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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. [Display omitted] • TEMPO-oxidized nanofibrils (TCNs) are effective to stabilize Pickering emulsions. • Clarify surface charge's contribution and further understand stabilization mechanism. • Relatively low charge density instead of high charge density for better stability. • Distinct oil droplet-decorated fibrillar structures enhance emulsion's stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Based on extensive experimental investigations on many different oxide nanoparticles, it is now a well-established view that the counter-ions exhibit ion specific effects due to their high charge density and strong interaction with oppositively charged surfaces. On the other hand, studies regarding co-ion effects are scarcely reported in the literature. In this study we have measured the surface charge densities and gel-times of silica nanoparticles in a number of salts which have the same counter-ions but different co-ions, i.e. anions in this case. Gel-times were measured in LiCl, NaCl, NaNO 3 , NaClO 4 , NaClO 3 and Na 2 SO 4 as well as in KCl, KNO 3 , and K 2 SO 4. We have seen clear correlations between the gel-times and the extent of ion pairing in the solutions; salts that have strong ion pairing exhibit longer gel-times than salts having highly dissociated ions. To better understand the mechanisms at work we have determined the surface charging of silica nanoparticles in these salt solutions and we have observed that the surface charging behavior of silica nanoparticles follows the trends seen in the gel-time studies. From our gel-time determinations and potentiometric measurements we can claim that there is a clear co-ion effect on the gelling and surface charging of silica nanoparticles. [ABSTRACT FROM AUTHOR]

• Preparation of charge impregnated surface using triboelectrification is studied. • Charge density profile is estimated from drop impact on pillared surface. • Drop translation over surface with charge density gradient has been established. • Higher charge gradient accelerates drop transport. • Velocity rises faster in case of higher surface contact angle. Though different methodologies like thermal and magnetic fields have been tried to control a droplet's mobility in biochemical and medical applications, charge imprinted super-amphiphobic surface is the recent and promising development in which droplets can be transported through any predefined path over the surface. Such surfaces are electrified by impacting water droplets from varying release heights through triboelectrification. Impacting droplets on pillared surface dynamics of the same have been analyzed to understand the nature of electrostatic charge distribution generated. Further to this, droplet actuation on such surfaces with surface charge gradient has been simulated. Charge separation inside the liquid droplet and charge accumulation near the interface has been visualized to understand the phenomenon. Asymmetry in droplet shape and charge distribution has been analyzed as the reason behind the droplet actuation. The effect of different charge density gradients and surface wettability over droplet mobility has also been studied. [ABSTRACT FROM AUTHOR]

