High-throughput viscoelastic characterization of cells in hyperbolic microchannels

Extensive research has demonstrated the potential of cell viscoelastic properties as intrinsic indicators of cell state, functionality, and disease. For this, several microfluidic techniques have been developed to measure cell viscoelasticity with high-throughput. However, current microchannel designs introduce complex stress distributions on cells, leading to inaccuracies in determining the stress-strain relationship and, consequently, the viscoelastic properties. Here, we introduce a novel approach using hyperbolic microchannels that enable precise measurements under a constant extensional stress and offer a straightforward stress-strain relationship, while operating at a measurement rate of up to 100 cells per second. We quantified the stresses acting in the channels using mechanical calibration particles made from polyacrylamide (PAAm) and found that the measurement buffer, a solution of methyl cellulose and phosphate buffered saline, shows strain-thickening following a power law up to 200 s-1. By measuring oil droplets with varying viscosities, we successfully detected changes in the relaxation times of the droplets and our approach could be used to get the interfacial tension and viscosity of liquid-liquid droplet systems from the same measurement. We further applied this methodology to PAAm microgel beads, demonstrating the accurate recovery of Young's moduli and the near-ideal elastic behavior of the beads. To explore the influence of altered cell viscoelasticity, we treated HL60 human leukemia cells with latrunculin B and nocodazole, resulting in clear changes in cell stiffness while relaxation times were only minimally affected. In conclusion, our approach offers a streamlined and time-efficient solution for assessing the viscoelastic properties of large cell populations and other microscale soft particles.

Quantitative investigation of surfactant monolayer bending tendency at an oil-polar solvent interface using DPD modeling and artificial neural networks

The bending tendency of a surfactant monolayer at an interface is critical in determining the type of emulsion formed and the proximity of the emulsion system to its equilibrium state. Despite its importance, the influence of interaction and surfactant structure on the bending tendency has not been quantitatively investigated. In this study, we develop and validate an artificial neural network (ANN) model based on the torque densities from dissipative particle dynamics (DPD) simulations to address this gap. With the validated ANN model, the relationship between surfactant monolayer bending tendency and all the interaction parameters, oil size, and surfactant structure (size and tail branching) was derived, from which the significance of each factor was ranked. With this ANN model, both the relationship and factor analysis can be instantly investigated without further DPD modeling. Furthermore, we expand the study to surfactant-oil-polar solvent (SOP) systems by varying the interaction parameters between polar solvents (PP). Our finding indicates that the interaction between polar solvents plays an important role in determining the bending tendency of surfactant monolayers; weaker intermolecular attraction between polar solvents makes surfactants tend to bend toward the oil phase (tend to form oil in polar solvent emulsion). Factor analysis reveals that increasing the repulsion between head-head (HH) or head-oil (HO) makes the model surfactants more polar-solvophilic, while increasing the repulsion between polar solvent-head (PH), tail-tail (TT) or oil-oil (OO) makes the model surfactants more lipophilic. The ANN model effectively reproduces the dependence of surfactant monolayer bending tendency on oil size, consistent with experimental observations, the larger the oil size, the higher the bending tendency toward the oil phase. The most intriguing insight derived from the ANN model here is that the effect of branching in the lipophilic tail will be enhanced by factors that make surfactants behave more lipophilic in a surfactant-oil-polar solvent (SOP) system, for rather polar-solvophilic surfactants, the effect of tail branching is negligible.

Effect of surfactant concentration on diffusion and microstructure in water-in-oil emulsions studied by low-field benchtop NMR and optical microscopy

Emulsions are ubiquitous in many consumer products, including food, cosmetics and pharmaceuticals. Whilst their macroscopic characterisation is well-established, understanding their microscopic behaviour is very challenging. In our previous work we investigated oil-in-water emulsions by studying the effect of water on structuring and dynamics of such systems. In the present work, we investigate the effect of surfactant concentration on microstructure and diffusion within the water-in-oil emulsion system by using low-field pulsed-field gradient (PFG) NMR studies carried out with a benchtop NMR instrument, in conjunction with optical imaging. The results reveal that at high surfactant concentration the formation of smaller droplets gives rise to a third component in the PFG NMR attenuation plot, which is mostly attributed to restricted diffusion near the droplet boundaries. In addition, structuring effects due to increase in surfactant concentration at the boundaries could also contribute to further slowing down water diffusion at the boundaries. As the surfactant concentration decreases, the average droplet size becomes larger and both restriction and structuring effects at the droplet boundaries become less significant, as suggested by the PFG NMR plot, whereby the presence of a third diffusion component becomes less pronounced.

