Increase In Charge Density Research Articles

(Invited) Limits of Polymer Electrolyte Membranes

Since their introduction in the 1960’s polymer electrolyte membranes, PEMS, for fuel cells have been extensively studied. Hundreds if not thousands of polymer systems have been synthesized and characterized to improve the critical properties of conductivity, chemical and mechanical durability as well as the lesser important properties of water and gas transport. It is well accepted that these properties are highly dependent on the chemistry of the polymer electrolyte backbone as well as the functional groups and how they organize on the molecular scale. Many models have been used to frame these properties to fit experimental data. What is done less-often is to use the models to then establish the limits of these. Using the conductivity of their small-molecule analogies, triflic acid for PFSA’s and benzene sulfonic acid for hydrocarbons we set limits on conductivity and permeability. Finally we will also look at how the two most common strategies of increasing PEM performance; increasing charge density and acid strength, are limited by mechanical and chemical durability requirements, respectively.

Effect of chitosan size on destabilization of oil/water emulsions stabilized by whey protein

High amounts of effluent with emulsified lipids are produced during dairy process due to the presence of proteins and others surface active compounds. The aim of this work was to understand the effect of chitosan size and charge density on the de-stabilization of dairy emulsions. Emulsion were composed by water, whey protein (WPI) and sunflower and added of chitosan or chitosan oligomers at different concentrations (0.66%, 0.35% and 0.1% w/v). At the emulsion pH (7.0), oligomers were more densely charged ( + 13.80 mV) than chitosan ( + 8.59 mV) which increased their electrostatic attraction to the negatively charged proteins present at the emulsion interface. The complexation was favored by the smaller oligomer size as compared to chitosan, therefore the emulsions added of oligomers showed intense phase separation. The confocal and optical microscopy showed a gel like structure formed by oligomer-protein complexes that surrounded the flocculated droplets in emulsions. Due to the more intense interactions of oligomers at the interface, emulsions containing oligomers presented higher G’ and apparent viscosity values than emulsions added of chitosan. The greater oligomer complexation to WPI retained more protein at the emulsion upper phase and reduced the chemical oxygen demand of the remained aqueous phase. These results indicate that is possible to potentialize the use of chitosan as de-emulsifier by the reduction of its size and increase of charge density.

Effects of liquid metal particles on performance of triboelectric nanogenerator with electrospun polyacrylonitrile fiber films

Liquid metal (LM) has been used as flexible electrodes for high performance triboelectric nanogenerators (TENGs), however it is unclear how the LM in tribo-layers would affect the performance of TENGs. Here, we report the investigation on the effects of LM particles incorporated into a tribo-layer on the performance of TENGs. The TENGs consist of a polyacrylonitrile (PAN) electrospinning nanofiber membrane, and a polytetrafluoroethylene (PTFE) thin film. LM particles with different concentrations are incorporated into PAN polymer matrix, and used to make the PAN nanofibers membranes by electrospinning. Result shows that the outputs of TENGs become much larger with the increase in LM content. Specifically, the current density increases by about 40%, and both the charge density and output voltage increase by nearly 70%. The overall output power is approximately 2 times higher for the TENG with 1.5 wt% LM concentration, as compared to those of TENGs with pure PAN tribo-layer. However, the output of PAN/LM-PTFE TENGs deteriorates drastically when the LM mass content is increased to 2.5 wt%, at which the composite contains a high density of LM spheroid and spindle particles, deteriorating the generation of triboelectric charge.

Formation potential of nine nitrosamines from polyacrylamide during chloramination

Cationic polymers, which are commonly used as flocculants and coagulant aids in water and wastewater treatment, have been recently reported to promote the formation of nitrosamines. Most of the findings to date are based on poly (epichlorohydrin dimethylamine) and poly (diallyldimethylammonium chloride), while few studies have considered nitrosamines formation of polyacrylamides. In this work, the nitrosamines formation from non-ionic, anionic and cationic polyacrylamides was evaluated. Moreover, the effects of chemical structures of cationic polyacrylamides (including molecular weight, charge density, and monomers) on nitrosamines formation were investigated. The results revealed that the highest amount of nitrosamines formation was formed from cationic polyacrylamide, followed by non-ionic polyacrylamide and anionic polyacrylamide. Molecular weight and various cationic monomers showed no significant effects on nitrosamines formation, but monomers generated significantly higher amount of nitrosamines formation than cationic polyacrylamides. Nitrosamines formation increased with the increasing charge density of cationic polyacrylamides, and FTIR analysis results showed that the quaternary amine groups preferentially reacted with chloramines than with amide groups. This work shed new light on the nitrosamines formation from water and wastewater treatment polymers.

