Critical Salt Concentration Research Articles

Mycotoxin Detection through Colorimetric Immunoprobing with Gold Nanoparticle Antibody Conjugates.

Driven by their exceptional optical characteristics, robust chemical stability, and facile bioconjugation, gold nanoparticles (AuNPs) have emerged as a preferred material for detection and biosensing applications in scientific research. This study involves the development of a simple, rapid, and cost-effective colorimetric immuno-sensing probe to detect aflatoxin B1 and zearalenone using AuNP antibody (AuNP-mAb) conjugates. Anti-toxin antibodies were attached to the AuNPs by using the physical adsorption method. The colorimetric immunosensor developed operates on the principle that the optical properties of the AuNP are very sensitive to aggregation, which can be induced by a critical high salt concentration. Although the presence of antibodies on the AuNP surface inhibits the aggregation, these antibodies bind to the toxin with higher affinity, which leads to exposure of the surface of AuNPs and aggregation in a salt environment. The aggregation triggers a noticeable but variable alteration in color from red to purple and blueish gray, as a result of a red shift in the surface plasmon resonance band of the AuNPs. The extent of the shift is dependent on the toxin exposure dose and can be quantified using a calibration curve through UV-Visible-NIR spectroscopy. The limit of detection using this assay was determined to be as low as 0.15 ng/mL for both zearalenone and aflatoxin B1. The specificity of the prepared immunoprobe was analyzed for a particular mycotoxin in the presence of other mycotoxins. The developed immunoprobe was evaluated for real-world applicability using artificially spiked samples. This colorimetric immunoprobe based on localized surface plasmon resonance (LSPR) has a reduced detection limit compared to other immunoassays, a rapid readout, low cost, and facile fabrication.

Salt-induced Fmoc-tripeptide supramolecular hydrogels: a combined experimental and computational study of the self-assembly.

Delving into the mechanism behind the molecular interactions at the atomic level of short-sequence peptides plays a key role in the development of nanomaterials with specific structure-property-function relationships from a bottom-up perspective. Due to their poor water solubility, the self-assembly of Fmoc-bearing peptides is usually induced by dissolution in an organic solvent, followed by a dilution step in water, pH changes, and/or a heating-cooling process. Herein, we report a straightforward methodology for the gelation of Fmoc-FFpY (F: phenylalanine; Y: tyrosine; and p: PO42-), a negatively charged tripeptide, in NaCl solution. The electrostatic interactions between Fmoc-FFpY and Na+ ions give rise to different nanofibrillar hydrogels with rheological properties and nanofiber sizes modulated by the NaCl concentration in pure aqueous media. Initiated by the electrostatic interactions between the peptide phosphate groups and the Na+ ions, the peptide self-assembly is stabilized thanks to hydrogen bonds between the peptide backbones and the π-π stacking of aromatic Fmoc and phenyl units. The hydrogels showed self-healing and thermo-responsive properties for potential biomedical applications. Molecular dynamics simulations from systems devoid of prior training not only confirm the aggregation of peptides at a critical salt concentration and the different interactions involved, but also corroborate the secondary structure of the hydrogels at the microsecond timescale. It is worth highlighting the remarkable achievement of reproducing the morphological behavior of the hydrogels using atomistic simulations. To our knowledge, this study is the first to report such a correspondence.

Effect of Salt Stress on Morphological Characteristics and Secondary Metabolites of Some Forage Pea Cultivars

