Technical review: Improvement of mechanical properties and suitability towards armor applications – Alumina composites

Ceramic Matrix Composites (CMCs) have many interesting properties, mainly light weight, cost efficiency, low density, high compressive strength, high hardness and durability. Hence, they emerged as a boon to the development of personnel armors in the past. The current work aims to review various new methodologies adapted for the reinforcement of Alumina (Al₂O₃) CMCs in recent times, including some of the interesting results obtained with respect to mechanical properties, suitability of the synthesized composites for armor applications, and the upcoming reinforcement trends. Finally, studies related to reinforcement in Al₂O₃ CMCs, specifically towards armor applications have been consolidated to arrive at some of the important inferences for concluding reasonably.     

Effect of microwave power irradiation on TiO2 nano-structures and binder free paste screen printed dye sensitized solar cells

Titanium dioxide (TiO₂) nanostructures (nanorods and nanoparticles) were prepared using a low-cost microwave irradiation method from a polyol medium of glycerol. Titanium glycerolate and TiO₂ powders were obtained in the glycerol medium for the first time with four different power densities (240?W, 480?W, 720?W, 960?W) of irradiation using a domestic microwave oven of 2.45?GHz, to understand the impact of power on morphology tuning. The structural and morphological features of the titanium glycerolate and TiO₂ powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Raman spectra analysis. The TiO₂ was successfully used in the fabrication of photovoltaic devices and as a proof-of-concept binder free paste was prepared and successfully employed for photo-anode using screen printing on the fluorine-doped tin oxide substrate.     

Bacteria-Responsive Self-Assembly of Antimicrobial Peptide Nanonets for Trap-and-Kill of Antibiotic-Resistant Strains

Bacterial trapping using nanonets is a ubiquitous immune defense mechanism against infectious microbes. These nanonets can entrap microbial cells, effectively arresting their dissemination and rendering them more vulnerable to locally secreted microbicides. Inspired by this evolutionarily conserved anti-infective strategy, a series of 15 to 16 residue-long synthetic β-hairpin peptides is herein constructed with the ability to self-assemble into nanonets in response to the presence of bacteria, enabling spatiotemporal control over microbial killing. Using amyloid-specific K114 assay and confocal microscopy, the membrane components lipoteichoic acid and lipopolysaccharide are shown to play a major role in determining the amyloid-nucleating capacity as triggered by Gram-positive and Gram-negative bacteria respectively. These nanonets displayed both trapping and killing functionalities, hence offering a direct improvement from the trap-only biomimetics in literature. By substituting a single turn residue of the non-amyloidogenic BTT1 peptide, the nanonet-forming BTT1-3A analog is produced with comparable antimicrobial potency. With the same sequence manipulation approach, BTT2-4A analog modified from BTT2 peptide showed improved antimicrobial potency against colistin-resistant clinical isolates. The peptide nanonets also demonstrated robust stability against proteolytic degradation, and promising in vivo efficacy and biosafety profile. Overall, these bacteria-responsive peptide nanonets are promising clinical anti-infective alternatives for circumventing antibiotic resistance.     

Experimental investigation and statistical analysis of additively manufactured onyx-carbon fiber reinforced composites

Availability of additive manufacturing has influenced the scientific community to improve on production and versatility of the components created with several associated technologies. Adding multiple substances through superimposing levels is considered as a part of three-dimensional (3D) printing innovations to produce required products. These technologies are experiencing an increase in development nowadays. It requires frequently adding substance and has capacity to fabricate extremely complex geometrical shapes. However, the fundamental issues with this advancement include alteration of capacity to create special products with usefulness and properties at an economically viable price. In this study, significant procedural parameters: layer designs/ patterns (hexagonal, rectangular and triangular) and infill densities (30%, 40%, and 50%) were considered to investigate into their effects on mechanical behaviors off fused deposition modeling or 3D-printed onyx-carbon fiber reinforced composite specimens, using a high-end 3D printing machine. Mechanical (tensile and impact) properties of the printed specimens were conclusively analyzed. From the results obtained, it was observed that better qualities were achieved with an increased infill density, and rectangular-shaped design exhibited an optimum or maximum tensile strength and energy absorption rate, when compared with other counterparts. The measurable relapse conditions were viably evolved to anticipate the real mechanical qualities with an accuracy of 96.4%. In comparison with other patterns, this was more closely predicted in the rectangular design, using regression models. The modeled linear regression helps to define the association of two dependent variables linked with properties of the dissimilar composite material natures. The models can further predict response of the quantities before and also guide practical applications.     