Mechanistic Insight into Photocatalytic Pathways of MIL-100(Fe)/TiO2 Composites.

The integration of metal-organic frameworks (MOFs) with semiconductors has attracted mounting attention for photocatalytic applications. However, more efforts are needed to unravel the interface structure in MOF/semiconductor composites and its role in charge transfer. Herein, a MIL-100(Fe)/TiO2 composite was synthesized as a prototypical photocatalyst and studied systematically to explore the interface structure and unravel the charge transfer pathways during the photocatalytic processes. The composite was fabricated by growing MIL-100(Fe) crystals on TiO2 using surface-coated FeOOH as the precursor. The as-prepared MIL-100(Fe)/TiO2 exhibited significantly improved photocatalytic performance over pristine TiO2, which was mainly because of the enhanced charge separation as confirmed by transient absorption spectroscopy analysis. This enhancement partially arose from the special chemical structure at the interface, where the Fe-O-Ti bond was formed. As verified by the density functional theory calculation, this distinct structure would create defect energy levels adjacent to the valence band maximum of TiO2. During the photocatalytic processes, the defect energy levels serve as sinks to capture excited charge carriers and retard the recombination, which subsequently leads to the increased charge density and promoted photocatalytic efficiency. Meanwhile, the intimate interactions between MIL-100(Fe) and TiO2 would also help to improve the charge separation by transferring photo-induced holes through the ligands to Fe-O clusters. These findings would advance the fundamental understanding of the interface structure and the charge transfer pathways in MOF/semiconductor composite photocatalysts.

Engineering Peptide-Based Polyelectrolyte Complexes with Increased Hydrophobicity.

Polyelectrolyte complexation is a versatile platform for the design of self-assembled materials. Here we use rational design to create ionic hydrophobically-patterned peptides that allow us to precisely explore the role of hydrophobicity on electrostatic self-assembly. Polycations and polyanions were designed and synthesized with an alternating sequence of d- and l-chiral patterns of lysine or glutamic acid with either glycine, alanine or leucine due to their increasing hydrophobicity index, respectively. Two motifs were considered for the oppositely charged patterned peptides; one with equal residues of charged and uncharged amino acids and the other with increased charge density. Mass spectroscopy, circular dichroism, H- and F-NMR spectroscopy were used to characterize the polypeptides. Polyelectrolyte complexes (PECs) formed using the sequences were characterized using turbidity measurements, optical microscopy and infrared spectroscopy. Our results show that the critical salt concentration, a key measure of PEC stability, increased with both increasing charge density as well as hydrophobicity. Furthermore, by increasing the hydrophobicity, the amount of PEC formed increased with temperature, contrary to purely ionic PECs. Lastly, we assessed the encapsulation behavior of these materials using a hydrophobic dye. Concluding that encapsulation efficiency increased with hydrophobic content of the complexes providing insight for future work on the application of these materials for drug delivery.

Adsorptive removal of C.I. Direct Yellow 142 from textile baths using nanosized silica-titanium oxide

