Urea (Polyurea) Greases

The review deals with greases in which organic ureas of various compositions and structures are used as thickeners. The nature of compounds participating in the synthesis of organic ureas and the main types of polyurea thickeners are considered. The physicochemical, tribological, and operation properties of plastic polyurea lubricants are discussed.     

C3-Symmetric, amino acid based organogelators and thickeners: a systematic study of structure-property relations

A class of C₃-symmetric amino acid based organogelators and thickeners featuring a rigid core have been developed. Structural variation yielded a number of compounds, the aggregation behaviour and resulting aggregates and gels of which were studied by FTIR spectroscopy, dropping ball measurements, differential scanning calorimetry and transmission electron microscopy. These studies showed that the nature of the core unit, the type of hydrogen-bonding units and the applied amino acids have a strong influence on the interactions, resulting in large differences in aggregation properties, thermal stability and morphology between the various compounds. The results provide a basis for a better understanding of the relation between aggregate/gel properties and molecular structure. The structural variation available for these compounds allows fine-tuning of the gelators with respect to aggregation behaviour and gel properties.     

四种新型D-A化合物的合成与光电性能研究

合成了H2Po-C70, H2Pp-C70, ZnPo-C70和ZnPp-C70 4种新型的D-A化合物; 通过紫外-可见吸收光谱、红外光谱、质谱和元素分析等多种手段对其进行了表征. 在光电化学电池中, 在GaAs电极上测量了这4种D-A化合物的光伏效应(PVE). 研究结果表明, H2P-C70/GaAs和ZnP-C70/GaAs电极的光生电压(ΔV)和光生电流(ΔI)比单纯的GaAs电极大得多, 据此能够确定这4种D-A化合物具有优良的光电性能.     

Glassy carbon electrodes modified with mixed covalent monolayers of choline, glycine, and glutamic acid for the determination of phenolic compounds

A series of mixed covalent monolayer carbon glassy electrodes (choline/amino acid/GCE) was prepared using choline and amino acids, and the properties were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The oxidations of phenolic compounds including dopamine hydrochloride, epinephrine and phenol have been studied. Electrooxidation of phenols, first leads to the formation of phenoxy radical, which reduces to phenols and hydroquinone; the reaction of polyoxyphenylene is effectively restrained at this electrode, unlike only at chlorine or amino acids modified electrode or bare electrode, which rapidly forms polyoxyphenylene and results in electrode passivation. Owing to significant improvement of electrode passivation shaped insulating polymerization, these mixed covalent monolayer carbon glassy electrodes show themselves excellent resistance ability for pollution, could be successfully used as amperometric sensor for phenolic compounds.     

Viscoelastic wormlike micelles and their applications

Viscoelastic wormlike micelles are important microstructures that relate to rhelogical properties of fluid in different applications. Recently, studies of structure and dynamic properties of wormlike micelle have extended to different surfactant type such as anionic, zwitterionic and polymeric surfactants. Applications have been found in oil fields, drag-reducing agents for district heating and cooling and thickeners for personal and home care products.     

含三苯基乙基苯氧基聚氧乙烯醚甲基丙烯酸酯功能单体的缔合型乳液增稠剂的制备及增稠机理

采用半连续法乳液聚合以甲基丙烯酸、丙烯酸乙酯、邻苯二甲酸二烯丙酯和不同量的功能单体三苯基乙基苯氧基聚氧乙烯醚甲基丙烯酸酯(SEM-25)为原料合成了疏水改性碱溶性增稠剂乳液. 测定了增稠剂乳液的粘度、透光率、pH、粒径及其分布, 结果表明随着pH值的增加, 乳液的粘度和透光率首先迅速升高, 然后缓慢下降. 随着SEM-25用量的增加, 乳胶粒的粒径先增大后减小. 与不含SEM-25的乳液增稠剂相比较, SEM-25低含量增稠剂的增稠效果和抗剪切性没有提高, 只有当SEM-25用量提高至单体质量的12%, 且乳液固含量大于0.65%时, 所制备缔合型增稠剂乳液的粘度和流变性比不含SEM-25的增稠剂才有明显提高. 在此基础上研究了增稠剂对苯丙乳液的增稠性. 含有增稠剂的苯丙乳液的粘度和透光率随pH值的变化与纯增稠剂乳液的变化类似. 只有当加入0.34 wt%苯丙乳液固体质量的增稠剂, 并且增稠剂中SEM-25含量达到5 wt%时苯丙乳液的粘度与使用不含SEM-25的增稠剂增稠的粘度相比才有明显增高. 在此基础上对增稠剂的增稠机理进行了探讨.     