Forage pea (Pisum sativum L.) is an annual legume forage crop grown in various regions of Türkiye. It is high in protein, carbohydrate, and digestible matter and contains minerals such as phosphorus, calcium, and vitamins A and D. Salinity stress is an important problem in the cultivation of forage peas. Salinity reduces the osmotic potential of soil solutes, making it difficult for the roots to absorb the water. This study aimed to determine some parameters of two registered forage pea cultivars at different concentrations of two salt types. The effects of these salts on the morphological characteristics and biochemical components of two different registered cultivars of pea, cv. Ateş and cv. Töre were investigated in the present study. The trials were conducted in pots and Na2SO4 and CaCl2 were applied at concentrations of 0, 50, 100 and 150 mM. As a result of the trials, the morphological characteristics like fresh and dry weights and lengths of roots and shoots were investigated along with the biochemical properties like total antioxidant activity and total phenolic content. The study was performed in 2 replicates to determine the effect of different salt types and concentrations. The critical salt concentration values for the change in shoot and root fresh weight among morphological traits were determined as 100 and 150 mM for secondary metabolites. While the cv. Töre forage pea showed the highest salt resistance in shoot and root fresh weights in the presence of Na2SO4 the cv. Ateş forage pea showed the lowest salt resistance in the presence of CaCl2. In terms of shoot and root dry weights, the cv. Töre forage pea showed the least resistance at 50 mM Na2SO4 concentration. As for plant length, the cv. Ateş forage pea cultivar showed the least resistance in shoot length at 150 mM CaCl2 concentration, while it showed the highest resistance in root length at this value. The highest total antioxidant activity for the cv. Ateş forage pea and the highest total phenolic content for the cv. Töre forage pea were determined at 150 mM CaCl2 concentration. The lowest total phenolic content value was estimated in the cv. Töre forage pea cultivar at 150 mM Na2SO4 salt concentration.

Influence of cation concentration and valence on the structure and texture of spray-dried supraparticles from colloidal silica dispersions

The structure and texture of supraparticles determine their properties and performance, thus playing a critical role in research studies as well as industrial applications. The addition of salts is a well-known strategy to manipulate the colloidal stability of nanoparticles. In this study, this approach is used to tune the structure of spray-dried supraparticles. Three different salts (NaCl, CaCl2, and AlCl3) were added to binary silica (SiO2) nanoparticle dispersions (of 40 and 400 nm in size) to change their colloidal stability by lowering the electrostatic repulsion or enhancing the cation bridging. Dependent on the cation valence of the added salt and the nanoparticle size, the critical salt concentration, which yields nanoparticle agglomeration, is reached at different salt amounts. This phenomenon is exploited to tune the final structure of supraparticles - obtained by spray-drying binary dispersions - from core-shell to Janus-like to well-mixed structures. This consequently also tunes textural properties, like surface roughness and the pore system of the obtained supraparticles. Our results provide insights for controlling the structure of spray-dried supraparticles by manipulating the stability of binary nanoparticle dispersions, and they establish a framework for composite particle design.

Effect of wettability and phase distribution on critical salt concentration for fines migration initiation in sandstone reservoirs

Fines migration in sandstone oil reservoirs during different field operations is influenced by the salinity of injected brine. When salinity drops below a critical salt concentration (CSC), fines migration is initiated, leading to pore throat blockage and formation damage. Factors such as rock wettability, fluid type, fines size and concentration, and flow rate contribute to the severity of this issue. However, the impact of phase distribution and rock wettability on the CSC remains unexplored. Most results are reported for water-wet systems, but in many cases, assuming a strong water-wet state is not accurate. The current research fills that gap and provides new insights by investigating the relationship between the CSC, phase distribution, and rock wettability.Upper Berea sandstone cores were used in this study, and the CSC was experimentally determined. Brine was injected into strong water-wet and weak water-wet core samples. The injection brine salinity was gradually reduced to identify the salinity at which fines migration initiated within the core. The analysis of pressure drops and effluent analysis was applied to estimate CSC at different wettability states.The step-by-step reduction in salinity led to CSCs of 0.12 M and 0.09 M NaCl for the weak water-wet core and strong water-wet core in the presence of oil, respectively. A weak water-wet system results in a higher CSC value compared to a strong water-wet system because fine particles are contained within a thin water film, and weak water wettability facilitates their easy migration under low reduced salinity conditions. The CSC corresponded to the point of maximum pressure difference and the highest concentrations of produced fines. The findings of this research provide valuable insights into the significant influence of rock wettability and phase distribution on the initiation of fines migration. These parameters must be carefully determined and considered during the design phase of production and enhanced oil recovery in sandstone reservoirs to ensure efficient operations.

