Surfactant Distribution Research Articles

Development of a New Dry Powder Aerosol Synthetic Lung Surfactant Product for Neonatal Respiratory Distress Syndrome (RDS) – Part II: In vivo Efficacy Testing in a Rabbit Surfactant Washout Model

PurposeSurfactant therapy incorporates liquid bolus instillation via endotracheal tube catheter and a mechanical ventilator in preterm neonates with respiratory distress syndrome (RDS). Aerosolized surfactants have generated interest and conflicting data on the efficacy of phospholipid (PL) dose requirements. We developed and characterized a synthetic lung surfactant excipient enhanced growth (SLS-EEG) dry powder aerosol product. In this study, we compare the in vivo performance of the new aerosol product with standard-of-care liquid instillation.MethodsJuvenile rabbits were sedated, anesthetized, intubated, and ventilated. Endogenous surfactant was depleted via whole lung lavage. Animals received either a standard dose of liquid Curosurf (200 mg PL/kg) instilled via a tracheal catheter, SLS-EEG powder aerosol (60 mg device loaded dose; equivalent to 24 mg PL/kg), or sham control. Gas exchange, lung compliance, and indices of disease severity were recorded every 30 min for 3.5 h and macro- and microscopy images were acquired at necropsy.ResultsWhile aerosol was administered at an approximately tenfold lower PL dose, both liquid-instilled and aerosol groups had similar, nearly complete recoveries of arterial oxygenation (PaO2; 96–100% recovery) and oxygenation index, and the aerosol group had superior recovery of compliance (P < 0.05). The SLS-EEG aerosol group showed less lung tissue injury, greater uniformity in lung aeration, and more homogenous surfactant distribution at the alveolar surfaces compared with liquid Curosurf.ConclusionsThe new dry powder aerosol SLS product (which includes the delivery strategy, formulation, and delivery system) has the potential to be a safe, effective, and economical alternative to the current clinical standard of liquid bolus surfactant instillation.

Thin-film flow due to an asymmetric distribution of surface tension and applications to surfactant deposition

Thin-film equations are utilised in many different areas of fluid dynamics when there exists a direction in which the aspect ratio can be considered small. We consider thin free films with Marangoni effects in the extensional flow regime, where velocity gradients occur predominantly along the film. In practice, because of the local deposition of surfactants or input of energy, asymmetric distributions of surfactants or surface tension more generally, are possible. Such examples include the surface of bubbles and the rupture of thin films. In this study, we consider the asymmetric thin-film equations for extensional flow with Marangoni effects. Concentrating on the case of small Reynolds number $ Re $ , we study the deposition of insoluble surfactants on one side of a liquid sheet otherwise at rest and the resulting thinning and rupture of the sheet. The analogous problem with a uniformly thinning liquid sheet is also considered. In addition, the centreline deformation is discussed. In particular, we show analytically that if the surface tension isotherm $\sigma = \sigma (\varGamma )$ is nonlinear (surface tension $\sigma$ varies with surfactant concentration $\varGamma$ ), then accounting for top–bottom asymmetry leads to slower (faster) thinning and pinching if $\sigma = \sigma (\varGamma )$ is convex (concave). The analytical progress reported in this paper allows us to discuss the production of satellite drops from rupture via Marangoni effects, which, if relevant to surface bubbles, would be an aerosol production mechanism that is distinct from jet drops and film drops.

Marangoni flows triggered by cationic-anionic surfactant complexation

HypothesisThe gradients in surfactant distribution at a fluid-fluid interface can induce fluid flow known as the Marangoni flow. Fluid interfaces found in biological and environmental systems are seldom clean, where mixtures of various surfactants are present. The presence of multi-component surfactant mixtures introduces the possibility of interactions among constituents, which may impact Marangoni flows and alter flow dynamics. ExperimentsWe employed flow visualization, surface tension and reaction kinetic measurements, and numerical simulations to quantitatively investigate the Marangoni flows induced by the reacting surfactant mixtures. Different binary surfactant mixtures were utilized for comparative analysis. FindingsThe impact of surfactant interactions on Marangoni flows is confirmed through the observation of diverse complex flow patterns that result from the combination of oppositely charged surfactants in varying composition ratios and concentrations. Unique flow patterns originate from the composition-dependent interfacial phenomena upon mixing surfactants. Our findings provide vital insights that could be used to guide the development of effective oil remediation or the spreading of waterborne pathogens in contaminated regions.

