ritesh vyas - Academia.edu (original) (raw)
Papers by ritesh vyas
International Journal of Molecular Sciences, 2010
Polyelectrolyte multilayers built via the layer-by-layer (LbL) method has been one of the most pr... more Polyelectrolyte multilayers built via the layer-by-layer (LbL) method has been one of the most promising systems in the field of materials science. Layered structures can be constructed by the adsorption of various polyelectrolyte species onto the surface of a solid or liquid material by means of electrostatic interaction. The thickness of the adsorbed layers can be tuned precisely in the nanometer range. Stable, semiconducting thin films are interesting research subjects. We use a conducting polymer, poly(p-phenylene vinylene) (PPV), in the preparation of a stable thin film via the LbL method. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to characterize the ionic conductivity of the PPV multilayer films. The ionic conductivity of the films has been found to be dependent on the polymerization temperature. The film conductivity can be fitted to a modified Randle's circuit. The circuit equivalent calculations are performed to provide the diffusion coefficient values.
Journal of Applied Physics, 2007
Polymer Thin Films, 2010
The need for miniaturized devices has driven the exponential development of nanotechnology during... more The need for miniaturized devices has driven the exponential development of nanotechnology during the past two decades. One special field of paramount practical applications is electrochemical systems at the nano-scale. For successful development in such fields, an in-depth analysis of mass and/or charge transfer mechanism is highly desired. In such a system, mass transfer often takes the form of ion transfer, which can also be viewed as charge transfer. For example, in fuel cell development, the catalyst layer deposited on a polyelectrolyte membrane would demand higher ionic (protonic) conductivity. In the electrochemical sensors, the overall performance depends largely upon sensitivity of the thin films to recognize the analyte and the speed to communicate the resultant signals with the underlying electrodes. These phenomena are closely related to the (ionic) mass transfer within such films. A clear understanding of mass transfer in such an electrochemical system is the prerequisite for any significant progress in devices. Fundamentally, three different types of mass-transfer phenomena exists for ionic species in electrolytes at electrodes: (1) diffusional transport under concentration gradient, (2) migration transport of oppositely charged ions under electric field of the electrode, and (3) convection transport due to physical stirring of the electrolyte. For electrodes modified with electroactive or redox films, the redox behavior is much more complicated. When the applied potential reaches the oxidation potential of the redox-active species in the film, the electron transfer from the electrode surface to the film is coupled with the simultaneous ionic transfer from electrolyte to the film for maintaining electro-neutrality. Thus, we observe two simultaneous mass-transfer processes at the same time and each one needs to be characterized individually. A detailed study of mass-transfer within such films would first require conceptual understanding of the main characterization technique used. We will conduct a literature survey on various models used to characterize such mass transfer in layer-by-layer (LbL) films, and then propose a model for characterizing mass-transfer in LbL films that contain nanoparticles.
Langmuir, 2007
Polyoxometalates possess many useful properties for electrochemical catalysis. These molecule-siz... more Polyoxometalates possess many useful properties for electrochemical catalysis. These molecule-size clusters can be assembled into thin films through the layer-by-layer method. In this study, we determined a cluster concentration range within which layer-by-layer (LbL) films have been successfully fabricated. We also find the influence of salt added to the deposition solutions. In an attempt to understand the self-assembly process at the molecular level, thermodynamic arguments, derived from complexation between nanoscale particles and oppositely charged polyelectrolyte chains, have been employed to interpret the adsorption of polyoxometalate clusters onto a cationic polymer layer. The scaling results describe the contact mode between a polymer chain and a cluster. The assembly can be visualized with assistance by understanding the contact between the polymer chain and the cluster.
The Journal of Physical Chemistry B, Sep 12, 2010
Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via t... more Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via the electrostatic layer-by-layer (LbL) method. The charged mass transport phenomena of these thin films have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+) as the redox probes. By adding a film resistance and a film capacitance to the conventional Randles equivalent circuit, we can calculate the diffusion coefficient values that help understand the microscopic nature of the thin films. When the negatively charged probe [Fe(CN)(6)](3-/4-) was used, lower diffusion coefficients were obtained for multilayers deposited from higher ionic strength solutions. This relationship was less obvious when the positively charged probe [Ru(NH(3))(6)](3+/2+) was used, in which the electrostatic attraction between PMo(12) clusters and the probe ions complicates the mass-transfer process. It is believed that the addition of salt to dipping solutions increases the tortuosity of the films so the mass transport takes longer paths, inducing lower diffusion coefficients. Higher PMo(12) loading causes lower diffusion coefficients due to the polyoxometalate clusters blocking the paths for charged probe ions.