Exogenous Selenium Endows Salt-Tolerant and Salt-Sensitive Soybeans with Salt Tolerance through Plant-Microbial Coactions

Soil salinization is a common abiotic stress that seriously affects soybean growth and yield, underscoring the need to enhance plant salt tolerance for sustainable agriculture development. Selenium is a beneficial element that has been shown to promote plant growth, development and stress resistance. This study employed pot experiments to investigate the effects of different salt levels (0, 50, 100 and 150 mM NaCl) on salt-tolerant (Zhonghuang 13) and salt-sensitive soybean (Dongnong 63) varieties. Additionally, the critical salt concentration (100 mM NaCl) was selected to explore the effects of exogenous selenium (0, 0.5, 1 and 3 mg·kg−1) on improving salt tolerance in salt-tolerant and salt-sensitive soybeans under salt stress. Results showed that as salt concentration increased, plant height, shoot and root fresh weight, SPAD value and enzyme activity of both salt-tolerant and salt-sensitive soybeans significantly decreased. The increasing concentration of exogenous selenium significantly decreased the proline content of salt-sensitive and salt-tolerant soybeans by 40.65–58.87% and 38.51–50.46%, respectively, and the MDA content by 19.33–30.36% and 16.94–37.48%, respectively. Selenium supplementation also reduced the content of Na+ in salt-sensitive and salt-tolerant soybeans and improved K+ absorption in soybeans, which increased the K+/Na+ ratio. Moreover, high-throughput sequencing of the 16S ribosomal RNA gene demonstrated that selenium application optimized the rhizosphere microecology structure of salt-tolerant and salt-sensitive soybean varieties and enhanced functional genes related to lipid metabolism, energy metabolism and cell motility of rhizosphere microorganisms. In summary, selenium application improved the salt tolerance of the two soybean varieties by enhancing the physiological resistance to salt stress and optimizing the structure and function of the rhizosphere microbial community.

Experimental analysis of the impact of ionic concentration and type on shale’s stability: dilute vs. concentrated salt solutions

ABSTRACT Wellbore instability in shale formations is one of the most bothersome problems leading to significant changes in shale’s petrophysical, mechanical, and chemical properties, and could cost billions of dollars annually. Drilling fluid’s ionic composition is one of the factors affecting wellbore stability. This paper investigates the impact of chemical osmosis, ionic diffusion, and diffusion osmosis on the stability of shale, identify the critical salt concentration, and examine the impact of ionic type and concentration on shale’s stability. Experimental methods include utilisation of two different shale cores (I and II), in which each core is cut into several samples, to conduct linear expansion and gravimetric measurement tests using different salt solutions (KCl, NaCl, and CaCl2) of various salt concentrations. Results show that the critical salt concentrations of shale I and II is 8 w/w%. Chemical osmosis is found to be a reliable method for water extraction out of shale if the critical salt concentration value is not surpassed. Beyond this value, ionic diffusion and diffusion osmosis in shale I and II were adversely affecting shale’s stability through swelling. The swelling and gravimetric ions and water uptake tests showed that shale is a leaky semi-permeable membrane, and that chemical osmosis could be jeopardised by ionic transport into shale. In this study, the cation type (Na+, K+, Ca+2) that makes up the salt was varied. The impact of cation type on the stability of shale was clear as the anion type was fixed. Since both cations and anions tend to diffuse into shale in the presence of a concentration gradient, it is proposed for future work to study the combined impact of cation and anion types on shale’s stability by varying the anion and cation types.

Glycan-Presenting Coacervates Derived from Charged Poly(active esters): Preparation, Phase Behavior, and Lectin Capture.

This study presents the preparation and phase behavior of glycan-functionalized polyelectrolytes for capturing carbohydrate-binding proteins and bacteria in liquid condensate droplets. The droplets are formed by complex coacervation of poly(active ester)-derived polyanions and polycations. This approach allows for a straightforward modular introduction of charged motifs and specifically interacting units; mannose and galactose oligomers are used here as first examples. The introduction of carbohydrates has a notable effect on the phase separation and the critical salt concentration, potentially by reducing the charge density. Two mannose binding species, concanavalin A (ConA) and Escherichia coli, are shown to not only specifically bind to mannose-functionalized coacervates but also to some degree to unfunctionalized, carbohydrate-free coacervates. This suggests non-carbohydrate-specific charge-charge interactions between the protein/bacteria and the droplets. However, when mannose interactions are inhibited or when non-binding galactose-functionalized polymers are used, interactions are significantly weakened. This confirms specific mannose-mediated binding functionalization and suggests that introducing carbohydrates reduces non-specific charge-charge interactions by a so far unidentified mechanism. Overall, the presented route toward glycan-presenting polyelectrolytes enables new functional liquid condensate droplets with specific biomolecular interactions.

