NMR Analysis of Hydroxyl-Terminated Polybutadiene End Groups and Reactivity Differences with Monoisocyanates

Nuclear magnetic resonance (NMR) spectroscopy was employed to investigate both the end group microstructure of R-45HTLO hydroxyl-terminated polybutadiene (HTPB) and reactivity rate differences among the different types of end groups. There is some conflict in the literature about the exact nature of the end groups and which resonance frequencies represent the three main types of methylene-hydroxyl end groups (cis, trans, or vinyl) and other possible branch point end groups (geraniol). NMR spectral analysis of small molecule model compounds supports the cis, trans, and vinyl end groups model. A model reaction scheme is proposed that produces branch points without the requirement of any “geraniol” structures. The reaction, with and without catalyst, of the various HTPB end groups with three different monoisocyanates (2-fluorophenyl isocyanate, phenyl isocyanate, and tert-butyl isocyanate) monitored by NMR spectroscopy, revealed different reactivity rates that are correlated with the assigned structures. In both the catalyzed and uncatalyzed reactions, the vinyl end groups reacted slower than the cis or trans end groups. As expected, the bulky isocyanates were the slowest to react, while the isocyanate group with electron withdrawing groups reacted the fastest. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2665–2671     

Sonochemical synthesis of a two‐dimensional supramolecular polymer with nanoporous morphology,linear thallophilic and covalent hydrogen‐bonding interactions

A new thallium‐based supramolecular polymer [Tl(μ₃–3‐HClb)(μ₃–3‐Clb)]_n ( 1 ), (3‐HClb = 3‐chloroperbenzoic acid), has been synthesized and structurally characterized by single crystal X‐ray crystallography. It has a two‐dimensional structure with linear thallophilic and covalent hydrogen‐bonding interactions. In order to evaluate the effects of concentration, ultrasonic irradiation and type of solvents on structure, morphology and thermal behavior of 1 , some experiments were designed, and eight samples of 1 were synthesized under different conditions. These samples were characterized by IR spectroscopy, thermogravimetric and differential thermal analyses, X‐ray powder diffraction and scanning electron microscopy.     

Role of Interaction in Enhancing the Epistemic Utility of 3D Mathematical Visualizations

Many epistemic activities, such as spatial reasoning, sense-making, problem solving, and learning, are information-based. In the context of epistemic activities involving mathematical information, learners often use interactive 3D mathematical visualizations (MVs). However, performing such activities is not always easy. Although it is generally accepted that making these visualizations interactive can improve their utility, it is still not clear what role interaction plays in such activities. Interacting with MVs can be viewed as performing low-level epistemic actions on them. In this paper, an epistemic action signifies an external action that modifies a given MV in a way that renders learners’ mental processing of the visualization easier, faster, and more reliable. Several, combined epistemic actions then, when performed together, support broader, higher-level epistemic activities. The purpose of this paper is to examine the role that interaction plays in supporting learners to perform epistemic activities, specifically spatial reasoning involving 3D MVs. In particular, this research investigates how the provision of multiple interactions affects the utility of 3D MVs and what the usage patterns of these interactions are. To this end, an empirical study requiring learners to perform spatial reasoning tasks with 3D lattice structures was conducted. The study compared one experimental group with two control groups. The experimental group worked with a visualization tool which provided participants with multiple ways of interacting with the 3D lattices. One control group worked with a second version of the visualization tool which only provided one interaction. Another control group worked with 3D physical models of the visualized lattices. The results of the study indicate that providing learners with multiple interactions can significantly affect and improve performance of spatial reasoning with 3D MVs. Among other findings and conclusions, this research suggests that one of the central roles of interaction is allowing learners to perform low-level epistemic actions on MVs in order to carry out higher-level cognitive and epistemic activities. The results of this study have implications for how other 3D mathematical visualization tools should be designed.     

A Rigorous Treatment of Energy Extraction from a Rotating Black Hole

The Cauchy problem is considered for the scalar wave equation in the Kerr geometry. We prove that by choosing a suitable wave packet as initial data, one can extract energy from the black hole, thereby putting supperradiance, the wave analogue of the Penrose process, into a rigorous mathematical framework. We quantify the maximal energy gain. We also compute the infinitesimal change of mass and angular momentum of the black hole, in agreement with Christodoulou’s result for the Penrose process. The main mathematical tool is our previously derived integral representation of the wave propagator. Research supported in part by the Deutsche Forschungsgemeinschaft. Research supported by NSERC grant # RGPIN 105490-2004. Research supported in part by the Humboldt Foundation and the National Science Foundation, Grant No. DMS-0603754. Research supported in part by the NSF, Grant No. 33-585-7510-2-30.     

