Synthesis and electro-optical properties of some ferroelectric liquid crystalline polymers

The synthesis and characterization of several series of ferroelectric side-chain polymers were presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurement were used to determine their thermal transitions and analyze their anisotropic textures. The influence of polymer backbones, flexible spacers, mesogenic cores as well as chiral end groups on the mesomorphic properties of the polymers was discussed. Furthermore, the dielectric relaxation properties of the obtained polymers were also evaluated.     

Enhancing the glass‐transition temperature of polyimide copolymers containing 2,2′‐bipyridine units by the coordination of nickel malenonitriledithiolate

Polyimide copolymers containing 2,2′‐bipyridine were synthesized and characterized. The glass‐transition temperatures (T_g's) of the polymers ranged from 260 to 300 °C. In contrast to most known organic chromophore‐containing polyimides, the polyimide copolymers in this study showed elevated T_g's (270–320 °C) after coordination with nickel malenonitriledithiolate inorganic chromophores. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 498–503, 2000     

Investigation of GaN crystal quality on silicon substrates using GaN/AlN superlattice structures

The crystal quality of GaN thin film on silicon using GaN/AlN superlattice structures was investigated. The growth was carried out on Si(111) for GaN(0001) in a metal‐organic vapor phase epitaxy system. Various GaN/AlN superlattice intermediate layers have been designed to decrease the dislocation density. The results showed that the etch pit density could be greatly reduced by one order of magnitude. Cross‐sectional transmission electron microscopy (XTEM) study confirmed the efficiency of GaN/AlN superlattice in blocking threading dislocation propagation in GaN crystal. The design of nine period GaN/AlN (20nm/2nm) superlattice has been evidenced to be effective in reducing the dislocation density and improving the crystal quality. In addition, the dislocation bending in GaN/AlN interface and dislocation merging is investigated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bioadhesive control of plasma proteins and blood cells from umbilical cord blood onto the interface grafted with zwitterionic polymer brushes

In this work, bioadhesive behavior of plasma proteins and blood cells from umbilical cord blood (UCB) onto zwitterionic poly(sulfobetaine methacrylate) (polySBMA) polymer brushes was studied. The surface coverage of polySBMA brushes on a hydrophobic polystyrene (PS) well plate with surface grafting weights ranging from 0.02 mg/cm(2) to 0.69 mg/cm(2) can be effectively controlled using the ozone pretreatment and thermal-induced radical graft-polymerization. The chemical composition, grafting structure, surface hydrophilicity, and hydration capability of prepared polySBMA brushes were determined to illustrate the correlations between grafting properties and blood compatibility of zwitterionic-grafted surfaces in contact with human UCB. The protein adsorption of fibrinogen in single-protein solutions and at complex medium of 100% UCB plasma onto different polySBMA brushes with different grafting coverage was measured by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. The grafting density of the zwitterionic brushes greatly affects the PS surface, thus controlling the adsorption of fibrinogen, the adhesion of platelets, and the preservation of hematopoietic stem and progenitor cells (HSPCs) in UCB. The results showed that PS surfaces grafted with polySBMA brushes possess controllable hydration properties through the binding of water molecules, regulating the bioadhesive and bioinert characteristics of plasma proteins and blood platelets in UCB. Interestingly, it was found that the polySBMA brushes with an optimized grafting weight of approximately 0.1 mg/cm(2) at physiologic temperatures show significant hydrated chain flexibility and balanced hydrophilicity to provide the best preservation capacity for HSPCs stored in 100% UCB solution for 2 weeks. This work suggests that, through controlling grafting structures, the hemocompatible nature of grafted zwitterionic polymer brushes makes them well suited to the molecular design of regulated bioadhesive interfaces for use in the preservation of HSPCs from human UCB.     

Computationally efficient learning of multivariate <Emphasis Type="Italic">t</Emphasis> mixture models with missing information

A finite mixture model using the multivariate t distribution has been well recognized as a robust extension of Gaussian mixtures. This paper presents an efficient PX-EM algorithm for supervised learning of multivariate t mixture models in the presence of missing values. To simplify the development of new theoretic results and facilitate the implementation of the PX-EM algorithm, two auxiliary indicator matrices are incorporated into the model and shown to be effective. The proposed methodology is a flexible mixture analyzer that allows practitioners to handle real-world multivariate data sets with complex missing patterns in a more efficient manner. The performance of computational aspects is investigated through a simulation study and the procedure is also applied to the analysis of real data with varying proportions of synthetic missing values.     

