Derjaguin-Landau-Verwey-Overbeek Research Articles

Impact of ionic strength on goethite colloids co-transported with arsenite (As3+) through a saturated sand column under anoxic condition: experiment and mathematical modeling

The knowledge about co-transport of goethite and As3+ to investigate the effect of goethite colloids on As3+ transport under various degrees of seawater intrusion, particular extremely conditions, in groundwater environment is still limited. The main objective is to investigate the influence of seawater intrusion on the sorption, migration, and reaction of As3+and goethite colloids into sand aquifer media under anoxic conditions by using the bench-scale and reactive geochemical modeling. The research consisted of two parts as follows: 1) column transport experiments consisting of 8 columns, which were packed by using synthesis groundwater at IS of 0.5, 50, 200, and 400mM referring to the saline of seawater system in the study area, and 2) reactive transport modeling, the mathematical model (HYDRUS-1D) was applied to describe the co-transport of As3+ and goethite. Finally, to explain the interaction of goethite and As3+, the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation was considered to support the experimental results and HYDRUS-1D model. The results of column experiments showed goethite colloids can significantly inhibit the mobility of As3+ under high IS conditions (>200mM). The Rf of As3+ bound to goethite grows to higher sizes (47.5 and 65.0μm for 200 and 400mM, respectively) of goethite colloid, inhibiting As3+ migration through the sand columns. In contrast, based on Rf value, goethite colloids transport As3+ more rapidly than a solution with a lower IS (0.5 and 50mM). The knowledge gained from this study would help to better understand the mechanisms of As3+ contamination in urbanized coastal groundwater aquifers and to assess the transport of As3+ in groundwater, which is useful for groundwater management, including the optimum pumping rate and long-term monitoring of groundwater quality.

A cost-effective purification strategy of ultra-long AgNWs for enhancing stability and durability of AgNWs/PU sensor

A large amount of silver nanoparticles (AgNPs) and short-sized silver nanowires (AgNWs) were produced in the reaction of AgNW synthesis by the polyol method. These impurities immensely affected the practical application of AgNWs dispersion. To promote the electrical property of AgNWs, it is necessary to develop a cost-effective method to separate impurities in AgNWs dispersion. Herein, we developed a new purification strategy called centrifugation-sedimentation separation-centrifugation to purify the ultra-long AgNWs (average length of 98.26 μm and the aspect ratio of 1240) synthesized by an improved polyol method. The yield of sedimentation separation was up to 78.1 % in this strategy. Based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the sedimentation mechanism of the ultra-long AgNWs and impurities was systematically investigated. The AgNWs/polyurethane (PU) composite foam prepared by the impregnation method with purified ultra-long AgNWs demonstrated a superior conductivity of 13227 S/m, which was twice than that of the composite foam with unpurified ultra-long AgNWs. The resistance variation of the purified ultra-long AgNWs-5/PU sensor was only elevating 11 % after 100 cycles of 100 % strain compression at 1 Hz frequency, while the AgNWs-5/PU sensor prepared from commercial 20 μm AgNWs showed a resistance change of up to 492 %. Our study provides a low-cost, highly selective, and efficient purification strategy for ultra-long AgNWs dispersions, and also demonstrates that ultra-long AgNWs can enhance the sensing stability and durability of AgNWs/PU foam sensors.

Transport and retention of nanobubbles in saturated porous media: Overlooked role of grain size and shape

Nanobubbles (NBs) are widely used in groundwater pollution treatment due to their unique properties such as small size and high gas mass transfer rate. Therefore, the transport behavior of NBs in the groundwater environment has attracted more attention. Due to the diversity and complexity of aquifer media in the natural environment, grain sands with different sizes and shapes are ubiquitous. Thus, consideration of grain size and shape in porous media is crucial to predict and evaluate the transport and fate of NBs in soil and groundwater systems. This work investigated the stability of NBs in pure water. The transport behavior and mechanism of NBs under different grain sizes and shapes were demonstrated by the column experiment, microscopic observation, and numerical simulation. The results showed that NBs had excellent stability, remaining in solution for more than 10 days. The retention of NBs in coarse, medium and fine sands was 23.5 %, 43.8 % and 50.8 %, respectively. The retention in sphere sands, oval sands and irregular sands was 22.9 %, 24.0 % and 43.8 %, respectively. The smaller grain size and roundness limited the NBs transport in the saturated porous media, which was mainly due to the complexity of the flow channel and the narrowing of the pore throat of fine sands and angular shape of irregular sand that would hinder the NBs transport. This was proved by the Derjaguin − Landau − Verwey − Overbeek (DLVO) theory and ultra − depth − of − field microscope. The BTCs of NBs were fitted by the one − site deposition model (only attachment) and two − site deposition model (attachment and straining), and it was found that two − site deposition model showed a better fit. The straining rate (kstr) was greater than the attachment rate (katt) in different grain sizes and shapes media, indicating that the retention mechanism of NBs in porous media was a synergistic mechanism dominated by pore straining and supplemented by electrostatic attraction.

