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Polymer Layer (polymer + layer)
Selected AbstractsSurface Structures in Thin Polymer Layers Caused by Coupling of Diffusion-Controlled Marangoni Instability and Local Horizontal Temperature GradientMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005Lothar Weh Abstract Summary: Surface tension-driven Marangoni convection causes the formation of regular surface structures in drying polymer layers. The shape of the surface structures formed during solvent evaporation depends on layer and interfacial dynamic parameters as well as external factors. The influence of a horizontal radial temperature gradient produced by a point heat source below the polymer layer on the diffusion-controlled Marangoni instability has been studied. In the region of the lateral temperature gradient, radial surface flow coupled with the interfacial instability leads to stripe, ladder, chevron and/or labyrinthine surface structures. Stepped ladder structures in a poly(vinyl butyral) layer produced by interfacial instability and heating with an ultrasonic sonotrode below the layer substrate. [source] Confinement effects on the morphology of photopatterned porous polymer monoliths for capillary and microchip electrophoresis of proteinsELECTROPHORESIS, Issue 14 2008Mei He Abstract We find that the morphology of porous polymer monoliths photopatterned within capillaries and microchannels is substantially influenced by the dimensions of confinement. Porous polymer monoliths were prepared by UV-initiated free-radical polymerization using either the hydrophilic or hydrophobic monomers 2-hydroxyethyl methacrylate or butyl methacrylate, cross-linker ethylene dimethacrylate and different porogenic solvents to produce bulk pore diameters between 3.2 and 0.4,µm. The extent of deformation from the bulk porous structure under confinement strongly depends on the ratio of characteristic length of the confined space to the monolith pore size. The effects are similar in cylindrical capillaries and D-shaped microfluidic channels. Bulk-like porosity is observed for a confinement dimension to pore size ratio >10, and significant deviation is observed for a ratio <5. At the extreme limit of deformation a smooth polymer layer ,300 nm thick is formed on the surface of the capillary or microchannel. Surface tension or wetting also plays a role, with greater wetting enhancing deformation of the bulk structure. The films created by extreme deformation provide a rapid and effective strategy to create robust wall coatings, with the ability to photograft various surface chemistries onto the coating. This approach is demonstrated through cationic films used for electroosmotic flow control and neutral hydrophilic coatings for electrophoresis of proteins. [source] Open-tubular capillary columns with a porous layer of monolithic polymer for highly efficient and fast separations in electrochromatographyELECTROPHORESIS, Issue 21 2006Sebastiaan Eeltink Abstract Open-tubular columns for CEC separations having inner-wall coated with a thin layer of porous monolithic polymer have been studied. A two-step process including (i),UV-initiated polymerization leading to a layer of porous poly(butyl methacrylate- co -ethylene dimethacrylate), and (ii),UV-initiated grafting of ionizable monomers appear to be well suited for the preparation of these columns. The thickness of the porous polymer layer is controlled by the percentage of monomers in the polymerization mixture and/or length of the irradiation time. The layer thickness significantly affects retention, efficiency, and resolution in open-tubular CEC. Under optimized conditions, column efficiencies up to 400,000 plates/m can be achieved. Use of higher temperature and application of pressure enables a significant acceleration of the open-tubular CEC separations. [source] Positively Charged Material Surfaces Generated by Plasma Polymerized Allylamine Enhance Vinculin Mobility in Vital Human Osteoblastss,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Henrike Rebl Abstract Several studies suggest that the modification of an implant surface by chemical means plays an important role in bone tissue engineering. Previously we have shown that osteoblast cell adhesion and spreading can strongly be increased by a positively charged surface. Cell adhesion and migration are two vital processes that are completely dependent on coordinated formation of focal adhesions. Changes in the organization of the actin cytoskeleton and the focal adhesions are essential for numerous cellular processes including cell motility and tissue morphogenesis. We examined the mobility of the cytoskeletally associated protein vinculin on functionalized surfaces using plasma polymerized allylamine (PPAAm), a homogenous plasma polymer layer with randomly distributed amino groups. In living, GFP,vinculin transfected osteoblastic cells we determined a significant increase in vinculin mobility and vinculin contact length on PPAAm compared to collagen I coated surfaces during the initial adhesion phase. We suggest that positive charges control the cell physiology which seems to be dominant over the integrin receptor binding to collagen I. The results emphasize the role of the surface charge for the