Effect of Synthesis Conditions on CuO-NiO Nanocomposites Synthesized via Saponin-Green/Microwave Assisted-Hydrothermal Method.

This work presents the synthesis of CuO-NiO nanocomposites under different synthesis conditions. Nanocomposites were synthesized by merging a green synthesis process with a microwave-assisted hydrothermal method. The synthesis conditions were as follows: concentration of the metal precursors (0.05, 0.1, and 0.2 M), pH (9, 10, and 11), synthesis temperature (150 °C, 200 °C, and 250 °C), microwave treatment time (15, 30, and 45 min), and extract concentration (20 and 40 mL of 1 g saponin/10 mL water, and 30 mL of 2 g saponin/10 mL water). The phases and crystallite sizes of the calcined nanocomposites were characterized using XRD and band gap via UV-Vis spectroscopy, and their morphologies were investigated using SEM and TEM. The XRD results confirmed the formation of a face-centered cubic phase for nickel oxide, while copper oxide has a monoclinic phase. The calculated crystallite size was in the range of 29-39 nm. The direct band gaps of the samples prepared in this work were in the range of 2.39-3.17 eV.

Exploring Calcium Manganese Oxide as a Promising Cathode Material for Calcium-Ion Batteries.

The dependence on lithium for the energy needs of the world, coupled with its scarcity, has prompted the exploration of postlithium alternatives. Calcium-ion batteries are one such possible alternative owing to their high energy density, similar reduction potential, and naturally higher abundance. A critical gap in calcium-ion batteries is the lack of suitable cathodes for intercalating calcium at high voltages and capacities while also maintaining structural stability. Transition metal oxide postspinels have been identified as having crystal structures that can provide low migration barriers, high voltages, and facile transport pathways for calcium ions and thus can serve as cathodes for calcium-ion batteries. However, experimental validation of transition metal oxide postspinel compounds for calcium ion conduction remains unexplored. In this work, calcium manganese oxide (CaMn2O4) in the postspinel phase is explored as an intercalation cathode for calcium-ion batteries. CaMn2O4 is first synthesized via solid-state synthesis, and the phase is verified with X-ray diffraction (XRD). The redox activity of the cathode is investigated with cyclic voltammetry (CV) and galvanostatic (GS) cycling, identifying oxidation potentials at 0.2 and 0.5 V and a broad insertion potential at -1.5 V. CaMn2O4 can cycle at a capacity of 52 mAh/g at a rate of C/33, and calcium cycling is verified with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and modeled with density functional theory (DFT) simulations. The results from the investigation concluded that CaMn2O4 is a promising cathode for calcium-ion batteries.

Polyvinylidene Fluoride-Based Gel Polymer Electrolytes for Calcium Ion Conduction: A Study of the Influence of Salt Concentration and Drying Temperature on Coordination Environment and Ionic Conductivity.

Calcium-ion batteries emerged as a potential sustainable alternative energy storage system; however, there remains the need to further develop electrolytes to improve their performance. We report a gel polymer electrolyte (GPE)-based on polyvinylidene fluoride (PVDF) for calcium ion conduction. The gel electrolyte was synthesized by combining a PVDF polymer host, Ca(TFSI)2 salt, and N-methyl-2-pyrrolidone (NMP) solvent. Using Fourier transform infrared spectroscopy, we analyze the effect of salt concentration and drying temperature on the degree of salt dissociation in the electrolyte. Our results show that the concentration of free cations in the electrolyte is primarily coordinated with NMP as well as PVDF, generating a suitable network for ion transport, i.e., a liquid electrolyte encompassed within a polymer matrix. We find that processing conditions such as drying temperature, which varies solvent content, play a critical role in developing polymer electrolytes that demonstrate optimal electrochemical performance. The GPEs are semicrystalline and stable up to 120 °C, which is critical for their use in applications such as in electric vehicles and renewable energy storage systems. The ionic conductivity of the GPEs exhibit Arrhenius-type behavior, and the total ionic conductivity at room temperature is suitable for applications, with values of 0.85 × 10-4 S/cm for 0.5 M and 3.56 × 10-4 S/cm for 1.0 M concentrations. The results indicate that the GPE exhibits high conductivity and good stability, making it a promising candidate for use in high-performance calcium ion batteries.

