Surfactant Solubility Research Articles

Formulation and characterization of nanoemulsion biopesticide from Balanite aegyptiaca seed kernel extract

Consumers’ growing awareness and desire for food free of pesticide residues led to the incubation of this research work. The study aimed at developing a nanoemulsion formulation of Balanite aegyptiaca seed kernel extract for use as a biopesticide. A preliminary study was carried out on the solubility and miscibility of surfactant, carrier, and deionized water utilizing the low-energy spontaneous emulsification method. Information from the study was then used to plot a ternary phase diagram (TPD) showing both the isotropic zone and the anisotropic zones, from which a point with a surfactant, oil, and water ratio (20:20:60) was selected from the isotropic zone for the formulation. The developed nanoemulsion was tested for stability and thermostability, and both results revealed the system was stable. Similarly, the physiochemical properties of the developed nanoemulsion system were characterized, and the results showed that the system revealed the following properties: mean particle size of 173.2±21.6, polydispersity index (PDI) of 0.403±0.038, surface tension of 32.53±0.71, viscosity of 37.33±0.67 mPas, and a pH of 4.92±0.02. The formulation appears homogeneous, clear, and transparent, which further indicates it’s a nanoemulsion formulation. Therefore, the nanoemulsion formulation of B. aegyptiaca seed kernel can serve as a safe and environmentally friendly substitute for synthetic pesticides in the management of plant diseases.

Exploring the role of aspartic acid in modulating micellization behavior of cationic cetyltrimethylammonium bromide

The study of the interaction between aspartic acid (Asp) and cetyltrimethylammonium bromide (CTAB) reveals important information about surfactant organization, surface tension, critical micelle concentration (CMC), and surface pressure. Because of enhanced surfactant solubility brought about by electrostatic interactions, Asp’s ionization lowers CTAB’s CMC. The maximal surface excess concentration falls with increasing Asp concentration, suggesting competition for surface adsorption. The minimum occupied area per surfactant molecule increases at the same time, indicating changed surfactant activity at the interface between air and water. Higher CTAB concentrations are associated with a decrease in surface tension, which suggests that when Asp concentration rises, micelle formation would be promoted. Saturation effects, on the other hand, happen at high Asp concentrations and interfere with micelle formation. These tendencies are supported by surface pressure measurements, highlighting the significance of ionic interactions in micelle behavior.Moreover, surfactant structuring is impacted by the packing parameter decreasing as Asp concentration increases. The changing balance between hydrophilic and hydrophobic interactions within the CTAB/Asp micellar complexes is further explained by variations in degree of counterion dissociation of micelles (α) values. The complex dynamics of ionic interactions and their impact on surfactant behavior in CTAB/Asp systems are highlighted by these studies.

The Development and Performance of a Gemini Viscoelastic Surfactant with Tricationic Groups Applied in Unconventional Oil and Gas Reservoir Stimulation

AbstractTo improve water solubility and salt tolerance of viscoelstic surfactants (VESs), modifying the spacer of Gemini VES was adopted and a novel Gemini VES nominated TC‐2OH, with tri‐cationic groups and double hydroxyls on the spacer, was developed. The basic surface activity properties of TC‐2OH and the molecular aggregate behavior stimulated by NaCl or NaSal were measured and analyzed to investigate the mechanism of viscoelastic fluid forming by TC‐2OH solution, and it proved that TC‐2OH is more sensitive to NaSal, compared with NaCl, due to the embedded structure of salicylate. The molecular structure of TC‐2OH imparts excellent solubility to itself, and with the assistance of ethanol, the dissolution time in water can be shortened to within 45 seconds. In addition, oscillation experiments, heat and shear resistant experiments, and drag reduction tests were conducted to study the advantage of NaSal for stimulating the formation of the slickwater compared with NaCl. The slickwater stimulated by NaSal indeed exhibit superior drag reduction and proppant carrying capacity. To effectively disassemble the wormlike micelles for gel breaking, ethylene glycol butyl ether performs better than the hydrocarbons because of its high polarity and water solubility. The gel breaking fluids of slickwater caused extremely low damage to the tight sandstone cores. The successful development of TC‐2OH enables instant preparation of slickwater and variable‐viscosity for fracturing in unconventional reservoirs, which also realizes convenient switching between the slickwater with different viscosity.