.The adsorption properties of the silica-titanium mixed oxide consisting of 80 wt.% SiO2 and 20 wt.% TiO2 (ST20) in relation to C.I. Direct Yellow 142 (DY142) were examined. The experimental adsorption capacity of ST20 for DY142 determined at room temperature equals 104.8 mg/g. The equilibrium data were fitted by means of the Freundlich, Langmuir and Tempkin isotherm models. The values of determination coefficients (r2) confirmed applicability of the Langmuir ( r^{2}=0.990) isotherm model, the monolayer capacity was found to be 106.5 mg/g. The kinetic parameters calculated from the pseudo-first-order (PFO) and pseudo-second-order (PSO) equations as well as the intraparticle diffusion (IPD) model revealed that the chemisorption is the rate limiting step as the r2 value obtained for the pseudo-second-order model equals 0.999. The PSO adsorption rate constant was found to be 0.070 g/mg min. The presence of additives such as electrolytes (Na2SO4 and Na2CO3) and surface active agents (anionic SDS, cationic CTAB and non-ionic Triton X-100) reduce dye retention compared to systems that do not contain these additives. The presence of the dye with the anionic character in the colloidal suspension of ST20 oxide particles results in considerable increase of the solid surface charge density. In the systems of mixed adsorbates (dye-surfactant and dye-salt) the specific changes in surface properties were obtained --the cationic surfactant has the greatest effect on the solid surface groups type and its concentration.

General adsorption model for H2S, H2Se, H2Te, NH3, PH3, AsH3 and SbH3 on the V2O5(0 0 1) surface including the van der Waals interaction

Density functional theory, including the van der Waals interaction, has been used to study the interaction between some small molecules with lone pairs and the V2O5(001) surface. Results reveal that the naked vanadium atom is the most important centre of attraction to the hazardous molecules considered in the present work, regardless of the vdW functional employed. The contour plot of each charge density difference shows an increase of charge density in the lone pair close to the surface. The attractive interaction between each adsorbed molecule and the surface proves to be weak, with a strong role of the vdW interaction.

Improvement in the passivation quality of catalytic-chemical-vapor-deposited silicon nitride films on crystalline Si at room temperature

We observe an improvement in the passivation quality of silicon nitride (SiNx) films formed on crystalline silicon wafers by catalytic chemical vapor deposition (Cat-CVD) under the storage at room temperature. Fluorescent light illumination enhances the improvement in the passivation quality of Cat-CVD SiNx films, although the passivation quality is also improved in the dark. We do not see any change of bonding configurations in the SiNx films by the storage at room temperature. Capacitance–voltage measurement reveals that an increase in positive charge density in the SiNx films improves their passivation quality. The improvement in the passivation quality of SiNx films is observed for SiNx films deposited at various substrate temperatures, and SiNx films deposited at higher temperature tends to show more significant improvement in the passivation quality.

Electrokinetic energy conversion of two-layer fluids through nanofluidic channels

Based on the Onsager reciprocal relation in the linear response regime, we first clarify the equivalence of thermodynamic and electric circuit analyses for electrokinetic energy conversion. Then we present a streaming-potential-based nanofluidic energy conversion system which comprises two immiscible fluids that form a flat interface in a slit-like channel. The validity of the Onsager reciprocal relation to such a two-fluid system is verified. The performance of such an energy converter is illustrated by considering two concrete oil–water systems with different properties. In both cases, we predict that the binary system with a thin oil layer increases both the maximum output power and the energy conversion efficiency, and this enhancement depends strongly on the mobile charges present at the oil–water interface, the salt concentration and the interface location. Concretely, for negatively charged interfaces, we find that the optimal efficiency increases with the interfacial charge for relatively thin oil layers; while for relatively thick oil layers, the interfacial charge has the opposite effect (i.e. reduction effect) on the energy conversion efficiency in the ranges of the parameters. We further investigate these systems from the viewpoint of energy transfer by deriving the related energy equation. We find that viscous dissipation consumes most of the power (more than 90 %), in both single-phase and two-fluid flows. However, the ratio of the viscous dissipation to the power input decreases with increase of the interfacial charge density for the case of a relatively thin oil layer in two-fluid flows. Meanwhile, although the presence of interfacial charges can lead to an increase in electrical dissipation, the amount of the increased power consumption is less than that of the reduced viscous dissipation in the case of a thin oil layer. Therefore, for two-fluid energy converters, the total power consumption can be reduced and the efficiency is improved.