New Insights into Aggregation Behaviors of the UV-Irradiated Dissolved Biochars (DBioCs) in Aqueous Environments: Effects of Water Chemistries and Variation in the Hamaker Constant.

The aggregation behavior of ubiquitous dissolved black carbon (DBC) largely affects the fate and transport of its own contaminants and the attached contaminants. However, the photoaging processes and resulting effects on its colloidal stability remain yet unknown. Herein, dissolved biochars (DBioCs) were extracted from common wheat straw biochar as a proxy for an anthropogenic DBC. The influences of UV radiation on their aggregation kinetics were systematically investigated under various water chemistries (pH, electrolytes, and protein). The environmental stability of the DBioCs before and after radiation was further verified in two natural water samples. Hamaker constants of pristine and photoaged DBioCs were derived according to Derjaguin-Landau-Verwey-Overbeek (DLVO) prediction, and its attenuation (3.19 ± 0.15 × 10-21 J to 1.55 ± 0.07 × 10-21 J after 7 days of radiation) was described with decay kinetic models. Pearson correlation analysis revealed that the surface properties and aggregation behaviors of DBioCs were significantly correlated with radiation time (p < 0.05), indicating its profound effects. Based on characterization and experimental results, we proposed a three-stage mechanism (contended by photodecarboxylation, photo-oxidation, and mineral exposure) that DBioCs might experience under UV radiation. These findings would provide an important reference for potential phototransformation processes and relevant behavioral changes that DBC may encounter.

Molecular Mechanisms of Sorbed Ion Effects during Boehmite Particle Aggregation.

Classical theories of particle aggregation, such as Derjaguin-Landau-Verwey-Overbeek (DLVO), do not explain recent observations of ion-specific effects or the complex concentration dependence for aggregation. Thus, here, we probe the molecular mechanisms by which selected alkali nitrate ions (Na+, K+, and NO3-) influence aggregation of the mineral boehmite (γ-AlOOH) nanoparticles. Nanoparticle aggregation was analyzed using classical molecular dynamics (CMD) simulations coupled with the metadynamics rare event approach for stoichiometric surface terminations of two boehmite crystal faces. Calculated free energy landscapes reveal how electrolyte ions alter aggregation on different crystal faces relative to pure water. Consistent with experimental observations, we find that adding an electrolyte significantly reduces the energy barrier for particle aggregation (∼3-4×). However, in this work, we show this is due to the ions disrupting interstitial water networks, and that aggregation between stoichiometric (010) basal-basal surfaces is more favorable than between (001) edge-edge surfaces (∼5-6×) due to the higher interfacial water densities on edge surfaces. The interfacial distances in the interlayer between aggregated particles with electrolytes (∼5-10 Å) are larger than those in pure water (a few Ångströms). Together, aggregation/disaggregation in salt solutions is predicted to be more reversible due to these lower energy barriers, but there is uncertainty on the magnitudes of the energies that lead to aggregation at the molecular scale. By analyzing the peak water densities of the first monolayer of interstitial water as a proxy for solvent ordering, we find that the extent of solvent ordering likely determines the structures of aggregated states as well as the energy barriers to move between them. The results suggest a path for developing a molecular-level basis to predict the synergies between ions and crystal faces that facilitate aggregation under given solution conditions. Such fundamental understanding could be applied extensively to the aggregation and precipitation utilization in the biological, pharmaceutical, materials design, environmental remediation, and geological regimes.

