ultraviolet band from 250 to 420 nm, a strong blue emission peaking at 450 nm was observed for these Eu-embedded zeolites annealed at 800 °C in a reducing atmosphere. The zeolite host with pores of molecular dimension was found to be an excellent host to isolate and stabilize the Eu(2+) ions. The as-obtained europium (II)-doped zeolite derivative showed an approximately 9 fold enhancement in blue emission compared to that of the general europium (II)-doped aluminosilicates obtained by conventional solid-state reaction, indicating that, by isolating active luminescence centers, it is promising to achieve highly luminescent materials. Also, the strong blue emission with broad UV excitation band suggests a potential candidate of phosphor for ultraviolet excited light-emitting diode.     

Fabrication and characterization of 3D printable nanocomposite filament based on cellulose nanocrystals and polylactic acid using ionic liquids

Nanocellulose, which is biodegradable and possesses excellent physicochemical properties, has high potential in many applications. However, its intrinsic hydrophilic nature makes it difficult to be used as fillers in most hydrophobic polymer composites. Here, cellulose nanocrystals (CNCs) were successfully prepared using 1-hexly-3-methylimidazolium hydrogen sulfate [Hmim][HSO₄] ionic liquid under optimized conditions at 71°C, ultra-sonication amplitude of 69%, and ultrasonication time of 23 min. The prepared CNCs were surface-modified using 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF₄]. A 3D printable nanocomposite filament containing CNCs embedded in polylactic acid was fabricated via extrusion process at 170°C. The prepared filaments were characterized using universal testing machine, field emission scanning electron microscopy, thermogravimetric analysis, and FTIR. It was shown that CNCs had a diameter and length of 10–24 and 60–400 nm, respectively. It was also found that incorporating 2 wt% of CNCs into the matrix phase increased filaments tensile strength by 2.5% (from 54.59 to 57.35 MPa) due to the plasticization effect of [Bmim][BF₄]. The prepared composites exhibited lower activation energies compared to neat PLA due to the small traces of sulfate group on F-CNC. The mechanical attributes of CNCs/PLA nanocomposites were retained at values comparable to that of fresh PLA and were demonstrated to be 3D printable.