Current Smart Materials - Current Issue

Emerging nanotechnology in the early 1990s introduced nanoscaled and advanced materials such as Carbon Nanotubes (CNT) with specific chemical structure and exceptional unique properties. Generally, among the various nanostructures particularly, nanotubes have shown their specific values due to their inherent characteristics. With the time being, new vistas were opened for developing other nanotube-based materials due to their remarked mechanical strength and versatile applications. In recent decades, BNNTs with promising applicability have been synthesized via several methods. This review highlights the synthetic strategies of Boron Nitride Nanotubes (BNNTs) with their potential applications in various applied sectors including energy, electronics and biomedical applications.

Background: Innovation mission in material science requires new approaches to form functional materials, wherein the concept of its formation begins in nano/micro scale. Rare earth oxides with general form (RE2O3; RE from La to Lu, including Sc and Y) exhibit particular proprieties, being used in a vast field of applications with high technological content since agriculture to astronomy. Despite their applicability, there is a lack of studies on the surface chemistry of rare earth oxides. Zeta potential determination provides key parameters to form smart materials by controlling interparticle forces, as well as their evolution during processing. This paper reports a study on zeta potential with emphasis on rare earth oxide nanoparticles. A brief overview of rare earths, as well as zeta potential, including sample preparation, measurement parameters, and the most common mistakes during this evaluation are reported. Methods: A brief overview of rare earths, including zeta potential, and interparticle forces are presented. A practical study on zeta potential of rare earth oxides - RE2O3 (RE as Y, Dy, Tm, Eu, and Ce) in aqueous media is reported. Moreover, sample preparation, measurement parameters, and common mistakes during this evaluation are discussed. Results: Potential zeta values depend on particle characteristics such as size, shape, density, and surface area. Besides, the preparation of samples, which involves electrolyte concentration and time for homogenization of suspensions, is extremely valuable to get suitable results. Conclusion: Zeta potential evaluation provides key parameters to produce smart materials through which interparticle forces can be controlled. Even though zeta potential characterization is mature, investigations on rare earth oxides are very scarce. Therefore, this innovative paper is a valuable contribution to this field.

Introduction: In the applications of room temperature detector for high-energy radiation, there are two critical requirements for the semiconducting material cadmium zinc telluride (CdZnTe): (1) high electrical resistivity to reduce the bulk leakage current and (2) low levels of structural defects which hinder the detectivity as trapping and recombination centers for the carriers. To enhance the performance of the detectors, an optimal single process has been developed in the melt growth of Cd0.8Zn0.2Te by directional solidification with controlled Cd overpressure to maximize the electrical resistivity as well as minimize the structural defects, including Te precipitates/inclusions of the grown CdZnTe crystals. Methods: Using the phase diagram data of pressure-temperature-composition (P-T-X), melt growth of Cd0.8Zn0.2Te crystals by directional solidification from a starting melt at 1145oC has been performed with various Cd overpressures controlled by the temperature of a Cd reservoir. The grown crystals were sliced and were characterized by electrical resistivity measurements and chemical analysis of Glow Discharge Mass Spectroscopy (GDMS). The structural defects were studied by the infrared (IR) transmission images taken by an IR microscope. Results: By doping of In (4-6 ppm, atomic) and growing with a Cd reservoir in the range of 785 to 825oC, the electrical conductivity was consistently higher than 109 W-cm and up to 2x1011 W-cm. From the trend of the Te precipitates density observed by the IR micrographs, it was concluded that a Cd reservoir temperature of 820+10oC resulted in the lowest precipitate density. Conclusion: The employment of a Cd reservoir temperature of 820+5oC during the growth process will provide the optimal Cd pressure over the melt at 1145oC to maximize the electrical resistivity as well as minimize the structural defects, including Te precipitates/inclusions of the grown Cd0.8Zn0.2Te crystals. Discussion: Since the solids of different compositions, x in the Cd1-xZnxTe system, have different liquidus/solidus temperatures as well as different homogeneity ranges. The procedure presented here for the Cd0.8Zn0.2Te solid may not be applicable to other compositions.

Aim: The design and synthesis of new molecules capable of forming self-assembled gels are indispensable to harvest new functional materials. Supramolecular gels have potential in many areas, particularly in biology and materials chemistry. Of the different types of applications, visual sensing of biologically relevant ionic analytes is a fairly recent trend. Here we describe naked-eye detection of fluoride ions involving sol-gel methodology. Methods: To execute this, cholesterol substituted pyridinium salts 1-4 have been designed and synthesized, of which compounds 3 and 4 served as potential gelators for the naked-eye detection of F- ions in DMSO and DMSO-H2O (1:1, v/v), respectively. Results: Addition of F- ions to the solutions of 3 and 4 in DMSO and DMSO: H2O (1:1, v/v) respectively, resulted in the formation of yellow and brown colored gels instantly at room temperature. Conclusion: Gelation study reveals that not only the aromatic surface is crucial for the selfaggregation of molecules via π-π stacking interactions, but also polarity, rigidity, and conformational flexibility of the molecules that govern the intermolecular association of gelators are important. Moreover, the incorporation of fluorophore (naphthalene) as an aromatic surface in the molecular designs enables the gelator molecules to execute the sensing of F- with a high degree of sensitivity in the solution phase.

