Contribution To Surface Charge Research Articles

Cellulose nanofibrils-stabilized food-grade Pickering emulsions: Clarifying surface charge's contribution and advancing stabilization mechanism understanding

Pickering emulsions stabilized by cellulose nanofibrils (CN) have sparked significant attention, however the fundamental mechanisms underpinning the stabilization process remain insufficiently elucidated. Focusing on an academic debate of surface charge's contribution to stabilization, this study first explored how the varying carboxyl group contents of TEMPO-oxidized CN (TCNs) impacted Pickering emulsions' formation and stability. TCNs with 662 μmol/g carboxyl groups exhibited distinctive attributes, including larger particle sizes (322 nm in length), improved thermal stability (maximum decomposition temperature of 317 °C), and increased viscosity (1.57 Paִִ⋅s) compared to their counterparts with 963–1011 μmol/g charge density. Notably, the former one, with a larger three-phase contact angle (51.5°), higher interfacial tension, and greater detachment energy (21.69 × 10−18 J), resulted in a homogeneous dispersion of spherical oil droplets and super-stable Pickering emulsions with a consistent emulsifying index of 100% over 30 days. These findings clearly clarified that TCNs with a lower charge density exhibit superior emulsifying properties. In addition, for the first time, a distinct oil droplet-decorated fibrillar structure was observed, probably suggesting that TCNs might be able to serve as anchoring matrixes to guide the distribution of oil droplets. These structures seemed to impeded the migration and accumulation of the oil droplets, consequently enhancing the stability of the resulting Pickering emulsions. To sum, this study clearly elucidated the role of surface charge in stabilizing cellulose-based Pickering emulsions and proposed a new model to expound the cellulose-oil interaction mechanisms, thus providing new theoretical and practical insights on utilization of CN as highly effective emulsifier for super-stable food-grade Pickering emulsions.

Diffusion and surface charge studies of waste cow dung derived highly porous carbon as a facile electrode for solid-state supercapacitors

Carbon-based materials generated from biowaste have recently attracted interest due to their exceptional surface and conductive properties. Cow dung derived porous carbon (CDPC) with a 3D structure and linked pores is synthesized in this study, making it an alternative electrode for supercapacitors (SC). Herein, we studied the diffusion and surface charge contribution and their relationship with the scan rate. Diffusion charge contribution is more prevalent at lower scan rates. Furthermore, a large fraction of surface charge contribution of 69.2 % at a high scan rate of 100 mV/s indicates rapid electrochemical kinetics and hence high-rate performance even at higher current densities. In addition, utilizing a 1 M H 2 SO 4 electrolyte, the CDPC electrode has attained a high specific capacitance value of 210 F/g at 0.5 A/g. Furthermore, symmetrical solid-state SC device displayed high energy density of 36 Wh/kg at good power density of 800 W/kg along with remarkable cyclic stability of 92.6 % after 10,000 charge-discharge cycles. Hence, these findings demonstrate that investigating surface and diffusion charge contributions opens up new avenues for tuning the supercapacitor performance. • Waste cow dung derived carbon obtained by hydrothermal carbonization and activation • Surface and diffusion charge contribution studies are performed for CDPC electrode. • Solid-state symmetrical SC assembled using two CDPC electrodes and gel electrolyte • Device retains long cycle life of 92.6 % after 10,000 charge-discharge cycles. • Device delivers high energy density of 40 Wh/kg at a power density of 907 W/kg.

A transversal approach to predict surface charge compensation in piezoelectric force microscopy

Piezoelectric force microscopy (PFM) has demonstrated to be a powerful tool to characterize ferroelectric materials. However, extrinsic effects, most notably, those resulting from surface charges, often mask or mirror genuine piezoelectric response, challenging PFM data understanding. The contribution of surface charges to PFM signal is commonly compensated by using appropriate external bias voltage, which is ad-hoc selected and sample dependent. Here, we determine the compensating voltage in thin films of different ferroelectric materials and we compare with the corresponding I-V characteristics recorded using suitable electrodes. It turns out that the sign and magnitude of the bias voltage required to compensate the surface charges are related to the asymmetry of the I-V characteristics. We propose that this relation results from the fact that the semiconducting properties of the material determine both the I-V dependence, and the sign of charged adsorbates. We show how to make use of this correlation to predict the required compensation voltage of a non-ferroelectric material and we show that spurious piezoelectric-like contributions are largely cancelled. The results provide guidelines to mitigate common extrinsic contributions in PFM imaging.

