Decrease In Surface Charge Density Research Articles

Preparation and Mechanism of Shale Inhibitor TIL-NH2 for Shale Gas Horizontal Wells.

In this study, a new polyionic polymer inhibitor, TIL-NH2, was developed to address the instability of shale gas horizontal wells caused by water-based drilling fluids. The structural characteristics and inhibition effects of TIL-NH2 on mud shale were comprehensively analyzed using infrared spectroscopy, NMR spectroscopy, contact angle measurements, particle size distribution, zeta potential, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The results demonstrated that TIL-NH2 significantly enhances the thermal stability of shale, with a decomposition temperature exceeding 300 °C, indicating excellent high-temperature resistance. At a concentration of 0.9%, TIL-NH2 increased the median particle size of shale powder from 5.2871 μm to over 320 μm, effectively inhibiting hydration expansion and dispersion. The zeta potential measurements showed a reduction in the absolute value of illite's zeta potential from -38.2 mV to 22.1 mV at 0.6% concentration, highlighting a significant decrease in surface charge density. Infrared spectroscopy and X-ray diffraction confirmed the formation of a close adsorption layer between TIL-NH2 and the illite surface through electrostatic and hydrogen bonding, which reduced the weakly bound water content to 0.0951% and maintained layer spacing of 1.032 nm and 1.354 nm in dry and wet states, respectively. Thermogravimetric analysis indicated a marked reduction in heat loss, particularly in the strongly bound water content. Scanning electron microscopy revealed that shale powder treated with TIL-NH2 exhibited an irregular bulk shape with strong inter-particle bonding and low hydration degree. These findings suggest that TIL-NH2 effectively inhibits hydration swelling and dispersion of shale through the synergistic effects of cationic imidazole rings and primary amine groups, offering excellent temperature and salt resistance. This provides a technical foundation for the low-cost and efficient extraction of shale gas in horizontal wells.

Facile construction of calcium titanate-loaded silk fibroin scaffolds hybrid frameworks for accelerating neuronal cell growth in peripheral nerve regeneration

Different concentrations of calcium titanate (CaTiO3) nanoparticles were loaded into the Silk fibroin (SF) solution to construct porous SF@CaTiO3 hybrid scaffolds, which were shown to have enhanced properties for stimulating peripheral nerve regeneration. Surface charges, crystallization intensity, wettability, porosity, and morphology were measured and analyzed. We analyzed the hybrid porous SF@CaTiO3 scaffolds that affected the expansion of Schwann cells. The results demonstrated a concentration-dependent influence on the dispersion of nanoparticles in the CaTiO3 hybridized SF scaffolds. Incorporating CaTiO3-NPs into the porous SF@CaTiO3 hybrid scaffolds can boost hydrophobicity while decreasing surface charge density and porosity. The hybridized scaffolds mostly had an orthorhombic calcium titanate crystal structure with amorphous Silk fibroin mixed. Schwann cell cultures revealed that SF@CaTiO3 hybrid scaffolds containing an optimal CaTiO3-NPs concentration could stimulate the proliferation, attachment, and protection of Schwann cell biological functions, suggesting the scaffolds' potential for use in peripheral nerve regeneration.

Significantly suppressing metal particle-induced surface charge accumulation of spacers in DC gas-insulated power transmission lines

In this letter, we report functions of surface roughening and fluorination on suppressing linear metal particle-induced spacer surface charge accumulation. An appropriate increase in spacer surface conductivity by short-term fluorination and roughening not only increases the metal particle lifting voltage, but also weakens the particle activation. The spacer surface charge shows reduced charge density in roughened spacer, while fluorination modification significantly suppresses the charge density on the spacer surface. For roughened and fluorinated samples, the decrease of surface charge density and the intrinsic lower electric field (due to an increase in conductivity) near the triple junction both contribute to a higher particle lifting voltage. The content in this letter provides an approach to effectively suppress the charge accumulation induced by linear metal particles.