Unconventional and conventional Pickering emulsions: Perspectives and challenges in skin applications

Pickering emulsions are free from molecular and classical surfactants and are stabilized by solid particles, creating long-term stability against emulsion coalescence. Additionally, these emulsions are both environmentally and skin-friendly, creating new and unexplored sensorial perceptions. Although the literature mostly describes conventional emulsions (oil-in-water), there are unconventional emulsions (multiple, oil-in-oil and water-in-water) with excellent prospects and challenges in skin application as oil-free systems, permeation enhancers and topical drug delivery agents, with various possibilities in pharmaceutical and cosmetic products. However, up to now, these conventional and unconventional Pickering emulsions are not yet available as commercial products. This review brings to the discussion some important aspects such as the use of phases, particles, rheological and sensorial perception, as well as current trends in the development of these emulsions.

Tween-80 on Water/Oil Interface: Structure and Interfacial Tension by Molecular Dynamics Simulations

Surfactants are used in many fields of the chemical industry in a wide range of applications. Generally, surfactants on water/oil interfaces reduce interfacial tension, enabling the formation of emulsions or providing greater stability to the emulsion formed. Although molecular dynamics has been extensively used and has achieved remarkable success in describing thermodynamic and molecular properties of systems with surface-active compounds, the traditional molecular simulation force fields considerably constrain the system size and the time scale of simulations. Here, we propose a coarse-grained model of polysorbate 80, a nonionic surfactant commercially known as Tween-80. Based on the proposed coarse-grained model, we evaluate the influence of the more internal ethylene oxide chain on the properties of the water/Tween-80/decane system. We verify with the simulation results that the model can reproduce the expected decrease in interfacial tension as the surfactant quantity increases in the simulations. Furthermore, we observe changes in the surfactant orientation as their quantity in the interface increases, indicating a preferential orientation for these molecules in the adsorption layer. We also assessed the partition coefficient of the surfactant between the two bulk phases by performing free energy calculations, which showed a higher affinity of Tween-80 surfactants with the water phase.

Formulation and Characterization of a Novel Palm-Oil-Based α-Mangostin Nano-Emulsion (PO-AMNE) as an Antimicrobial Endodontic Irrigant: An In Vitro Study

Aim: To formulate and characterize a palm-oil-in-water-based α-Mangostin nano-emulsion (PO-AMNE) endodontic irrigant, in order to evaluate its antibacterial efficacy against Enterococcus faecalis, Staphylococcus epidermidis, and Candida albicans biofilms, as well as its capacity to remove smear layer. Methods: The solubility of α-Mangostin in various oils was determined and selected, surfactants and co-surfactants were used for the nano-emulsion trial. PO-AMNE was prepared and optimized. The MIC was performed, and the antimicrobial efficacy was estimated against biofilms. The optimized 0.2% PO-AMNE irrigant antimicrobial efficacy in a tooth model was done using colony-forming units. The treated teeth were processed by scanning electron microscopic examination for debris and smear layer removal. An Alamar Blue assay was used to evaluate cell viability. The optimization of the PO-AMNE irrigant was performed using Box–Behnken statistical design. Results: The optimized 0.2% PO-AMNE irrigant was found to have a particle size of 340.9 nm with 0.246 PDI of the dispersed droplets, and a zeta potential (mV) of −27.2 ± 0.7 mV. The MIC values showed that 0.2% PO-AMNE (1.22 ± 0.02) were comparable to 2% CHX (1.33 ± 0.01), and 3.25% NaOCl (2.2 ± 0.09) had the least inhibition for E. faecalis. NaOCl (3.25%) showed the maximum inhibition of S. epidermidis (0.26 ± 0.05), whereas 0.2% PO-AMNE (1.25 ± 0.0) was comparable to 2% CHX (1.86 ± 0.07). For C. albicans, 2% CHX (8.12 ± 0.12) showed the least inhibition as compared to 0.2% PO-AMNE (1.23 ± 0.02) and 3.25% NaOCl (0.59 ± 0.02). The 0.2% PO-AMNE irrigant was then evaluated for its antimicrobial efficacy against the three biofilms, using colony-forming units. The 0.2% PO-AMNE was comparable to both 3.25% NaOCl and 2% CHX in inhibiting the growth of biofilms. The 0.2% PO-AMNE and 17% EDTA eliminated the smear layer with the lowest mean scores (p < 0.001). Finally, 0.2% PO-AMNE was shown to be biocompatible when compared to 17% EDTA, 3.25% NaOCl, and 2% CHX in immortalized oral keratinocyte cells. Conclusion: Overall, the formulated 0.2% PO-AMNE irrigant was an effective antimicrobial and biocompatible which could combat endodontic-infection-related polymicrobial biofilms.

