The document discusses a theoretical investigation of the tunable Donnan potential and electrokinetic flow in a biomimetic nanochannel functionalized with pH-regulated polyelectrolyte brushes. The study finds that the electrokinetic flow velocity can be tuned by modulating the Donnan potential with a nanofluidic field effect transistor under various solution properties like pH and salt concentration. The electrostatic gating effect on the Donnan potential depends significantly on the solution properties but insignificantly on the thickness of the polyelectrolyte brush layer.
Exploiting the potential of 2-((5-(4-(diphenylamino)- phenyl)thiophen-2-yl)me...Akinola Oyedele
A comprehensive experimental study is reported on the optical and electrical characteristics of 2-((5-(4-
(diphenylamino)phenyl)thiophen-2-yl)methylene)malononitrile (DPTMM) when used as molecular donor
in an organic solar cell (OSC) device structure.
The document summarizes a study on producing conductive poly(vinyl alcohol)/polyaniline (PVA/PANI) nanofibers through electrospinning. PVA/PANI solutions with weight ratios of 92:8 and 84:16 were electrospun to form nanofibers. Scanning electron microscopy showed the average fiber diameters decreased with increasing PANI content. Fourier transform infrared spectroscopy confirmed the presence of both PVA and PANI in the blended fibers. Conductivity measurements found the 92:8 PVA/PANI nanofibers had an electrical conductivity of 2.3x10-3 S/cm, higher than pure PVA nanofibers. However, 84:16 P
1. Pt nanoparticles were decorated on carbon nano onions (CNOs) to investigate their potential for supercapacitors and field emission applications.
2. Electrochemical tests found the specific capacitance of Pt-CNOs was 342.5 F/g, over six times higher than pristine CNOs, due to easier electrolyte access in the active material.
3. Density functional theory calculations revealed an enhanced density of states near the Fermi level for Pt-CNOs.
4. Field emission measurements showed Pt-CNOs achieved a current density of 0.63 mA/cm2 at 4.5 V/mm, higher than pristine CNOs, attributed to
The document investigates the physical aging of carbon nanotube/PEDOT:PSS nanocomposite thin films with different multi-walled carbon nanotube (MWCNT) concentrations using electrochemical impedance spectroscopy. The key findings are:
1) The aging rate and change in electrical resistance decreases with increasing MWCNT concentration, from 21.2% change for pure PEDOT:PSS to 6.8% change at 0.1 wt.% MWCNT.
2) MWCNTs restrict the mobility of polymer chains near the MWCNT/PEDOT:PSS interface, reducing the aging rate.
3) An equivalent circuit model with tunneling resistance and capacitance components fits the imped
Study of hlgs and transfer integrals of dna bases for investigating charge co...IAEME Publication
This document summarizes a study investigating the charge transport properties of DNA bases through calculation of their molecular orbital energies, transfer integrals, and HOMO-LUMO gaps. The key points are:
1) Molecular orbital energies of adenine, guanine, thymine and cytosine were calculated using Gaussian 03 to derive transfer integrals and HOMO-LUMO gaps.
2) Transfer integrals indicate guanine has the highest probability for hole transport while cytosine has the highest for electron transport.
3) All DNA bases have HOMO-LUMO gaps much larger than thermal energy, showing they are suitable for use in nanoelectronic devices at room temperature.
International Journal of Engineering Research and Development (IJERD)IJERD Editor
This summary provides the key details about the document in 3 sentences:
The document analyzes the surface tension of osteoblast cells in a microchip. It studies how electrical pulses, electrode configuration, microchannel dimensions, and suspension media properties affect the surface tension of the inner and outer layers of osteoblast cell membranes. The document develops a 3D microfluidic model and electrical circuit model to investigate the membrane surface tension and how it is impacted by various parameters like pulse characteristics, electrodes, microchannel, and suspension media.
OFET Preparation by Lithography and Thin Film Depositions ProcessTELKOMNIKA JOURNAL
This document summarizes research on preparing an organic field-effect transistor (OFET) using lithography and thin film deposition processes. The key points are:
1. An OFET was prepared with a bottom contact structure using copper phthalocyanine as the active layer deposited via vacuum evaporation on a silicon substrate.
2. Lithography was used to pattern gold source and drain electrodes, followed by deposition of the copper phthalocyanine thin film.
3. Electrical characterization of the completed OFET showed current increasing with drain voltage and gate voltage, indicating p-type accumulation mode operation, though saturation was not observed possibly due to a high threshold voltage.
Exploiting the potential of 2-((5-(4-(diphenylamino)- phenyl)thiophen-2-yl)me...Akinola Oyedele
A comprehensive experimental study is reported on the optical and electrical characteristics of 2-((5-(4-
(diphenylamino)phenyl)thiophen-2-yl)methylene)malononitrile (DPTMM) when used as molecular donor
in an organic solar cell (OSC) device structure.
The document summarizes a study on producing conductive poly(vinyl alcohol)/polyaniline (PVA/PANI) nanofibers through electrospinning. PVA/PANI solutions with weight ratios of 92:8 and 84:16 were electrospun to form nanofibers. Scanning electron microscopy showed the average fiber diameters decreased with increasing PANI content. Fourier transform infrared spectroscopy confirmed the presence of both PVA and PANI in the blended fibers. Conductivity measurements found the 92:8 PVA/PANI nanofibers had an electrical conductivity of 2.3x10-3 S/cm, higher than pure PVA nanofibers. However, 84:16 P
1. Pt nanoparticles were decorated on carbon nano onions (CNOs) to investigate their potential for supercapacitors and field emission applications.
2. Electrochemical tests found the specific capacitance of Pt-CNOs was 342.5 F/g, over six times higher than pristine CNOs, due to easier electrolyte access in the active material.
3. Density functional theory calculations revealed an enhanced density of states near the Fermi level for Pt-CNOs.
4. Field emission measurements showed Pt-CNOs achieved a current density of 0.63 mA/cm2 at 4.5 V/mm, higher than pristine CNOs, attributed to
The document investigates the physical aging of carbon nanotube/PEDOT:PSS nanocomposite thin films with different multi-walled carbon nanotube (MWCNT) concentrations using electrochemical impedance spectroscopy. The key findings are:
1) The aging rate and change in electrical resistance decreases with increasing MWCNT concentration, from 21.2% change for pure PEDOT:PSS to 6.8% change at 0.1 wt.% MWCNT.
2) MWCNTs restrict the mobility of polymer chains near the MWCNT/PEDOT:PSS interface, reducing the aging rate.
3) An equivalent circuit model with tunneling resistance and capacitance components fits the imped
Study of hlgs and transfer integrals of dna bases for investigating charge co...IAEME Publication
This document summarizes a study investigating the charge transport properties of DNA bases through calculation of their molecular orbital energies, transfer integrals, and HOMO-LUMO gaps. The key points are:
1) Molecular orbital energies of adenine, guanine, thymine and cytosine were calculated using Gaussian 03 to derive transfer integrals and HOMO-LUMO gaps.
2) Transfer integrals indicate guanine has the highest probability for hole transport while cytosine has the highest for electron transport.
3) All DNA bases have HOMO-LUMO gaps much larger than thermal energy, showing they are suitable for use in nanoelectronic devices at room temperature.
International Journal of Engineering Research and Development (IJERD)IJERD Editor
This summary provides the key details about the document in 3 sentences:
The document analyzes the surface tension of osteoblast cells in a microchip. It studies how electrical pulses, electrode configuration, microchannel dimensions, and suspension media properties affect the surface tension of the inner and outer layers of osteoblast cell membranes. The document develops a 3D microfluidic model and electrical circuit model to investigate the membrane surface tension and how it is impacted by various parameters like pulse characteristics, electrodes, microchannel, and suspension media.
OFET Preparation by Lithography and Thin Film Depositions ProcessTELKOMNIKA JOURNAL
This document summarizes research on preparing an organic field-effect transistor (OFET) using lithography and thin film deposition processes. The key points are:
1. An OFET was prepared with a bottom contact structure using copper phthalocyanine as the active layer deposited via vacuum evaporation on a silicon substrate.
2. Lithography was used to pattern gold source and drain electrodes, followed by deposition of the copper phthalocyanine thin film.
3. Electrical characterization of the completed OFET showed current increasing with drain voltage and gate voltage, indicating p-type accumulation mode operation, though saturation was not observed possibly due to a high threshold voltage.
