This document summarizes an investigation of the adsorption of carboxymethyl cellulose (NaCMC) onto gamma-aluminum oxide (γ-Al2O3) particles. Key findings include:
1) Electrophoretic and electro-optical measurements both show that NaCMC adsorption causes the particle charge to be overcompensated above a concentration of 1x10-3 g/L NaCMC.
2) Frequency plateaus in electro-optical effect measurements shift to lower frequencies with NaCMC adsorption, indicating a decrease in particle relaxation frequency.
3) Relaxation times increase with NaCMC concentration as the adsorbed polymer enlarges the particle size, though the effect is
Juornal of Physics Condensed Matter - Article IRossen Hristov
This document summarizes a study that investigated the mobility of counterions condensed on carboxymethyl cellulose (CMC) polymer chains adsorbed onto alumina colloid particles. Previous studies using electro-optical techniques reported that condensed counterions are mobile in alternating electric fields. However, the current study uses an amplitude approach, measuring particle polarizability at increasing CMC concentration rather than frequency dependence. Results indicate condensed counterions do not contribute to particle polarization at 1 kHz, suggesting they are immobile in sinusoidal fields up to 0.5 kV/cm and 1 kHz. Comparison of polarizability and electrophoretic mobility supports the conclusion that condensed counterions are immobilized on the CMC chains.
The document summarizes a study that investigated how the photoluminescence quantum yield of lead selenide quantum dots is affected by increasing excitation energy. Three samples of PbSe quantum dots were synthesized with different diameters and characterized. It was found that the quantum yield decreased as the excitation energy increased, likely due to the formation of multi-exciton states within single quantum dots that lead to non-radiative Auger processes. The quantum yield was measured using an integrating sphere method and by analyzing absorption and emission spectra of the samples excited at different wavelengths. The results supported the expectation that higher excitation energies reduce quantum yield.
Efficient production of negative hydrogen ions in RF plasma by using a self-b...IJERA Editor
Volume production of negative hydrogen ions is established efficiently in a pure hydrogen RF discharge plasma by using a self-biased grid electrode for production of low electron-temperature and high density plasma. Using this electrode both high and low electron temperature plasmas are produced in the regions separated by the grid electrode in the chamber, in which the electron temperature in the downstream region is controlled by the mesh size and plasma production parameters. The production rate of negative ions depends strongly on the electron temperature varied by the RF input power and hydrogen pressure. In the case of the grid electrode with the 5 mesh/in., the negative hydrogen ions are produced effectively in the downstream region in the hydrogen pressure range of 0.9 −2.7 Pa. In addition, the production rate of the negative ion 퐻 − raises from 62 % to 87 % at 0.9 Pa by changing the RF power from 20 W to 80W.
Investigating Hybrid Organic-Inorganic Tin Perovskites for Li-ion Battery App...Jiankun Pu
We investigated tin perovskites (ASnX3) for lithium-ion batteries by analyzing their intercalation energy, formation energy, octahedral distortion factor, etc. We hope to utilize these data to establish a machine learning model to help us fast predict the intercalation energy of other tin-based perovskites.
This document summarizes research investigating graphene/cerium oxide nanoparticles as an electrode material for supercapacitors. Scanning electron microscopy images showed the layered structure of graphene with cerium oxide nanoparticles dispersed across the surface. Electrochemical testing found the electrode achieved a maximum specific capacitance of 11.09 F g−1 in 3 M NaCl electrolyte. Charge/discharge cycling showed good reversibility and 37% increase in capacitance after 500 cycles. The graphene/cerium oxide composite performed better than cerium oxide alone due to graphene's conductivity and the formation of an electrical double layer at the electrode interface.
This document summarizes research on the electrical conductivity of Ba-Sr-Co-Fe cathode materials for solid oxide fuel cells (SOFCs). Single phase cubic Ba0.5Sr0.5Co1-xFexO3-δ compositions were synthesized via gel combustion and cation complexation routes. Electrical conductivity measurements showed that conductivity initially increased with temperature up to a maximum then decreased, attributed to oxygen loss from the lattice. Fe substitution had little effect on conductivity. While BSCF shows potential as an SOFC cathode, further work is needed to increase conductivity to meet requirements of current IT-SOFCs.
This document discusses principles of ionization and ion dissociation in mass spectrometry. It covers topics like ionization energy, processes that occur during electron ionization like formation of molecular ions and fragment ions, and ionization by energetic electrons. It also discusses concepts like vertical transitions, where electronic transitions occur much faster than nuclear motions. The document provides background information on fundamental gas phase ion chemistry concepts in mass spectrometry.
A Study of Electrical and Magnetic Properties of La+3 Substituted Ni-Zn Ferritesiosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Juornal of Physics Condensed Matter - Article IRossen Hristov
This document summarizes a study that investigated the mobility of counterions condensed on carboxymethyl cellulose (CMC) polymer chains adsorbed onto alumina colloid particles. Previous studies using electro-optical techniques reported that condensed counterions are mobile in alternating electric fields. However, the current study uses an amplitude approach, measuring particle polarizability at increasing CMC concentration rather than frequency dependence. Results indicate condensed counterions do not contribute to particle polarization at 1 kHz, suggesting they are immobile in sinusoidal fields up to 0.5 kV/cm and 1 kHz. Comparison of polarizability and electrophoretic mobility supports the conclusion that condensed counterions are immobilized on the CMC chains.
The document summarizes a study that investigated how the photoluminescence quantum yield of lead selenide quantum dots is affected by increasing excitation energy. Three samples of PbSe quantum dots were synthesized with different diameters and characterized. It was found that the quantum yield decreased as the excitation energy increased, likely due to the formation of multi-exciton states within single quantum dots that lead to non-radiative Auger processes. The quantum yield was measured using an integrating sphere method and by analyzing absorption and emission spectra of the samples excited at different wavelengths. The results supported the expectation that higher excitation energies reduce quantum yield.
Efficient production of negative hydrogen ions in RF plasma by using a self-b...IJERA Editor
Volume production of negative hydrogen ions is established efficiently in a pure hydrogen RF discharge plasma by using a self-biased grid electrode for production of low electron-temperature and high density plasma. Using this electrode both high and low electron temperature plasmas are produced in the regions separated by the grid electrode in the chamber, in which the electron temperature in the downstream region is controlled by the mesh size and plasma production parameters. The production rate of negative ions depends strongly on the electron temperature varied by the RF input power and hydrogen pressure. In the case of the grid electrode with the 5 mesh/in., the negative hydrogen ions are produced effectively in the downstream region in the hydrogen pressure range of 0.9 −2.7 Pa. In addition, the production rate of the negative ion 퐻 − raises from 62 % to 87 % at 0.9 Pa by changing the RF power from 20 W to 80W.
Investigating Hybrid Organic-Inorganic Tin Perovskites for Li-ion Battery App...Jiankun Pu
We investigated tin perovskites (ASnX3) for lithium-ion batteries by analyzing their intercalation energy, formation energy, octahedral distortion factor, etc. We hope to utilize these data to establish a machine learning model to help us fast predict the intercalation energy of other tin-based perovskites.
This document summarizes research investigating graphene/cerium oxide nanoparticles as an electrode material for supercapacitors. Scanning electron microscopy images showed the layered structure of graphene with cerium oxide nanoparticles dispersed across the surface. Electrochemical testing found the electrode achieved a maximum specific capacitance of 11.09 F g−1 in 3 M NaCl electrolyte. Charge/discharge cycling showed good reversibility and 37% increase in capacitance after 500 cycles. The graphene/cerium oxide composite performed better than cerium oxide alone due to graphene's conductivity and the formation of an electrical double layer at the electrode interface.
