Piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics synthesized by spray drying method

Potassium-sodium niobate was synthesized at 800 °C for 1 h using dried precursors in a powder form obtained by the spray drying method. Different samples were sintered from 1060 to 1120 °C for 2 h reaching a relative density as high as 96% of the theoretical value. Piezoelectric and ferroelectric properties were studied for these samples and some of the most prominent results are: k_p, d₃₁, 2P_r, and 2E_C of 0.36, 39 pC/N, 29 μC/cm² and 16.5 kV/cm, respectively, for the sample sintered at 1080 °C. The methodology presented in this study can be used to synthesize submicrometer powders.     

Continuous Flow Fabrication of Block Copolymer–Grafted Silica Micro‐Particles in Environmentally Friendly Water/Ethanol Media

Polymer‐grafted inorganic particles (PGIPs) are attractive building blocks for numerous chemical and material applications. Surface‐initiated controlled radical polymerization (SI‐CRP) is the most feasible method to fabricate PGIPs. However, a conventional in‐batch reaction still suffers from several disadvantages, including time‐consuming purification processes, low grafting efficiency, and possible gelation problems. Herein, a facile method is demonstrated to synthesize block copolymer–grafted inorganic particles, that is, poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMEMA)‐b‐poly(N‐isopropylacrylamide) (PNIPAM)–grafted silica micro‐particles using continuous flow chemistry in an environmentally friendly aqueous media. Immobilizing the chain transfer agent and subsequent SI‐CRP can be accomplished sequentially in a continuous flow system, avoiding multi‐step purification processes in between. The chain length (MW) of the grafted polymers is tunable by adjusting the flow time or monomer concentration, and the narrower molar mass dispersity (Р< 1.4) of the grafted polymers reveals the uniform polymer chains on the particles. Moreover, compared with the in‐batch reaction at the same condition, the continuous system also suppresses possible gelation problems.     

Intercalative poly(carbazole) precursor electropolymerization within hybrid nanostructured titanium oxide ultrathin films

A protocol for nanostructuring and electropolymerization of a hybrid semiconductor polycarbazole-titanium oxide ultrathin film is described. Ultrathin (<100 nm) films based on polycarbazole precursor polyelectrolytes and titanium oxide (TiOx) have been fabricated by combining the layer-by-layer (LbL) and surface sol-gel layering techniques. Film growth was followed and confirmed through UV-vis spectroscopy, ellipsometry and quartz crystal microbalance with dissipation (QCM-D). Subsequent anodic electrochemical oxidation of the carbazole pendant units afforded a conjugated polymer network (CPN) film within intercalating TiOx layers of cross-linked and π-conjugated carbazole units. Cyclic voltammetry (CV), UV-vis, and fluorescence spectroscopy measurements confirmed this process. The LbL-driven polyelectrolyte deposition process resulted in a quantified electrochemical response, proportional to the number of layers, while the TiOx acted as a dielectric spacer limiting electron transfer kinetics and attenuating energy transfer in fluorescence. Electro-optical properties were compared with other polycarbazole thin film materials with respect to bandgap energy (Eg). The straightforward protocol in film nanostructuring and barrier/dielectric properties of the inorganic oxide slab (denoted here as, TiOx) should enable applications in organic light-emitting diodes (OLEDs), dielectric mirrors, planar waveguides, and photovoltaic devices for these hybrid ultrathin films.     

Exponential stability of slowly varying discrete systems with multiple state delays

We give sufficient conditions for the exponential stability of a class of perturbed time‐varying difference equations with multiple delays and slowly varying coefficients. Under appropriate growth conditions on the perturbations, combined with the ‘freezing’ technique, we establish explicit conditions for global exponential stability. Copyright © 2012 John Wiley & Sons, Ltd.     

Nanostructured, molecularly imprinted, and template-patterned polythiophenes for chiral sensing and differentiation

An innovation to thin-film molecular imprinting is presented for the sensitive detection and effective discrimination of chiral compounds using a portable quartz crystal microbalance transduction technique. The facile approach involves i) colloidal sphere layering of latex particles onto the surface via a Langmuir-Blodgett-like technique followed by ii) template molecular imprinting using electrodeposition of a single functional and cross-linking monomer.     

House of Cards Nanostructuring of Graphene Oxide and Montmorillonite Clay for Oil–Water Separation

Noncovalent interactions are ubiquitous in our daily living. Nature employs hydrophobic effects, π–π interactions, hydrogen bonding, van der Waals forces, and electrostatic interactions in many biological processes such as protein folding. In the same manner, scientists exploit this plethora of inherently reversible noncovalent interactions as dials to design robust and smart materials. Electrostatic interaction is particularly interesting due to the simplicity of its concept, i.e., opposite charges attract. However, to our knowledge, the electrostatic interaction between two different 2D nanomaterials has not been investigated in literature. A myriad of natural and synthetic 2D nanomaterials should be explored for what may be an exciting cocktail of synergistic and tunable properties brought about by their charges and physical properties. This contribution highlights an interesting phenomena when organic, negatively charged graphene oxide and inorganic, positively charged montmorillonite (MMT) clay edges are brought into contact.     

Measurements of horizontal three‐phase solid‐liquid‐gas slug flow: Influence of hydrate‐like particles on hydrodynamics

Gas hydrate formation is a main flow assurance concern in oil and gas production. Understanding the effects of the introduction of solid particles in the slug flow is essential to improve the efficiency and safety of multiphase production. The purpose of the present work is the experimental characterization of solid‐liquid‐gas slug flow with the presence of dispersed hydrate‐like particles. Experimental tests were carried out with inert polyethylene particles of 0.5‐mm diameter with density similar to gas hydrates (938 kg/m³). The test section comprised a 26‐mm ID, 9‐m length horizontal duct of transparent Plexiglas. High Speed Imaging and resistivity sensors was used to analyze the slug flow unit cell behavior due to the introduction of the solid particles and to measure the unit cell translational velocity, the slug flow frequency, the bubble and slug lengths, and the phase fractions. Two distinct concentrations of solid particles were tested (6 and 8 g/dm³). © 2018 American Institute of Chemical Engineers AIChE J, 64: 2864–2880, 2018     

Characterization and thermophysical properties of unsaturated polyester-layered silicate nanocomposites

The thermophysical properties of unsaturated polyester (UPE) nanocomposites reinforced by organo-montmorillonite clay nanoplatelets are reported. The organo-clay nanoplatelets were sonicated in acetone for 2 hours to be dispersed in the UPE matrix. Vacuum extraction removed not only the acetone but also the styrene present in the UPE solution. The same mechanical and thermophysical properties of UPE were regained after adding the lost amount of styrene to the UPE solution. Both delaminated and intercalated clay morphologies were observed by transmission electron microscopy. It was found that the sonication process was effective to delaminate clay nanoplatelets for more homogeneous dispersion, dependent on organic chemical modifications for clay nanoplatelets. A higher storage modulus enhancement was obtained when the organo-clay nanoplatelets were delaminated and more homogeneously dispersed. The reinforcing effect of both delaminated and intercalated clay nanoplatelets was theoretically evaluated with the Halpin-Tsai equations. It was evaluated that the aspect ratio of delaminated clay nanoplatelets was approximately 150. The increase of the storage modulus below and above the glass transition temperature was achieved without reducing glass transition temperature and Izod impact strength with increasing clay content.