Fluorescent Waveguide Lattices for Enhanced Light Harvesting and Solar Cell Performance.

We present the properties and performance of fluorescent waveguide lattices as coatings for solar cells, designed to address the significant mismatch between the solar cell's spectral response range and the solar spectrum. Using arrays of microscale visible light optical beams transmitted through photoreactive polymer resins comprising acrylate and silicone monomers and fluorescein o,o'-dimethacrylate comonomer, we photopolymerize well-structured films with single and multiple waveguide lattices. The materials exhibited bright green-yellow fluorescence emission through down-conversion of blue-UV excitation and light redirection from the dye emission and waveguide lattice structure. This enables the films to collect a broader spectrum of light, spanning UV-vis-NIR over an exceptionally wide angular range of ±70°. When employed as encapsulant coatings on commercial silicon solar cells, the polymer waveguide lattices exhibited significant enhancements in solar cell current density. Below 400 nm, the primary mode of enhancement is through down-conversion and light redirection from the dye emission and collection by the waveguides. Above 400 nm, the primary modes of enhancement were a combination of down-conversion, wide-angle light collection, and light redirection from the dye emission and collection by the waveguides. Waveguide lattices with higher dye concentrations produced more well-defined structures better suited for current generation in encapsulated solar cells. Under standard AM 1.5 G irradiation, we observed nominal average current density increases of 0.7 and 1.87 mA/cm2 for single waveguide lattices and two intersecting lattices, respectively, across the full ±70° range and reveal optimal dye concentrations and suitable lattice structures for solar cell performance. Our findings demonstrate the significant potential of incorporating down-converting fluorescent dyes in polymer waveguide lattices for improving the current spectral and angular response of solar cell technologies toward increasing clean energy in the energy grid.

Plating and Stripping Calcium Metal in Potassium Hexafluorophosphate Electrolyte toward a Stable Hybrid Solid Electrolyte Interphase.

The use of calcium (Ca) metal anodes in batteries is currently challenged by the development of a suitable solid electrolyte interface (SEI) that enables effective Ca2+ ion transport. Native calcium electrolytes produce a passivation layer on the surface of the calcium electrodes during cycling, causing a decrease in capacity during cycling and the need for large overpotentials. The use of a hybrid SEI is a strategy to mitigate the uncontrolled production of a passivation layer and reduce the overpotentials needed for the plating and stripping of calcium. Here, we report the development of a hybrid potassium (K)/Ca SEI layer investigated in symmetric Ca//Ca cell configurations. Using KPF6 salt in a ternary mixture of carbonate solvent (EC/EMC/DMC), Ca//Ca cells can be cycled up to 200 h at a capacity of 0.15 mAh/cm2 with a current density of 0.025 mA/cm2. The symmetrical cells consistently cycle at overpotentials of 1.8 V. Ex-situ X-ray diffraction (XRD) of cycled electrodes reveals plating and stripping of both calcium and potassium. Energy dispersive X-ray (EDX) maps confirm the plating of calcium and potassium during galvanostatic cycling. Scanning electron microscopy (SEM) cross-sectional views of the calcium electrodes reveal a continuous SEI layer formed over the calcium metal. XRD analysis reveals the SEI layer consists of K-based inorganics along with the identification of permanent and transient phases. FTIR outlines the parallel plating of both calcium and potassium at both regions of redox activity. Raman spectroscopy of the electrolyte reveals compositional changes over the course of cycling that promote increased plating and stripping. The results indicate that potassium electrolytes are a possible route for tuning the SEI to enable reversible calcium electrochemical cycling.