This document summarizes research on the electrical conductivity of Ba-Sr-Co-Fe cathode materials for solid oxide fuel cells (SOFCs). Single phase cubic Ba0.5Sr0.5Co1-xFexO3-δ compositions were synthesized via gel combustion and cation complexation routes. Electrical conductivity measurements showed that conductivity initially increased with temperature up to a maximum then decreased, attributed to oxygen loss from the lattice. Fe substitution had little effect on conductivity. While BSCF shows potential as an SOFC cathode, further work is needed to increase conductivity to meet requirements of current IT-SOFCs.
This document discusses principles of ionization and ion dissociation in mass spectrometry. It covers topics like ionization energy, processes that occur during electron ionization like formation of molecular ions and fragment ions, and ionization by energetic electrons. It also discusses concepts like vertical transitions, where electronic transitions occur much faster than nuclear motions. The document provides background information on fundamental gas phase ion chemistry concepts in mass spectrometry.
A Study of Electrical and Magnetic Properties of La+3 Substituted Ni-Zn Ferritesiosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Synthesis of low spin iron complex as potential redox mediator for DSCsdanielmorales91
This document discusses the synthesis of low spin iron complexes as potential redox mediators for dye sensitized solar cells. The complexes [Fe(bphen)3]2+/3+ are proposed as they may have a large redox potential and fast self-exchange electron rate due to a smaller reorganizational energy. Characterization techniques like NMR, ESR, and cyclic voltammetry will be used. The complexes will be tested in electrolytes with porphyrin dyes and device performance metrics like J/V and IPCE spectra will be analyzed. Modifying the ligands may tune the redox potential to optimize the open circuit voltage while allowing dye regeneration.
This document reviews the polarization resistance method for determining instantaneous corrosion rates of metals. It discusses how polarization resistance (Rp) is derived from electrode kinetics equations and relates Rp to corrosion current density and rate. A variety of time domain electrochemical methods can be used to experimentally determine Rp, including potential step, current step, and potentiodynamic techniques. Factors that can complicate accurate measurement of Rp are also examined, such as diffusion effects, film formation, and non-uniform current/potential distributions.
Introduction to electrochemistry by t. haraToru Hara
This document provides an introduction to electrochemistry. It discusses how electrochemistry involves the conversion of chemical energy to electrical energy, as in primary batteries where a spontaneous reaction between zinc and copper electrodes produces a flow of electrons. It also discusses the reverse process of converting electrical energy to chemical energy, as in secondary batteries that can be recharged. Key concepts covered include oxidation, reduction, standard reduction potentials, anodes, cathodes, and how electrochemical cells work through balanced redox reactions while conserving mass and charge.
- The document studies using water as an alternative solvent to the commonly used acetonitrile for applying organic layers from diazonium salts.
- When using water, the diazonium salt solution had to be replaced every couple days to maintain a consistent concentration, as the salt decomposed over time, turning the solution orange.
- Preliminary results found that layers could be applied using water as a solvent, but it may lack control over completeness of the layer compared to acetonitrile.
This presentation discusses the application of electromotive force (E.M.F.) measurement. It describes eight applications: 1) determination of equilibrium constants, 2) determination of solubility of sparingly soluble salts, 3) determination of valence, 4) determination of thermodynamic functions, 5) determination of pH of a solution, 6) potentiometric titrations, 7) determination of activity coefficients, and 8) determination of transference numbers. Potentiometric titration techniques are discussed for acid-base, oxidation-reduction, and precipitation titrations. Determination of E.M.F. using cells allows calculation of various chemical properties and equilibrium constants.
Structural, Electronic and Gamma Shielding Properties of BxAl1-xAsIJMERJOURNAL
ABSTRACT: The structural and electronic properties of BxAl1-xAs ternary alloys in the zincblende structure were systematically investigated by using the first principles calculations. The local density approximation was used for exchanged and correlation interaction. The calculated band gap bowing parameter was discovered to be mightily composition dependent of the Boron concentration. Additionally, we have calculated some gamma shielding parameters of BxAl1-xAs ternary alloys. Primarily, the values of mass attenuation coefficients (μρ) were calculated using WinXCom computer program and then these parameters were utilized to calculate the values of electron density (Nel) and effective atomic number (Zeff) in the wide energy range (1 keV - 100 GeV).
This document summarizes the electrochemical synthesis and corrosion inhibiting properties of a poly N-methyl aniline coating doped with di-N-propyl malonic acid on stainless steel. Cyclic voltammetry was used to polymerize N-methyl aniline in a solution containing di-N-propyl malonic acid on a stainless steel electrode. An adherent red polymer film was obtained. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques showed that this polymer coating provided excellent corrosion protection of stainless steel in 0.5M sulfuric acid solution, with inhibition efficiencies above 99% as indicated by large increases in charge transfer resistance and decreases in corrosion current density compared to uncoated stainless steel.
This document provides an overview of interfacial electrochemistry. It discusses how interfaces form boundaries between different phases of matter and influence interactions with the environment due to changed atomic structures. Most electrochemical events occur at interfaces, making interfacial electrochemistry important. When two dissimilar materials contact, charge separation occurs across the interface, creating an interfacial potential difference. The document also describes models of the electrical double layer that forms at electrode-electrolyte interfaces, such as the Helmholtz-Perrin and Gouy-Chapman models.
The document discusses the synthesis of molecular electronic components for use as rectifiers. It explores substituting electron-rich and electron-poor rings separated by single bonds, as was theorized could act as rectifiers. It details optimizing the synthesis of dibromohemiquinone (Br2-HBQ) through varying reaction conditions, achieving a maximum 66% yield. Proof-of-concept substitutions were performed and frontier orbital energies were calculated to determine the best molecules for bonding to gold electrodes.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
Conductometric analysis measures the electrical conductivity of solutions to determine analyte concentration. It works by measuring how easily ions move through the solution when a current is applied. There are several types of conductometric titrations including acid-base, redox, and complexometric titrations. Conductometric titrations can determine the endpoint graphically without needing indicators and work well for colored, weak, or turbid solutions. The conductivity is measured using a conductometer with conductivity cells and platinum electrodes to apply a current and measure the solution's resistance.
Dielectric, Electric and Thermal Behavior of La3+ doped Co-Zn NanoferriteIOSRJAP
Dielectric, Electric and Thermal properties of rare earth La3+ material doped in Co0.5Zn0.5 Lax Fe(2- x)O4 (where x=0.025, 0.050, 0.075, 0.100, 0.125) reaction nanocrystalline ferrites were synthesized by sol-gel auto combustion method. The electric, dielectric constant and Thermal properties were investigated. The dielectric constants and dielectric loss of the samples was observed between the 100Hz and 5 MHz. The resistivities of the prepared samples were measured from 0 Volt to 550 Volts at the constant temperature 2000C using the Two Probe method. The Thermal properties were characterized by Thermo Gravimetric and Differential Thermal Analysis (TGDTA).
Determination of the hydrogen coefficient diffusion DH in the MmNi3.55Mn0.4Al...AI Publications
The hydrogen storage alloys MmNi3.55Mn0.4Al0.3Co0.75-xFex (0 ≤ x ≤0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. The discharge capacity reaches its maximum in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 270, 266, 260, 210 and 200 mAh/g after 12 charge-discharge cycles. The diffusion behaviour of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 5.86 10-10, 1.95 10-9, 3.44 10-9, 2.96 10-9 and 4.98 10-10 cm2 s-1. However, the values of the charge transfer coefficients are respectively equal to 0.35, 0.6, 0.5, 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.