• The effects of channel shape and surface charge on the ion current rectification in asymmetric nanochannels were comprehensively investigated. • Simple increase or decrease of the spatial size will not beneficial for improving the ICR performance. • The specified asymmetric surface charge on the outer wall surface can strongly enhance the ICR performance. • The research results provide essential insights on the ion transport and useful guidelines for the design and performance optimization of biological sensors and nanofluidic devices. Ion current rectification (ICR) in nanochannels has attracted increasing attention for its great potential in the applications of ionic circuits and biological sensors. Herein, the influence of nanochannel shape and surface charge on the ion transport and ICR performance of asymmetric nanochannels was numerically investigated. Firstly, three asymmetric nanochannels with different shapes (bullet, conical, and trumpet) were constructed to investigate the spatial size effect on the ICR behavior. And then selected the best-performing one to further analyze the effect of the surface charge on the ICR. In the investigation of spatial size effect, it is found that the increases and the decreases of spatial size will not be beneficial for improving the ICR performance and the conical nanochannel exhibits the best performance. In the investigation of surface charge effect, it is found that specified asymmetric surface charge on the outer wall surface enhances the corresponding ICR performance, revealing the cooperative role with inner wall surface charge. Besides, it is found that the outer wall surface charge is dominant when the nanochannel length is small and the inner wall surface charge is dominant when the nanochannel length is large. Moreover, the finite length enhancement effect for ICR performance is illustrated by tuning the range of outer wall surface charged zone, indicating the charged zone near the entrance and exit plays the dominant role on ion transport. The obtained results provide essential insights on the ion transport and useful guidelines for the design and performance optimization of biological sensors and nanofluidic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• An experimental method for surface charge density at liquid-liquid interface based on streaming potential setup is proposed. • After validation, the setup measures the surface charge at the surfactant-free decane-KCl solution interface. • The negative surface charge at the decane-KCl solution interface is confirmed, which is found to increase when increasing the pH. Surface charging at immiscible liquid-liquid interface is essential to the emulsion stability, surfactant adsorption, and various engineering applications such as drug delivery and mineral flotation. However, droplet electrophoresis, as a widely-used electrokinetic method to measure the surface charge density, has various limitations in physical modeling and sample preparation. In this work, an alternative experimental method based on streaming potential setup is proposed. A Y-Y shaped microchannel was used to make a flat and stable liquid-liquid interface. The inner wall was coated with polymer to suppress the interference of the solid-liquid interfacial electrokinetics in the liquid-liquid one. The experimental setup was first verified by revisiting the aqueous solution-silicon surface charging, after which the surfactant-free decane-KCl solution interface charging was investigated. The negative surface charge at the decane-KCl solution interface is confirmed and found to increase when increasing the pH. This result is compatible with the probable charging mechanism that the acquired negative surface charge results from hydroxyl ion adsorption onto the interface. The proposed method enables the simplicity and flexibility for further side-by-side studies on the liquid-liquid interface charging mechanism and will inspire the quantitative macroscopic interfacial modeling for numerous scenarios, such as the droplet electrophoresis and interfacial electro-hydrodynamics. [Display omitted] [ABSTRACT FROM AUTHOR]

• The coupling effect of surface charge and boundary slip are studied. • The boundary slip tends to decrease the surface charge density. • The surface charge in turn reduces the boundary slip. • The boundary slip greatly enhances the energy conversion. • Output power deviates significantly upon the constant and coupling property. Inspired by the universal phenomena in nature and advances in nanotechnology, the ion transport in nanochannel receives increasing attention and shows great promising in energy conversion. The precedent studies generally predicted the ion transport by tuning the single physical parameter, the understanding of ion dynamics in the real multi-physical coupling systems is still scarce. Here, an ion transport model coupled with surface charge and slip effects is proposed to investigate the energy conversion behavior in nanochannel. The results show that the surface charge density increases with the increasing bulk concentration, nanochannel size and solution pH. The original boundary slip tends to decrease the surface charge density and the surface charge in turn reduces the boundary slip significantly, which manifests the strong coupling effect of diverse factors. The output power and energy conversion efficiency increases first and then decrease with the increasing bulk concentration and pH. The increase of channel size is beneficial for promoting output power, but unfavorable on energy conversion efficiency. More important, the boundary slip greatly enhances the output power and energy conversion efficiency, leading to a maximum output power and energy conversion efficiency is 2.7 pW and 30%, respectively. As a proof of concept, this work shows the distinct deviation in power generation in ion nanochannel with the constant and dependent physical property, providing the useful information to guide the design of real fluidic energy devices. [Display omitted] [ABSTRACT FROM AUTHOR]

The ability to retain localized charges at the surface or interface of dielectric materials is a universal property that applies to many different fields such as tribocharging, charge nanopatterning, nanoxerography, etc. Once the surface is charged, its stability and subsequent discharging rate will determine the potential applications of a given system. This decay rate is properly defined by the macroscopic equations which depend on dielectric constants and conductivities of the two media. Here, we derive the equations to model the decay of charge distributions localized at the surface/interface of materials and solve them avoiding additional approximations made so far. Addressing the problem in the Fourier space, we arrive to a compact generic equation which provides a useful tool to determine both the bulk and surface conductivities of a material. Furthermore, we show that Kelvin Probe Force Microscopy (KPFM) is a particularly suited method to exploit this tool. Monitoring the charge decay of previously injected charge patches on silicon dioxide (SiO 2), together with an appropriated data analysis, we verify the behavior predicted by our equations. This allows us to characterize the surface and bulk conductivities of SiO 2 layers as well as its dependence with the relative humidity. [Display omitted] • Surface charging of dielectric materials is a universal property. • The dependence of the surface charge decay rate with the system geometry is established. • Surface and bulk conductivities are obtained with Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

