The effect of electrostatic field on the micro-crystal morphology of polymer films

The micro-crystal morphology of the films of isotactic polypropylene (iPP), poly(3-dodecylthiophene) (P3DDT) and iPP/P3DDT blend grown in different electrostatic environments has been investigated by using scanning electron microscope. The experimental results show that the micro-crystal morphology of polymer films was strongly dependent on electrostatic field. It was found that the micro-crystal morphology of the films of iPP, P3DDT and iPP/P3DDT blend grown in the electrostatic field was in the form of dendrite crystals, in which main stems were aligned in the field direction, and some branches of P3DDT were ruptured. However, the micro-crystals of the films of iPP, P3DDT and iPP/P3DDT blend have no crystal orientation in the absence of electrostatic field. (C) 2001 Elsevier Science Ltd. All rights reserved.

Formation of mesophase mono-domains and micro-structures in thin films of a series of copolyethers containing both odd-numbered methylene units

The structural and morphological evolution of mono-domains in thin films has been investigated for a series of liquid crystalline (LC) copolyethers. The copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4 ' -biphenylyl)-2-(4-hydroxyl-phenyl)propane (TPP) with 1,7-dibromoheptane and 1,11-undecane at different compositions (coTPPs-7/11). In contrast to the solution-cast thin films without annealing, which exhibit the isotropic homogeneous molecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the high-temperature columnar phase (Phi '). Similar to the nucleation process in polymer crystallization, transmission electron microscopic observations show that small mono-domains appear in the initial stage of annealing, where molecules form a uniaxial in-plane chain orientation. With increasing annealing time, the molecular orientation gradually became tilted with respect to the substrate surface, and finally, a uniaxial homeotropic molecular orientation was achieved after a prolonged annealing time. The lateral size of mono-domains was found to increase continuously with annealing time and grew into a circular shape, indicating an isotropic lateral growth scheme which implies a hexagonal molecular packing proved by the electron diffraction experiments.

Morphology and structure of micro-fibrillar crystal of nylon 10 10

The nanoscale and microscale fibrillar crystals of nylon 10 10 were obtained by atomizing the very dilute formic acid solution. The length-diameter ratio of these fibrillar crystals increases as the concentration of the atomizing solution increases. Electron diffraction (ED) analysis showed that the hydrogen-bonded sheet in these solution-grown fibrillar crystals was imperfect and had a lower order. Both electron diffraction and characteristic morphology show that melt-crystallized fibrillar crystals always possess perfect packing order and stable structure. A rather perfect ED pattern of the triclinic form of nylon 10 10 along the [001] zone was obtained by tilting the specimen 41 degrees along the elongated direction of the crystal. Fibrillar crystals from bulk have a great tendency to aggregate with parallel packing to form crystal clusters, which look like shish kebabs in morphology. Spherulite is observed occasionally in the domains with very rich sample. (C) 2001 Elsevier Science Ltd. All rights reserved.

Electrochemical growth and characterization of polyoxometalate-containing monolayers and multilayers on alkanethiol monolayers self-assembled on gold electrodes

A general strategy has been developed for fabrication of ultrathin monolayer and multilayer composite films composed of nearly all kinds of polyoxometalates (POMs), including isopolyanions (IPAs), and heteropolyanions (HPAs). It involves stepwise adsorption between the anionic POMs and a cationic polymer on alkanethiol (cysteamine and 3-mercaptopropionic acid) self-assembled monolayers (SAMs) based on electrostatic interaction. Here a Keggin-type HPA SiMo11VO405- was chosen as a main representative to elucidate, in detail, the fabrication and characterization of the as-prepared composite films. A novel electrochemical growth method we developed for film formation involves cyclic potential sweeps over a suitable potential range in modifier solutions. It was comparatively studied with a commonly used method of immersion growth, i.e., alternately dipping a substrate into modifier solutions. Growth processes and structural characteristics of the composite films are characterized in detail by cyclic voltammetry, UV-vis spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), micro-Fourier transform infrared reflection-absorption spectroscopy (FTIR-RA), and electrochemical quartz crystal microbalance (EQCM). The electrochemical growth is proven to be more advantageous than the immersion growth. The composite films exhibit well-defined surface waves characteristic of the HPAs' redox reactions. In addition, the composite films by the electrochemical growth show a uniform structure and an excellent stability. Ion motions accompanying the redox processes of SiMo11VO405- in multilayer films are examined by in situ time-resolved EQCM and some results are first reported. The strategy used here has been successfully popularized to IPAs as well as other HPAs no matter what structure and composition they have.

