Salt Ion Concentration Research Articles

A one-step polyvinyl alcohol/polyacrylamide/polyacrylic acid/dimethyl sulfoxide/CaCl2 hybrid hydrogel enabling anti-fatigue, anti-freeze and anti-dehydration for wearable strain sensor

Hydrogel with fatigue resistance, freezing tolerant and dehydration resistance are peculiarly attractive in strain sensors. The hydrogel soaked in organic solvent is an effective strategy to improve freezing resistance and dehydration resistance, while this may result in poor conductivity. Moreover, ion-incorporation is considered to be the most feasible method for solving above concern, while high concentration of salt ions will result in weak mechanical properties. Therefore, the facile preparation of anti-freezing and anti-dehydration hydrogels with excellent fatigue resistance remains a challenge. Herein, a polyvinyl alcohol/polyacrylamide/polyacrylic acid/dimethyl sulfoxide/CaCl2 hybrid hydrogel was designed and fabricated through a facile one-step method to balance a variety of outstanding properties. On account of the hybridization design of multi-materials, the hybrid hydrogel exhibited high ionic conductivity (∼0.2 S/m), strength (∼0.36 MPa) and stretchability (∼825 %). Meanwhile, the hybrid hydrogel demonstrated prominent freezing resistance, dehydration resistance and fatigue resistance. The mechanical properties almost no deterioration after 1000 stretching cycle at 100 % strain, exposure to environment for 30 days or freeze at low temperature. Besides, the hybrid hydrogel-based stain sensor showed a linear sensitivity (GF = 1.12 over 0–400 % strain), quickly responsivity (200 ms), and could monitor various human activities steadily, demonstrating distinguished potential for use in wearable health monitoring and flexible electric skins.

Dynamics of major plant nutrients and enzymatic activities in soil influenced by application of biochar and organic waste.

The concentration of salt ions influences the availability and plant nutrients dynamics in the soil. Proper management of these ions can enhance food grain production, helping to feed the growing population. In this experiment, nine fertility combinations were followed to enhance the soil organic carbon and reduce the salt toxicity and monitor the plant nutrient availability. An incubation experiment was conducted for the period of one year with different organic soil amendments in combinations including biochar (BC), pressmud (PM), and farm yard manure (FYM) as follow: T1-control, T2-RDF, T3-FYM (10 t/ha), T4-PM (10 t/ha), T5-BC (10 t/ha), T6-FYM (5 t/ha) + PM (5 t/ha), T7-FYM (5 t/ha) + BC (5 t/ha), T8-PM (5 t/ha) + BC (5 t/ha), T9-FYM (5 t/ha) + BC (2.5 t/ha) + PM (2.5 t/ha). Results showed that addition of organic substance (10 t/ha) significantly (p < 0.05) affected soil pH and electric conductivity. Plant nutrient availability (N, K, and S) was also influenced by application of organic substance (10 t/ha). Organic C and available N were recorded the highest in the treatment T7 (FYM-5 t/ha + BC -5 t/ha); whereas, the highest available K and S were observed in treatment T5 (BC-10 t/ha). The microbial soil fertility indicators (alkaline phosphatases, arylsulphatase, dehydrogenase activity and microbial biomass carbon) were measured the highest in FYM (5 t/ha) + BC (5 t/ha) applied treatment. In conclusion, application of organic substance 10 t/ha (biochar alone or with FYM) improved the plant nutrient availability and soil microbial activities in saline soil. It could be a suitable option for enhancing the soil fertility in saline soils.

Surfactant-enhanced dispersion stability of cellulose nanocrystals and enhanced oil recovery performance