The abnormal stability of bulk nanobubbles has attracted substantial attention from academia and industry since classical Epstein–Plesset theory predicts that gas bubbles cannot keep stable thermodynamic equilibrium spontaneously. The dual nature of ionic surfactants, acting simultaneously as charge carriers and attenuators of surface tension at the gas–liquid interface, enables them to play a unique role in bulk nanobubble stabilization. Herein the stability of bulk nanobubbles in anionic, cationic and nonionic surfactant solutions over a wide range of concentration is studied. Experimental results show that different kinds of surfactant molecules are involved in the nucleation and stabilization of bulk nanobubbles in different ways. We demonstrate that the accumulation of net charges carried by surfactant ions at the interface is predominantly responsible for stabilizing nanobubbles, instead of the reduction of surface tension. With theoretical calculations, we further quantify the coupling action of interfacial tension and surface charge on the stable equilibrium state of bulk nanobubbles. The result illustrates that the interfacial tension and the degree of gas saturation together determine the upper limit of the bubble size that can exist stably. Our study identifies a route to explore the intrinsic mechanism of bulk nanobubble's stability. [Display omitted] • Stability of bulk nanobubbles in ionic and nonionic surfactant solutions is studied. • Surfactant molecules are involved in the nucleation and stabilization of nanobubbles. • Accumulation of net charges is predominantly responsible for stabilizing nanobubbles. • Coupling action of interfacial tension and surface charge is revealed. • Interfacial tension and gas supersaturation together determine the upper bound size. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl compounds (PFCs) are environmental toxicants and their widespread detection and accumulation in the environment can be detrimental to the ecosystem. In this study, surface charge of GO membranes was engineered to enhance selectivity of graphene oxide (GO) membranes and for the removal of perfluorooctanoic acid (PFOA ∼400 Da) in real concentration ranges in wastewater streams. The structure and physicochemical properties of the GO and modified GO nanosheets and their corresponding membranes were assessed using several characterization techniques. The modified GO membranes showed a water flux of 83.1 ± 1 L m−2 h−1 together with maximum rejection efficiency of 98.4% for 50 ppm PFOA at pressure of 0.45 MPa, which is the highest value reported to date. Compared to the GO membrane, the modified GO membrane exhibited higher water flux and PFOA rejection efficiency by 300% and 70%, respectively. The high surface charged and electron rich GO nanosheets reduce the interlayer spacing in the modified membrane and simultaneously enhance the surface hydrophilicity which leads to increased PFOA retention and enhanced water permeation. These results point to the potential of the modified GO membranes for wastewater treatment. [Display omitted] • Surface of graphene oxide membrane was engineered by positive and negative chargers. • PDDA and PSS were used to, respectively, create positive and negative charges. • The modified membranes showed high increase in water-flux and PFOA rejection efficiency. • The obtained rejection efficiency for PFOA molecules by PDDA-GO membranes was 98.4%. [ABSTRACT FROM AUTHOR]

Ferrihydrite is a poorly crystalline iron (hydr)oxide and highly efficient adsorbent for heavy metals. Al-substitution in ferrihydrite is ubiquitous in nature. However, the effect of Al-substitution on the surface reactivity of ferrihydrite remains unclear due to its low crystallinity. The present study aims to clarify the microstructure and interfacial reaction of Al-substituted ferrihydrite. Al-substitution had little effect on the morphology and surface site density of ferrihydrite, while the presence of ≡AlOH−0.5 sites resulted in higher proton affinity and surface positive charge of ferrihydrite. Besides, the affinity constant of Pb2+ adsorption on the surface of ferrihydrite decreased at higher Al content, which further decreased the adsorption performance of ferrihydrite for Pb2+. The modeling results revealed that bidentate complex was the dominant Pb complexation species on the surface of ferrihydrite, which was less affected by Al-substitution. The present study provides important insights into the effect of Al-substitution on the interfacial reaction at the ferrihydrite-water interface. The obtained parameters may facilitate the future advance of surface complexation model. [Display omitted] • Pb2+ adsorption on Al-substituted ferrihydrite was studied by CD-MUSIC model. • The presence of Al–O sites contributed to a higher proton affinity and surface charge. • Al-substitution decreased the adsorption performance of ferrihydrite for Pb2+. • Bidentate complexes were the dominant Pb species on the surface of ferrihydrite. [ABSTRACT FROM AUTHOR]

