Increase In Ionic Strength Research Articles

Adsorption of antibiotics on microplastics (MPs) in aqueous environments: The impacts of aging and biofilms

Microplastics (MPs) that accumulate in natural water bodies through various pathways inevitably undergo aging and biofilm attachment. These variations can alter the physicochemical properties of the MPs and thus affect their abilities to adsorb other pollutants. In this study, we chose virgin polyethylene (V-PE) as the experimental MP and generated aged, biofilm-developed and biofilm-developed with aged polyethylene (A-PE, B-PE and B-A-PE) via Fenton advanced oxidation and lake water incubation methods. Then, the adsorption of tetracycline hydrochloride (TC-HCl) and cefalexin (CFX) on V-PE, A-PE, B-PE and B-A-PE was investigated. The results showed that the capacities for adsorption of TC-HCl or CFX on the four polyethylene MPs (PEMPs) increased in the order V-PE < A-PE < B-PE < B-A-PE. The order was attributed to differences in the surface roughnesses, crystallinities, surface functional groups and biofilm biomass of the four PEMPs. Kinetic experiments and isotherms indicated that nonlinear multilayer adsorption occurred via physicochemical actions, such as diffusion, hydrophobic interactions, hydrogen bonding interactions, electrostatic interactions and biodegradation. Specifically, the adsorption of TC-HCl or CFX by V-PE and A-PE was predominantly controlled by diffusion, whereas B-PE and B-A-PE were chemically active. In addition, it is worth noting that biofilms may shield antibiotics from electrostatic interactions with the B-PE and B-A-PE surfaces, and an increase in ionic strength inhibited the adsorption of TC-HCl and CFX by the four PEMPs. Our study provides an important reference for determining the adsorption of antibiotics by MPs in natural waters.

Facilitated transport of toluene and naphthalene with humic acid in high- and low-permeability systems: Role of ionic strength and cationic type

The occurrence of colloids on pollutants transport in groundwater has attracted more attention. However, the research on the regulation mechanism of colloids on combined pollutants transport in heterogeneous aquifers is limited. In this study, a series of tank experiments were conducted to systematically investigate the effects of ionic strength, and cation type on humic acid (HA) facilitated transport of toluene (TOL), and naphthalene (NAP) in high- and low-permeability systems. The results showed that HA facilitated pollutants transport in low Na+ solution. In Ca2+ solution, the presence of HA hindered pollutants transport, and the inhibition increased with the increase of ionic strength. Both in Na+ solution and low Ca2+ solution, the influence of heterogeneous structure on pollutant transport played a dominant role, and TOL and NAP had a greater transport potential in the high permeability zone (HPZ) due to the preferential flow. Whereas, deposition of HA aggregates, and electrostatic attractive interaction had negative effects on transport than groundwater flow in high Ca2+ solution. Pollutants were prone to accumulate at the bottom of the HPZ, and the top of the low permeability zone (LPZ). These new findings provide insights into the mechanism of colloids influence on the pollutants transport in heterogenous aquifer.

THE EFFECT OF IONIC STRENGTH ON THE ACID – BASE PROPERTIES OF GLYCINE IN AN AQUEOUS SOLUTION

The processes of glycine ionization (Gly) have been studied by potentiometry and the values of pKa1 and pKa2 at 288.15 K, the ionic strength of the solution (Na(H)CIO4) have been calculated) 0.1, 0.25, 0.5, 0.75, 1.0 mol/l and concentrations 1.0÷3.0 · 10-3 mol/l with a confidence probability of P = 0.95. With an increase in ionic strength and temperature, the pK of both amino and carboxyl groups and functional groups of the side radical decreases, which indicates an increase in the degree of their ionization and is consistent with the theory of weak electrolytes.