Electrochemical quartz crystal microbalance study of the electrochemical behavior of riboflavin at gold electrodes

The electrochemical and adsorption behaviors of riboflavin (RF) at gold electrodes has ken studied by using an electrochemical quartz crystal microbalance (EQCM). Useful information is obtained not only about electrochemical behavior but also about mass changes on the electrode surface. The electrochemical properties and frequency shifts were investigated in RF solutions at different pH values, concentrations and scan rates. Reversible voltammograms were observed for pH less than or equal to 9.71. There was no electrochemical reaction for pH > 9.71. The maximum current response was obtained at about pH 8. The current response was proportional to the square root of scan rates when the concentration of RF was lower than 1.0 x 10(-4) mol L-1 (pH 6.92). On the contrary, at concentrations higher than 1.0 x 10(-4) mol L-1 (pH 6.92), it was proportional to the scan rates.

Electrochemical scanning tunneling microscopy and electrochemical quartz crystal microbalance study of the adsorption of phenanthraquinone accompanied by an electrochemical redox reaction on the Au electrode

In situ electrochemical scanning tunneling microscopy (ECSTM) and an electrochemical quartz crystal microbalance (EQCM) have been employed to follow the adsorption/desorption processes of phenanthraquinone (PQ sat. in 0.1 mol l(-1) HClO4, solution) accompanied with an electrochemical redox reaction on the Au electrode. The result shows that: (1) the reduced form PQH(2) adsorbed at the Au electrode and the desorption occurred when PQH(2) was oxidized to PQ; (2) the adsorption process initiates at steps or kinks which provide high active sites on the electrode surface for adsorption, and as the potential shifts to negative, a multilayer of PQH(2) may be formed at the Au electrode; (3) the reduced PQH(2) adsorbed preferentially in the area where the tip had been scanned continually; this result suggests that the tip induction may accelerate the adsorption of PQH(2) on the Au(111) electrode. Two kinds of possible reason have been discussed; (4) high resolution STM images show the strong substrate lattice information and the weak monolayer adsorbate lattice information simultaneously. The PQH(2) molecules pack into a not perfectly ordered condensed physisorbed layer at potentials of 0.1 and 0.2 V with an average lattice constant a = 11.5 +/- 0.4 Angstrom, b = 11.5 +/- 0.4 Angstrom, and gamma = 120 +/- 2 degrees; the molecular lattice is rotated with respect to the substrate lattice by about 23 +/- 2 degrees. (C) 1997 Elsevier Science S.A.

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.

Study of cupric hexacyanoferrate-modified platinum electrodes using probe beam deflection and electrochemical quartz crystal microbalance techniques

The ion exchange mechanism accompanying the oxidation/reduction processes of cupric hexacyanoferrate-modified platinum electrodes in different aqueous electrolyte solutions has been studied by means of in situ probe beam deflection and the electrochemical quartz crystal microbalance technique. The results demonstrate that the charge neutrality of the film during the reoxidation/reduction process is accomplished predominantly by the movement of cations, but anions and/or solvent are also participator(s). Moreover, in KHC8H4O4 (potassium biphthalate) solution, the EQCM data obtained from chronoamperometry experiment are more complicated than those in KCl and K2SO4 solutions. (C) 1997 Elsevier Science Ltd.

Electrochemical behavior of FAD at a gold electrode studied by electrochemical quartz crystal microbalance

The electrochemical behavior of flavine adenine dinucleotide (FAD) at a gold electrode involving adsorption of the reduced form FADH(2) and desorption of the oxidized form FAD has been studied by using electrochemical quartz crystal microbalance (EQCM). EQCM can present information not only about the electrochemical behavior but also about the mass changes on the electrode surface. The electrochemical properties and frequency shifts were investigated in FAD solutions at different pH values, concentrations and scan rates. Reversible voltammograms were observed when pH<4.5 and irreversible voltammograms were found when pH greater than or equal to 4.5. It is found to be a diffusion controlled process when the concentration of FAD is lower than 2x10(-4) moll(-1) (pH 1.5). On the contrary, at concentrations higher than 2x10(-4) moll(-1) (pH 1.5), it is found to be an adsorption controlled process.