Migration of Salt Ions in Frozen Hydrate-Saturated Sand: Effect of Silt and Clay Particles

Permafrost composed of sand with silt and clay components may store stable and metastable gas hydrates, which can lose stability under a flux of dissolved salts from natural or production-related solutions (seawater, brines from cryopegs, drilling fluids, etc.). The flux of salt ions is controlled externally by temperature and pressure as well as by the salinity of solutions and the properties of fine-grained (<0.05 mm) components in permafrost. The effect of silt and clay percentage and mineralogy (kaolinite or montmorillonite) on the patterns of salt and water transport and the related dissociation of pore gas hydrates in frozen sand is studied in laboratory experiments. The experiments are conducted in conditions that can maintain the self-preservation of gas hydrates: a constant negative temperature of −6 °C and a pressure of 0.1 MPa. Sediments with higher clay percentages show slower migration and accumulation of salt ions and the higher critical salt concentration required for the onset of gas hydrate dissociation. The flux of Na+ to sand samples containing montmorillonite is lower than to those with kaolinite. On the other hand, salt migration and hydrate dissociation are faster in sand with higher silt contents. The experimental results form the basis for a generalized model of main mechanisms that drive salt transport in frozen hydrate-bearing sediments interacting with saline solutions.

Reliability of chemical osmosis as a practical method to extract water out of shale and promote shale’s mechanical stability

Wellbore instability in shale formations is one of the most bothersome problems leading to significant changes in shale’s petrophysical, mechanical, and chemical properties, and could cost billions of dollars annually. Drilling fluid’s ionic composition is one of the factors affecting wellbore stability. This paper investigates the impact of chemical osmosis, ionic diffusion, and diffusion osmosis on the stability of shale, identify the critical salt concentration, and examine the impact of ionic type and concentration on shale stability. Experimental methods include utilization of shale I and II through linear expansion and gravimetric measurement tests using different salts. Results show that the critical salt concentration in shale I and II is 8 w/w%. Chemical osmosis is found to be a reliable method for water extraction out of shale if critical concentration value is not surpassed. Beyond this value, the ionic diffusion and diffusion osmosis in shale I and II were adversely affecting shale’s mechanical and chemical stability. The swelling and gravimetric ions and water uptake tests showed that shale is a leaky semi-permeable membrane, and that chemical osmosis could be jeopardized by ionic transport into shale. However, the water transport impact on changes in the thickness of diffuse double layer of clay needs to be investigated. The impact of temperature on water and ions transportation into shale needs to be examined to reflect in-situ conditions. In this study, the cation type that makes up the salt was varied while the anion type was fixed. Since both cations and anions tend to diffuse into shale in the presence of a concentration gradient, it is recommended to vary the anion type to study the combined impact of cation and anion type on shale stability.

Heteroprotein complex between soy protein isolate and lysozyme: Protein conformation, lysozyme activity, and structural characterization

Heteroprotein complexes are formed by electrostatic interactions of oppositely charged proteins in a purely aqueous environment. Understanding the relationship between their structural and functional properties will contribute to their tailor-made applications. Therefore, this study investigated the protein conformation, assembling structure, and enzyme activity of soy protein isolate/lysozyme (SPI/LYS) complexes at mass ratios of 2:1 (soluble complex) and 1:1.3 (stoichiometric ratio). Electrostatic complexation increased the surface hydrophobicity of complexes. Their surface hydrophobicity decreased with increasing NaCl concentrations and reached the theoretical values at the critical salt concentration of 200 mM NaCl. Electrostatic complexation did not decrease the LYS activity (∼43,000 units/mg). SPI/LYS complexes exhibited flocculated structures in which the two proteins were unevenly distributed; these were typical amorphous complexes. High dilution disassembled these complexes over 5 μm into particles of ∼100 nm, and NaCl reduced the size of these particles. Immobilized water was detected in the complexes formed by particle flocculation.

Competitive effects of salt and surfactant on the structure of nanoparticles in a binary system of nanoparticle and protein.

Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) experiments have been carried out to study the competitive effects of NaCl and sodium dodecyl sulfate (SDS) surfactant on the evolution of the structure and interactions in a silica nanoparticle-Bovine serum albumin (BSA) protein system. The unique advantage of contrast-matching SANS has been utilized to particularly probe the structure of nanoparticles in the multi-component system. Silica nanoparticles and BSA protein both being anionic remain largely individual in the solution without significant adsorption. The non-adsorbing nature of protein is known to cause depletion attraction between nanoparticles at higher protein concentrations. The nanoparticles undergo immediate aggregation in the nanoparticle-BSA system on the addition of a small amount of salt [referred as the critical salt concentration (CSC)], much less than that required to induce aggregation in a pure nanoparticle dispersion. The salt ions screen the electrostatic repulsion between the nanoparticles, whereby the BSA-induced depletion attraction dominates the system and contributes to the nanoparticle aggregation of a mass fractal kind of morphology. Further, the addition of SDS in this system interestingly suppresses nanoparticle aggregation for salt concentrations lower than the CSC. The presence of SDS gives rise to additional electrostatic repulsion in the system by binding with the BSA protein via electrostatic and hydrophobic interactions. For salt concentrations higher than the CSC, the formation of clusters of nanoparticles is inevitable even in the presence of protein-surfactant complexes, but the mass fractal kind of branched aggregates transform to surface fractals. This has been attributed to the BSA-SDS complex induced depletion attraction along with salt-driven screening of electrostatic repulsion. Thus, the interplay of depletion and electrostatic and hydrophobic interactions has been utilized to tune the structures formed in a multicomponent silica nanoparticle-BSA-SDS/NaCl system.

Low-frequency elastic plateau in linear viscoelasticity of polyelectrolyte coacervates

A thorough study is made of the dependences on salt concentration and polymer chain lengths of the low-frequency plateau of coacervates of poly (diallyl dimethyl ammonium chloride), PDADMAC, and poly (sodium 4-styrenesulfonate), PSS. The reliability and reproducibility of these measurements are carefully checked by determining the frequency-dependent stress limits of the rheometer through the use of reference fluids and by repeat experiments with coacervates. Long-time frequency sweeps show that coacervates with less salt are more repeatable than those with higher salt. A low-frequency plateau reliably appears only below a critical salt concentration, and the magnitude of the plateau depends strongly on salt concentration and chain lengths of both polycation and polyanion. It is only present for the molecular weight of the polycation, PDADMAC, higher than 100 kDa, but the magnitude of the plateau is more strongly influenced by the chain length of the polyanion, PSS. Possible causes of the low-frequency plateau are discussed.

Influence of “Hydrophobicity” on the Composition and Dynamics of Polyelectrolyte Complex Coacervates

Various types of specific interactions are believed to supplement the major entropic driving forces responsible for spontaneous liquid–liquid phase separations in mixtures of oppositely charged polyelectrolytes. Among these interactions, hydrophobicity has recently been probed experimentally via the synthesis and complex formation of polyelectrolytes bearing hydrophobic pendant groups or backbones. In this work, poly(4-vinylpyridines), P4VP, were N-alkylated with chains from one to six carbons in length. The fully alkylated polycations were complexed with poly(sodium methacrylate) to yield polyelectrolyte complexes or coacervates (PECs). Counterintuitively, PECs made with N-methyl to N-butyl P4VP were less stable to the addition of salt the longer the alkane chain, being easier to dope and having a lower critical salt concentration for dissolution. In contrast, the linear viscoelastic response of these PECs varied little. A transition in doping and properties was observed with N-pentyl and N-hexyl chains, the latter having a much higher modulus and much less sensitivity to salt concentration. Small-angle X-ray scattering suggested a new morphology for the N-pentyl and N-hexyl P4VP PECs, with interacting/phase separating alkane chains providing a transition into hydrophobicity-dominated PECs.

