Hierarchical weeping willow nano-tree growth and effect of branching on dye-sensitized solar cell efficiency

In this paper we have demonstrated the simple, low cost, low temperature, hydrothermal growth of weeping willow ZnO nano-trees with very long branches to realize high efficiency dye-sensitized solar cells (DSSCs). We also discuss the effects of branching on solar cell efficiency. By introducing branched growth on the backbone ZnO nanowires (NWs), the short circuit current density and the overall light conversion efficiency of the branched ZnO NW DSSCs increased to almost four times that for vertically grown ZnO NWs. The efficiency increase is attributed to the increase in surface area for higher dye loading and light harvesting and also to reduced charge recombination through direct conduction along the crystalline ZnO branches. As the length of the branches increased, the branches became flaccid and the increase in solar cell efficiency slowed down because the effective surface area increase was hindered by branch bundling during the drying process and subsequent decrease in the dye loading.     

Formation and behavior of composite CO2 hydrate particles in a high-pressure water tunnel facility

Sinking CO₂ composite particles consisting of seawater, liquid CO₂, and CO₂ hydrate were produced by a coaxial flow injector fed with liquid CO₂ and artificial seawater. The particles were injected into a high-pressure water tunnel facility to permit determination of their settling velocities and dissolution rates. Injections were performed at fixed pressures approximately equivalent to 1200-m, 1500-m, and 1800-m depths and at temperatures varying from approximately 2 to 5 °C. Immediately after injection, the cylindrical particles were observed to break away from the injector tip and often aggregated into sinking clusters. The seawater flow in the tunnel was then adjusted in a countercurrent flow mode to suspend the particles in an observation window so that images of the particles could be recorded for later analysis. The flow would often break or cause rearrangement of some of the clusters. Selected individual particles and some clusters were studied until they became too hydrodynamically unstable to follow. In general, the flow required to suspend clusters or individual particles decreased with time as the particles dissolved. For example, one particle was produced and observed for over 6 min at an average pressure of 15.022 MPa and an average temperature of 5.1 °C. Its sinking rate, determined from the flow required for stabilization, changed from 37.2 to 3.3 mm/s over this time. Particle sinking rates were compared to correlations from the literature for uniform cylindrical objects. Reasonable agreement was observed for short times; however, the observed decrease in sinking velocity with time was greater than that predicted by the correlations for longer times. Particle dissolution rates, based on changes in diameter, were also determined and varied from 5 to . A pseudo-homogeneous mass transfer model was used to predict single-particle dissolution rates. Good agreement was achieved between experimental dissolution data and the modeling results.     

Hot melt mixing and foaming of soluplus® and indomethacin

The hot melt mixing (HMM) process was used to dissolve 30 wt% of a model drug, indomethacin (INM), in Soluplus® a water soluble polymer excipient. Comprehensive characterization of the HMM‐prepared samples, using differential scanning calorimetry, X‐ray diffraction, Fourier Transform Infrared spectroscopy, and optical microscopy, strongly suggests that INM was in amorphous state, forming a solid solution with the polymer. Furthermore, to understand the impact of foaming on INM's release profile, the HMM product was foamed in a batch process using supercritical carbon dioxide (CO₂). Dissolution tests of HMM and reference samples were conducted in aqueous solutions with pH 7.4 and 1.2. In all cases INM's release showed strong pH‐dependency; faster release and a greater amount of INM was released at pH 7.4 than at pH 1.2. For pure INM and the physical mixture, the drug's ionizable character results in the observed pH‐dependency. While for the HMM samples it is also a consequence of theformation of hydrogen bonds between Soluplus® and INM which hinder polymer dissolution at pH 1.2. It was observed that the release rate of INM from different sample types at pH 7.4 decreased in the following sequence: foamed HMM > unfoamed HMM > crystalline INM > physical mixture. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Polymers prepared using cleavable initiators: Synthesis, characterization and degradation

Following the great interest in polymers based on degradable monomers and degradable cross-linkers, there is now an increasing activity in the controlled synthesis of polymers using degradable initiators. The degradation of polymers bearing residues of degradable initiators has three unique effects: (a) creation of functional end-groups, (b) controlled reduction in molecular weight, and (c) controlled reduction in the degree of branching. Degradation of such polymers has been done for various reasons, including the production of end-functionalized polymers with freshly prepared thiol end-groups for specific adsorption on to gold surfaces, the transformation of a physical gel to a solution, the conversion of end-linked networks to end-functionalized star polymers and the characterization of their core functionality, and the fabrication of nanoporous membranes by the etching of cylindrical nanophases out of a diblock copolymer film. To date, a variety of labile groups have been employed in these initiators, with most notable example the disulfide, while some other groups are yet to be used.     