Cellulose nanocrystals (CNCs) have attracted more and more attention in EOR. CNCs are abundant and renewable, with nanoscale dimensions, excellent rheological properties, and easy-to-modify surface properties. However, the colloid stability of CNCs under high salinity conditions is poor, which limits their application in enhanced oil recovery (EOR). In order to improve the stability of CNCs in the salt environment, the effect of the mixed system of sodium dodecyl benzenesulfonate (SDBS) and polyoxyethylene sorbitan monooleate (Tween 80) on the dispersion stability of CNCs in the presence of different valence salt ions was investigated systematically. The dispersion stability of CNCs was investigated by using the ζ-potential and dynamic light scattering (DLS) techniques. The mixed surfactants improved the dispersion stability of CNCs within the studied salt ion concentration range (Na+ ≤ 300 mM, Ca2+ ≤ 10 mM, Mg2+ ≤ 10 mM). The stabilization mechanism of CNCs was explained by the electrostatic effect and spatial stabilization effect. In the presence of salt ions, the adsorption behavior of mixed surfactants on the surface of CNCs in the presence and absence of crude oil was revealed through molecular dynamics (MD) simulations. Microscopic displacement experiments indicated that due to the small particle size of CNCs in salt environments, the pores were not blocked, resulting in a significant improvement in the oil displacement performance.

The Phase Distribution Characteristics and Interphase Mass Transfer Behaviors of the CO2-Water/Saline System under Gathering and Transportation Conditions: Insights on Molecular Dynamics.

In order to investigate the interphase mass transfer and component distribution characteristics of the CO2-water system under micro-scale and nano-scale transport conditions, a micro-scale kinetic model representing interphase mass transfer in the CO2-water/saline system is developed in this paper. The molecular dynamics method is employed to delineate the diffusion and mass transfer processes of the system's components, revealing the extent of the effects of variations in temperature, pressure, and salt ion concentration on interphase mass transfer and component distribution characteristics. The interphase mass transfer process in the CO2-water system under transport conditions can be categorized into three stages: approach, adsorption, and entrance. As the system temperature rises and pressure decreases, the peak density of CO2 molecules at the gas-liquid interface markedly drops, with their aggregation reducing and their diffusion capability enhancing. The specific hydration structures between salt ions and water molecules hinder the entry of CO2 into the aqueous phase. Additionally, as the salt concentration in water increases, the density peak of CO2 molecules at the gas-liquid interface slightly increases, while the density value in the water phase region significantly decreases.

Enabling room temperature solid-state lithium batteries by blends of copolymers and ionic liquid electrolytes

High lithium-concentration phosphonium ionic liquids electrolytes have shown outstanding properties even overcoming ammonium derivatives in terms of viscosity and transport properties. Consequently, they have been also combined with fluorinated polymers, such as poly(vinylidene fluoride) (PVDF) or poly(ionic liquids), for solid-state batteries with satisfying performance at 50 °C. The aim of this work is to develop highly lithium conducting solid-state electrolyte (≥0.1 mS cm−1) at room temperature but maintaining solid-state properties. For this, polymer electrolytes based on ISOBAM alternating copolymer (isobutylene and maleic anhydride) and ionic liquid (P111i4FSI) were developed. The composition-dependent behavior of the solid electrolytes was studied in terms of electrochemical impedance spectroscopy (EIS), reaching σLi+ of 0.52 mS cm−1; differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) under different ionic liquid electrolyte loadings and salt concentration. The polymer electrolytes presented a solid-like behavior in the range of 25 to 90 °C with a storage modulus of 2.3·104 Pa. Finally, the best free-standing membrane electrolytes were tested and compared electrochemically in lithium symmetrical cells and lithium iron phosphate full cells exhibiting an excellent cycling at room temperature.

A novel coupled hydrothermal–mechanical model and numerical analysis of unsaturated bentonite considering the influence of salt ions

The quantitative research on swelling properties of bentonite considering the influence of salt ions under the effect of hydrothermo-mechanical coupling is relatively weak. Based on a calculation model for the swelling characteristics of bentonite from a fractal perspective, this work proposes a novel coupled multifield control equation for unsaturated bentonite considering the influence of salt ions. The numericalization of the coupling control equation was completed by secondary development of a numerical analysis platform. The new theoretical model’s dependability and validity were validated by comparing it to experimental data. The evolution of the related-field quantities under the multifield coupled effect in salt-bearing environments was obtained, and the effect of salt ion concentration was analyzed. The calculation showed that the temperature of bentonite changed periodically with changing ambient temperature. Temperature gradient induces migratory movement of water from high to low temperature regions. The hollow axisymmetric soil sample gradually saturated from outside to inside with increasing water injection rate at the outer cylindrical surface. The swelling pressure of bentonite will increase with an increase in water content, whereas the presence of salt ions weakened the swelling behavior. Temperature and relative humidity were less affected by salt ion concentration.

