Effect of Monomer Composition on the Performance of Polymer‐Stabilized Liquid Crystals with Two‐Step Photopolymerization

Polymer‐stabilized cholesteric liquid crystal (PSCLC) films with broadband reflection based on two‐step photopolymerization are fabricated. Owing to the helical twisting power (HTP) value of the chiral dopant (CD) decreasing with increasing temperature, PSCLC films with broadband reflection are obtained by two‐step polymerization anchoring helical pitch of different length at two different temperature points. The effect of monomer composition on the PSCLC reflection properties before and after polymerization was studied. The results show that the free‐radical monomers with appropriate concentration and cationic monomers with sufficient concentration are vital for the formation of PSCLC films with broadband reflection. In addition, the experiments show that the increase in the functionality and rigidity of the cationic monomer has a positive effect on the broadening of the reflection band. This study can provide guidance and reference for the selection of monomer species and concentration in PSCLC preparation. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1126–1132     

Alkylaluminum activator effects on polyethylene branching using a N,N′‐nickel precatalyst appended with bulky 4,4′‐dimethoxybenzhydryl groups

Ten unsymmetrical N,N'‐bis (imino) acenaphthene‐nickel (II) halide complexes, [1‐[2,6‐{(4‐MeOC₆H₄)₂CH}₂–4‐MeC₆H₂N]‐2‐(ArN)C₂C₁₀H₆]NiX₂, each appended with one N‐2,6‐bis(4,4'‐dimethoxybenzhydryl)‐4‐methylphenyl group, have been synthesized and characterized. The molecular structures of Ni1 , Ni3 , Ni5 and Ni6 highlight the variation in steric protection afforded by the inequivalent N‐aryl groups; a distorted tetrahedral geometry is conferred about each nickel center. On activation with diethylaluminum chloride (Et₂AlCl) or methylaluminoxane (MAO), all complexes showed high activity at 30°C for the polymerization of ethylene with the least bulky bromide precatalysts ( Ni1 and Ni4 ), generally the most productive, forming polyethylenes with narrow dispersities [M_w/M_n: < 3.4 (Et₂AlCl), < 4.1 (MAO)] and various levels of branching. Significantly, this level of branching can be influenced by the type of co‐catalyst employed, with Et₂AlCl having a predilection towards polymers displaying significantly higher branching contents than with MAO [T_m: 33.0–82.5°C (Et₂AlCl) vs. 117.9–119.4°C (MAO)]. On the other hand, the molecular weights of the materials obtained with each co‐catalyst were high and, in some cases, entering the ultra‐high molecular weight range [M_w range: 6.8–12.2 × 10⁵ g mol^?1 (Et₂AlCl), 7.2–10.9 × 10⁵ g mol^?1 (MAO)]. Furthermore, good tensile strength (ε_b up to 553.5%) and elastic recovery (up to 84%) have been displayed by selected more branched polymers highlighting their elastomeric properties.     

Study on the Amyloid A $\beta$42 with Accelerated Molecular Dynamics Simulations *

One major cause of Alzheimer's disease (AD) is evidently due to the aggregation and deposition of amyloid $\beta$ peptides (A$\beta$) in the brain tissue of the patient. Preventing misfolding and self-aggregation of A$\beta$ protein can reduce the formation of highly toxic polymer, which is important for the treatment of AD. Among them, the $\alpha$-helix consisting of 42 residues (A$\beta$42) is the main component of senile plaques in AD. In this paper, 500 ns accelerated molecular dynamics are performed at different temperatures (300 K, 350 K, 400 K, 450 K) to study of the effect of temperature-induced conformation changes of A$\beta$42 protein during the unfolding process respectively.     

Efficient and stereoselective synthesis of thiosulfinates from disulfide using cumene hydroperoxide in the presence of titanium-based catalyst systems

Abstract

An efficient and stereoselective procedure of oxidizing disulfide to thiosulfinate 2a using CHP as the oxidant and economically available Ti(O-i-Pr)₄/L-DET/H₂O as catalysts were developed. The reaction went smoothly under mild conditions with synthetic useful yield and the workup for obtaining the final product is quite convenient.     

A machine learning method for computing quasi-potential of stochastic dynamical systems

Nonlinear Dynamics - The concept of quasi-potential plays a central role in understanding the mechanisms of rare events and characterizing the statistics of transition behaviors in stochastic...     

Investigation of chemical changes in Polygonatum kingianum after traditional processing by multiple fingerprint profiles in combination with multivariate methods

Polygonati Rhizoma (Huangjing) is traditional medicine in China, which can only be used as medicine after being processed. However, there is a limited theoretical basis for analyzing the changes in chemical components after traditional processing. In this study, analytical techniques including Fourier transform infrared spectroscopy, high-performance gel permeation chromatography–evaporative light scattering detection, and HPLC–diode array detection were proposed to perform multiple fingerprint analyses of the changes in the processed materials; the total sugar was also determined. Moreover, the chemometric studies, including hierarchical cluster analysis and principal component analysis, were used to visualize the discrimination of raw and processed materials. The results revealed that the chemical constituents had been profoundly changed following sample processing. In conclusion, these methods could be successfully used to compare raw and processed materials of Polygonatum kingianum, which could be used to elaborate the rationality of processing from the perspective of chemical composition.     

Improved cycling stability of P2-type Na0.71Co0.96O2 cathode material by optimizing Ti doping

Journal of Solid State Electrochemistry - The electrode materials with long cycle life are important for the large-scale application of sodium ion batteries. In this work, P2-type...     

Prediction of adsorption isotherms of C3H6/C3H8 on hierarchical porous HP–Cu–BTC

The isotherms of C₃H₆ and C₃H₈ on three distinct HP–Cu–BTCs were determined using the static volumetric capacity technique across the pressure range 0–100 kPa, and the resulting experimental data set was regressed using the dual–site sips (DSS) model. The kinetics and thermodynamics of C₃H₆ and C₃H₈ on HP–Cu–BTCs were studied. The results show that the adsorption kinetics of the three samples conform to the pseudo–first–order kinetic model, indicating that the adsorption process of the HP–Cu–BTCs samples is the adsorption process with physical adsorption as the control step. The thermodynamic analysis results show that the adsorption of propylene and propane on the surface of HP–Cu–BTCs are a spontaneous exothermic process, because the transition of propylene and propane from three–dimensional motion to two–dimensional motion leads to a decrease in the system entropy. In addition, the isosteric heat of adsorption ($Q_{st}$) was used to predict the isotherms of C₃H₆ and C₃H₈ at 298 and 303 K, respectively. When the predicted and experimental values are compared, the predicted isotherms are shown to be fully associated with the experimental values, with mean relative errors (MRE%) of less than 2%. Additionally, the C₃H₆ and C₃H₈ adsorption isotherms and selectivity for C₃H₆ adsorption were predicted using a combination of the DSS model and ideal adsorbed solution theory (IAST). The findings suggest that the overall adsorption capacity of the mixes rose as the mole fraction of C₃H₆ increased, but the adsorption capacity of the equimolar C₃H₆ and C₃H₈ in the three HP–Cu–BTC combinations was smaller than the pure component. Additionally, an undetectable shift in C₃H₆/C₃H₈ selectivity was seen when the molar percentage of C₃H₆ increased.     

An Approximation Scheme for Reflected Stochastic Differential Equations with Non-Lipschitzian Coefficients

Journal of Theoretical Probability - In this paper, we study a numerical approximation scheme for reflected stochastic differential equations (SDEs) with non-Lipschitzian coefficients in a bounded...