High Local Charge Density Research Articles

Electro-Responsive Breathing Transition of Conductive Hydrogel for Broadband Kinetic Energy Harvesting.

Reclaiming kinetic energy from vibrating machines holds great promise for sustainable energy harvesting technologies. Nevertheless, the impulsive current induced by vibrations is incompatible with conventional energy storage devices. The energy-management system necessitates novel designs of soft materials for lightweight, miniaturized, and integrated high-frequency electrochemical devices. Here, this work develops a conductive hydrogel with an electro-responsive polymeric network. The electro-responsive breathing transition of the crosslinking points facilitates the expeditious formation of a localized electrolyte layer. This layer features an exceedingly high local charge density, surpassing that of a saturated electrolyte solution by an order of magnitude, and thus enabling rapid charge transport under the influence of an applied voltage. The micro-capacitor based on the gel exhibits record-high capacitance of ≈2 mF cm-2 when the frequency of energy input reaches up to 104 Hz. This work also demonstrates a prototype battery charger that harvests energy from a running car engine. This study presents a feasible strategy for waste energy recycling using integrated electrochemical devices, opening a new avenue for ambient energy management.

Molecular dynamics studies of hematite surfaces with PAM, HPAM and metasilicate

In the search to improve the obtaining of iron ore, different additives have been proposed to improve this activity. A deeper study is necessary to understand the affinities of different additives on iron ore and thus be able to search for or synthesize new additives according to the desired objective. In this work, the affinities of the iron mineral represented by the hematite crystal on the neutral 001 surfaces at pH ~9 are studied by molecular dynamics methods, in the presence of waters with low salinity and high salinity. The additives to be studied are a sodium metasilicate dispersant, a neutral polyacrylamide (PAM) flocculant, and 25% anionic polyacrylamide (HPAM). The study considered the calculation of the minimum distance between the surface and the additives. The results show that the affinity of the metasilicate is high with the surface. In the case of PAM polymers, their adsorption decreased as the number of salts increased. In the case of HPAM, the adsorption is greater than in PAM and improved with the addition of salts. This indicates that hematite is a surface with a high local charge density that attracts charged groups such as metasilicates and HPAM. the neutral PAM polymer is adsorbed but to a lesser extent due to its neutrality. The presence of salts indicates that there is competition for adsorption on hematite with respect to PAM, but that the salt is beneficial to HPAM due to the formation of cationic bridges. These results will help in the search for additives for the concentration or dispersion of iron ore.

The enhanced performance of capacitive-type humidity sensors based on ZnO nanorods/WS2 nanosheets heterostructure

Zinc oxide (ZnO) is a promising candidate for humidity-sensing materials due to its low-cost preparation, superior chemical and thermal stability, controllable surface morphology, and low water solubility. However, pristine ZnO-based humidity sensors suffer from poor response and large hysteresis that limit their application. In this study, n-type semiconducting tungsten disulfide (WS2) was utilized to form ZnO nanorods/WS2 nanosheets heterostructure grown on indium tin oxide coplanar electrode-coated glass substrate. The capacitive-type humidity sensing characteristics were investigated at room temperature. The results show that for humidity ranges of 18–85 % RH, three deposition cycles of WS2 nanosheets onto ZnO nanorods produced significant improvements in the response, sensitivity, and hysteresis with an unchanged response and recovery times compared to pristine ZnO sensors. This improved sensor performance might be due to the ability of WS2 to provide more water molecule adsorption sites. The formation of an n-n junction between ZnO and WS2 created interfaces with high local charge density and built an internal electric field that increase the water dissociation rate. The improved hysteresis might be due to water molecule adsorption on WS2 nanosheets is physical adsorption that facilitates the desorption process.

Impact of enzymatic hydrolysis on the interfacial rheology of whey protein/pectin interfacial layers at the oil/water-interface

Aim of the present study was to investigate the complex formation of β-lactoglobulin (β-LG) hydrolysates and different types of pectin at the oil/water-interface by dynamic interfacial pressure and the properties of the complexes by interfacial rheology (dilatation and shear). The degree of hydrolysis (DH) of β-LG was varied (3 and 6%) as well as the degree of methoxylation of the pectins, i.e. two low-(LMP, 32 and 35%) and two high-methoxylated (HMP, 64%) pectins were used. The pectins exhibited different local charge densities, due to enzyme specificity during demethoxylation. All experiments were performed at a constant biopolymer content (0.01 wt%), pH (4.0) and temperature (22 °C). β-LG/pectin interactions clearly delayed interfacial adsorption, which was more pronounced for LMP with a high local charge density. With increasing DH of β-LG, the interfacial adsorption was accelerated, however β-LG/pectin layers exhibited higher dilatational elastic moduli than hydrolysate/pectin layers. In contrast to dilatational rheology, β-LG formed weaker interfacial layers than its hydrolysates during shear time sweeps, despite the presence of pectin. Pectin and hydrolysates exhibited strong viscoelastic interfacial layers partially more than one order of magnitude higher than β-LG. However, during shear amplitude sweeps all interfacial layers were resistant to increasing strain and the films collapsed within the same region. Therefore, targeted structural modifications using enzymes with high specificity enables the production of β-LG hydrolysates and demethoxylated pectins with tailored functionality with respect to their interfacial rheology characteristics.