Biodegradation and optimization of bilge water in a sequencing batch reactor using response surface methodology

Bilge water is a significant source of pollution in the marine environment and has captured widespread international attention. In this study, a sequencing batch reactor (SBR) combined with strain S2 identified as Bacillus licheniformis was employed to assess the biodegradation of Chemical Oxygen Demand (COD) from bilge water. The influencing variables such as temperature, pH level and inoculum concentration on the performance SBR system were optimized by utilizing response surface methodology (RSM). The experimental results showed that the maximum COD removal of 77.81% was reached at the optimal SBR operation conditions of temperature 35.44 °C pH 8.13, and inoculum concentration 31.47 mL. In the practical application of SBR, it was found that the decrease in hydraulic retention time (HRT) was accompanied by a decrease in COD degradation rate. The biodegradation kinetics of COD in bilge water were well fitted with the first-order equation with a higher R² value of 0.98106. In conclusion, COD in bilge water can be efficiently biodegraded by SBR under the optimization of RSM.

Comprehensive review of the interfacial behavior of water/oil/surfactant systems using dissipative particle dynamics simulation

A comprehensive understanding of interfacial behavior in water/oil/surfactant systems is critical to evaluating the performance of emulsions in various industries, specifically in the oil and gas industry. To gain fundamental knowledge regarding this interfacial behavior, atomistic methods, e.g., molecular dynamics (MD) simulation, can be employed; however, MD simulation cannot handle phenomena that require more than a million atoms. The coarse-grained mesoscale methods were introduced to resolve this issue. One of the most effective mesoscale coarse-grained approaches for simulating colloidal systems is dissipative particle dynamics (DPD), which bridges the gap between macroscopic time and length scales and molecular-scale simulation. This work reviews the fundamentals of DPD simulation and its progress on colloids and interface systems, especially surfactant/water/oil mixtures. The effects of temperature, salt content, a water/oil ratio, a shear rate, and a type of surfactant on the interfacial behavior in water/oil/surfactant systems using DPD simulation are evaluated. In addition, the obtained results are also investigated through the lens of the chemistry of surfactants and emulsions. The outcome of this comprehensive review demonstrates the importance of DPD simulation in various processes with a focus on the colloidal and interfacial behavior of surfactants at water-oil interfaces.

Suppression of Filament Defects in Embedded 3D Printing

Embedded 3D printing enables the manufacture of soft, intricate structures. In the technique, a nozzle is embedded into a viscoelastic support bath and extrudes filaments or droplets. While embedded 3D printing expands the printable materials space to low-viscosity fluids, it also presents new challenges. Filament cross-sections can be tall and narrow, have sharp edges, and have rough surfaces. Filaments can also rupture or contract due to capillarity, harming print fidelity. Through digital image analysis of in situ videos of the printing process and images of filaments just after printing, we probe the effects of ink and support rheology, print speeds, and interfacial tension on defects in individual filaments. Using model materials, we determine that if both the ink and support are water-based, the local viscosity ratio near the nozzle controls the filament shape. If the ink is slightly more viscous than the support, a round, smooth filament is produced. If the ink is oil-based and the support is water-based, the capillary number, or the product of the ink speed and support viscosity divided by the interfacial tension, controls the filament shape. To suppress contraction and rupture, the capillary number should be high, even though this leads to trade-offs in roughness and roundness. Still, inks at nonzero interfacial tension can be advantageous, since they lead to much rounder and smoother filaments than inks at zero interfacial tension with equivalent viscosity ratios.

Study on the formation and stability of polyol-in-oil emulsion

In this study, the influence of polyols, emulsifiers and oils on the formation and stability of polyol-in-oil (P/O) emulsions was investigated. The interfacial tension in P/O systems is much lower than that of water-oil systems, so polyols and oils showed a greater affinity, which was not conducive to the stability of the emulsion system. High compatibility of the emulsifier and the inner and outer phases was the key to the formation of stable emulsions. Using polyethylene glycol 400 (PEG) as polyol phase, mineral oil or squalane as oil phase and cetyl PEG/PPG-10/1 dimethicone (EM 90) as emulsifier, long-term stable P/O emulsions with homogeneous droplets were successfully prepared.

DPD Simulation on the Transformation and Stability of O/W and W/O Microemulsions

The dissipative particle dynamics simulation method is adopted to investigate the microemulsion systems prepared with surfactant (H1T1), oil (O) and water (W), which are expressed by coarse-grained models. Two topologies of O/W and W/O microemulsions are simulated with various oil and water ratios. Inverse W/O microemulsion transform to O/W microemulsion by decreasing the ratio of oil-water from 3:1 to 1:3. The stability of O/W and W/O microemulsion is controlled by shear rate, inorganic salt and the temperature, and the corresponding results are analyzed by the translucent three-dimensional structure, the mean interfacial tension and end-to-end distance of H1T1. The results show that W/O microemulsion is more stable than O/W microemulsion to resist higher inorganic salt concentration, shear rate and temperature. This investigation provides a powerful tool to predict the structure and the stability of various microemulsion systems, which is of great importance to developing new multifunctional microemulsions for multiple applications.