This document discusses devices used in electrochemical analysis and auxiliary laboratory devices. It describes galvanic cells, electrodes, and potentiometric devices used to determine ionic composition. It also discusses auxiliary devices like centrifuges and thermostats. Conductometers and coulometers are described which measure conductivity by applying a low voltage alternating current between electrodes to avoid electrolysis. pH meters and glass electrodes are summarized which can directly measure pH by relating the electrode voltage to hydrogen ion concentration.
Dynamic Stereochemistry and What role does conformation plays on stereochemistry is being exemplified in this presentation. Useful for the Undergraduate and Postgraduates students of Pharmacy, Pharmaceutical Chemistry and Chemical Sciences
Theoretical study of the effect of hydroxy subgroup on the electronic and spe...Alexander Decker
This document summarizes a theoretical study that used density functional theory calculations to investigate the effect of adding hydroxyl groups to the azulene molecule in different positions. The study found that adding hydroxyl groups (electron-withdrawing groups) decreases the energy gap of the molecules, making electrons easier to excite. It also decreases the ionization potential and increases the electron affinity, improving the electronic properties and making the molecules more soluble and conductive. Molecule 6, with hydroxyl groups in specific positions, was found to have the best properties for use as an n-type organic semiconductor. Vibrational frequency calculations showed good agreement with experimental data for the azulene molecule and identified characteristic vibrations induced by the addition of hydroxyl groups
- The document discusses an undergraduate investigation using point contact spectroscopy (PCS) to study quantum criticality in materials. PCS has traditionally been used to determine scattering information in metals and energy gaps in superconductors. A recent theory suggests PCS may also detect non-Fermi liquid behavior associated with quantum criticality.
- The investigation began by using PCS to study the superconductor FeTe0.55Se0.45 to establish ballistic contacts. It then aimed to use PCS to search for signatures of quantum fluctuations in the quantum critical material YFe2Al10 above the superconductor's critical temperature. This may provide evidence for detecting quantum critical behavior through PCS.
This document summarizes research on a series of siloxane-based side chain liquid crystal polymers where the length of the coupling chain between the mesogenic unit and polymer backbone was systematically varied. All polymers exhibited a smectic phase and the nematic-isotropic transition temperature increased with longer coupling chain length. Electro-optic measurements found that threshold voltage for reorientation decreased with increasing chain length due to changes in intrinsic curvature elasticity rather than orientational order. A model is presented where constraints from coupling the mesogenic units to the backbone influence the observed electric-optic properties as chain length varies.
1) Morpheus3D is a company that develops innovative 3D dental solutions including Morpheus3D Dental Solution. It has received praise from the medical, academic, and industry fields in Korea and globally.
2) The company has six core competencies including hardware and software technologies for 3D scanning, modeling, and analysis. It has achieved significant overseas expansion distributing its dental and aesthetic solutions.
3) The company's products include the Neo 3D facial scanner and Morpheus3D Dental Solution software for 3D modeling, simulation, and superimposition in orthodontic treatment planning.
Este documento presenta un plan de negocios para crear un vivero de plantas ornamentales en Tulcán, Ecuador. El vivero se llamará "MAXILEAL" y cultivará y venderá suculentas y geranios. El objetivo general es satisfacer la demanda insatisfecha de variedades de plantas mediante la producción de nuevas variedades a través de injertos. El vivero también brindará asesoría sobre el cuidado de plantas y su significado místico, romántico y esotérico según el color y la forma. El v
El documento habla sobre el control presupuestario. Explica que es importante planificar y monitorear los gastos para asegurar que se cumplan las metas financieras. También enfatiza la necesidad de realizar ajustes cuando sea necesario para mantener el equilibrio entre los ingresos y egresos.
El documento discute el papel cambiante del Estado, las políticas públicas y la evaluación. Explica que el Estado debe evolucionar de proveedor universal a catalizador y protector. Define las políticas públicas como acciones para resolver problemas considerados públicos. Finalmente, argumenta que se necesita un modelo de gobernanza colaborativo y evaluación de políticas públicas para desarrollar políticas eficaces.
Synthesis of low spin iron complex as potential redox mediator for DSCsdanielmorales91
This document discusses the synthesis of low spin iron complexes as potential redox mediators for dye sensitized solar cells. The complexes [Fe(bphen)3]2+/3+ are proposed as they may have a large redox potential and fast self-exchange electron rate due to a smaller reorganizational energy. Characterization techniques like NMR, ESR, and cyclic voltammetry will be used. The complexes will be tested in electrolytes with porphyrin dyes and device performance metrics like J/V and IPCE spectra will be analyzed. Modifying the ligands may tune the redox potential to optimize the open circuit voltage while allowing dye regeneration.
This document reviews the polarization resistance method for determining instantaneous corrosion rates of metals. It discusses how polarization resistance (Rp) is derived from electrode kinetics equations and relates Rp to corrosion current density and rate. A variety of time domain electrochemical methods can be used to experimentally determine Rp, including potential step, current step, and potentiodynamic techniques. Factors that can complicate accurate measurement of Rp are also examined, such as diffusion effects, film formation, and non-uniform current/potential distributions.
Introduction to electrochemistry by t. haraToru Hara
This document provides an introduction to electrochemistry. It discusses how electrochemistry involves the conversion of chemical energy to electrical energy, as in primary batteries where a spontaneous reaction between zinc and copper electrodes produces a flow of electrons. It also discusses the reverse process of converting electrical energy to chemical energy, as in secondary batteries that can be recharged. Key concepts covered include oxidation, reduction, standard reduction potentials, anodes, cathodes, and how electrochemical cells work through balanced redox reactions while conserving mass and charge.
- The document studies using water as an alternative solvent to the commonly used acetonitrile for applying organic layers from diazonium salts.
- When using water, the diazonium salt solution had to be replaced every couple days to maintain a consistent concentration, as the salt decomposed over time, turning the solution orange.
- Preliminary results found that layers could be applied using water as a solvent, but it may lack control over completeness of the layer compared to acetonitrile.
This presentation discusses the application of electromotive force (E.M.F.) measurement. It describes eight applications: 1) determination of equilibrium constants, 2) determination of solubility of sparingly soluble salts, 3) determination of valence, 4) determination of thermodynamic functions, 5) determination of pH of a solution, 6) potentiometric titrations, 7) determination of activity coefficients, and 8) determination of transference numbers. Potentiometric titration techniques are discussed for acid-base, oxidation-reduction, and precipitation titrations. Determination of E.M.F. using cells allows calculation of various chemical properties and equilibrium constants.
Structural, Electronic and Gamma Shielding Properties of BxAl1-xAsIJMERJOURNAL
ABSTRACT: The structural and electronic properties of BxAl1-xAs ternary alloys in the zincblende structure were systematically investigated by using the first principles calculations. The local density approximation was used for exchanged and correlation interaction. The calculated band gap bowing parameter was discovered to be mightily composition dependent of the Boron concentration. Additionally, we have calculated some gamma shielding parameters of BxAl1-xAs ternary alloys. Primarily, the values of mass attenuation coefficients (μρ) were calculated using WinXCom computer program and then these parameters were utilized to calculate the values of electron density (Nel) and effective atomic number (Zeff) in the wide energy range (1 keV - 100 GeV).
This document summarizes the electrochemical synthesis and corrosion inhibiting properties of a poly N-methyl aniline coating doped with di-N-propyl malonic acid on stainless steel. Cyclic voltammetry was used to polymerize N-methyl aniline in a solution containing di-N-propyl malonic acid on a stainless steel electrode. An adherent red polymer film was obtained. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques showed that this polymer coating provided excellent corrosion protection of stainless steel in 0.5M sulfuric acid solution, with inhibition efficiencies above 99% as indicated by large increases in charge transfer resistance and decreases in corrosion current density compared to uncoated stainless steel.