Salt ions improve soybean protein isolate/curdlan complex fat substitutes: Effect of molecular interactions on freeze-thaw stability

Although emulsion gels show significant potential as fat substitutes, they are vulnerable to degreasing, delamination, and other undesirable processes during freezing, storage, and thawing, leading to commercial value loss in terms of juiciness, flavor, and texture. This study investigated the gel strength and freeze-thaw stability of soybean protein isolate (SPI)/curdlan (CL) composite emulsion gels after adding sodium chloride (NaCl). Analysis revealed that adding low salt ion concentrations promoted the hardness and water-holding capacity (WHC) of fat substitutes, while high levels displayed an inhibitory effect. With 40 mM NaCl as the optimum concentration, the hardness increased from 259.33 g (0 mM) to 418.67 g, the WHC increased from 90.59 % to 93.18 %, exhibiting good freeze-thaw stability. Confocal laser scanning microscopy (CLSM) and particle size distribution were used to examine the impact of salt ion concentrations on protein particle aggregation and the damaging effect of freezing and thawing on the proteoglycan complex network structure. Fourier-transform infrared spectroscopy (FTIR) and protein solubility evaluation indicated that the composite gel network structure consisted of covalent contacts between the proteoglycan molecules and hydrogen bonds, playing a predominant role in non-covalent interaction. This study showed that the salt ion concentration in the emulsion gel affected its molecular interactions.

Temperature-responsive salt-resistant poly(sulfobetaine methacrylate)-based emulsifiers for heavy oils

The emulsions prepared with most currently reported emulsifiers are stable only at room temperature and are susceptible to demulsification at higher temperatures. This thermal instability prevents their use in high-temperature and high-salt environments encountered oilfield extraction. To address this issue, in this study, two temperature-responsive emulsifiers, PSBMA and CS-PSBMA, were synthesized. Both emulsifiers exhibited the ability to form stable emulsions within the temperature range of 60–80 °C and undergo demulsification at 20–40 °C. A comprehensive investigation was conducted to assess the impact of emulsifier concentration, water-to-oil ratio, and salt ion concentration on the stability of emulsions formed by these two emulsifiers. The results demonstrated their remarkable emulsification capabilities across diverse oil phases. Notably, the novel emulsifier CS-PSBMA, synthesized through the grafting chitosan (CS) onto PSBMA, not only exhibits superior emulsion stability and UCST temperature responsiveness but also significantly enhanced the salt resistance of the emulsion. Remarkably, the emulsion maintained its stability even in the presence of monovalent salt ions at concentrations up to 2 mol/L (equivalent to a mineralization level of 1.33 × 105 mg/L in water) and divalent salt ions at concentrations up to 3 mol/L (equivalent to a mineralization level of 2.7 × 105 mg/L in water). The emulsions stabilized by both emulsifiers are resilient to harsh reservoir conditions and effectively emulsify heavy oils, enabling high-temperature emulsification and low-temperature demulsification. These attributes indicate their promising potential for industrial applications, particularly in the field of enhanced oil recovery.

Chloride ion sequestration by vetiver root biosorption: isotherm, kinetic, and thermodynamic analyses and ANN prediction

ABSTRACT The present research investigates the potential of activated vetiver root powder as a bioadsorbent for removing chloride ions from saline aqueous environments, especially relevant for addressing agricultural water scarcity. Factors such as pH, biomass dosage, contact duration, and initial salt ion concentration were examined. Thermodynamic analysis provided insights into the adsorption process, demonstrating the feasibility, non-spontaneous behavior, and exothermic nature of chloride ion adsorption onto activated vetiver root powder. The batch adsorption of chlorides adhered to the Langmuir equation and a pseudo-second-order kinetic model, demonstrating a monolayer adsorption capacity of 17.58 mg/g for activated vetiver powder. An artificial neural network (ANN) was used to develop a predictive model for estimating the percentage removal of chloride ions. The values of R2 and mean squared error were used to determine the predictive performance of the ANN. In the near term, prospective commercial uses of activated vetiver powder merit further investigation through in-depth research using real wastewater containing salinity-inducing ion.