Restricted colloidal-bound phosphorus release controlled by alternating flooding and drying cycles in an alkaline calcareous soil

Colloid-facilitated phosphorus (P) migration plays an important role in P loss from farmland to adjacent water bodies. However, the dynamics of colloidal P (Pcoll) release as influenced by irrigation in alkaline calcareous soil remains a knowledge gap. The present study, monitored the dynamic change of Pcoll under different water management strategies: 1) control, 2) flooding, and 3) alternating flooding and drying cycles. Soil water-dispersible colloids (0.6 nm-1 μm) were extracted by combining filtration and ultrafiltration methods. The contents of P, cation and organic carbon in the water-dispersible colloids were determined and the stability and mineral composition of colloidal fractions were characterized. The results showed that Pcoll ranged from 16.5 to 25.5 mg kg−1 and represented 42.8%–64.9% of the water-extracted P in the control. Flooding significantly decreased the Pcoll content by 16.0%–62.1% (mean 32.7%) and it may be attributed to the dissolution of colloidal iron (Fe) bound P. The alternating flooding and drying treatment significantly reduced the Pcoll content by 11.6%–88.0% (mean 67.6%). The Pcoll content of the flooding event was always greater than the Pcoll content of the drying event during flooding and drying cycles. Redundancy analysis and random forest modeling showed that the colloidal calcium (Ca) and ionic strength in soil solutions had negative correlations with the Pcoll content, and pH, ionic strength and truly dissolved P were the critical factors affecting Pcoll. Drying of the flooded soil led to the decrease of pH and the increase of ionic strength, colloidal Ca content and positive charges of colloid surfaces, which promoted colloid aggregation and enhanced soil P sorption capacity. This restricted the loss potential of Pcoll. In summary, controlled flooding and drainage when managed correctly have a role to play in mitigating Pcoll loss from P-enriched calcareous soils.

Elimination of malachite green from aqueous and saline water by laterite-derived Na-polyferrosialate and polyferrophosphosialate geopolymers: A comparative study

In this study, two laterites (LA)-based geopolymers were synthesized using alkalination (GPAL) and phosphoric acid-activation (GPAC) approaches and applied to scavenge malachite green (MG) dye from aqueous (non-saline) and saline water. The precursor (LA) and geopolymers were characterized by XRF, XRD, TG/DTA SEM, and FTIR techniques. Alkalination and acid-activation resulted in morphologically distinguishable geopolymers with different porosity structures. The dissolution of mineral phases and chemical composition was dependent on the activation medium, resulting in Na-polyferrosialate and polyferrophosphosialate geopolymers for GPAL and GPAC, respectively. The adsorption kinetics data were best described by the pseudo-first-order (PFO) model wherein the adsorption rate, denoted by rate constant (k1), increased with an increase in ionic strength (salinity). The equilibrium data were best modelled by the Sips isotherm. GPAL had a higher maximum adsorption capacity (Qms) than GPAC in both aqueous (non-saline) and saline water. The adsorption capacities were increased in saline solution relative to aqueous solutions without NaCl, from 12.4 to 54.1 mg/g and from 57.1 to 92.0 mg/g for GPAC and GPAL, respectively. The adsorption mechanism entailed electrostatic interactions, hydrogen bonding and hydrophobic interactions. Salinity decreased the solubility of MG and increased the hydrophobic interactions and affinity of MG, implied by apparent equilibrium constant (Ka), resulting in increased adsorption density (Qms). These results indicate that alkaline-based geopolymers are better candidates for scavenging MG dye from water, especially in saline environments.

The investigation of the binding ability between sodium dodecyl sulfate and Cu (II) in urban stormwater runoff