Rational Design of Plant Hairpin-like Peptide EcAMP1: Structural–Functional Correlations to Reveal Antibacterial and Antifungal Activity

Plant antimicrobial peptides from the α-hairpinins family (hairpin-like peptides) are known to possess a wide range of biological activities. However, less is known about the structural determinants of their antimicrobial activity. Here, we suggest that spatial structure as well as surface charge and hydrophobicity level contribute to the antimicrobial properties of α-hairpinin EcAMP1 from barnyard grass (Echinochloa cruss-galli) seeds. To examine the role of the peptide spatial structure, two truncated forms of EcAMP1 restricted by inner and outer cysteine pairs were synthesized. It was shown that both truncated forms of EcAMP1 lost their antibacterial activity. In addition, their antifungal activity became weaker. To review the contribution of surface charge and hydrophobicity, another two peptides were designed. One of them carried single amino acid substitution from tryptophan to alanine residue at the 20th position. The second one represented a truncated form of the native EcAMP1 lacking six C-terminal residues. But the α-helix was kept intact. It was shown that the antifungal activity of both modified peptides weakened. Thereby we can conclude that the secondary structural integrity, hydrophobic properties, and surface charge all play roles in the antimicrobial properties of α-hairpinins. In addition, the antibacterial activity of cereal α-hairpinins against Gram-positive bacteria was described for the first time. This study expands on the knowledge of structure–function interactions in antimicrobial α-hairpinins.

SnO2/SnxMo1−xO3−x solid solution nanocomposites: Demonstration of enhanced lithium storage behavior with general synergistic effects

SnO2/SnxMo1−xO3−x solid solution-based nanocomposites have been prepared via a two-step hydrothermal and following annealing processes. At a Sn/Mo molar ratio of 1:2 (the Sn/Mo = 1:2), a single-phase SnxMo1−xO3−x with ionic flake-like structure can be obtained; while, a SnO2/SnxMo1−xO3−x solid solution nanocomposite can be obtained at a Sn/Mo molar ratio of 1:1 (the Sn/Mo = 1:1), which combines with iconic sphere and flake-like structure. Then, electrochemical properties are systematically studied with pure SnO2 and pure MoO3 comparisons as anodes for LIBs. The after cycled Sn/Mo = 1:1 electrode could contain three phases of metallic Sn, MoO2 and an amorphous Sn-Mo oxides, which provide a general synergistic effect to enhance the surface charge contribution, reduce the charge transfer resistance and increase the reaction kinetics. Specifically, the Sn/Mo = 1:1 electrode exhibits a high initial coulombic efficiency of 73.5% with an excellent reversible lithium storage capacity of 735 mAh g−1 at a current density of 0.4 A g−1 after 500 cycles, and a high-rate performance with a specific capacity of 337 mAh g−1 can be obtained at current density of 4 A g−1. This work could provide some inspirations to design solid solution-based nanocomposite with a general synergistic effect to enhance the electrochemical performance for lithium storage application.

Surface and diffusion charge contribution study of neem leaves derived porous carbon electrode for supercapacitor applications using acidic, basic, and neutral electrolytes

Biowastes derived carbon based materials are recently gaining attention due to their extraordinary surface and conductive characteristics. Herein, neem leaves derived porous carbon (NAC) with a 3D framework and interconnected pores are synthesized which shows hierarchal pore size distribution along with good conductivity that makes it a suitable electrode material for supercapacitors. However, the surface charge contribution highly affects the electrochemical performance of the electrodes. In addition, a high fraction of surface charge contribution suggests the fast electrochemical kinetics and hence shows the ability of the electrode to work at a high charge-discharge rate. Therefore, the NAC electrode showed a maximum surface contribution of 72% in 6M KOH electrolyte as compared to 1M H2SO4 (21%) and 1M Na2SO4 (20%) electrolyte. Furthermore, the NAC electrode shows a specific capacitance value of 178 F/g using a 6M KOH electrolyte, which is much higher than 93 F/g for 1M H2SO4 and 136.7 F/g for 1M Na2SO4 electrolyte at the constant scan rate of 5 mV/s. Therefore, these results confirm that the study of surface and diffusion charge contribution gives new directions to tune the electrochemical performance of supercapacitor electrodes.