Modelling the effect of soluble surfactants on droplet deformation and breakup in simple shear flow

A hybrid lattice Boltzmann and finite difference method is applied to study the influence of soluble surfactants on droplet deformation and breakup in simple shear flow. First, the influence of bulk surfactant parameters on droplet deformation in two-dimensional shear flow is investigated, and the surfactant solubility is found to influence droplet deformation by changing average interface surfactant concentration and non-uniform effects induced by non-uniform interfacial tension and Marangoni forces. In addition, the droplet deformation first increases and then decreases with Biot number, increases significantly with adsorption number $k$ and decreases with Péclet number or adsorption depth; and among the parameters, $k$ is the most influential one. Then, we consider three-dimensional shear flow and investigate the roles of surfactants on droplet deformation and breakup for different capillary numbers and viscosity ratios. Results show that in the soluble case with $k=0.429$ , the droplet exhibits nearly the same deformation as in the insoluble case due to the balance between surfactant adsorption and desorption; upon increasing $k$ from 0.429 to 1, the average interface surfactant concentration is greatly enhanced, leading to significant increase in droplet deformation. The critical capillary number of droplet breakup $C{{a}_{cr}}$ is identified for varying viscosity ratios in clean, insoluble and soluble ( $k=0.429$ and 1) systems. As the viscosity ratio increases, $C{{a}_{cr}}$ first decreases and then increases rapidly in all systems. The addition of surfactants always favours droplet breakup, and increasing solubility or $k$ could further reduce $C{{a}_{cr}}$ by increasing average interface surfactant concentration and local surfactant concentration near the neck during the necking stage.

Coupled bulk and interfacial transport of surfactants governs the settling of a drop towards a wall

Surfactant-like impurities are omnipresent in multiphase emulsions and may substantially affect the motion of small droplets by altering their interfacial properties. Usually these surfactants are soluble in the bulk and undergo adsorption–desorption onto the interface which modifies their surface concentration and hence their overall influence on droplet motion. Yet, the impact of the bulk solubility and transport of surfactants on droplet dynamics, especially in the presence of bounding walls, remains poorly understood. As such, in this article, we assess the impact of bulk soluble surfactants on the settling of a spherical drop towards a plane wall. We consider coupled bulk and interfacial transport of surfactants, mediated by adsorption–desorption processes and construct a semi-analytical framework for arbitrary values of ‘bulk interaction parameter’, which dictates the strength of adsorption–desorption kinetics compared with bulk diffusion. Our results indicate that while mass exchange between the bulk and the interface can remobilize the drop, a finite bulk diffusion rate restricts this process and therefore slows down the drop. This also results in bulk concentration depletion near the south pole and accumulation near the north pole, the extent of which becomes strongly asymmetric with an enhanced intensity of depletion, as the drop approaches the wall. Presence of the wall and bulk solubility are found to aid each other towards remobilizing the drop by aptly modifying the interfacial concentration. Our results may provide fundamental insights into the kinetics of surfactant-laden drops, with potential applications in food and pharmaceutical industries, separation processes, etc.

Fabricating supramolecular lyotropic crystals at subzero temperatures: The pivotal role of antifreeze and nanostructures

The classical lyotropic liquid crystals (LLCs) prepared in pure water are not adapted to subzero temperatures. However, the fabrication of cryogenic LLCs is highly significant for gaining profound insights into self-assembly at extremely low temperatures. A proficient solution strategy, namely introducing alcohol antifreeze to water, faces a challenge in balancing frozen resistance and efficient self-assembly. Herein, we address this unmet challenge by selecting four alcohols with comparable structure to fabricate cryogenic LLCs system through the supramolecular self-assembly of a long-chain non-ionic surfactant. The freezing point, surfactant solubility, and self-assembly behavior at subzero temperatures were investigated. The alcohol antifreeze plays a significant role in depressing water freezing point and governing assembled microstructures. Both experimental and computational results revealed that alcohols bearing more hydroxyl groups are efficient to lower water freezing point while remain the capability to induce surfactant self-assembly. They can realize solvophobic balance and strong hydrogen-bond interactions. A simple approach based on Gordon parameter was established to evaluate the suitability as an anti-freezing medium for amphiphile self-assembly. Strikingly, a new LLCs system capable of withstanding the extremely low temperature of −80 °C was developed, which shows interestingly continuous phase transitions as temperature lowers to subzero. Overall, this study provides valuable insights into cryogenic supramolecular self-assembly, and offers a significant foundation and evaluation method for the selection of appropriate alcohol antifreeze for cryogenic self-assembly.