Decoding a novel green and effective antimicrobial agent: Glycerol monolaurate stable in nanosystem

Food microbiological control is the key to protecting food quality. However, glycerol monolaurate (GML), as a generally recognized safe antimicrobial agent, limits its antibacterial activity due to its poor water solubility. Ultrasound-assisted construction of essential oil nanosystems is an ingenious way to solve the above problems. In this study, essential oil-based nanoemulsions (NEs) were constructed by replacing traditional oil phase with tea tree essential oil (TTO) stabilized GML and enhanced antibacterial properties. The results demonstrated that uniform droplets could only be formed when the GML content in the nanosystem was below 50 mg/mL. NEs showed favorable optical properties with a turbidity below 0.1 and a whiteness index below 35, and they were Newtonian fluids (viscosity <0.005 Pa s). Besides, the nanosystem exhibited excellent stability even at extreme pH (1 or 11) and high salt ion concentration (500 mM), where droplet sizes of above system were still less than 100 nm after 15 d. Notably, GML alone cannot exert effective antibacterial effects against E. coli and S. aureus, whereas the encapsulation of GML into the nanosystem allowed it to exert antibacterial activity successfully. Banana was selected to validate the availability of NEs, and the treated groups maintained their attractive appearances and quality after 20 d. Overall, this work developed a new nanosystem to stabilize GML, allowing it to exert antimicrobial activity effectively.

Magnesium Ion Gated Ion Rejection through Carboxylated Graphene Oxide Nanopore: A Theoretical Study.

While nanoporous graphene oxide (GO) is recognized as one of the most promising reverse osmosis desalination membranes, limited attention has been paid to controlling desalination performance through the large GO pores, primarily due to significant ion leakage resulting in the suboptimal performance of these pores. In this study, we employed a molecular dynamics simulation approach to demonstrate that Mg2+ ions, adhered to carboxylated GO nanopores, can function as gates, regulating the transport of ions (Na+ and Cl-) through the porous GO membrane. Specifically, the presence of divalent cations near a nanopore reduces the concentration of salt ions in the vicinity of the pore and prolongs their permeation time across the pore. This subsequently leads to a notable enhancement in salt rejection rates. Additionally, the ion rejection rate increases with more adsorbed Mg2+ ions. However, the presence of the adsorbed Mg2+ ions compromises water transport. Here, we also elucidate the impact of graphene oxidation degree on desalination. Furthermore, we design an optimal combination of adsorbed Mg2+ ion quantity and oxidation degree to achieve high water flux and salt rejection rates. This work provides valuable insights for developing new nanoporous graphene oxide membranes for controlled water desalination.

Polysaccharide from Clitocybe squamulosa: Gel-forming properties and its compound effect with food thickener

To study the gel-forming properties of polysaccharide from the fruiting body of Clitocybe squamulosa (CSFP) and its degradation product (UH-CSFP), the changes in steady-state and dynamic rheological properties of CSFP and UH-CSFP under different conditions (polysaccharide mass fraction, temperature, pH, and salt ion concentration) were studied. Polysaccharides with good gel-forming properties were selected and mixed with common edible thickeners (gelatin, guar gum, and locust bean gum), after which the properties of the composite gel were assessed. The steady-state rheological results showed that CSFP and UH-CSFP were pseudoplastic fluids, their apparent viscosity decreased with increasing temperature, the viscosity was greatest when the pH was 7. The addition of Na+ and Ca2+ could increase the viscosity, and the viscosity of UH-CSFP was lower than that of CSFP at the same mass fraction. The results of dynamic rheology indicated that G´ and G´´ of CSFP and UH-CSFP increased with increasing mass fraction, pH, and ion concentration (0.01 M to 1 M), and G´´ was always smaller than G´ indicating weak gel behavior. The thixotropy-related experimental results showed that the thixotropy ring area of CSFP and UH-CSFP increased with increasing mass fraction, the ring area of CSFP was larger than that of UH-CSFP, and the gel strength of CSFP was greater than that of UH-CSFP. The results of CSFP and three types of edible gels showed that the composite gels were pseudoplastic fluids, and their apparent viscosity was ranked (in descending order) as follows: guar bean gum, locust bean gum, and gelatin. The addition of CSFP improved the gel-forming properties of guar gum but did not significantly improve the gel properties of locust bean gum and gelatin. This study provides a theoretical basis for the selection of processing methods and the application of polysaccharides.

