Counter Charges Research Articles

Understanding the Role of Removable Solid Additives: Selective Interaction Contributes to Vertical Component Distributions.

Sequentially deposited organic solar cells (SD-OSCs) have attracted great attention owing to their ability in achieving a more favorable, vertically phase-separated morphology to avoid the accumulation of counter charges at absorber/transporting layer interfaces. However, the processing of SD-OSCs is still quite challenging in preventing the penetration of small-molecule acceptors into the polymer donor layer via erosion or swelling. Herein, solid additives (SAs) with varied electrostatic potential distributions and steric hinderance are introduced into SD-OSCs to investigate the effect of evaporation dynamics and selective interaction on vertical component distribution. Multiple modelings indicate that the π-π interaction dominates the interactions between aromatic SAs and active layer components. Among them, p-dibromobenzene shows a stronger interaction with the donor while 2-chloronaphthalene (2-CN) interacts more preferably with acceptor. Combining the depth-dependent morphological study aided by multiple X-ray scattering methods, it is concluded that the evaporation of SAs can drive the stronger-interaction component upward to the surface, while having minor impact on the overall molecular packing. Ultimately, the 2-CN-treated devices with reduced acceptor concentration at the bottom surface deliver a high power conversion efficiency of 19.2%, demonstrating the effectiveness of applying selective interactions to improve the vertical morphology of OSCs by using SAs with proper structure.

Molecular understanding of cation effects on double layers and their significance to CO-CO dimerization.

Cation effects have been shown in numerous experiments to play a significant role in electrocatalysis. To understand these effects at the molecular level, we systematically investigate the structures and capacitances of electric double layers with a variety of cations as counter charges at Pt(111)-COad/water interfaces with ab initio molecular dynamics. It is encouraging to find that the computed Helmholtz capacitances for different cations are in quantitative agreement with experiments, and that the trend of cation effects on capacitances shows clear correlation with the structures of interface cations of differing sizes and hydration energies. More importantly, we demonstrate the Helmholtz capacitance as the key descriptor for measuring the activity of CO-CO dimerization, the rate-determining step for C2+ formation in electroreduction of CO and CO2. Our work provides atomistic insights into cation effects on electric double layers and electrocatalysis that are crucial for optimizing electrode and electrolyte materials.

Counter charge cluster formation in molecular doping of molybdenum disulfide

Studies of molybdenum disulfide (MoS2) gas sensor prototypes report orders of magnitude higher sensitivity toward nitrogen dioxide (NO2) over ammonia (NH3). Based on the cluster formation model and density functional theory calculations of charge transfer, NO2 was found to form a tightly bound cluster of counter charges upon carrier donation. In contrast, NH3 forms only a semi-localized cluster of counter charges over a wide area of MoS2, creating a larger collision cross section of coulomb interaction between the charge carrier and the counter charges. We discuss the potential effect of counter charge cluster localization on the efficiency of molecular doping.

N-dopants optimize the utilization of spontaneously formed photocharges in organic solar cells

N-dopants optimize the utilization of spontaneously formed photocharges by reducing the exciton binding energy and segregating the counter charges in non-fullerene acceptors.

Interface charge transport of multilayer devices for exact analysis of charge behavior in organic optoelectronic devices

A unipolar charge device was utilized to gain information of the charge balance in organic optoelectronic devices to enhance efficiency and operational stability. Usually, a unipolar charge device is designed as a multilayer structure to improve charge transport and block injection of counter charges from electrodes. In this paper, the correlation between charge transport across the interlayer and corresponding bulk electrical parameters from quasi-static analysis was investigated. Although only the interlayer material was modified, the charge carrier mobility and drift charge carrier density of the light-emitting layer were totally changed, which originated from large series resistance due to charge accumulation at the interface. This result indicates that quantitative analysis of electrical properties from unipolar charge devices should be performed as background analysis to ensure efficient interface charge transport during operation.