International Journal of Molecular Sciences, 2010
Polyelectrolyte multilayers built via the layer-by-layer (LbL) method has been one of the most pr... more Polyelectrolyte multilayers built via the layer-by-layer (LbL) method has been one of the most promising systems in the field of materials science. Layered structures can be constructed by the adsorption of various polyelectrolyte species onto the surface of a solid or liquid material by means of electrostatic interaction. The thickness of the adsorbed layers can be tuned precisely in the nanometer range. Stable, semiconducting thin films are interesting research subjects. We use a conducting polymer, poly(p-phenylene vinylene) (PPV), in the preparation of a stable thin film via the LbL method. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to characterize the ionic conductivity of the PPV multilayer films. The ionic conductivity of the films has been found to be dependent on the polymerization temperature. The film conductivity can be fitted to a modified Randle's circuit. The circuit equivalent calculations are performed to provide the diffusion coefficient values.
Journal of Applied Physics, 2007
Polymer Thin Films, 2010
The need for miniaturized devices has driven the exponential development of nanotechnology during... more The need for miniaturized devices has driven the exponential development of nanotechnology during the past two decades. One special field of paramount practical applications is electrochemical systems at the nano-scale. For successful development in such fields, an in-depth analysis of mass and/or charge transfer mechanism is highly desired. In such a system, mass transfer often takes the form of ion transfer, which can also be viewed as charge transfer. For example, in fuel cell development, the catalyst layer deposited on a polyelectrolyte membrane would demand higher ionic (protonic) conductivity. In the electrochemical sensors, the overall performance depends largely upon sensitivity of the thin films to recognize the analyte and the speed to communicate the resultant signals with the underlying electrodes. These phenomena are closely related to the (ionic) mass transfer within such films. A clear understanding of mass transfer in such an electrochemical system is the prerequisite for any significant progress in devices. Fundamentally, three different types of mass-transfer phenomena exists for ionic species in electrolytes at electrodes: (1) diffusional transport under concentration gradient, (2) migration transport of oppositely charged ions under electric field of the electrode, and (3) convection transport due to physical stirring of the electrolyte. For electrodes modified with electroactive or redox films, the redox behavior is much more complicated. When the applied potential reaches the oxidation potential of the redox-active species in the film, the electron transfer from the electrode surface to the film is coupled with the simultaneous ionic transfer from electrolyte to the film for maintaining electro-neutrality. Thus, we observe two simultaneous mass-transfer processes at the same time and each one needs to be characterized individually. A detailed study of mass-transfer within such films would first require conceptual understanding of the main characterization technique used. We will conduct a literature survey on various models used to characterize such mass transfer in layer-by-layer (LbL) films, and then propose a model for characterizing mass-transfer in LbL films that contain nanoparticles.
Langmuir, 2007
Polyoxometalates possess many useful properties for electrochemical catalysis. These molecule-siz... more Polyoxometalates possess many useful properties for electrochemical catalysis. These molecule-size clusters can be assembled into thin films through the layer-by-layer method. In this study, we determined a cluster concentration range within which layer-by-layer (LbL) films have been successfully fabricated. We also find the influence of salt added to the deposition solutions. In an attempt to understand the self-assembly process at the molecular level, thermodynamic arguments, derived from complexation between nanoscale particles and oppositely charged polyelectrolyte chains, have been employed to interpret the adsorption of polyoxometalate clusters onto a cationic polymer layer. The scaling results describe the contact mode between a polymer chain and a cluster. The assembly can be visualized with assistance by understanding the contact between the polymer chain and the cluster.
The Journal of Physical Chemistry B, Sep 12, 2010
Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via t... more Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via the electrostatic layer-by-layer (LbL) method. The charged mass transport phenomena of these thin films have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+) as the redox probes. By adding a film resistance and a film capacitance to the conventional Randles equivalent circuit, we can calculate the diffusion coefficient values that help understand the microscopic nature of the thin films. When the negatively charged probe [Fe(CN)(6)](3-/4-) was used, lower diffusion coefficients were obtained for multilayers deposited from higher ionic strength solutions. This relationship was less obvious when the positively charged probe [Ru(NH(3))(6)](3+/2+) was used, in which the electrostatic attraction between PMo(12) clusters and the probe ions complicates the mass-transfer process. It is believed that the addition of salt to dipping solutions increases the tortuosity of the films so the mass transport takes longer paths, inducing lower diffusion coefficients. Higher PMo(12) loading causes lower diffusion coefficients due to the polyoxometalate clusters blocking the paths for charged probe ions.