测接触角法确定偶联剂的最佳用量

偶联剂是一类能在无机填料和聚合物基材之间形成“分子桥”、改善两者之间相容性或提高两者之间相互作用能力的化合物。将经偶联剂改性的无机填料填充到聚合物中可以制得成本低、性能好的复合材料。由于偶联剂用量多少将对复合材料的性能产生较大影响,因此建立一种准确、简便地确定偶联剂最佳用量的方法有着十分重要的理论和实际应用意义。     

Photobioelectronic studies with thylakoid membranes

The research described in this paper presents a method for chemically modifying the surface of plant photosynthetic membranes in such a way that electrical contact can be made. Colloidal platinum was prepared, precipitated directly onto thylakoid membranes from aqueous solution, and entrapped on fiberglass filter paper. This composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength (400–700 nm) in the chlorophyll absorption spectrum. Experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem-I reduction site of photosynthesis and that electron transfer occurs across the interface between photosystem I and the catalyst. When contacted with metal electrodes, the thylakoid-platinum combination was capable of generating a sustained flow of current through an external load resistor. Procedures for preparing this material and experimental data on its catalytic and electronic properties are presented. Also presented is an analysis of the flow of photocurrent in terms of the interfacial electron transfer reactions that occur at the interfaces of the components of the assembly.     

Electrokinetic and contact angle measurements of grafted carbon fibers

 The grafting method that has successfully been applied to methacrylic acid and liquid crystalline monomers was expanded to prepare amphoteric carbon fiber surfaces using 2-(N,N-dimethylamino)ethyl methacrylate as monomer. The obtained carbon fiber surfaces were characterized by contact angle and ζ-potential measurements. The expected basic behavior was not observed, instead an amphoteric character of the modified carbon fiber surface was found. The fiber surfaces display a basic character in the acidic pH-range, while they are acidic in the alkaline part of the pH-scale. An important influence is derived from the amount of initiator used to graft the monomers onto the fibers. The smaller the initiator concen-tration used during polymerization, the larger the amount of amino functionalities introduced to the carbon fiber surface. The wetting behavior versus water depends on the overall conformation of the immobilized polymer. During immersion into water the polymer acts hydrophobic, while during emersion, a hydrophilic character is observed, probably derived from conformational changes and swelling during the contact angle measure-ments in water. Received: 9 June 1998 Accepted: 13 August 1998     

A novel approach to study the isothermal behaviour of substances after 0.01–1 s from the chemical process initiation

New modifications of a contact heater are suggested for investigating thermal decomposition processes, as well as for determining kinetic characteristics of substances under conditions of intense heating to a fixed constant temperature.

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Zusammenfassung Zur Untersuchung von thermischen Zersetzungsprozessen und der Bestimmung der Reaktionskinetik von Substanzen bei intensivem Erhitzen auf vorgegebene konstante Temperaturen wird eine neue Abart von Kontakterhitzern beschrieben.

     

Diffusion current on a nonuniform electrode: Calculation with integral equations

Identity of mathematical problems concerning calculation of the distribution of reactants’ concentrations and the current near the surface of a nonuniform (strip) electrode and distribution of displacements and forces in the case of an elastic layer “antiplane” deformation caused by the punch action. Formulas for calculating the current at a strip electrode are derived for various ratios between the electrode width and the diffusion layer thickness by means of asymptotic methods designed for calculating problems of mechanical contact interactions. It is noted that calculations of the diffusion current for involved activity distributions at the electrode surface may benefit from asymptotic methods of mechanics of contact interactions.     

Contributions of restructuring and oxidation to the aging of the surface of plasma polymers containing heteroatoms

The properties and composition of plasma polymer surfaces stored in air can change considerably over time, especially as a result of oxidative reactions. When plasma polymers contain an element other than O, it is possible to probe for mechanisms in addition to oxidation that contribute to the aging of the surface. Plasma polymers containing N were fabricated from either 1,3-diaminopropane (DAP),n-heptylamine (nHA), or allylamine (AA), and studied by X-ray photo-electron spectroscopy (XPS) and air/water contact angles (CA). For each of the plasma polymers, a multiexponential increase in the O/C ratio was observed over time using XPS. The N/C ratios remained constant (AA) or decreased somewhat (nHA and DAP). In contrast, the trends in CA values differed, declining for the nHA surfaces, rising for the AA, and changing little for the DAP. Surface roughness, assessed by scanning tunnelling or atomic force microscopy, did not change over time. The diverse adjustments in the polarity of each surface and the similar compositional changes between them are reconcilable if the aging of the plasma polymer surface is a manifestation of the superposition of concurrent oxidative reactions and partial surface reorientation; the former introduce polar groups and the latter transports then from the surface to deeper regions beyond the CA probe depth but within the XPS analysis depth. These processes vary between different plasma polymers. Data for the alkylamine plasma polymers is also compared with that for two plasma polymers fabricated from methanol. The change in composition, but not polarity, of the DAP surface after 4 days of storage demonstrates the importance of using multiple techniques to characterize the aging of plasma polymer surfaces.     