Electrochemical behaviorof carbon paste electrode modified with Carbon Nanofi...IJERA Editor
The electrochemical behavior of carbon paste electrode modified with carbon nanofibers has been studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scaning electron microscopy. The response of modified electrodein ferroferricyanidesolutionshows reversible behavior and significant increment in current value compared to the bare CPE indicating that CNFs act as efficient electron mediator to catalyze reactions at the surface. The modified electrode has been used to study the electrochemical response of bisphenol Ausing different electrochemical techniques such as cyclic voltammetry, linear sweep voltammetry, differential pulse voltammetry and square wave voltammetry. The oxidation peak of BPA was observed at about 0.53 V in phosphate buffer solution at pH 6.7. The oxidation peak current of BPA varied linearly with concentration over a wide range of 5µmol L-1 to 400 µmol L-1 and the detection limit of this method was found to be 0.55 µmol L
Biophysical Journal Dna Translocation Governed By Interactions With Solid Sta...thewaves21
This study investigates the dynamics of DNA translocation through solid-state nanopores between 2.7-5 nm in diameter. The researchers find that decreasing the pore diameter from 5 to 2.7 nm increases translocation times by an order of magnitude. Translocation times also exhibit a steep temperature dependence, nearly three times larger than expected based on viscosity. Mean translocation times scale with DNA length as two power laws, depending on the length of the DNA. Surprisingly, they also find a transition in the fraction of ion current blocked by DNA, from length-independent for short DNA to length-dependent for longer DNA. The results suggest that interactions between DNA and the nanopore walls dominate translocation dynamics in small pores, slowing
This document contains the curriculum vitae of Nihar R. Pradhan, who is currently a postdoctoral research associate at the National High Magnetic Field Laboratory in Tallahassee, Florida. His research focuses on nanotechnology, including the synthesis and characterization of two-dimensional materials like transition metal dichalcogenides. Some of his work involves fabricating field-effect transistors from these materials and investigating their electrical and optical properties. He has a Ph.D. in Physics from Worcester Polytechnic Institute and several years of experience as a postdoctoral researcher.
Pentacene-Based Organic Field-Effect Transistors: Analytical Model and Simula...IDES Editor
Organic Field-Effect Transistors, OFETs, attract
much interest recently and their proficiency and hence
applications are being enhanced increasingly. However, only
analytical model of old field-effect transistors, developed for
silicon-based transistors, and their relevant numerical
analyses have been used for such devices, so far. Increasing
precision of such models and numerical methods are essential
now in order to modify OFETs and propose more effective
models and methods. This study pegs at comparing current
analytical model, simulation methods and experiment data
and their fitness with each other. Certainly, four aspects of
results of three abovementioned approaches were examined
comparatively: sub-threshold slope, on-state drain current,
threshold voltage and carrier mobility. We embark to analyze
related experiment data of OFETs made by pentacene, as the
organic material, along with various organic gate insulators
including CyEP, PVP, PMMA, Parylene-C and Polyimide and
then to offer their results, comparatively.
Effect of multi wall carbon nanotube content on the electrical and rheologica...Bambang Afrinaldi
The document investigates the effect of multi-wall carbon nanotube (MWCNT) content on the electrical and rheological properties of polypropylene-based nanocomposites. It finds that the electrical percolation threshold occurs at 1.3 wt% MWCNT content, where the electrical conductivity increases by several orders of magnitude. The rheological percolation threshold is found to occur between 1.2-1.4 wt% MWCNT content, where the storage modulus significantly increases. Well dispersion of MWCNT in the polymer matrix is observed through SEM analysis.
This document describes the fabrication and testing of a high-performance tandem organic solar cell with novel active layers. It utilizes a record-efficiency polymer, PBTI3T, in combination with other polymers like PTB7 and PSBTBT-Si to further enhance efficiency. Absorption spectra of the polymers show offset peaks that minimize spectral overlap when combined in a tandem device. Tandem devices were fabricated with PBTI3T and either PTB7 or PSBTBT-Si as the active layers. Results showed one of the highest open-circuit voltages reported and an overall power conversion efficiency above 6%, demonstrating the potential of tandem organic photovoltaics using high-efficiency polymers.
This document discusses applications of carbon nanotubes for drug delivery systems. Carbon nanotubes have unique properties like high surface area and thermal conductivity that make them promising candidates for drug transport and delivery. They can be functionalized for biomedical applications through covalent and non-covalent methods. Carbon nanotubes show potential as drug carriers for cancer treatment, transdermal drug delivery, cardiac regulation, and tissue regeneration. Different synthesis techniques like arc discharge, laser ablation, and chemical vapor deposition are used to produce carbon nanotubes in large quantities.
Electrodeposited pt on three dimensional interconnected graphene as a free st...tshankar20134
The document summarizes research on using a three-dimensional interconnected graphene structure as an electrode support for platinum nanoparticles for fuel cell applications. Key points:
1) Graphene was grown into a 3D foam-like structure using chemical vapor deposition on a nickel foam template, creating a seamless porous structure with high surface area and conductivity.
2) Platinum nanoparticles were deposited on the 3D graphene using pulsed electrodeposition, allowing control over particle size and uniform dispersion.
3) The 3D graphene with platinum nanoparticles showed improved catalytic activity for methanol oxidation compared to carbon fibers, due to the unique 3D structure, high surface area, and high conductivity of the graphene support.
This study focuses on optimizing a polymer membrane nanopore platform for DNA sequencing by examining its interactions with the protein gramicidin A. The polymer membrane must maintain stability under an applied voltage to successfully incorporate a protein nanopore for sensing. Gramicidin A is used as a molecular force probe to understand how the polymer's hydrophobic region affects the protein's conformation. Specifically, the polymer's forces and their impact on gramicidin A's channel and non-channel states will be quantified. Ultimately, tailoring the polymer to achieve the most stable, low-noise protein insertion could enable fast, efficient DNA sequencing through a nanopore array.
This document discusses core holders used to test rock core samples from underground reservoirs. It describes how core holders apply radial and axial pressure to core samples to simulate reservoir conditions and allow for permeability and other tests. It provides details on common types of core holders including Hassler, biaxial, and triaxial, and tests they can perform like permeability, porosity, and relative permeability. It also notes some limitations of using core samples including non-representative rocks and incomplete core recovery.
The document discusses electric field, potential, and energy. It defines electric potential as the work done to move a unit positive charge from infinity to a point in an electric field. Electric potential is a scalar quantity measured in volts. Equipotentials are regions in space where the electric potential has a constant value, forming equipotential surfaces or lines. Analogies are drawn between electric and gravitational fields, such as both following inverse square laws and having field lines and equipotentials.
Electric potential difference (voltage)Jean Tralala
The document discusses concepts related to work, energy, and electric fields. It defines key terms like gravitational potential energy, gravitational potential, electric potential energy, electric potential, and electric potential difference. Gravitational potential energy and electric potential energy are defined as the energy stored in an object due to its position in a gravitational or electric field. Gravitational potential and electric potential refer to the potential energy per unit mass or charge. The electric potential difference between two points is the change in electric potential energy when a charge is moved between those points.
7.2 relationship between electric current and potential differenceAdlishah Risal Bili
Malaysia SPM syllabus Form 5 Physics Chapter 7. Part 2: Electric Current and Potential Difference
::Slide-making service available. For more info, contact coolcikgu@gmail.com::
Contact us for your presentation design needs: lesson / teaching, wedding, seminar, workshop, client pitch etc.
This document covers potential difference, power, and resistance in electrical circuits. It defines potential difference as another term for voltage and describes how batteries provide potential difference to allow the conversion of electrical energy into other forms like light. It gives examples of electrical energy being converted to energy in a toaster or heat in a wire. It defines power as the rate of doing work, measured in watts, and provides the formulas to calculate power as P=VI, P=I^2R, and P=V^2/R. It describes using data loggers and circuits to measure voltage, current, and calculate power, and how resistance affects current in a circuit. Components that obey Ohm's law are identified.
Ch19 Electric Potential Energy and Electric PotentialScott Thomas
This document provides learning objectives and content about electric potential energy and electric potential. It discusses key concepts such as electric field, electric potential, equipotential surfaces, and capacitors. Specifically, it defines electric potential as electric potential energy per unit charge. It also explains that equipotential surfaces represent positions of equal electric potential and that the electric field is perpendicular to equipotential surfaces. Finally, it introduces capacitors as devices that can store electric potential energy between two conductors, such as the plates of a parallel plate capacitor, and how dielectrics are used to increase a capacitor's capacitance.
The document is a set of lecture notes on electromagnetic theory created by Akshansh Chaudhary based on course content from Dr. K.K. Singh. It contains over 150 pages of content on the subject along with diagrams and examples. The notes were created for educational purposes and are provided without warranty for accuracy. All rights to the content are reserved by the creator.
This document provides an overview of zeta potential, including:
- Zeta potential is the electric potential at the boundary between the double layer and bulk solution surrounding charged particles suspended in a colloidal system.
- Factors that affect zeta potential include pH, thickness of the double layer, and concentration of formulation components.
- Zeta potential is important for predicting particle interactions and stability in colloidal systems based on DLVO theory of electrostatic repulsion and van der Waals attraction.
- Measurement techniques include electrophoresis and electroacoustic methods to determine particle mobility from which zeta potential is calculated.
The document discusses electromagnetic theory, including Coulomb's law, electric field intensity, Gauss's law, electric flux density, electric potential, polarization in dielectrics, boundary conditions, Biot-Savart's law, Ampere's circuit law, magnetic flux density, Faraday's law, and motional EMF. Key topics covered include the relationship between electric and magnetic fields, conditions for electric and magnetic fields at boundaries between media, and how changing magnetic fields induce electromotive forces based on Faraday's law of induction.