Compound Cleaning Agent for Oily Sludge from Experiments and Molecular Simulations

This paper reported a new oily sludge compound cleaning agent formula, which used a combination of molecular simulation and experimental methods to study its interfacial formation energy (IFE), and exciting results were obtained. From a total of 24 surfactants in five categories, sodium silicate (Na₂SiO₃), sodium dodecylbenzene sulfonate, and fatty alcohol polyoxyethylene polyoxypropylene ether (JFC-SF) were screened out because of their excellent washing oil effect. Under a reasonable orthogonal system, when the mass ratio of the three surfactants was 3:1:1, the oil desorption effect was the best, the oil residual rate could reach 2.13%, and the oil removal efficiency could reach 93.53%. Verified by the molecular dynamics simulation module, the absolute value of the interface binding energy was the largest at this compound ratio, which was 465.71 kcal/mol. More importantly, we have discussed in depth the mechanism of adsorption and permeation of oily sludge by cleaning agents. Through single-factor influence experiments, the following optimized working condition parameters of the cleaning agent were determined: cleaning conditions with an agent content of 4%, a temperature of 70 °C, a stirring speed of 400 rpm, a cleaning time of 30 min, and a liquid-solid ratio (L/S) of 4:1. The research results laid the foundation for resource utilization, harmlessness, and reduction of oily sludge in the Liaohe oilfield.

Molecular modeling of interfacial layer-by-layer assembly towards functionalized capsule materials

Encapsulated nanomaterials, such as polymer-coated nanoemulsions, have highly tunable properties leading to versatile applications. A current lack of understanding of the fundamentals governing the choice of "capsule" materials (polyelectrolyte + surfactant) and its ensuing performance effectively precludes their widespread use. Computational methods can start to redress this by discovering molecule-scale attributes that significantly control the design of capsule materials tuned to fit desired properties. We use molecular dynamics (MD) to carry out the layer-by-layer (LbL) assembly of six unique polyelectrolyte bilayer systems at a surfactant-mediated interface, modeling early-stage capsule synthesis. Monolayer thickness is related to layer density and polyelectrolyte/surfactant interaction energy through polyelectrolyte molecular weight and radius of gyration, respectively, yielding a simple relationship between absorption kinetics and layer structure. For the second monolayer, faster absorption kinetics are observed for pairings of polyelectrolytes with similarly sized functional groups. Surfactants with a more delocalized charge on the head-group catalyze the build-up of ions at the interface, resulting in faster absorption kinetics and greater confinement of the encapsulated material but leading to thicker, less uniform bilayers. These relationships between capsule building block molecules and nanomaterial capsule properties provide a foundation for property prediction and rational design of optimized multi-functional capsule materials.

Biodegradable Amphoteric Surfactants in Titration-Ultrasound Formulation of Oil-in-Water Nanoemulsions: Rational Design, Development, and Kinetic Stability

Amphoteric amphiphilic compounds, due to their unique properties, may represent a group of safe and biocompatible surface-active agents for effective colloidal stabilization of nanoformulations. For this reason, the aim of this work was to develop and characterize the oil-in-water nanoemulsions based on two betaine-derived surfactants with high biodegradability, i.e., cocamidopropyl betaine and coco-betaine. In the first step, we investigated ternary phase diagrams of surfactant-oil-water systems containing different weight ratios of surfactant and oil, as the betaine-type surfactant entity (S), linoleic acid, or oleic acid as the oil phase (O), and the aqueous phase (W) using the titration-ultrasound approach. All the received nanoemulsion systems were then characterized upon droplets size (dynamic light scattering), surface charge (electrophoretic light scattering), and morphology (transmission electron as well as atomic force microscopy). Thermal and spinning tests revealed the most stable compositions, which were subjected to further kinetic stability analysis, including turbidimetric evaluation. Finally, the backscattering profiles revealed the most promising candidate with a size <200 nm for potential delivery of active agents in the future cosmetic, pharmaceutical, and biomedical applications.

Development of organogel-based emulsions to enhance the loading and bioaccessibility of 5-demethylnobiletin

5-Demethylnobiletin (5-DMN), identified in the aged citrus peels, has received increasing attentions due to its outstanding bioactivity among citrus polymethoxyflavones (PMFs). However, the poor water solubility and high crystallinity limit its oral bioavailability. Besides, the solubility of 5-DMN in the oil is very limited, which restricts its loading capacity in emulsions for bioavailability enhancement. In this study, an organogel formulation was developed to improve the solubility of 5-DMN in medium-chain triacylglycerols by 3.5 times higher without crystal formation during 5-day storage at room temperature. Increasing the gelator (i.e., sugar ester) concentration led to the increase of viscosity and a gel-like structure of the organogel. The ternary phase diagram of organogel-based emulsions was explored, and 40% organogel was selected as the oil phase for emulsion preparation. Increasing the concentration of Tween 80 from 0% to 6% decreased the droplet size and viscoelasticity of the emulsions. Two in vitro models, the pH-stat lipolysis model and TNO gastro-intestinal model (TIM-1), were applied to investigate the bioaccessibility of 5-DMN in different delivery systems. Compared with the conventional emulsion and oil suspension, the pH-stat lipolysis demonstrated that the organogel-based emulsion was the most efficient tool to enhance 5-DMN bioacccessibility. Moreover, TIM-1 digestive study indicated that 5-DMN bioaccessibility delivered by organogel-based emulsions was about 3.26-fold higher than that of oil suspension. Our results suggested that the organogel-based emulsion was an effective delivery route to enhance the loading and bioaccessibility of lipophilic compounds of high crystallinity.