Vinylimidazole-Based Polymer Electrolytes with Superior Conductivity and Promising Electrochemical Performance for Calcium Batteries.

Calcium batteries are next-generation energy storage technologies with promising techno-economic benefits. However, performance bottlenecks associated with conventional electrolytes with oxygen-based coordination chemistries must be overcome to enable faster cation transport. Here, we report an imidazole-based polymer electrolyte with the highest reported conductivity and promising electrochemical properties. The polymerization of vinylimidazole in the presence of calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI)2) salt creates a gel electrolyte comprising a polyvinyl imidazole (PVIm) host infused with vinylimidazole liquid. Calcium ions effectively coordinate with imidazole groups, and the electrolytes present room temperature conductivities of >1 mS/cm. Reversible redox activity in symmetric Ca cells is demonstrated at 2 V overpotentials, stable cycles at 0.1 mA/cm2, and areal capacities of 0.1 mAh/cm2. Softer coordination, polarizability, and closer coordinating site distances of the imidazole groups can explain the enhanced properties. Hence, imidazole is a suitable chemical benchmark for the future design and advancement of polymer electrolytes for calcium batteries.

Multidirectional Polymer Waveguide Lattices for Enhanced Ultrawide-Angle Light Capture in Silicon Solar Cells.

We report the synthesis and characterization of a polymer thin-film structure consisting of two intersecting broadband optical waveguide lattices, and its performance in wide-angle optical energy collection and conversion in silicon solar cells. The structures are synthetically organized via the concurrent irradiation of photoreactive polymer blends by two arrays of intersecting, microscale optical beams transmitted through the medium. Through optical beam-induced photopolymerization and photopolymerization-induced phase separation, well-organized lattices are produced comprising of cylindrical core-cladding waveguide architectures that intersect one another. The optical waveguide properties of the lattices transform the transmission characteristics of the polymer film so that incident optical energy is collected and transmitted along the waveguide axes, rather than their natural directions dictated by refraction, thereby creating efficient light-collecting capability. The embedded structures collectively impart their wide-angle acceptance ranges to enable the film to efficiently collect and interact with light over a large angular range (±70°). When employed as the encapsulant material for a commercial silicon solar cell, the novel light collection and transmission properties result in greater wide-angle conversion efficiency and electrical current density, compared to a single vertically aligned waveguide array. The sustained and greater conversion of light afforded by the encapsulating optical material promises to increase solar cell performance by enabling ultrawide-angle solar energy conversion.

Simulations of Structure and Morphology in Photoreactive Polymer Blends under Multibeam Irradiation.

We present a theoretical study of the organization of photoreactive polymer blends under irradiation by multiple arrays of intersecting optical beams. In a simulated medium possessing an integrated intensity-dependent refractive index, optical beams undergo self-focusing and reduced divergence. A corresponding intensity-dependent increase in molecular weight induces polymer blend instability and consequent phase separation, whereby the medium can evolve into an intersecting waveguide lattice structure, comprising high refractive index cylindrical cores and a surrounding low refractive index medium (cladding). We conduct simulations for two propagation angles and a range of thermodynamic, kinetic, and polymer blend parameters to establish correlations to structure and morphology. We show that spatially correlated structures, namely, those that have a similar intersecting three-dimensional (3D) pattern as the arrays of intersecting optical beams, are achieved via a balance between the competitive processes of photopolymerization rate and phase separation dynamics. A greater intersection angle of the optical beams leads to higher correlations between structures and the optical beam pattern and a wider parameter space that achieves correlated structures. This work demonstrates the potential to employ complex propagating light patterns to create 3D organized structures in multicomponent photoreactive soft systems.

Superhydrophobic Polymer Composite Surfaces Developed via Photopolymerization.