Flexible Organic Photovoltaic Cells with In Situ Nonthermal Photoreduction of Spin‐Coated Graphene Oxide Electrodes

The first reduction methodology, compatible with flexible, temperature‐sensitive substrates, for the production of reduced spin‐coated graphene oxide (GO) electrodes is reported. It is based on the use of a laser beam for the in situ, non‐thermal, reduction of spin‐coated GO films on flexible substrates over a large area. The photoreduction process is one‐step, facile, and is rapidly carried out at room temperature in air without affecting the integrity of the graphene lattice or the flexibility of the underlying substrate. Conductive graphene films with a sheet resistance of as low as 700 Ω sq^?1 and transmittance of 44% can be obtained, much higher than can be achieved for flexible layers reduced by chemical means. As a proof of concept of our technique, laser‐reduced GO (LrGO) films are utilized as transparent electrodes in flexible, bulk heterojunction, organic photovoltaic (OPV) devices, replacing the traditional ITO. The devices displayed a power‐conversion efficiency of 1.1%, which is the highest reported so far for OPV device incorporating reduced GO as the transparent electrode. The in situ non‐thermal photoreduction of spin‐coated GO films creates a new way to produce flexible functional graphene electrodes for a variety of electronic applications in a process that carries substantial promise for industrial implementation.     

Fe(PyTACN)‐Catalyzed cis‐Dihydroxylation of Olefins with Hydrogen Peroxide

A family of iron complexes with general formula [Fe(II)(^R,Y,XPyTACN)(CF₃SO₃)₂], where ^R,Y,XPyTACN=1‐[2′‐(4‐Y‐6‐X‐pyridyl)methyl]‐4,7‐dialkyl‐1,4,7‐triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N‐4 and N‐7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis‐dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(^Me,Me,HPyTACN)(CF₃SO₃)₂] ( 7 ), was identified as the most efficient and selective cis‐dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7 , 2 equiv. of H₂O₂ as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis‐dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn‐diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe‐catalyzed cis‐dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron‐deficient and aromatic olefins.     

Assessment of energy dissipation mechanisms for AT-cut QCM sensors with high frequency impedance analysis and optimization heuristics

In the present contribution, five unloaded AT-cut quartz crystal microbalance (QCM) sensors with nominal resonant frequencies equal to 5, 5.2 and 10 MHz, bearing silver (5.2 MHz) and gold electrodes (5 and 10 MHz) on their main surfaces, were bonded on a high pressure cell and studied with respect to their electrical and frequency response in the temperature range from 20 °C to 150 °C at a nitrogen atmosphere (P?=?1 atm). The goal was the qualitative and the quantitative identification of energy dissipation mechanisms of quartz resonators, based on their electrical response and effective properties (quartz viscosity and oscillation area). Electrical response measurements took place with high frequency impedance analysis (HF-IA), while admittance data were processed with the use of equivalent circuit theory and the Differential Evolution heuristic for nonlinear optimization, equipped with an error analysis module. Apart from the inherent energy dissipation due to sensor mounting and electrode related mass and stress effect, dissipation was also induced due to the manifestation of thermally active point defects at temperatures between 65 °C and 145 °C. These point defects are attributed to the movement of interstitial sodium ions within the crystal lattice. Energy dissipation was also observed due to temperature dependent (70–90 °C) creep deformation of the 60Sn-40Pb solder joints which bonded the mounted sensors to the experimental setup. A critical discussion on the magnitude of all observed dissipation mechanisms is presented.     

Experimental study on spreading and evaporation of inkjet printed pico-liter droplet on a heated substrate

In this work, the spreading and evaporation of 2–70 pL droplet (17–50 μm diameter) of water and ethylene glycol jetted by drop-on-demand piezo-driven jetting head on the heated substrate are studied. According to the experimental results, the interfacial oscillation phenomena of water droplet whose Ohnesorge number (Oh) is about 10^?2 is similar to that in inviscid impact driven region, while that of ethylene glycol droplet (Oh ≈10^?1) is similar to that in highly viscous impact driven region followed by capillary driven extra spreading. In addition, various time scales used for nano/micro-liter droplets agree well with the times for interfacial oscillation, viscous damping, extra wetting, and evaporation in pico-liter droplets. In the case of water droplet, the spreading processes end before the evaporation becomes significant. However, in the case of highly viscous ethylene glycol droplet, the extra wetting overlaps the evaporation at high temperature.     

Design of Concrete Flexural Members Strengthened in Shear with FRP

The present study describes a simple design model for the calculation of the fiber-reinforced polymer (FRP) contribution to the shear capacity of strengthened RC elements according to the design formats of the Eurocode, American Concrete Institute, and Japan Concrete Institute. The key element in the model is the calculation of an effective FRP strain, which is calculated when the element reaches its shear capacity due to concrete diagonal tension. Diagonal tension failure may be combined with FRP debonding or tensile fracture, and the latter also may occur at a stage beyond the ultimate shear capacity. An upper limit (maximum) to the FRP effective strain also is defined and aimed at controlling crack opening. The effective strain, obtained through calibration with >75 experimental data, is shown to decrease with the FRP axial rigidity divided by the concrete shear strength. It also is demonstrated that the contribution of FRP to shear capacity is typically controlled by either the maximum effective strain or by debonding and, for a given concrete strength, it increases linearly with the FRP axial rigidity until the latter reaches a limiting value beyond which debonding controls and the gain in shear capacity is relatively small. However, proper anchoring (e.g., full wrapping) suppresses the debonding mechanism and results in considerable increases in shear capacity with the FRP axial rigidity. Finally it is demonstrated that, when compared with others, the proposed model gives better agreement with most of the test results available.