An arbitrary Lagrangian–Eulerian formulation for the numerical simulation of flow patterns generated by the hydromedusa Aequorea victoria

A new geometrically conservative arbitrary Lagrangian–Eulerian (ALE) formulation is presented for the moving boundary problems in the swirl-free cylindrical coordinates. The governing equations are multiplied with the radial distance and integrated over arbitrary moving Lagrangian–Eulerian quadrilateral elements. Therefore, the continuity and the geometric conservation equations take very simple form similar to those of the Cartesian coordinates. The continuity equation is satisfied exactly within each element and a special attention is given to satisfy the geometric conservation law (GCL) at the discrete level. The equation of motion of a deforming body is solved in addition to the Navier–Stokes equations in a fully-coupled form. The mesh deformation is achieved by solving the linear elasticity equation at each time level while avoiding remeshing in order to enhance numerical robustness. The resulting algebraic linear systems are solved using an ILU(k) preconditioned GMRES method provided by the PETSc library. The present ALE method is validated for the steady and oscillatory flow around a sphere in a cylindrical tube and applied to the investigation of the flow patterns around a free-swimming hydromedusa Aequorea victoria (crystal jellyfish). The calculations for the hydromedusa indicate the shed of the opposite signed vortex rings very close to each other and the formation of large induced velocities along the line of interaction while the ring vortices moving away from the hydromedusa. In addition, the propulsion efficiency of the free-swimming hydromedusa is computed and its value is compared with values from the literature for several other species.     

Two‐phase flow electrosynthesis: Comparing N‐octyl‐2‐pyrrolidone–aqueous and acetonitrile–aqueous three‐phase boundary reactions

A microfluidic double channel device is employed to study reactions at flowing liquid–liquid junctions in contact with a boron‐doped diamond (BDD) working electrode. The rectangular flow cell is calibrated for both single‐phase liquid flow and biphasic liquid–liquid flow for the case of (i) the immiscible N‐octyl‐2‐pyrrolidone (NOP)–aqueous electrolyte system and (ii) the immiscible acetonitrile–aqueous electrolyte system. The influence of flow speed and liquid viscosity on the position of the phase boundary and mass transport‐controlled limiting currents are examined. In contrast to the NOP–aqueous electrolyte case, the acetonitrile–aqueous electrolyte system is shown to behave close to ideal without ‘undercutting’ of the organic phase under the aqueous phase. The limiting current for three‐phase boundary reactions is only weakly dependent on flow rate but directly proportional to the concentration and the diffusion coefficient in the organic phase. Acetonitrile as a commonly employed synthetic solvent is shown here to allow effective three‐phase boundary processes to occur due to a lower viscosity enabling faster diffusion. N‐butylferrocene is shown to be oxidised at the acetonitrile–aqueous electrolyte interface about 12 times faster when compared with the same process at the NOP–aqueous electrolyte interface. Conditions suitable for clean two‐phase electrosynthetic processes without intentionally added supporting electrolyte in the organic phase are proposed. Copyright © 2008 John Wiley & Sons, Ltd.     

Biodiesel production in the presence of heterogeneous catalyst of alumina: Study of kinetics and thermodynamics

In the current research, biodiesel production was investigated in the presence of solid catalysts of K₂CO₃/Al₂O₃ by transesterification of rapeseed oil. The specifications of produced fatty acid methyl esters like viscosity and flash point were studied, and it was noted that they complied with the requirements of ASTM D6751. In addition, the kinetic and thermodynamic parameters were explored considering the temperature changes between 318.15 and 348.15 K. Mass transfer resistance (external diffusion or internal diffusion) over the catalyst was neglected with regard to theWeisz-Prater criterion and Mears criterion. The kinetic models containing Eley-Rideal, Langmuir-Hinshelwood, pseudo–first-order, pseudo–second-order, and α-order models were investigated. Corrected Akaike information criterion was utilized to find the best model fitted with the experimental data. The greatest illustration for the K₂CO₃/Al₂O₃-catalyzed reaction was the nonlinear model with an order of α = 1.287 and the activation energy of 12.12 kJ/mol. Using transition state theory (Eyring-Polanyi equation), the activation Gibbs free energy, activation enthalpy, and activation entropy were calculated at different temperatures. The equilibrium thermodynamic properties depicted that this process is endothermic and spontaneous toward biodiesel production and tends to be irreversible.