Effect of surfactants on the degree of polydispersity of a suspension of polystyrene latex spheres

The problem of satisfying the needs of the domestic market of the Russian Federation for creating domestic particle size standard reference materials in liquids to ensure uniformity in measurements of the granulometric composition of aerosols and powdery substances is considered. It is known that, under various conditions, monodisperse suspensions of polystyrene latex spheres can be synthesized, both monodisperse and polydisperse samples being obtainable. The effect of the composition and solubility of surfactants in a styrene-based water emulsion on the particle size of suspensions obtained as a result of emulsion polymerization, and their polydispersity, has been investigated. The metrological characteristics of polystyrene suspensions based on sodium, potassium, and lithium laureths synthesized in this study were determined using dynamic light scattering and laser diffraction techniques. It has been found that the size and degree of polydispersity of particles in suspensions based on lauric acid salts is primarily influenced by the solubility of the surfactant and the surface tension of the interfacial layer formed between styrene and water at the time of particle formation. The effect of the rate of reaction, as well as the concentration of surfactants, on the size and polydispersity of the synthesized particles, has been studied. It has been found that when potassium persulfate is used as the initiator in the reaction, particle size distributions are monodisperse for suspensions based on sodium or potassium laureate. The polydispersity degree of lithium laureate-based suspensions is approximately 1.5 to 2 times higher compared to other suspension samples. When azoisobutyronitrile is used as an initiator, all suspensions samples are monodisperse. It has been experimentally determined that the achievement of monodisperse samples is due to the polymer-monomer particle formation time, which is comparable to the monomer transformation rate. The results obtained will be utilized in the development and establishment of particle size standard reference materials for storage and reproduction of particle size values within a liquid medium.

Exploring the impact of surfactant types and formulation variables on the EACN of crude and model oils

Characterizing the hydrophobicity of oils remains a significant challenge for the academic and industrial scientific communities, striving to optimize the formulation of Surfactant/Oil/Water (SOW) systems. Various descriptors, including the required Hydrophilic-Lipophilic Balance (required HLB) and the Equivalent Alkane Carbon Number (EACN), have been proposed to characterize oil hydrophobicity. Indeed, it is already known that the EACN of crude oils can be rapidly determined through dynamic Phase Inversion Temperature-induced (PIT) experiments. The study herein presents an alternative method to characterize the EACN of crude and model oils through dynamic Salinity-induced Phase Inversion (SPI) using two reference SOW systems, one with the ionic extended surfactant propyl heptyl propoxylated sodium sulfate (i-C3C7PO4SO4Na) and the other with the nonionic surfactant decyl tetraethylene glycol ether (C10EO4). Results reveal that the EACN of crude and model oils strongly depend not only on the chosen formulation variable but also on the nature of the surfactant. Discrepancies in EACN values for crude oils range between −0.2 and 3.3 units. These differences are justified by several factors: the segregation of the polar fraction for crude oils and its dependence with temperature, the high solubility of the nonionic surfactant in polar oils and the differing structures of both surfactants at the interface that changes the effective packing parameter of the system. When inversing a crude oil at high salinity conditions using temperature as formulation variable, a weighted average EACN value obtained with salinity from the two surfactants yields more realistic results than the EACN obtained from PIT. These findings found a direct application in the enhanced oil recovery field in which the attainment of ultra-low interfacial tension is essential to have an efficient crude oil desaturation.