Contribution of surface charges on high‐voltage DC silicon rubber insulators to DC flashover performance

In this study, the results of measurement for DC flashover characteristics of silicon rubber insulators in the presence of surface charges and in terms of geometric characteristics have been examined and analysed. In the carried out experimental tests, the surface of different insulators was charged by an external corona source and both the metal end fittings were kept grounded while the needles have been connected to a certain applied negative and positive DC voltages and then surface electric charge measured. A series of flashover tests have been carried out on the charged insulators under positive DC voltages to investigate the effects of surface charges. The experimental results revealed that positive electric charges reduced flashover performance while negative charges increased the flashover voltage level. Also, the experimental modelling of DC flashover of charged insulators regarding the ratio of shed spacing to shed depth and specific leakage distance in terms of surface electric charges, revealed that flashover voltage gradient of the charged insulator is most affected by specific leakage.

Sol-gel synthesis, structural refinement, and electrochemical properties of potassium manganese phosphate for supercapacitors

Using sol-gel thermolysis method, potassium manganese phosphate (a mixture of KMnPO4⋅H2O and KMnPO4 phases) was synthesized for supercapacitor applications. XRD analysis revealed phase composition and crystal structure of the prepared material. The dittmarite-type structure of KMnPO4⋅H2O as the primary phase was identified through full profile Rietveld refinement technique. The possible four normal modes of vibrations ν1(A1), ν2(E), ν3(F2), and ν4(F2) were analyzed through FTIR spectrum. Submicron-sized particles are identified using FE-SEM and TEM images. The layered structure of potassium manganese phosphate was corroborated through SAED pattern. Electrochemical performances of the mixed potassium manganese phosphate are investigated using cyclic voltammetry (CV) to identify the suitable aqueous electrolytes (1 M KOH, 1 M LiOH, and 1 M NaOH). It provides the maximum specific capacitance of 516 F g−1 at 2 mV s−1 in 1 M KOH aqueous electrolyte. The Trasatti plot revealed that the observed high specific capacitance mainly arises from the inner surface charge contribution. The electrode shows the better specific capacity of 329 F g−1 at a current density of 0.6 mA cm−2 in galvanostatic charge-discharge measurements. The electrochemical impedance spectral analysis (EIS) further corroborates that the charge-transfer resistance (Rct) is low in 1 M KOH (2.25 Ω) electrolyte than in 1 M LiOH (9.2 Ω) and 1 M NaOH (50.7 Ω) electrolytes.

Dual contribution of surface charge and protein-binding affinity to the cytotoxicity of polystyrene nanoparticles in nonphagocytic A549 cells and phagocytic THP-1 cells

ABSTRACTKnowledge that links the physicochemical properties of nanoparticles (NP) to their toxicity is key to evaluating and understanding mechanisms underlying toxicity and developing appropriate testing methods for NP; however, this is currently limited since only a small set of NP have been used, with typically poor control of their physical properties. In this study, eight types of polystyrene NP (PLNP) were synthesized with different functional groups, but all based on an identical core. In vitro cell-based assays were performed to determine the influence of changes in physicochemical properties, such as charge, hydrodynamic size, and protein binding potential, in relation to NP-mediated toxicity. The PLNP were incubated with nonphagocytic A549 cells or phagocytic differentiated THP-1 cells for 4 h with/without fetal bovine serum (FBS), followed by incubation for 20 h in FBS-supplemented medium with/without a washing step, to assess cell-type specificity and impact of protein corona formation. The effect of surface charge on cytotoxicity differed between A549 cells and THP-1 cells. In nonphagocytic A549 cells, the zeta potential of PLNP exhibited a negative correlation with cytotoxicity, partly due to the level of coronated protein that might affect cellular uptake. In phagocytic THP-1 cells, the zeta potential of PLNP showed a positive correlation with cytotoxicity but coronated protein levels displayed no marked association with cytotoxicity, owing to the professional uptake efficacy of phagocytic cells. The consistency of our data with THP-1 cells with the surface charge paradigm in nanotoxicology suggests that phagocytic cells are the predominant targets for lung inflammatory reactions induced by PLNP.