This document discusses the concept of zeta potential, which is the electric potential at the boundary between the particle surface and the surrounding liquid. It defines zeta potential and explains factors that affect it such as pH and ionic strength. The document also describes how zeta potential is measured using electrokinetic phenomena like electrophoresis. Finally, it discusses applications of zeta potential measurement and DLVO theory of colloid stability.
Ion Channel Simulations for Potassium, Sodium, Calcium, and Chloride Channels...Iowa State University
Computer simulations of realistic ion channel structures have always been challenging and a subject of rigorous study. Simulations based on continuum electrostatics have proven to be computationally cheap and reasonably accurate in predicting a channel's behavior. In this paper we discuss the use of a device simulator, SILVACO, to build a solid-state model for KcsA channel and study its steady-state response. SILVACO is a well-established program, typically used by electrical engineers to simulate the process flow and electrical characteristics of solid-state devices. By employing this simulation program, we have presented an alternative computing platform for performing ion channel simulations, besides the known methods of writing codes in programming languages. With the ease of varying the different parameters in the channel's vestibule and the ability of incorporating surface charges, we have shown the wide-ranging possibilities of using a device simulator for ion channel simulations. Our simulated results closely agree with the experimental data, validating our model.
https://www.sciencedirect.com/science/article/abs/pii/S0169260706002276
Computer simulations of realistic ion channel structures have always been challenging and
a subject of rigorous study. Simulations based on continuum electrostatics have proven to
be computationally cheap and reasonably accurate in predicting a channel’s behavior. In
this paper we discuss the use of a device simulator, SILVACO, to build a solid-state model for
KcsA channel and study its steady-state response. SILVACO is a well-established program,
typically used by electrical engineers to simulate the process flow and electrical characteristics
of solid-state devices. By employing this simulation program, we have presented an
alternative computing platform for performing ion channel simulations, besides the known
methods of writing codes in programming languages. With the ease of varying the different
parameters in the channel’s vestibule and the ability of incorporating surface charges,
we have shown the wide-ranging possibilities of using a device simulator for ion channel
simulations. Our simulated results closely agree with the experimental data, validating our
model.
Ion Channel Fluctuations in Transmemembrane Proteins within Cell MembranesIowa State University
The transmembrane proteins known as ion channels play a role in controlling and preserving the ionic concentrations across the cell membrane. Modeling the flux of ions in and out of these channels on an atomic level is essential for understanding several neurological diseases and related pharmaceutical discoveries. Recent experimental research has provided information on the channel's physical structure which can be used to create realistic ion transport models. Different trajectories exist for the ions entering the channel, each having its own probability of occurrence. Variables that measure these trajectories are the translocation and return probabilities, average lifetime, and spectral density of the ion number fluctuations. Theoretical analysis of ion transport has been restricted to low-resolution continuum diffusion-based or kinetic-based models which do not consider important factors that have an effect on ionic conduction. This paper extends previous models by an electro-diffusion model which takes into account the effects of electric fields, energy barriers, and rate-limited association/dissociation of ions with surface charges present inside the channel. Derived from the analytical model are the survival probability and spectral density.
Electrochemical behaviorof carbon paste electrode modified with Carbon Nanofi...IJERA Editor
The electrochemical behavior of carbon paste electrode modified with carbon nanofibers has been studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scaning electron microscopy. The response of modified electrodein ferroferricyanidesolutionshows reversible behavior and significant increment in current value compared to the bare CPE indicating that CNFs act as efficient electron mediator to catalyze reactions at the surface. The modified electrode has been used to study the electrochemical response of bisphenol Ausing different electrochemical techniques such as cyclic voltammetry, linear sweep voltammetry, differential pulse voltammetry and square wave voltammetry. The oxidation peak of BPA was observed at about 0.53 V in phosphate buffer solution at pH 6.7. The oxidation peak current of BPA varied linearly with concentration over a wide range of 5µmol L-1 to 400 µmol L-1 and the detection limit of this method was found to be 0.55 µmol L
Biophysical Journal Dna Translocation Governed By Interactions With Solid Sta...thewaves21
This study investigates the dynamics of DNA translocation through solid-state nanopores between 2.7-5 nm in diameter. The researchers find that decreasing the pore diameter from 5 to 2.7 nm increases translocation times by an order of magnitude. Translocation times also exhibit a steep temperature dependence, nearly three times larger than expected based on viscosity. Mean translocation times scale with DNA length as two power laws, depending on the length of the DNA. Surprisingly, they also find a transition in the fraction of ion current blocked by DNA, from length-independent for short DNA to length-dependent for longer DNA. The results suggest that interactions between DNA and the nanopore walls dominate translocation dynamics in small pores, slowing
This document contains the curriculum vitae of Nihar R. Pradhan, who is currently a postdoctoral research associate at the National High Magnetic Field Laboratory in Tallahassee, Florida. His research focuses on nanotechnology, including the synthesis and characterization of two-dimensional materials like transition metal dichalcogenides. Some of his work involves fabricating field-effect transistors from these materials and investigating their electrical and optical properties. He has a Ph.D. in Physics from Worcester Polytechnic Institute and several years of experience as a postdoctoral researcher.
Pentacene-Based Organic Field-Effect Transistors: Analytical Model and Simula...IDES Editor
Organic Field-Effect Transistors, OFETs, attract
much interest recently and their proficiency and hence
applications are being enhanced increasingly. However, only
analytical model of old field-effect transistors, developed for
silicon-based transistors, and their relevant numerical
analyses have been used for such devices, so far. Increasing
precision of such models and numerical methods are essential
now in order to modify OFETs and propose more effective
models and methods. This study pegs at comparing current
analytical model, simulation methods and experiment data
and their fitness with each other. Certainly, four aspects of
results of three abovementioned approaches were examined
comparatively: sub-threshold slope, on-state drain current,
threshold voltage and carrier mobility. We embark to analyze
related experiment data of OFETs made by pentacene, as the
organic material, along with various organic gate insulators
including CyEP, PVP, PMMA, Parylene-C and Polyimide and
then to offer their results, comparatively.
Effect of multi wall carbon nanotube content on the electrical and rheologica...Bambang Afrinaldi
The document investigates the effect of multi-wall carbon nanotube (MWCNT) content on the electrical and rheological properties of polypropylene-based nanocomposites. It finds that the electrical percolation threshold occurs at 1.3 wt% MWCNT content, where the electrical conductivity increases by several orders of magnitude. The rheological percolation threshold is found to occur between 1.2-1.4 wt% MWCNT content, where the storage modulus significantly increases. Well dispersion of MWCNT in the polymer matrix is observed through SEM analysis.
This document describes the fabrication and testing of a high-performance tandem organic solar cell with novel active layers. It utilizes a record-efficiency polymer, PBTI3T, in combination with other polymers like PTB7 and PSBTBT-Si to further enhance efficiency. Absorption spectra of the polymers show offset peaks that minimize spectral overlap when combined in a tandem device. Tandem devices were fabricated with PBTI3T and either PTB7 or PSBTBT-Si as the active layers. Results showed one of the highest open-circuit voltages reported and an overall power conversion efficiency above 6%, demonstrating the potential of tandem organic photovoltaics using high-efficiency polymers.
This document discusses applications of carbon nanotubes for drug delivery systems. Carbon nanotubes have unique properties like high surface area and thermal conductivity that make them promising candidates for drug transport and delivery. They can be functionalized for biomedical applications through covalent and non-covalent methods. Carbon nanotubes show potential as drug carriers for cancer treatment, transdermal drug delivery, cardiac regulation, and tissue regeneration. Different synthesis techniques like arc discharge, laser ablation, and chemical vapor deposition are used to produce carbon nanotubes in large quantities.
Electrodeposited pt on three dimensional interconnected graphene as a free st...tshankar20134
The document summarizes research on using a three-dimensional interconnected graphene structure as an electrode support for platinum nanoparticles for fuel cell applications. Key points:
1) Graphene was grown into a 3D foam-like structure using chemical vapor deposition on a nickel foam template, creating a seamless porous structure with high surface area and conductivity.
2) Platinum nanoparticles were deposited on the 3D graphene using pulsed electrodeposition, allowing control over particle size and uniform dispersion.
3) The 3D graphene with platinum nanoparticles showed improved catalytic activity for methanol oxidation compared to carbon fibers, due to the unique 3D structure, high surface area, and high conductivity of the graphene support.
This study focuses on optimizing a polymer membrane nanopore platform for DNA sequencing by examining its interactions with the protein gramicidin A. The polymer membrane must maintain stability under an applied voltage to successfully incorporate a protein nanopore for sensing. Gramicidin A is used as a molecular force probe to understand how the polymer's hydrophobic region affects the protein's conformation. Specifically, the polymer's forces and their impact on gramicidin A's channel and non-channel states will be quantified. Ultimately, tailoring the polymer to achieve the most stable, low-noise protein insertion could enable fast, efficient DNA sequencing through a nanopore array.