Nanopore-based active oil droplet filtration under negative DC dielectrophoresis for oily wastewater treatment

Efficient separation of oil droplets from oily wastewater is an essential task for handling the world water crisis and environmental pollution. However, existing passive oil/water separation technologies suffer from the drawbacks of relatively low separation efficiency and strict material requirements. We present an active dielectrophoretic oil/water separation technique without inducing further environmental contamination. Based on the non-uniform electric field generated through insulated nanopores under direct current (DC) voltage, an oil droplet experiences a negative dielectrophoresis (nDEP) force because of its weaker dielectric property compared with wastewater. Meanwhile, electroosmotic flow also occurs in oil/water separation devices due to the ion motion inside the electric double layer of the nanopore solid surface. Through developing a multiphysical model for immiscible oil/water flow under hybrid electrokinetic effects, the oil/water separation is investigated at different parametric conditions. Electrokinetic filtration of oil droplets through nanopores is successfully achieved when the nDEP force is dominant rather than the electroosmotic electrohydrodynamic (EHD) force for oil droplet movement. To enhance the oil/water separation rate, the relative strength between nDEP force and EHD force on an oil droplet is consolidated via increasing DC voltage, decreasing surface charge density, and optimizing the nanopore configuration. The designed active oil/water separation using DC-DEP offers significant potential for future oily wastewater treatment.

Detection of lysine molecular ions in solution gated field effect transistors based on unmodified graphene

The electrical transport in graphene interfaced with different ions in solution gated graphene field effect transistors (GFETs) is the subject of active studies due to its importance in sensor fabrication. Most of the developed GFET biological sensors use graphene that has been modified. The difficulty in the modification procedure and the reduction in quality of graphene that it causes are important drawbacks for applications. Therefore, we focus on GFETs based on unmodified graphene gated by aqueous solutions containing lysine amino acids. We observed that an increase in the ionic concentration of lysine in these solutions leads to a suppression of unipolar electron conductance of graphene in GFETs. This dependence is opposite to the dependence typically observed in gating solutions containing smaller atomic ions. We attribute the observed suppression to electric field screening of the graphene surface from water molecules by lysine ions which are larger and have lower charge density compared to atomic ions. This novel phenomenon leads to an overall decrease of surface charge density in molecular layers formed at the graphene interface and can be applied in GFET sensors with unmodified graphene that detect the presence and concentration of large molecules in the gating solutions.

Intermediate layer for enhanced triboelectric nanogenerator

Triboelectric nanogenerator (TENG) has shown great advances in converting low-frequency discrete mechanical energy into electricity and multifunctional real-time self-powered sensing systems. It has confirmed that the air breakdown effect is the main factor limiting the maximum effective power output of the TENG. Charges generated on the surface of TENGs diffuse into the atmosphere and internal triboelectric layer, resulting in charge loss and decrease of surface charge density. Breaking through the limitation of air breakdown and prolonging charge decay time are the two priorities for boosting TENG output. By embedding superior intermediate layer into TENG induced output enhancement provides an effective strategy to improve the output performance. Here, the working mechanisms of different materials belonging to the classifications of metals, inorganic non-metal materials, and organic polymers as the intermediate layer are reviewed elaborately. Moreover, the influences of structure parameters, such as thickness of dielectric layer, dielectric layer number, and ground connection design are discussed accordingly. Future challenges and optimizations for improvement of the intermediate layer are finally presented in the review.

A pH-Resolved View of the Low Salinity Effect in Sandstone Reservoirs

Core plug and field tests have shown that significantly more oil can be produced from sandstone reservoirs when the water that is injected to maintain pressure in the reservoir has lower salinity than regular seawater. We investigated the adhesion between functional groups known to dominate in crude oil and grains from reservoir sandstone as a function of pH and salinity. We used atomic force microscopy (AFM) in chemical force mapping mode, and we functionalized the AFM tips both with −CH3, to model adhesion of hydrophobic molecules, and with −COO(H), to model polar compounds. As the pH increased, the adhesion force decreased. The behavior was similar for the two types of tips, but adhesion was higher for the polar tip. The average adhesion at pH 4.5 for the −COO(H) tip in artificial seawater (ASW) was close to 300 pN, and 200 pN in ASW diluted by a factor of 20. For the −CH3 tip, adhesion was ∼200 pN in high salinity and 140 pN in low salinity. Regardless of the salinity, adhesion decreased as pH increased. To gain understanding about the controlling processes, we examined our data in light of the Dejarguin–Landau–Verwey–Overbeek (DLVO) theory and the Henderson–Hasselbalch expression. The commonly used form of the DLVO relationship could not account for the pH dependence. It predicts adhesion to be independent of pH in high-salinity solution and strongly dependent on pH in low salinity, opposite to the experimental evidence. Although DLVO theory cannot be expected to quantitatively represent real systems, it is unlikely that DLVO would predict reversed behavior. Our results indicate that the extended double layer, which is one of the prevailing explanations for the low salinity effect, is not the full explanation. Decrease in surface charge density at low salinity plays an important role. The change in adhesion as pH increases above 5.5, which is the typical pH of sandstone reservoirs, to the neutral range could enhance oil recovery. This is probably a factor in the effectiveness of alkaline flooding and might be an inherent factor in the production that results from flooding with seawater, which is typically pH 8.3. However, the buffering effect in sandstone reservoirs, which maintains pH at ∼5.5, suggests that benefits from controlling pH for EOR could be marginal.