Study on the Properties of Compound Surfactants with PO Groups

The compound surfactant system has considerable development prospects for improving oil recovery. A synergistic effect can be achieved through the orderly arrangement of the two surfactants on the interface, which can make up for the performance defects of a single surfactant. In this paper, the effects of the number of propylene oxides (PO) in composite surfactants on interfacial tension and emulsion stability were systematically studied. The results showed that the solubility of composite surfactants was significantly improved under high-salinity conditions by adding anionic–nonionic surfactants to a single anionic surfactant. The interfacial tension of composite surfactants shows a V-shaped change of first decreasing and then increasing with the increase in PO groups. As the number of PO groups increases, the emulsion first increases and then decreases. Among the series of composite surfactants, LBAS/C12PO10S has the lowest interfacial tension, reaching the order of 10−3 mN/m, and the emulsion formed by it exhibits superior stability. This indicates that the synergistic effect of the two surfactants can be improved by adjusting the number of PO groups. Furthermore, the LBAS/C12PO10S composite system can be mixed with crude oil to form Winsor III microemulsion, which has great potential for application in enhanced oil recovery via chemical flooding.

Dual-responsive emulsion system: Unraveling pH and host-guest interactions for emulsion stability and enhanced oil recovery

Surfactants facilitate the formation of crude oil emulsions in the petroleum reservoir and reduce oil-water interfacial tension, playing a crucial role in tertiary oil recovery. The host-guest interactions between β-cyclodextrin (β-CD) and surfactant molecules can regulate the solubility and hydrophobic interactions of surfactants, further regulating the interfacial and solution aggregation behaviors of the system. A ternary system composed of β-CD, nonionic surfactant Span 80, and anionic amino acid surfactant was designed to act as emulsion stabilizers and promote emulsion formation. Due to the pH responsiveness of the amino acid surfactant and host-guest interactions between the hydrophobic tail of the surfactant and β-CD, the emulsions exhibit dual responsiveness. The pH and β-CD host-guest interaction dual responsiveness determines the emulsion properties. By adjusting the proportion of β-CD in the ternary system and solution pH, the stability, droplet morphology, and rheological properties of the emulsions are all significantly affected. Interactions among emulsion stabilizers as well as their interfacial behaviors were analyzed using 1H NMR spectroscopy and interfacial tension analysis. This type of emulsion was also tested in core flooding experiments, clearly showing that the response of the emulsions to host-guest interactions can enhance crude oil recovery. Incorporating a higher concentration of β-CD into the system can boost additional secondary oil recovery by approximately 32%, while its pH responsiveness facilitates the demulsification of the system after the flooding. These research findings not only highlight the unique properties of the multi-responsive emulsion but also deepen our understanding of the interactions between surfactants. The ternary stabilizer system developed in this study demonstrates broad potential applications in flooding and oil-water separation.

Stability and thinning of liquid jets in the presence of soluble surfactants.

The dynamics of many multiphase fluid systems involve the thinning and eventual break up of a slender fluid filament or a liquid jet. The interfacial instability that controls the rate of jet thinning depends on the relative magnitudes of capillary, viscous, and inertial stresses. Surfactants add an additional layer of physicochemical dynamics by reducing the surface tension of the interface and introducing reverse Marangoni flows in response to surface concentration gradients. Surfactants may also introduce an intrinsic surface rheology that affects jet thinning. Quantifying these effects has been a significant problem in chemical physics and a topic of key research interest. Recent studies have shown that insoluble surfactants delay thread thinning and suppress instabilities in Newtonian jets. However, the role of surfactant solubility in liquid jet stability is still unknown. In this work, we use linear stability analysis to quantitatively show the stabilizing effects of Marangoni stresses, surfactant adsorption and desorption time, and intermolecular forces upon adsorption. We highlight the seemingly indistinguishable way in which various surfactant properties result in the same outcome. We also identify a surface dissipative contribution that arises from the interplay of Marangoni flows with finite adsorption and desorption, which acts as an "apparent" surface viscosity. We verify predictions of our linear stability results against numerical simulations and conclude by noting that tuning surface activity and kinetics of adsorbed surfactants or particles can potentially suppress droplet formation, which is of significant impact in the printing industry and in the control of the spread of aerosols.