Fabrication of superhydrophobic materials using incumbent techniques involves several processing steps and is therefore either quite complex, not scalable, or often both. Here, the development of superhydrophobic surface-patterned polymer-TiO2 composite materials using a simple, single-step photopolymerization-based approach is reported. The synergistic combination of concurrent, periodic bump-like pattern formation created using irradiation through a photomask and photopolymerization-induced nanoparticle (NP) phase separation enables the development of surface textures with dual-scale roughness (micrometer-sized bumps and NPs) that demonstrate high water contact angles, low roll-off angles, and desirable postprocessability such as flexibility, peel-and-stick capability, and self-cleaning capability. The effect of nanoparticle concentration on surface porosity and consequently nonwetting properties is discussed. Large-area fabrication over an area of 20 cm2, which is important for practical applications, is also demonstrated. This work demonstrates the capability of polymerizable systems to aid in the organization of functional polymer-nanoparticle surface structures.

Gel Polymer Electrolytes Based on Cross-Linked Poly(ethylene glycol) Diacrylate for Calcium-Ion Conduction.

Calcium batteries are promising alternatives to lithium batteries owing to their high energy density, comparable reduction potential, and mineral abundance. However, to meet practical demands in high-performance applications, suitable electrolytes must be developed. Here, we report the synthesis and characterization of polymer gel electrolytes for calcium-ion conduction prepared by the photo-cross-linking of poly(ethylene glycol) diacrylate (PEGDA) in the presence of solutions of calcium salts in a mixture of ethylene carbonate (EC) and propylene carbonate (PC) solvents. The results show room-temperature conductivity between 10-5 and 10-4 S/cm, electrochemical stability windows of ∼3.8 V, full dissociation of the salt, and minimal coordination with the PEGDA backbone. Cycling in symmetric Ca metal cells proceeds but with increasing overpotentials, which can be attributed to interfacial impedance between the electrolyte and calcium surface, which inhibits charge transfer. Calcium may still be plated and stripped yielding high-purity deposits and no indication of significant electrolyte breakdown, indicating that high overpotentials are associated with an electrically insulating, yet ion-permeable solid electrolyte interface (SEI). This work provides a contribution to the study and understanding of polymer gel materials toward their improvement and application as electrolytes for calcium batteries.

Spontaneous Massive Intrarenal Hemorrhage in a Patient With De Novo Ureteropelvic Junction Obstruction.

This case represents an even rarer presentation of ureteropelvic junction obstruction (UPJO), that of a spontaneous life-threatening hemorrhage into the renal pelvis of a patient with previously unknown UPJO. Unique to this patient was the emergent nature of the presentation, requiring life-saving surgery. A review of the literature follows a discussion of the case.

Observation of intensity dependent phase-separation in photoreactive monomer-nanoparticle formulations under non-uniform visible light irradiation.

We report observations of photopolymerization driven phase-separation in a mixture of a photo-reactive monomer and inorganic nanoparticles. The mixture is irradiated with visible light possessing a periodic intensity profile that elicits photopolymerization along the depth of the mixture, establishing a competition between photo-crosslinking and thermodynamically favorable phase-separating behavior inherent to the system. In situ Raman spectroscopy was used to monitor the polymerization reaction and morphology evolution, and reveals a key correlation between irradiation intensity and composite morphology extending the entire depth of the mixture, i.e. unhindered phase-separation at low irradiation intensity and arrested phase-separation at high irradiation intensity. 3D Raman volume mapping and energy dispersive X-ray mapping confirm that the intensity-dependent irradiation process dictates the extent of phase separation, enabling single-parameter control over phase evolution and subsequent composite morphology. These observations can potentially enable a single-step route to develop polymer-inorganic composite materials with tunable morphologies.

Microfiber Optic Arrays as Top Coatings for Front-Contact Solar Cells toward Mitigation of Shading Loss.