Effect of thickener structure on paper-coating color properties

Physical and chemical properties of clay-based paper-coating colors have been characterized. The “surface potential” (zeta potential) of kaolin particles used in paper-coating formulations was determined as functions of pH and sodium polyacrylate (used as a dispersant) concentration. The optimal pH and dispersant concentration have been established. The effect of adsorption of two different thickeners on the kaolinite particle potential was also investigated. The rheological properties of coating colors, thickened with an associative polymer and a commonly used thickener, have been compared. The rheological behavior of all the coating colors studied was found to be similar, except for the magnitude of the elastic modulus, which was considerably larger for the more hydrophobic thickener. The water-retention properties of the colors could be qualitatively correlated with the molecular structure of the thickeners. An interaction mechanism (e.g. formation of hydrophobic micellar domains) between kaolinite particles and the associative polymer has been proposed. Received: 10 August 2000/Accepted: 2 January 2001     

Studies in the field of electrochemistry of organic compounds in 2000–2006

This review presents the author’s views on the state-of-art in the electrochemistry of organic compounds, based on the analysis of the data published from 2000 to 2006. The number of publications that consider to one or another extent the electrochemical reactions involving organic compounds constantly increases. The range of problems studied is intimately related with the demands of new technologies. The largest number of publications are devoted to the electrochemical polymerization and the properties of polymeric films on the electrode surface and also to the mechanism of electrode reactions of metal-complex compounds and their properties. The directions such as electrochemistry of nanomaterials and the methods of modification of electrodes are largely associated with the use of electroactive polymers. Fine organic electrosynthesis including the technological developments in the destruction of organic compounds, e. g., for cleaning of waste water, fade to the background. A new direction in this field is the development of amperometric sensors that employ modified electrodes based on electrochemically activated polymeric films.     

粘弹性蠕虫状胶束及其应用

介绍了粘弹性蠕虫状胶束的形成、类型、基本性质及其应用情况.粘弹性蠕虫状胶束具有重要的微观结构,因其特殊的流变性能而在不同领域具有重要应用.最近,蠕虫状胶束的结构和动态性质的研究已经延伸到不同类型的表面活性剂,如阴离子、两性离子和聚合物表面活性剂.目前,其应用领域已经拓展到油田、社区冷热流体的减阻、个人护理和家庭清洁产品的增稠剂等方面.     

Coating Paper with the Fluorescence Assistant of Ternary Complexes of CMC/Eu/TTA

Carboxymethyl cellulose (CMC), one of the derivatives of cellulose, are mainly used as thickeners, dispersants, adhesives, extenders and films because of their water solubility and gel-forming properties. Especially, because it presents more and more excellent properties on the making paper technology, the great of paper engineers attach importance to it.     

Electrochemical rectification by redox-labeled bioconjugates: molecular building blocks for the construction of biodiodes

In the present work, we describe the properties of a bifunctional redox-labeled bioconjugate at electrode surfaces mediating the electron transfer across the electrode-electrolyte interface. We show that the assembly of ferrocene-labeled streptavidin on biotinylated electrodes results in a reproducible unidirectional current flow in the presence of electron donors in solution. Such rectifying films were built up by spontaneous binding of tetrameric streptavidin molecules to biotin centers immobilized on the electrode surface. Due to the high affinity of biotin to streptavidin, such bifunctional films completely bind any biotinylated compounds. The charge transport between donors in solution and the Au electrode is mediated by the ferrocene moieties, allowing us to develop a molecular rectifier. Our experimental results suggest that such redox-labeled proteins with a high binding capacity constitute a promising alternative to organic compounds used in molecular electronics.     