Construction and characterization of egg white protein-gallic acid-xanthan gum-based emulsion and oleogel

In this work, the egg white protein-gallic acid-xanthan gum covalent complexes were used to construct emulsions and oleogels and the effects of different concentrations of the complexes on the properties of emulsions and oleogels were investigated. The results showed that the values of emulsion D[4,3] and ζ-potential decreased with increasing complex concentration, while the emulsion stability index increased. The emulsions exhibited good centrifugal stability against changes in temperature, salt ion concentration and pH value. The emulsions prepared with high concentrations of the complexes (0.6–1.0%, wt) showed good viscoelasticity and gelation properties. The oil binding capacity increased from 75.86% to 98.04% as the concentration of oleogel increased from 0.2% to 0.4% (wt), and all the oleogels exhibited a strong gel network structure (G'>G″). Compared with the bulk oil, the oleogel had a stronger antioxidant capacity, and with increasing the concentration of the complexes, the antioxidant ability of the produced oleogel enhanced. This study may provide a theoretical basis for the preparation of protein-polysaccharide-polyphenol based oleogels and their application as solid fat substitutes in the food industry.

Solar driven thermal responsive polyionic liquid/PDDA semi-IPN hydrogel for near-room temperature membrane-free osmotic desalination

The designed thermally responsive polyionic liquid (TPIL)/ poly (diallyl dimethylammonium chloride) (PDDA) hydrogel with a semi-interpenetrating (semi-IPN) structure, containing highly charged chloride anions, was fabricated to explore the comprehensive capabilities of solar driven membrane-free osmotic desalination. Introducing linear PDDA polyelectrolyte with higher charge density has effectively excluded salt ions from entering the TPIL hydrogel matrix due to the strong charge concentration gradient established between the hydrogel and the saline reservoir. Meanwhile, the thermo-sensitivity of the polyionic liquid/PDDA semi-IPN (PNCl) hydrogel enabled the release of absorbed salt-depleted water at a temperature above the Lower Critical Solution Temperature (LCST). The multiple purification process established by partial submersion of PNCl hydrogel in saline enabled continual reduction of the salt ion concentration during the upwards transportation of water along the polyelectrolyte network. Moreover, a mushroom-shaped hydrogel demonstrated enhanced the effectiveness in long-term cyclic desalination. The “mushroom cap” was loaded with photo-thermal conversion fillers (Ti3C2Tx MXene) to achieve higher photo-thermal conversion efficiency for water recovery. A record high salt rejection rate of more than 93% was obtained for membrane-free osmotic desalination. More importantly the whole desalination/water absorption/release process was solely supported by gently heating the PNCl hydrogel under the illumination of renewable solar energy.

Molecular design of switchable nanochannels modified by zwitterion polymer chains with dissipative particle dynamics simulation

Conventional artificial nanochannels have obvious shortcomings in permeability regulation and environmental friendliness, which challenge their practical applications. Polymer-modified switchable nanochannels are considered as a potential solution owing to their high chemoselectivity and controllability. Herein, systematic dissipative particle dynamics (DPD) simulations are performed to investigate the conformational transition and stretching behavior of polysulfobetaine in the presence of an explicit solvent. Polysulfobetaine is one kind of zwitterion polymer with a responsive property to the change of salt ion concentration, which is grafted onto the internal surface of the nanochannel to achieve the "open-close-open" switch. The simulation results indicate that the grafting ratio of 1.52 chains/rc2 (rc is a reduced unit of length, 1 rc = 0.857 nm) and salt ion concentration of 5 wt% NaCl are optimal parameters to achieve the "open-close-open" functionality. Specifically, salt ions promote the closure of nanochannels via regulating the electrostatic attraction of the polymer chain in z-direction and the excluded volume effect caused by conservative forces. On the other hand, the competition mechanism between electrostatic force and conservative force is revealed, i.e. at low salt concentration, electrostatic force dominates and close the nanochannel; With salt ions concentration increasing, conservative force gradually exceeds electrostatic force, and becomes the dominant force and reopens the nanochannel. This study provides some molecular insights for the design of stimulus-responsive artificial nanochannels, which may find application in the exploitation of natural gas hydrates, such as temporary plugging agents in well drilling for gas hydrate reservoirs.

