Interfacial Adsorption Research Articles

Influence of Aqueous Phase Salt and Oil Phase Surfactants and Viscosity on the Dynamic Interfacial Tension and Coalescence Timescales.

Liquid-liquid separation is a critically important process in the treatment of emulsions that can occur in our environment, such as oily stormwater, shipboard bilgewater, or off-shore oil spill treatment. Effective filtration systems, including coalescing filters, are essential for mitigating these environmental pollutants. Achieving this requires a comprehensive understanding of liquid-liquid interface dynamics influenced by additives and surfactants. Furthermore, understanding the impact of surfactants on emulsion stability in saline environments is vital for optimizing filtration processes and ensuring the protection of marine and freshwater ecosystems. In this work, these effects are highlighted using measurements performed across a range of droplet size, surfactant concentration, viscosity ratios, and saline presence. Dynamic IFT measurements are conducted using the pendant drop method for water in light mineral oil, with and without salt in the water phase. The effect of salt addition is also highlighted by using microfluidic coalescence experiments, in which it was found that the addition of salt increases the dimensionless drainage time below the critical micelle concentration. The second focus of this work is to study the effect of bulk phase viscosity on the stability. Dynamic IFT measurements are performed at both millimeter and micrometer scales using pendant drop experiments and microfluidic tensiometry, respectively, involving light and heavy mineral oils with varying SPAN80 surfactant concentrations. The surfactant diffusivity and interfacial adsorption and desorption rates are then extracted by fitting a surfactant diffusion and equation of state equations to the dynamic IFT measurements. The results of the IFT decay, surfactant diffusivity, and adsorption rates are compared at two different viscosity ratios. This study also compares the times required for IFT relaxation with the film drainage times in water-in-oil systems. The comparison aids in comprehending the impact of competing timescales during film drainage. The findings presented in this paper offer valuable insights into the design and optimization of liquid-liquid filtration systems, especially when operating under challenging environmental conditions, such as in saline environments. The principles explored here can be applied to improving industrial water treatment and in the design of advanced filtration technologies for chemical and petrochemical industries, particularly those involving flow, contributing to more sustainable and efficient practices in handling emulsified waste streams.

Effects of Spontaneous Curvature on Interfacial Adsorption and Collapse of Phospholipid Monolayers.

To function effectively, pulmonary surfactant must adsorb rapidly to the alveolar air/water interface, but avoid collapse from the interface when compressed to low surface tensions. Prior studies show that phospholipids in the cylindrical monolayers of the inverse hexagonal (HII) phase adsorb quickly. The monolayers have negative curvature, defined by the concave shape of the hydrophilic face. Formation of the HII structures, however, involves significant disruption of optimal chain-packing. Samples with significant spontaneous curvature, formed in the absence of applied force, may nonetheless have lamellar structures. The experiments here tested whether planar lamellar bilayers formed by phospholipids with negative spontaneous curvature might adsorb rapidly but collapse slowly. Prior studies have shown that binary mixtures of dioleoyl phosphatidylcholine-dioleoyl phosphatidylethanolamine (DOPC-DOPE) with higher mol fractions of DOPE (XPE) have more negative spontaneous curvature. Samples with higher XPE adsorbed more rapidly but also collapsed more quickly. Over that range of XPE, small angle X-ray scattering showed only lamellar structures. The HII phase was undetectable. The results suggest that the innate tendency of the phospholipids to form curved structures has primary importance for adsorption rather than the presence of HII structures. Planar structures are insufficient to minimize the tendency of spontaneous curvature to promote collapse. These findings are consistent with adsorption and collapse that occur via rate-limiting structures with significant negative curvature.