design of artificial scaffolds in bone repair. [source] Synthetic Hydrophilic Materials with Tunable Strength and a Range of Hydrophobic Interactions,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Olha Hoy Abstract The ability to vary, adjust, and control hydrophobic interactions is crucial in manipulating interactions between biological objects and the surface of synthetic materials in aqueous environment. To this end a grafted polymer layer (multi-component mixed polymer brush) is synthesized that is capable of reversibly exposing nanometer-sized hydrophobic fragments at its hydrophilic surface and of tuning, turning on, and turning off the hydrophobic interactions. The reversible switching occurs in response to changes in the environment and alters the strength and range of attractive interactions between the layer and hydrophobic or amphiphilic probes in water. The grafted layer retains its overall hydrophilicity, while local hydrophobic forces enable the grafted layer to sense and attract the hydrophobic domains of protein molecules dissolved in the aqueous environment. The hydrophobic interactions between the material and a hydrophobic probe are investigated using atomic force microscopy measurements and a long-range attractive and contact-adhesive interaction between the material and the probe is observed, which is controlled by environmental conditions. Switching of the layer exterior is also confirmed via protein adsorption measurements. [source] Sensitive Explosive Vapor Detection with Polyfluorene LasersADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ying Yang Abstract Distributed feedback organic semiconductor lasers based on polyfluorene are shown to be suitable for use as chemical sensors for the detection of nitroaromatic-based explosive vapors. The laser threshold is increased by a factor of 1.8 and the slope efficiency is reduced by a factor of 3 after exposure to the vapor. The sensing efficiency depends strongly on the excitation energy with a maximum efficiency of 85%. The temporal dynamics of the laser response to the analyte have been investigated. The laser emission falls to 60% of its initial value in 46,s. A model is developed to offer some insight into the diffusion of the vapor molecules inside the polymer layer. [source] Optically-Pumped Lasing in Hybrid Organic,Inorganic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Myoung Hoon Song Abstract Here, the use of metal oxide layers both for charge transport and injection into an emissive semiconducting polymer and also for the control of the in-plane waveguided optical modes in light-emitting diodes (LEDs) is reported. The high refractive index of zinc oxide is used to confine these modes away from the absorbing electrodes, and include a nano-imprinted grating in the polymer layer to introduce distributed feedback and enhance optical out-coupling. These structures show a large increase in the luminescence efficiency over conventional devices, with photoluminescence efficiency increased by up to 45%. Furthermore, optically-pumped lasing in hybrid oxide polymer LEDs is demonstrated. A tuneable lasing emission is also obtained in a single device structure by employing a graduated thickness of a zinc oxide inter-layer. This demonstrates the scope for using such architectures to improve the external efficiency of organic semiconductor LEDs, and opens new possibilities for the realization of polymer injection lasers. [source] Poly(,-caprolactone)-Functionalized Carbon Nanotubes and Their Biodegradation Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2006H.-L. Zeng Abstract Biodegradable poly(,-caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the "grafting from" approach based on in-situ ring-opening polymerization of ,-caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT-supported macroinitiators (MWNT-OH). The resulting products have been characterized with Fourier-transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the "hard" core and the hairy polymer layer as the "soft" shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT,PCL nanohybrids in low-boiling-point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4,days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL-functionalized CNTs in bionanomaterials, biomedicine, and artificial bones. [source] Ionic/Electronic Hybrid Materials Integrated in a Synaptic Transistor with Signal Processing and Learning FunctionsADVANCED MATERIALS, Issue 22 2010Qianxi Lai A synaptic transistor is fabricated by integrating ionic/electronic hybrid materials to emulate biological synapses with spike signal processing, learning, and memory functions. A potential spike generates transient ionic fluxes in a polymer layer in the transistor gate, triggering an excitatory postsynaptic current in the transistor drain. Temporally correlated pre- and post-synaptic spikes modify ions stored in the polymer, resulting in the nonvolatile modification of the transistor with spike-timing-dependent plasticity. [source] Polymer Photovoltaic Cells Sensitive to the Circular Polarization of LightADVANCED MATERIALS, Issue 20 2010Jan Gilot Chiral conjugated polymer is used to construct a photovoltaic cell whose response depends on the circular polarization of the incoming