This document provides an overview of interfacial electrochemistry. It discusses how interfaces form boundaries between different phases of matter and influence interactions with the environment due to changed atomic structures. Most electrochemical events occur at interfaces, making interfacial electrochemistry important. When two dissimilar materials contact, charge separation occurs across the interface, creating an interfacial potential difference. The document also describes models of the electrical double layer that forms at electrode-electrolyte interfaces, such as the Helmholtz-Perrin and Gouy-Chapman models.
The document discusses the synthesis of molecular electronic components for use as rectifiers. It explores substituting electron-rich and electron-poor rings separated by single bonds, as was theorized could act as rectifiers. It details optimizing the synthesis of dibromohemiquinone (Br2-HBQ) through varying reaction conditions, achieving a maximum 66% yield. Proof-of-concept substitutions were performed and frontier orbital energies were calculated to determine the best molecules for bonding to gold electrodes.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
Conductometric analysis measures the electrical conductivity of solutions to determine analyte concentration. It works by measuring how easily ions move through the solution when a current is applied. There are several types of conductometric titrations including acid-base, redox, and complexometric titrations. Conductometric titrations can determine the endpoint graphically without needing indicators and work well for colored, weak, or turbid solutions. The conductivity is measured using a conductometer with conductivity cells and platinum electrodes to apply a current and measure the solution's resistance.
Dielectric, Electric and Thermal Behavior of La3+ doped Co-Zn NanoferriteIOSRJAP
Dielectric, Electric and Thermal properties of rare earth La3+ material doped in Co0.5Zn0.5 Lax Fe(2- x)O4 (where x=0.025, 0.050, 0.075, 0.100, 0.125) reaction nanocrystalline ferrites were synthesized by sol-gel auto combustion method. The electric, dielectric constant and Thermal properties were investigated. The dielectric constants and dielectric loss of the samples was observed between the 100Hz and 5 MHz. The resistivities of the prepared samples were measured from 0 Volt to 550 Volts at the constant temperature 2000C using the Two Probe method. The Thermal properties were characterized by Thermo Gravimetric and Differential Thermal Analysis (TGDTA).
Determination of the hydrogen coefficient diffusion DH in the MmNi3.55Mn0.4Al...AI Publications
The hydrogen storage alloys MmNi3.55Mn0.4Al0.3Co0.75-xFex (0 ≤ x ≤0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. The discharge capacity reaches its maximum in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 270, 266, 260, 210 and 200 mAh/g after 12 charge-discharge cycles. The diffusion behaviour of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 5.86 10-10, 1.95 10-9, 3.44 10-9, 2.96 10-9 and 4.98 10-10 cm2 s-1. However, the values of the charge transfer coefficients are respectively equal to 0.35, 0.6, 0.5, 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.
This document discusses devices used in electrochemical analysis and auxiliary laboratory devices. It describes galvanic cells, electrodes, and potentiometric devices used to determine ionic composition. It also discusses auxiliary devices like centrifuges and thermostats. Conductometers and coulometers are described which measure conductivity by applying a low voltage alternating current between electrodes to avoid electrolysis. pH meters and glass electrodes are summarized which can directly measure pH by relating the electrode voltage to hydrogen ion concentration.
Dynamic Stereochemistry and What role does conformation plays on stereochemistry is being exemplified in this presentation. Useful for the Undergraduate and Postgraduates students of Pharmacy, Pharmaceutical Chemistry and Chemical Sciences
Theoretical study of the effect of hydroxy subgroup on the electronic and spe...Alexander Decker
This document summarizes a theoretical study that used density functional theory calculations to investigate the effect of adding hydroxyl groups to the azulene molecule in different positions. The study found that adding hydroxyl groups (electron-withdrawing groups) decreases the energy gap of the molecules, making electrons easier to excite. It also decreases the ionization potential and increases the electron affinity, improving the electronic properties and making the molecules more soluble and conductive. Molecule 6, with hydroxyl groups in specific positions, was found to have the best properties for use as an n-type organic semiconductor. Vibrational frequency calculations showed good agreement with experimental data for the azulene molecule and identified characteristic vibrations induced by the addition of hydroxyl groups
- The document discusses an undergraduate investigation using point contact spectroscopy (PCS) to study quantum criticality in materials. PCS has traditionally been used to determine scattering information in metals and energy gaps in superconductors. A recent theory suggests PCS may also detect non-Fermi liquid behavior associated with quantum criticality.
- The investigation began by using PCS to study the superconductor FeTe0.55Se0.45 to establish ballistic contacts. It then aimed to use PCS to search for signatures of quantum fluctuations in the quantum critical material YFe2Al10 above the superconductor's critical temperature. This may provide evidence for detecting quantum critical behavior through PCS.
This document summarizes research on a series of siloxane-based side chain liquid crystal polymers where the length of the coupling chain between the mesogenic unit and polymer backbone was systematically varied. All polymers exhibited a smectic phase and the nematic-isotropic transition temperature increased with longer coupling chain length. Electro-optic measurements found that threshold voltage for reorientation decreased with increasing chain length due to changes in intrinsic curvature elasticity rather than orientational order. A model is presented where constraints from coupling the mesogenic units to the backbone influence the observed electric-optic properties as chain length varies.
1) Morpheus3D is a company that develops innovative 3D dental solutions including Morpheus3D Dental Solution. It has received praise from the medical, academic, and industry fields in Korea and globally.
2) The company has six core competencies including hardware and software technologies for 3D scanning, modeling, and analysis. It has achieved significant overseas expansion distributing its dental and aesthetic solutions.
3) The company's products include the Neo 3D facial scanner and Morpheus3D Dental Solution software for 3D modeling, simulation, and superimposition in orthodontic treatment planning.
Este documento presenta un plan de negocios para crear un vivero de plantas ornamentales en Tulcán, Ecuador. El vivero se llamará "MAXILEAL" y cultivará y venderá suculentas y geranios. El objetivo general es satisfacer la demanda insatisfecha de variedades de plantas mediante la producción de nuevas variedades a través de injertos. El vivero también brindará asesoría sobre el cuidado de plantas y su significado místico, romántico y esotérico según el color y la forma. El v
El documento habla sobre el control presupuestario. Explica que es importante planificar y monitorear los gastos para asegurar que se cumplan las metas financieras. También enfatiza la necesidad de realizar ajustes cuando sea necesario para mantener el equilibrio entre los ingresos y egresos.
El documento discute el papel cambiante del Estado, las políticas públicas y la evaluación. Explica que el Estado debe evolucionar de proveedor universal a catalizador y protector. Define las políticas públicas como acciones para resolver problemas considerados públicos. Finalmente, argumenta que se necesita un modelo de gobernanza colaborativo y evaluación de políticas públicas para desarrollar políticas eficaces.
Leukocytární esteráza je enzym, který se hojně vyskytuje v neutrofilech. Jejich rozpadem se uvolňuje do výpotku. Pomocí kolorimetrických testačních proužků lze diagnostikovat přítomnost leukocytární esterázy a tím i neutrofilů ve výpotku. Tím lze zjistit, zda je výpotek infekční či neinfekční etiologie. Cílem studie je stanovení senzitivity a specificity vyšetření leukocytární esterázy pomocí testačních proužků AUTION Sticks (Arkray) ve výpotcích různé etiologie získaných při zánětlivých postiženích pohybového aparátu.
El documento describe la diferencia entre medios de comunicación, hipermedia y multimedia. Los medios de comunicación incluyen textos, imágenes, video y audio para transmitir información, mientras que la hipermedia es un conjunto interactivo de estos medios. La multimedia se refiere al uso de múltiples medios para presentar información y forma parte de la hipermedia. Un proyecto multimedia utiliza tecnología para organizar páginas que combinan elementos como imágenes y sonidos.