This document discusses core holders used to test rock core samples from underground reservoirs. It describes how core holders apply radial and axial pressure to core samples to simulate reservoir conditions and allow for permeability and other tests. It provides details on common types of core holders including Hassler, biaxial, and triaxial, and tests they can perform like permeability, porosity, and relative permeability. It also notes some limitations of using core samples including non-representative rocks and incomplete core recovery.
The document discusses electric field, potential, and energy. It defines electric potential as the work done to move a unit positive charge from infinity to a point in an electric field. Electric potential is a scalar quantity measured in volts. Equipotentials are regions in space where the electric potential has a constant value, forming equipotential surfaces or lines. Analogies are drawn between electric and gravitational fields, such as both following inverse square laws and having field lines and equipotentials.
Electric potential difference (voltage)Jean Tralala
The document discusses concepts related to work, energy, and electric fields. It defines key terms like gravitational potential energy, gravitational potential, electric potential energy, electric potential, and electric potential difference. Gravitational potential energy and electric potential energy are defined as the energy stored in an object due to its position in a gravitational or electric field. Gravitational potential and electric potential refer to the potential energy per unit mass or charge. The electric potential difference between two points is the change in electric potential energy when a charge is moved between those points.
7.2 relationship between electric current and potential differenceAdlishah Risal Bili
Malaysia SPM syllabus Form 5 Physics Chapter 7. Part 2: Electric Current and Potential Difference
::Slide-making service available. For more info, contact coolcikgu@gmail.com::
Contact us for your presentation design needs: lesson / teaching, wedding, seminar, workshop, client pitch etc.
This document covers potential difference, power, and resistance in electrical circuits. It defines potential difference as another term for voltage and describes how batteries provide potential difference to allow the conversion of electrical energy into other forms like light. It gives examples of electrical energy being converted to energy in a toaster or heat in a wire. It defines power as the rate of doing work, measured in watts, and provides the formulas to calculate power as P=VI, P=I^2R, and P=V^2/R. It describes using data loggers and circuits to measure voltage, current, and calculate power, and how resistance affects current in a circuit. Components that obey Ohm's law are identified.
Ch19 Electric Potential Energy and Electric PotentialScott Thomas
This document provides learning objectives and content about electric potential energy and electric potential. It discusses key concepts such as electric field, electric potential, equipotential surfaces, and capacitors. Specifically, it defines electric potential as electric potential energy per unit charge. It also explains that equipotential surfaces represent positions of equal electric potential and that the electric field is perpendicular to equipotential surfaces. Finally, it introduces capacitors as devices that can store electric potential energy between two conductors, such as the plates of a parallel plate capacitor, and how dielectrics are used to increase a capacitor's capacitance.
The document is a set of lecture notes on electromagnetic theory created by Akshansh Chaudhary based on course content from Dr. K.K. Singh. It contains over 150 pages of content on the subject along with diagrams and examples. The notes were created for educational purposes and are provided without warranty for accuracy. All rights to the content are reserved by the creator.
This document provides an overview of zeta potential, including:
- Zeta potential is the electric potential at the boundary between the double layer and bulk solution surrounding charged particles suspended in a colloidal system.
- Factors that affect zeta potential include pH, thickness of the double layer, and concentration of formulation components.
- Zeta potential is important for predicting particle interactions and stability in colloidal systems based on DLVO theory of electrostatic repulsion and van der Waals attraction.
- Measurement techniques include electrophoresis and electroacoustic methods to determine particle mobility from which zeta potential is calculated.
The document discusses electromagnetic theory, including Coulomb's law, electric field intensity, Gauss's law, electric flux density, electric potential, polarization in dielectrics, boundary conditions, Biot-Savart's law, Ampere's circuit law, magnetic flux density, Faraday's law, and motional EMF. Key topics covered include the relationship between electric and magnetic fields, conditions for electric and magnetic fields at boundaries between media, and how changing magnetic fields induce electromotive forces based on Faraday's law of induction.
This document discusses the concept of zeta potential, which is the electric potential at the boundary between the particle surface and the surrounding liquid. It defines zeta potential and explains factors that affect it such as pH and ionic strength. The document also describes how zeta potential is measured using electrokinetic phenomena like electrophoresis. Finally, it discusses applications of zeta potential measurement and DLVO theory of colloid stability.
Ion Channel Simulations for Potassium, Sodium, Calcium, and Chloride Channels...Iowa State University
Computer simulations of realistic ion channel structures have always been challenging and a subject of rigorous study. Simulations based on continuum electrostatics have proven to be computationally cheap and reasonably accurate in predicting a channel's behavior. In this paper we discuss the use of a device simulator, SILVACO, to build a solid-state model for KcsA channel and study its steady-state response. SILVACO is a well-established program, typically used by electrical engineers to simulate the process flow and electrical characteristics of solid-state devices. By employing this simulation program, we have presented an alternative computing platform for performing ion channel simulations, besides the known methods of writing codes in programming languages. With the ease of varying the different parameters in the channel's vestibule and the ability of incorporating surface charges, we have shown the wide-ranging possibilities of using a device simulator for ion channel simulations. Our simulated results closely agree with the experimental data, validating our model.
https://www.sciencedirect.com/science/article/abs/pii/S0169260706002276
Computer simulations of realistic ion channel structures have always been challenging and
a subject of rigorous study. Simulations based on continuum electrostatics have proven to
be computationally cheap and reasonably accurate in predicting a channel’s behavior. In
this paper we discuss the use of a device simulator, SILVACO, to build a solid-state model for
KcsA channel and study its steady-state response. SILVACO is a well-established program,
typically used by electrical engineers to simulate the process flow and electrical characteristics
of solid-state devices. By employing this simulation program, we have presented an
alternative computing platform for performing ion channel simulations, besides the known
methods of writing codes in programming languages. With the ease of varying the different
parameters in the channel’s vestibule and the ability of incorporating surface charges,
we have shown the wide-ranging possibilities of using a device simulator for ion channel
simulations. Our simulated results closely agree with the experimental data, validating our
model.
Ion Channel Fluctuations in Transmemembrane Proteins within Cell MembranesIowa State University
The transmembrane proteins known as ion channels play a role in controlling and preserving the ionic concentrations across the cell membrane. Modeling the flux of ions in and out of these channels on an atomic level is essential for understanding several neurological diseases and related pharmaceutical discoveries. Recent experimental research has provided information on the channel's physical structure which can be used to create realistic ion transport models. Different trajectories exist for the ions entering the channel, each having its own probability of occurrence. Variables that measure these trajectories are the translocation and return probabilities, average lifetime, and spectral density of the ion number fluctuations. Theoretical analysis of ion transport has been restricted to low-resolution continuum diffusion-based or kinetic-based models which do not consider important factors that have an effect on ionic conduction. This paper extends previous models by an electro-diffusion model which takes into account the effects of electric fields, energy barriers, and rate-limited association/dissociation of ions with surface charges present inside the channel. Derived from the analytical model are the survival probability and spectral density.
The Effects of Nano Fillers on Space Charge Distribution in Cross-Linked Poly...IJECEIAES
The performance of polymeric insulation will be distorted by the accumulation of space charge. This will lead to local electric field enhancement within the insulation material that can cause degradation and electrical breakdown. The introduction of nanofillers in the insulation material is expected to reduce the space charge effect. However, there is a need to analyze potential nanofillers to determine the best option. Therefore, the objective of this research work is to examine two types of nanofillers for Cross-Linked Polyethylene (XLPE); Zinc Oxide (ZnO) and Acrylic (PA40). The effects of these nanofillers were measured using the Pulsed-Electro Acoustic (PEA) method. The development of space charge is observed at three different DC voltage levels in room temperature. The results show that hetero charge distribution is dominant in pure XLPE materials. The use of both nanofiller types have significant effect in decreasing the space charge accumulation. With nanofillers, the charge profile changed to homo-charge distribution, suppressing the space charge formation. Comparison between both the nanofillers show that PA40 has better suppression performance than ZnO.
1) Electrogenic pumps like the Na+/K+ ATPase transport ions across membranes using energy from ATP hydrolysis. This leads to a net movement of charge across the membrane.
2) Early models assumed passive ion diffusion established ion gradients, but problems arose. Equations were developed but inconsistencies emerged when applying them to plant cells.
3) The mechanism of the Na+/K+ ATPase involves ions binding deep within the protein and moving through access channels to binding sites. Transient currents from external ions like K+ and Na+ moving through these channels have been measured.
The document discusses capillary electrophoresis (CE), including its key terminology, instrumentation, flow dynamics, and factors that affect separation efficiency such as capillary diameter, voltage, and temperature. CE uses narrow capillaries to perform high-efficiency separations of charged molecules. When an electric field is applied, electroosmotic flow and electrophoretic migration move solutes through the capillary at different rates depending on their size and charge. Precise temperature control and optimization of factors like voltage and capillary diameter are important for achieving high resolution separations.