Numerical investigation of the contraction of neutral-charged diblock copolymer brushes in electric fields

Using self-consistent field theory (SCFT), the contraction of neutral-charged A-B diblock copolymer brushes in electric fields generated by opposite surface charges on two parallel electrodes has been numerically investigated. The diblock copolymer chains were grafted with the free end of the neutral block to one electrode and immersed in a salt-free solution sandwiched between the two electrodes. The numerical results reveal that the charged monomers, A-B joint segment and the tail exhibit bimodal distributions under external electric fields, which are absent for homopolymer polyelectrolyte brushes. The dependences of the relative populations and peak positions of the two modes on various parameters such as block ratio, grafting density, chain length and strength of the applied electric field were systematically examined and the underlining mechanisms were elucidated. It was found in this study that, if the total amount of surface charges on the grafting electrode is no more than that of the counter-ions in the system, overall charge neutrality is generally maintained inside the brushes when including the contribution of surface charges on the grafting electrode. In such a case, the counter-ions expelled from the brushes are highly enriched in the immediate vicinity of the second electrode and an approximate charge balance between these expelled counter-ions and the opposite surface charges on the second electrode is achieved.

Numerical self-consistent field theory study of the response of strong polyelectrolyte brushes to external electric fields.

The response of strong polyelectrolyte (PE) brushes grafted on an electrode to electric fields generated by opposite surface charges on the PE-grafted electrode and a second parallel electrode has been numerically investigated by self-consistent field theory. The influences of grafting density, average charge fraction, salt concentration, and mobile ion size on the variation of the brush height against an applied voltage bias were investigated. In agreement with molecular dynamics simulation results, a higher grafting density requires a larger magnitude of voltage bias to achieve the same amount of relative change in the brush height. In the experimentally relevant parameter regime of the applied voltage, the brush height becomes insensitive to the voltage bias when the grafting density is high. Including the contribution of surface charges on the grafting electrode, overall charge neutrality inside the PE brushes is generally maintained, especially for PE brushes with high grafting density and high average charge fraction. Our numerical study further reveals that the electric field across the two electrodes is highly non-uniform because of the complex interplay between the surface charges on the electrodes, the charges on the grafted PE chains, and counterions.

Convective transport of boron through a brackish water reverse osmosis membrane

In this work, cross-flow filtration experiments using a brackish water reverse osmosis polyamide membrane have been performed to gather boron rejection data as function of feed concentration, pressure, pH and salinity. Increasing transmembrane pressure increases the permeation of boron indicating that convective flow is important. This result is in contrast to the normal assumption that solution diffusion dominates in such systems. The extended Nernst–Planck equation with a Donnan-steric partition coefficient is used to analyse the transport mechanisms of both neutral boric acid and negatively charged borate ions through the RO membrane. The contribution of surface charge is experimentally determined by streaming potential measurements and the electrokinetic surface charge density is then calculated as a function of ionic strength and pH. It is found that a 0.380nm pore radius and an effective membrane porosity of 0.05 shows good agreement with experimental data. Charge screening becomes more dominant with increasing ionic strength and this contribution is readily incorporated into the model. The study extends our understanding of the transport mechanism of boric acid and borate ions which can assist in predicting the performance of polyamide reverse osmosis membranes. It also raises questions as to the true mechanism of transport through such a membrane.

X-ray linear dichroism dependence on ferroelectric polarization

X-ray absorption spectroscopy and photoemission electron microscopy are techniques commonly used to determine the magnetic properties of thin films, crystals, and heterostructures. Recently, these methods have been used in the study of magnetoelectrics and multiferroics. The analysis of such materials has been compromised by the presence of multiple order parameters and the lack of information on how to separate these coupled properties. In this work, we shed light on the manifestation of dichroism from ferroelectric polarization and atomic structure using photoemission electron microscopy and x-ray absorption spectroscopy. Linear dichroism arising from the ferroelectric order in the PbZr0.2Ti0.8O3 thin films was studied as a function of incident x-ray polarization and geometry to unambiguously determine the angular dependence of the ferroelectric contribution to the dichroism. These measurements allow us to examine the contribution of surface charges and ferroelectric polarization as potential mechanisms for linear dichroism. The x-ray linear dichroism from ferroelectric order revealed an angular dependence based on the angle between the ferroelectric polarization direction and the x-ray polarization axis, allowing a formula for linear dichroism in ferroelectric samples to be defined.