Recovery of biochar particles laden with lead in saturated porous media by DC electric field

The co-transport behavior of environmental pollutants with biochar particles has aroused great interests from researchers due to the concerns about pollutant diffusion and environmental exposure after biochar is applied to soil. In this work, the recovery and co-transport behavior of biochar micron-/nano-particles (BCMP and BCNP) and lead (Pb2+) in saturated porous media were investigated under different ionic strength conditions (IS = 1, 5 and 10 mM) under a direct current electric field. The results showed that the electric field could significantly enhance the mobility of Pb adsorbed biochar particles, particularly BCNP. The recovery of Pb laden biochar particles was improved by 1.8 folds, reaching 78.8% at maximum under favorable condition at +0.5 V cm−1. According to the CDE (Convection-Dispersion-Equation) model and DLVO (Derjaguin-Landau-Verwey-Overbeek) theory analysis, the electric field facilitated the transport of Pb carried biochar mainly by increasing the negative charges on biochar surface and improving the repulsive force between biochar and porous media. High IS was favorable for biochar transport under the electric field, but inhibited desorbing Pb2+ from biochar (18% by maximum at IS = 10 mM). By switching the electric field power, a two-stage strategy was established to maximize the recovery of both biochar particles and Pb, where BCNP and Pb recovery were higher than electric field free case by 90% and 35%, respectively. The findings of this study can help build a biochar recovery approach to prevent potential risks from biochar application in heavy metal contaminated soil remediation.

Impact of natural organic matter and inorganic ions on the stabilization of polystyrene micro-particles

The orthokinetic coagulation of irregularly shaped polystyrene micro-particles (PS-MP) was investigated in solutions of inorganic cations with different valence (NaCl, CaCl2, LaCl3) using a coagulation jar test set-up combined with light extinction particle counting. The stabilizing effect of model natural organic matter (NOM from reverse-osmosis (RO-NOM), humic (HA) & fulvic acid (FA)) and of surface water components (SW-NOM) was studied. Collision efficiencies were calculated from the decrease in particle concentration applying first order reaction kinetics. The coagulation of PS-MP followed Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with regard to ionic charge in solution. Highest collision efficiencies were obtained close to the suspected critical coagulation concentrations for CaCl2 (12 mM) and LaCl3 (5.5 mM) whereas for NaCl no CCC was found within the applied concentration range (10–1000 mM). The addition of NOM effectively stabilized PS-MP at low ionic strength (10 mM NaCl) in the order HA > RO-NOM > FA > SW-NOM at concentrations of dissolved organic carbon (DOC) as low as 0.2–0.5 mg/L DOC through electrostatic repulsion. PS-MP were effectively stabilized in 6.1 mg DOC/L of SW-NOM even at high ionic strength (100 mM MgCl2). Coagulation at intermediate ionic strength (10 mM MgCl2) was only observed for SW-NOM concentrations below 0.6 mg/L DOC. The results showed that even low NOM concentrations prevent PS-MP from orthokinetic coagulation in the presence of high ion concentrations. The study provides further insight in the orthokinetic coagulation behavior of PS-MP in the presence of NOM and highlights the importance of NOM for the stabilization of microplastics in aquatic suspensions. Further research is needed to elucidate the behavior of MP in turbulent systems to predict the mobility MP in aquatic systems such as rivers.

Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model

Microplastics (MPs) vary in shape and surface characteristics in the environment. The attachment of MPs to surfaces can be studied using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, this theory does not account for the shape MPs. Therefore, we investigated the attachment of spherical, pear-shaped, and peanut-shaped polystyrene MPs to quartz sand in NaCl and CaCl2 solutions using batch tests. The attachment of MPs to quartz sand was quantified using the attachment efficiency (alpha). Subsequently, alpha behaviors were interpreted using energy barriers (EBs) and interaction minima obtained from extended DLVO calculations, which were performed using an equivalent sphere model (ESM) and a newly developed equivalent Cassini model (ECM) to account for the shape of the MPs. The ESM failed to interpret the alpha behavior of the three MP shapes because it predicted high EBs and shallow minima. The alpha values for spherical MPs (0.62–1.00 in NaCl and 0.48–0.96 in CaCl2) were higher than those for pear- and peanut-shaped MPs (0.01–0.63 in NaCl and 0.02–0.46 in CaCl2, and 0.01–0.59 in NaCl and 0.02–0.40 in CaCl2, respectively). Conversely, the ECM could interpret the alpha behavior of pear- and peanut-shaped MPs either by changes in EBs or interaction minima as a function of orientation angles and electrolyte ionic strength. Therefore, the particle shape must be considered to improve the attachment analyses.

A Meta-Analysis to Revisit the Property-Aggregation Relationships of Carbon Nanomaterials: Experimental Observations versus Predictions of the DLVO Theory.