Electrostatic interaction of charged surfaces with semipermeable membranes

We have investigated the ion density distribution and electrostatic disjoining pressure of the size-asymmetric electrolytes in the gap between the semipermeable membranes and the charged surface by using the density functional theory. The present theory is in reasonably good agreement with the simulation data whereas the Poisson-Boltzmann equation does not describe the electrostatic properties of the electrolytes near a charged surface. The ion density distribution and the electrostatic disjoining pressure depend strongly on the size-asymmetric electrolytes in charge and size as well as the ion density of the electrolyte. The finite size of the ions leads to a large repulsive electrostatic disjoining pressure in the gap. However, the effect of the gap width on the repulsive electrostatic disjoining pressure is very small. The repulsive electrostatic disjoining pressure increases with increasing or decreasing surface charge density with its having a minimum value near a neutral surface. The surface charge amplification and the charge reversal phenomenon are observed for a neutral semipermeable membrane with a charged surface. A positively charged surface enhances the charge surface amplification whereas a negatively charged surface enhances the charge reversal phenomenon.

Influence of Charge Density and Ionic Strength on the Aggregation Process of Cellulose Nanocrystals in Aqueous Suspension, as Revealed by Small-Angle Neutron Scattering

Aggregation of rodlike colloidal particles is investigated here through the aggregation process by either increasing ionic strength or decreasing surface charge density of cellulose nanocrystals (CNCs). The form factor of the nanoparticles is characterized up to the Guinier plateau using small-angle neutron scattering (SANS) extended to very small scattering vector Q. Ionic strength, above the threshold of screening charges, brings aggregative conditions that induced fractal organizations for both charged and uncharged CNCs. These two structures display respective fractal dimensions of 2.1 for charged CNCs at high ionic strength and 2.3 for desulfated CNCs over more than a decade of the scattering vector Q, irrespective of salinity, revealing a denser structuration for neutral particles. This is discussed in the framework of aggregation of rodlike particles with an aspect ratio higher than 8. Furthermore, dilution of the rod gel led to disentanglement of the network of fractal aggregates with a subsequent macroscopic sedimentation of the suspensions, with a characteristic time that depends upon the ionic strength and surface charge density. It revealed a threshold independent of salt content around 2.5 g/L and the metastable out-of-equilibrium character of CNC suspensions.

Influence of ionic strength on the surface charge and interaction of layered silicate particles

The surface charge densities and surface potentials of selected phyllosilicate surfaces were calculated from AFM surface force measurements and reported as a function of ionic strength at pH 5.6. The results show that the silica faces of clay minerals follow the constant surface charge model because of isomorphous substitution in the silica tetrahedral layer. A decreasing surface charge density sequence was observed as follows: muscovite silica face>kaolinite silica face>talc silica face, which is expected to be due to the extent of isomorphous substitution. In contrast, at pH 5.6, the alumina face and the edge surface of kaolinite follow the constant surface potential model with increasing ionic strength, and the surface charge density increased with increasing ionic strength.The cluster size of suspended kaolinite particles at pH 5.6 was found to increase with increasing ionic strength due to an increase in the surface charge density for the alumina face and the edge surface. However, the cluster size decreased at 100mM KCl as a result of an unexpected decrease in the surface charge of the alumina face. When the ionic strength continued to increase above 100mM KCl, the van der Waals attraction dominated and larger clusters of micron size were stabilized.