Reversible Adhesion with Polyelectrolyte Brushes Tailored via the Uptake and Release of Trivalent Lanthanum Ions

Applications of end-tethered polyelectrolyte “brushes” to modify solid surfaces have been developed and studied for their colloidal stabilization and high lubrication properties. Current efforts have expanded into biological realms and stimuli-responsive materials. Our work explores responsive and reversible aspects of polyelectrolyte brush behavior when polyelectrolyte chains interact with oppositely charged multivalent ions and complexes, which act as counterions. There is a significant void in the polyelectrolyte literature regarding interactions with multivalent species. This paper demonstrates that interactions between solid surfaces bearing negatively charged polyelectrolyte brushes are highly sensitive to the presence of trivalent lanthanum, La3+. Lanthanum cations have unique interactions with polyelectrolyte chains, in part due to their small size and hydration radius which results in a high local charge density. Using La3+ in conjunction with the surface forces apparatus (SFA), adhesion has been...

The cytotoxicity of silver nanoparticles coated with different free fatty acids on the Balb/c macrophages: an in vitro study

Nanoparticles (NPs) can adsorb different molecules, because of their high local charge density and specific surface area. The toxicity of NPs is changed after adsorption, which may be different from unbound or unbound NPs. In this study, unbound silver nanoparticles (Ag NPs) and Ag NPs coated with different free fatty acids (FFAs) including lauric acid, alpha linoleic acid, oleic acid, and palmitic acid were incubated with mouse macrophages for 24 hours at 37 °C. After incubation, their toxicities, reactive oxygen species (ROS) generation, and uptake were separately investigated. This study showed that FFA-coated Ag NPs had less toxicity, higher uptake, and less ROS generation than unbound Ag NPs. Based on the results, unbound Ag NPs aggregated in RPMI1640 medium, and their size distribution was near 100–1000 nm. But all FFA-coated Ag NPs had nano metric size (near 20--40 nm) without agglomeration.

Overall Charge and Local Charge Density of Pectin Determines the Enthalpic and Entropic Contributions to Complexation with β-Lactoglobulin

The complex formation between β-lactoglobulin and pectins of varying overall charge and local charge density were investigated. Isothermal titration calorimetry experiments were carried out to determine the enthalpic contribution to the complex formation at pH 4.25 and various ionic strengths. Complex formation was found to be an exothermic process for all conditions. Combination with previously published binding constants by Sperber et al. (Sperber, B. L. H. M.; Cohen Stuart, M. A.; Schols, H. A.; Voragen, A. G. J.; Norde, W. Biomacromolecules 2009, 10, 3246-3252) allows for the determination of the changes in the Gibbs energy and the change in entropy of the system upon complex formation between β-lactoglobulin and pectin. The local charge density of pectin is found to determine the balance between enthalpic and entropic contributions. For a high local charge density pectin, the main contribution to the Gibbs energy is of an enthalpic nature, supported by a favorable entropy effect due to the release of small counterions. A pectin with a low local charge density has a more even distribution of the enthalpic and entropic part to the change of the Gibbs energy. The enthalpic part is reduced due to the lower charge density, while the relative increase of the entropic contribution is thought to be caused by a change in the location of the binding place for pectin on the β-lactoglobulin molecule. The association of the hydrophobic methyl esters on pectin with an exposed hydrophobic region on β-lg results in the release of water molecules from the hydrophobic region and surrounding the methyl esters of the pectin molecule. An increase in the ionic strength decreases the enthalpic contribution due to the shielding of electrostatic attraction in favor of the entropic contribution, supporting the idea that the release of water molecules from hydrophobic areas plays a part in the complex formation.

Influence of the overall charge and local charge density of pectin on the complex formation between pectin and β-lactoglobulin

The complex formation between β-lactoglobulin (β-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMP B and HMP R are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pH c, the pH where soluble complexes of β-lg and pectin are formed and pH ϕ, the pH of phase separation, both as a function of ionic strength. pH c decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH ϕ passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between β-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of β-lg and pectin showed charge regulation in β-lg–pectin complexes. Around pH 5.5–5.0 the pK as of β-lg ionic groups are increased to induce positive charge on the β-lg molecule; around pH 4.5–3.5 the pK a values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with β-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.

Positive temperature coefficient of resistivity in paraelectric (Ba,Sr)TiO3 thin films

The previously reported positive temperature coefficient of the resistivity (PTCR) observed in paraelectric BST thin films was again analyzed in terms of the non-Ohmic resistance as a result of an anode interface energy barrier induced by the high local charge density and interface energy states. The decrease in the low frequency dielectric constant, which is the dielectric constant relevant to the PTCR effect, with increasing temperature has a larger effect on the anode energy barrier than the temperature increase itself under a high bias voltage. In this case, the slope in the current-voltage curve at higher temperature decreases, which appears as the PTCR effect when the resistance is measured as a function of temperature under high voltages.

Synthesis, Characterization, and Potentiometric Behavior of Cationic Polyelectrolytes

Abstract Various amino monomers differing in the number of amine groups and the environment of the site were synthetized. These monomers were copolymerized with acrylamide, and the polymeric ammonium salts were characterized by viscometry, light scattering, and pH titration. Evidence of interactions between neighboring cationic sites was observed for a copolymer with a high local charge density due to three amino groups in the comonomer unit.