Exploring the oil-water interfacial behaviour of pea protein-guar gum/gellan gum mixtures relating to stability and in vitro protein digestion of model pea milk system

Polysaccharides are effective stabilisers for plant-based milks, but their interfacial adsorption behaviours in plant milk system and effects on plant protein digestibility are still unclear. This study analysed the oil-water interfacial adsorption behaviours of pea protein concentrate (PPC) and isolate (PPI) mixed with neutral guar gum and anionic gellan gum to understand the stability and in vitro protein digestion of corresponding model pea milk system. Adding guar gum or gellan gum enhanced the interfacial adsorption stability of pea proteins without compromising proteolysis during gastrointestinal digestion. Gellan gum performed better than guar gum for long-term co-stabilising the emulsion with pea proteins, due to its electrostatic repulsion with pea proteins and stronger steric hindrance induced by thicker adsorbed interfacial layers (~10 % or ~37 % higher thickness than guar gum counterparts) as detected by a quartz crystal microbalance with dissipation (QCM-D) after rinsing. The model pea milks with 0.1 % (wt%) gellan gum were stable at 4 °C for 28 days regardless of protein types. The presence of polysaccharides at the interface enabled oil droplets to be kept separate during in vitro gastrointestinal digestion, improving the final proteolysis by ~4 to ~27 %. This result is conducive to selecting polysaccharides for developing pea protein-based beverages.

Atmospheric cold plasma pretreatment for effective enhancement of covalent crosslinking between coconut globulin and tannic acid: Improving interfacial activity and emulsifying properties

Atmospheric cold plasma (ACP) represents a promising approach for enhancing covalent interactions between proteins and polyphenols, circumventing the drawbacks associated with traditional methods. This study aims to investigate the enhancement of covalent interactions between coconut globulin (CG) and tannic acid (TA) facilitated by ACP at varying pH levels. At acidic pH, ACP treatment was found to promote free radical-induced covalent cross-linking between CG and TA, whereas at pH 7.0 and 9.0, ACP treatment enhanced quinone-induced covalent cross-linking. In contrast, the covalent crosslinking induced by quinone significantly disrupted the protein structure, leading to greater exposure of hydrophobic groups. At pH 9.0, the CG-TA complex treated with ACP exhibited the highest interfacial activity, with an interfacial adsorption mass of 5292 ng/cm2. This was accompanied by improvements in droplet size, viscosity, and stability of the CG-TA-stabilized emulsion. These findings offer novel insights into the covalent modification of proteins and polyphenols, thereby broadening the potential applications of food protein.

Hydroxyapatite‐spent cathode carbon block modified asphalt and molecular dynamics simulation study

AbstractThe highly toxic substances contained in spent cathode carbon blocks (SCCB) pose a serious threat to human health and the ecological environment, and are difficult to recycle. To address this issue, we utilize H2O2 to oxidize cyanides and grow hydroxyapatite (HAP) on spent cathode carbon blocks to adsorb fluoride ions, achieving controlled removal of cyanides and fluorides. Subsequently, the hydroxyapatite‐spent cathode carbon block composite material (H‐SCCB) is applied to modified asphalt, and simulations of the interaction between hydroxyapatite interfaces and asphalt components are conducted. The results indicate that the total cyanide and fluoride ion concentrations in the experimental wastewater meet the discharge standards for industrial wastewater in China. Hydroxyapatite successfully grows on SCCB, presenting a rich porous structure and significantly increased surface area. Mechanical testing shows that 4% H‐SCCB exhibits optimal performance, with a 23.28% increase in complex modulus (G*) compared to the matrix asphalt. Creep recovery capability (R) increases by 54.32% and 7%, respectively. Additionally, molecular dynamics simulations reveal that the interface adsorption between hydroxyapatite and asphalt binder is primarily influenced by electrostatic forces. Under the influence of hydroxyapatite, the diffusion abilities of asphalt four components are as follows: resin > aromatic > saturate > asphaltene.