Monitoring CO2 Intrusion and Associated Geochemical Transformations in a Shallow Groundwater System Using Complex Electrical Methods

The risk of CO(2) leakage from a properly permitted deep geologic storage facility is expected to be very low. However, if leakage occurs it could potentially impact potable groundwater quality. Dissolved CO(2) in groundwater decreases pH, which can mobilize naturally occurring trace metals commonly contained in aquifer sediments. Observing such processes requires adequate monitoring strategies. Here, we use laboratory and field experiments to explore the sensitivity of time-lapse complex resistivity responses for remotely monitoring dissolved CO(2) distribution and geochemical transformations that may impact groundwater quality. Results show that electrical resistivity and phase responses correlate well with dissolved CO(2) injection processes. Specifically, resistivity initially decreases due to increase of bicarbonate and dissolved species. As pH continues to decrease, the resistivity rebounds toward initial conditions due to the transition of bicarbonate into nondissociated carbonic acid, which reduces the total concentration of dissociated species and thus the water conductivity. An electrical phase decrease is also observed, which is interpreted to be driven by the decrease of surface charge density as well as potential mineral dissolution and ion exchange. Both laboratory and field experiments demonstrate the potential of field complex resistivity method for remotely monitoring changes in groundwater quality due to CO(2) leakage.

The microstructure of DNA-egg yolk phosphatidylcholine-gemini surfactants complexes: effect of the spacer length

The length of spacer of gemini surfactants affects the DNA packing in DNA-neutral phospholipid-gemini surfactant complexes. The microstructure of complexes DNA-egg yolk phosphatidylcholine (EYPC)-alkane-α,ω-diyl-bis(dodecyl­dimethylammonium bromides) (CnGS, spacer n=2-12, n is even) was studied using small angle X-ray diffraction. At EYPC:CnGS=1:1 mol/mol, the condensed lamellar phase was identified in complexes with CnGS, n=2-4, whereas longer spacer (n≥6) induced a hexagonal phase. The condensed lamellar phase Lαc was observed in the range 2\≤ EYPC:GnGS≤10 (mol/mol) in all complexes. The distance between adjacent DNA strands increases linearly with decreasing surface charge density of EYPC-CnGS vesicles. We determined the increase in dDNA 0.40±0.03 nm/1 mol of EYPC from the slope of dDNA=f (molEYPC/molCnGS) in the range of molar ratios 2≤EYPC:CnGS≤5. At lower surface charge density, EYPC:CnGS>5 mol/mol, the length of CnGS spacer (n=6-10) modulates the DNA-DNA distance. Both the short spacer of CnGS and the low molar ratio EYPC:CnGS result in the closest DNA-DNA packing. A high surface charge density of membrane was reported as a key parameter for transfection efficiency of Lαc phase-forming complexes.

An ionic surfactant-mediated Langmuir–Blodgett method to construct gold nanoparticle films for surface-enhanced Raman scattering

A gold nanoparticle film for surface-enhanced Raman scattering (SERS) was successfully constructed by an ionic surfactant-mediated Langmuir-Blodgett (LB) method. The gold film was formed by adding ethanol to a gold colloid/hexane mixture in the presence of dodecyltrimethylammonium bromide (DTAB). Consequently, gold nanoparticles (AuNPs) assembled at the water/hexane interface due to the decrease in surface charge density of AuNPs. Since DTAB binds the gold surface by a coulombic force, rather than a chemical bonding, it is easily replaced by target molecules for SERS purposes. The SERS enhancement factor of the 80 nm gold nanoparticle film was approximately 1.2 × 10(6) using crystal violet (CV) as a Raman dye. The SERS signal from the proposed DTAB-mediated film was approximately 10 times higher than that from the octanethiol-modified gold film, while the reproducibility and stability of this film compared to an octanethiol-modified film were similar. This method can also be applied to other metal nanostructures to fabricate metal films for use as a sensitive SERS substrate with a higher enhancement factor.