Conducting polymer based flexible super capacitors [autosaved]Jishana Basheer
Conducting polymers have potential in flexible supercapacitors due to their redox properties. Polyaniline, polypyrrole and polythiophene are promising conducting polymers. Graphene composites with these polymers improve performance by preventing aggregation and enabling fast ion transport. Future work aims to develop ternary composites and asymmetric capacitors to further increase energy density without sacrificing power. Conducting polymers work best in asymmetric configurations using different polymers or a polymer-carbon composite to expand the operating voltage window.
Organic field-effect transistors (OFETs) use organic semiconductors like pentacene that can be deposited through low-cost solution processing. OFETs have the potential for applications requiring flexibility and large-area coverage. Pentacene has shown high carrier mobility, with mobilities on par with amorphous silicon in the best OFETs. While progress has been made, understanding charge transport and developing n-type and ambipolar materials remains an area of ongoing research to further improve organic electronics.
Molecular Mean-Field Theory of Ionic Solutions: a Poisson-Nernst-Planck-Biker...Bob Eisenberg
We have developed a molecular mean-field theory — fourth-order Poisson-
Nernst-Planck-Bikerman theory — for modeling ionic and water flows in biological ion channels
by treating ions and water molecules of any volume and shape with interstitial voids,
polarization of water, and ion-ion and ion-water correlations. The theory can also be used to
study thermodynamic and electrokinetic properties of electrolyte solutions in batteries, fuel
cells, nanopores, porous media including cement, geothermal brines, the oceanic system, etc.
The theory can compute electric and steric energies from all atoms in a protein and all ions
and water molecules in a channel pore while keeping electrolyte solutions in the extra- and
intracellular baths as a continuum dielectric medium with complex properties that mimic
experimental data. The theory has been verified with experiments and molecular dynamics
data from the gramicidin A channel, L-type calcium channel, potassium channel, and
sodium/calcium exchanger with real structures from the Protein Data Bank. It was also
verified with the experimental or Monte Carlo data of electric double-layer differential capacitance
and ion activities in aqueous electrolyte solutions. We give an in-depth review of
the literature about the most novel properties of the theory, namely, Fermi distributions of
water and ions as classical particles with excluded volumes and dynamic correlations that
depend on salt concentration, composition, temperature, pressure, far-field boundary conditions
etc. in a complex and complicated way as reported in a wide range of experiments.
The dynamic correlations are self-consistent output functions from a fourth-order differential
operator that describes ion-ion and ion-water correlations, the dielectric response (permit2
tivity) of ionic solutions, and the polarization of water molecules with a single correlation
length parameter.
1. INTRODUCTION
Water and ions give life. Their electrostatic and kinetic interactions play essential roles
in biological and chemical systems such as DNA, proteins, ion channels, cell membranes,
2014-Nitrogen-doped hollow activated carbon nanofibers as high.pdfAshirvathamD
This document summarizes research on nitrogen-doped hollow activated carbon nanofibers (HACNFs) as electrode materials for supercapacitors. Key findings include:
1) HACNFs were prepared via concentric electrospinning and NH3 activation, resulting in a unique hollow structure and high nitrogen doping (up to 8.2%).
2) The HACNFs exhibited a high specific capacitance of 197 F/g, 1.33 times that of solid nanofibers, due to their hollow architecture and nitrogen doping.
3) The HACNFs also demonstrated excellent rate capability (72.1% retention at 20 A/g) and cycling stability
Examples of Electrical Property Characterization and Application ExperiencesJacob Feste
This document summarizes an experiment that investigated the mechanical and electrical properties of a PDMS nanoparticle composite with varying percentages of carbon black. Mechanical properties were measured through tensile testing of samples with 0-20% carbon black, showing a linear increase in tensile strength with higher percentages. Electrical properties were determined by measuring output voltages relating to resistance changes for samples with 14-19% carbon black using a Wheatstone bridge circuit. The results supported the rule of mixtures for mechanical properties but had high error for some electrical measurements. Overall, the experiment aimed to relate the composite's properties to characteristics expected for a nanoparticle composite material.
Paper electrophoresis is a technique used to separate charged biomolecules like proteins and nucleic acids. It works by applying an electric field to a strip of filter paper soaked in buffer solution. The charged molecules migrate along the paper at different rates depending on their size and charge, separating into distinct bands. Key factors that affect separation are the properties of the sample molecules, the electric field strength and voltage gradient, the buffer composition and pH, and interactions with the paper medium. Paper electrophoresis has applications in clinical testing, forensic analysis, and environmental monitoring.
The document summarizes a study of the electronic transport properties of carbon nanobuds (CNBs) using density functional theory calculations. CNBs are hybrid carbon nanostructures formed by attaching fullerenes to single-walled carbon nanotubes. The study finds that attaching fullerenes to form CNBs with a (14,0) carbon nanotube reduces electron transmission across the structure compared to the pristine nanotube. Localized states near the bud region cause strong backscattering, lowering transmission. Current-voltage characteristics show that while the pristine nanotube is semiconducting, CNB formation does not change this behavior. CNBs may have applications in nanoelectronics
This document provides an overview of electrophoresis, a technique used to separate charged molecules using an electric field. It defines electrophoresis as the migration of charged molecules under an external electric field. The document then discusses the principle, theory, factors affecting migration, and main types of electrophoresis - including moving boundary electrophoresis, zone electrophoresis using paper, gels, capillaries, and isotachophoresis and isoelectric focusing which separate molecules based on their electric charge and isoelectric point.
Foram investigadas as interações entre os pesticidas atrazina, imazaquin, metribuzin e paraquat com o polímero condutor poli-(o-etoxianilina)-POEA, utilizando-se as técnicas de microscopia de força atômica (AFM), espectrofotometria de ultravioleta visível (UV-Vis) e
espectroscopia de impedância eletroquímica. Os estudos de microscopia de força atômica em filmes automontados mostraram um aumento na rugosidade do filme polimérico, quando exposto aos pesticidas atrazina, imazaquin e metribuzin e uma diminuição na rugosidade do filme
polimérico exposto ao pesticida paraquat. Isso evidencia a existência de interação química, provavelmente, ligação iônica entre o nitrogênio presente na POEA e os grupos presentes nos pesticidas estudados. Os estudos de ultravioleta visível mostraram uma maior interação entre a
POEA e o pesticida imazaquin. Por meio de medidas elétricas realizadas (espectroscopia de impedância eletroquímica) com um sensor formado por filme de POEA, foi possível distinguir e determinar o limite de detecção dos pesticidas em solução aquosa, o que corrobora com os estudos por AFM e UV-Vis.
Electrical transport properties of nanocrystalline and bulk nickel.pdfProximaCentauri15
In this work, the comparative study on the electrical transport properties of nanocrystalline nickel
ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance
spectroscopy in a wide range of frequencies (100 Hz–1 MHz) and temperatures (40 °C–320 °C). The
dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model
and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel
ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric
permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple
relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power
law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to
correlated barrier hopping (CBH) mechanism near 200 °C. The estimated values of Mott parameters
are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by
scaling curves of imaginary impedance (Z) andmodulus (M). The comparison between the Z and
M spectra indicates that both long-range and short-rangemovement of charge carriers contribute to
dielectric relaxation with short-range charge carriers predominating at low temperatures while longrange
charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist
plot indicates the presence of grain boundary contribution to the electrical conduction process for the
nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by
stretching exponential factor (β) which has been estimated by fitting the modifiedKWW
(Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is
found to be strongly temperature dependent and its value for the nanocrystalline sample is less than
that of the bulk system which is explained on the basis of dipole-dipole interaction.
Formation and annihilation of E4 centers in ZnO - Influence of hydrogen - A. ...Chidanand Bhoodoo
The document discusses the formation and annealing behavior of E4 centers in zinc oxide (ZnO) under the influence of hydrogen implantation. It finds that the concentration of E4 centers, which have an energy level of 0.57 eV below the conduction band, increases linearly with proton and deuterium ion fluence during implantation. Isothermal annealing experiments show that the E4 centers exhibit first-order kinetics with an activation energy of 0.6 eV, and the annealing rate is strongly enhanced by higher hydrogen fluence. A model where interstitial hydrogen enhances the migration and reaction of E4 centers describes the experimental observations well. Based on theoretical predictions and previous work, the document tentatively assigns the E4 center to the oxygen
This document discusses a study on the effect of curing on the activation energy and dielectric properties of carbon black-epoxy composites at different temperatures and frequencies. The key findings are:
1) The activation energy was found to be higher for room temperature cured carbon black-epoxy samples compared to thermally cured samples, indicating curing behavior affects activation energy.
2) Dielectric constants of thermally cured samples were higher than room temperature cured samples.
3) Activation energy decreased with increasing carbon black concentration in the composite, likely due to increased polarization energy and charge carrier density.
4) Dielectric constant increased with temperature but decreased with increasing frequency for both cured sample types.
Synthesis and characterication of water soluble conjugated polymer brush for ...Hnakey Lora
This document discusses the synthesis and characterization of water-soluble conjugated polymer brushes for sensor applications. It describes how conjugated polyelectrolytes (CPEs) can change their optical properties in response to environmental perturbations, making them useful for sensing biomolecules. However, linear CPEs have limitations like low water solubility. The document then discusses how attaching highly charged polymer side chains overcomes these limitations by increasing water solubility and quantum yield. Several new CPE brushes were successfully synthesized and shown to have properties desirable for sensing, like optical stability in complex media.