Effect of Electrolytes on Solution and Interfacial Behaviors of Double Chain Cationic-Nonionic Surfactant Mixtures for Hydrophobic Surface Wetting and Oil/Water Emulsion Stability Applications

The solution behaviors of the binary mixture of double chain cationic surfactant didodecyldimethylammonium bromide (DDAB) with nonionic surfactants of varied head groups, EO-9 and EO-40, in the presence and absence of electrolytes were studied and found nonideal behavior. The different physicochemical properties such as Gibb's surface excess (Γ), minimum area per molecule (A_min), and interaction parameters at bulk (β^M) and interface (β^σ) were calculated. In the presence of nonionic surfactants, lowering of CMC, CVC, and surface tension at these two concentrations of DDAB were observed. The β^M and β^σ values indicate strong interaction between DDAB and EO-40 mixed system. Further, addition of electrolytes to the mixed systems show increased interaction and change of physicochemical properties because of the combination of electrical and salting out effects.

Effects of ethylene oxide chain length on crystallization of polysorbate 80 and its related compounds

As a result of the synthesis protocol polyoxyethylene sorbitan monooleate (polysorbate 80, PS80) is a highly complex mixture of compounds. PS80 was therefore separated into its main constituents, e.g. polyoxyethylene isosorbide esters and polyoxyethylene esters, as well as mono- di- and polyesters using preparative high-performance liquid chromatography. In this comprehensive study the individual components and their ethoxylation level were verified by matrix assisted laser desorption/ionization time-of-flight and their thermotropic behavior was analyzed using differential scanning calorimetry and X-ray diffraction. A distinct correlation was found between the average length of the ethylene oxide (EO) chains in the headgroup and the individual compounds' ability to crystallize. Importantly, a critical number of EO units required for crystallization of the headgroup was determined (6 EO units per chain or 24 per molecule). The investigation also revealed that the hydrocarbon tails only crystallize for polyoxyethylene sorbitan esters if saturated. PS80 is synthesized by reacting with approximately 20 mol of EO per mole of sorbitol, however, the number of EO units in the sorbitan ester in commercial PS80 products is higher than the expected 20 (5 EO units per chain). The complex behavior of all tested compounds revealed that if the amount of several of the linear by-products is reduced, the number of EO units in the chains will stay below the critical number and the product will not be able to crystallize by the EO chains.

A strategy for power generation from bilgewater using a photosynthetic microalgal fuel cell (MAFC)

Microbial fuel cells (MFCs) have recently been applied to generate electricity from oily wastewater. Although MFCs that utilize microalgae to provide a self-supporting oxygen (O₂) supply at the cathode have been well discussed, those with microalgae at the anode as an active biomass for treating wastewater and producing electrons are still poorly studied and understood. Here, we demonstrated a bilgewater treatment using single- and double-chamber microalgal fuel cells (SMAFC and DMAFC) capable of generating energy with a novel microalgal strain (Chlorella sorokiniana) that was initially isolated from oily wastewater. Compared to previous MFC studies using green algae, relatively high voltage output (151.3-160.1 mV, 71.3-83.4 mV m^-2 of power density) was observed in the SMAFC under O₂ controlled systems (i.e., acetate addition or light/dark cycle). It was assumed that, under the O₂ depletion, alternative electron acceptors such as bicarbonate may be utilized for power generation. A DMAFC showed better power density (up to 23.9%) compared to the SMAFC due to the separated cathode chamber which fully utilizes O₂ as an electron acceptor. Both SMAFC and DMAFC removed 67.2-77.4% of soluble chemical oxygen demands (SCOD) from the synthetic bilgewater. This study demonstrates that the application of algae-based MFCs is a feasible strategy to treat oil-in-water emulsion while generating electricity.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters β^m and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (K_m) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.