A carbon single crystal electrode for an electrochemical quartz crystal microbalance study

A highly ordered single crystal carbon material, highly oriented pyrolytic graphite (HOPG) has been successfully employed as a working electrode in an electrochemical quartz crystal microbalance study. RTV silicone rubber is selected to adhere the HOPG film onto the quartz crystal surface. Such modified quartz crystal can oscillate with stable frequency. The electrode modified in this way has good electrochemical properties.

THE APPLICATION OF ULTRAMICROELECTRODE IN HOMOGENEOUS CATALYTIC REACTION .5. ELECTROCHEMICAL-BEHAVIOR OF MACRO-MICRO-MACRO TRIPLE AND MICRO-MICRO TWIN ELECTRODES AND THE QUASI-FIRST-ORDER HOMOGENEOUS CATALYTIC REACTION (EC') AT GENERATION/COLLECTION ELECT

A new type of macro-micro-macro triple electrode has been fabricated, the steady-state currents of solution redox species have been observed at an ultramicroband electrode by linear potential scan voltammetry, and generation/collection experiments have al

Electrochemical investigations of micro-droplets formed on metals during the deliquescence of salt particles in atmosphere

CORROSION; WATER; SPECTROSCOPY; CHLORIDE; ZINC; NUCLEATION; INTERFACE; ELECTRODE; SURFACES; GROWTH

Phenomenon of micro-droplets formation on metals during the deliquescence of salt particles in atmosphere

CORROSION; MECHANISM; WATER; ZINC

Establishment of a micro-particle bombardment transformation system for Dunaliella saliva

In this study, we chronicle the establishment of a novel transformation system for the unicellular marine green alga, Dunaliella salina. We introduced the CaMV35S promoter-GUS construct into D. saliva with a PDS1000/He micro-particle bombardment system. Forty eight h after transformation, via histochemical staining, we observed the transient expression of GUS in D. salina cells which had been bombarded under rupture-disc pressures of 450 psi and 900 psi. We observed no GUS activity in either the negative or the blank controls. Our findings indicated that the micro-particle bombardment method constituted a feasible approach to the genetic transformation of D. salina. We also conducted tests of the cells' sensitivity to seven antibiotics and one herbicide, and our results suggested that 20 mu g/ ml of Basta could inhibit cell growth completely. The bar gene, which encodes for phosphinothricin acetyltransferase and confers herbicide tolerance, was introduced into the cells via the above established method. The results of PCR and PCR-Southern blot analyses indicated that the gene was successfully integrated into the genome of the transformants.

Genetic transformation in Kappaphycus alvarezii using micro-particle bombardment: a potential strategy for germplasm improvement

This study investigated the delivery of a SV40 promoter driving lacZ gene into cells of Kappaphycus alvarezii using particle bombardment. Thallus pieces 0.5-0.8 mm in diameter and 1 cm in length were prepared as gene recipients. Bombardment parameters of 450 psi (rupture pressures) x 6 cm (particle travel distances), 650 psi x 6 cm, 1,100 psi x 6 cm and 1,100 psi x 9 cm were used. A significant increase in transformation efficiency from about 33% under the rupture pressure of 450 psi to 87% at 650 psi was observed in transformed thalli. Most of the positive cells appeared in epidermal cells bombarded at 450 psi, whereas positive signals were seen in both epidermal and medullary cells at 650 psi. No positive transient expression was detected at a bombardment of 1,100 psi, or in negative or blank controls. For the conditions tested, the best parameter was obtained at 650 psi at a distance of 6 cm. Thus, the strategy of taking vegetative thalli as recipients, using particle bombardment, and combining this with micro-propagation, together with developing an in vivo selectable marker, is a viable way to produce stable transformants, to eliminate chimeric expression, and to achieve transgenic breeding in K. alvarezii.