In this study, the Escherichia coli ( E. coli ) strain ATCC 11775 was studied to determine its surface charging properties in a range of different aqueous salt solutions, with the aim of evaluating its potential as a monitor organism for water treatment. Zeta potential measurements were carried out in various solutions containing: NaCl, CaCl 2 , MgSO 4 , ZnSO 4 and C 14 TAB, at different pH values and concentrations. Interestingly, it was found that the zeta potential of this strain of E. coli remained fairly constant at pH values over about 6, in 1 mM NaCl solutions. In order to explain the cell surface charging properties, a simple, mass action surface ionization model was developed. This model indicates that the surface charging of these E. coli cells can be modeled simply using the ionization behavior of the acid groups in the common anionic membrane lipid phosphatidylserine (PS). There appeared to be no specific, strong adsorption of either divalent anions or cations, until high salt concentrations, above about 0.1 M. The results suggest that at high concentrations both Ca 2+ and SO 4 2− ions are strongly adsorbed at the cell surface. However reduction of the magnitude of the surface electrostatic potential, due to Ca 2+ ion adsorption, did not appear to cause any cellular binding. In comparison, cationic surfactant was strongly adsorbed by the cell membrane surface, even at concentrations of 0.1 mM, and light scattering studies indicated that the adsorption of the surfactant appeared to lyse the cell membrane and release internal cellular materials leading to a significant reduction in cell size. [ABSTRACT FROM AUTHOR]

[Display omitted] • P(MMA-co-DMAEMA) was synthesized and blended with polysulfone UF membrane. • Blend PSF-PMD membrane was quaternized to increase surface positive charge. • Membrane was grafted with 2-carboxyethyl acrylate for surface neutralization. • Neutralization resulted in comprehensive anti-fouling smooth membrane surface. • Surface charge control is simple and effective to mitigate membrane fouling. In this study, a new poly(methyl methacrylate-co-dimethyl aminoethyl methacrylate) (P(MMA-co-DMAEMA))-based membrane was fabricated and modified to control surface charge in order to improve fouling resistance. The positively-charged P(MMA-co-DMAEMA) copolymer was first synthesized from the free radical polymerization of methyl methacrylate (MMA) and dimethylamino-2-ethyl methacrylate (DMAEMA). The copolymer was blended with polysulfone and cast into a membrane via nonsolvent-induced phase separation. The membrane was then quaternized using iodomethane and neutralized by grafting 2-carboxylethyl acrylate via UV irradiation. The membrane surface charge, composition, morphology, hydrophilicity, and anti-fouling properties were evaluated. Surface charge control of the membrane resulted in outstanding antibacterial activity and fouling resistance against model protein foulants. While the incorporation of P(MMA-co-DMAEMA) in the membrane and its quaternization greatly improved the surface hydrophilicity of the membrane and endowed positive surface charge as well. Neutralization of the blend membrane endowed a smooth and electroneutral surface layer on the membrane surface, which led to not only excellent anti-bacterial activity and comprehensive resistance against charged foulants, but also high flux retention after simple membrane washing. Dynamic filtration using protein and bacterial foulants revealed the ability of the membrane with almost zero net surface charge to regulate fouling even in practical filtration applications. The results in this study exhibit a simple and effective method for mitigation of membrane fouling propensity for practical application. [ABSTRACT FROM AUTHOR]