Associative thickeners. Part I: Synthesis,rheology and aggregation behavior

Nonionic associative thickeners with systematic changes in chemical composition have been synthesized. Rheological measurements of thickened latexes are presented as well as measurements of relaxation times, intrinsic viscosity and osmotic pressure of polymers in pure water solution. We find that the general hydrophobicity of the polymers' end groups control both rheology and efficiency. Hydrophobic parts in the interior of the polymer do not seem to effect rheology in latex systems. Viscosity increases with molecular weight in the low molecular region (Mw<10000), and passes through a maximum in the high molecular region. The thickeners seem to form micelle-like aggregates even at very low concentrations, while at higher concentrations the viscoelastic properties may be modeled by means of one Maxwell element. Only the network relaxation times but not the network structure seems to be dependent on the polymers' end group.     

Dental Amalgam in Voltammetry. Some Preliminary Results

ABSTRACT

Liquid mercury and liquid diluted mercury amalgams have been superior as electrode material for the use of voltammetry for analytical purposes. This is mainly due to the high overvoltage to hydrogen, which enables one to use a wide potential range for the measurements. Due to the toxicity of mercury and liquid diluted mercury compounds, the use of such compounds are increasingly restricted, and cannot be included in voltammetric devices for field and online applications.

The present authors have studied the properties of dental amalgam and related solid amalgams as electrode material in voltammetry. Due to the special properties of dental amalgam compared with mercury itself it is not toxic.

It has been found that dental amalgam and related solid amalgams have a very high overpotential to hydrogen, allowing one to carry out trace analyses at potentials sufficiently negative to allow determination of e.g. zinc, cobalt, nickel and iron at trace levels. This have previously been difficult except when using a mercury or a mercury film electrode.

The present preliminary paper describes such electrodes and some practical applications for trace heavy metal analyses, using differential pulse stripping voltammetry. Such determinations are very important for field and online analyses of pollutants in soil and groundwater, and the electrode can be used repeatedly. Further improvements can obviously be obtained by optimising the composition of the alloy.     

Microelectrode Applications of Pulsed Electrochemical Detection

Pulsed electrochemical detection (PED) has been applied to the direct (i.e., requires no derivatization), sensitive and reproducible detection of numerous polar aliphatic compounds (e.g., carbohydrates, amines, and thiols). These compounds, many of which have biological significance, typically have been classified as non‐electroactive for detection under constant applied potentials and have poor optical detection properties. PED exploits the electrocatalytic activity of noble metal (e.g., Au and Pt) electrode surfaces to oxidize various polar functional groups using multi‐step potential‐time waveforms to realize amperometric/coulometric detection while maintaining uniform and reproducible electrode activity. The response mechanisms in PED are dominated by the surface properties of the electrode, and as a consequence, members of each chemical class of compounds produce virtually identical voltammetric responses. Thus, the full analytical potential is achieved when combined with an a priori separation. Although popularized in combination with high performance liquid chromatography, the combination of PED with highly efficient microseparation techniques offer the analyst unique advantages. This paper reviews the fundamental aspects of PED especially at microelectrodes, and its application in microchromatographic and electrophoretic separation techniques, including microchip devices.     

Electrochemical properties of composite materials based on platinum modified with molybdenum compounds

The composite coating Pt-MoOx is produced by an electrochemical technique under potentiodynamic conditions on the surface of a preliminarily prepared electrode of glassy carbon. The inclusion of molybdenum into the composition of the obtained electrode deposit is confirmed by the data of cyclic voltammetry and the secondary-electron emission spectra. In the cyclic voltammograms that are obtained in a 2 M solution of sulfuric acid one can distinguish a pair of peaks at potentials equal to 0.46 V (anodic run) and 0.3 V (cathodic run), which are connected with the redox transitions experienced by molybdenum compounds. It is discovered that the obtained deposit possesses catalytic properties with respect to the oxygen reduction reaction. The number of electrons that are corresponding to the redox transitions experienced by molybdenum compounds is calculated. It amounts to 0.27 electrons per molybdenum atom.     