Co‐assembly behavior of oppositely charged thermoresponsive elastin‐like polypeptide block copolymers

AbstractThe formation of complex coacervate core micelles (C3Ms) was observed by mixing two oppositely charged elastin‐like polypeptides (ELP)‐based diblock copolymers, each composed of a neutral and a charged moiety. The physical properties of C3Ms as a function of pH, temperature, and salt concentration were analyzed by UV–visible spectrometry, dynamic light scattering (DLS), 1H NMR, and small angle X‐ray scattering (SAXS). In distilled water (or low salt conditions), below the transition temperature (Tt), ELP mixtures induced the C3Ms with a complex coacervate core and a neutral corona; meanwhile, above the Tt, they aggregated by the hydrophobic interaction among the neutral coronas. However, as the salt concentration increased, the induced C3Ms gradually dissociated; while above the critical micellar temperature (CMT) and critical salt concentration (CSC), inverted hydrophobic core micelles surrounded by the charged blocks were created. Based on these results, we demonstrate that the co‐assembly behavior of two oppositely charged diblock ELPs is harnessed by the salt concentration and temperature.

Impact of the Salt Concentration and Biophysical Cohesion on the Settling Behavior of Bentonites

The flocculation behavior of clay minerals in aquatic environments is an important process in estuarine and riverine dynamics, where strong gradients in salinity can locally occur. Various contradicting observations have been reported in the literature on the impact of salt concentration on the settling process of cohesive sediments. To address this issue in a systematic manner, we investigate the settling behavior of clay minerals as a function of the salt concentration of the ambient water. Specifically, we focus on montmorillonite as a prototype clay mineral with a high cation exchange capacity (CEC). To this end, we study suspensions of Wyoming bentonite (Volclay SPV) as a very important constituent for many constructional and industrial purposes. We perform an experimental campaign to study the settling behavior of moderately turbid montmorillonite concentrations in monovalent salt solutions with different salinities (sodium chloride) to represent different environments ranging from deionized to ocean water, respectively. The subsequent settling process was monitored by taking pictures by a camera in regular time intervals over a total observation time up to 48 h. In addition, a modified hydrometer analysis is conducted to determine the grain size distribution (in terms of an equivalent diameter) of the flocculated clay suspension in salt water. Despite the rather high cation exchange capacity of the investigated clay (CEC=88.1), our results show that the settling speed drastically increases within a range of 0.6–1.0 PSU and stays approximately constant for higher salinities. This critical salt concentration is defined here as the critical coagulation concentration (CCC) and lies well below the salinity of natural open water bodies. The hydrometer analysis revealed that 60% of the agglomerates exceed the equivalent grain size of 20 μm. Finally, the findings of this study are supplemented with experiments studying the effect of Extracellular Polymeric Substances (EPS) on the flocculation behavior of bentonite in salt water. Our results demonstrate that salinity is the original trigger for flocculation, whereas EPS allows for even larger floc size but it does not play a significant role for the settling processes of bentonite in estuarine environments.

Migration of Salt Ions in Frozen Hydrate-Saturated Sediments: Temperature and Chemistry Constraints

Migration of dissolved salts from natural (cryopeg brines, seawater, etc.), or artificial sources can destabilize intrapermafrost gas hydrates. Salt transport patterns vary as a function of gas pressure, temperature, salinity, etc. The sensitivity of the salt migration and hydrate dissociation processes to ambient temperature and to the concentration and chemistry of saline solutions is investigated experimentally on frozen sand samples at a constant negative temperature (−6 °C). The experiments show that the ambient temperature and the solution chemistry control the critical salt concentration required for complete gas hydrate dissociation. Salt ions migrate faster from more saline solutions at higher temperatures, and the pore moisture can reach the critical salinity in a shorter time. The flux density and contents of different salt ions transported to the samples increase in the series Na2SO4–KCl–CaCl2–NaCl–MgCl2. A model is suggested to account for phase transitions of pore moisture in frozen hydrate-saturated sediments exposed to contact with concentrated saline solutions at pressures above and below the thermodynamic equilibrium, in stable and metastable conditions of gas hydrates, respectively.