Free-energy-based lattice Boltzmann model for emulsions with soluble surfactant

We propose a diffuse interface model to simulate a system of two immiscible liquids with surfactant. This model is based on a modified Ginzburg-Landau free energy functional to account for non-ionic soluble surfactants and couples the Navier-Stokes equations with two Cahn-Hilliard transport equations to represent immiscible fluids and surfactant concentration. The governing equations are solved using a lattice Boltzmann framework. The proposed model is validated for Langmuir and Frumkin adsorption isotherms when applied to simulate a planar interface and a spherical drop equilibration. The model ensures numerical stability and accurate results for low and high surfactant concentrations, and the diffuse interface thickness remains constant even for high surfactant loads. The model also allows achieving a surface tension reduction of 45-50% compared to the clean system, even at low surfactant concentrations. The appropriate surfactant mobility and solubility values are recommended for different values of the strength of nonlinear surfactant coupling.

Geochemical Analysis of Hardness on the Adsorption of Surfactants in Carbonates Under Severe Thermodynamic Conditions: Surface Complexation Modeling Approach

Abstract Several core-flooding-based experimental studies demonstrated the effect of calcium and magnesium ions and it is found that these hard ions have detrimental effects on oil recovery during chemical-enhanced oil recovery operations. However, studies regarding the coupled effect of hard ions and surfactant adsorption are very limited. Thus, this study aims to present a novel approach that can capture mineral-brine, brine-oil, and brine-surfactant interactions in the presence of hard ions (Ca2+ and Mg2+). Also, we introduced four oil-surfactant-based surface complexation geochemical reactions (SCGR) in the presence of hard ions for the first time to analyze the oil-surfactant interactions. The developed thermodynamic-based geochemical model is compared and validated with recent core-flooding data. Our results illustrate that the use of oil-surfactant SCGR is important and should be captured for detailed surfactant adsorption. Thus, we observed that in the presence of hard ions, surfactant adsorption increases with the increase in temperature, which is due to the surge in kinetic energy. We also observed that a reduction in hardness reduces the adsorption of surfactants. Additionally, increasing surfactant concentration led to a minor increase in the adsorption of surfactant with a significant increase in its concentration in the discharge/effluent. Therefore, the hard ions (Ca2+ and Mg2+) concentration has a substantial negative effect, as they reduce the solubility of surfactant and increase its adsorption. Furthermore, the lowest level of surfactant adsorption was accomplished by injecting ten times diluted water (<0.070 mg/g).

Adsorption of surfactant molecules onto the surface of colloidal particles: Case of like-charged species

Mixed systems of nanoparticles and surfactants have a broad range of applications from consumer products and medicine to inkjet printing and oil recovery. The interparticle interactions can be tuned in presence of surfactants and are dependent on surface charge of both species, particle’s wettability, surfactant solubility, and solution conditions such as electrolyte concentration and pH. The case of oppositely charged particles and surfactants has been extensively examined in the literature, primarily to tune the wettability of particles. In contrast, the behavior in systems of like-charged species such as negatively charged particles and anionic surfactants remains poorly understood, with conflicting findings reported in previous studies on the adsorption of surfactants. By conducting a comprehensive investigation, in this study we shed light on the factors that influence the adsorption of surfactant onto the particle surface, both promoting and preventing it, and unravel the underlying mechanisms governing such behavior. Silica nanoparticles were used as the negatively charged particle, sodium dodecyl sulfate (SDS) was used as the surfactant and potassium nitrate was used as the salt, while the pH was adjusted by potassium hydroxide and nitric acid, to investigate the effect of surfactants on the surface characteristics of the silica nanoparticles under various operating conditions. The zeta potential of particles along with the solution conductivity were obtained via mobility measurements. Using this information, the solution’s Debye length and the particle’s surface charge density were estimated. It was found that interpreting the outcome solely based on the zeta potential data might not reveal the adsorption of SDS onto the particle surface as no supercharging effect could be detected in some cases. However, shifting the perspective to charge density shows that SDS increased the particles charge density for pH values in the range of 2–5, corresponding to the pH conditions at which vicinal and geminal silanol groups are dissociated. This effect was more pronounced at moderate total ionic strengths between 1 and 10 mM, where SDS activity was found to be higher and the Debye length was sufficiently short. The increase in the particle’s charge density was attributed to the tail-down adsorption of SDS onto the particle surface via entropically-driven interactions. These findings offer valuable insights into like-charged mixed particle/surfactant systems and bring clarity to the scientific community regarding this complex and previously inconclusive topic.