A novel antimicrobial peptide-derived vehicle for oligodeoxynucleotide delivery to inhibit TNF-α expression

Indolicidin (IL), an antimicrobial peptide, was investigated as a vehicle to promote oligodeoxynucleotides (ODNs) delivery. To increase charge density, IL was dimerized by adding a cysteine to its C or N terminus, which was denoted as ILC or CIL, respectively. In contrast to IL, cytotoxicity of ILC and CIL was significantly reduced because these dimeric peptides were longer than IL, which restricted their insertions to cell membrane. In contrast to ILC, CIL displayed well loading efficiency. These peptides were applied to deliver ODNs against tumor necrosis factor-α (TNF-α) because TNF-α is a pro-inflammatory cytokine which plays an important role in immunological diseases. Although IL/ODN slightly reduced TNF-α expression, the high cytotoxicity restricted its application window. Furthermore, ILC/ODN was incapable of inducing gene silence due to its low encapsulation efficiency and poor endosomal escape. In contrast, CIL exhibited excellent ODN transportation and the internalized CIL/ODN complexes may escape from endosomes. Therefore, TNF-α expression can be specifically reduced by CIL/ODN complexes, and the silence effect was maintained longer than 14 h. This study provides a useful strategy of peptide vehicle design, which may facilitate the delivery of not only ODN but also other oligonucleotides, including siRNA and miRNA, to promote gene silence application.

A spatially varying charge model for regulating site-selective protein adsorption and cell behaviors.

Implanted materials that enter the body first interact with proteins in body fluids, and cells then perceive and respond to the foreign implant through this layer of adsorbed proteins. Thus, spatially specific regulation of protein adsorption on an implant surface is pivotal for mediating subsequent cellular behaviors. Unlike the surface modulation strategy for traditional biomaterials, in this research, materials with a nonuniform spatial distribution of surface charges were designed to achieve site-selective protein adsorption and further influence cell behavior by charge regulation. Spatially varying microdomains with different levels of piezoelectricity were generated via a focus laser beam-induced phase transition. In addition, after polarization, the zones with different levels of piezoelectricity showed significant differences in surface charge density. The results of scanning Kelvin probe force microscopy (SKPM) showed that the surface charge on the material exhibits a nonuniform spatial distribution after laser irradiation and polarization. Site-specific charge-mediated selective protein adsorption was demonstrated through a protein adsorption experiment. Cell behavior analysis showed that the increase in charge density was conducive to promoting cell adhesion and the formation of filopodia while the nonuniform spatial distribution of charge promoted an oriented arrangement of cells; both features accelerated cell migration. This study provides a new method for spatially regulating protein adsorption through surface charges to further influence cell behaviors.

Chemically modified cellulose nanocrystals as polyanion for preparation of polyelectrolyte complex

Bacterial cellulose nanocrystals (BCNCs) have hydrophilic surfaces due to hydroxyl groups but are water-insoluble. The carboxymethylation improves the solubility of cellulose in polar media through the insertion of carboxymethyl groups. This study aims to evaluate the use of two different alcoholic solvents in the carboxymethylation reaction of BCNCs: ethanol and isopropanol. BCNCs were obtained under two hydrolysis conditions: sulfuric acid (BCNC-S) and combination of sulfuric and hydrochloric acids (BCNC-S/Cl). Two techniques (NMR and titration) were used to determine the degree of substitution (DS) values. Carboxymethylation of BCNC-S/Cl led to high DS compared to BCNC-S and the use of isopropanol promoted an even greater DS. The thermal properties were not affected after the chemical modification. However, functionalization provided an increase in the negative charge density at the surface of nanostructures and a change in the crystal structure (cellulose type Iα for amorphous), making this material a potential polyanion for the synthesis of polyelectrolyte complexes (PECs). The micrographs showed that the nanocrystals became soluble after carboxymethylation. Carboxymethylated bacterial cellulose nanocrystals hydrolyzed through the mixture of inorganic acids and modified using isopropanol (CBCNC-S/Cl-IPA) was a suitable polyanion to produce PECs with chitosan. The PECs produced had particle size ranging from 276 to 588 nm and zeta potential ranging from − 24.3 to + 39.0 mV.