Highly redox‐stable and electrochromic aramids with morpholinyl‐substituted triphenylamine units

A novel morpholinyl‐substituted, triphenylamine‐based diamine monomer, namely 4,4′‐diamino‐4″‐(4‐morpholinyl)triphenylamine, was synthesized and polymerized with various aromatic dicarboxylic acids via the phosphorylation polyamidation reaction leading to a series of electroactive aromatic polyamides (aramids). All aramids were readily soluble in polar organic solvents and could be solution cast into tough and flexible films with high thermal stability. Cyclic voltammograms of the aramid films on the indium‐tin oxide‐coated glass substrate exhibited a pair of reversible oxidation waves with very low onset potentials of 0.36 − 0.41 V (vs. Ag/AgCl) in acetonitrile solution. The polymer films showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency, high contrast ratio, and rapid switching time. The optical transmittance change (Δ%T) at 650 nm between the neutral state and the fully oxidized state is up to 90%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1289–1298     

Synthesis,Structures, and Photophysics of Polynuclear Silver(I) Thiolate and Silver(I) Thiocarboxylate Complexes with Dppm Ligands

Trinuclear silver(I) thiolate and silver(I) thiocarboxylate complexes [Ag₃(μ‐dppm)₃(μ_n‐SR)₂](ClO₄) [n = 2, R = C₆H₄Cl‐4 ( 1 ) and C{O}Ph ( 2 ); n = 3, R = tBu ( 3 )], pentanuclear silver(I) thiolate complex [Ag₅(μ‐dppm)₄(μ₃‐SC₆H₄NO₂‐4)₄](PF₆) ( 4 ), and hexanuclear silver(I) thiolate complexes [Ag₆(μ‐dppm)₄(μ₃‐SR)₄]Y₂ [Y = ClO₄, R =C₆H₄CH₃‐4 ( 5 ) and C₁₀H₇ (2‐naphthyl) ( 7 ); Y = PF₆, R = C₆H₄OCH₃‐4( 6 )], were synthesized [dppm = bis(diphenylphosphanyl)methane] and their crystal structures as well as photophysical properties were studied. In the solid state at 77 K, trinuclear silver(I) thiolate and silver(I) thiocarboxylate complexes 1 and 2 exhibit luminescence at 470–523 nm, tentatively attributed to originate from the ³IL (intraligand) of thiolate or thiocarboxylate ligands, whereas hexanuclaer silver(I) thiolate complexes 5 and 7 produce dual emission, in which high‐energy emission is tentatively attributed to come from the ³IL of thiolate ligands and low‐energy emission is tentatively assigned to come from the admixture of metal ··· metal bond‐to‐ligand charge‐transfer (MMLCT) and metal‐centered (MC) excited states.     

New and Bioactive Sesquiterpenes from Schisandra sphenanthera

Three new sesquiterpenes, schisansphenins A ( 1 ) and B ( 2 ) and (?)‐γ‐cuparenol ( 3 ), were isolated from an acetone extract of the fruits of Schisandra sphenanthera. The known compound 4 was isolated for the frist time from a natural source. The structures of the isolated compounds were elucidated through extensive spectroscopic analyses, particularly 2D‐NMR experiments (¹H,¹H‐COSY, HMQC, HMBC, and NOESY). A plausible biogenetic pathway for schisansphenin B ( 2 ) is proposed. Compounds 2 and 3 significantly reduced activation of NF‐AT and NF‐κB in the luciferase‐reporter assay.     

Transient mixed convection flow of a second grade viscoelastic fluid past an inclined backward facing step

The transient mixed convection of a second-grade viscoelastic fluid past an inclined backward facing step was studied numerically. The combined effects of the Reynolds number, the elastic effect, the inclined angle of the flow channel on the reattachment length, and the phenomena of heat transfer are examined during the development of the flow field. The Gauss-Seidal method with successive over relaxation was implemented to solve the stream-vorticity and energy equations. The results indicate that the reattachment length increases to the maximum as the inclined angle increases up to 150° or 180°. At these cases, the point of reattachment is close to the point of the local maximum value of Nu_x or is overshooting it. It is observed that the reattachment length increases as the Reynolds number increases or the elastic coefficient decreases. In the meantime, the contact point of the isotherm on the upper plate moves upward and is close to upstream flow as the inclined angle is around 150°.