Perm-selectivity consisting of water flux J w and solute flux J s or in form of J s /J w ratio is an important parameter of designing Forward Osmosis (FO) membrane as it indicates the membrane performance and how much solute replenishment over the extracted pure water from the feed solution. Parameter J s /J w ratio is dependent on hydrodynamic condition i.e cross-flow velocity (CFV), solute type i.e. diffusivity, trans -membrane surface potential. This study employed Cellulose Triacetate (CTA) membrane for representing low-charge membrane and Polyamide-Thin Film Composite (PA-TFC) for the membrane of highly negative surface charge. Six (6) different models were used to quantify the effect of external mass transfer, the ideal solution, non-ideal solution, trans -membrane surface potential on the transport of solute across the membrane. Our new model was proven to improve the prediction of perm-selectivity. The improvement was attributed to the application of trans -membrane potential-dependent solute partitioning for solute permeability correction and the application of experimentally obtained mass transfer coefficient. By the incorporation of the Donnan effect in determining the transmembrane potential, it was found that in the low charge membrane namely CTA, the dominant transport mechanism was diffusion, while in a highly negative surface charged membrane namely TFC, the partition of solute to be the dominant mechanism. Operation at a low CFV posed less impact of the membrane charge. The newly developed model provided a good foundation for FO process design under different CFVs and modified surface charges. [Display omitted] • The solute transport is affected by the membrane surface charge which is incorporated in our developed model. • The incorporation of surface charge dependent-solute partitioning was noticed. • The implementation of experimental mass transfer coefficient was proven to improve the prediction of perm-selectivity. • Optimally high negative charge of the membrane or optimally low CFV operation was suggested for implementation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alkali/zinc-activated fly ash nanocomposites were prepared using hydrothermal method. • Decoration with ZnO favorably enhanced the surface area and charge of nanocomposites. • Negative surface charge plays a major role in methylene blue adsorption. • The prepared nanocomposites have high adsorption and antibacterial activities. Fly ash (FA), obtained as waste materials from industrial power plants, is generated in large quantities and low recycling. In this study, re-generation of waste FA as cost-effective materials with adsorbent and antibacterial applications was assessed. Alkaline/zinc-activated fly ash nanocomposite (A-FA/Zn) was prepared using one-pot hydrothermal technique. Those nanocomposites are characterized by high surface area and negatively surface charge, which are important influences contributing to an enhancement in adsorption capacity via increase in the number of adsorptive sites and electrostatic interaction between dye molecules-nanocomposites. Additionally, the presence of Zn ions in the prepared nanocomposites represents a key advantage with respect to enhancing antibacterial activity. The feasibility of further enhancing adsorption and antibacterial mechanisms was also examined. It is anticipated that the findings of this study will provide useful information with respect to the development of simple, eco-friendly and low-cost A-FA/Zn with multifunctional applications as organic dye removal and antibacterial purposes. [ABSTRACT FROM AUTHOR]

• Surface tension, size and ζ of OS β G aggregates induced by temperature/pH were probed. • Compactness of hydrophobic and hydrophilic domains was both temperature/pH dependent. • Balance of different molecular interactions confirmed OS β G aggregates structure. • The aggregate formation for OS β G was driven collectively by enthalpy and entropy. • Transition mechanism of OS β G aggregates induced by pH and temperature was established. Environmental temperature and pH induced significant changes in the size and surface charge (ζ) of octenylsuccinated oat β -glucan aggregates. The underlying mechanisms were explored by using 1H-NMR, fluorescence spectra, thermodynamic analysis, and SAXS. At pH 6.5, the size decreased with temperature while ζ continuously increased. With increasing pH at 293 K, parabolic and U-shaped trends were observed in the size and ζ , peaking at pH 8.5 and 6.5, respectively. At any tested pH, the size decreased with temperature. Overall, ζ significantly increased with temperature at each pH. As temperature increased, the compactness of hydrophobic-domains increased while the compactness of hydrophilic-domains decreased. In an acidic environment, both the compactness increased with decreasing pH, but in an alkaline environment, they decreased with pH. The compactness changes were co-driven by enthalpy and entropy and corresponded to changes in the hydrophobic interactions in hydrophobic-domains, hydrogen bonds in hydrophilic-domains and electrostatic repulsions among octenylsuccinate molecules. [ABSTRACT FROM AUTHOR]