DLVO Modeling to Predict Critical Salt Concentration to Initiate Fines Migration Pre- and Post-Nanofluid Treatment in Sandstones

Summary The critical salt concentration (CSC) of injected water used for various water-based oil recovery operations is the salt concentration below which fine particles are released and their migration starts within sandstone reservoirs containing clays. This phenomenon could be one of the potential causes of formation damage and associated injectivity and productivity declines. This paper proposes a novel method of quantifying surface forces between fines and sand grains and using DLVO (named after Derjaguin, Landau, Verwey, and Overbeek) modeling to predict a CSC pre- and post-nanofluid treatment. Furthermore, the effectiveness of varying concentrations of silica nanoparticles (SNPs) in controlling fines migration and reducing CSC was modeled by the DLVO approach and experimentally validated. The experimental CSC was determined by performing corefloods and analyzing effluent turbidity and absorbance under various salinities of the injected brine to validate the developed models. The zeta potentials of sand-fine-brine (SFB) systems were measured and ranged from −35.2 to 29.5 mV. The average size of fine particles was 800 to 900 nm based on scanning electron microscopy (SEM) results. Using DLVO modeling before the application of nanoparticles (NPs), the CSC was predicted to be 0.11 M (6,400 ppm) NaCl brine, at which the total DLVO interaction energy shifted from attraction to repulsion. Moreover, another DLVO model was developed considering the effect of SNPs. Models predicted 0.085 M (4,900 ppm) and 0.075 (4,400 ppm) NaCl CSC values after the application of 0.05 and 0.1 wt% SNPs, respectively. Afterward, corefloods were performed that showed that the experimental results of CSC with and without SNPs treatment were in close agreement with the DLVO models. Fines migration was observed at 0.08 M (4,700 ppm) and 0.07 M (4,100 ppm) salinity after nanofluid treatments. Many oil recovery processes, including but not limited to low-salinity waterflooding and alkaline flooding, require the estimation of the CSC to avoid formation damage. The proposed DLVO model is instrumental to predict the CSC for monovalent NaCl brine pre- and post-nanofluid application without requiring extensive experimental work. Moreover, the use of nanofluid showed promising results in terms of fines migration control and reduction in CSC.

Predicting the critical salt concentrations of monovalent and divalent brines to initiate fines migration using DLVO modeling

Fine particles are released from sandstone reservoirs at a salinity known as the critical salt concentration (CSC), which is strongly dependent on monovalent and divalent ions in the permeating liquid. Formation water is an ionic liquid, and when the salinity of the sand-fine-brine (SFB) system goes below the CSC, repulsive surface forces increase, and fine particles are dislodged from the sand surface plugging the pore throat as a result of fines migration. In this study, the effect of monovalent and divalent ions is modeled using the DLVO theory, and CSCs are predicted for monovalent and divalent salts individually and in different combinations. Using the average fine particle size and zeta potential of the SFB system, DLVO models are developed considering attractive and repulsive surface forces for various concentrations of monovalent and divalent salts to predict CSC. Zeta potentials were measured or collected from previous studies. The DLVO models predict the CSCs of 0.11 M, 0.04 M, 0.0001 M, and 0.0001 M for NaCl, KCl, CaCl2, and MgCl2, respectively, and all the results are found to be in close agreement with the experimental CSCs. Furthermore, several mixtures of NaCl and CaCl2 are utilized, and CSCs are predicted. This study showed that divalent ions significantly reduce the CSC, and their presence in the formation water and injection water is beneficial to control fines migration even at low salinity of the injection water. The application of our developed method to predict CSC yields reliable and accurate results without requiring extensive experimentation.

The cost of bacterial predation via type VI secretion system leads to predator extinction under environmental stress

SummaryAs a common gut pathogen, Campylobacter jejuni (C. jejuni) harbors the Type VI Secretion System (T6SS) that injects toxic effectors into neighboring cells, modulating microbial competitions in the harsh gut environment. Using bile salt as a natural stressor and T6SS-positive C. jejuni as a predator, we show that T6SS activity could entail a cost during bacterial predation under environmental stress. Our data suggest bile salt influx and subsequent DNA damage due to the prey-driven activation of the T6SS. We further combined experiments and mathematical modeling to explore how the stress-induced “predation cost” determines ecological outcomes. Consistent with a population-dynamics model, we found predator extinction above a critical bile salt concentration and prey-predator coexistence below this level. Moreover, we utilized the predation cost as an effective strategy facilitating host defense against C. jejuni infection. Together, we elucidate how predator dominance versus extinction emerges from the interplay between environmental stress and the T6SS machinery.