Quantitative Evaluation of the Effects of Salt Concentration and pH on the Self-Assembly of Kaolin Nanoplatelets.

Diffusion of pollutants in the earth's strata threatens both the environment and human health. The clay soil microstructure that plays a crucial role in the diffusion of pollutants is significantly influenced by the pore water chemistry. However, there is still a lack of quantitative evaluation of pore water chemistry on clay fabric evolution. To bring new insights, we systematically examined the impact of water chemistry (mainly refers to salt ion concentration and pH) on the self-assembly form (fabric) of kaolin platelets and evaluated the fabric quantitatively. The results show that as the salt ion concentration increases, the "kaolin book" structure is formed, which can be captured by the (001) and (020) pole figures. Under acidic conditions, kaolin platelets turn randomly arranged; however, with the increase of pH, the edge-to-face (EF) microstructure of kaolin platelets gradually changes to a face-to-face (FF) structure. Under alkali-eq conditions, kaolin platelets form a dispersion assembly dominated by FF repulsion. However, the strong alkaline condition triggers the decomposition of kaolin, leading to a notable decrease in the maximum pole density. The conclusions were substantiated through insightful AFM tests. Moreover, we addressed the advantages and limitations of 1DXRD and 2DXRD by analyzing the trend between the OI and pole density, with 2DXRD being favored for its accuracy. Overall, this study provides insights into clay platelets and the self-assembly of kaolin under different water chemistry conditions, which have significant implications for predicting and modeling the physical properties of clay under special environmental conditions.

Sorption of modified clay minerals in pore solution of fired clay brick under pulsed current

This experimental study examines the influence of salt ions from poultice compositions entered into the contaminated fired clay brick with applied continuous and pulsed DC current across contaminated brick sample. The concentration of salt ions in the brick samples after electrokinetic (EK) treatment was also determined. For this purpose, the brick samples were intentionally contaminated with 15 g/kg of sodium chloride (NaCl) for 10 days. Subsequently, a series of experiments were conducted utilizing electrokinetic treatment by the application of different poultices. During electrokinetic experiments, a constant DC voltage of 9 V was applied across electrodes. The results show that by employing buffering elements in kaolin clay poultice; only 55 % of Cl− ions were removed with energy consumption of 219Wh in the presence of pulsed DC current, which is very low as compare to conventional continuous DC current having (up to 84 %) removal efficiency of Cl− ions but with energy consumption of 301Wh. According to existing results, further experimental development is needed to improve the desalination efficiency and reduce the energy consumption using pulsed DC current in order to expand the application scope of this work.

Water chemistry role in the stability of CO2 foam for carbon sequestration in water aquifers

Injection of CO2 foam into saline aquifers is a practical method to store CO2; however, generating stable CO2 foam at high temperatures and salinities remains a challenging task. Therefore, this research fully explains the effect of formation water components (NaCl, CaCl2, MgCl2, Na2SO4, and NaHCO3) on the stability of generated foam under harsh conditions. In this regard, a high-temperature and high-pressure (HPHT) foam analyzer was used to investigate the foamability and stability of CO2 foam at 100 °C and 1000 psi. The liquid phase contained 0.5 wt% of Armovis surfactant dissolved into 0.1, 0.5, and 1M concentrations of formation water ions. Moreover, the dynamic surface tension of the selected surfactant solutions was investigated using an optical tensiometer. For the first time, this paper investigates the behavior of foam during the foaming process. During the injection of CO2, the average bubble count for the low salt concentration increased sharply and then dropped until it plateaued. However, the average bubble count for the higher salt concentration gradually increased until the foaming process stopped. These phenomena occurred because of the kinetic adsorption rate of the surfactant micelles at the interface. Additionally, we studied the effect of salt concentrations on bubble count half-life, bubble coarsening, and foam volume decay during the static condition. We observed that the increase in salt concentration resulted in more stable foam due to the reduction of CO2 solubility in water. The foam half-life for 0.1 M of NaCl was 190 min, while it was more than 250 min for 1M of NaCl. A similar trend was observed for CaCl2 and MgCl2. The results of the HPHT foam analyzer concluded that the higher concentration of salt ions presented a more stable foam. Also, the use of Armovis surfactant is promising for the stabilization of CO2 foam at high temperatures and salinities.