Particle interactions in kaolinite suspensions and corresponding aggregate structures

The surface charge densities of the silica face surface and the alumina face surface of kaolinite particles, recently determined from surface force measurements using atomic force microscopy, show a distinct dependence on the pH of the system. The silica face was found to be negatively charged at pH>4, whereas the alumina face surface was found to be positively charged at pH<6, and negatively charged at pH>8. The surface charge densities of the silica face and the alumina face were utilized in this study to determine the interaction energies between different surfaces of kaolinite particles.Results indicate that the silica face–alumina face interaction is dominant for kaolinite particle aggregation at low pH. This face–face association increases the stacking of kaolinite layers, and thereby promotes the edge–face (edge–silica face and edge–alumina face) and face–face (silica face–alumina face) associations with increasing pH, and hence the maximum shear-yield stress at pH 5–5.5. With further increase in pH, the face–face and edge–face association decreases due to increasing surface charge density on the silica face and the edge surfaces, and decreasing surface charge density on the alumina face. At high pH, all kaolinite surfaces become negatively charged, kaolinite particles are dispersed, and the suspension is stabilized. The face–face association at low pH has been confirmed from cryo-SEM images of kaolinite aggregates taken from suspension which show that the particles are mostly organized in a face–face and edge–face manner. At higher pH conditions, the cryo-SEM images of the kaolinite aggregates reveal a lower degree of consolidation and the edge–edge association is evident.

Electrical double layers’ interaction between oppositely charged particles as related to surface charge density and ionic strength

Phyllosilicates with net negative surface charge and Fe/Al oxides with net positive surface charge co-exist in variable charge soils and the interaction between these oppositely charged particles affects the stability of mixed colloids, aggregation, and even the surface chemical properties of variable charge soils. The overlapping of the diffuse layers of electrical double layers between kaolinite and goethite, hematite, gibbsite and γ-Al 2O 3 was investigated in this article based on the change of zeta potential and electrokinetic charge density induced by the addition of Fe/Al oxides. The results indicated that in the range of pH from 3 to 7, the kaolinite is negatively charged and the Fe/Al oxides are positively charged, and the overlapping of the diffuse layers led to the increase in zeta potential and the decrease in surface charge density of binary-system containing kaolinite and Fe/Al oxides compared with the single kaolinite system. The presence of gibbsite resulted in the strongest interaction of electrical double layers between this and kaolinite, followed by goethite and hematite. The interaction extent of electrical double layers between kaolinite and Fe/Al oxides increased with the amount of Fe/Al oxides added. The interaction also resulted in the increase in IEP of the binary-system containing kaolinite and Fe/Al oxides. The increase in ionic strength led to the decrease in the thickness of colloid diffuse layer and thus resulted in the reduction of overlapping of the diffuse layers between kaolinite and Fe/Al oxides.

Fractionation of protein, RNA, and plasmid DNA in centrifugal precipitation chromatography using cationic surfactant CTAB containing inorganic salts NaCl and NH(4)Cl.

Centrifugal precipitation chromatography (CPC) is a separation system that mainly employs a moving concentration gradient of precipitating agent along a channel and solutes of interest undergo repetitive precipitation-dissolution, fractionate at different locations, and elute out from the channel according to their solubility in the precipitating agent solution. We report here for the first time the use of a CPC system for fractionation of protein, RNA, and plasmid DNA in clarified lysate produced from bacterial culture. The cationic surfactant cetyltrimethylammonium bromide (CTAB) was initially used as a precipitating agent; however, all biomolecules showed no differential solubility in the moving concentration gradient of this surfactant and, as a result, no separation of protein, RNA, and plasmid DNA occurred. To overcome this problem, inorganic salts such as NaCl and NH(4)Cl were introduced into solution of CTAB. The protein and RNA were found to have higher solubility with the addition of these salts and separated from the plasmid DNA. Decreasing surface charge density of CTAB upon addition of NaCl and NH(4)Cl was believed to lead to lower surfactant complexation, and therefore caused differential solubility and fractionation of these biomolecules. Addition of CaCl(2) did not improve solubility and separation of RNA from plasmid DNA.