The Phosphoinositide Phosphatase SopB Manipulates Membrane Surface Charge and Trafficking of the Salmonella-Containing Vacuole

Shifts in electrostatic surface charge of membranes have recently been highlighted as a significant factor contributing to protein targeting to the plasma membrane and nascent phagosomes. Intracellular, vacuole-adapted pathogens may also regulate surface charge of their vacuoles to establish a replicative niche. Since Salmonella enterica serovar Typhimurium controls trafficking of the Salmonella-containing vacuole (SCV) and inhibits its fusion with lysosomes, we investigated the contribution of surface charge to this process. Using recently developed fluorescent biosensors, we show that the bacterial phosphoinositide phosphatase SopB controls membrane surface charge of nascent SCVs by reducing levels of negatively charged lipids phosphatidylinositol-4,5-bisphosphate and phosphatidylserine. This SopB activity results in dissociation of a number of host-cell endocytic trafficking proteins from this compartment and inhibits SCV-lysosome fusion. Moreover, inducible reduction of negative charge rescues DeltasopB bacteria-containing SCVs from fusion with lysosomes. These results reveal a membrane-charge-based mechanism used by S. Typhimurium to control SCV maturation.

Contribution of Surface Charge to Bovine Serum Albumin Adsorption on Hydroxyapatite Ceramic Particles

Protein adsorption is driven by various interactions. The contribution of surface charge to bovine serum albumin (BSA) adsorption on hydroxyapatite (HA) ceramic was investigated by adjusting the liquid environment in which the solid particles dispersed. Zeta potentials of HA and the adsorption of BSA on the surface were tested as a function of pH, ionic strength, Ca2+ and PO4 3- concentrations in the aqueous solutions, and the results showed that both of them were greatly affected by those experimental variations. Besides, the amount of adsorbed BSA was related to the variation of zeta potential of HA, as could be well understood in terms of electrostatic interactions.

Intra- versus Intermolecular Interactions in Monellin: Contribution of Surface Charges to Protein Assembly

The relative significance of weak non-covalent interactions in biological context has been much debated. Here, we have addressed the contribution of Coulombic interactions to protein stability and assembly experimentally. The sweet protein monellin, a non-covalently linked heterodimeric protein, was chosen for this study because of its ability to spontaneously reconstitute from separated fragments. The reconstitution of monellin mutants containing large surface charge perturbations was compared to the thermostability of structurally equivalent single-chain monellin containing the same sets of mutations under varying salt concentrations. The affinity between monellin fragments is found to correlate with the thermostability of single chain monellin, indicating the involvement of the same underlying Coulombic interactions. This confirms that there are no principal differences in the interactions involved in folding and binding. Based on comparison with a previous mutational study involving hydrophobic core residues, the relative contribution of Coulombic interactions to stability and affinity is modest. However, the Coulombic perturbations only affect the association rates of reconstitution in contrast to perturbations involving hydrophobic residues, which affect primarily the dissociation rates. These results indicate that Coulombic interactions are likely to be of main importance for the association of protein assembly, relevant for functions of proteins.

Screened electrostatics of charged particles on a water droplet

We study the electrostatic properties of charged particles trapped at an interface in a water-in-oil microemulsion. The electrostatic potential and the counterion distribution in the water droplet are given in terms of the ratio of the Debye screening length kappa(-1) and the droplet radius R. In the limit R-->infinity we recover the well-known results for a flat interface. Finite-size corrections are obtained in terms of the small parameter 1/kappaR. Part of the counterions spread along the interface and form a charged layer of one Debye length thickness. In particular, there is a uniform surface charge contribution. We derive explicit expressions for the electric field, the mobile charge density, and the charge-induced pressure on the interface.