Determination of bacterial surface charge density via saturation of adsorbed ions

Bacterial surface charge is a critical characteristic of the cell’s interfacial physiology that influences how the cell interacts with the local environment. A direct, sensitive, and accurate experimental technique capable of quantifying bacterial surface charge is needed to better understand molecular adaptations in interfacial physiology in response to environmental changes. We introduce here the method of second-harmonic light scattering (SHS), which is capable of detecting the number of molecular ions adsorbed as counter charges on the exterior bacterial surface, thereby providing a measure of the surface charge. In this first demonstration, we detect the small molecular cation, malachite green, electrostatically adsorbed on the surface of representative strains of Gram-positive and Gram-negative bacteria. Surprisingly, the SHS-deduced molecular transport rates through the different cellular ultrastructures are revealed to be nearly identical. However, the adsorption saturation densities on the exterior surfaces of the two bacteria were shown to be characteristically distinct. The negative charge density of the lipopolysaccharide coated outer surface of Gram-negative Escherichia coli (6.6 ± 1.3 nm−2) was deduced to be seven times larger than that of the protein surface layer of Gram-positive Lactobacillus rhamnosus (1.0 ± 0.2 nm−2). The feasibility of SHS-deduced bacterial surface charge density for Gram-type differentiation is presented.

The construction of sea urchin spines-like polypyrrole arrays on cotton-based fabric electrode via a facile electropolymerization for high performance flexible solid-state supercapacitors

The most explored flexible supercapacitors based on PPy electrodes face a huge challenge of poor cycle performance. Here, we demonstrate successful construction of sea urchin spines-like PPy arrays on cotton-based fabric electrode via a facile electropolymerization and employ it in enhancing the cyclic stability of the supercapacitors without recombination of PPy with other capacitive materials. This novel fabric electrode (called EPPy-PPy/NF/CF) consists of a cotton fabric (CF) coated with PVA-co-PE nanofibers (NF) as a flexible substrate (NF/CF). The formation mechanism of the spiny PPy with nanocavities is explored, and the effects of surface wettability of the support electrode (PPy/NF/CF), micellar size, and bubble generation on the nucleation and growth of the PPy during electropolymerization are elucidated. Significantly, the flexible solid-state symmetrical EPPy-PPy/NF/CF supercapacitor exhibits striking cycling stability with 100% retention after 10,000 cycles at a current density of 4 mA cm−2. The superior cyclic stability can be attributed to the spiny PPy arrays, which can shorten the transmission paths of counter ions and charges, thereby weakening stress-induced damages to the PPy skeleton. Additionally, this flexible supercapacitor also shows a great potential for application in portable and wearable electronic devices.

Dielectric properties of water and ice: a unified treatment

Broadband dielectric spectra of water and ice reveal similar temperature run of the static permittivity, ε(0), and spectral shape of the Debye relaxation. We suggest an approach to describe these features uniformly. We extend to ice the model recently developed by us for water. The model explains the 6 orders magnitude difference between the Debye relaxation time in water and ice, as well as alike temperature behavior of ε(0), by bipolar diffusion of counter charges.

Deterministic Convergence and Strong Regularity

Abstract Bayesians since Savage ([1972]) have appealed to asymptotic results to counter charges of excessive subjectivity. Their claim is that objectionable differences in prior probability judgements will vanish as agents learn from evidence, and individual agents will converge to the truth. Glymour ([1980]), Earman ([1992]) and others have voiced the complaint that the theorems used to support these claims tell us, not how probabilities updated on evidence will actually behave in the limit, but merely how Bayesian agents believe they will behave, suggesting that the theorems are too weak to underwrite notions of scientific objectivity and intersubjective agreement. I investigate, in a very general framework, the conditions under which updated probabilities actually converge to a settled opinion and the conditions under which the updated probabilities of two agents actually converge to the same settled opinion. I call this mode of convergence ‘deterministic’, and derive results that extend theorems in (Huttegger [2015b]). The results here lead to a simple characterization of deterministic convergence for Bayesian learners and give rise to an interesting argument for what I call ‘strong regularity’, the view that probabilities of non-empty events should be bounded away from zero. 1Introduction2Preliminaries3Deterministic Convergence4Consensus in the Limit5Strong Regularity6ConclusionAppendix

High-Resolution Insights into the Stepwise Self-Assembly of Nanofiber from Bioactive Peptides

Peptide self-assembly has a profound biological significance since self-assembled bioactive peptides are gifted with improved bioactivity as well as life-span. In this study, peptide self-assembly was investigated using a therapeutic peptide, PTP-7S (EENFLGALFKALSKLL). Combining experiments of atomic force microscopy (AFM), circular dichroism (CD), and 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence spectra, PTP-7S showed the α-helical structure and was found self-assembling into nanofibers in solution. Relying on the coarse-grained (CG) dynamic simulations, the self-assembling of PTP-7S was revealed as a stepwise process that peptide monomers first clustered into peptide-assembling units (PUs) with charged surface, and then the PUs integrated together to construct nanofibril aggregates. Different roles of the nonbonded driving forces did play in the two phases: the hydrophobic force and electrostatic interaction acted as the predominant motivations in the formation of PUs and nanofiber, respectively. Moreover, the electrostatic interaction helped to guide the longitudinal growth of peptide nanofibers. A sequence principle is proposed for peptide self-assembling in aqueous solution: a balance of the counter charges and sufficient hydrophobicity degree. The self-assembled PTP-7S displayed good anticancer activity, proteases resistance, and sustained drug-release, showing a great potential for clinical application. This study reveals the molecular mechanism in explaining PTP-7S self-assembly and it is beneficial for future innovation of the self-assembled bioactive peptides.

