The effect of different cementing strategies and adhesive interface aging on microtensile bond strength (μTBS) of lithium disilicate ceramics to dentin

This study evaluated the effect of different cementing strategies and adhesive interface aging on microtensile bond strength (μTBS) of lithium disilicate ceramic (IPS e.max CAD) to dentin. Forty coronal dentin fragments were randomly assigned to four groups according to the cementing strategy used to bond lithium disilicate ceramic to coronal dentin surface (n = 10): U200 (self-adhesive resin cement (RC) RelyX U200®/3 M ESPE), SBU (single-step self-etching adhesive system (AS) Single Bond Universal®/3 M ESPE + RelyX ARC®/3 M ESPE RC), AdperSB (two-step etch-and-rinse AS Single Bond 2®/3 M + RelyX ARC®/3 M ESPE RC) and Scotchbond (three-step etch-and-rinse AS Scotchbond Multi-Purpose®/3 M + RelyX ARC®/3 M RC). After 48 h, the ceramic-tooth blocks were sectioned perpendicular to the adhesive interface in the form of sticks and randomly subdivided into two groups according to when they were to be submitted to μTBS testing: immediately or 6 months after storage in water. Some sticks were kept for analysis of the adhesive interface by scanning electron microscopy (SEM). The μTBS test was performed in a universal testing machine (0.5 mm/min). The data (MPa) were analyzed using split-plot ANOVA and Tukey’s test (α = 0.05). Water storage decreased μTBS in all cementing strategies. The μTBS was greatest in the Scotchbond group and lowest in the U200 group, at both storage times. No signs of interface degradation were detected under SEM after water storage. In conclusion, water storage decreased bond strength, regardless of the adhesive cementation strategy, and that the three-step adhesive system/dual-cure resin cement ultimately performed better in terms of bond strength.     

Enhanced UV- and visible-light driven photocatalytic performances and recycling properties of graphene oxide/ZnO hybrid layers

Light induced catalytic processes have attracted significant attention during the last years for wastewater treatment due to their efficiency in decomposition of organic contaminants. In this study we report the synthesis of graphene oxide (GO)/ZnO hybrid layers with high photocatalytic efficiency using laser radiation. The results show that the hybrid layers exhibit much improved photodecomposition efficiency as compared to pure GO or ZnO both under UV and visible-light irradiation. The enhanced photocatalytic efficiency of the hybrid as compared to the reference pure ZnO and GO layers was attributed to the contribution of GO to the separation and transport of the photogenerated charge carriers. Additionally, under visible light irradiation the organic molecules can act as first sensitizers in the degradation process. The recyclability of the layers was also investigated through repetitive photodegradation cycles under UV- or visible-light irradiation. After consecutive degradation runs, the hybrid photocatalyst layers were still stable and retained high degradation efficiency, ensuring reusability. The photocatalytic activity of the layers was correlated with the gradual change of their chemical structure during consecutive degradation cycles. Owing to the high photodegradation efficiency, reusability, and ease of recovery the synthesised hybrid layers consisting of easily available materials are suitable for environmental purification applications.     

Temperature Stability of Lead‐Free Niobate Piezoceramics with Engineered Morphotropic Phase Boundary

The temperature dependence of piezoelectric properties (direct piezoelectric coefficient d₃₃, converse piezoelectric coefficient d₃₃(E = 0), strain S and electromechanical coupling coefficient k_p) for two niobate‐based lead‐free piezoceramics have been contrasted. 0.92(Na_0.5K_0.5)NbO₃–0.02(Bi_1/2Li_1/2)TiO₃–0.06BaZrO₃ (6BZ/2BLT/92NKN) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at room temperature and 0.92(Na_0.5K_0.5)NbO₃–0.03(Bi_1/2Li_1/2)TiO₃–0.05BaZrO₃ (5BZ/3BLT/92NKN) features an MPB engineered to be located below room temperature. At 30°C, d₃₃, d₃₃(E = 0), S (at 2 kV/mm), and k_p are 252 pC/N, 230 pm/V, 0.069%, 0.51 for 5BZ/3BLT/92NKN; and 348 pC/N, 380 pm/V, 0.106%, 0.57 for 6BZ/2BLT/92NKN, respectively. With increasing temperature, the piezoelectric properties decrease. At 200°C, d₃₃, d₃₃(E = 0), S (at 2 kV/mm), and k_p are 170 pC/N, 160 pm/V, 0.059%, 0.36 for 5BZ/3BLT/92NKN; and 181 pC/N, 190 pm/V, 0.061%, 0.39 for 6BZ/2BLT/92NKN. It is found that the electromechanical coupling coefficient has a better temperature stability than the piezoelectric coefficient in the studied system due to a large temperature‐dependent compliance change. The results demonstrate that engineering an MPB is highly effective in tailoring temperature stability of piezoceramics.     