Microfiber optic array structures are fabricated and employed as an optical structure overlaying a front-contact silicon solar cell. The arrays are synthesized through light-induced self-writing in a photo-crosslinking acrylate resin, which produces periodically spaced, high-aspect-ratio, and vertically aligned tapered microfibers deposited on a transparent substrate. The structure is then positioned over and sealed onto the solar cell surface. Their fiber optic properties enable collection of non-normal incident light, allowing the structure to mitigate shading loss through the redirection of incident light away from contacts and toward the solar cell. Angle-averaged external quantum efficiency increases nominally by 1.61%, resulting in increases in short-circuit current density up to 1.13 mA/cm2. This work demonstrates a new approach to enhance light collection and conversion using a scalable, straightforward, light-based additive manufacturing process.

Superhydrophobic Microporous Substrates via Photocuring: Coupling Optical Pattern Formation to Phase Separation for Process-Tunable Pore Architectures.

We present a new approach to synthesize microporous surfaces through the combination of photopolymerization-induced phase separation and light pattern formation in photopolymer-solvent mixtures. The mixtures are irradiated with a wide-area light pattern consisting of high and low intensity regions. This light pattern undergoes self-focusing and filamentation, thereby preserving its spatial profile through the mixture. Over the course of irradiation, the mixture undergoes phase separation, with the polymer and solvent located in the bright and dark regions of the light profile, respectively, to produce a binary phase morphology with a congruent arrangement as the optical pattern. A congruently arranged microporous structure is attained upon solvent removal. The microporous surface structure can be varied by changing the irradiating light profile via photomask design. The porous architecture can be further tuned through the relative weight fractions of photopolymer and solvent in the mixture, resulting in porosities ranging from those with discrete and uniform pore sizes to hierarchical pore distributions. All surfaces become superhydrophobic (water contact angles >150°) when spray-coated with a thin layer of polytetrafluoroethylene nanoparticles. The water contact angles can be enhanced by changing the surface porosity via the processing conditions. This is a scalable and tunable approach to precisely control microporous surface structure in thin films to create functional surfaces and antiwetting coatings.

Polymer Encapsulants Incorporating Light-Guiding Architectures to Increase Optical Energy Conversion in Solar Cells.

The fabrication of a new type of solar cell encapsulation architecture comprising a periodic array of step-index waveguides is reported. The materials are fabricated through patterning with light in a photoreactive binary blend of crosslinking acrylate and urethane, wherein phase separation induces the spontaneous, directed formation of broadband, cylindrical waveguides. This microstructured material efficiently collects and transmits optical energy over a wide range of entry angles. Silicon solar cells comprising this encapsulation architecture show greater total external quantum efficiencies and enhanced wide-angle light capture and conversion. This is a rapid, straightforward, and scalable approach to process light-collecting structures, whereby significant increases in cell performance may be achieved.

Coupling nonlinear optical waves to photoreactive and phase-separating soft matter: Current status and perspectives.

Nonlinear optics and polymer systems are distinct fields that have been studied for decades. These two fields intersect with the observation of nonlinear wave propagation in photoreactive polymer systems. This has led to studies on the nonlinear dynamics of transmitted light in polymer media, particularly for optical self-trapping and optical modulation instability. The irreversibility of polymerization leads to permanent capture of nonlinear optical patterns in the polymer structure, which is a new synthetic route to complex structured soft materials. Over time more intricate polymer systems are employed, whereby nonlinear optical dynamics can couple to nonlinear chemical dynamics, opening opportunities for self-organization. This paper discusses the work to date on nonlinear optical pattern formation processes in polymers. A brief overview of nonlinear optical phenomenon is provided to set the stage for understanding their effects. We review the accomplishments of the field on studying nonlinear waveform propagation in photopolymerizable systems, then discuss our most recent progress in coupling nonlinear optical pattern formation to polymer blends and phase separation. To this end, perspectives on future directions and areas of sustained inquiry are provided. This review highlights the significant opportunity in exploiting nonlinear optical pattern formation in soft matter for the discovery of new light-directed and light-stimulated materials phenomenon, and in turn, soft matter provides a platform by which new nonlinear optical phenomenon may be discovered.