Studies on the Synthesis and Application Properties of a Betaine Surfactant with a Benzene Ring Structure

Two novel betaine surfactants with distinct hydrophilic headgroups were synthesized, including carboxybetaine surfactant (DCB) and sulfobetaine surfactant (DSB). Their properties of reducing the interfacial tension (IFT) of Xinjiang crude oil/water were studied under alkaline-free conditions, as were their thermal stability, wettability, and emulsification properties. The chemical structures of the target products were characterized and analyzed by using 1H-NMR and 13C-NMR. The experimental results indicate that the introduction of a benzene ring to the hydrophobic group can improve the solubility and high-temperature resistance of the betaine surfactant. Thermogravimetric analysis showed that the degradation temperature of the synthesized betaine was above 190 °C. As the concentration of the betaine solution increased, DSB (0.0750 mmol/L) showed a lower critical micelle concentration (CMC) than DCB (0.1852 mmol/L). The wetting ability of DCB was significantly higher than that of DSB, and their contact angles on paraffin film decreased to 28.36° and 35.26°. In addition, both DCB and DSB can reduce the IFT of Xinjiang crude oil/water to ultra-low levels (10−3 mN/m) in the absence of alkali. The appropriate ion concentration has a synergistic effect on the surfactant to reduce the interfacial tension of oil/water and the effect of the three ions on the interfacial tension was as follows: Na+ < Ca2+ < Mg2+.

Recent Advances in Improving the Bioavailability of Hydrophobic/Lipophilic Drugs and Their Delivery via Self-Emulsifying Formulations

Formulations based on emulsions for enhancing hydrophobic and lipophilic drug delivery and its bioavailability have attracted a lot of interest. As potential therapeutic agents, they are integrated with inert oils, emulsions, surfactant solubility, liposomes, etc.; drug delivering systems that use emulsion formations have emerged as a unique and commercially achievable accession to override the issue of less oral bioavailability in connection with hydrophobic and lipophilic drugs. As an ideal isotropic oil mixture of surfactants and co-solvents, it self-emulsifies and forms fine oil in water emulsions when acquainted with aqueous material. As droplets rapidly pass through the stomach, fine oil promotes the vast spread of the drug all over the GI (gastrointestinal tract) and conquers the slow disintegration commonly seen in solid drug forms. The current status of advancement in technologies for drug carrying has promulgated the expansion of innovative drug carriers for the controlled release of self-emulsifying pellets, tablets, capsules, microspheres, etc., which got a boost for drug delivery usage with self-emulsification. The present review article includes various kinds of formulations based on the size of particles and excipients utilized in emulsion formation for drug delivery mechanisms and the increase in the bioavailability of lipophilic/hydrophobic drugs in the present time.

Interplay of bulk soluble surfactants and interfacial kinetics governs the stability of two-layer channel flows.

The linear stability of two-layer channel flows in the presence of bulk-soluble surfactants is investigated here, taking into account the rheological properties of the interface. The interfacial stresses are quantified using the Boussinesq-Scriven model, while the surfactant kinetics is assumed to follow the Frumkin isotherm, which accounts for their non-ideal behavior. Our results show that in general, the bulk solubility of surfactants has a stabilizing effect on the interface, both with and without the presence of inertia. On the other hand, the interfacial viscosities play a more complex role, depending on the viscosity ratios of the two fluids, the thickness of the fluid layers, the strength of the surface tension gradients, and the extent of inertia. We show that depending on the strength of inertia and the variability in the surface tension, the interfacial rheology may either stabilize or destabilize the base flow. However, for sufficiently small Reynolds numbers, the surface viscosity always has a stabilizing influence. Our results may be used to better design stable co-flow systems with applications in various processes such as surface coating, preparation of fluid lenses, as well as in a host of multi-purpose microfluidic devices.

Understanding the Hydration Thermodynamics of Cationic Quaternary Ammonium and Charge-Neutral Amine Surfactants.