Zr-based MOF as a support for lipase immobilization to enhance enzymatic transesterification for biodiesel production

The development of novel biocatalysts is essential to promote the commercialization of biodiesel production by transesterification reaction. In this paper, Rhizopus oryzae lipase (ROL) was immobilized on an amino-functionalized zirconium-based metal organoskeleton by interfacial adsorption. The immobilization conditions were optimized and the enzymatic properties were tested, and the resulting novel biocatalysts exhibited higher stability and heat resistance. SEM, XRD and BET analyses were used to characterize the biocatalysts and carrier materials. The catalytic performance of ROL@UiO-66-NH2 in the production of biodiesel by transesterification reaction was explored, and the production process was optimized by response surface method. The results showed that the conversion rate of FAEE reached 82.05% at molar ratio of ethanol/oil of 15.43:1, reaction temperature of 50.28°C, reaction time of 120.9 min, DES addition of 48.08 wt%, biocatalyst addition of 3 wt%, and ultrasonic power of 90 W. In addition, ROL@UiO-66-NH2 demonstrated good recyclability, with the catalytic efficiency remaining at 71.87% after five cycles.

A straight-forward fabrication of yuba films with controllable mechanical properties by oil-in-water emulsion model system rather than soymilk

The traditional process of producing yuba films from soybeans strictly limits the development of its industrial production due to the numerous processes and intricate procedures involved. In this study, a straight-forward and effective strategy was proposed to substitute soymilk with an emulsion made from soybean protein isolate and soybean oil for the formation of yuba films. It was found that the mechanical properties of yuba films formed through this method were controlled by the concentrations of proteins and oils. As the protein concentrations increased, a higher ratio of adsorbed proteins adhered to the surface of oil droplets, which in turn facilitated the recombination of proteins and the formation of larger aggregates during heat incubation. The rheological properties and interfacial adsorption behavior suggested that larger protein aggregates exhibited a greater diffusion rate and were more prone to unfolding and re-crosslinking at the interface through heat induction, resulting in the formation of stronger protein networks. Confocal laser scanning microscope images revealed a notable increase in the density of oil distribution within the yuba films as the oil concentrations in the pre-emulsion rose. Combined with the dense protein network formed at high protein concentrations, the elongation of yuba films was significantly increased.

Water-in-water emulsions stabilized by nano-chitin

A water-in-water (W/W) emulsion consists of microdroplets was formed by the spontaneous liquid–liquid separation by mixing polyacrylic acid and chitosan oligosaccharide in water, and these microdropletes were stabilized by nano-chitin, formed water-in-water Pickering emulsions. By taking the advantage of interfacial adsorption of nano-chitin, the W/W emulsion droplets composed of polyacrylic acid/chitosan oligosaccharide (COS/PAA) polyelectrolyte coacervate were successfully stabilized. Research results indicated that composite microspheres were formed by the nano-chitin stabilized COS/PAA emulsion, and the size of these composite microspheres was related to the concentration and morphology of the nano-chitin. As the concentration of nano-chitin increases, the size of the composite microspheres first increases and then decreases, gradually becoming more uniform; whereas a decrease in the length of nano-chitin will lead to an increase in the size of the composite microspheres. The formation of composite microspheres may be due to the electrostatic interactions between nano-chitin and the emulsion droplets. In addition, the composite microspheres exhibit the best release effect for berberine hydrochloride at a pH value of 3.

Structure-property relationship of pea protein microgels as fat analogues in Pickering oil-in-water emulsions: effect of salt addition.

The design of plant-based microgels provides a platform for food ingredients to enhance palatability and functionality. This work aimed to explore the modifying effect of salt addition (KCl) on the structure of pea protein microgel particles (PPI MPs), on the interfacial adsorption and characteristics of formed emulsions as fat analogues. Salt addition (0-200 mmol L-1) promoted a structural transformation from α-helix to β-sheet, increased the surface hydrophobicity (from 1160.8 to 2280.7), and increased the contact angle (from 56.73° to 96.47°) of PPI MPs. The electrostatic shielding effect led to the tighter packing of MPs with irregular structures and lowered the adsorption energy barrier. Notably, salt-treated PPI MPs could adjust their adsorption state at the interface. The discernible adsorption of PPI MPs with 200 mmol L-1 salt addition that possessed enhanced anti-deformation ability dominated the interfacial stabilization, whereas a relatively rougher stretched continuous interfacial film formed after spreading and deformation of 0 mmol L-1 MPs. A tribological test suggested that emulsion stabilized by MPs at 0 (0.0053) and 80 mmol L-1 (0.0068) had similar friction coefficients to commercial mayonnaise (0.0058), whereas a higher salt concentration (200 mmol L-1) lowered its oral sensation due to the adsorption layer and enhanced the resistance to droplet coalescence during oral processing. Salt could be a modifier to tune the structure of microgels, and further promote the formation and attributes of emulsions. This study would improve application attributes of PPI MPs in the design of realistic fat analogues. © 2024 Society of Chemical Industry.

