Effect of capillary pressure in nanobubbles on their adhesion to particles under foam flotation. Part 3

The energy possibility of the transition of free bubbles A to adherent bubbles M, or the A → M (TAM) transition, is calculated on substrates with different wetting abilities: extremely hydrophilic (Φ), extremely hydrophobic (Γ), and with incomplete wetting ability (H _x ), where x is the substrate surface fraction covered by a monolayer of collector molecules). Calculations of TAM for bubbles with a diameter (d _e ) of 2 mm to 20 nm on Φ, Γ, and H _x substrates showed that the change in specific energy (ΔG/V) in a bubble in the case of TAM depends on the value of d _e , substrate wetting ability, and surface area of its contact with the bubble. According to the results of studies, high capillary pressure (P _c) in nanobubbles M promotes their instantaneous spreading over the substrate. Herewith, P _c decreases considerably. The adhesion and spreading processes occur as a single process, irreversibly, one-way, and fast, because they are not complicated by counterprocesses. Upon a decrease in equatorial diameter d _e and wetting ability of the substrate, the decrease in G/V reaches several million J/m³. The actual simultaneity of the processes of bubble adhesion and spreading is illustrated by microphotographs of larger bubbles with a luminescent apolar reagent eliminating the effect of wetting hysteresis that is easily overcome in nanobubbles in the case of high P _c values.     

Programmable end milling of thermoplastics

The end milling of industrial and engineering thermoplastics on numerically controlled machine tools is considered. Specifically, attention focuses on the sources and prevention of machining defects. Recommendations are made regarding the selection of the tool geometry, the cutting conditions, and the mill trajectory.     

Influence of the position of InGaAs quantum dot array on the spectral characteristics of AlGaAs/GaAs photovoltaic converters

Results of a comparative study of the internal quantum yield of AlGaAs/GaAs photovoltaic converters (PVCs) with variable position of the array of vertically coupled InGaAs quantum dots (QDs) are presented. It is established that the QD array placed immediately at the i-region/base interface does not change the PVC sensitivity compared to that for QDs arranged inside the i-region of the p-n junction. However, the QD array shifted to the base or the back potential barrier decreases the contribution of a base layer to the PVC photocurrent and reduces the photosensitivity of the QD-based medium.     

UV curable lens production using molecular weight controlled PEEK based acrylic oligomer (Ac-PEEK)

We produced UV curable lenses with properties blocking short wave UV light. In the UV-curable formulations, we used an oligomer (Ac-PEEK) with another urethan oligomer (Mw = 2000). Radically active, molecular weight controlled Ac-PEEK was obtained by reacting 2-hydroxyl ethyl methacrylate with molecular- weight- controlled and isocyanate terminated PEEK (Mn = 4500). We characterized all synthesized monomer, oligomer and optical materials with UV/Vis spectrophotometer with interferogram, elemental analyser, mass spectrophotometer, proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermal gravimetric analyzer, differential scanning calorimeter, scanning electron microscopy and gas chromatography. Results suggested that newly synthesized oligomer with the structure of PEEK absorbs short wave UV-light. Ageing tests [ISO 11979-5, Ophthalmic implants—intraocular lenses (IOL)—Part 5: Biocompatibility] performed on the IOL materials were successful. High contact angle of the obtained lenses suggests that all lenses were hydrophobic and SEM results revealed that lenses are morphologically homogeneous. Based on all positive properties just mentioned, we safely conclude that the lenses produced in this study are very promising for IOL production.     

Degradation kinetics of PVC plasticized with different plasticizers under isothermal conditions

The aim of the present work is to elucidate the degradation kinetics of polyvinyl chloride (PVC) plasticized with some phthalate and nonphthalate plasticizers. A PVC thermomat instrument was utilized to maintain the isothermal degradation conditions at 140 and 160°C, and to suppress the oxidative degradation by means of nitrogen flow. The conductivity measurements were performed to follow hydrogen chloride (HCl) gas which is released upon PVC degradation and trapped in water. Dehydrochlorination of plasticized PVC films occurred with activation energies of about 23–160 and 26–117 kJ mol^?1 and the isokinetic temperatures, at which the dehydrochlorination rate constants of all p‐PVC films would have the same value, were found to be 171 and 128°C for initial and linear regions of dehydrochlorination curve, respectively. Plasticizer incorporation contributes to the stability of the films particularly after the consumption of stabilizer due to the dehydrochlorination. Influence of temperature rise by 20°C on the degradation rate constant is the lowest for DINCH having p‐PVC films as 0.36 and 0.42% increment at the initial region and linear region, respectively. On the other hand, DOTP reveals greater stability than the others do since the compensation ratio of the PVC film having DOTP is greater than the other films. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41579.     

Effects of mixing techniques and dentin moisture conditions on push-out bond strength of ProRoot MTA and Biodentine

Objective: To evaluate the influence of manual and mechanical mixing techniques as well as the effects of moisture on the push-out bond strength of ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK, USA) and Biodentine (Septodont, Saint Maur des Fosses, France) to radicular dentin.

Material and methods: Two hundred and forty dentin discs were assigned into three groups with respect to the moisture condition tested: (1) dry, (2) paper points, (3) wet. The discs were further divided into four subgroups according to the calcium silicate cements (CSCs) and mixing techniques used: (1) ProRoot MTA mixed manually, (2) ProRoot MTA mixed mechanically, (3) Biodentine mixed manually, and (4) Biodentine mixed mechanically. Bond strengths of the cements to root canal dentin were measured using a push-out test setup. The data were statistically analyzed using three-way ANOVA and Bonferroni post hoc test p = 0.05.

Results: The data indicated that the push-out bond strength values were significantly affected by CSCs, mixing techniques, and moisture conditions (p < 0.001). Dry conditions caused a significant decrease in bond strength values for both CSCs (p < 0.001). The mean bond strength of Biodentine was significantly higher than that of ProRoot MTA, regardless of the mixing techniques and moisture conditions (p < 0.001). Mechanical mixing favored bond strength values statistically compared to manual mixing (p < .001).

Conclusion: The mixing techniques and moisture conditions have an effect on the push-out bond strengths of ProRoot MTA and Biodentine. Dry samples and manual mixing of cements deteriorate the push-out bond strengths values.