The simultaneous presence of heavy metals and surfactants in runoff induces complexation and ecological harm during migration. However, interactions between these pollutants are often overlooked in past studies. Thus, investigating heavy metal-surfactant complexes in runoff is imperative. In this work, Cu (II) and sodium dodecyl sulfate (SDS) were selected to investigate the interaction between heavy metals and surfactants due to the higher detected frequency in runoff. Through 1H NMR and FTIR observation of hydrogen atom nuclear displacement and functional group displacement of SDS, the change of SDS and Cu (II) complexation was obtained, and then the complexation form of Cu (II) and SDS was verified. The results showed that solution pH values and ionic strength had significant effects on the complexation of Cu (II). When the pH values increase from 3.0 to 6.0, the complexation efficiency of SDS with Cu (II) increased by 12.12% at low concentration of SDS, which may be attributed to the excessive protonation in the aqueous solution at acidic condition. The increase of ionic strength would inhibit the complexation reaction efficiency by 19.57% and finally reached the platform with concentration of NaNO3 was 0.10 mmol/L, which was mainly due to the competitive relationship between Na (I) and Cu (II). As a general filtering material in stormwater treatment measures, natural zeolite could affect the interaction between SDS and Cu (II) greatly. After the addition of SDS, the content of free Cu (II) in the zeolite-SDS-Cu (II) three-phase mixed system was significantly reduced, indicating that SDS had a positive effect on the removal of Cu (II) from runoff. This study is of great significance for investigating the migration and transformation mechanism of SDS and Cu (II) in the future and studying the control technology of storm runoff pollution.

Effect of bentonite and composite-modified carbonized fiber on Cu(II) and Cr(VI) adsorption by purple soil

Bentonite and different composite-modified carbonized fibers were used to amend purple soil (PS) to investigate the effects of material combination on Cu(Ⅱ) and Cr(Ⅵ) adsorption by PS. The thermodynamic and kinetic characteristics of Cu(Ⅱ) and Cr(Ⅵ) adsorption were investigated by batch treatment, and the adsorption changes of Cu(Ⅱ) and Cr(Ⅵ) on the amended PS under various pH, ionic strength, and temperature were compared. Results were as follows. (1) The adsorption isotherms of Cu(Ⅱ) and Cr(Ⅵ) on the amended PS conformed to the Freundlich model, and the maximal adsorption capacities for Cu(Ⅱ) and Cr(Ⅵ) ranged 343.33–741.89 and 151.11–311.39 mmol/kg, respectively. (2) The Cu(Ⅱ) and Cr(Ⅵ) adsorption by the amended PSs was mainly multilayer adsorption and primarily driven by chemisorption. (3) High and low pH levels were beneficial to Cu(Ⅱ) and Cr(Ⅵ) adsorption, respectively. The amount of Cu(Ⅱ) and Cr(Ⅵ) adsorption initially increased and then decreased with the increase in ionic strength, with the maximum adsorption observed at 0.1 mol/L ionic strength. (4) High temperature was conducive to the Cu(Ⅱ) and Cr(Ⅵ) adsorption, which was determined as a spontaneous, endothermic, and entropy-increasing process.

Modulation of Gold Nanoparticle Ligand Structure-Dynamic Relationships Probed Using Solution NMR.

Ligand dynamics plays a critical role in the chemical and biological properties of gold nanoparticles (AuNPs). In this study, ligands featuring hydrophobic alkanethiol interiors and hydrophilic shells were used to systematically examine the effects of ligand headgroups on the ligand dynamics. Solution nuclear magnetic resonance (NMR) spectroscopy provided quantitative insight into the monolayer ligand dynamics. Notably, the introduction of hydrophobic moieties to the cationic headgroups significantly decreased ligand conformational mobility; however, variations in hydrophobicity among these moieties had a limited effect on this reduction. Further examination of ligand dynamics under various physiological conditions, including ionic strength and temperature, showed that ligands bound to the AuNP surface become less conformationally mobile with an increase in ionic strength or decreasing temperature. This exploration of ligand dynamics provides insight into designing nanoparticles tailored to specific biological applications.

Enhanced removal of aqueous arsenic(III) by sulfidated nanoscale zero-valent iron under oxic conditions: Performance and mechanism