Este documento presenta la investigación sobre la influencia francesa durante el proceso de independencia de Chile entre 1817 y 1823. Plantea como problema central determinar si existió dicha influencia militar y establece hipótesis al respecto. Define objetivos generales y específicos, y delimita el área y periodo de estudio. Explica la metodología cualitativa y deductiva, basada en fuentes primarias y bibliografía. Busca comprender el contexto internacional y los aportes de actores extranjeros durante la emancipación chilena.
Start-ups and Spinouts: the Fuzzy Front-End & the Hard Yards… is it worth it...Brian McCaul
This document discusses startups and spinouts, and whether they are worth pursuing. It notes that while startups are often touted as job creators, research shows only a small percentage of high-growth firms are responsible for new job creation. Successful startups tend to have proprietary technology, network effects, economies of scale, and strong branding. University spinouts in particular help commercialize new technologies and can stimulate innovation and enterprise ecosystems. While most startups fail, taking more risks through early-stage funding could help identify the high-growth firms of the future. Creating a lean startup process may help startups test ideas faster and fail early.
Histórico del precio de la leche a puerta de corral en VenezuelaOscarina Castillo
El documento presenta estadísticas sobre los precios de la leche cruda y el queso artesanal pagados a productores en mayo de 2015 en Venezuela, incluyendo promedios, desviaciones estándares, rangos de precios, y comparaciones con precios de marzo y diciembre de 2014. Muestra que el 51% de las ventas a nivel de finca corresponden a leche cruda, 38% a queso, y 11% a ambos productos.
El documento proporciona una introducción al hardware de los ordenadores, describiendo los sistemas analógicos y digitales, la definición de ordenador personal, hardware y software. Explica los componentes clave de un ordenador como la CPU, placa base, memoria, BIOS, periféricos de entrada/salida y almacenamiento. Describe los diferentes tipos de tarjetas de expansión como las tarjetas gráficas, de sonido y de red.
Sally está devastada después de que su hijo Jimmy muera de cáncer a pesar de los esfuerzos de los médicos. Mientras llora en la habitación de Jimmy, Sally encuentra una carta supuestamente escrita por él desde el cielo, diciendo que ya no sufre y está con Dios y Jesús. La carta intenta consolar a Sally diciendo que Dios estaba con Jimmy durante su enfermedad al igual que estuvo con Jesús.
Горбунов Н.А., Государственная морская академия им. С.О. Макарова, г. Санкт-Петербург
Разработка плазменных технологий для прямого фотоэлектрического преобразования с сфокусированного солнечного излучения
This document summarizes an ab initio study of the absorption spectra of silver clusters containing 5-8 atoms. The authors used linear response equation-of-motion coupled cluster methods and a relativistic effective core potential to calculate transition energies and oscillator strengths for the stable structures as well as isomeric forms of these clusters. They investigated the influence of structural properties on the spectroscopic patterns and the role of d-electrons. Their calculated absorption spectra provide predictions of the optical response properties in the gas phase that can be compared to experimental data from clusters in rare gas matrices or helium droplets.
This document provides information on Auger Electron Spectroscopy (AES). It discusses two modes for displaying AES spectra: direct and differential. The differential mode enhances peaks and is more commonly used. AES can be used to identify elements based on their characteristic Auger peaks. However, peak identification is complicated by chemical shifts that change peak positions based on chemical environment. The document also discusses challenges of using AES for insulating materials due to surface charging effects and methods for charge neutralization.
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...Mahdi Robat Sarpoushi
This document summarizes research on using graphene nanosheets as electrode materials for supercapacitors. The researchers investigated the effect of ion size and properties on the pseudocapacitance and double layer capacitance of graphene electrodes in different electrolytes. They found that the electrode showed better double layer characteristics in NaOH electrolyte compared to LiBr electrolyte. This was attributed to the smaller size and higher mobility of ions in NaOH, allowing more ions to be stored on the graphene surface. Electrochemical tests showed the electrode exhibited both double layer capacitance and pseudocapacitance, with pseudocapacitance contributing more in LiBr electrolyte. The morphology of the graphene nanosheets formed a continuous porous network suitable for
This document discusses the adsorption of carboxymethyl cellulose (CMC) onto alumina particles. CMC and alumina were chosen because their surface charges can be altered by pH, allowing the study of particle aggregation and stabilization. Electric light scattering and microelectrophoresis techniques were used to measure how CMC adsorption affects the electric polarizability and surface charge of the alumina particles over time and across a range of CMC concentrations. The results provide conditions for complete CMC adsorption and suspension stability.
The document summarizes an experiment investigating fac/mer isomerism in a low spin iron(II) complex. A complex was synthesized from iron(II) tetrafluoroborate, benzylamine, and 2-pyridinecarboxaldehyde, yielding 79.7% product. NMR showed a high ratio of facial to meridional isomers. UV-vis spectroscopy determined molar extinction coefficients of 6081.9 and 4518.4 L/mol-cm at 516.5 and 561.3 nm, respectively.
XPS is a surface-sensitive technique that uses X-rays to eject electrons from a material's surface and measure their kinetic energy. This provides information about the material's elemental composition, chemical state, and electronic structure within the top 10-100 angstroms. XPS works based on the photoelectric effect - X-rays eject core level electrons, and the electron binding energy is determined from the kinetic energy measurement and known X-ray energy. Each element produces characteristic peaks allowing identification. Chemical shifts provide information about chemical environment. XPS is widely used for materials characterization and analysis of thin films, corrosion, polymers, and more.
This document describes a method for coating metallic surfaces with thin films of nano-dimensional carbon to reduce secondary electron emission and suppress multipactor phenomena. Carbon nano-particles 1-10 nm in size are produced using a multispark discharge in ethyl alcohol. Thin films are then deposited on copper plates via two methods: evaporation of a colloidal solution or electrophoresis. Secondary electron emission measurements found that samples coated with films deposited by evaporation or long-time electrophoresis had lower maximum emission and higher first crossover energy compared to uncoated samples, inhibiting multipactor excitation.
Experiment 4: Electropolymerized Conducting Polymers.
Introduction:
Conductive polymers (CP) exhibit very useful properties such as flexibility, solubility [1], electrical conductivity, low energy optical transitions, low ionization potential, and high electron affinity.[2] These characterizations make them such effective candidates for many applications such as antistatic and antimagnetic shielding devices[3], microwave attenuation[4], light emitting devices, optical sensors, enzymatic biosensors[5], electronic circuits, and detectors of odors and flavors. The most widely known conducting polymers are polypyrole, polyanaline, and polythiophene. By applying an electrical potential (reversible reaction), these polymers can be reduced. The role of these polymers when they are used as active templates in biosensor applications is the immobilization of dynamic species on the electrode. This will contribute to enhancing the sensitivity and the accuracy of analyte detection. CPs have been used for stabilizing numerous biological species such as enzymes, antibodies, haptens, DNA, and more interestingly the whole cells. [1]
Aim:
The aim of performing this experiment is to create a conducting polypyrrole film which consists of a stabilized enzyme, identify the film and its characteristics, and utilize it as glucose biosensor.
Procedure:
“Refer to Manual for NANO 3101/8302, Electropolymerized Conducting Polymers, Flinders University, p.24-29.”
Results and Discussion:
In the biosensor uses, the deposition of the polymers on the electrode surface can be done by applying an oxidative potential. During this action, the enzymes can be stabilized, and by modifying the deposition time, the amounts of the deposited layer can be recreated. The sensitivity, selectivity, and the accuracy of detection of the biosensors are reliant on the architecture of the polymer, the biological activity of the enzymatic immobilization, and the electropolymerisation circumstances.
