Recent advances in molecular electronics based on carbon nanotubes

Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: (i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties, (ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes, and (iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we outline the main issues concerning the development of carbon nanotubes based electronics applications and review our recent results in the field.     

Viscometric determination of the molecular weight of polymers in the low molecular weight region

In order to overcome the difficulty of the determination of the molecular weight of a polymer in the low molecular weight region by viscometry using the Mark–Houwink–Sakurada (MHS) equation, we have proposed the Dondos–Benoit relationship [η]^?1 = A₂ + AM^?1/2, for a number of polymer–solvent systems, for which we give the numerical values of the parameters A₁ and A₂. Furthermore, we suggest a method for the determination of the above parameters using the MHS constants a and k.     

Studies on determination of molecular weight for ultrahigh molecular weight partially hydrolyzed polyacrylamide

The molecular weight characterization of partially hydrolyzed polyacrylamide (HPAM) for enhanced oil recovery use is rather difficult because of its ultrahigh molecular weight copolymer and polyelectrolyte behaviors in solution. In this work the effects of aqueous NaCl solution concentration and degree of hydrolysis of polymer on molecular dimension were studied. A simple and precise method for determining molecular weight of HPAM is presented. The molecular weight of HPAM with any degree of hydrolysis can be calculated from the [η]−M_w equation of unhydrolyzed PAM in an H₂O system by measuring , of HPAM obtained in aqueous NaCl solutions by extrapolating salt concentration to infinity. Because the values of of HPAM of different degrees of hydrolysis are all equal to the corresponding [η] value of the unhydrolyzed PAM of the same degree of polymerization, the molecular weight of HPAM of any degree of hydrolysis can thus be calculated from the [η] − M_w equation for PAM homopolymer. © 1996 John Wiley & Sons, Inc.     

凝胶色谱法在聚丙烯分子量及分子量分布测定中的应用

根据聚丙烯在凝胶色谱柱上的淋洗特点,确定了测定其分子量及分子量分布试验条件;采用示差和黏度双检测凝胶色谱系统,利用普适校正方法,不需要Mark常数K、α值,可直接测定聚丙烯分子量分布并给出分子量分布曲线;采用统计方法计算数均分子量、重均分子量、黏均分子量,可以为课题研究提供一定的依据和指导。     

Recent molecular advances on downstream plant responses to abiotic stress

Abiotic stresses such as extremes of temperature and pH, high salinity and drought, comprise some of the major factors causing extensive losses to crop production worldwide. Understanding how plants respond and adapt at cellular and molecular levels to continuous environmental changes is a pre-requisite for the generation of resistant or tolerant plants to abiotic stresses. In this review we aimed to present the recent advances on mechanisms of downstream plant responses to abiotic stresses and the use of stress-related genes in the development of genetically engineered crops.     

One-point method for determination of number-average molecular weight

The following well-known equation permits the ready determination of M _n from a single osmotic pressure measurement at a known concentration, if the second virial coefficient is previously given: On this basis, the one-point method was investigated to determine the number-average molecular weight. It was found that this method was applicable to commercial polymers. However, in this application, the dependence of Γ₂ on molecular weight distribution has to be kept in mind.     

On the molecular weight determination of bisphenol-A polycarbonate

In order to assess the reliability of absolute molecular weights of bisphenol-A polycarbonate samples measured by size exclusion chromatography, the results obtained from two experimental systems and two calibration methods are compared with each other as well as with data provided by light scattering determinations. The interest of coupling a light scattering detector to the chromatographic system is discussed.     

聚丙烯酰胺分子量测定准确度探讨

本文对流径时间、恒温温度,浓度等误差通过计算及实验检测分析其对分子量测定准确度的影响。     

Potentiometric determination of the molecular weight of polymers

Summary The determination of acid end-groups of acrylamide and acrylonitrile polymers initiated by cerium (IV)-malonic acid, cerium (IV)-tartaric acid and cerium (IV)-citric acid redox initiators systems was made in aqueous and nonaqueous media potentiometrically. The effect of solvent, titrant and electrode system on the half-neutralization potentials and number-average molecular weights, , were determined potentiometrically and were studied. These values were compared with those obtained by viscosimetric and conductometric methods.     