Background: Innovation in ceramic materials relies on the processing of powders. Yttria, also known as yttrium oxide, belongs to the rare-earth group (RE2O3 - RE from La to Lu, including Sc and Y). Due to the great properties and end-use of RE-based materials since agriculture until astronomy, studies on processing, sintering and microstructural evolution of RE-based materials are essential to provide new materials with improved characteristics. The aim of this paper is to obtain dense compacts of yttria by powder technology, in which the effect of sintering temperature on sample's microstructure is evaluated. Methods: Yttria powders (Y2O3) were characterized by Photon Correlation Spectroscopy (PCS), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Cylindrical powder compacts were produced by uniaxial compaction, followed by hydrostatic compaction. Sintered samples obtained under sintering temperatures from 1350 to 1550ºC were evaluated by SEM, XRD, apparent density, and true density. Results: Cubic C-type yttria powders exhibited a mean particle size (d50) of 1.6μm, and morphology like acicular. Powder compacts (diameter x height) of 9.57mm ± 0.01 x 1.53mm ± 0.01 presented mean apparent density of 53.69% (based on free powder density). Sintered samples at 1550ºC exhibited the most densification, 65.0% related to the green density and 91.0% related to theoretical density, respectively. Conclusion: Yttria cylindrical compacts with dense microstructure, and symmetric dimensions were formed by powder technology from powders with a mean particle size of 6.51μm, by compaction methods (uniaxial and hydrostatic), followed by sintering. The most densification of samples was achieved by the sintering condition of 1550ºC for 2h, providing samples with a theoretical density of 91%. These results provide useful subsidies to advance toward full densification of yttria-based materials.

Background: Polysaccharide based gastro-retentive drug delivery systems (GRDDSs) can retain in the gastric fluid of stomach for a longer time and release the entrapped drug in a controlled and localized manner, which can ensure optimal drug concentration at the site of action with improved bioavailability and reduced side effects of acid-suppressive drugs like ranitidine. Objective: The objective of the present study was to design smart polymers for gastro-retentive drug delivery of ranitidine through ionic-gelation of carboxymethyl cellulose (CMC) and sodium alginate (ALG). Methods: The optimal reaction conditions for the synthesis of beads were evaluated by varying reaction parameters during synthesis and were obtained as CMC = 1.5% (w/v), ALG = 0.5% (w/v) and CaCl2= 0.1 M with maximum equilibrium swelling ratio (2922.50 ± 0.90)%. The drug loading was carried out by simultaneous and swelling equilibrium methods. Beads were characterized by SEM, PXRD, FTIR, TGA, bead size and swelling studies. Results: Increase in Ca2+ ions and ALG concentration resulted in a decrease in swelling capacity and an increase in bead size. Beads got collapsed in phosphate buffer solution and swelling occurred through the non-Fickian diffusion mechanism. Floating beads with (51.05 ± 0.25)% entrapment efficiency for the simultaneous drug loading method exhibited the Fickian diffusion mechanism and best fitted in the Higuchi model. The diffusion coefficient and initial rate of drug release in simulated gastric fluid demonstrated swelling controlled gastro-retentive release of ranitidine. Conclusion: These smart polymeric beads have the potential to use as a promising candidate for the design of GRDDSs for the treatment of gastric ulceration and gastro-oesophageal reflux disease.

Background: Acoustic power transfer is a method for wireless energy transfer to implanted medical devices that permits a greater range of separation between transmitter and receiver than is possible with inductive power transfer. In some cases, short-distance ultrasonic power transfer may be employed; consequently, their operation may be complicated by the near-field aspects of piezoelectric acoustic energy transfer. Methods: A piezoelectric energy transfer system consisting of two lead zirconate titanate (PZT) transducers was analyzed in this work using a combination of experimental measurements and computer simulations. Results: Simulations using the COMSOL Software package showed good agreement with measured output voltage as a function of the distance between and alignment of the transmitter and receiver with water as a medium. We also simulated how operating frequency affects power transfer efficiency at various distances between the transmitter and receiver and found reasonable agreement with experiments. We report model predictions for power transfer efficiency as a function of the thickness and diameter of the transmitter and receiver. Conclusion: The results show that with proper choice of parameters, piezoelectric systems can provide high power transfer efficiency in the near-field region.