Direct Imprinting of Porous Silicon via Metal‐Assisted Chemical Etching

Conventional lithographical techniques used for bulk semiconductors produce dramatically poor results when used for micro and mesoporous materials such as porous silicon (PS). In this work, for the first time, a high‐throughput, single‐step, direct imprinting process for PS not involving plastic deformation or high‐temperature processing is reported. Based on the underlying mechanism of metal‐assisted chemical etching (MACE), this process uses a pre‐patterned polymer stamp coated with a noble metal catalyst to etch PS immersed in an HF‐oxidizer mixture. The process not only overcomes the difficulties in patterning PS but it does so with a stamp that may be reused multiple times depending on its chemical and mechanical degradation. The process is shown to be capable of centimeter‐scale parallel 3D patterning with sub‐20 nm resolution. It is found that PS facilitates mass transport of reactants and products, and the overall etch rate is limited by local depletion of reactants. The versatility of this direct imprinting technique is demonstrated by its ability to produce curvilinear and planar 3D features (e.g., paraboloids, parabolic cylinders, sinusoidal waves, and straight sidewall channels). Miniaturized optical elements such as diffraction gratings and microconcentrators are built and characterized highlighting potential use of PS in silicon photonics.     

Enhanced 3D fluorescence live cell imaging on nanoplasmonic substrate

We have created a randomly distributed nanocone substrate on silicon coated with silver for surface-plasmon-enhanced fluorescence detection and 3D cell imaging. Optical characterization of the nanocone substrate showed it can support several plasmonic modes (in the 300-800 nm wavelength range) that can be coupled to a fluorophore on the surface of the substrate, which gives rise to the enhanced fluorescence. Spectral analysis suggests that a nanocone substrate can create more excitons and shorter lifetime in the model fluorophore Rhodamine 6G (R6G) due to plasmon resonance energy transfer from the nanocone substrate to the nearby fluorophore. We observed three-dimensional fluorescence enhancement on our substrate shown from the confocal fluorescence imaging of chinese hamster ovary (CHO) cells grown on the substrate. The fluorescence intensity from the fluorophores bound on the cell membrane was amplified more than 100-fold as compared to that on a glass substrate. We believe that strong scattering within the nanostructured area coupled with random scattering inside the cell resulted in the observed three-dimensional enhancement in fluorescence with higher photostability on the substrate surface.     

Influence of PVP on Bi25FeO40 microcubes for Supercapacitors and Dye-Sensitized Solar Cells applications

Journal of Materials Science: Materials in Electronics - Polyvinylpyrrolidone (PVP)-assisted Bi25FeO40 microcubes have been synthesized through hydrothermal technique and the effect of morphology...     

Reaction induced multifunctional TiO2 rod/particle nanostructured materials for screen printed dye sensitized solar cells

This study investigates the potential of utilizing multifunctional nanostructured materials for the efficient light trapping and electron transport in solar cells by combining titanium dioxide (TiO₂) rods and nanoparticles. A simple solvothermal method was adopted for the synthesis of coupled morphology adopting the desired precursor with the constant concentration and temperature. The reaction duration (12, 24, 36 and 48 h) was varied and the materials resultant physical, optical and structural characteristics were elucidated to determine the nature of the prepared material. The crystallographic phase of the synthesized samples was determined with XRD and Raman analysis. From the experimental data it is hypothesized that the surface plane of anatase (105) is involved in the deformation of the structure and the formation of the rutile phase. To further investigate on the formation of mixed phase in the prepared sample a computation study was performed using density functional theory coupled to the Hubbard U correction (DFT + U) as a function of volume in both the anatase and rutile phases. The relative stability of the O–Ti–O networks is explored starting from ultrathin materials for four different sizes, of anatase and rutile nanorods separately. Finally, the synthesized TiO₂ materials were used to prepare screen printed dye sensitized solar cell (DSSC) devices and their respective properties were quantified.