Although sulfidated nanoscale zero-valent iron (S-nZVI) has shown significant promise in the removal of aqueous inorganic arsenic (As), there is a scarcity of studies comprehensively investigating their performance under oxic conditions, as well as the mechanism involving oxidation being elucidated. In this study, the synthesized S-nZVI exhibited a distinctive core-shell structure, characterized by an outer shell comprising iron oxides and FeS, while also demonstrating increased specific surface areas and decreased pHZPC value. Batch experiments revealed that sulfidation significantly enhanced the As(III) removal efficiency of nZVI under oxic conditions by increasing both the reaction rates and adsorption capacity (qm = 495.23 mg/g). Furthermore, several critical factors influencing the As(III) removal by S-nZVI were investigated, indicating that increased initial As(III) concentrations, initial pH values, and co-existing anions concentrations had negative impacts on the removal process; however, an increase in ionic strength showed certain positive effects. Based on the profiles of As and Fe, roles of reactive species, and characterization of reacted products, it could be concluded that As(III) removal by S-nZVI involves the synergistic effect of adsorption, co-precipitation, and oxidation. More importantly, sulfidation facilitated the corrosion of Fe0, accelerating the release of Fe2+ and promoting the activation of single-electron molecular oxygen reactions, thereby further enhancing the total As removal efficiency. This study highlights the excellent potential of S-nZVI for effectively removing As(III) under oxic conditions.

Double layer characteristics of droplets dispersed with Na2CO3 in EMSF that is applied to dehydration of Shale oil

Shale oil is highly mineralized by salt ions, which makes it difficult to demulsify and dehydrate. The synergistic electromagnetic field (EMSF) is a more efficient method than AC electric field (ACEF) to enhance Shale oil dehydration. However, the critical coalescence conditions and transformation mechanism of droplets dispersed with electrolyte ions in EMSF still lack research. Herein, a series of Na2CO3-dispersed droplets with different ionic strengths were prepared, and the critical coalescence electric intensity (Ec) of the droplets under ACEF and EMSF were compared. Micro high-speed experiments revealed that Ec of droplets under EMSF is higher. Under the action of both EMSF and ACEF, Ec decreases with the increase of ionic strength Is. An ion enrichment theory is proposed to explain the relationship between ion strength and potential energy. This study provides technical guidance for the performance regulation of EMSF-based equipment to enhance oil-water separation, the allowable optimal voltage should be higher than that of the electrostatic coalescer, and the adjustment range is 3.81 %–5.88 %.

Photoreforming of glycerol to produce hydrogen from natural water in a compound parabolic collector solar photoreactor

To improve TiO2 for H2 generation, one strategy for the separation of photogenerated charges is the formation of heterostructures with other materials. In particular, NiO is a photocatalyst known for its good stability and low cost. However, no studies at pilot scale using solar energy have been described. Consequently, an evaluation of a physical NiO:TiO2 mixture at pilot scale (25 L) with natural irradiation (2.10 m2 of sun-exposed surface) and with simultaneous glycerol photoreforming was explored. NiO:TiO2 50 mg·L−1 resulted in the highest hydrogen production, showing an STH = 1.44%, considering only the UV fraction of the solar irradiation. H2 and CO2 production were analysed by on-line GC; Glycerol, dissolved organic carbon, carboxylic acids and nickel leaching were also evaluated. The NiO:TiO2 mixtures rendered a systematically lower H2 production in natural water than in high-purity water. The increase of ionic strength increased the mean size of particle clusters, promoting rapid sedimentation. All this indicates the importance of testing under real field conditions for attaining reliable solar to hydrogen (STH) efficiency.

Enrichment of surface charge contributes to the stability of surface nanobubbles

Surface nanobubbles are spontaneously formed at the interface between hydrophobic surfaces and aqueous solutions, which show extraordinarily longer lifetime than that was predicted by the classical thermodynamics model. In the present work, by using a surface plasmon resonance microscopy (SPRM) to quantitatively measure the dissolution kinetics of individual surface nanobubbles in real time, we explored the effects of ionic strength and pH value on the dissolution rates (lifetime) of nanobubbles. The results revealed that nanobubbles could exist stably for a long time in low-concentration electrolyte solutions or high-concentration non-electrolyte solutions, while they dissolved quickly in high-concentration electrolyte solutions. With the increase of ionic strength, the dissolution rates were accelerated by 2–3 orders of magnitude, and thus the lifespan of these surface nanobubbles was significantly shortened. In addition to ionic strength, it was further found that, with the increase of acidity or alkalinity of the solution, the dissolution rates of the surface nanobubbles were faster than that in neutral solution. These results demonstrated that the interfacial charge enrichment significantly contributed to the extraordinary stability of the surface nanobubbles.