Contradicting relationships between physicochemical properties of nanomaterials (e.g., size and ζ-potential) and their aggregation behavior have been constantly reported in previous literature, and such contradictions deviate from the predictions of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. To resolve such controversies, in this work, we employed a meta-analytic approach to synthesize the data from 46 individual studies reporting the critical coagulation concentration (CCC) of two carbon nanomaterials, namely, graphene oxide (GO) and carbon nanotube (CNT). The correlations between CCC and material physicochemical properties (i.e., size, ζ-potential, and surface functionalities) were examined and compared to the theoretical predictions. Results showed that the CCC of electrostatically stabilized carbon nanomaterials increased with decreasing nanomaterial size when their hydrodynamic sizes were smaller than ca. 200 nm. This is qualitatively consistent with the prediction of the DLVO theory but with a smaller threshold size than the predicted 2 μm. Above the threshold size, the material ζ-potential can be correlated to CCC for nanomaterials with moderate/low surface charge, in agreement with the DLVO theory. The correlation was not observed for highly charged nanomaterials because of their underestimated surface potential by the ζ-potential. Furthermore, a correlation between the C/O ratio and CCC was observed, where a lower C/O ratio resulted in a higher CCC. Overall, our findings rationalized the inconsistency between experimental observation and theoretical prediction and provided essential insights into the aggregation behavior of nanomaterials in water, which could facilitate their rational design.

Environmental colloid behaviors of humic acid - Cadmium nanoparticles in aquatic environments

Humic acid (HA), a principal constituent of natural organic matter (NOM), manifests ubiquitously across diverse ecosystems and can significantly influence the environmental behaviors of Cd(II) in aquatic systems. Previous studies on NOM-Cd(II) interactions have primarily focused on the immobilization of Cd(II) solids, but little is known about the colloidal stability of organically complexed Cd(II) particles in the environment. In this study, we investigated the formation of HA-Cd(II) colloids and quantified their aggregation, stability, and transport behaviors in a saturated porous media representative of typical subsurface conditions. Results from batch experiments indicated that the relative quantity of HA-Cd(II) colloids increased with increasing C/Cd molar ratio and that the carboxyl functional groups of HA dominated the stability of HA-Cd(II) colloids. The results of correlation analysis between particle size, critical aggregation concentration (CCC), and zeta potential indicated that both Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions contributed to the enhanced colloidal stability of HA-Cd(II) colloids. Column results further confirmed that the stable HA-Cd(II) colloid can transport fast in a saturated media composed of clean sand. Together, this study provides new knowledge of the colloidal behaviors of NOM-Cd(II) nanoparticles, which is important for better understanding the ultimate cycling of Cd(II) in aquatic systems.

Colloidal Zeta Potential Modulation as a Handle to Control the Crystallization Kinetics of Tin Halide Perovskites for Photovoltaic Applications.

Tin halide perovskites (THPs) have demonstrated exceptional potential for various applications owing to their low toxicity and excellent optoelectronic properties. However, the crystallization kinetics of THPs are less controllable than its lead counterpart because of the higher Lewis acidity of Sn2+, leading to THP films with poor morphology and rampant defects. Here, a colloidal zeta potential modulation approach is developed to improve the crystallization kinetics of THP films inspired by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. After adding 3-aminopyrrolidine dihydro iodate (APDI2) in the precursor solution to change the zeta potential of the pristine colloids, the total interaction potential energy between colloidal particles with APDI2 could be controllably reduced, resulting in a higher coagulation probability and a lower critical nuclei concentration. In situ laser light scattering measurements confirmed the increased nucleation rate of the THP colloids with APDI2. The resulting film with APDI2 shows a pinhole-free morphology with fewer defects, achieving an impressive efficiency of 15.13 %.

Colloidal Zeta Potential Modulation as a Handle to Control the Crystallization Kinetics of Tin Halide Perovskites for Photovoltaic Applications

AbstractTin halide perovskites (THPs) have demonstrated exceptional potential for various applications owing to their low toxicity and excellent optoelectronic properties. However, the crystallization kinetics of THPs are less controllable than its lead counterpart because of the higher Lewis acidity of Sn2+, leading to THP films with poor morphology and rampant defects. Here, a colloidal zeta potential modulation approach is developed to improve the crystallization kinetics of THP films inspired by the classical Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) theory. After adding 3‐aminopyrrolidine dihydro iodate (APDI2) in the precursor solution to change the zeta potential of the pristine colloids, the total interaction potential energy between colloidal particles with APDI2 could be controllably reduced, resulting in a higher coagulation probability and a lower critical nuclei concentration. In situ laser light scattering measurements confirmed the increased nucleation rate of the THP colloids with APDI2. The resulting film with APDI2 shows a pinhole‐free morphology with fewer defects, achieving an impressive efficiency of 15.13 %.