One Question,Multiple Answers: Biochemical and Biophysical Screening Methods Retrieve Deviating Fragment Hit Lists

Fragment‐based lead discovery is gaining momentum in drug development. Typically, a hierarchical cascade of several screening techniques is consulted to identify fragment hits which are then analyzed by crystallography. Because crystal structures with bound fragments are essential for the subsequent hit‐to‐lead‐to‐drug optimization, the screening process should distinguish reliably between binders and non‐binders. We therefore investigated whether different screening methods would reveal similar collections of putative binders. First we used a biochemical assay to identify fragments that bind to endothiapepsin, a surrogate for disease‐relevant aspartic proteases. In a comprehensive screening approach, we then evaluated our 361‐entry library by using a reporter‐displacement assay, saturation‐transfer difference NMR, native mass spectrometry, thermophoresis, and a thermal shift assay. While the combined results of these screening methods retrieve 10 of the 11 crystal structures originally predicted by the biochemical assay, the mutual overlap of individual hit lists is surprisingly low, highlighting that each technique operates on different biophysical principles and conditions.     

On the coupling in molecular motions: A novel molecular micro-structure approach to the physical meaning of the Ngai's coupling parameter

Summary The dielectric behaviour through DETA system has been studied for six PVC samples of distinct molecular microstructure in terms of content and associated surroundings and conformation of the local configurations mmr termini of isotactic sequences. Both the dielectric studies and the microstructure of the samples, as obtained by stereospecific substitution reaction of an additive-free commercial PVC are to be published in detail separately. For purposes of clarity some of the results are mentioned in Experimental section. The phenomenological correlation between the β parameter as defined by Ngai's theory and the microstructure of the samples, quantities both issued from the above quoted work, is considered in the present paper with the objective of providing some novel ideas on the physical meaning, at molecular level, of the Ngai's coupling parameter, in the light of mobility constraints and local free volume associated with mmr structure at its likely conformations. Received: 16 March 2001/Revised version: 18 June 2001/Accepted: 24 July 2001     

Convenient thionation of triglycerides with lawessons reagent

Thionation using the Lawesson’s reagent (LR) led to quantitative and selective replacement of carbonyl groups (C=O) with thionocarbonyl groups (C=S). Mixtures of thionotriglycerides were obtained by reaction of 2,4-bis (p-methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide in suspension with triglycerides (TG). With a molar ratio (LR)/(TG)=3∶2, there was complete exchange of C=O with C=S in the carboxylic groups of the TG. The yield is over 90%. The two P=S ligands in the LR confer a double reactivity, producing a high power of thionation. Fourier transform infrared spectroscopy was employed for quantitative and qualitative characterization of the thionated TG and for monitoring the progress of partial or total thionation as conditioned by the molar ratios of the starting compounds. Thus, with molar ration LR/TG of 0.108, 0.36, and 0.72, we obtained around 6, 20, and 40% of C=O conversion, respectively.     

Short Crack R-Curves in Ferroelectric and Electrostrictive PLZT

This work describes the measurement of R -curve behavior in ferroelectric ceramics using four-point bend specimens with controlled semielliptical surface cracks. The results are compared for two compositions of lead lanthanum zirconate titanate. One exhibits ferroelastic behavior, the other electrostrictive linear elastic behavior. R -curves are measured in the crack length regime of 0.1 to 0.8 mm. The ferroelastic composition displays a toughness increase from 0.5 to 1.2 MPa·m^1/2. The linear elastic composition displays a flat R -curve. The R -curve behavior is attributed to ferroelastic toughening.     

Processing and Mechanical Properties of Al2O3/Ni3Al Composites with Interpenetrating Network Microstructure

Composites with microstructures of interpenetrating networks were manufactured by gas pressure infiltration of Ni₃Al into porous preforms of aluminum oxide. Composites with Ni₃Al contents of between 15% and 30% by volume were made and evaluated mechanically at temperatures between room temperature and 1000°C. The fracture strength, the fracture toughness, Young's modulus, and the thermal expansion coefficient were measured for each composite and test condition and were correlated with the microstructures of the composites. Composites with low Ni₃Al contents had strengths below 400 MPa, presumably due to microcracking along the interface between the Ni₃Al and the Al₂O₃. The composite with the highest content of Ni₃Al, 30 vol%, had a mean fracture strength of 675 ± 16 MPa, a Weibull modulus of 23.9, and a room-temperature toughness of 9.2 ± 0.5 MPa·m^1/2.     

A representative and comprehensive review of the electrical and thermal properties of polymer composites with carbon nanotube and other nanoparticle fillers

In this review we present the results of our literature investigation into the electrical and thermal properties of carbon nanotube polymer composites. A short selection of data relating to conductive polymer composites with various fillers is provided for comparison. The effects of filler properties such as type and size, the use of hybrid fillers, fabrication methods for polymer composites and the importance of the modeling of the electronic and thermal transport mechanisms are discussed, as are more general factors influencing the properties of these composites. This review represents a comprehensive survey and constructive study and should serve as a useful reference tool for industrial and academic researchers working in this field. © 2017 Society of Chemical Industry