Aqueous solubility and interfacial adsorption of surfactants are important for numerous applications. Using molecular dynamics, we have studied the effect of the type of the polar headgroup (cationic quaternary ammonium and charge-neutral amine) and length of the alkyl tail on the hydration free energy of surfactants in infinite dilution. In addition, we have studied the effect of replacing the terminal methyl group of the alkyl tail with a more polar hydroxyl group on the hydration free energy. Quaternary ammonium surfactants have strongly favorable hydration free energies, whereas charge-neutral amine surfactants have unfavorable hydration free energies. The contribution of the quaternary ammonium group in reducing the hydration free energy is estimated to be as large as ∼63 kBT and that of the charge-neutral amine group to be 3 kBT. Both surfactants and their corresponding alkanes have minima in the free energy at the air-water interface. The quaternary ammonium group contributes to a 6 kBT decrease in the free energy of transfer from air-water interface to bulk aqueous phase (termed henceforth as interface transfer free energy). The amine group, on the other hand, has a net zero interface transfer free energy. The interface transfer free energies of surfactants are both enthalpically and entropically unfavorable. The enthalpic penalty is attributed to the loss of water-water interactions. Interestingly, surfactant molecules gain entropy upon their transfer from the air-water interface to the aqueous phase, but this increase is more than compensated by the loss in the entropy of water molecules, presumably due to the ordering of water molecules around the surfactants. Replacing the terminal methyl group of the alkyl tail with a hydroxyl group in quat surfactants reduces their hydration free energy by 10 kBT, thus making them more soluble in water. Attaching a hydroxyl group to the alkyl tail also inhibits their micelle forming tendency in the bulk aqueous phase. Overall, this work reveals how tuning the molecular characteristics of surfactants can help to achieve the desirable aqueous solubility, interfacial properties, and micellization tendency of surfactants.

Development and Evaluation of Topical Ethosomal Gel for Fungal Infections.

Fungal infections are one of the most common dermatological issues worldwide. Candida species-caused fungal infections are frequent on the cutaneous surface. Eberconazole (EBZ) has the strongest antifungal action against Candida spp., the major source of fungal infections. In the present study, the cold method followed by probe sonication was used to create EBZ-loaded ethosomal dispersion. The solubility of ethosomes in different lipids and surfactants was used to choose these components. Under magnetic stirring, the dispersion was absorbed into a carbopol 934 gel. In vitro antifungal activity was performed using the Agar well diffusion method, and their topical effectiveness against pathogenic Candida albicans was compared to that of a marketed formulation containing EBZ. Eberconazol incorporated into gel displayed sustained release in an in vitro release assay. Based on the zone of inhibition diameters, EBZ formulation was determined to be efficient against C. albicans when compared to the commercialized cream and plain gel. Based on these findings, the current study found that EBZ possesses significant antifungal efficacy against C. albicans.

Surfactant-laden film lining an oscillating cap: problem formulation and weakly nonlinear analysis

A surfactant-laden liquid film that lines the inside of an oscillating spherical cap is considered as a model of lung alveoli. Pulmonary surfactant solubility is described by Langmuir adsorption kinetics, modified by incorporating the intrinsic compressibility of the adsorbed monolayer. A novel boundary condition, supported by experimental data and scaling arguments, is applied at the rim. The condition enforces mass conservation of water and surfactant by matching the ‘large-scale’ dynamics of the alveolus to ‘small-scale’ equilibrium over mid-alveolar septa of small but finite thickness. Linear and weakly nonlinear analysis around the conditions in a non-oscillating cap indicates that the occurrence of shearing motion in the liquid is related to the non-zero film thickness over the rim, and shearing velocity at the interface is predicted an order-of-magnitude lower than the velocity of radial oscillation. Marangoni stresses dominate the interfacial dynamics, but capillary stresses affect significantly the interior flow field. In particular, they produce spatial modulations in flow rate, surface concentration of surfactant and wall shear stress, whose length scale varies with $Ca^{-1/3}$ , i.e. is determined by a balance between capillary and viscous forces. Non-zero adsorption kinetics modifies at first order only the amplitude and phase of surface concentration, but affects all other variables at second order. In particular, it sets a steady drift of surfactant away from the alveolus and towards the rim. Finally, an attempt is made to relate the present predictions to physiological findings about air flow and particle deposition inside alveoli, and about shear stress-inflicted damage in diseased lungs.