Effect of ANSA as an additive on electrodeposited Sn-Ag-Cu alloy coatings in deep eutectic solvent

This study investigates the electrodeposition of Sn-Ag-Cu ternary solder coating in a choline chloride-ethylene glycol DES using 1-amino-2-naphthol-4-sulfonic acid (ANSA) as an additive. The mechanism of ANSA was evaluated through UV–visible absorption spectroscopy, infrared spectroscopy, and CV. The results demonstrate that ANSA, as a multifunctional organic compound, influences the electrodeposition process through its sulfonic acid, amino, and naphthyl groups. When the ANSA concentration is below 600 ppm, its primary action is through an interfacial adsorption mechanism, where lone pairs of electrons on nitrogen and oxygen atoms adsorb onto the electrode surface, and the bulky naphthyl ring inhibits the formation of large deposits. As the ANSA concentration exceeds 600 ppm, complexation becomes the dominant mechanism, competing with the complexation of chloride ions (Cl−) in the choline chloride electrolyte. SEM analysis indicates that as the ANSA concentration increases, the deposited coatings become smoother, denser, and exhibit finer grain sizes. The Scharifker-Hills model was employed to analyze the CA curves before and after the addition of ANSA, revealing that the nucleation mechanism of Sn-Ag-Cu alloy deposition gradually transitions from instantaneous nucleation to progressive nucleation with increasing ANSA concentration.

Enhancement of interaction between Shenhua coal and GON-based dispersant with “surface-to-surface” adsorption by regulating the oxidation degree of GON: Experiments and simulations

The present study focuses on the synthesis of several graphene oxide nanosheet (GON)-based dispersants with an adsorption mode of “surface-to-surface” for the preparation of Shenhua coal (SC) water slurry (SCWS), achieved by grafting allyl polyoxyethylene ether (APEG) onto GON edges with varying degrees of oxidation using emulsion polymerization and esterification techniques. The impacts of the oxidation degree of GON on its structural characteristics and the performance of GON-based dispersants in SCWS were comprehensively assessed through a range of experimental techniques, alongside molecular dynamics (MD) simulations. Results demonstrated that with the increase in oxidation degree, there was an elevation of oxygen-containing groups, in which the content of COH decreased while the content of COC increased. Among all dispersants, GA-2, which was synthesized using GON-2 as the raw material with a graphite-to-KMnO4 mass ratio of 1:2.5, exhibited superior viscosity-reducing and stabilizing abilities compared to other dispersants. All SCWSs demonstrated pseudoplastic fluid behavior and showed good agreement with the Herschel-Bulkley model. After the adsorption of dispersants in SC, both the Zeta potential and surface wettability of SC significantly improved, especially with GA-2. The interaction mechanism between the dispersant and SC was analyzed by establishing and employing three adsorption models (M-1, M-2, and M-3). The interfacial adsorption structure confirmed that the dispersant exhibited “surface-to-surface” mode on coal through hydrophobic interaction, hydrogen bonding, and π–π interaction. Energy studies revealed that M-2 with the highest Eads (−105.31 kcal/mol) demonstrated superior adsorption strength compared to M-1 and M-3. Investigations into water molecule mobility revealed that the interaction between the GON-based dispersant and SC resulted in a reduction of water molecule mobility, thereby promoting water molecule aggregation to facilitate the formation of hydration films and enhance SCWS stability. In summary, an optimal oxidation degree of GON was found to be crucial for enhancing the performance of GON-based dispersants; higher oxidation levels may hinder dispersant adsorption on coal surfaces by converting hydroxyl and carboxyl groups into epoxide groups, thus impairing the conjugated structure.