Об инкрементах неустойчивости волн различной симметрии на движущейся относительно материальной среды объемно заряженной струе

The increments of instability of capillary waves with arbitrary symmetry (with arbitrary azimuthal numbers ) on the surface of a volume charged cylindrical jet of an ideal incompressible dielectric fluid moving relative to an ideal incompressible material dielectric medium are investigated. It is shown that at not too high velocities of the jet motion, with an increase in the volume charge density, the axisymmetric mode ( m=0) becomes unstable first, then the bending mode ( m=1), and then the bending-deformation mode (m=2 ).This sequence of realization of the instability of azimuthal modes and determines the patterns of fragmentation of charged jets in the experiments. At jet speeds comparable to the critical for the realization of aerodynamic instability, the first loses stability mode whis . For all azimuthal modes, the dependences of the maximum increments on the wave numbers are determined.

Electro-optical and dielectric performance analysis: the influence of azo dye on polymer/LC composite structures

In the present work, electro-optical and dielectric properties of polymer/LC doped with azo dye methyl red (MR) were investigated. Norland optical adhesive (NOA65) and nematic liquid-crystal (E63-coded nematic liquid crystal) materials were used to compose of polymer/LC composite structure. A doping agent ratio of MR was chosen 1% wt/wt in polymer/LC composite structure. Dielectric measurements of the obtained samples were held between 10 Hz and 10 MHz at room temperature using dielectric/impedance analyzer. Physical parameters such as dielectric permittivity, dielectric anisotropy, electric modulus, loss tangent, relaxation frequency, relaxation time, threshold voltage, and splay elastic constant were obtained from experimental data. Optical bandgap values of polymer/LC and polymer/LC/MR composite structures were estimated using UV spectroscopy technique. Polymer/LC composite structures’ electro-optical properties were affected the MR dispersal which was reduced the anchoring force between polymer and LC molecules; therefore, threshold voltage and splay elastic constant decreased. In addition, dispersal of MR caused a decrease in optical bandgap values of polymer/LC composite structures. Due to the increase in charge density caused by MR, the value of the current passing through the polymer/LC composite structures increased as well as its dependence on voltage. Results show that MR dispersal enhanced electro-optical and dielectric properties of polymer/LC composite structures and makes it suitable to design new based on optoelectronic device applications.

Enhancement of colloidal particle and lignin removal from pre-hydrolysis liquor by pectinase pre-treatment – Study on model substances

Removal of colloidal particle and lignin from pre-hydrolysis liquor (PHL) is important for the subsequent processing and utilization of the saccharides in the PHL. Cationic polymers treatment is a common method for the purpose, and pectinase pre-treatment of PHL can improve the efficiency of the treatment with cationic polymers. To investigate the mechanism of pectinase pre-treatment for improvement of the cationic polymer efficiency, polygalacturonic acid (PGA) was added in the colloidal lignin and dissolved lignin model substances systems, respectively, and the effects of polygalacturonic acid (PGA) and its pectinase pre-treatment on the removal of colloidal and dissolved lignin in the following cationic polymer treatment process were studied. The results showed that the presence of PGA caused the increase of negative charge density of the colloidal lignin and dissolved lignin systems, which lowered the efficiency of the cationic polymers and negatively affected the removal of both the colloidal lignin and the dissolved lignin. After pectinase treatment, the PGA present in the colloidal and dissolved lignin system was degraded and the negative effects on the cationic polymers were eliminated, and the efficiency of the cationic polymers was improved. Compared to the colloidal lignin and dissolved lignin systems with PGA, less cationic polymers were needed for the same systems with pectinase treatment to obtain the similar lignin removal level.

Full spectrum light driven photocatalytic in-situ epitaxy of one-unit-cell Bi2O2CO3 layers on Bi2O4 nanocrystals for highly efficient photocatalysis and mechanism unveiling

