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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Electrochemically Modulated Permeability Of Poly(Aniline) And Composite Poly(Aniline)−Poly(Styrenesulfonate) Membranes, D. L. Pile, Y. Zhang, Andrew C. Hillier
Electrochemically Modulated Permeability Of Poly(Aniline) And Composite Poly(Aniline)−Poly(Styrenesulfonate) Membranes, D. L. Pile, Y. Zhang, Andrew C. Hillier
Andrew C. Hillier
The influence of oxidation state on the permeability of several probe molecules through conducting polymer membranes comprising composites of poly(aniline) and poly(styrenesulfonate) was examined in aqueous solution. Pure poly(aniline) membranes displayed a characteristic increase in permeability between reduced and half-oxidized states for neutrally charged phenol and negatively charged 4-hydroxybenzenesulfonate. In contrast, positively charged pyridine experienced decreased permeability through the membrane when poly(aniline) was switched from the reduced to the half-oxidized state. This behavior can be explained by a combination of oxidation-induced film swelling and the anion-exchange character of the positively charged membrane. The membrane composition was modified to include a …
Rapid And Reversible Generation Of A Microscale Ph Gradient Using Surface Electric Fields, Eric L. May, Andrew C. Hillier
Rapid And Reversible Generation Of A Microscale Ph Gradient Using Surface Electric Fields, Eric L. May, Andrew C. Hillier
Andrew C. Hillier
We report a method for the rapid and reversible generation of microscale pH gradients using a spatially varied electric field. A linear gradient in electrochemical potential is produced on an electrode surface consisting of a platinum catalyst layer on indium−tin oxide-coated glass by the application of two different potential values at spatially distinct surface locations. The resulting potential gradient drives the oxidation and reduction of water at different rates along the surface, as dictated by the local applied potential. A nonuniform distribution of pH in the neighboring solution results due to the variation in surface reaction rates. The extent and …
Scanning Electrochemical Mapping Of Spatially Localized Electrochemical Reactions Induced By Surface Potential Gradients, Shrisudersan Jayaraman, Erin L. May, Andrew C. Hillier
Scanning Electrochemical Mapping Of Spatially Localized Electrochemical Reactions Induced By Surface Potential Gradients, Shrisudersan Jayaraman, Erin L. May, Andrew C. Hillier
Andrew C. Hillier
The influence of a surface potential gradient on the location and extent of electrochemical reactions was examined using a scanning electrochemical microscope. A linear potential gradient was imposed on the surface of a platinum-coated indium tin oxide electrode by applying two different potential values at the edges of the electrode. The applied potentials were used to control the location and extent of several electrochemical reactions, including the oxidation of Ru(NH3)62+, the oxidation of H2, and the oxidation of H2 in the presence of adsorbed CO. Scanning electrochemical mapping of these reactions was achieved by probing the feedback current associated with …
Combinatorial Synthesis And Reactivity Screening Of Electro-Oxidation Catalyst Gradients, Shrisudersan Jayaraman, Andrew C. Hillier
Combinatorial Synthesis And Reactivity Screening Of Electro-Oxidation Catalyst Gradients, Shrisudersan Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Combinatorial methods represent an appealing experimental method for the discovery of heterogeneous catalysts. One can efficiently identify candidate materials or sample vast regions of composition space using a combination f dense catalyst libraries and high-throughput reactivity screening techniques. This is particularly appealing for the discovery of novel catalysts for low temperature fuel cells where multi-component systems have shown improved performance.
Directed Electrodeposition Of Polymer Films Using Spatially Controllable Electric Field Gradients, Erin L. Ratcliff, Andrew C. Hillier
Directed Electrodeposition Of Polymer Films Using Spatially Controllable Electric Field Gradients, Erin L. Ratcliff, Andrew C. Hillier
Andrew C. Hillier
We report a method for the directed electrodeposition of polymer films in various patterns using spatially controllable electric field gradients. One- and two- dimensional surface electric field gradients were produced by applying different potential values at spatially distinct locations on an electrode surface. Variations in the resulting local electrochemical potentials were used to spatially manipulate the rate of electrodeposition of several polymers. By controlling the electric field gradient in the presence of sequentially varying deposition solutions, complex polymer patterns could be produced. One-dimensional structures consisting of alternating bands of polyaniline and either poly(phenylene) oxide or poly(aminophenylene) oxide were produced, as …
Grating-Coupler Assisted Infrared Reflection Absorption Spectroscopy For The Characterization Of Organic Thin Films, Bipin K. Singh, Andrew C. Hillier
Grating-Coupler Assisted Infrared Reflection Absorption Spectroscopy For The Characterization Of Organic Thin Films, Bipin K. Singh, Andrew C. Hillier
Andrew C. Hillier
We demonstrate how grating-coupler assisted infrared reflection absorption spectroscopy can be used to simultaneously determine the chemical identity and relative thickness of organic thin films. With a grating substrate, a threshold anomaly associated with passing off of the −1 diffracted order occurs at grazing angles of incidence, resulting in a sharp absorbance in the infrared. The position of this peak is sensitive to the grating geometry as well as the dielectric environment near its surface. Thus, shifts in the peak position can be used to determine the relative thickness of adsorbed films or quantify molecular adsorption events. To illustrate the …
High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier
High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier
Andrew C. Hillier