Differential binding of gallic acid and epigallocatechin gallate to whey protein affects the interfacial adsorption and gastric digestion of O/W emulsion

Whey protein isolate (WPI) was reacted with 20, 120, and 240 μmol/g gallic acid (GA) or epigallocatechin gallate (EGCG) at 21 °C. Equilibrium dialysis testing indicated a stronger binding capacity of whey proteins with EGCG compared to GA. Both phenolics, especially EGCG, tended to reduce the adsorption of WPI at the oil–water interface and decreased the elasticity modulus (Ed) of the interfacial film. Yet, binding with 20 μmol/g of EGCG and GA (less so) resulted in significantly improved emulsifying activity of WPI, but the emulsion stability was decreased at all phenolic concentrations (except at 240 μmol/g). There was an overall improvement of pepsinolysis of both α-lactalbumin and β-lactoglobulin. In comparison with GA, EGCG yielded more pronounced effects on WPI interfacial adsorption, dilatational rheology, and peptic digestion.

Investigation of the double layer structure of 1-butyl-3-methylimidazolium thiocyanate at the air-water interface using sum-frequency generation vibrational spectroscopy.

The interfacial structure and adsorption behavior of 1-butyl-3-methylimidazolium thiocyanate ionic liquids (ILs) aqueous solutions were investigated using sum-frequency generation vibrational spectroscopy (SFG-VS) and surface tension measurements. Polarization-dependent measurements revealed a dramatic increase in the SFG signal for both CH and CN stretching modes with increasing ILs concentration, reaching a maximum at a mole fraction of 0.01. This concentration dependence was accompanied by a dramatic drop in surface tension. Upon further increasing the concentration, surface tension varied slightly and reached a constant value, while the SFG signal decreased significantly. Quantitative polarization analysis showed that as the bulk concentration increased, the apparent molecular orientation of the SCN- transition dipole at the interface changed from 51° to 46°, and the tilt angle of CH3 group of the butyl chain attached to the imidazole cationic ring changed from 18° to 32°. The decrease in the SFG signal can be explained by the formation of a double layer adsorption structure at the air/water interface. It was also demonstrated that the anions were adsorbed at the interface simultaneously with the cationic group, rather than by successive adsorption as proposed in a previous study. Using the Shereshefsky model, the thermodynamic Gibbs free energy of adsorption deduced from surface tension data was compared with SFG results.

Tyramine-assisted fluorescent labeling of polysaccharides: Characterization, and interfacial properties

Fluorescence labeling has been widely used in various fields, including fluorescent sensors, biochemistry, medical and chemical research. This study proposed an efficient strategy for the detection and microanalysis of polysaccharides. Soy hull polysaccharide (SHP) was successfully labeled with fluorescein isothiocyanate (FITC) via an amination reaction using tyramine as a linker. The labeled polysaccharide (FTSHP) was characterized by fluorescence, UV–visible, flourier transform infrared (FT-IR), 1H NMR, differential scanning calorimetry (DSC) and interfacial tension. The results indicated that the labeling efficiency of FTSHP with different concentration of FITC (0.20–0.35 wt%) was 1.51 %, 1.58 %, 1.63 %, and 1.67 %, respectively, with fluorescence intensity increasing as FITC concentration increased. Moreover, the interfacial adsorption capacity and thermal stability of FTSHP were significantly improved compared to SHP. This labeling method offers a promising approach for detection and analysis of polysaccharides, providing new insights into the study of other natural polysaccharides.

Effect of gas type on properties of anionic surfactant foam system

The foam drainage technique is considered to be a promising measure for solving the problem of liquid accumulation in natural gas wells and gathering pipelines. However, differences in gases can greatly affect the performance of surfactant foam, thus limiting the application of this technology. To elucidate the mechanism of natural gas components influencing foam properties, the interfacial properties of hydrocarbon gas-surfactant-water system were analyzed thermodynamically and kinetically by combining molecular dynamics simulations and foaming experiments. The results show that with the increasing alkane chain length, the foaming volume and half-life of the foam are gradually rising, while the gas–liquid interfacial tension is decreasing, which is consistent with the results of molecular dynamics simulations. Compared with air, hydrocarbon gases are more beneficial for foam generation and stabilization. The interfacial adsorption of alkane molecules and the interaction between alkanes and surfactants are the main factors affecting the interfacial tension and film stability of different systems.