All-solid-state potentiometric sensors for ascorbic acid by using a screen-printed compatible solid contact

The development of all-solid-state potentiometric ion selective electrodes for monitoring of ascorbic acid, by using a screen-printed compatible solid contact is described. The applied methodology is based on the use of PVC membrane modified with some firstly-tested ionophores (triphenyltin(IV)chloride, triphenyltin(IV)hydroxide and palmitoyl-l-ascorbic acid) and a novel one synthesized in our laboratory (dibutyltin(IV) diascorbate). Synthesis protocol and some preliminary identification studies are given. A conductive graphite-based polymer thick film ink was used as an internal solid contact between the graphite electrode and the PVC membrane. The presence and the nature of the solid contact (plain or doped with lanthanum 2,6-dichlorophenolindophenol (DCPI)) seem to enhance the analytical performance of the electrodes in terms of sensitivity, dynamic range, and response time. The analytical performance of the constructed electrodes was evaluated with potentiometry, constant-current chronopotentiometry and electrochemical impedance spectroscopy (EIS). The interference effect of various compounds was also tested. The potential response of the optimized Ph₃SnCl-based electrode was linear against ascorbic acid concentration range 0.005-5.0 mM. The applicability of the proposed sensors in real samples was also tested. The detection limit was 0.002 mM ascorbic acid (50 mM phosphate, pH 5 in 50 mM KCl). The slope of the electrodes was super-Nernstian and pH dependent, indicating a mechanism involving a combination of charge transfer and ion exchange processes. Fabrication of screen-printed ascorbate ISEs has also been demonstrated.     

ELECTROSPRAYING/ELECTROSPINNING OF POLY(γ-STEARYL-L-GLUTAMATE): FORMATION OF SURFACES WITH SUPERHYDROPHOBICITY

  Electrospraying/electrospinning of poly(γ-stearyl-L-glutamate) (PSLG) was investigated on a series solutions with different concentrations in chloroform. Field emission scanning electron microscopy (FESEM) and attenuated total reflectance Fourier transform infrared spectroscopy (FT-IR/ATR) were used to characterize the morphology and structure of the electrosprayed/electrospun polypeptide mats. It was found that electrospraying of PSLG with concentrations lower than 16 wt% afforded beads, while microfibers could be electrospun at the concentration of 22 wt%. The hydrophobicity of the electrosprayed/electrospun PSLG mats was investigated with static water contact angle (WCA) and tilt angle measurements. It was demonstrated that the superhydrophobic surfaces of PSLG with WCAs and tilt angles in the ranges of 150°-170° and 16.5°-4.2°, respectively, were obtained through electrospraying/electrospinning process.     

触头用银合金粉末的氧化性能和氧化后的组织结构

通过热重实验和扫描电子显微等方法，研究了４种触头用银合金粉末的氧化性能及氧化后的组织结构。发现Ａｇ－Ｓｎ－ＲＥ合金粉末氧化以后，在粉末表层形成一层纯银层，其组织结构理想；它的氧化性能最好，适于制备触头材料。Ａｇ－Ｓｎ－ＲＥ合金粉末的优良氧化性能与其氧化后理想的组织结构有关。稀土元素可以降低合金粉末的氧化温度，其它影响作用有待于进一步研究。     

Adsorption of polyamides and polyamide–silane mixtures at glass surfaces

The individual and combined adsorption behavior of polyamides and two different silanes to multicomponent glass surfaces was probed with a combination of x‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and static contact angle measurements. Samples were analyzed with and without solvent rinsing to separate the weakly bound (physisorbed) and more strongly bound (chemisorbed) species. High‐resolution XPS on N 1s revealed that the polyamides adsorb to the glass surfaces via protonated amine species at the acidic (OH) sites on the glass surface. Angle‐resolved XPS confirmed this by showing that the alkyl portion of the polymer is oriented away from the glass interface. In competitive coadsorption studies it was found that amino‐terminated silanes preferentially adsorb to the glass surface, relegating the polyamide to a physisorbed outer layer. When mercaptoterminated silanes were competitively coadsorbed the polyamide was preferentially adsorbed even when present at a concentration twenty times less than that of the silane. Altogether, this work reveals the strong interaction between surface silanols and amino‐functionalized organics. Copyright © 2003 John Wiley & Sons, Ltd.