light. The selectivity for left and right polarized light as a function of the thickness of the polymer layer is accounted for by modeling of the optical properties of all layers inside the device. [source] Ordered High-Density Si [100] Nanowire Arrays Epitaxially Grown by Bottom Imprint MethodADVANCED MATERIALS, Issue 27 2009Zhang Zhang A novel bottom imprint method to fabricate high-quality Si [100] nanowire arrays is demonstrated. This new approach combines the functions of a high-ordering AAO template as a stamp and template simultaneously. By the protective polymer layer in the hot imprint, the vertical 40,nm Si nanowire arrays grow epitaxially on the Si substrate with a narrow size distribution [source] Radical Polymers for Organic Electronic Devices: A Radical Departure from Conjugated Polymers?ADVANCED MATERIALS, Issue 22 2009Kenichi Oyaizu Abstract Radical polymers are aliphatic or nonconjugated polymers bearing organic robust radicals as pendant groups per repeating unit. A large population of the radical redox sites allows the efficient redox gradient-driven electron transport through the polymer layer by outer-sphere self-exchange reactions in electrolyte solutions. The radical polymers are emerging as a new class of electroactive materials useful for various kinds of wet-type energy storage, transport, and conversion devices. Electric-field-driven charge transport by hopping between the densely populated radical sites is also a remarkable aspect of the radical polymers in the solid state, which leads to many dry-type devices such as organic memories, diodes, and switches. [source] Strain Rate Effects in the Mechanical Response of Polymer-Anchored Carbon Nanotube Foams,ADVANCED MATERIALS, Issue 3 2009Abha Misra Strain rate effects on the mechanical properties of carbon nanotube forests are studied, and several related interesting new phenomena are reported. Dense vertically aligned foam-like forests of carbon nanotubes are anchored on a thin, flexible polymer layer to provide structural stability, particularly at the higher strain rates. Permanent deformation and for the first time the delamination and crumbling of carbon nanotube walls is observed. [source] Synthesis of bipolar charge transporting block copolymers and characterization for organic light-emitting diodeJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2010Kousuke Tsuchiya Abstract A series of hole and electron transporting random and block copolymers consisting of triphenylamine moiety as a hole transporting unit and oxadiazole moiety as an electron transporting unit have been prepared via a nitroxide mediated radical polymerization. Oxadiazole monomers with t -butyl or trifluoromethyl groups, 2 and 7, respectively, were used for copolymerization. Photoluminescent measurements of polymers revealed that the formation of the exciplex between triphenylamine and oxadiazole units tends to occur in the order of random copolymers, block copolymers, and polymer blends, implying phase-separated morphologies in block or blend systems. The polymers were applied for OLED devices, and we found that the morphology in the polymer layer critically affected device performance. The block copolymer comprising hole and electron transporting units with the composition of 14/86 showed the highest external quantum efficiency over 10%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1461,1468, 2010 [source] Functionalization of multiwalled carbon nanotube via surface reversible addition fragmentation chain transfer polymerization and as lubricant additivesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2008Xiaowei Pei Abstract Polymer-grafted multiwalled carbon nanotube (MWCNT) hybrid composite which possess a hard backbone of MWCNT and a soft shell of brush-like polystyrene (PSt) were synthesized. The reversible addition fragmentation chain transfer (RAFT) agents were successfully immobilized onto the surface of MWCNT first, and PSt chains were subsequently grafted from sidewall of MWCNT via RAFT polymerization. Chemical structure of resulting product and the quantities of grafted polymer were determined by Fourier transform infrared, thermal gravimetric analysis, nuclear magnetic resonance, and X-ray photoelectron spectra. Transmission electron microscopy and field emission scanning electron microscopy images clearly indicate that the nanotubes were coated with a polymer layer. Furthermore, the functionalized MWCNT as additives was added to base lubricant and the tribological property of resultant MWCNT lubricant was investigated with four-ball machines. The results indicate that the functionalization led to an improvement in the dispersion of MWCNT and as additives it amended the tribological property of base lubricant. The mechanism of the significant improvements on the tribological properties of the functionalized MWCNT as additives was discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3014,3023, 2008 [source] Improved EL efficiency of fluorene-thieno[3,2- b]thiophene-based conjugated copolymers with hole-transporting or electron-transporting units in the main chainJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2006Eunhee Lim Abstract New electroluminescent polymers (poly(9,9,-dioctylfluorene- co -thieno[3,2- b]thiophene- co -benzo[2,3,5]thiadiazole) (P1) and poly(9,9,-dioctylfluorene- co -thieno[3,2- b]thiophene- co -benzo[2,3,5]thiadiazole- co -[4-(2-ethylhexyloxyl)phenyl]diphenylamine (P2)) possess hole-transporting or electron-transporting units or both in the main chains. Electron-deficient benzothiadiazole and electron-rich triphenylamine moieties were incorporated into the polymer backbone to improve the electron-transporting and hole-transporting characteristics, respectively. P1 and P2 show greater solubility than poly(9,9,-dioctylfluorene- co -thieno[3,2- b]thiophene (PFTT), without sacrificing their good thermal stability. Moreover, owing to the incorporation of the electron-deficient benzothiadiazole unit, P1 and P2 exhibit remarkably lower LUMO levels than PFTT, and thus, it should facilitate the electron injection into the polymer layer from the cathode electrode. Consequently, because of the balance of charge mobility, LED devices based on P1 and P2 exhibit greater brightness and efficiency (up to 3000 cd/m2 and 1.35 cd/A) than devices that use the pristine PFTT. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 243,253, 2006 [source] Reversible addition,fragmentation chain-transfer graft polymerization of styrene: Solid phases for organic and peptide synthesisJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2002Leonie Barner Abstract The ,-initiated reversible addition,fragmentation chain-transfer (RAFT)-agent-mediated free-radical graft polymerization of styrene onto a polypropylene solid phase has been performed with cumyl phenyldithioacetate (CPDA). The initial CPDA concentrations range between 1 × 10,2 and 2 × 10,3 mol L,1 with dose rates of 0.18, 0.08, 0.07, 0.05, and 0.03 kGy h,1. The RAFT graft polymerization is compared with the conventional free-radical graft polymerization of styrene onto polypropylene. Both processes show two distinct regimes of grafting: (1) the grafting layer regime, in which the surface is not yet totally covered with polymer chains, and (2) a regime in which a second polymer layer is formed. Here, we hypothesize that the surface is totally covered with polymer chains and that new polymer chains are started by polystyrene radicals from already grafted chains. The grafting ratio of the RAFT-agent-mediated process is controlled via the initial CPDA concentration. The molecular weight of the polystyrene from the solution (PSfree) shows a linear behavior with conversion and has a low polydispersity index. Furthermore, the loading of the grafted solid phase shows a linear relationship with the molecular weight of PSfree for both regimes. Regime 2 has a higher loading capacity per molecular weight than regime 1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4180,4192, 2002 [source] Determination of the Thermal Resistance of the Polymer,Ceramic Interface of Alumina-Filled Polymer CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Richard F. Hill To model the thermal conductivity of polymer composites that are filled with ceramic powders, the conductivity of each component as well as the interfacial resistance at each ceramic,polymer boundary must be known. An indirect method to determine this interfacial boundary resistance is proposed by preparing large-scale "macromodel" simulations of the polymer,ceramic interface. Macromodels, prepared by spin-coating a polymer layer onto sapphire wafers, were formed in a sapphire,polymer,sapphire sandwich type structure. The interfacial boundary thermal resistance was calculated from thermal resistance measurements made on the macromodels. [source] Fabrication of Photonic/Microfluidic Integrated Devices Using an Epoxy PhotoresistMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2010Thomas Kowpak Abstract Using a single layer of SU-8 photoresist to fabricate optical waveguide cores and microfluidic channels on Pyrex glass is an ideal way to achieve photonic/microfluidic integration on a single chip. To address the problem of poor bonding, a thin nanoscale intermediate polymer layer was applied to reduce the stress generated from the material processing while maintaining strong adhesion between the patterning polymer layer and Pyrex. It was found that a 186,600,nm thick intermediate layer of a specialty epoxy photoresist effectively served the purpose without deteriorating the optical performance of the involved waveguides. Quality photonic/microfluidic integrated devices with satisfied optical performance were fabricated. [source] Surface Structures in Thin Polymer Layers Caused by Coupling of Diffusion-Controlled Marangoni Instability and Local Horizontal Temperature GradientMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005Lothar Weh Abstract Summary: Surface tension-driven Marangoni convection causes the formation of regular surface structures in drying polymer layers. The shape of the surface structures formed during solvent evaporation depends on layer and interfacial dynamic parameters as well as external factors. The influence of a horizontal radial temperature gradient produced by a point heat source below the polymer layer on the diffusion-controlled Marangoni instability has been studied. In the region of the lateral temperature gradient, radial surface flow coupled with the interfacial instability