Sub-nanomolar sensing of ionic mercury with polymeric electrospun nanofibers

Ethyl cellulose (EC) based electrospun nanofibers were exploited for sub-nanomolar level optical chemical sensing of ionic mercury. An azomethine ionophore was used as Hg (I) and Hg (II) sensing material. Ethyl cellulose nanofibers with varying amounts of the ionic liquid; 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) were prepared and characterized. The nanofibers were fabricated by electrospinning technique. The offered chemosensor allow determination of mercury ions in a large linear working range between 1.0 × 10⁻¹⁰ and 1.0 × 10⁻⁴ mol L⁻¹. Limit of detection was found to be 0.07 nM which makes this technique alternative to cold-vapor atomic absorption spectrometry (CV-AAS), flame emission methods and to inductively coupled plasma-mass spectrometry (ICP-MS).     

Influences of liquid elastomer additive on the behavior of short glass fiber reinforced epoxy

In this study, improvements in mechanical and thermal behavior of short glass fiber (GF) reinforced diglycidyl ether of bisphenol-A (DGEBA) based epoxy with hydroxyl terminated polybutadiene (HTPB) modification have been studied. A silane coupling agent (SCA) with a rubber reactive group was also used to improve the interfacial adhesion between glass fibers and an epoxy matrix. 10, 20, and 30 wt% GF reinforced composite specimens were prepared with and without silane coupling agent treatment of fibers and also HTPB modification of epoxy mixture. In the ruber modified specimens, hardener and HTPB were premixed and left at room temperature for 1 hr before epoxy addition. In order to observe the effects of short glass fiber reinforcement of epoxy matrix, silane treatment of fiber surfaces, and also rubber modification of epoxy on the mechanical behavior of specimens, tension and impact tests were performed. The fracture surfaces and thermal behavior of all specimens were examined by scanning electron microscope (SEM), and dynamic mechanical analysis (DMA), respectively. It can be concluded that increasing the short GF content increased the tensile and impact strengths of the specimens. Moreover, the surface treatment of GFs with SCA and HTPB modification of epoxy improved the mechanical properties because of the strong interaction between fibers, epoxy, and rubber. SEM studies showed that use of SCA improved interfacial bonding between the glass fibers and the epoxy matrix. Moreover, it was found that HTPB domains having relatively round shapes formed in the matrix. These rubber domains led to improved strength and toughness, due mainly to the “rubber toughening” effect in the brittle epoxy matrix.     

Emission based sub-nanomolar silver sensing with electrospun nanofibers

In this work, the first use of electrospun nanofibrous materials as highly responsive fluorescence quenching-based optical silver sensors is reported. Poly(methyl methacrylate) and ethyl cellulose were used as polymeric support materials. Silver sensing materials were fabricated by electrospinning technique. A fiber-optic bundle was used for measurements. Sensors were based on the change in the fluorescence signal intensity of methoxy azomethine ionophore (M-AZM). The preliminary results of Stern-Volmer analysis show that the sensitivities of electrospun nanofibrous membranes to detect silver ions are 10-100-fold higher than those of the thin film based sensors. The extraordinary sensitivities can be attributed to the high surface area of the nanofibrous membrane structures. It was found that the stability of the sensing agent in the employed matrix materials was excellent and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 5 months. Our stability tests are still in progress.     

Aqueous Phase Glycerol Reforming with Pt and PtMo Bimetallic Nanoparticle Catalysts: The Role of the Mo Promoter

The turnover rate (TOR, normalized to sites measured by CO chemisorption before reaction) and selectivity for the aqueous phase reforming of glycerol have been determined for Pt/C and PtMo/C catalysts. While the TOR of PtMo/C is higher than that of Pt/C by about 4 times at comparable conversion, the selectivity to C–O bond cleavage is higher, thus reducing the H₂ yield at high conversion. Under reaction conditions on Pt/C, CO is observed as the most abundant Pt surface species with a fractional coverage of about 0.6 using operando X-ray absorption spectroscopy. Since there is little CO in the effluent (CO₂:CO ratios > 100:1, when CO is detected), it is thought that surface CO is converted to H₂ and CO₂ by the water gas shift reaction. DFT calculations suggest that the role of metallic Mo is to alter the electronic properties of Pt lowering the binding energy of CO and reducing the activation energies of dehydrogenation and C–O bond cleavage. Because the activation energy for C–O cleavage is lowered more than for dehydrogenation, the selectivity for C–O bond cleavage is increased, ultimately lowering the H₂ yield compared to Pt/C.     