In this experiment, the glucose oxidase (enzyme) was immobilized in a conducting polypyrole film on an electrode to find out their appropriateness as a functioning electrode. The performance of the electrode was measured through a Cyclic Voltammogram (CV) of ferricyanide
The geometric area of the electrode was measured by a ruler, and it was found to be 3.14 mm ²which is identical to 0.00314 cm².
The Randles-Sevcik equation is used in the redox reactions
at 25 C °
Where is the peak current, A is the electrode area (cm²), n is the number of electrons involved, C is the concentration of the bulk (mol/ml) for active species, v is the scan rate (V/s), and D is the diffusion coefficient.
n = 1, therefore
, therefore = 0.002756809.
V = 20mV/s = 0.02 V/s, therefore
C = 10 mM = 0.01 mol/L = 0.00001 mol/mL.
can be determined from figure.1
Figure 1: Cyclic Voltammograms (CV) as a function of escalating the scan rate for Platinum Electrode in ferrricyanide solution.
This c ...
Zno and znopbs heterojunction photo electrochemical cellseSAT Journals
Abstract Photo Electrochemical Cell (PEC) can also be used for splitting of water into hydrogen and Oxygen. Here, ZnO nanorod PEC has been prepared in hydrothermal method and ZnO/PbS quantum dot PEC has been prepared by hydrothermal method and chemical bath deposition method. UV-Visible spectroscopy has been observed. Flat band voltage, bandwidth and majority charge carriers have been calculated from Mott-Schottky. Impedance variation at semiconductor and electrolyte junction has been observed with Electrochemical Impedance Spectroscopy (EIS). Keywords: Hydrothermal, Chemical bath, ZnO/PbS, UV-Vis, Mott-Schottky, EIS.
1) The document analyzes reflectance spectra of Bi2Se3 to study electron excitation from deeper energy levels. Absorption is high for photon energies above the band gap, allowing analysis of light-matter interactions.
2) Calculations of effective electron density (neff) and dielectric constant (εeff) using sum rules show contributions from d-electron transitions in Bi2Se3 up to 25 eV, indicating deeper energy levels.
3) Comparison of plasma frequencies from different measurement methods shows good agreement, validating the analysis of reflectance spectra to study electron excitations from deeper zones in Bi2Se3.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Iaetsd synthesis and characterization of cdIaetsd Iaetsd
1. The document describes the photoelectrochemical deposition of CdxHg1-xTe thin films on a selenium-modified gold electrode. Selenium generated from the photocorrosion of tellurium reacts with cadmium and mercury ions in the electrolyte to form the ternary semiconductor films.
2. Characterization using electrochemical quartz crystal microgravimetry, voltammetry, Raman spectroscopy, EDX, and UV reflectance spectroscopy showed that the composition and band gap of the deposited CdxHg1-xTe films could be modulated by controlling the electrolyte composition.
3. The films exhibited n-type semiconductor behavior. Their composition and band gap values ranged from mercury telluride
XPS is a surface-sensitive technique that uses X-rays to eject electrons from the surface of a sample. It can be used to determine the elemental composition, empirical formula, chemical or electronic state of elements present in the surface. The principle is based on the photoelectric effect where X-rays eject core shell electrons of an atom. The kinetic energy of these photoelectrons is measured to determine the elemental identity and chemical state. XPS provides information down to 10-100 Angstroms from the surface and is useful for applications like failure analysis, corrosion studies, and analyzing thin film coatings and polymers.
the effect of nickel incorporation on some physical properties of epoxy resinINFOGAIN PUBLICATION
The J-E characteristics of samples of epoxy resins mixed with nickel powder in different concentrations have been tested and a log-log straight line behaviour in both the low- and high field regions is observed. Ni-concentration has significant influence on the calculated constants of the J-E relationship. The d.c. electrical resistivity (ρ) of the samples are measured from the room temperature up to about 400 K. The variation of ρ with T obeys the exponential relation of ordinary dielectrics in three temperature regions. The parameters characterizing the ρ -T dependence change considerably with Ni-concentration. Due to the existence of nickel in different concentration a "true" compensation effect is observed with three characteristic compensation temperatures. The mechanical hardness of the samples was investigated as a function of Ni-concentration.
1) The document investigates the effect of cation and anion sizes on the charge storage capabilities of graphite nanosheets as electrode materials for electrochemical double layer capacitors.
2) Scanning electron microscope images confirm the layered structure of the graphite nanosheets used, which are 12nm thick with 3.36 Angstrom spacing between layers.
3) Electrochemical measurements using cyclic voltammetry and impedance spectroscopy indicate that the graphite electrodes exhibited better charge storage and delivery in 3M NaCl electrolyte compared to NaOH and KOH electrolytes, due to the smaller ion sizes matching better with the graphite structure.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
DIELECTROPHORETIC DEFORMATION OF ERYTHROCYTES ON TRANSPARENT INDIUM TIN OXIDE...Larry O'Connell
1. The document presents a protocol for patterning transparent indium tin oxide (ITO) electrodes and investigates their efficacy for dielectrophoretically deforming erythrocytes compared to existing gold electrodes.
2. ITO electrodes were fabricated through a multi-step reactive ion etching process involving photoresist patterning and chromium/nickel masking layers. The transparent ITO electrodes allow full visualization of adhered cells, unlike opaque gold electrodes.
3. Erythrocytes suspended in a glucose solution were dielectrophoretically deformed at increasing electric field strengths on the ITO electrodes. Images were captured at each voltage step to measure cell deformation without occlusion from the electrodes.
Study of Microstructural, Electrical and Dielectric Properties of La0.9Pb0.1M...Scientific Review SR
The present work studies the microstructural and electrical properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 ceramics synthesized by solid-state route method. Microstructure and elemental analysis of both samples were carried out by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) method, respectively. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted structure. The XRD data were further analyzed by Rietveld refinement technique. Raman analysis reveals that Y atom substitutes La site into the LPMO with shifting of phonon modes. The temperature variation of resistivity of undoped and Y-doped La0.9Pb0.1MnO3 samples have been investigated. The electrical resistivity as a function of temperature showed that all samples undergo an metal-insulator (M-I) transition having a peak at transition temperature TMI. Y-doping increases the resistivity and the metal-insulator transition temperature (TMI) shifts to lower temperature. The temperature-dependent resistivity for temperatures less than metal-insulator transition is explained in terms the quadratic temperature dependence and for T > TMI, thermally activated conduction (TAC) is appropriate. Variation of frequency dispersion in permittivity and loss pattern due to La-site substitution in LPMO was observed in the dielectric response curve.
10.1016-j.mssp.2015.01.037-Electrochemical investigation of graphene_nanoporo...Mahdi Robat Sarpoushi
This study investigated the effect of mixing graphene nanosheets and nanoporous carbon black on the surface morphology and electrochemical performance of electrodes prepared for supercapacitors. Electrodes containing 80% nanoporous carbon black, 10% graphene nanosheets, and 10% PTFE binder showed the highest specific capacitance of 10.22 F/g. The addition of nanoporous carbon black increased the proportion of outer charge stored on the electrode relative to the total charge stored, indicating higher current response and voltage reversal at the end potentials. Scanning electron microscopy images showed that adding nanoporous carbon black particles arranged the graphene nanosheets in different directions, increasing the specific surface area and changing diffusion characteristics to improve capacitance and reversibility
10.1016-j.mssp.2015.01.037-Electrochemical investigation of graphene_nanoporo...