leads to stripe, ladder, chevron and/or labyrinthine surface structures. Stepped ladder structures in a poly(vinyl butyral) layer produced by interfacial instability and heating with an ultrasonic sonotrode below the layer substrate. [source] An Electrochemical Robotic System for the Optimization of Amperometric Glucose Biosensors Based on a Library of Cathodic Electrodeposition PaintsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2004Sabine Reiter Abstract Summary: A library of 148 cathodic electrodeposition paints was synthesized and the properties of related amperometric glucose biosensors were evaluated. For this a novel automatic electrochemical robotic system was designed. The automatic biosensor fabrication and characterization sequence involves the electrochemically induced precipitation of the cathodic paint on the electrode surface in the presence of glucose oxidase, the conditioning of the obtained polymer layer, the recording of a glucose calibration graph and the quantitative dissolution of the polymer film and cleaning of the electrode surface. Schematic representation of the developed electrochemical robotic system for electrochemical screening in microtiter plates. [source] Nano-floating gate capacitor with SnO2 quantum dots distributed in polyimide dielectricsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009Dong Uk Lee Abstract Self-assembled SnO2 quantum dots were fabricated by a chemical process between a BPDA-PDA polyamic acid and a Sn film. A nano-floating gate capacitor having metal,insulator,semiconductor structure has been formed on p-type Si substrate with SnO2 quantum dots and dielectric polymer layer. The size and density of fabricated SnO2 quantum dot were about 15 nm and 2.4 × 1011 cm,2, respectively. The electrical properties of the nano-floating gate capacitor have been investigated by measuring capacitance,voltage characteristics. Then, the flat-band voltage shift due to charging of the electron in SnO2 quantum dot was ranged from 1.2 V to 4 V. And the transmission electron microscopy and the optical absorption spectra have been measured to investigate the morphology and absorbance of the SnO2 quantum dots embedded in polyimide. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanowire,quantum-dot,polymer solar cellPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2008A. Nadarajah Abstract We report first results on a new solar cell structure which incorporates n-type ZnO nanowires, an undoped CdSe layer, obtained from quantum dot precursors, and a p-type polymer layer as the main components. In the fabrication process the quantum dot layer is converted to a conformal ,30 nm thick polycrystalline film. The fabrication of the cell occurs in lab air at temperatures below 100 °C. Several intermittent annealing steps raise the energy conversion efficiency to approximately 1%. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication of field emitters using GaN particlesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Yuichiro Minakuchi Abstract The field emission from GaN particles has been demonstrated successfully for the first time. The novel field emitting device has a simple structure consisting of an electrically conductive polymer layer and GaN particles spread randomly on it. The GaN particles used for this device, which were synthesized in advance by the two-stage vapor phase method, have vertices and ridges formed by well-developed crystal planes. The electron emission started at an electric field of about 20 V/,m, and the current reached 10 nA at 28 V/,m. The maximum current density was 0.26 mA/cm2at 43 V/,m. The Fowler-Nordheim (F-N) plot of the I - V data indicated that the observed electron emission is originated from the F-N tunneling. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A stochastic flow model for a tubular solution polymerization reactorPOLYMER ENGINEERING & SCIENCE, Issue 11 2007Ardson dos S. Vianna Jr. Residence time distributions were evaluated experimentally for three tubular solution polymerization reactors to analyze aspects of the fluid-dynamic behavior of these reactors. The analysis of the available experimental data indicates that the flow characteristics of these reactors may be subject to stochastic perturbations. A stochastic flow model is then proposed by assuming that a viscous polymer layer is formed in the proximities of the reactor walls and that plugs of polymer material are released at random during the operations. This model is able to represent the available experimental data fairly well for three tubular reactors with different configurations. POLYM. ENG. SCI., 47:1839,1846, 2007. © 2007 Society of Plastics Engineers [source] Chemorheology of model filled rubber compounds during curingPOLYMER ENGINEERING & SCIENCE, Issue 11 2001Jianfen J. Cai The rheological behavior and crosslinking kinetics of model filled rubber compounds during curing were investigated. The effect of chemical composition of monodisperse size particles, prepared by emulsifier-free emulsion polymerization, on dynamic moduli and gelation time of the filled compounds was studied. All filled systems showed much shorter gelation times than the pure matrix in the order PSVP < PS < PMMA , Pure Matrix. The dynamic moduli during curing