A comparative study of surfactant distribution and fate (western and eastern) Egyptian Mediterranean coasts focusing on its environmental toxicity

One of the most difficult-to-manage new contaminants constantly released into the environment is linear alkylbenzene sulphonate (LAS), an anionic surfactant. Significant volumes of LAS are received by the Mediterranean coast of Egypt. The current study is a comprehensive assessment of the environmental fate of the LAS 1505 km off the Mediterranean coast of Egypt in the fall of 2023 in order to track its geographic spread and eventual demise in the water column. Critical analysis of LAS revealed that it is vertically distributed in various ways according to sources, uses, production amounts, and salinity levels. The vertical variation of LAS can be explained by its amphiphilic structure. A significant increase in surfactant concentration (>300 μg/L) was recorded in 66% and 43% of the total samples, ranging from 301.128 to 455.36 and from 304.556 to 486.135 for the western and eastern sides along the Egyptian Mediterranean coast, respectively. Evaluation of the average acute and chronic risk quotient (RQ) along the investigated locations revealed that fish were the most susceptible to LAS in both long and short exposure periods. The presented results also indicated significant LAS toxicity to three trophic levels (RQ values > 1). LAS toxicity to marine organisms was greater in the western than in eastern coastal regions according to acute and chronic mixture risk characterization ratios (RCRmix). The three trophic levels in the study area had the following order of acute relative contribution (RC) to LAS toxicity: fish > invertebrates > algae. The ANOVA test results showed that in both the western and eastern regions, LAS varied significantly (p < 0.05) with salinity (1.04E-60 and 5.44E-42) and depth (6.02E-65 and 1.59E-47), respectively. In addition, a significant difference was observed using the ANOVA test between the eastern and western regions of the Egyptian Mediterranean coast.

Finite ion size effects on electrophoresis of a dielectric surfactant-laden droplet in a non-dilute electrolyte

The ion steric repulsion and ion-solvent interactions, due to the finite size of ions, are analyzed for electrophoresis of a droplet in a non-dilute electrolyte in which the ionic volume fraction is O(0.01). In this study, the viscosity of the suspension medium is considered to be dependent on the local ionic volume fraction. The electrochemical potential of the finite-sized ions is modified to take into account the steric interactions. The impact of the Marangoni stress due to the non-uniform distribution of the non-ionized surfactant is taken into account. Governing equations are solved under a weak applied field consideration. At a lower range of surface charge density, the mobility is found to increase with the droplet viscosity, in which the Marangoni stress is found to enhance the mobility. The counterion saturation created by the ion steric interaction attenuates the screening of the surface charge and hence, enhances the mobility. However, the enhanced viscosity of the medium for the non-dilute electrolyte reduces the mobility and this reduction is higher in a monovalent electrolyte as compared to a multivalent electrolyte. The standard model shows a singularity in mobility when the surface potential is varied. However, the dependence of mobility on surface potential in the modified model is found to exhibit a smooth variation.

Distribution and suitability of pulmonary surfactants as a vehicle for topically applied antibodies in healthy and SARS-CoV-2 infected rodent lungs

The use of natural pulmonary surfactants (PS) as a drug delivery vehicle for biologics is a more recent therapeutic modality. Herein, we tested different contents of PS regarding their physicochemical properties under stress conditions. The PS content of 12.25 mg/ml (Formulation B) showed desired properties such as an isotonic osmolality ∼300 mOsm/kg and an acceptable viscosity of 8.61 cSt, being lower than in commercially available PS solutions. Formulation B passed the specifications of surface lowering capacities of >80 % total lung capacity and physiologically desired formulation properties were independent of the antibody used in the composition. The identified formulation showed the capability of significantly increasing the oxygen saturation in ex vivo isolated perfused rat lungs, compared to a control and up to 30 min post lavage. In the in vivo setting, we showed that intratracheal administration of a human mAB with and without pulmonary surfactant led to higher amounts of delivered antibody within the alveolar tissue compared to intravenous administration. The antibody with the PS formulation remained longer in the alveolar tissues than the antibody without the PS formulation. Further, SARS-CoV-2 infected Golden Syrian hamsters showed that the intranasally applied antibody reached the site of infection in the alveoli and could be detected in the alveolar region 24 h after the last administration. With this work, we demonstrated that pulmonary surfactants can be used as a pulmonary drug delivery mechanism for antibodies and may subsequently improve the antibody efficacy by increasing the residence time at the desired site of action in the alveolar tissue.