Preparation and characterization of nanosized lignin from oil palm (Elaeis guineensis) biomass as a novel emulsifying agent

A study was carried out to determine the effectiveness of lignin, extracted from oil palm (Elaeis guineensis) biomass as water-in-oil (W/O) emulsifying agent. To achieve this goal, soda lignin (SL) was extracted via soda pulping process and a series of nanosized soda lignin (NSL) were prepared using homogenizer at three different speed i.e. 10,400 rpm (NSL 10), 11,400 rpm (NSL 11) and 12,400 rpm (NSL 12) for one hour. All prepared samples were characterized by FT-IR, UV-Vis spectroscopy, thermogravimetric analysis (TGA), zeta potential analyser, Transmission Electron Microscope (TEM) and Extreme High Resolution Field Emission Scanning Electron Microscope (XHR-FESEM). The result of FTIR showed that there is no prominent change occurred in spectra of all samples while a good stability was reflected by TGA curves. The percentage of creaming index and visual observations of all samples demonstrated that NSL 12 and dosage 2 g (out of 1 g, 1.5 g and 2 g) were found to be the best among all samples. Furthermore, the results of IFT indicate that NSL 12 was proven to be more stable than the commercial product. Therefore, NSL 12 is selected for toxicological studies and was found safe in both, in vitro and in vivo studies.

Synthesis of Guerbet Amine-Oxide for Enhanced Oil Recovery

Guerbet amine-oxide was synthesized by using Guerbet acid, N,N′-diethyl-1,3-propanediamine and hydrogen peroxide. Its structure was confirmed by FT-IR spectra and mass spectra. The critical micelle concentration (CMC) and the interfacial tension between the crude oil and water were measured. The results showed that the CMC of the Guerbet amine-oxide is 2.14 × 10−5 mol/L and the interfacial tension could be lowered to ultralow levels. The core flood test showed that the surfactant and polymer binary system could increase oil recovery by 24.7% above the water flood.

Different strategies of foam stabilization in the use of foam as a fracturing fluid

An attractive alternative to mitigate the adverse effects of conventional water-based fluids on the efficiency of hydraulic fracturing is to inject foam-based fracking fluids into reservoirs. The efficiency of foaming fluids in subsurface applications largely depends on the stability and transportation of foam bubbles in harsh environments with high temperature, pressure and salinity, all of which inevitably lead to poor foam properties and thus limit fracturing efficiency. The aim of this paper is to elaborate popular strategies of foam stabilization under reservoir conditions. Specifically, this review first discusses three major mechanisms governing foam decay and summarizes recent progress in research on these phenomena. Since surfactants, polymers, nanoparticles and their composites are popular options for foam stabilization, their stabilizing effects, especially the synergies in composites, are also reviewed. In addition to reporting experimental results, the paper also reports recent advances in interfacial properties via molecular dynamical simulation, which provide new insights into gas/liquid interfacial properties under the influence of surfactants at molecular scale. The results of both experiments and simulations indicate that foam additives play an essential role in foam stability and the synergic effects of surfactants and nanoparticles exhibit more favorable performance.

In-situ activated nanoparticle as an efficient and recyclable foam stabilizer for enhancing foam separation of LAS

Linear alkylbenzene sulfonate (LAS) is a particular member of the emerging contaminants, because of its increasingly ubiquitous use and tremendous harm to the environment and wastewater treatment plant. Herein, we develop a novel two-stage foam separation to recover LAS (18.7-91.0 mg/L) from laundry wastewater. We first reported the fabrication of activated silica nanoparticle (SNP) via a facile and scalable in-situ approach. To obtain a desirable surface property, the key design element was the utilization of amphoteric surfactant, viz. cocamidopropyl betaine, as the modifier. In the first-stage, activated SNP could serve as an efficient foam stabilizer to improve the foam stability and the interfacial adsorption of LAS. Remarkably, LAS concentration in effluent decreased to very low levels of 1.9-2.9 mg/L with a proper enrichment ratio, and met the emission standard. In the second-stage, we originally adopted the intensification of liquid drainage to selectively recycle activated SNP from LAS. An inclined foam channel (IFC) covered by hydrophobic coating was constructed and the maximum recovery percentage of SNP reached 91.5%, indicating that the activated SNP was recyclable. This work definitely proves that the integration of nanotechnology in foam separation can make wastewater treatment more efficient and less expensive.

Protobiotic Systems Chemistry Analyzed by Molecular Dynamics

Systems chemistry has been a key component of origin of life research, invoking models of life's inception based on evolving molecular networks. One such model is the graded autocatalysis replication domain (GARD) formalism embodied in a lipid world scenario, which offers rigorous computer simulation based on defined chemical kinetics equations. GARD suggests that the first pre-RNA life-like entities could have been homeostatically-growing assemblies of amphiphiles, undergoing compositional replication and mutations, as well as rudimentary selection and evolution. Recent progress in molecular dynamics has provided an experimental tool to study complex biological phenomena such as protein folding, ligand-receptor interactions, and micellar formation, growth, and fission. The detailed molecular definition of GARD and its inter-molecular catalytic interactions make it highly compatible with molecular dynamics analyses. We present a roadmap for simulating GARD's kinetic and thermodynamic behavior using various molecular dynamics methodologies. We review different approaches for testing the validity of the GARD model by following micellar accretion and fission events and examining compositional changes over time. Near-future computational advances could provide empirical delineation for further system complexification, from simple compositional non-covalent assemblies towards more life-like protocellular entities with covalent chemistry that underlies metabolism and genetic encoding.