increased with increasing interactions between particles and matrix. Physical crosslinking, due to either particle clustering or a network of filler particles with an adsorbed polymer layer, made a significant contribution to the overall crosslink density and the gelation of rubber compounds. As a result, the dynamic mechanical properties and curing kinetics of the rubber compounds varied with the chemical nature of the filler particles. [source] Minimizing analyte electrolysis in electrospray ionization mass spectrometry using a redox buffer coated emitter electrode,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 9 2010Emese Peintler-Krivan An emitter electrode with an electroactive poly(pyrrole) (PPy) polymer film coating was constructed for use in electrospray ionization mass spectrometry (ESI-MS). The PPy film acted as a surface-attached redox buffer limiting the interfacial potential of the emitter electrode. While extensive oxidation of selected analytes (reserpine and amodiaquine) was observed in positive ion mode ESI using a bare metal (gold) emitter electrode, the oxidation was suppressed for these same analytes when using the PPy-coated electrode. A semi-quantitative relationship between the rate of oxidation observed and the interfacial potential of the emitter electrode was shown. The redox buffer capacity, and therefore the lifetime of the redox buffering effect, correlated with the oxidation potential of the analyte and with the magnitude of the film charge capacity. Online reduction of the PPy polymer layer using negative ion mode ESI between analyte injections was shown to successfully restore the redox buffering capacity of the polymer film to its initial state. Published in 2010 by John Wiley & Sons, Ltd. [source] Double Modification of Electrode Surface for the Selective Detection of Epinephrine and Its Application to Flow Injection Amperometric AnalysisELECTROANALYSIS, Issue 22 2009Guang-Ri Xu Abstract A glassy carbon electrode having two polymer layers has been applied to selectively detect epinephrine. The inner layer formed by electropolymerization of macrocyclic nickel complex functioned as an electrocatalyst for epinephrine oxidation and the outer layer composed of hydrolyzed polyurethane ,-benzyl L -glutamate as a screening layer. Differential pulse voltammetry showed almost 100% recovery of epinephrine even in 100-fold excess of interferents. When applied to a dual glassy carbon electrode as an amperometric detector in flow injection analysis, a linear response over 0.1,,M and 10,,M was obtained. Recovery tested for 5-fold diluted human urine samples was 97.5%. [source] Thermosensitive Nanostructures Comprising Gold Nanoparticles Grafted with Block Copolymers,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007D. Li Abstract Binary thermosensitive nanocomposites are fabricated by grafting block copolymers of poly(N -isopropylacrylamide) and poly(methoxy-oligo(ethylene glycol) methacrylate) onto gold nanoparticles through consecutive, surface-initiated, atom-transfer radical polymerization (ATRP). These Au@copolymer nanocomposites display a well-defined core/shell nanostructure and have two thermosensitive points near 33 and 55,°C in an aqueous suspension corresponding to the thermally induced conformational transition of inner homopolymer segments and outer oligo(ethylene glycol)-containing copolymer layer, respectively. Silver nanoparticles trapped within Au@copolymer nanocomposites with weakly crosslinked shells display thermally modulated catalytic activity as heterogeneous catalysts because of the thermosensitive collapse of the polymer layers. [source] Cover Picture: A Novel Method to Orient Semiconducting Polymer Films (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005Mater. Abstract A new technique for orienting thin polymer semiconductor films is reported by Österbacka and co-workers on p.,1095. The technique uses the mechanical force of a shrinking polymer transferred through a polymer multilayer structure. The orientation is obtained using three polymer layers, where the uppermost layer shrinks resulting in orientation of the semiconductor film beneath the intermediate layer. The topmost and intermediate polymer films are removed to reveal the oriented surface. The cover shows a crossed-polarizer microscopy image of an oriented regio-regular poly(3-hexylthiophene) film. We present a new technique for orienting polymer semiconductor thin films. In our technique, polymer chains are rigorously oriented without using any mechanical tools and with minimal risk of film contamination. The technique is based on the mechanical force resulting from the in-plane shrinkage exerted by a shrinker (top layer) that is used to orient the semiconductor beneath an intermediate layer; the latter acting as a force mediator. The chain orientation is demonstrated by several techniques such as crossed-polarizer microscopy, atomic force microscopy, grazing-incidence X-ray diffraction, and polarized absorption. The orientation geometry is controlled by the shrinking process and the shrinker area. The semiconductivity of the film only stems from the transistor device structures under study, and the method can therefore be generalized. [source] | ||||||||||||||||||||||||||||