Electrokinetics and behavior near the interface of colloidal particles in non-polar dispersions.

The electrokinetics and charging of nonpolar colloidal dispersions subjected to a voltage are investigated by electric current and optical measurements. From electric current measurements in response to an alternating triangular voltage with a peak value of a few hundred volts, we find that polystyrene toner particles are compacted near the electrodes and their charge increases by more than a factor of 20. The important increase of charge is interpreted by a mechanism in which counter charges, which are originally at the particle surface, are desorbed. Optical measurements performed under a dc voltage of the order of a few hundred volts demonstrate that the charge of the particles can again decrease or even be inverted. These phenomena are attributed to the movement of counter charged species from the interface layers onto the surface of the particles. The findings of this study are relevant for electrophoretic displays and liquid toner printing.

Theoretical Modeling of Erosion-Corrosion of Stainless Steel in NaCl Solution Containing Silica Sand

Erosion-corrosion is an intricate interaction between mechanical damage process (e.g. solid particle impingement) and electrochemical corrosion process which generally results in severe material loss and premature equipment failure. One of the phenomena that are attracting a lot of attentions is the so-called critical flow velocity (CFV) at which the corrosion state transit from passivation to depassivation. Experimental study indicates that the CFV is a function of sand concentration, sand size, sand density, material under erosion corrosion, and polarization potential. It is envisioned that the CFV and phenomenal laws related to the CFV are keys to elucidate the mechanisms of erosion-corrosion in depth. The first level of the systematical modeling for erosion-corrosion is to define the flow field in the sand impingement apparatus using a CFD simulation tool. The second level is to give a theoretical description of the interaction between sand and the alloy surface (specifically the passivating film) based on the concepts of collision dynamics. The experimental results are analyzed using the model. The third level of the modeling is to conduct a molecular dynamics (MD) simulation to probe the damaging process in a molecular scale. The combination of the CFD and collision dynamics models correctly predicts the pattern of erosion-corrosion of the stainless steel surface under an impingement stream. The dependences of CFV on the concentration of sand and size of the particles are correctly predicted by the model. The dependence of the CFV on the applied potential can also be accounted for by the model. Further analysis indicate that the CFV has no direct relation to the breakdown of the passivating film but correlates with the balance between thinning of the passivating film by impingement and repassivation of the corrosion system. The MD modeling gives a new perspective of the effect of impingement in that the minimum impact causing film thinning by sand is the impact that eliminates the counter charges of the electric double layer (EDL) on the fluid side. The modeling work reconfirms the previous observations that erosion-corrosion is a phenomenon characterized with interactions and cross impacts among mechanical and electrochemical processes.

Osteogenic evaluation of collagen membrane containing drug-loaded polymeric microparticles in a rat calvarial defect model.

The aim of this study was to develop a functional collagen membrane that is treated with poly (lactic-co-glycolic acid) (PLGA) nanoparticles loaded with dexamethasone (DEX) as a bioactive molecule for guided bone regeneration (GBR). The DEX-loaded PLGA microparticles prepared using water-in-oil standard emulsion method were precoated with positively charged polyethylenimine molecules and later immobilized onto the surface of the collagen membrane; the microparticles were physically immobilized using counter charges of positively charged PLGA microparticles and the negatively charged collagen membrane surface. The release profile of DEX over a 4-week immersion study indicated an initial burst release followed by a sustained release. The performance of this system was investigated using rats with calvarial bone defects. The in vivo evaluation of the defects filled with membrane containing DEX-loaded PLGA microparticles indicated enhanced volume and quality of new bone formation compared with defects that were either unfilled or filled with membrane alone. This innovative platform for bioactive molecule delivery more potently induced osteogenesis, which may be exploited in implantable membranes for stem cell therapy or improved in vivo performance. In conclusion, this newly developed collagen membrane treated with drug-loaded PLGA microparticles might be applicable as a promising bone graft substitute for GBR.