We present an experimental system that combines differential electrochemical mass spectrometry with hydrodynamic flow consisting of an impinging jet in a wall-tube configuration. This assembly allows simultaneous detection of electrochemical signals along with monitoring of dissolved gas species using differential electrochemical mass spectrometry under well-defined hydrodynamic conditions and over a wide range of mass transfer rates. The working electrode is deposited directly onto a thin, hydrophobic membrane, which also serves as the inlet to the mass spectrometer. This inlet provides extremely rapid mass detection as well as a high flux of products from the electrode surface into the mass spectrometer. …
Surface Plasmon Resonance Imaging Of Biomolecular Interactions On A Grating-Based Sensor Array, Bipin K. Singh, Andrew C. Hillier
Surface Plasmon Resonance Imaging Of Biomolecular Interactions On A Grating-Based Sensor Array, Bipin K. Singh, Andrew C. Hillier
Andrew C. Hillier
A surface plasmon resonance sensor array based upon a grating substrate was developed for the detection of biomolecular interactions. The substrate consisted of a gold grating prepared by wet chemical treatment of a commercial recordable compact disk. A custom-built floating pin microspotter was constructed to deliver solutions containing ω-functionalized linear alkanethiols to the grating surface and produce an array of sensor elements with different exposed functional end groups. This array platform can be used to study biomolecular interactions in a label-free, sensitive, and high-throughput format. To illustrate the performance of this device, a test protein (bovine serum albumin) was exposed …
A Multi-Electrode Electrochemical And Scanning Differential Electrochemical Mass Spectrometry Study Of Methanol Oxidation On Electrodeposited Ptxruy, K. Jambunathan, S. Jayaraman, Andrew C. Hillier
A Multi-Electrode Electrochemical And Scanning Differential Electrochemical Mass Spectrometry Study Of Methanol Oxidation On Electrodeposited Ptxruy, K. Jambunathan, S. Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Methanol electro-oxidation was studied on a series of electrodeposited PtxRuy catalysts constructed as multielement band electrodes. A combination of electrochemical and scanning differential electrochemical mass spectrometry measurements were performed to evaluate the composition-dependence of methanol oxidation, methanol decomposition, CO2 current efficiency, and the product distribution at 25 and 50 °C. At 25 °C, cyclic voltammetry revealed that the presence of Ru led to enhanced methanol oxidation rates over that of pure Pt. Methanol decomposition showed a similar composition-dependence. Mass spectrometry measurements revealed the evolution of HCOOH and CO2 during methanol oxidation and allowed indirect determination …
Construction And Reactivity Screening Of A Surface Composition Gradient For Combinatorial Discovery Of Electro-Oxidation Catalysts, Shrisudersan Jayaraman, Andrew C. Hillier
Construction And Reactivity Screening Of A Surface Composition Gradient For Combinatorial Discovery Of Electro-Oxidation Catalysts, Shrisudersan Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Materials possessing gradients in composition or structure are of interest for a range of applications, including the construction of functionally graded structural materials, as novel sensor and actuator platforms, and to control the site-specific binding of proteins and cells on surfaces. Gradients can also be used as sample libraries for combinatorial materials discovery that present an extremely dense sample set.
Construction Of A Tethered Poly(Ethylene Glycol) Surface Gradient For Studies Of Cell Adhesion Kinetics, K. Mougin, A. S. Ham, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Construction Of A Tethered Poly(Ethylene Glycol) Surface Gradient For Studies Of Cell Adhesion Kinetics, K. Mougin, A. S. Ham, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Andrew C. Hillier
Surface gradients can be used to perform a wide range of functions and represent a novel experimental platform for combinatorial discovery and analysis. In this work, a gradient in the coverage of a surface-immobilized poly(ethylene glycol) (PEG) layer is constructed to interrogate cell adhesion on a solid surface. Variation of surface coverage is achieved by controlled transport of a reactive PEG precursor from a point source through a hydrated gel. Immobilization of PEG is achieved by covalent attachment of the PEG molecule via direct coupling chemistry to a cystamine self-assembled monolayer on gold. This represents a simple method for creating …
Construction Of Cell-Resistant Surfaces By Immobilization Of Poly(Ethylene Glycol) On Gold, K. Mougin, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Construction Of Cell-Resistant Surfaces By Immobilization Of Poly(Ethylene Glycol) On Gold, K. Mougin, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Andrew C. Hillier
Considerable effort has been expended in efforts to create surfaces that resist the adsorption of proteins and cells for biomedical applications. The majority of such work has focused on surfaces constructed from bulk polymers or thin polymer films. However, the fabrication of surfaces via self-assembled monolayers (SAMs) has attracted considerable interest because of the robustness, versatility, and wide-ranging applicability of these materials. SAMs are particularly appealing for biological systems where well-defined surface chemistries can be created to facilitate coupling, biorecognition, or cell adhesion along with a host of other applications in biochemistry and biotechnology.
A Combined Triboelectrochemical Qcm For Studies Of The Cmp Of Copper, Wenquan Lu, Jian Zhang, Frank Kaufman, Andrew C. Hillier
A Combined Triboelectrochemical Qcm For Studies Of The Cmp Of Copper, Wenquan Lu, Jian Zhang, Frank Kaufman, Andrew C. Hillier
Andrew C. Hillier
In order to improve our understanding of the fundamental surface processes associated with the chemical mechanical planarization ~CMP! of metals, we have developed an experimental tool that combines the high resolution mass sensing capabilities of the quartz crystal microbalance ~QCM! with a triboelectrochemical testing system. A electrochemical QCM is combined with a polishing tool and force sensor in order to perform controlled surface abrasion while simultaneously monitoring mass changes and electrochemical signals at the metal/solution interface. This system can be used to simulate a metal polishing process with in situ surface measurement capabilities. Typical parameters that can be measured include …