Experimental and theoretical studies on water adsorption and capillary condensation in nanopores of calcium carbonate

Understanding the water vapor sorption in nanopores has significant implications for hydrocarbon extraction and waste storage. This study presents gravimetric water sorption isotherms of nanoporous calcium carbonates. A methodology for quantifying equilibrium water sorption through matrix potential, even as the matrix potential approaches zero is introduced. This method facilitated the determination of adsorption via the Derjaguin‒Landau‒Verwey‒Overbeek (DLVO) theory and of capillary condensation, including the conjugate state, based on Young's Laplace equation. The relative errors between the experimental and calculated values ranged from 0.24% to 10.42%. Quantitative parameters characterizing the water distribution were calculated, and their dependences on water sorption were analyzed. The increase in water sorption over time exhibited a gradual decline, which was better described by a second-order exponential decay function. The stable decline point of the sorption rates ranged from 13.24% to 22.47% of the total time. In most cases, water vapor sorption in the pores is dominated by adsorption, with nanopores showing enhanced adsorption due to weaker inhibition of sidewall effects compared to an increase in adsorption sites. Notably, a substantial increase in equilibrium water sorption occurs when the matrix potential exceeds −106 MPa, corresponding to a relative humidity exceeding 96.6%, indicating strong capillary condensation. Additionally, nanoscale pores exhibit a pronounced propensity for capillary condensation when the pore throat diameter is less than 3.5 nm. These findings enhance our understanding of water sorption in tight rock formations when direct measurements are unavailable, with implications for estimating multiphase fluid transport in unconventional reservoirs.

Colloidal Stability of PFSA-Ionomer Dispersions. Part I. Single-Ion Electrostatic Interaction Potential Energies.

Charged colloidal particles neutralized by a single counterion are increasingly important for many emerging technologies. Attention here is paid specifically to hydrogen fuel cells and water electrolyzers whose catalyst layers are manufactured from a perfluorinated sulfonic acid polymer (PFSA) suspended in aqueous/alcohol solutions. Partially dissolved PFSA aggregates, known collectively as ionomers, are stabilized by the electrostatic repulsion of overlapping diffuse double layers consisting of only protons dissociated from the suspended polymer. We denote such double layers containing no added electrolyte as "single ion". Size-distribution predictions build upon interparticle interaction potential energies from the Derjaguin-Landau-Verwey-Overbeek (DLVO) formalism. However, when only a single counterion is present in solution, classical DLVO electrostatic potential energies no longer apply. Accordingly, here a new formulation is proposed to describe how single-counterion diffuse double layers interact in colloidal suspensions. Part II (Srivastav, H.; Weber, A. Z.; Radke, C. J. Langmuir 2024 DOI: 10.1021/acs.langmuir.3c03904) of this contribution uses the new single-ion interaction energies to predict aggregated size distributions and the resulting solution pH of PFSA in mixtures of n-propanol and water. A single-counterion diffuse layer cannot reach an electrically neutral concentration far from a charged particle. Consequently, nowhere in the dispersion is the solvent neutral, and the diffuse layer emanating from one particle always experiences the presence of other particles (or walls). Thus, in addition to an intervening interparticle repulsive force, a backside osmotic force is always present. With this new construction, we establish that single-ion repulsive pair interaction energies are much larger than those of classical DLVO electrostatic potentials. The proposed single-ion electrostatic pair potential governs dramatic new dispersion behavior, including dispersions that are stable at a low volume fraction but unstable at a high volume fraction and finite volume-fraction dispersions that are unstable with fine particles but stable with coarse particles. The proposed single-counterion electrostatic pair potential provides a general expression for predicting colloidal behavior for any charged particle dispersion in ionizing solvents with no added electrolyte.