Atomic Scale and Interface Interactions in Redox-Based Resistive Switching Memories

Controlling electrochemical processes at interfaces or within thin films at the atomic scale is a key factor for further development of future nanoelectronics and information technology. This aspect becomes even more important considering concepts beyond conventional data storage like neuromorphic and memristive systems, demonstrating learning abilities and allowing logic operations.Redox-based resistive switching memories (ReRAM) are major candidates to fulfil all requirements for low power consumption, ultrafast operation, high information density and non-volatility. Their metal/solid-electrolyte/metal structure makes the preparation process simple and compatible with current CMOS technology. In ReRAMs, the solid electrolyte thickness varies in the range between few nanometers up to some ten nanometers. Due to the small dimensions, the high electric fields in the order of E ~ 108 Vm– 1, and current densities of j ~ 109 Acm– 2, the interface regions are dynamically changing as a function of the thermodynamic and operation conditions. Deposited as nanoscale films, even macroscopic insulating materials like SiO2 and Ta2O5 are able to conduct ions, and electrochemical measurements well known from the liquid electrochemistry can be performed.The talk gives an overview on the current state-of-the-art knowledge on redox-based resistive switching ReRAMs, focusing on the electrochemical dynamics at the metal/solid-electrolyte interfaces of nanoscaled thin films and quantum effects. The electrochemical kinetics during formation of nanofilaments will be discussed along with influence of the local environment and the generic relevance of the counter charges. The relation of these studies to the more fundamental issue of describing the microscopic electrochemical processes at the atomic scale will be emphasized.

A radically new suggestion about the electrodynamics of water: Can the pH index and the Debye relaxation be of a common origin?

The structure of pure water is commonly viewed as an openwork matrix of hydrogen-bonded H2O molecules with a Debye relaxation dynamics. The matrix is filled with free ions of low concentration , which makes water a weak electrolyte with . Traditionally, the Debye relaxation is considered having no relevance to the dc water conductivity (or the pH index): while the Debye relaxation is caused by the dynamics of intact H2O molecules, the dc conductivity, in contrast, is due to self-dissociation of H2O into H3O+ and OH− ions. Here, we consider a microscopic mechanism, which could unify the Debye and the dc dynamics, namely the Brownian-like motion of strongly interacting ions. The model comprehensively describes the low-energy electrodynamics of water (up to ) giving however an unexpected outcome: water behaves as if it had far more free ions than the standard model assumes. High concentration of counter charges results in a polarization structure of water. We recognize full well that such a radical model is contrary to many years of research on the dynamics, thermodynamics, and dielectric properties of water; but the results seem logically consistent and may prove stimulating.

India–Pakistan Peace Process

Attempts to stay engaged in a process of sustained dialogue and achieve incremental progress towards peace by the Indian and Pakistani political leadership suffered another setback in the form of cross-border firing and allegations of ceasefire violations along the Line of Control and the international boundary in 2013. While New Delhi’s Congress party-led regime, facing parliamentary elections in 2014, buckled under pressure from an intrusive media and the opposition political parties, the new civilian government in Islamabad, in its edgy relationship with the country’s powerful military, put the peace project in the back burner. As allegations and counter charges flew, incapacities of both countries to bring the situation under control were reinforced. The article uses this case study to assess the intent of as well as limitations on leadership of both countries for staying engaged in a process of dialogue. Not just their commitment to peace, but the ability to defy the limitations would shape the future of Indo–Pak relations, the article argues.

Quantifying Artifacts in Ewald Simulations of Inhomogeneous Systems with a Net Charge

Ewald summation, which has become the de facto standard for computing electrostatic interactions in biomolecular simulations, formally requires that the simulation box is neutral. For non-neutral systems, the Ewald algorithm implicitly introduces a uniform background charge distribution that effectively neutralizes the simulation box. Because a uniform distribution of counter charges typically deviates from the spatial distribution of counterions in real systems, artifacts may arise, in particular in systems with an inhomogeneous dielectric constant. Here, we derive an analytical expression for the effect of using an implicit background charge instead of explicit counterions, on the chemical potential of ions in heterogeneous systems, which (i) provides a quantitative criterium for deciding if the background charge offers an acceptable trade-off between artifacts arising from sampling problems and artifacts arising from the homogeneous background charge distribution, and (ii) can be used to correct this artifact in certain cases. Our model quantifies the artifact in terms of the difference in charge density between the non-neutral system with a uniform neutralizing background charge and the real neutral system with a physically correct distribution of explicit counterions. We show that for inhomogeneous systems, such as proteins and membranes in water, the artifact manifests itself by an overstabilization of ions inside the lower dielectric by tens to even hundreds kilojoules per mole. We have tested the accuracy of our model in molecular dynamics simulations and found that the error in the calculated free energy for moving a test charge from water into hexadecane, at different net charges of the system and different simulation box sizes, is correctly predicted by the model. The calculations further confirm that the incorrect distribution of counter charges in the simulation box is solely responsible for the errors in the PMFs.