Amine-modified SiO2 aerogel for efficient adsorption of low-pressure CO2: Response surface methodology optimization and adsorption mechanism

Amine-modified SiO2 aerogel (AMSA) has shown tremendous potential in CO2 capture due to its unique three-dimensional network structure and excellent stability. However, it still faces many challenges in the preparation optimization, adsorption enhancement at low CO2 partial pressure, and mechanism elucidation. Hence, in this paper, the response surface methodology is employed for the first time and the optimal preparation conditions for AMSA are determined. A regression model is successfully established to accurately predict the CO2 adsorption capacity of AMSA under different synthesis conditions (with a relative error of only 0.98 %). Additionally, the AMSA prepared at optimal conditions exhibits high CO2 adsorption capacity of 2.11 mmol/g and excellent stability (only decreased by 1.44 % after 8 cycles) at 10 % CO2 partial pressure, indicating enormous application potential. Notably, the CO2 adsorption mechanism by AMSA at different temperatures and partial pressures are revealed in detail through fitting with the Freundlich isotherm and the double-exponential model, as well as thermodynamic parameter calculations. Firstly, the CO2 adsorption behavior belongs to the multi-layer adsorption behavior with uneven energy of active sites. Secondly, the CO2 adsorption capacity and rate are jointly controlled by molecular motion and chemical reaction equilibrium, diffusion and chemical reaction steps, respectively. Finally, the adsorption process is exothermic and spontaneous, and the level of disorder decreases at the gas-solid interface. This study not only achieves efficient adsorption of low-pressure CO2, but also deepens the understanding of gas-solid interface adsorption mechanisms, providing scientific basis and technological support for the development of novel efficient AMSA adsorbent materials.

Enhancing emulsion stability and adsorption of Pickering emulsions using alkylated cellulose nanofibers

Cellulose nanofibers (CNFs) extracted from plant cell walls form a three-dimensional network in water and stabilize the dispersion of droplets, which are used as emulsion stabilizers. In this study, four types of alkyl-grafted CNFs (ACNFs) with different lengths of dialkyl chains (diC4, diC6, diC8, and diC10) were synthesized by the surface modification of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized CNF (TOCNF) to improve the stability of oil-in-water Pickering emulsions (PEs). The ACNF-stabilized emulsions with a 20/80 ratio of oil/water were prepared using two different oils (olive oil and eucalyptus oil) and the ACNF 1.0 % dispersion, and the changes over time were investigated at approximately 25 °C. Compared to TOCNF, the ACNFs provided more stable olive oil-PE (o-PE) and eucalyptus oil-PE (e-PE) although the stabilization behaviors of o-PE and e-PE differed. Olive oil, which contained rich long-chain fatty acids, was more likely to interact with the ACNFs, thereby promoting the interfacial adsorption of oil droplets. On the other hand, eucalyptus oil is mainly composed of 1,8-cineole and does not have alkyl chains, so the interaction with the ACNFs was weak and therefore, sufficient interfacial adsorption could not be obtained. The results of the particle size distribution and viscosity measurements also showed that the ACNFs contributed significantly to the stabilization of o-PE. Based on the overall experimental results, it was determined that the diC6-ACNF gave the most significant stability improvement. Therefore, we designed an alkylated CNF that mimics diC6-ACNF for MD simulations. MD simulations showed that hydrophobic modification created a hydrophobic interaction between the alkyl chain and dodecane molecules as the oil, leading to the enhancing adsorption of ACNF at the oil droplet interfaces.