Electrophoresis is a technique where charged particles or molecules migrate in a medium under the influence of an electric field. Positively charged particles move toward the cathode, and negatively charged particles move toward the anode. Factors like the particle's charge, size, shape, buffer composition, and electric field strength determine its electrophoretic mobility. Electrophoresis is used to separate and analyze proteins, cells, and other biological samples based on these properties.
2. In living cells, the charge properties of biological ion channels
can be modulated by an external stimulus,6
implying that their
charges are strongly dependent on the solution environments
like pH and salt concentration due to the deprotonation and
protonation reactions of functional groups on biological ion
channels. Inspired by this, numerous studies have been
conducted by using pH-tunable PE brush-functionalized
nanochannels as biomimetic smart nanochannels for versatile
applications.6,7
Considering the growing expansion of relevant
applications using these biomimetic nanofluidics, this study
investigates, for the first time, the FET control of the Donnan
potential and the EKF in a nanochannel with a layer of pH-
tunable, zwitterionic, PE brushes, referred to as a PE-modified
nanochannel. The key practical parameters including the
background salt concentration, pH, and the properties
(thickness and softness) of the PE brush layer on the FET
control of the Donnan potential and the EKF velocity are
investigated.
2. MATHEMATICAL MODEL
Figure 1 depicts the schematic of the PE-modified nanochannel,
which comprises a dielectric nanochannel and a layer of
homogeneously structured PE brushes end-grafted to the inner
channel wall. The uniform thickness of the PE layer is Rm, and
half height of the nanochannel is H. The FET includes a thin
dielectric layer of thickness δ and a gate electrode fabricated on
the outer surface of the dielectric layer. Cartesian coordinate,
(x, y), with the origin located at the bottom solid channel/PE
layer interface is used in this study. A uniform electric field E of
strength Ex is externally applied parallel to the PE-modified
nanochannel to generate the EKF, which is controlled by the
Donnan potential, ψd, through modulating the gate potential,
Vg, imposed on the gate electrode. For convenience, we assume
that the Donnan potential, ψd, considered in this study is the
electrical potential at the solid channel/PE layer interface.
The following assumptions are used in this study: (i) The
nanochannel is filled with a viscous, Newtonian, incompressible
fluid containing N types of ionic species, and the EKF is fully
developed along the channel (i.e., x-direction). (ii) The
homogeneous PE layer is ion-penetrable and its morphology
deformation41
is not considered in this study. (iii) The
properties of the fluid such as viscosity and permittivity within
the PE layer are the same as those outside it.42,43
(iv) The
dielectric channel/PE layer interface is uncharged. (v) No-slip
plane with zero fluid velocity occurs at the dielectric channel/
PE layer interface. (vi) The nanochannel’s length and width are
much larger than its height; therefore, the considered problem
can be viewed as a nanoslit between two parallel plates. (vii)
The half height of the nanochannel is much larger than the
thickness of the electrical double layer (EDL), λD = κ−1
. Under
this condition, the EDLs of the two parallel plates do not
overlap in the y-direction. This assumption is valid for most
experimental conditions in nanofluidic applications. For
example, the electrolyte concentration in typical nanofluidic
experiments ranges from 1 to 1000 mM, yielding the
corresponding λD varying from 9.6 to 0.3 nm, which is much
smaller than the half height in most nanofluidic devices.12,44,45
Therefore, the effect of ion concentration polarization46−48
stemming from the selective transport of cations and anions in
nanochannels can be ignored. Under the aforementioned
assumptions, the electrical potential stemming from the
charged PE layers, concentrations of ionic species, and the
EKF velocity are uniformly distributed along the x-direction.
Molecular chains in biological systems typically show a pH
regulation nature, implying that their charges are highly
dependent on the local proton concentration. To mimic this
pH tunable nature, the PE brushes are assumed to carry
zwitterionic functional groups (e.g., lysine), PE∼COOH and
PE∼NH2, which have the following dissociation/association
reactions:
∼ ↔ ∼ +
∼ + ↔ ∼
− +
+ +
PE COOH PE COO H ,
PE NH H PE NH2 3 (1)
The equilibrium constants of the above reactions are,
respectively, KA = NPE∼COO
−[H+
]/NPE∼COOH and KB =
NPE∼NH3
+/NPE∼NH2
[H+
], with [H+
] and Nj being the molar
concentration of H+
ions and the volume site density of the jth
functional group (j = PE∼COOH, PE∼COO−
, PE∼NH2, and
PE∼NH3
+
). The total site densities of acidic and basic functional
groups are NA = NPE∼COO
− + NPE∼COOH and NB = NPE∼NH3
+ +
NPE∼NH2
, respectively. Assuming that the concentration of H+
ions follows the Boltzmann distribution, [H+
] = [H+
]0
exp(−Fψ/RT), the volume charge density within the PE layer
becomes the following:
ρ = − +
= −
+ −
+
−
+ −
ψ
ψ
ψ
∼ ∼
+
+
+
− +
⎧
⎨
⎪
⎩
⎪
⎫
⎬
⎪
⎭
⎪
( )
( )
( )
F N N
F
K N
K
K N
K
( )
[H ] exp
[H ] exp
1 [H ] exp
m
A
A
F
RT
B
F
RT
F
RT
PE COO PE NH
A
0
B 0
B 0
3
(2)
In the above, [H+
]0 is the bulk molar concentration of H+
ions;
ψ is the electrical potential; R, T, F are, respectively, the
universal gas constant, absolute temperature, and Faraday
constant.
Suppose that the background electrolyte is KCl and its pH (=
−log[H+
]0) is adjusted by KOH and HCl. Four major ionic
species (i.e., N = 4) including H+
, K+
, Cl−
, and OH−
are
considered. Let Ci0 (in mM), i = 1, 2, 3, and 4, be the bulk
concentrations of these ions, respectively, and CKCl be the
background salt concentration. Electroneutrality yields the
Figure 1. Schematics of the FET control of the Donnan potential (ψd)
and the electrokinetic flow (EKF) in a pH-tunable, PE-modified
nanochannel filled with an electrolyte solution containing four ionic
species: H+
, K+
, Cl−
, and OH−
. The blue line depicts the profile of the
EKF velocity.
The Journal of Physical Chemistry C Article
dx.doi.org/10.1021/jp504588b | J. Phys. Chem. C 2014, 118, 19806−1981319807
3. following relations for the bulk ionic concentrations:49,50
C10 =
10(−pH+3)
and C40 = 10−(14−pH)+3
; C20 = CKCl and C30 =
CKCl+10(−pH+3)
−10−(14−pH)+3
for pH ≤ 7; and C20 = CKCl −
10(−pH+3)
+ 10−(14−pH)+3
and C30 = CKCl for pH > 7.
On the basis of the above assumptions, the electrical
potentials within the dielectric layer and liquid, ψ and ϕ,
respectively, and the EKF velocity, u, are governed by the
following:40
ψ
δ= − ≤ ≤
d
dy
y0, 0
2
2
(3)
∑ϕ ρ ρ
ε ε ε ε
ϕ
ρ
ε ε
= −
+
= − −
− ≤ ≤
=
⎛
⎝
⎜
⎞
⎠
⎟
d
dy
h
Fz C
z F
RT
h
y H
1
exp
, 0
e m
f f i
i i
i
m
f
2
2
0 0 1
4
0
0 (4)
∑
μ
ϕ
λ
= − − + ≤ ≤
=
⎛
⎝
⎜
⎞
⎠
⎟
d u
dy
E
Fz C
z F
RT
hu
y Hexp , 0x
i
i i
i
m
2
2
1
4
0 2
(5)
Here, ρe is the mobile space charge density; zi is the valence of
the ith ionic species; ε0 and εf are the absolute permittivity of
vacuum and the relative permittivity of the liquid phase,
respectively; μ is the dynamic fluid viscosity; h is the unit region
function (h = 1, the region inside the PE layer; h = 0, the region
outside it); λm = (μ/γm)1/2
is the softness (or Brinkman
screening length) of the PE layer with γm being the
hydrodynamic frictional coefficient of that layer.
The boundary conditions for eqs 3−5 are as follows:
at the gate electrode (y = −δ),
ψ = Vg (6)
at the dielectric solid channel/PE layer interface (y = 0),
ψ ϕ ψ= = d (7a)
ε ε
ψ
ε ε
ϕ
− + =
d
dy
d
dy
0d f0 0
(7b)
=u 0 (7c)
at the PE layer/liquid interface (y = Rm),
ϕ ϕ| = |= =− +
y R y Rm m (8a)
ϕ ϕ
=
= =− +
d
dy
d
dy
y R y Rm m (8b)
| = |= =− +u uy R y Rm m (8c)
=
= =− +
du
dy
du
dy
y R y Rm m (8d)
and at the center of the nanochannel (y = H),
ϕ
ϕ
= =
d
dy
0
(9a)
=
du
dy
0
(9b)
In the above, εd is the relative permittivity of the dielectric layer.