Electrostatic Interactions in the Closed and Open States of Voltage-Gated Proton Channels

Voltage-gated proton channels (Hv1) play important roles in the respiratory burst, in pH regulation, in spermatozoa, in apoptosis, and in cancer metastasis. Unlike other voltage-gated cation channels, the Hv1 channel lacks a centrally located pore formed by the assembly of subunits. Instead, the proton permeation pathway in the Hv1 channel is within the voltage-sensing domain of each subunit. The gating mechanism of this pathway is still unclear. Mutagenic and fluorescence studies suggest that the fourth transmembrane segment, S4, functions as the voltage sensor and that there is an outward movement of S4 during channel activation. Using thermodynamic mutant cycle analysis, we find that the conserved positively charged residues in S4 are stabilized by counter charges in the other transmembrane segments both in the closed and open states. We construct models of both the closed and open states of Hv1 that are consistent with the mutant cycle analysis. These structural models suggest that electrostatic interactions between transmembrane segments in the closed state pull hydrophobic residues together to form a hydrophobic plug in the center of the voltage-sensing domain. Outward movement of S4 removes the hydrophobic plug, as if this hydrophobic plug works as the gate that prevents protons to permeate the Hv1 channel in the closed state.

Lipid Affinity to the Voltage-Gated Potassium Channel KvAP

Voltage-gated potassium channels (KV) are formed by a central conducting pore surrounded by four voltage sensor domains. Functional studies have revealed that biophysical properties of lipid molecules in the channels environment can have strong effects on the activity of KV channels. Here, we investigated the influence of different lipids as well as their affinity to KvAP channels. We carried out electrophysiology measurements by fusing vesicles containing purified channels into planar lipid bilayers with varied lipid compositions. We found that KvAP properties are mainly determined by the lipid composition in the vesicles and not the lipids in the bulk bilayer, suggesting that KvAP has a preferential affinity to the lipids it comes in contact with first. It also shows that there is very limited exchange of the annular lipids around the channels. Even with time and at higher temperature, lipids from the bilayer did not mix with those of the vesicles, suggesting a strong channel-lipid interaction or confinement of lipid molecules to a microdomain around the channel. The annular lipids in immediate proximity of the VSD determines the mid-activation point of KvAP. Additionally, a bulk effect from positively charged lipids forming the bilayer affected the slope of the conductance-voltage curves. Here, the energy barriers and thus the kinetic rates of pore opening and entering the inactivated state are affected. This effect could be neutralized by addition of counter charges to the bilayer. Our results suggest that the binding site proposed also for other Kv channels has a similar affinity for different phospho- and non-phospholipids whereas exchange with bulk lipids is very restricted. Apart from the structural information, this has also implications on the experimental design when working with membrane proteins reconstituted in planar lipid bilayer.

Generic Relevance of Counter Charges for Cation-Based Nanoscale Resistive Switching Memories

Resistive switching memories (ReRAMs) are the major candidates for replacing the state-of-the-art memory technology in future nanoelectronics. These nonvolatile memory cells are based on nanoionic redox processes and offer prospects for high scalability, ultrafast write and read access, and low power consumption. The interfacial electrochemical reactions of oxidation and reduction of ions necessarily needed for resistive switching result inevitably in nonequilibrium states, which play a fundamental role in the processes involved during device operation. We report on nonequilibrium states in SiO2-based ReRAMs being induced during the resistance transition. It is demonstrated that the formation of metallic cations proceeds in parallel to reduction of moisture, supplied by the ambient. The latter results in the formation of an electromotive force in the range of up to 600 mV. The outcome of the study highlights the hitherto overlooked necessity of a counter charge/reaction to keep the charge electroneutrality in cation-transporting thin films, making it hard to analyze and compare experimental results under different ambient conditions such as water partial pressure. Together with the dependence of the electromotive force on the ambient, these results contribute to the microscopic understanding of the resistive switching phenomena in cation-based ReRAMs.