Use of Pyrolysed Almond and Walnut Shells (PAS and PWS) for the Adsorption of Cationic Dye: Reusing Agro-Waste for Sustainable Development

Agro-wastes are recognised as a carbon-rich source, which can be converted into value-added products in sustainable development. In this study, the effect of pH, contact time, initial concentration, and ionic strength were evaluated in Methylene Blue (MB) adsorption by using an activated carbon obtained from pyrolysed almond (PAS) and walnut shells (PWS). The characterisation of PAS and PWS was conducted by SEM-EDX, FT-IR and BET analysis. The removal efficiency of 6 mg/L initial MB concentration improved from 10.6% to 50.42% for PAS, when the adsorbent dose was increased from 0.5 g to 3.5 g in 1 L dye solution. It also improved from 14.8% to 48.7% for PWS, when the adsorbent dose was increased from 0.5 g to 3.5 g. The adsorption fits well with the Freundlich isotherm model and the second-order kinetic model is more favourable. In the adsorption experiments using PWS, 48% removal efficiency was obtained in the absence of NaCl. Depending on the increasing NaCl concentration, the removal efficiencies showed a decrease. 36% removal efficiency was obtained for PWS when 2500 mg/L NaCl was used. In the adsorption experiments using PAS, 40% removal efficiency was obtained in the absence of NaCl. When 500 mg/L NaCl was used, the maximum removal efficiency improved to 48%. However, with the increase in ionic strength, removal efficiencies decreased to approximately 39%. This study revealed that PAS and PWS could be used effectively instead of commercial activated carbon, which also provides an advantageous option from an economic point of view.

Role of Domain-Domain Interactions on the Self-Association and Physical Stability of Monoclonal Antibodies: Effect of pH and Salt.

Monoclonal antibodies (mAbs) make up a major class of biotherapeutics with a wide range of clinical applications. Their physical stability can be affected by various environmental factors. For instance, an acidic pH can be encountered during different stages of the mAb manufacturing process, including purification and storage. Therefore, understanding the behavior of flexible mAb molecules in acidic solution environments will benefit the development of stable mAb products. This study used small-angle X-ray scattering (SAXS) and complementary biophysical characterization techniques to investigate the conformational flexibility and protein-protein interactions (PPI) of a model mAb molecule under near-neutral and acidic conditions. The study also characterized the interactions between Fab and Fc fragments under the same buffer conditions to identify domain-domain interactions. The results suggest that solution pH significantly influences mAb flexibility and thus could help mAbs remain physically stable by maximizing local electrostatic repulsions when mAbs become crowded in solution. Under acidic buffer conditions, both Fab and Fc contribute to the repulsive PPI observed among the full mAb at a low ionic strength. However, as ionic strength increases, hydrophobic interactions lead to the self-association of Fc fragments and, subsequently, could affect the aggregation state of the mAb.

Influence of pH and ionic strength on the physicochemical and structural properties of soybean β-conglycinin subunits in aqueous dispersions

Understanding the impact of pH and ionic strength on the physicochemical and structural properties of soy proteins at subunit level is essential for design and fabrication of many plant-based foods. In this study, soybean β-conglycinin and its subunit fractions αα′ and β were dispersed in solutions with different pH values (3.7, 7.6, and 9.0) at low (5 mM NaCl) and high (400 mM NaCl) ionic strengths, respectively. The solubility, rheology, particle size, zeta potential, microstructure, secondary structure, and tertiary structure of the different dispersions were analyzed using a range of analytical methods. The β-conglycinin, αα′- and β-subunits aggregated near the isoelectric point (pH 3.7). Increasing the ionic strength led to the assembly of more homogeneous units. An increase in ionic strength at pH 7.6 and pH 9.0 led to electrostatic screening, which promoted dissociation of the aggregates. The β-subunit showed a greater sensitivity to pH and ionic strength than the αα′-subunits. Based on the evidence from a range of analytical methods, the highly hydrophilic extension region of the αα′-subunits played an important role in determining the stability of the β-conglycinin dispersions under different environmental conditions. Moreover, the N-linked glycans appeared to impact the conformation and aggregation state of the β-conglycinin.