Equation 7a denotes that the electrical potential is continuous
at the dielectric solid channel/PE layer interface; however, the
transverse electric field, as depicted in eq 7b, is not continuous
because of the difference in the dielectric permittivities (εf and
εd) at that interface. The “0” term on the right-hand side of eq
7b arises from the assumption that the nanochannel/PE layer
interface is uncharged as described previously. Equations 8a−8d
depict that the electrical potential, and both electric and flow
fields are continuous at the PE layer/liquid interface. Equation
9a expresses that at the center of the nanochannel, the electrical
potential arising from the charged PE layer vanishes and the
ionic concentrations reach their bulk values (due to the
assumption of no EDLs overlapping i.e., H ≫ λD).
3. RESULTS AND DISCUSSION
The present problem is numerically solved by COMSOL
Multiphysics (version 3.5a), which has been used to numeri-
cally simulate the electrokinetic transport in PE-modified
nanopores without FET control,43,47,51−53
and in solid-state
nanopores with FET.18,24−27
For illustration, we consider a
biomimetic FET-gated silica nanochannel with a relative
permittivity εd = 3.9 (SiO2),26
a thickness of dielectric layer δ
= 30 nm, and the half height H = 100 nm under an application
of uniform electric field Ex = 20 kV/m. To simulate pH-tunable
and zwitterionic characteristics of biomimetic nanochannels, we
consider the constitution of the PE layer consisting of amino
acid-like PE chains with lysine groups4,31
with pKA = 2.5 (α-
carboxyl), pKB = −8.5 (α-amino),54
and NA = NB = 600 mol/
m3
.55
Consequently, the isoelectric point (IEP) of the PE layer
is 5.6. The softness degree of the soft layer, λm, is set to 1 nm,
Figure 2. Variations of the electrical potential ϕ (a), and the EKF velocity, u(b) in the y-direction, at Ex = 20 kV/m, pKA = 2.5, pKB = 8.5, NA = 600
mol/m3
, NB = 600 mol/m3
, pH = 8, CKCl = 5 mM, λm = 1011
nm, Rm = 0.1 nm, and Vg = 0 V.
The Journal of Physical Chemistry C Article
dx.doi.org/10.1021/jp504588b | J. Phys. Chem. C 2014, 118, 19806−1981319808
4. unless specified elsewhere, which has been shown to be in the
range for biological PE layers (i.e., 0.1−10 nm).55,56
The
remaining constants are R = 8.31 JK−1
mol−1
, T = 298 K, F =
96487 Cmol−1
, ε0 = 8.854 × 10−12
CV−1
m−1
, εf = 78.5, and μ =
10−3
kg m−1
s−1
.
3.1. Code Verification. The applicability of the present
numerical scheme is examined by applying it to the case of the
spatial distributions of the electrical potential and the EKF
velocity in a solid-state nanochannel without the PE layer. The
previous results of which were solved using a rigid nanochannel
by Yeh et al.28
For comparison, we let λm = 1011
nm and Rm(≪
λD) = 0.1 nm. The former makes the present PE-modified
nanochannel close to the rigid nanochannel, and the latter
ensures that the thickness of the PE layer is thin enough
compared to that of EDL so that the distribution of the
electrical potential inside the PE layer is not appreciably
influenced by its presence.57
Since the PE layer is very thin,
implying that the net charge in that layer is extremely small, the
electrical potential is small in the nanochannel, as shown in
Figure 2a. Figure 2 depicts the distributions of the electrical
potential ϕ and the EKF velocity u near a PE-modified
nanochannel. The present numerical results (symbols) agree
well with the analytical results in a solid-state nanochannel
(solid lines) derived by Yeh et al.28
This suggests that the
numerical scheme for the present model is correct.
In subsequent discussions, FET control of the Donnan
potential and the EKF velocity in a pH-regulated PE-modified
nanochannel under various key parameters, including the
applied gate potential, Vg, the background solution properties
such as salt concentration, CKCl, and pH, and the thickness and
softness of the PE layer, Rm and λm, respectively, are examined.
3.2. FET Control of Donnan Potential. Typically in solid-
state gated nanofluidics,15,17−19,58
the zeta potential and,
accordingly, the electrokinetic transport can be regulated by
controlling the gate potential, Vg, applied to the gate electrode.
This comes from the fact that a strong transverse equilibrium
electric field, stemming from the potential difference within the
dielectric layer, makes the surface charge of the nanochannel
tunable.15,26
Figure 3 illustrates the field effect modulation of
the Donnan potential, ψd, as a function of Vg for various levels
of CKCl and pH. This figure explicitly reveals that ψd can be
modulated from negative to positive by increasing the gate
potential. This field control characteristics, similar to tuning
zeta potential in solid-state gated nanofluidics,15,17−19,58
has the
potential for regulating the electrokinetic transport in nano-
fluidics with functionalized PE brush layers. Figure 3 also shows
that the critical value of Vg, Vg,c, at which ψd = 0, decreases with
an increase in CKCl (Figure 3a) and a decrease in pH if pH > 5.6
(Figure 3b). Note that if the pH < 5.6 (pH = 4 in Figure 3b),
then the PE layer is positively charged and, therefore, the
Donnan potential keeps positive as Vg varies. The behavior that
Vg,c decreases with an increase in CKCl is due to thinner EDL at
higher salt concentrations, resulting in more counterions
accumulated within the PE layer and, accordingly, smaller
effective charge density in the PE layer, |ρm + ρe|.59
As the pH
increases, more negatively charged PE∼COO−
groups are
dissociated from functional groups PE∼COOH at lower proton
concentration, resulting in an increase in the charge density of
the PE layer (|ρm|) and |ρm+ρe|. Therefore, a higher Vg,c is
required as pH increases, as shown in Figure 3b.
The influences of the background salt concentration, CKCl,
and pH on the field effect regulation of Donnan potential, ψd,
are depicted in Figure 4. This figure shows that if the FET is
turned off (i.e., Vg = 0), then the Donnan potential can be
tuned from positive to negative by the solution pH, but cannot
regulated by the salt concentration. The former is expected
because the considered PE layer reveals a zwitterionic, pH
tunable feature, carrying positive (negative) charges if pH < 5.6
Figure 3. Variations of the Donnan potential ψd with the gate potential Vg for various CKCl at pH = 8, (a), and for various solution pH at CKCl = 10
mM(b) when λm = 1 nm and Rm = 5 nm.
Figure 4. Variation of the Donnan potential ψd with the solution pH for various Vg at CKCl = 1 mM, (a), and with CKCl for various Vg at pH = 8, (b),
when λm = 1 nm, and Rm = 5 nm.
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5. (pH > 5.6). The latter arises from the fact that the charge
nature of the PE layer is not influenced by the salt
concentration.59
However, if the FET is active (i.e., Vg > 0),
the modulated Donnan potential, as shown in Figure 4, can be
regulated from negative to positive with both pH and CKCl.
Regulation of the Donnan potential by pH is expected since the
charge property of the PE layer is pH-tunable. The latter
suggests that one can even change the sign of the Donnan
potential in gated PE-modified nanochannels by changing the
background salt concentration. This interesting behavior is
different from the FET control of the zeta potential in a solid-
state nanochannel,28−30
where the sign of the zeta potential
does not change with the variation in the salt concentration..
This feature can be attributed to the ion-permeable PE layer/
liquid interface, while the channel/liquid interface in a solid-
state nanochannel is impermeable to ions. As CKCl increases,
the EDL thickness decreases, resulting in a greater number of
counterions concentrated inside the PE layer. This results in a
smaller magnitude of the effective charge density, |ρm + ρe|, of
the PE layer59
and Donnan potential, ψd, as observed in Vg = 0
V (solid line) of Figure 4b. Therefore, the Donnan potential
can be regulated from negative to positive at sufficiently high
salt concentration when Vg > 0 V. The dependence of the
effective charge density within the PE layer on the salt
concentration yields a salt concentration-dependent Donnan
potential behavior.
Figure 4 also shows that if the gate potential is relatively high
(e.g., Vg = 15 V), then ψd has a local maximum with the
variation in pH when pH is low (Figure 4a), and as CKCl varies
when CKCl is high (Figure 4b). Note that the charge density of
the PE layer, ρm, is positive (negative) when pH is lower
(higher) than its IEP (5.6). As described previously, an increase
in CKCl results in more counterions confined inside the PE
layer, reducing significantly its effective charge density.