Unlocking interfacial effects in NiTiO3-TiO2 eutectic composite: Enhancing overall electrocatalytic and photoelectrochemical water splitting

This study introduces a novel approach to tackle the urgent demand for catalysts possessing both bifunctional capabilities and efficient photocatalytic properties. By employing the micro-pulling down method, a NiTiO3/TiO2 eutectic composite is synthesized, creating an interface rich structure. This composite is utilized as a photo-anode, displaying a significant photocurrent of 3.5 mA/cm2 at 1.4 V. Through annealing in an H2 atmosphere, the catalytic performance is finely adjusted, revealing distinct electrochemical activities at the interface of NiTiO3 and TiO2. Enhanced interfacial adsorption is confirmed by scanning electrochemical microscopy post-annealing. Remarkably, the annealed NiTiO3/TiO2 exhibits outstanding overall water-splitting efficiency, with minimal overpotentials of 80 mV (at 10 mA/cm2) and 120 mV (at 50 mA/cm2) for the HER and OER, respectively. The low Tafel slope (41 mV dec-1) underscores rapid water splitting kinetics. Density functional theory (DFT) calculations suggest that NiTiO3-TiO2 heterostructure can enhanced the catalytic properties of the surface providing higher adsorption of the electrolyte ions during catalytic reactions. This study establishes a straightforward crystal growth strategy for the design of highly effective, enduring, and bifunctional photocatalytic catalysts, signaling promising advancements in water splitting technology.

Influence of hydrophobic groups in polyglycerol ester emulsifier at oil-polyol interface: Interfacial adsorption behavior and its relationship with emulsification effect

This study investigated the variance in adsorption behavior of polyglycerol emulsifiers at the oil- polyol interface and its consequential impact on emulsion properties and stability. The critical micelle concentration (CMCIFT), saturation adsorption capacity (Γ∞), and Langmuir constant (κ) of the emulsifier were determined through measurements of dynamic interfacial tension between glycerol and mineral oil with varying hydrophobic chains. Results indicated that the CMCIFT exhibits an increase corresponding to the rising number of hydrophobic chains. Emulsifiers with differing initial particle sizes were synthesized, and the actual emulsifying area (SA), theoretical covering area (ST), and emulsifying index (EI) at the interface were calculated. Variations in coverage rate led to disparate adsorption behavior and arrangement of the emulsifier at the interface, thereby impacting emulsion stability. This study establishes a theoretical foundation for predicting the stability trend of polyol/oil (P/O) emulsions.

Hydrophobic and positively charged magnetic nanoparticles for enhanced oil recovery from concentrated emulsion wastewaters

With the development of petroleum industry, a large amount of oil-in-water (O/W) emulsion wastewaters were produced, resulting in serious environmental pollution and resource waste. Up till now, magnetic nanoparticles (MNPs) were frequently reported in emulsion wastewater treatment and mainly focused on the water purification, but little effort was devoted to the facile recovery of oil resource. In the present work, a class of hydrophobic and positively charged MNPs, namely dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DOTAC)-coated MNPs (M−DOTAC), was carefully synthesized by regulating DOTAC anchoring density on Fe3O4@SiO2, and then employed to treat the concentrated emulsion wastewaters stabilized by anionic sodium dodecyl benzene sulfonate (SDBS) or nonionic Tween-80. M−DOTAC with relatively high DOTAC density (M−DOTAC 1.8) exhibited higher positive charge density and hydrophobicity, and hence could significantly promote the oil droplet coalescence and mergence via the electrostatic attraction and hydrophobic adsorption bridging as well as the hydrophilic-lipophilic transition of interfacial adsorption layer. Accordingly, with addition of moderate dosage of M−DOTAC 1.8, the emulsion was broken and divided into three layers: (1) a continuous oil layer was formed in the upper layer which could be directly recycled; (2) the middle layer was composed of MNPs-tagged oil droplets/flocs; (3) the bottom layer was the clearer water phase. The optimal recovery rate of oil resource reached ∼ 60 % in SDBS stabilized system, and further increased to ∼ 98 % in Tween-80 stabilized system. However, the oil recovery rate was declined at an excessive dosage of M−DOTAC 1.8 due the formation of double emulsion. Besides, M−DOTAC 1.8 exhibited good reusability. These results indicated the fabricated M−DOTAC had great application prospect in treating emulsion wastewaters containing high oil content.