Regulation of Interfacial Anchoring Orientation of Anisotropic Nanodumbbells.

Nanoparticles exhibiting geometrical and chemical anisotropies hold promise for environmentally responsive materials with tunable mechanical properties. However, a comprehensive understanding of their interfacial behaviors remains elusive. In this paper, we control the interfacial anchoring orientation of polystyrene nanodumbbells by adjusting interparticle forces. The film nanostructure is characterized by the orientation angle analysis of individual dumbbells from cross-sectional EM data: dumbbells undergo orientation transitions from a distinctive horizontal bilayer to an isotropic anchoring when electrostatic repulsion is suppressed by either an ionic strength increase or surface amine-modification. This anchoring orientation influences the film's mechanical properties and foam stability, as investigated by a 2D isotherm and dark/bright-field microscopy measurements. Our findings highlight the potential for precise control of supra-colloidal structures by modulating particle alignment, paving the way for smart delivery systems.

Transport and Model Calculation of Microplastics Under the Influence of Ionic Type, Strength, and Iron Oxide

Microplastics (MPs) in soil have attracted extensive attention as an emerging pollutant, and the transport of MPs is affected by their own physical and chemical properties, the chemical composition of soil solutions, and soil minerals. However, in the presence of oxides, the underlying mechanism for the transport of MPs in different ionic types and ionic strengths is still not fully understood. In this study, the effects of ionic type, ionic strength, and iron oxide on the transport of polystyrene microplastics (PSMPs) with different functional groups were investigated through stability experiments and transport experiments. The colloid transport model, CD-MUSIC model, and DLVO theory were used to explore the transport mechanism. The results showed that normalized concentrations (c/c0) of PSMPs were 0.99 in the NaH2PO4 background and 0.94 in the CaCl2 background, respectively, which indicated that the strongest stability of PSMPs was observed in the former and the weakest in the latter. Different ionic types had different effects on the transport of PSMPs. For the cations Na+ and Ca2+, Ca2+ strongly inhibited PSMPs transport in pure quartz sand because of the bridging effect and strong charge neutralization effect; the recovery rate of the PSMPs in the effluent was (43.83±1.71)%, and a first-order retention coefficient on the second kinetic Site-2 (k2a) was 1.54 min-1. The presence of iron oxide enhanced the inhibition, the recovery rate of the PSMPs in the effluent decreased to (6.04±0.40)%, and k2a increased to 5.33 min-1. For the anions Cl- and PO43-, the transport of PSMPs in pure quartz sand was dominated by surface electronegativity of PSMPs, and PSMPs exhibited lower electronegativity under Cl- background and thus showed higher recovery[(92.95±0.63)%] and lower k2a (0.19 min-1). However, in the presence of iron oxides, the Zeta potential of the quartz sand surface was the controlling factor for PSMPs transport. According to results of the CD-MUSIC model, PO43- could be easily adsorbed on the iron oxide surface to form innersphere complexes, which reduced the surface electronegativity of the iron-loaded quartz sand and enhanced the transport of PSMPs, higher recovery[(76.22±1.39)%], and lower k2a (0.66 min-1). Moreover, the species of the formed innersphere complex was controlled by the PO43- concentration, and different species of innersphere complexes had distinct negative surface charges. Higher surface electronegativity of the iron-loaded quartz sand was observed under higher PO43- concentration, which was not conducive to the transport of PSMPs. Further, the transport ability of PSMPs decreased with the increase in ionic strength. Finally, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the variation in the primary barrier between PSMPs and the collector under the conducted experimental conditions, which helped better elucidate the transport behavior of PSMPs. The variation in the primary barrier was consistent with the transport ability of PSMPs, and a higher primary barrier indicated a larger repulsion between PSMPs and the collector, which was in favor of PSMPs transport.