Synthesis and molecular weight determination of urethane-based anionomers

Summary Anionomer prepolymers based on poly(propylene oxide) (PPG), 4,4-dicyclohexylmethane diisocyanate (H₁₂MDI) and dimethylol propionic acid (DMPA) were synthesized in bulk. The molecular weight of the prepolymers was determined by vapour pressure osmometry (VPO) and gel permeation chromatography (GPC).     

Recent advances in the purification,characterization and structure determination of lipases

Recently, lipases have been purified from mammalian, bacterial, fungal and plant sources by different methodologies. Purified lipases subsequently have been characterized for molecular size, metal binding capabilities, glycoside and phosphorus contents, and substrate specificities. Primary structures of several lipases have been determined either from amino acid or nucleic acid sequences. Lipases sequenced to date share sequence homologies including a significant region, Gly-X-Ser-X-Gly, that is conserved in all. The Ser residue is suspected to be essential for binding to lipid substrates.     

一种用高效凝胶渗透色谱测试褐藻胶分子量及分子量分布的方法

提出了一种用凝胶色谱与常规检测器检测褐藻胶分子量及其分布的方法。用高效凝胶渗透色谱(GPC)与示差检测器(RID)结合,建立了以普鲁兰标准品为对照的相对重均分子量、相对数均分子量与GPC–MALLS(多角度激光散射)测试的褐藻胶绝对重均分子量、绝对数均分子量间的转换关系,得到了用GPC–RID检测相对分子量计算褐藻胶绝对分子量和多分散系数的方法。结果表明,GPC–RID法经转换公式得到的重均分子量、数均分子量和多分散系数与GPC–MALLS法的相对误差在?12%以内。基于GPC–RID法可较准确地获得褐藻胶的绝对分子量及多分散系数,使用通用检测器可节约仪器投资,降低检测成本。     

Recent advances in the determination of the structure of fatty acids via ozonolysis

Important factors and new techniques in the application of ozonolysis to the localization of double bond positions in unsaturated fatty acids are elaborated. Solvent polarity was shown to exert a profound influence on the yield and composition of ozonides. The influence of fatty acid structure on ozonide formation and the thin-layer chromatography (TLC) of ozonides of a number of different types of unsaturated fatty acids are illustrated. Simple methods for the ozonization of unsaturated fatty acid esters and the cleavage of ozonides by reduction and pyrolysis are described. Applications of ozonolysis to the determination of the structures of geometric isomers, hydroxy, epoxy and cyclic olefinic fatty acids, and the localization of radioactivity along the chain of unsaturated fatty acids are illustrated. Presented as a Short Course Lecture of the American Oil Chemists' Society in Pomona, California, August 1965, and the 2nd International Course on Methods for Lipid Research, Milan, Italy, September 1965.     

Variation of refractive index of polystyrene with molecular weight: Effect on the determination of molecular weight distributions

Sensitive refractive index measurements on solutions have indicated that the narrow molecular weight polystyrene samples prepared by the Mellon Institute method exhibit a small systematic molecular weight–refractive index dependence up to 300,000 and higher. This upper limit is higher than had previously been suggested. Sensible consistency is generally assumed above a few thousand molecular weight. The effect on this molecular weight–refractive index dependence on gel permeation chromatography and light-scattering molecular weight measurements on polystyrene standards is illustrated.     

Recent advances in magnetic hydrogels

Smart hydrogels that respond to magnetic fields have attracted increasing interest in recent years. This is as a result of their numerous potential applications such as tunable delivery vehicles, magnetic resonance imaging contrast agents, hyperthermal therapy agents, etc. In this review, we summarize the methods for preparing magnetic hydrogels. Then we give an overview of magnetic hydrogels with various applications. Finally, the current limitations in the preparation and application of magnetic hydrogels are discussed and perspectives will be proposed for the next generation of hydrogels. © 2016 Society of Chemical Industry