ADSORPTION OF METAL IONS ON STEARIC ACID-NONADECANE PARTICLES IN AQUEOUS SOLUTION

The adsorption of metal ions at the stearic acid/electrolyte and nnonadccane-stearic acid mixture/electrolyte interface was investigated by means of the potentiometric titration, zeta potential and adsorption measurements. It was found that the studied colloidal suspensions exhibited an adsorption affinity towards multivalent metal ions. The adsorption of Ca2+, Cd2+ and Al3+ ions caused a strong decrease of surface charge density and zeta potential values in this systems. The adsorption reactions occur by way of cation exchange with protons from two surface carboxyl groups. Al high metal concentrations, in adsorption reactions there are involved also carboxyl groups from the subsurface layer. On the basis of the adsorption data, the cation surface complexation constants were calculated by Shindler's method.

Low-frequency dispersion of surface conducting particles as measured by means of electrorotation

Electrorotation of glutaraldehyde-fixed red blood cells (RBCs) has been investigated in the frequency range from 16 Hz to 30 MHz. Special emphasis has been given to the low-frequency range (16 Hz–2 kHz). In this region, a distinctly new type of co-field rotation peak was observed. Native RBCs also show low-frequency rotation, but much less pronounced. The low-frequency rotation is nonmonotonous with regard to conductivity. With increasing external conductivity, the low-frequency rotation speed reaches a maximum of around 3.5 mS/m and decreases again when the external conductivity is increased further. The low-frequency co-field rotation peak was observed between 30 Hz and 70 Hz except at very low conductivity almost independent of electrolyte concentration. Decreasing surface charge density by means of neuraminidase led to a reduction of the rotation speed in the low-frequency range. The position of the peak remained unaffected by changes of the surface charge density. These experimental results are not consistent with the typical Pauli–Schwan- and Maxwell–Wagner-dispersion. They rather suggest the presence of a concentration polarization mechanism responsible for the low-frequency electrorotation peak.

Design of highly ion conductive polyether/salt hybrids

Several kinds of charged groups, carboxylate, sulfonate, benzenesulfonate, sulfonamide, pyridinium, or triethylammonium groups were introduced to the terminal of poly(ethylene oxide) (PEO) oligomers to analyze the effect of the terminal charged structure on the bulk ionic conductivity. For cation conductors, the ionic conductivity increased with increasing the dissociation constant of the terminal group due to the increase in the number of carrier ions for the same MW of the PEO part. The glass transition temperature ( T g) of the matrices increased with decreasing the MW of the PEO part from 2000 to 200. Since the segmental motion of the matrix considerably affects the mobility of carrier ions, the ionic conductivity is a maximum when the T g of matrix is a minimum. The PEO/salt hybrids with larger cations showed higher ionic conductivity because of the decrease of surface charge density. PEO oligomers having pyridinium or triethylammonium group were prepared with various anions. In these anion conductors, the ionic conductivity showed less dependence on the MW of the PEO part than for cation conductors. Furthermore, the smaller anions showed higher ionic conductivity in contrast to the cation conductor. The interaction of the anions with the ether oxygen should be much weaker than that for the cations, and the phase condition of these PEO/salt hybrids is scarcely affected.

Decrease in surface charge density of Klebsiella pneumoniae treated with cefodizime and enhancement of the phagocytic function of human polymorphonuclear leucocytes stimulated by the drug-treated bacteria.

Treatment of Klebsiella pneumoniae 109 with cefodizime, ceftazidime, cefbuperazone, cefotaxime or flomoxef at a sub-minimum inhibitory concentration (sub-MIC) (1/4 MIC) for 1 h altered its morphology. The bacteria treated with cefodizime at sub-MICs (1/8, 1/4 MIC) enhanced the chemiluminescencence (CL) of human polymorphonuclear leucocytes (PMNs), implying an increase in the production of active oxygen species in association with phagocytosis, whereas the cells treated with other cephalosporins at the same sub-MICs did not. Furthermore, a significant decrease in electrophoretic mobility was induced by the bacteria treated with cefodizime at sub-MICs (1/8, 1/4 MIC), but other cephalosporins neither increased nor decreased the electrophoretic mobility significantly. These findings suggested that cefodizime caused a morphological change, with a decrease in negative surface charge density of K. pneumoniae, more easily than ceftazidime, cefbuperazone, cefotaxime or flomoxef, followed by an increase in the phagocytic activity of PMNs.