Carbon nanotubes/alizarin red S–poly(vinylferrocene) modified glassy carbon electrode for selective determination of dopamine in the presence of ascorbic acid

A modified electrode was fabricated by electrochemical formation of poly(vinylferrocene) on the multi-wall carbon nanotube-alizarin red S matrix covered glassy carbon electrode. A higher electrochemical activity was obtained to the electrocatalytic oxidation of dopamine. The electrode surface was characterized electrochemically and spectroscopically. Poly(vinylferrocene) (PVF) in electrode was used as an electron transfer mediator in the electrochemical oxidation of compounds due to its perfect reversible redox properties. Multi-wall carbon nanotubes (MWCNTs) / alizarin red S (ARS)–PVF electrode was used to the determination of dopamine in the presence of ascorbic acid in 0.1 M sulphate buffer solution at pH 7. The performance of the MWCNTs/ARS–PVF electrode was evaluated by DPV and amperometry.     

Polymeric bilayer modified microelectrodes for in-vivo determination of neurotransmitter dopamine

A composite polymer carbon fiber electrode modified with Nafion and cellulose acetate is described.The modified electrode discriminates against both anionic reactants and big molecular organic compounds.The bilayer configuration is prepared in two steps.First,the carbon fiber electrode is coated with Nafion,then followed by air evaporation of the solvent,the electrode is dipped in a cellulose acetate solution and hydrolyzed for a selected time.The permeability of the film is explored by use of rotating disk electrode measurements.Parameters affecting the film electrochemistry are investigated.The resulting electrodes show high selectivity and stability in body fluids.For in-vivo voltammetry,the composite polymer modified electrode has been used for detection of the oxidative current of neurotransmitter dopamine in rat brain,while it inhabits the oxidation of anionic neurotransmitter metabolites and some electroactive compounds.     

Capillary Electrophoretic Identification of Commercial Gelling Agents

Gelling agents based on polysaccharides have become extremely important in the food industry. As more and more products like soups and sauces have become available in lyophilized form, thickeners have to be added to give a controlled consistency to the finished meal. A capillary electrophoretic method has been developed to investigate the monosaccharide composition of hydrolyzed thickeners. 2-Aminoanthracene was used as a derivatization reagent to allow sensitive fluorescence detection. This system was applied to a set of standard thickeners as well as to food samples.     

Amperometric and voltammetric detection of hydrazine using glassy carbon electrodes modified with carbon nanotubes and catechol derivatives

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with carbon nanotubes (CNTs) and catechol compounds. First, 25 microL of DMSO-CNTs solutions (0.4 mg/mL) was cast on the surface of GC electrode and dried in air to form a CNTs film. Then the GC/CNTs modified electrode immersed into a chlorogenic acid, catechine hydrate and caffeic acid solution (electroless deposition) for a short period of time (2-80s). The cyclic voltammogram of the modified electrode in aqueous solution shows a pair of well-defined, stable and nearly reversible redox couple (quinone/hydroquinone) with surface confined characteristics. The combination of unique electronic and electrocatalytic properties of CNTs and catechol compounds results in a remarkable synergistic augmentation on the response. The electrochemical reversibility and stability of modified electrode prepared with incorporation of catechol compound into CNTs film was evaluated and compared with usual methods for attachment of catechols to electrode surfaces. The transfer coefficient (alpha), heterogeneous electron transfer rate constants (k(s)) and surface concentrations (Gamma) for GC/CNTs/catechol compound modified electrodes were calculated through the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time and high sensitivity toward oxidation of hydrazine in phosphate buffer solutions at pH range 4-8. The modified electrode retains its initial response for at least 2 months if stored in dry ambient condition. The properties of modified electrodes as an amperometric sensor for micromolar or lower concentration detection of hydrazine have been characterized.