Antimicrobial emulsions: Formulation of a triggered release reactive oxygen delivery system

The enzyme glucose oxidase mediates the oxidation of glucose to produce reactive oxygen species (ROS), such as hydrogen peroxide. This reaction and its products are key to providing honey with its antimicrobial properties. Currently, honey is an adherent, highly viscous product that produces ROS by means of a water-initiated reaction. These properties reduce clinical usability and present a formulation problem for long term stability. This study aims to engineer a water-in-oil emulsion containing an engineered honey (SurgihoneyRO™) that is easy to administer topically and is controllably activated in-situ. Paraffin oil continuous emulsions formulated using the emulsifier polyglycerol polyricinoleate displayed shear-thinning characteristics. Viscosities between 1.4 and 19.3 Pa·s were achieved at a shear rate representative of post-mixing conditions (4.1 s^-1) by changing the volume of the dispersed phase (30-60%). Notably, this wide viscosity range will be useful in tailoring future formulations for specific application mechanisms. When exposed to water and shear, these emulsion systems were found to undergo catastrophic phase inversion, evidenced by a change in conductivity from 0 μS in the non-aqueous state, to >180 μS in the sheared, inverted state. Encouragingly, sheared formulations containing ≥50% SurgihoneyRO™ generated sufficient levels of ROS to inhibit growth of clinically relevant Gram-positive and Gram-negative bacteria. This study demonstrates an ability to formulate ROS producing emulsions for use as an alternative to current topical antibiotic-based treatments. Promisingly, the ability of this system to release water-sensitive actives in response to shear may be useful for controlled delivery of other therapeutic molecules.

Surfactant addition to enhance bioavailability of bilge water in single chamber microbial fuel cells (MFCs)

Effective remediation of bilge water, a shipboard oily liquid waste, is important for both commercial and military vessels due to the domestic and international regulations. In this study, bilge water was used as a substrate for exoelectrogenic bacteria and biodegradation of bilge water and concurrent electricity generation were investigated using Pseudomonas putida ATCC 49128 in single chamber microbial fuel cells (MFCs). To enhance bioavailability of the bilge water, two types of surfactants were added (100 ppm) into the oily wastewater containing 0.1% standard bilge mix (SBM) and their impacts on electricity production were evaluated under various conditions. Anionic surfactant (sodium dodecyl sulfate, SDS) addition increased soluble chemical oxygen demand (SCOD) by forming micelle, producing maximum power density of 225.3 ± 3.2 mW m^-2. However, the MFC with nonionic surfactant (Triton X-100) produced only 2.3 ± 0.1 mW m^-2 due to no enhancement on biodegradable SCOD. A high NaCl concentration (100-500 mM) adversely affected power production due to decrease in available SCOD caused by emulsion coalescence. This is a first study to use surfactants to enhance bioavailability of non-biodegradable oily wastewater in a single chamber MFC.

Quillaja Saponin Characteristics and Functional Properties

Consumer concerns about synthetically derived food additives have increased current research efforts to find naturally occurring alternatives. This review focuses on a group of natural surfactants, the Quillaja saponins, that can be extracted from the Quillaja saponaria Molina tree. Quillaja saponins are triterpenoid saponins comprising a hydrophobic quillaic acid backbone and hydrophilic sugar moieties. Commercially available Quillaja saponin products and their composition and properties are described, and the technofunctionality of Quillaja saponins in a variety of food, cosmetic, and pharmaceutical product applications is discussed. These applications make use of the biological and interfacial activities of Quillaja saponins and their ability to form and stabilize colloidal structures such as emulsions, foams, crystallized lipid particles, heteroaggregates, and micelles. Further emphasis is given to the complexation and functional properties of Quillaja saponins with other cosurfactants to create mixed surfactant systems, an approach that has the potential to facilitate new interfacial structures and novel functionalities.

An Evaluation of the Physicochemical Properties of Stabilized Oil-In-Water Emulsions Using Different Cationic Surfactant Blends for Potential Use in the Cosmetic Industry

