Conducting moisture sensitive reactions under mechanochemical conditions

Dry organic solvents are used for various organic reactions that employ moisture sensitive reagents. The processes to dry these solvents are hazardous and costly. Setting up reactions in an open atmosphere while using moisture sensitive reagents has little to no effect on the rate or yield of the reaction under mechanochemical conditions. We believe this is partly due to the gaseous nature of the water vapor in the air compared to the dissolved water and oxygen in solution.     

Fate of the Wiedemann–Franz Law near Quantum Critical Points of Electron Systems in Solids

We introduce and analyze two different scenarios for violation of the Wiedemann–Franz law in strongly correlated electron systems of solids, close to a topological quantum critical point (TQCP) where the density of states N(0) diverges. The first, applicable to the Fermi-liquid (FL) side of the TQCP, involves a transverse zero-sound collective mode that opens a new channel for the thermal conductivity, thereby enhancing the Lorenz number L(0) relative to the value L0 =π² k _B ²/3e ² dictated by conventional FL theory. The second mechanism for violation of the WF law, relevant to the non-Fermi-liquid (NFL) side of the TQCP, involves the formation of a flat band and leads instead to a reduction of the Lorenz number.     

A NON-EMPIRICAL LCAO MO SCF INVESTIGATION OF SOME ASPECTS OF STRUCTURE AND BONDING IN THE THIATHIOPHTHEN RING SYSTEM

Abstract

Non-empirical LCAO MO SCF calculations have been performed on prototype symmetrical and unsymmetrical thiathiophthen ring systems to investigate structure and bonding as a function of change in geometry. Substituent effects have been investigated and it is shown that within the theoretical limitations the energy differences between symmetrical and unsymmetrical structures are quite small. Comparison has been made with UPS and ESCA data pertaining to valence and core levels respectively and some consideration given to the thiathiophthen radical anion and dianion ring systems.     

Application of Modern Analytical Techniques to the Investigation of Cellulose Nitrates

Abstract

Despite contemporary inroads made into the textile market by synthetic fibers, cellulose remains one of the world's most important textile materials. This can be rationalized in terms of several factors, the most important of which is the ready availability and continuing supply of this naturally occurring fiber. It has been estimated that vegetation produces about 100 billion tons of cellulose a year [1], and it is partly due to this fact that cellulose has maintained its position and competitive price in world markets.     

Methylation of Dimedone

In connection with our synthetic approach to pentacyclic triterpenes,¹ we have required substantial amounts of 2,5,5-trimethyl-1,3-cyclohexanedione (methyldimedone, 2), which is available by methylation of dimedone (1).² However, methylation may also afford the 2,2-dimethyl product 3, the methyl ether 4, and the C, O-dimethyl product 5.     

Electrostatics and the electro-optic behaviour of chiral smectics C: 'block' polarization screening of applied voltage and 'V-shaped' switching

We present a new model for the physics of thresholdless switching in chiral smectics. In the limit of high polarization, the electro-optics of chiral smectic C liquid crystals are dominated by two distinct electrostatic effects. Complete (surface to surface) 'stiffening' of the polarization field by its charge self-interaction causes the polarization to orient as a uniform block. Complete screening of applied electric field by polarization charge leads to voltage-induced orientation where the electric field in the liquid crystal is exactly zero, These effects, both operative during the 'V-shaped' portion of thresholdless transmission vs. voltage curves, combine to produce 'V-shaped' switching.     

A Sustainable Freeze‐Drying Route to Porous Polysaccharides with Tailored Hierarchical Meso‐ and Macroporosity

Bio‐derived polysaccharide aerogels are of interest for a broad range of applications. To date, these aerogels have been obtained through the time‐ and solvent‐intensive procedure of hydrogel fomation, solvent exchange, and scCO2 drying, which offers little control over meso/macropore distribution. A simpler and more versatile route is developed, using freeze drying to produce highly mesoporous polysaccharide aerogels with various degrees of macroporosity. The hierarchical pore distribution is controlled by addition of different quantities of t‐butanol (TBA) to hydrogels before drying. Through a systematic study an interesting relationship between the mesoporosity and t‐butanol/water phase diagram is found, linking mesoporosity maxima with eutectic points for all polysaccharides studied (pectin, starch, and alginic acid). Moreover, direct gelation of polysaccharides in aqueous TBA offers additional time savings and the potential for solvent reuse. This finding is a doorway to more accessible polysaccharide aerogels for research and industrial scale production, due to the widespread accessibility of the freeze drying technology and the simplicity of the method.

     

Phenylene-Bridged Perylene Monoimides as Acceptors for Organic Solar Cells: A Study on the Structure–Property Relationship

A series of non-fullerene acceptors based on perylene monoimides coupled in the peri position through phenylene linkers were synthesized via Suzuki-coupling reactions. Various substitution patterns were investigated using density functional theory (DFT) calculations in combination with experimental data to elucidate the geometry and their optical and electrochemical properties. Further investigations of the bulk properties with grazing incidence wide angle X-ray scattering (GIWAXS) gave insight into the stacking behavior of the acceptor thin films. Electrochemical and morphological properties correlate with the photovoltaic performance of devices with the polymeric donor PBDB-T and a maximum efficiency of 3.17 % was reached. The study gives detailed information about structure–property relationships of perylene-linker-perylene compounds.     

Accelerating dynamical-fermion computations using the rational hybrid Monte Carlo algorithm with multiple pseudofermion fields

There has been much recent progress in the understanding and reduction of the computational cost of the hybrid Monte Carlo algorithm for lattice QCD as the quark mass parameter is reduced. In this letter we present a new solution to this problem, where we represent the fermionic determinant using n pseudofermion fields, each with an nth root kernel. We implement this within the framework of the rational hybrid Monte Carlo algorithm. We compare this algorithm with other recent methods in this area and find it is competitive with them.