Molecular Dynamics Simulation of a Brine Droplet under an Electric Field: Distinct Behavior Shown by NaCl and CaCl2.

Electrostatic demulsification is a promising technique to disrupt petroleum emulsions. However, the presence of salts in the emulsion can influence the effectiveness of the electric field. In this work, we target an understudied area, namely, the effect of salt ion type and concentration on the stability of brine droplets when exposed to an electric field. Molecular dynamics (MD) simulations are performed on a series of water-in-oil emulsion systems consisting of a water or brine droplet surrounded by an oil phase containing toluene and model asphaltene molecules (N-(1-hexylheptyl)-N'-(5-carboxylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe)). The brine droplet contains either NaCl or CaCl2, with concentrations varying from 0 to ∼11 wt %. An external electric field is applied, which has a strength ranging from 0 to 1 V/nm. Our results show that as the electric field increases, the bare water droplet exhibits progressive deformation from the original spherical shape to an ellipsoid, a spindle, and finally a cylinder. When the brine droplets are exposed to a low electric field (≤0.5 V/nm), they behave similar to the bare water droplet. However, at a high electric field (≥0.75 V/nm), both NaCl and CaCl2 brine droplets are stabilized in the bulk oil and maintain the spherical or ellipsoidal shape by ejecting salt ions toward the electrodes at high salt concentrations (≥7.8 wt %), which induces a counter electric field that weakens the destabilization of the droplet by the applied field. At low salt concentrations (≤4.5 wt %), brine droplets containing NaCl or CaCl2 display different behaviors: the former tends to shift toward an electrode, whereas the latter stays in the bulk oil phase. The contrasting phenomena are the result of combined effects of brine droplet net charge and C5Pe adsorption on the droplet surface: a large net charge and low C5Pe adsorption tend to drive the droplet toward an electrode. This study provides useful insights into the important role of salt ions in electrostatic demulsification of petroleum emulsions.

Effects of calcium ions on the particle performance of luteolin-loaded zein-gum arabic-tea polyphenols ternary complex nanoparticles

Zein-gum arabic-tea polyphenols ternary complex nanoparticles have been developed for the encapsulation of luteolin, but there are still shortages existed in their particle properties such as encapsulation efficiency, stability, and release ability of luteolin. To improve their performance, calcium ions (Ca2+) were employed as a cross-linking stabilizer to investigate their effects on particle properties and functional performance. Particle parameters, physicochemical stability, antioxidant activity, and in vitro simulated gastrointestinal digestion were evaluated based on zetasizer measurement and multi-spectral methods, which were analyzed using Graphpad Prism v6.0.2. As a result, low concentrations of Ca2+ induced the formation of smaller and more compact nanoparticles with improved luteolin encapsulation efficiency, while higher concentrations had the opposite effect. Hydrophobic, electrostatic, and hydrogen bonding interactions were found to be responsible for nanoparticle assembly and stability with Ca2+ incorporation. Appropriate amounts of Ca2+ promoted the physicochemical stability of the nanoparticles under different conditions such as pH, salt ion concentration, temperature, and storage time. Additionally, low levels of Ca2+ strengthened the antioxidant activity of the nanoparticles and improved sustained release of luteolin under in vitro gastrointestinal conditions. These findings suggest that zein-gum arabic-tea polyphenols nanoparticles assembled with Ca2+ have potential applications as a delivery system for bioactive substances.