One of the most complex problems in hair care formulations is the duality of the surfactants used. In this regard, such surfactants must be cationic so as to interact with the negatively charged cuticle surface of hair. However, these interdependencies typically lead to non-ideal values for the required hydrophilic–lipophilic balance (HLB) in the oil phase. This study was designed to evaluate the physicochemical properties of several oil-in-water emulsion prototypes for the potential use in hair conditioners. Here, a base formulation was utilized, incorporating binary mixtures of cationic surfactants in different proportions. The cationic surfactants employed were hydroxyethyl-behenamidopropyl-diammonium chloride, behentrimonium methosulphate, cetrimonium chloride, and (iv) Polyquaterniumpolyquaternium-70. The surfactants were evaluated for their capability to decrease the surface tension in an aqueous solution through contact angle measurements between the oily phase and the aqueous phase. The required HLB of the oil phase was also determined. The emulsification process was developed using standard preparation methods. For three months, the prototypes with high viscosity were packed in containers and stored in a stability chamber at accelerated conditions (40 ± 2 °C and 75 ± 5% RH). During this time, the size, size polydispersity, zeta potential, viscosity, rheological profile, and creaming index were all evaluated monthly. The results showed a slight change in the physical stability of the prototypes, where the droplet size increased moderately, however, did little to destabilize the formulations. This suggests that the mixtures of cationic surfactants used could be useful for technological developments in hair conditioning products.

Nanodroplets at Membranes Create Tight-Lipped Membrane Necks via Negative Line Tension

The response of biomembranes to aqueous-phase separation and to the resulting water-in-water droplets has been recently studied on the micrometer scale using optical microscopy and elasticity theory. When such a droplet adheres to the membrane, it forms a contact area that is bounded by a contact line. For a micrometer-sized droplet, the line tension associated with this contact line can usually be ignored compared with the surface tensions. However, for a small nanoscopic droplet, this line tension is expected to affect the membrane-droplet morphology. Here, we use molecular simulations to study nanodroplets at membranes and to gain insight into these line tension effects. The latter effects are shown to depend strongly on another key parameter, the mechanical tension experienced by the membrane. For a large membrane tension, a droplet adhering to the membrane is only partially engulfed by the membrane, and the membrane-droplet system exhibits an axisymmetric morphology. A reduction of the membrane tension leads to an increase in the contact area and a decrease in the interfacial area of the droplet, initially retaining its axisymmetric shape, which implies a circular contact line and a circular membrane neck. However, when the tension falls below a certain threshold value, the system undergoes a morphological transition toward a non-axisymmetric morphology with a non-circular membrane neck. This morphology persists until the nanodroplet is completely engulfed by the membrane and the membrane neck has closed into a tight-lipped shape. The latter morphology is caused by a negative line tension, which is shown to be a robust feature of membrane-droplet systems. A closed membrane neck with a tight-lipped shape suppresses both thermally activated and protein-induced scission of the neck, implying a reduction in the cellular uptake of nanodroplets by pinocytosis and fluid-phase endocytosis. Furthermore, based on our results, we can also draw important conclusions about the time-dependent processes corresponding to the surface nucleation and growth of nanodroplets at membranes.

Formulation of oil-in-water emulsions for pesticide applications: impact of surfactant type and concentration on physical stability

Oil-in-water (O/W) emulsions can be utilized as effective pesticide delivery systems in the agricultural industry. In this study, the effects of hydrophile-lipophile balance (HLB), concentration, and location of surfactants on the formation and physical stability of O/W emulsions suitable for pesticide applications was investigated using dynamic light scattering and vertical laser profiling. A non-polar pesticide (lambda-cyhalothrin) was used as a model. The pesticide emulsion with the highest stability was obtained using a commercial non-ionic surfactant (polyoxyethylene castor oil ether, EL-20) with a required HLB value of 10.5. Emulsion stability increased as the surfactant concentration was increased from 2 to 6%, which was attributed to the formation of smaller oil droplets during emulsification. Emulsions prepared with the surfactant initially in the oil phase were more stable than those prepared with it initially in the aqueous phase. The optimum formulation of the pesticide emulsion was determined as follows: 5% lambda-cyhalothrin (active ingredient) and 6% EL-20 (surfactant) dissolved in 5% S-200 (aromatic hydrocarbon, as oil phase), then deionized water up to 100%, which met the quality indicators set by the FAO standards. The present study is expected to provide useful information to improve the stability of pesticide emulsions for commercial applications.

Emulsions in porous media: From single droplet behavior to applications for oil recovery

Emulsions are suspensions of droplets ubiquitous in oil recovery from underground reservoirs. Oil is typically trapped in geological porous media where emulsions are either formed in situ or injected to elicit oil mobilization and thus enhance the amount of oil recovered. Here, we briefly review basic concepts on geometrical and wetting features of porous media, including thin film stability and fluids penetration modes, which are more relevant for oil recovery and oil-contaminated aquifers. Then, we focus on the description of emulsion flow in porous media spanning from the behaviour of single droplets to the collective flow of a suspension of droplets, including the effect of bulk and interfacial rheology, hydrodynamic and physico-chemical interactions. Finally, we describe the particular case of emulsions used in underground porous media for enhanced oil recovery, thereby discussing some perspectives of future work. Although focused on oil recovery related topics, most of the insights we provide are useful towards remediation of oil-contaminated aquifers and for a basic understanding of emulsion flow in any kind of porous media, such as biological tissues.