Biomediated control of colloidal silica grouting using microbial fermentation

Colloidal silica grouting is a ground improvement technique capable of stabilizing weak problematic soils and achieving large reductions in soil hydraulic conductivities for applications including earthquake-induced liquefaction mitigation and groundwater flow control. In the conventional approach, chemical accelerants are added to colloidal silica suspensions that are introduced into soils targeted for improvement and the formation of a semi-solid silica gel occurs over time at a rate controlled by suspension chemistry and in situ geochemical conditions. Although the process has been extensively investigated, controlling the rate of gel formation in the presence of varying subsurface conditions and the limited ability of conventional methods to effectively monitor the gel formation process has posed practical challenges. In this study, a biomediated soil improvement process is proposed which utilizes enriched fermentative microorganisms to control the gelation of colloidal silica grouts through solution pH reductions and ionic strength increases. Four series of batch experiments were performed to investigate the ability of glucose fermenting microorganisms to be enriched in natural sands to induce geochemical changes capable of mediating silica gel formation and assess the effect of treatment solution composition on pH reduction behaviors. Complementary batch and soil column experiments were subsequently performed to upscale the process and explore the effectiveness of chemical, hydraulic, and geophysical methods to monitor microbial activity, gel formation, and engineering improvements. Results demonstrate that fermentative microorganisms can be successfully enriched and mediate gel formation in suspensions that would otherwise remain highly stable, thereby forgoing the need for chemical accelerants, increasing the reliability and control of colloidal silica grouting, enabling new monitoring approaches, and affording engineering enhancements comparable to conventional colloidal silica grouts.

Oscillatory Rheology of Three-Phase Coal Froths: Effects of Ionic Strength

The rheologic properties of a three-phase coal froth are critical to understanding the interfacial properties that are associated with its stability. Due to the fragile nature of froth, oscillatory rheology was used to make sure that the froths were not damaged during measurement. To reveal the relationship between a coal froth’s rheology and its stability, oscillatory rheology was used in this study. The viscoelastic behaviors of coal froths were analyzed, which illustrated that the storage modulus (G′) of a coal froth is larger than its loss modulus (G″), showing that coal froth is solid-like. The complex viscosity of the coal froths decreased with an increase in angular frequency, meaning that coal froth is shear-thinning. The dependence of froth rheology on ionic strength was investigated, which showed that an increase in ionic strength led to an enhancement of the storage modulus G′, as well as a decrease in tanδ (G″/G′). The coal froths tended to be more rigid and viscous with an increase in ionic strength. The mechanism of the effect of ionic strength on froth rheology was explored using electrical double layers, cryo-SEM, and particle fractions. As the ionic strength increased, the thickness of the electrical double layer decreased, which strengthened the interaction between the particles in the froth; in addition, the solid fraction in the froth increased with an increase in the ionic strength, so the value of G′ and the froth’s stability both increased.

Thermal Gelation of Proteins from Cajanus cajan Influenced by pH and Ionic Strength.

Cajanus cajan [pigeon pea (PP)] is an important legume crop for subsistence agriculture and its seeds are an alternative plant-based protein source. PP protein isolates (PPI) are able to form heat-induced gels that could be used for food applications. The aim of this work was to study the influence of pH (2.1, 3.9, 6.3, and 8.3) and ionic strength (μ) (0.10 and 0.54) on thermal stability and thermal gelation of PPI obtained by alkaline extraction (pH8.0) and isoelectric precipitation. Thermal stability of PPI changed with pH variation at low ionic strength (μ = 0.10), decreasing this dependence with the increase of ionic strength (μ = 0.54). At μ = 0.10, gelation capacity of PPI was lower at pH2.1 and pH3.9. These gels presented a coarse network, which entails low WHC. At pH6.3 and pH8.3, gels showed a solid-like character with a compact and homogeneous matrix, with better WHC. At μ = 0.54, gel formation was favoured at pH2.1 and pH3.9. G'20/G'95 ratio values and differential solubility results suggest that hydrogen bonds and electrostatic interactions could play an important role in gel formation at pH6.3 and pH8.3.