The development and contribution of surface charge by crop residues in two Malawian acid soils

The effects of maize and soya bean residues on the pH and charge of a loamy sand (Kawalazi) and a sandy clay loam (Naming'omba) from Malawi were measured to determine both the indirect effect of the residues on soil charge through the changes in pH, and the direct contribution of charge carried on the residue surfaces. The soils had pH values (10 mM CaCl 2) of 4.3 and 5.0 and organic matter contents were 1.4% and 2.7%, respectively. The clay fractions were dominated by kaolinite and goethite, and mica was present in both samples. The soils were incubated for 28 days with maize ( Zea mays) and soya bean ( Glycine max) residues. The maximum addition of residue (12.0%) in the Kawalazi and Naming'omba soils increased the pH from 4.3 and 5.0 to 4.8 and 5.3 (maize) and to 9.0 and 8.8 (soya bean), respectively. Negative charge increased from 2.1 and 4.7 cmol c kg −1 to 3.8 and 7.5 (maize) and to 5.3 and 9.3 cmol c kg −1 (soya bean). Positive charge increased from 0.72 and 0.62 to 0.87 and 0.85 cmol c kg −1 (maize) and to 0.75 and 0.68 (soya bean). The charge contribution by the residues was calculated by difference between the charge on a sample incubated with residue and the charge on a soil without residue limed to the same pH value. Up to 100 cmol c negative charge and 10 cmol c of positive charge per kg of residue were directly contributed to the soil–residue mixture, the amounts depending on the type of residue, the extent to which the residue was decomposed in the soil and the pH of the mixture. The Anderson and Sposito method [Soil Sci. Soc. Am. J. 55 (1991) 1569] was used to partition the permanent negative charge (holding Cs +) from variable negative charge (holding Li +). In the pH range 3.7–6.5 the maize residue contributed between 3 and 26 cmol c of variable charge per kg of residue in the Kawalazi soil and between 6 and 25 cmol c per kg of residue in the Naming'omba soil. For soya bean the values were between 1 and 28 and between 4 and 68 cmol c per kg of residue, respectively. At a given pH value, the charge tended to increase with time of incubation and for a given addition of residue, pH decreased during incubation. Addition of residues contributed no permanent negative charge and the charge on the soil measured by Cs adsorption was independent of pH change caused by the residue showing that the method is valid for soil–residue mixtures. With time there was a decrease in the amount of permanent charge probably due to masking as humic material become adsorbed on mineral surfaces.

On the Applicability of DLVO Theory to the Prediction of Clay Colloids Stability

The stability behavior of Na–montmorillonite colloids has been studied by combining the analysis of their surface charge properties and time-resolved dynamic light scattering experiments. The chemical surface model for several types of clays, including montmorillonite, has to take into account the double surface charge contribution due to their permanent structural charge and to their pH-dependent charge, which is developed at the edge sites, therefore, these stability studies were carried out as a function of both ionic strength and pH. DLVO theory is largely applied for the prediction of the stability of many colloidal systems, including the natural ones. This work shows that the stability behavior of Na–montmorillonite colloids cannot be satisfactorily reproduced by DLVO theory, using the surface parameters experimentally obtained. Particularly, this theory is unable to explain their pH-dependent stability behavior caused by the small charge at the edge sites. Based on these results, a literature review of DLVO stability prediction of clay colloids was performed. It confirmed that this theory is not capable of taking into account the double contribution to the total surface charge and, at the same time, pointed out the main uncertainties related to the appropriate use of the input parameters for the calculation as, for example, the Hamaker constant or the surface potential.

Opa expression correlates with elevated transformation rates in Neisseria gonorrhoeae.

Neisseria gonorrhoeae is naturally competent for DNA transformation. Under most conditions encountered in vivo, gonococci express one or more opacity (Opa) proteins on their surfaces. Recently, it was shown that DNA preferentially binds to the surfaces of Opa-expressing organisms compared to those of isogenic Opa-negative strains, presumably due to the numerous cationic residues in the predicted surface-exposed loops of the Opa protein. This study examined whether Opa-DNA interactions actually influence DNA transformation of the gonococcus. The data show that Opa-expressing gonococci are more efficient recipients of DNA for transformation and are more susceptible to exogenous DNase I treatment at early stages during the DNA transformation process than non-Opa expressors. Furthermore, inhibition of the transformation process was demonstrable for Opa(+) populations when either nonspecific DNA or the polyanion heparin was used. Overall, the data suggest that Opa expression, with its presumptive positive surface charge contribution, promotes DNA transformation by causing a more prolonged sequestration of donor DNA at the cell surface, which translates into more efficient transformation over time.