Experimental study on heat transfer performance enhancement of pulsating heat pipes induced by surfactants

Pulsating heat pipe (PHP) is considered as a promising technique to address the thermal dissipation issues in micro-electronic devices, but its heat transfer performance needs to be further enhanced urgently. In this study, the PHP comprehensive performance experimental system was established. Then, the influence of surfactant sodium dodecyl sulfate (SDS) aqueous solution on the heat transfer performance of PHP was experimentally investigated and the visualization of PHP with surfactant was also accomplished. Additionally, based on Marangoni effect and surface tension, a comprehensive analysis was conducted on the impact mechanism of surfactants on PHP. The experimental results indicated that the oscillatory disturbance of the liquid slug inside the PHP is enhanced by the addition of SDS, and the resulting pressure imbalance and temperature difference enhance the directional flow of the working fluid. Meanwhile, under the operating conditions of 30 W working thermal power and the solution concentration of 0.001 wt%, the thermal resistance of PHP was reduced by 30.7 % compared with that of deionized water (DI water). This indicated that the working fluid with low concentration SDS could increase the area of liquid film and reduce the thermal resistance, which is induced by the surface tension and Marangoni effect due to the uneven distribution of surfactants. However, the thermal resistance of PHP with the SDS concentration of 0.2 wt% is higher than that of DI. This means that high concentration of SDS would deteriorate the startup characteristics and the heat transfer performance of PHP. Therefore, high concentrations of surfactants should be avoided from practical application of PHP.

Surfactant-laden liquid thread breakup driven by thermal fluctuations

The breakup of liquid threads into droplets is crucial in various applications, such as nanoprinting, nanomanufacturing, and inkjet printing, where a detailed understanding of the thinning neck dynamics allows for a precise droplet control. Here, the role of surfactant in the breakup process is studied by many-body dissipative particle dynamics, in particular, the various regime transitions and thread profiles, shedding light on molecular-level intricacies of this process hitherto inaccessible to continuum theory and experiments. Moreover, the role of surfactant in the most unstable perturbation, the formed droplet size, and surfactant distributions have been unraveled. As surfactant concentration rises, both the wavelength and time to breakup steadily increase due to the lowering of surface tension below the critical micelle concentration (CMC) and viscous effects introduced by micelles above the CMC. These changes prior to the breakup lead to larger droplets being formed in cases with higher surfactant concentration. We also compared the thinning dynamics to existing theoretical predictions, revealing that the surfactant-laden breakup starts at the inertial regime and transitions into the thermal fluctuation regime when the concentration is increased. Thus, we illuminate the hitherto poorly investigated and intricate breakup process of surfactant-laden liquid threads driven by thermal fluctuations, contributing to a deeper understanding of this process at molecular scales.

Design and fabrication of a three-dimensional asymmetric neonate lung model to study surfactant transport in airways

Neonatal respiratory distress syndrome is a potentially life-threatening condition that is often treated with the delivery of exogenous surfactants through a process called surfactant replacement therapy. This therapy includes the administration of the liquid surfactant through an endotracheal tube and mechanical ventilation. Due to the difficulty of imaging neonate lungs during this therapy, the success of surfactant delivery is often determined by observational techniques and evaluation of blood oxygen levels. The limitation of imaging creates challenges in evaluating the distribution of surfactant in airways. To address this limitation, we designed a computational, eight-generation, asymmetric neonate lung model using morphometric data to mimic the geometric structure of the human airway tree and fabricated it using an additive manufacturing technique. We used our model to study two-aliquot delivery of a clinically rated liquid surfactant under two different orientations to evaluate its distribution in airways. Our study offers a complex lung airway tree design that mimics the native geometry of the human airway tree to enable studies of therapeutics transport in airways.

Improved lattice Boltzmann model for moving contact-line with soluble surfactant

Modeling moving contact-line with surfactant has become a widely sought methodology due to its scientific relevance and extensive applications. Within the phase field framework, we present an improved lattice Boltzmann (LB) model for simulating moving contact-line dynamics with soluble surfactant. In this model, a LB equation is used to solve the Navier–Stokes equations, and another two LB equations are utilized to solve the two Cahn–Hilliard-like equations. The modified chemical potentials are incorporated in the LB model by using an equivalent variant of the free energy functional and the corresponding equilibrium distribution functions are also amended. These modifications could circumvent the degraded accuracy of previous LB models in capturing the interfacial behavior and surfactant distribution, and also improve the well-posedness of the LB model. In addition, a dynamic contact angle formulation is introduced to account for the surfactant effect on surface wettability and the resulting contact angle is further implemented in the LB model via a popular geometrical wetting approach. We comprehensively evaluate the numerical performance of the LB model by simulating some benchmark problems. It is found that the LB model achieves a higher accuracy than previous LB models in solving the phase field and surfactant profiles, and also numerical prediction of moving contact-line dynamics with surfactant shows good agreement with the analytical solution. Finally, the LB model is applied to investigate droplet shearing dynamics on solid substrate. The influences of capillary number and solid wetting property on droplet deformation and breakup are analyzed in detail.