Particle deposition and clogging as an Obstacle and Opportunity for sustainable energy

Fine particle motions have significant implications in porous media, manifesting in various natural phenomena and industrial applications. The movement of particles can lead to channel blockage, resulting in clogging. Depending on the context, clogging can be either advantageous or detrimental. At the scale of fine particles, physiochemical interactions play a crucial role in the clogging process. To examine the influence of these interactions, we have coupled the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory into the Computational Fluid Dynamic-Discrete Element (CFD-DEM) approach. Aside from the physical properties of the fracture systems and the characteristics of fine particles, the injection rate also plays a pivotal role in clogging occurrence. Consequently, we investigated 10 different injection rates and modeled 20 simulation setups with identical particle insertion rates to concurrently analyze the effects of the DLVO theory and injection rate. Our study focused on examining the impact of these parameters on particle behavior in various regions of the domain, including particle-particle force, fluid-particle force, transitional velocity, rotational velocity, fluid velocity, and fluid-particle momentum exchange. Our findings reveal that the DLVO force significantly influences fluid and particle characteristics within the throat blockage. Our results indicated that DLVO consideration increased the particle concentrations by more than 40% before the throat. Moreover, our results demonstrate a transition between different injection rates, where a slight change in injection rate (i.e., 0.06μm/s) can change the system's behavior. We identified a critical fluid injection rate, whereby injecting fluid into the system at a rate surpassing the critical velocity can prevent clogging, while lower rates result in clogging occurrence.

Tracking colloidal silica particles to evaluate their dispersion and interactions in concentrated suspensions under shear force applications.

This study aimed to characterize interactions within colloidal silica particles in their concentrated suspensions, using rheo-confocal measurements and imaging, followed by image analysis. We studied the effect of shear rate (0-500s-1) and solution pH (6, 10) on the dispersion degree of colloidal silica particles via the determination and comparison of interparticle distances and their modeling. Images corresponding to different shear rates were analyzed to identify the coordinates of the particles. These coordinates were further analyzed to calculate the distance among the particles and then their surface-to-surface distance normalized by the particle diameter (H/D). It was found that the population of the particles per unit area of the image and H/D varied with increasing shear rate. The comparison between experimentally measured and theoretically calculated H/D identified that for some particles, the former was shorter than the latter, indicating the unexpected attractions among them against the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Then, the modification of previously reported equations for H/D was suggested and confirmed its validity. Assuming pair potential interaction and hydrodynamic interaction were the main non-DLVO interactions, their magnitudes were calculated and confirmed the significance of pH and shear application strength on particle dispersion/coagulation.

Revealing the contradiction between DLVO/XDLVO theory and membrane fouling propensity for oil-in-water emulsion separation

Oil fouling is the crucial issue for the separation of oil-in-water emulsion by membrane technology. The latest research found that the membrane fouling rate was opposite to the widely used theoretical prediction by Derjaguin-Landau-Verwey-Overbeek (DLVO) or extended DLVO (XDLVO) theory. To interpret the contradiction, the molecular dynamics was adopted to explore the molecular behavior of oil and emulsifier (Tween 80) at membrane interface with the assistance of DLVO/XDLVO theory and membrane fouling models. The decreased flux attenuation and fitting of fouling models proved that the existence of Tween 80 effectively alleviated membrane fouling. Conversely, DLVO/XDLVO theory predicted that the membrane fouling should be exacerbated with the increase of Tween 80 concentration in O/W emulsion. This contradiction originated from the different interaction energy between oil/Tween 80 molecules and polyether sulfone (PES) membrane. The favorable free energy of Tween 80 was resulted from the sulfuryl groups in PES and hydrogen bonds (O-H…O) formation further strengthened the interaction. Therefore, Tween 80 could preferentially adsorb on membrane surface and form an isolation layer by demulsification and steric hindrance and resist the aggregation of oil, which effectively alleviated membrane fouling. This study provided a new insight in the interpretation of interaction in O/W emulsion.

Identifying the mechanisms behind the stability of silica nano- and micro-particles: Effects of particle size, electrolyte concentration and type of ionic species