However, an increase in CKCl also results in an increase in
|ρm| due to the excluded effect of H+
ions by the other
counterions, K+
.59
If the latter dominates over the former,
which becomes remarkable at sufficiently high CKCl, then ψd
decreases accordingly, as depicted in the regime of high salt
concentration in Figure 4b. Similarly, although a more
significant deviation of pH from the IEP of the PE layer
results in an increase in |ρm|, a more significant deviation of pH
from 7 also increases the ionic strength (a thinner EDL
thickness), lowering |ρm + ρe| and, accordingly, |ψd|. Since the
PE layer, if pH < 5.6 and Vg > 0, is positively charged, an
increase in the ionic strength with decreasing pH becomes the
dominant aspect of the behavior of ψd, and ψd decreases
accordingly at sufficiently low pH. These Vg, pH, and salt
concentration-dependent Donnan potential behaviors, there-
fore, imply that a FET-gated nanochannel with functionalized
pH-tunable PE layers is more flexibly capable of regulating the
charge property of the nanochannel and, accordingly, the
transport of ions and fluid inside by adjusting the solution
properties, including pH and salt concentration, and the gate
potential.
Figures 3 and 4 also reveal that the FET control of ψd is
significant when the salt concentration, CKCl, is low and the pH
is near the IEP of the PE layer, but becomes insignificant when
CKCl is high and pH appreciably deviates from the IEP. The
behavior of ψd for various CKCl is similar to the FET control of
zeta potential in a solid-state nanochannel.30
As the salt
concentration increases, the EDL thickness decreases, resulting
in more counterions condensed inside the PE layer. Therefore,
the FET is harder to effectively tune the Donnan potential at
relatively high salt concentration. Similarly, because the
magnitude of the charge density of the biomimetic PE layer
increases with the degree of the deviation of pH from its IEP,
more counterions are condensed within the PE layer. Thus,
with FET, it is harder to tune the Donnan potential when the
pH significantly deviates from the IEP.
3.3. FET Control of EKF Velocity. It is known that the
electrokinetic transport of fluid in a nanochannel can be
controlled by FET, which has potentials in improving the
performance of the nanopore sensing of DNA51
and
bionanoparticles.52
To comprehensively understand the FET
control of the EKF in a biomimetic PE-modified gated
nanochannel, we plot the EKF velocity profiles near the
charged nanochannel for various gate potential, Vg, background
salt concentration, CKCl, and pH in Figure 5. This figure shows
that the EKF velocity profile can be regulated by controlling the
values of Vg, CKCl, and pH. In addition to Vg, which was verified
by Benson et al.40
for the case of the PE layer with fixed
charges, the direction of the EKF can also be changed by pH, as
depicted in Figure 5c. If the bulk solution pH is high (pH = 8
and 10 in Figure 5c), then the PE layer becomes negatively
charged, and the resulting EKF is in the same direction of the
imposed electric field. In addition, EKF velocity increases with
Figure 5. Spatial variations of the EKF velocity for various gate
potential Vg, (a), background salt concentrations CKCl, (b), and
solution pH, (c), when λm = 1 nm, Rm = 5 nm, and Ex = 20 kV/m. (a)
CKCl = 1 mM and pH = 8; (b) Vg = 5 V and pH = 8; (c) Vg = 5 V and
CKCl = 1 mM. The pink regions highlight the region of the PE layer on
the nanochannel.
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6. increasing pH. For sufficiently low pH (pH = 4 and 6 in Figure
5c), the PE layer turns into a positively charged one. Therefore,
the direction of the EKF is opposite to that of the applied
electric field. This feature can be applied to control the
transport of biomolecules in nanofluidics, which have a pH-
tunable nature, and can be accredited to the pH regulation of
the Donnan potential, as illustrated in Figures 3 and 4.
It is worth noting in Figure 5b that the EKF velocity inside
the PE layer (pink region) increases with an increase in CKCl,
but far away from the PE layer it decreases with an increase in
CKCl. The latter is attributed to the decrease in Donnan
potential with increasing CKCl, which is accordance with the
typical electroosmotic flow behavior in a solid-state nano-
channel29
where the zeta potential decreases with an increase in
CKCl.29
The former is particular in PE-modified nanochannels
and can be attributed to more mobile ions gathered inside the
PE layer. This is because the motivity of the EKF within the PE
layer is primarily dominated by the amount of mobile ions. In
PE-modified nanochannels, as CKCl increases, the EDL
decreases accordingly, resulting in more mobile counterions
gathered in the vicinity of the PE layer/liquid interface and,
accordingly, a larger EKF velocity.
3.4. Influence of PE layer Properties. Because the electric
potential distribution in PE-modified nanochannels is not
affected by its softness parameter (λm),43
we only illustrate the
influence of the thickness of the PE layer, Rm, on the Donnan
potential, ψd, in Figure 6. Figure 6a suggests that the magnitude
of ψd modulated by the FET is insignificantly dependent on Rm.
This is because an increase in Rm results in not only an increase
in the net charges of the PE layer but also a decrease in the
equilibrium electric field within the PE layer. The former is
obstructive, but the latter is beneficial for the tuning
performance of the FET. As a result, the influence of Rm on
the performance of regulating Donnan potential by the FET is
inappreciable. A similar phenomenon is observed in Figure 6b,
where the modulated ψd is plotted as a function of the
background salt concentration, CKCl. This figure clearly shows
that ψd is nearly independent of Rm if Rm is sufficiently large.
Figure 7 depicts the influence of the softness (λm) and
thickness (Rm) of the PE layer on the EKF in a biomimetic PE-
modified nanochannel when Ex = 20 kV/m. To make the
presentation clear, we focus mainly on the EKF velocity
distribution near the charged nanochannel and highlight the
PE/liquid interface as a pink dotted line. Lines and symbols
represent the results at Vg = 0 and 5 V, respectively. Apparently,
Figure 7 shows that the EKF velocity with FET control (Vg = 5
V) is higher than that without FET control (Vg = 0 V) because
the PE layer is negatively charged at pH = 8. In Figure 7a, the
larger the softness parameter (the deeper the penetration depth
of fluid into the PE layer) the more significant is the FET
control on EKF, yielding a larger deviation of the EKF velocity
between Vg = 0 and 5 V, even though the Donnan potential of
PE-modified nanochannel is independent of λm. This can be
attributed to a larger friction force stemming from the PE layer
for smaller λm, reducing the driving force of the EKF. In
addition, the difference of the EKF velocity between Vg = 0 and
5 V is remarkable if Rm is small, as shown in Figure 7b. This
implies that Rm has a significant effect on the FET control of
the EKF in PE-modified nanochannels for thinner PE layer.
This is because the charge density of the PE layer decreases as
Rm decreases, allowing the FET to tune the EKF more easily.
Figure 6. Variations of the Donnan potential ψd with the gate potential Vg, (a), and background salt concentration CKCl, (b), for various thickness of
the PE layer Rm at λm = 1 nm. (a) pH = 8 and CKCl = 1 mM; (b) pH = 8 and Vg = 5 V.
Figure 7. Spatial variations of the EKF velocity for various softness degree of the PE layer λm at Ex = 20 kV/m when Rm = 6 nm, pH = 8, and CKCl = 1
mM, (a), and for various Rm when λm = 1 nm, pH = 8, and CKCl = 1 mM (b). Lines and symbols denote the results at Vg = 0 and 5 V, respectively.
The pink dotted lines highlight the PE layer/liquid interfaces.
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7. 4. CONCLUSIONS
Controlling the Donnan potential and the electrokinetic flow
(EKF) in a biomimetic polyelectrolyte (PE)-modified nano-
channel, consisting of a solid-state nanochannel functionalized
by a pH-regulated, zwitterionic, PE brush layer, by a field effect
transistor (FET) is investigated for the first time. Taking into
account practical effects such as multiple ionic species and
protonation and deprotonation reactions of functional groups
within the PE layer, the present study extends previous models
to a case closer to reality because the charge density of the PE
layer is strongly dependent on the local solution properties,
including background salt concentration and pH. The obtained
results show that both the Donnan potential and the EKF
velocity can be regulated by the FET. Control of the Donnan
potential of the PE-modified nanochannel, in turn, controls the
EKF. The performance of the field effect control depends on
the solution properties including the background salt
concentration and pH, and the thickness and softness
parameter of the PE layer. Different from the solid-state
gated nanochannel, where the polarity of zeta potential can be
regulated only by the transverse gate potential, the sign of the
Donnan potential of the biomimetic PE-modified nanochannel
can be tuned by the background salt concentration, pH, and the
gate potential. The field effect on the Donnan potential
depends highly on the background salt concentration and pH,
but insignificantly on the thickness of the PE layer. The FET
control performance of the Donnan potential is superior when
the salt concentration is low and the solution pH is near the
IEP of the PE layer. However, in addition to the salt
concentration and pH, the softness and thickness of the PE
layer significantly affect the FET control of the EKF in a PE-
modified nanochannel. The degree of the FET control on the
EKF is remarkable when the softness parameter of the PE layer
is large and its thickness is small.
■ AUTHOR INFORMATION
Corresponding Authors
*Fax: +886-5-5312071; e-mail: lhyeh@yuntech.edu.tw.
*E-mail: sqian@odu.edu.
Author Contributions
§
These authors contributed equally to this work.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work is supported by the Ministry of Science and
Technology of the Republic of China under Grants 102-2221-
E-224-052-MY3, 103-2221-E-224-039-MY3 (L.H.Y.), and 102-
2622-E-224-011-CC3 (T.H.C.).
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