Rossen - BF Article
1. INVESTIGATION OF CARBOXYMETHYL CELLULOSE ADSORPTION ON A
MODEL CHARGED INTERFACE
R. Hristov
Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria
Correspondence to: Rossen Hristov
E-mail: rchristov@ipc.bas.bg
ABSTRACT
This report concerns electro-optical study of colloid-polyelectrolyte complexes of sodium carboxymethyl cellulose (NaCMC)
and gamma-aluminium oxide (γ-Al2O3) at pH 6.0 and fixed ionic strength. A frequency plateau shrink and a shift towards
lower frequencies were observed after NaCMC adsorption especially near the point of zero charge. The electro-optical effect
dependence on electric field strength shows that the coated particles reach full orientation at lower values of the applied
electric field than particles with the highest charge density, previously investigated. Electrophoretic measurements, used as an
additional analysis of the changes in the suspensions, showed particles’ charge overcompensation above 1⋅10−3
g/L NaCMC
and a saturation of electrophoretic mobility at the highest investigated concentrations of the polymer.
Keywords: adsorption, colloid, electro-optics, interface,
polyelectrolytes
Introduction
The adsorption of polyelectrolytes (PE) on colloid particles
has attracted the attention of many researchers due to their
various practical applications – stabilization of suspensions in
biological, medical and chemical industrial processes, gene
therapy (4), fabrication of nanomaterials (2), modification of
surfaces for changes of their adhesion properties, etc.
γ-Al2O3 is a detailed investigated amphoteric oxide with
well-defined surface covered by Al2(OH)3. It forms fractal-
shaped anisometric aggregates of particles stuck together in
the process of their industrial formation. The sticking is not
dense so the aggregates are porous. Unlike the ideal
anisometric shapes – rods, discs, rotational ellipsoids, etc.,
traditionally used in the electro-optic studies because of their
shape simplicity, fractal structures are much more widespread
in nature. That is why γ-Al2O3, being fractal and amphoteric,
can be used as a model surface allowing investigation of
adsorption behaviour of both positively and negatively
charged PEs, biopolyelectrolytes and their derivatives on a
much more realistic interface. The disadvantage of that
interface is that the electro-optical parameters are difficult to
be calculated because of its complexity. Despite this,
successful exploration of such complex surfaces would be
able to expand the practical applicability of electro-optics as a
method.
This study carried out at pH 6.0, was made as a
prolongation of a previous one made at pH 4.5 at which γ-
Al2O3 particles possess maximal positive charge (3). At lower
pH values its solutions begin to lose their colloid state and
gradually turn into molecular solutions improper to be
investigated by the electro-optical method – electric light
scattering, applicable only for colloid systems studies. The
point of zero charge (PZC) of the suspension is at pH 8.5 so
the suspension is with middle by magnitude positive charge
at pH 6.0. Above the PZC the oxide particles are negatively
charged but this charge range is not in interest for the present
investigation because the adsorbed NaCMC is negatively
charged in aqueous solution due to dissociation of the sodium
ions. This difference between the charges signs of the
particles and the polymer is important for the adsorption
process because it depends basically on the forces of
electrostatic attraction between the charged macromolecules
and the counter-charged solid-liquid interface.
Suitable particles concentration (0.5 g.dm-3
) was
preliminary defined to be within the linear part of the
concentration dependence of the electro-optical effect (EOE)
with big enough signal/noise ratio. The previously used
particle concentration 0.1 g.dm-3
(3), was found to be
unsuitable for the present investigation because the
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2. suspensions flocculated after PE addition. Despite that,
present results and these in Ref. (3) are comparable due to the
fact that the data are expressed by the relative EOE – ΔI/I0,
not by the absolute one, ΔI.
Materials and methods
The γ-Al2O3 and the NaCMC are products of “Degussa”.
According to the electron micrographs (1) the oxide
aggregates size is about 300 nm and consist of about 20 nm
single spherical particles. The mean specific surface of the
suspension is about 200 m2
/g. The NaCMC (“Blanose
12M31FD”) with molecular mass 250 kDa has 103
monomers
and its degree of substitution is 1.2.
Oxide particles were sonicated for 30 seconds to increase
their adsorption surface (Ultrasonic Disintegrator UD-11
automatic, frequency 22 ± 1.65 kHz). Adsorption was
achieved by mixing equal volumes of aqueous solutions of
PE and γ-Al2O3 with pH (6.0) and ionic strength (2.5⋅10-
4
mol.dm-3
), followed by stirring for 30 minutes with
magnetic bar. The adsorption conditions were adjusted by the
use of 0.2 M HCl, NaOH and NaCl. Suitable NaCMC
concentrations (in the range 5⋅10-4
– 5⋅10-2
g.dm-3
) were
determined by electrophoresis.
The electro-optical method – electric light scattering – is
based on the orientation of charged anisometric colloid
particles in electric field, detected by light scattering at
observation angle 900
. The orientation degree depends on the
electric field strength and determines the difference (ΔI = IE -
I0) in the scattered light intensity when the field is applied (IE)
or absent (I0) – absolute EOE, ΔI. The ratio ΔI/I0 is called
relative EOE. When the system is optically stable, the
variation of the EOE reflects directly the changes in the
particles’ electric polarizability (γ). The steady-state
EOE (ΔIs/I0) allows investigation of the geometrical and the
optical properties of the colloid particles. The optical, the
geometrical and the electrical properties are linked and
dependent on each another. This dependence is expressed by
the following formula: ΔIs/I0 = G . (γ E2
15 kBT), where G is
an optical function, E is the applied electric field strength, kB
– the Boltzman constant, T – the absolute temperature.
B
When the electric field is turned off, the particles disorientate
because of the Brownian motion. This is an important
parameter called relaxation or decay time (τ) which depends
on particles size definable by certain formula so it can give a
notion of suspensions polydispersity. Decay time values are
linked with the rotational diffusion coefficient Dr as it
follows: τ = 1/ 6Dr (5).
Results and Discussion
The electrophoretic mobility Ueph (Fig. 1) of the oxide
particles after adsorption of NaCMC alters insignificantly at
low PE concentrations because they are insufficient to cause
considerable particles charge decrease. At 1·10-3
g.dm-3
NaCMC, the particles charge is completely neutralized, the
suspensions flocculate and no mobility in electric field exists
so this is the isoelectric point. At higher concentrations the
oxide particles reverse their charge sign. Above 3·10-2
g.dm-
3
NaCMC the electrophoretic mobility (Ueph) is constant so
adsorption amount of PE has reached its maximum. The
electrophoretic measurements prove that NaCMC adsorption
really happens.
Fig. 1. Electrophoretic mobility dependence (Ueph) of the oxide particles on
NaCMC concentration at pH 6.0 and ionic strength 2.5⋅10-4
mol.dm-3
.
Insetted: Dependence of the electric polarizability (γ) of the oxide particles
on NaCMC concentration
The small insetted graphic on Fig. 1 represents the
dependence of the electric polarizability (γ) of the particles on
the NaCMC concentration. The comparison between both
graphics indicates analogous behaviour detected
independently by the use of two methods – electro-optics and
electrophoresis. Before overcharging, the two parameters
(Ueph and γ) decrease, and above charge inversion – they
increase. Of course, unlike electrophoretic mobility, electric
polarizability cannot possess negative values. Comparison of
alteration tendencies of the values modules is important in
that case.
The amplitudes of the frequency and field strength
dependencies of the EOE indicate EOE decrease below PZC
and an increase above it. This is a widely observed behaviour
BIOTECHNOL. & BIOTECHNOL. EQ. 23/2009/SE XI ANNIVERSARY SCIENTIFIC CONFERENCE
SPECIAL EDITION/ON-LINE 120 YEARS OF ACADEMIC EDUCATION IN BIOLOGY
45 YEARS FACULTY OF BIOLOGY
867
3. in that kind of studies due to the changes in the electric
polarizability of the particles caused by the PE adsorption. So
it is not surprising.