Silica nanofluids have emerged as promising agents for various applications, such as water treatment, CO2 absorption, and chemical enhanced oil recovery (CEOR). However, their effectiveness can be hindered when transported through porous media, especially in challenging downhole environments. Aggregation of nanofluid suspensions can damage formation integrity, and brine fluids may unintentionally transport fine micro silica particles, warranting an in-depth examination of micro-particle behavior and stability. This study synthesized silica particles of different sizes (10 nm, 50 nm, 1 μm and 2 μm) and meticulously characterized them using advanced techniques of transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), fourier-transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), thermal gravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. Subsequently, 560 combinations (in 5 series of 112 experiments) of micro- and nano-fluids in the presence of four different salts (NaCl, CaCl2, MgSO4 and MgCl2) were prepared. The stability and sedimentation of these combinations were investigated based on zeta potential, particle size, pH, electrical conductivity, and UV-spectrophotometry. The results indicated that sodium ions were effective for maintaining suspension stability at lower salt concentrations, while magnesium ions were preferred for higher salinities. Particle size increase led to instability at low salinities but stability at high salinities, where enthalpy dominated over entropy. Derjaguin-Landau-Verwey-Overbeek (DLVO) modeling accurately predicted particle interactions and aggregation tendencies. This investigation enhanced the understanding of the mechanisms governing silica particle stability through diverse analytical methods, addressing their limitations. The analysis of UV data over time revealed insights into sedimentation and aggregation kinetics. In summary, this study comprehensively explored the behavior and stability of silica particles in nano- and micro-fluids, shedding light on their performance in applications ranging from enhanced oil recovery to water treatment.

Elevated temperature effects (T > 100 °C) on the interfacial water and microstructure swelling of Na-montmorillonite

Montmorillonite-based barriers are key elements of the engineered barrier systems (EBS) in geological disposal facilities (GDF). Their performance at temperatures above 100 °C is not sufficiently understood to assess the possibility of raising the temperature limits in GDF designs that could reduce construction costs and CO2 footprint. The present work provides new fundamental insights through molecular dynamics (MD) simulations of Na-montmorillonite's water-clay interactions and swelling pressure at temperatures 298–500 K and basal spacings of 1.5–3.5 nm. At temperatures above 100 °C, the swelling behaviour is governed by the attractive van der Waals force and the repulsive hydration force instead of the repulsive electrostatic (double layer) force. The swelling pressure reduction with increasing temperature is related to the weakened hydration repulsion and electric double layer repulsion, which result from the deterioration of the interlayer water layer structure and the shrinkage of the electric double layer. The applicability and breakdown of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory at elevated temperatures are examined. By excluding the osmotic contribution in the DLVO theory, the summation of the van der Waals interaction in DLVO and an additional non-DLVO hydration interaction can predict our MD system's swelling under high temperatures. The findings of this study provide a fundamental understanding of the swelling behaviour and the underlying molecular-level mechanisms of the clay microstructure under extreme conditions.

Evaluation for water stability of bitumen mixture with multi-scale method

The interaction forces were investigated between matrix bitumen and four kinds of aggregates, including basalt, granite, limestone A, and limestone B in various pH solutions. The aim was to accurately evaluate the water damage resistance of bitumen mixtures at macroscopic and microscopic levels with a conjunctive method of boiling water tests, atomic force microscopy (AFM) colloidal probe technique, zeta potential measurements, and molecular dynamics simulation. Macroscopic evaluation was conducted through indoor water-boiled flaking rate tests to analyze the flaking rate and adhesion class of bitumen and aggregate. The microscopic forces were measured by AFM probe technique between bitumen and aggregate, zeta potential measurements were carried out and the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was employed to interpret the bitumen–aggregate interaction behaviors. Molecular dynamics simulations were considered to explain the interface binding tendency between bitumen and aggregate. The AFM force measurements showed that the long-range repulsion forces changed to attractive forces and high adhesive forces with the pH change from 4 to 6. However, the strong long-range repulsive forces were decreased, compounded with a relative low adhesion in the alkaline solution. The long-range force between granite and bitumen was a strong attraction, and adhesion was strong when the solution pH was 4, which is a more special phenomenon. It may be due to the electrostatic attraction between the positive charge on the granite surface and the negative charge on the bitumen surface. Zeta potential values of bitumen droplets and aggregate particles exhibited an overall decreasing trend with increasing solution pH, and the variation of surface potential value is consistent with the variation trend of long-range force between aggregate and bitumen. The microscopic forces between bitumen and aggregate measured by AFM were validated by molecular dynamics simulations, revealing a strong correlation between debonding work and interfacial forces. The results indicate that the adhesion between aggregates and bitumen in aqueous solution followed the order: limestone A > limestone B > basalt > granite, and alkaline conditions are not conducive to preventing water damage in bitumen mixtures. It provides insights into the water stability mechanism of bitumen-aggregate at macroscopic and microscopic scales, offering theoretical support for preventing water damage in bitumen pavements.