Increasing light capture in silicon solar cells with encapsulants incorporating air prisms to reduce metallic contact losses.

Silicon solar cells are the most widely deployed modules owing to their low-cost manufacture, large market, and suitable efficiencies for residential and commercial use. Methods to increase their solar energy collection must be easily integrated into module fabrication. We perform a theoretical and experimental study on the light collection properties of an encapsulant that incorporates a periodic array of air prisms, which overlay the metallic front contacts of silicon solar cells. We show that the light collection efficiency induced by the encapsulant depends on both the shape of the prisms and angle of incidence of incoming light. We elucidate the changes in collection efficiency in terms of the ray paths and reflection mechanisms in the encapsulant. We fabricated the encapsulant from a commercial silicone and studied the change in the external quantum efficiency (EQE) on an encapsulated, standard silicon solar cell. We observe efficiency enhancements, as compared to a uniform encapsulant, over the visible to near infrared region for a range of incident angles. This work demonstrates exactly how a periodic air prism architecture increases light collection, and how it may be designed to maximize light collection over the widest range of incident angles.

A Clinicopathological Profile of Prostate Cancer in Trinidad and Tobago.

Aim. To conduct a clinicopathological review of all prostate biopsies performed in a tertiary referral centre in Trinidad and Tobago over a period of 30 months. Methods. The records of all patients who had prostate biopsies from January 2012 to July 2014 were reviewed. Clinical and pathologic data were compiled and subsequently analysed using SPSS version 20. Results. From January 2012 to July 2014, 617 transrectal ultrasound guided prostate biopsies were performed. Pathological data were found for 546 patients of whom 283 (51.8%) were confirmed carcinoma of the prostate. Moderately differentiated tumors (Gleason 7) were the most common group. Using the D'Amico risk classification, most cases were found to be high risk (63.1%). Afro-Trinidadians comprised 72.1% of the patients with prostate cancer. Afro-Trinidadians were also more likely to have high risk and high grade disease as well as high PSA values. Conclusion. This study demonstrates that over half of our biopsies are eventually positive for cancer and most cases were high risk. Afro-Trinidadians comprised a disproportionate number of those diagnosed with prostate cancer and had a greater risk of high risk disease.

Evaluation of a pulsed xenon ultraviolet light device for isolation room disinfection in a United Kingdom hospital.

BACKGROUND: Pathogen transmission from contaminated surfaces can cause hospital-associated infections. Although pulsed xenon ultraviolet (PX-UV) light devices have been shown to decrease hospital room bioburden in the United States, their effectiveness in United Kingdom (UK) hospitals is less understood. METHODS: Forty isolation rooms at the Queens Hospital (700 beds) in North London, UK, were sampled for aerobic bacteria after patient discharge, after manual cleaning with a hypochlorous acid-troclosene sodium solution, and after PX-UV disinfection. PX-UV device efficacy on known organisms was tested by exposing inoculated agar plates in a nonpatient care area. Turnaround times for device usage were recorded, and a survey of hospital staff for perceptions of the device was undertaken. RESULTS: After PX-UV disinfection, the bacterial contamination measured in colony forming units (CFU) decreased by 78.4%, a 91% reduction from initial bioburden levels prior to terminal cleaning. PX-UV exposure resulted in a 5-log CFU reduction for multidrug-resistant organisms (MDROs) on spiked plates. The average device turnaround time was 1 hour, with minimal impact on patient throughput. Ward staff were enthusiastic about device deployment, and device operators reported physical comfort in usage. CONCLUSIONS: PX-UV use decreased bioburden in patient discharge rooms and on agar plates spiked with MDROs. The implementation of the PX-UV device was well received by hospital cleaning and ward staff, with minimal disruption to patient flow.