In-situ epitaxial growth is a fascinating strategy to nicely couple two low dimensional semiconductors as highly efficient composite photocatalysts. Meanwhile, organic contaminants in the photocatalytic process are usually decomposed into greenhouse gas (CO2) that can’t be reused. Herein, we reported a green full spectrum light (UV, visible and NIR lights) induced epitaxial growth strategy to synthesize highly efficient Bi2O4/Bi2O2CO3 heterostructure photocatalyst by reusing waste carbon source, in which one-unit-cell Bi2O2CO3 layers (1.0 nm) in-situ grew on the surface of Bi2O4 nanocrystals during the photocatalytic degradation of rhodamine B (RhB) or phenol. More importantly, 13C nuclear magnetic resonance (NMR) spectroscopy confirmed that the carbon element in Bi2O2CO3 was from the photocatalytic degradation of organic contaminations. Furthermore, density functional theory (DFT) calculations confirm that the Bi2O4 nanocrystals with exposed {-101} facets have the larger percentage of undercoordinated Bi atoms, which provided favorable conditions for the in-situ epitaxy of Bi2O2CO3 during the photocatalytic reaction. Additionally, the increased charge density near the Fermi level resulted in improved photoresponsivity of Bi2O4/Bi2O2CO3 composite and the coalescence of Bi2O4 and Bi2O2CO3 could favor the travel of photogenerated carriers from one to another owing to the close work functions for Bi2O4 (4.295 eV) and Bi2O2CO3 (4.410 eV). As we expected, the Bi2O4/Bi2O2CO3 composite presented higher photocatalytic activity for phenol and ciprofloxacin (CIP) degradation than pure Bi2O4 nanocrystals. The possible degradation pathway of CIP in aqueous solution and photocatalytic mechanism of Bi2O4/Bi2O2CO3 composite were also proposed based on liquid chromatography mass spectrometer (LC–MS) analysis and experimental results. This work provides a green strategy for designing highly efficient photocatalysts.

Actuation increase in polypyrrole bilayer by photo-activated dopants

A new methodology to increase the polypyrrole (PPy) bilayer actuation displacement is presented, based on photo-activated dopants generating secondary charges. Two dopants, dodecyl benzenesulfonate (DBS) and the photo-active dopant 2-diazo-1-naphthol-5-sulfonic acid (DNSA), were compared in this study. PPy/DBS, PPy/DBS-DNSA and PPy/DNSA bilayers on polyethylene terephthalate were formed and their actuation properties in aqueous electrolyte were investigated applying cyclic voltammetry and square wave potential steps. Exposure to solar irradiation increased PPy/DBS-DNSA and PPy/DNSA bilayer bending displacements by two and three times, respectively, accompanied by increased charge density during the reversible redox cycles. UV–vis and Fourier transform infrared (FTIR) measurements were also performed to follow the photo reaction of the photo-active dopants.

Ab initio investigation of Fe substitution effect on magnetostructural transition of CoMnGe

First-principles calculations for the ferromagnetic systems (Co,Fe)MnGe and Co(Mn,Fe)Ge show the hexagonal cell volume decreases as an amount of Fe increases mainly because of the reduction of the lattice constant c. The Fe substitution produces a reduction in the distance between adjacent atoms along the direction of the c axis and an increase in charge density between those atoms. This enhancement of the covalent bond is responsible for the hexagonal-structure stabilization or a decrease of the structural transition temperature from hexagonal to orthorhombic phases.

Effect of halides on the solvation of poly(ethylene oxide) in the ionic liquid propylammonium nitrate

HypothesisThe solvation characteristics of poly(ethylene oxide) (PEO) in nanostructured protic ionic liquids (PILs) are driven by polymer-solvent interactions in the polar domains of the PIL. This work hypothesises that the nanostructure of a PIL can be altered via halide addition, directly affecting the solvation of PEO. ExperimentsSmall angle neutron scattering (SANS) is used to explore the conformation of 38 kDa PEO dissolved in the PIL propylammonium nitrate (PAN), a mol fraction of 10% propylammonium chloride (PACl) in PAN, and a mole fraction of 10% propylammonium bromide (PABr) in PAN. FindingsEach of these solutions are shown to behave as a good solvent for PEO, as determined by their Flory exponents and Zimm plot analysis. The quality of solvation is reduced by the addition of the halide salt, with the order of solvation as follows: PAN > Br− addition > Cl− addition. Our experimental observations are consistent with the recently reported solvation structure of PEO in these solutions (Stefanovic et al., 2018). The increased charge density from NO3− to Br− to Cl− results in greater net ionic interaction between the ionic charge centres. As PEO interacts with PAN primarily through the ammonium hydrogens of the cation, this increased ionic interaction effectively displaces the PEO, resulting in poorer solvation.