Comparison of the Effectiveness of Bonding Composite to Zirconia as a Repair Method

Chipping of the veneering porcelain is often reported in the literature. Intraoral repair of chipped veneering porcelain provides an option when the restoration cannot be removed and replaced. This in vitro study investigated the bond strength of two porcelain repair methods to the zirconia ceramic after different aging conditions. A total of 120 (Vita InCeram YZ) samples were divided into two main groups according to the different repair methods (n = 60). The first method was using a porcelain repair kit (Bisco), and the second method was repairing with a universal adhesive (Single Bond Universal Adhesive) and a composite resin (Z100). Each group was divided into two subgroups (n = 30) according to surface modification (with or without airborne particle abrasion). Each group was then divided into three subgroups (n = 10) depending on aging conditions. Shear bond strength tests were performed to measure the adhesion strength between composite and zirconia surfaces. Statistical analysis was performed with 3‐way ANOVA, followed by Tukey HSD test (α = 0.05). Surface conditioning by airborne particle abrasion affected the strength values in the repair kit group compared with conventionally repaired group. Conventionally repaired group showed statistically significant higher bond strength values than repair kit group.     

Spatial calibration of structured illumination fluorescence microscopy using capillary tissue phantoms

Quantitative assessment of microvascular structure is relevant to the investigations of ischemic injury, reparative angiogenesis and tumor revascularization. In light microscopy applications, thick tissue specimens are necessary to characterize microvascular networks; however, thick tissue leads to image distortions due to out-of-focus light. Structured illumination confocal microscopy is an optical sectioning technique that improves contrast and resolution by using a grid pattern to identify the plane-of-focus within the specimen. Because structured illumination can be applied to wide-field (nonscanning) microscopes, the microcirculation can be studied by sequential intravital and confocal microscopy. To assess the application of structured illumination confocal microscopy to microvessel imaging, we studied cell-sized microspheres and fused silica microcapillary tissue phantoms. As expected, structured illumination produced highly accurate images in the lateral (X-Y) plane, but demonstrated a loss of resolution in the Z-Y plane. Because the magnitude of Z-axis distortion was variable in complex tissues, the silica microcapillaries were used as spatial calibration standards. Morphometric parameters, such as shape factor, were used to empirically optimize Z-axis software compression. We conclude that the silica microcapillaries provide a useful tissue phantom for in vitro studies as well as spatial calibration standard for in vivo morphometry of the microcirculation.     

Controlling Structural Anisotropy of Anisotropic 2D Layers in Pseudo‐1D/2D Material Heterojunctions

Chemical vapor deposition and growth dynamics of highly anisotropic 2D lateral heterojunctions between pseudo‐1D ReS₂ and isotropic WS₂ monolayers are reported for the first time. Constituent ReS₂ and WS₂ layers have vastly different atomic structure, crystallizing in anisotropic 1T′ and isotropic 2H phases, respectively. Through high‐resolution scanning transmission electron microscopy, electron energy loss spectroscopy, and angle‐resolved Raman spectroscopy, this study is able to provide the very first atomic look at intimate interfaces between these dissimilar 2D materials. Surprisingly, the results reveal that ReS₂ lateral heterojunctions to WS₂ produce well‐oriented (highly anisotropic) Re‐chains perpendicular to WS₂ edges. When vertically stacked, Re‐chains orient themselves along the WS₂ zigzag direction, and consequently, Re‐chains exhibit six‐fold rotation, resulting in loss of macroscopic scale anisotropy. The degree of anisotropy of ReS₂ on WS₂ largely depends on the domain size, and decreases for increasing domain size due to randomization of Re‐chains and formation of ReS₂ subdomains. Present work establishes the growth dynamics of atomic junctions between novel anisotropic/isotropic 2D materials, and overall results mark the very first demonstration of control over anisotropy direction, which is a significant leap forward for large‐scale nanomanufacturing of anisotropic systems.     

Fracture strength of composite resins for endodontically treated molars

Objectives: The purpose of this study was to evaluate the effect of different fabrication techniques on the fracture strength of the composite resin-based inlay restorations of endodontically treated molars. Methods: Sixty mandibular molars were divided into six groups (n = 10) designated according to the treatment as: Group-1: Control group, intact teeth; Group-2: Filtek Ultimate Universal restorative with incremental technique; Group-3: Filtek Bulk Fill Posterior restorative; Group-4: Biodentine with Filtek Ultimate Universal restorative; Group 5: everX Posterior with Filtek Ultimate Universal restorative; and Group-6: Lava Ultimate CAD/CAM restorative. The standard mesio-occluso-distal cavities were prepared and the roots filled for all the teeth, except those of the control group. Following the placement of the restorations, the fracture resistance of the specimens was measured. The data were analyzed by the one-way analysis of variance and Tukey’s post hoc test. Results: While Group-1 (2815.80 N) exhibited significantly higher fracture strength than the other groups (p < 0.05), Groups-2 (2062.20 N), 3 (2166.00 N), 5 (2355.60 N), and 6 (2340.70 N) exhibited statistically similar results (p > 0.05). The Biodentine group (1480.50 N) exhibited significantly lower fracture strength than the rest of the groups (p < 0.05). Conclusions: The CAD/CAM and manual build-up techniques exhibited statistically similar results with the exception of Biodentine, which exhibited a significantly lower in vitro performance compared to the other composites used in the study. The fiber-supported composite everX Posterior increased the fracture strength of the endodontically treated teeth.