The plateaus of the frequency dependencies (Fig. 2) begin
at 400 Hz both for uncoated particles and all colloid-PE
complexes at the pH and the ionic strength of the experiment.
Its upper boundary, however, shifts. For the uncoated
particles it is 10 kHz, for the complexes with 5·10-3
g.dm-3
NaCMC and below this concentration, it is 5 kHz. Above
5·10-3
g.dm-3
NaCMC the upper boundary of the frequency
plateaus gradually shrinks to 3 kHz. The EOE decreases after
the plateau frequencies. So does the relaxation frequency of
the coated particles. This is easy to be seen in the insetted
plot in Fig. 2 where the frequency dependences are
normalised to unity for better visualization. The plateau of an
aqueous γ-Al2O3 suspension, containing no added indifferent
electrolyte, is between 1 kHz and 10 kHz (3). So the lower
boundary of all the studied colloid solutions is shifted
towards the hertz frequency region. This result can be
observed both for the coated particles and the uncoated ones.
Therefore NaCMC adsorption is not the reason for this shift.
It must be due to the added low molecular electrolyte because
the suspensions are with changed ionic strength and pH by
comparison with the pure aqueous suspension.
Fig. 2. Electro-optical effects on electric field frequency of -Al2O3
suspensions at 340V, pH 6.0, ionic strength 2.5 10-4 mol.dm-3. NaCMC
concentrations (g.dm-3): ∎, no NaCMC; ○, 1·10-4; , 5·10-4; ⋆, 5·10-3; ,
1·10-2; , 5·10-2. Insetted: Electro-optical effects dependence on field
frequency represented by normalisation to unity: ▫, aqueous suspension of -
Al2O3.
The shift in the upper boundary of the frequency plateau
towards the lower frequencies, however, is observed just for
the suspensions containing coated particles. So this result
may be attributed to NaCMC adsorption.
Relaxation times detection at disorientation of the
particles after switching off the applied electric field is the
electro-optical way to detect the fact of adsorption (except the
electrophoresis). The adsorbed PE amounts enlarge the
particles dimensions, so they disorient slower and the decay
times increase proportionally to PE concentrations at constant
electric field intensity. In Fig. 3 the decay time changes with
electric field strength are presented.
As it is seen, the low concentrations of NaCMC – 1·10-
4
g.dm-3
and 5·10-4
g.dm-3
, do not change significantly the
relaxation times. The adsorbed amount of PE is too low and
the colloid particles dimensions do not change considerably.
The complexes with constant electrophoretic mobility display
significant increase in the particles sizes in comparison with
the ones at low PE concentrations. Surprisingly, the decay
times’ differencies of the suspensions containing low
NaCMC concentrations do not correspond to the differencies
between their concentration values. Similar tendency is also
observed in the case of the suspensions with the highest
NaCMC concentrations. Their decay time values are close to
one another whereas the concentration difference is half an
order. Only at low field strength, when the biggest particles
are orientated, a considerable difference can be noted in that
case. Analogous results were also obtained previously (3).
This discrepancy in the case of the low NaCMC
concentrations may be explained with the complex structure
of the oxide aggregates. Being fractals, build by numerous
individual particles stuck together, but not densely, they
possess cavities big enough to allow the macromolecules
chains to get inside and adsorb at the inner interface. So the
particle dimensions do not change as much as they would if
no cavities existed. Of course, the outer surface is much
more accessible, so the macromolecules adsorption at it is
most probable and further concentration increase, though,
leads to increase in the particles dimensions. The complexes
with constant electrophoretic mobility, practically do not
sense concentration changes because the NaCMC film at
their interface is maximally dense and the electrostatic
repulsion between the macromolecules in the film do not
allow adsorption of additional PE chains.
The EOE dependences on the electric field strength
(Fig. 3, insetted) are measured at 1 kHz – a value from the
plateaus of all the frequency dependences. The field strength
dependences show that maximally overcharged particles
manifest significantly lower EOE than the uncoated ones.
This also may be attributed to γ-Al2O3 structural
characteristics. PE amounts adsorbed at the outer surface,
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45 YEARS FACULTY OF BIOLOGY
868
4. responsible for the increase in the electric polarizability and
the EOE above the PZC, are not sufficient to reach the
polarizability values of the bare interfaces.
Fig. 3. Dependence of the γ-Al2O3 particles relaxation times on field intensity
at pH 6.0, ionic strength 2.5⋅10-4
mol.dm-3
, NaCMC concentrations (g.dm-3
):
∎, no NaCMC; ○, 1·10 ; ◆, 5·10 ; △, 1·10 ; ▶, 5·10 Insetted: The-4 -4 -2 -2
γ-Al2O3
suspensions EOE on. electric field intensity at the same experimental condi-
tions
The first concentration above the PZC – 5·10-3
g.dm-3
,
possesses hardly measurable EOE. It appears at values of the
electric field intensity at which the EOEs of the other
suspensions saturate so the electric polarizability of these
particles must be too close to zero to overleap the sensitivity
of the electro-optical device. Surprisingly, such a result is not
observed for the suspension containing 5·10-4
g.dm-3
NaCMC
although both concentration values are equally distant from
the PZC – half an order. The steady state EOE is better
achievable at the present experimental conditions than at
pH 4.5 (3) where at the maximal electric field intensities that
our electro-optical device can generate, the EOE
demonstrates just an approach to saturation. Apparently, this
result is due to the fact that at the two pH values (4.5 and 6.0)
the particles charge is different. Consequently, that inequality
is a reason for adsorption of unequal PE amounts causing
unequal electric polarizability of the colloid-PE complexes.
Thus, at constant electric field strength the lower
polarizability at pH 6.0 saturates, whereas the bigger one at
pH 4.5 does not.
Conclusions
In summary the following conclusions can be derived:
The NaCMC adsorption causes a decrease in the
relaxation frequency of the oxide particles.
The low molecular electrolyte present in the investigated
colloid solutions is a reason for the overall shift of the
frequency plateau towards the hertz region. It begins at
400 Hz instead at 1 kHz as in the case of aqueous oxide
suspension.
Colloid-PE complexes at the present experimental
conditions express an easily achievable steady-state EOE in
comparison with the previous investigation (3).
The increase in the relaxation times expresses
disproportional correlation with the concentration increase.
This observation suggests that the chains of the
macromolecules may penetrate into the cavities existing in
the γ-Al2O3 colloid particle and adsorb at their inner surfaces.
Acknowledgment
The author is grateful to Assoc. Prof. A.M. Zhivkov and Dr.
M. Buleva from the Rostislaw Kaischew Institute of Physical
Chemistry, Bulgarian Academy of Sciences for the help and
the stimulating discussions concerning the experimental work
and the interpretation. He is also grateful to Anna Y. Gyurova
for the wording of the article.
REFERENCES
1. Buleva M., Stoimenova M. (1991), Journal of Colloid
and Interface Science, 141, 426-432.
2. Decher G. (1997) Science, 277, 1232.
3. Hristov R.Pl. (2009) Investigation of carboxymethyl
cellulose adsorption on alumina nanoscale particle,
National conference with international participation
“Nature Sciences’2008”, Faculty of Nature Sciences,
University of Shоumen "Episkop K. Preslavski", in press
4. Rädler J., Kotlover I., Salditt T., Safiyna C. (1997)
Science, 275, 810.
5. Stoylov S.P. (1991) Colloid Electro-optics – theory,
techniques, applications, Colloid Science - Series of
Monographs 129, Academic Press Ltd, p. 120.
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