Dynamics of surfactant-laden drops in shear flow by lattice Boltzmann method

We developed and applied a diffuse interface lattice Boltzmann method for simulating immiscible liquids with soluble surfactants using a modified Ginzburg–Landau free energy functional. We first validated the approach through simulations of planar interfaces and drop equilibration in quiescent fluid. The proposed method accurately captures the phase and surfactant fields with diminishing spurious velocities of 10−6. We systemically examined the effects of capillary number, comparing viscous to surface forces, the combined effect of surfactant and viscosity ratio (λ) of the drop to the continuous phase, and the bulk surfactant load on the deformation and breakage in a shear flow. At a given capillary number (0.05&amp;lt;Ca&amp;lt;0.32), drop behavior is influenced by reduced surface tension, tip-stretching, Marangoni stresses, and surface dilution. These effects either promote (by tip-stretching) or hinder (via Marangoni stresses, surface dilution) the surfactant distribution at the interface, consequently affecting the final drop morphology. As Ca increases, the competition between the viscosity ratio and the presence of surfactant determines drops' topological changes. The presence of surfactants can overcome the effect of viscosity ratio (when 0.05≤λ≤1.7) and promote drop breakup, whereas highly viscous drops (either λ&amp;lt;0.05 or λ&amp;gt;1.7) do not break. Furthermore, high surfactant loads result in higher drop deformation and earlier drop breakup. In brief, our method successfully captures the dynamics of surfactant-laden drops in shear flow, elucidating the complex interplay between flow hydrodynamics and surfactant transport with 3D quantitative phase and surfactant concentration fields.

Effects of surfactants on droplet deformation and breakup in water-in-oil emulsions under DC electric field: A molecular dynamics study

The presence of surfactants in water-in-oil (W/O) emulsions can increase the susceptibility of water droplets to breakup under an electric field, resulting in intensified emulsification. To elucidate the mechanism underlying the electrodynamic behavior of surfactant-containing water droplets in oil, this study has employed molecular dynamics (MD) simulations to investigate the impact of surfactants on droplet deformation and breakup under a DC electric field. The results indicate that despite the formation of hydrogen bonds between surfactants and water molecules, a higher number of van der Waals interactions were formed between them. Upon reaching maximum deformation, the droplet experiences a reduction in deformation due to increased steric hindrance of the oil phase and decreased surfactant adsorption. Eventually, the droplet reaches a steady state with a lower degree of deformation. The enhanced dispersion attraction between n-hexane and Span-80 facilitates the migration of surfactants to the oil phase, weakening the interaction between surfactants and the droplets. The migration of the surfactant drags the surrounding water molecules, increasing droplet deformation. During droplet deformation, hydrogen bonds with a lifetime of 0.88 ps can be formed between the surfactants. The combined influence of hydrated ions, surfactant-related interactions, media effects, and migration effects leads to the breakup of surfactant-containing droplets. During droplet breakup, there is an uneven distribution of surfactants on the droplet surface. Increasing the concentration of surfactants appropriately can prolong the time required for droplet breakup. The simulation findings presented in this paper offer new insights and inspiration for enhancing the electrostatic demulsification of emulsions containing surfactants.

PH and redox dual-responsive Pickering emulsion based on silica nanoparticles and novel ferrocene surfactant

Responsive Pickering emulsions capable of responding to external stimuli have been extensively studied, however, there are few studies on double-responsive Pickering emulsions. Here in, a novel ferrocene surfactant (FcACUa) was synthesized and combined with aminated silica nanoparticles (0.5 wt%) to stabilize pH and redox sensitive smart Pickering emulsions. The carboxyl groups act as pH-sensitive parts, while ferrocene serves as the redox-responsive center. Stability and pH/redox response performance of the emulsions were investigated through various methods, such as the contact angle, macroscopic states, creaming index, microscopic images, droplet size distributions, etc. All atom molecular dynamics and dissipative particle dynamics simulations were used to probe the distribution of nanoparticles and surfactant at the water-oil interface, as well as to reveal the stabilization and pH/redox response mechanisms of the Pickering emulsions. Pickering emulsions can be reversibly switched between stable and unstable by adding HCl and NaOH or adding H2O2 and N2H4·H2O. After five pH-induced cycles, the emulsion shows no significant degradation or morphological changes. However, for the redox induced emulsification demulsification process, the size of the emulsion drops increases with the increase of the number of cycles. This work provides insights into the Pickering emulsion stabilization mechanism and the regulation mechanisms of pH and redox stimulation, which may have potential value in emulsion polymerization, biphasic catalysis, and oil and gas transportation.

Molecular Dynamics Simulation of the Effects of Complex Surfactants on Oil-Water Interaction and Aggregation Characteristics at the Interface.

In response to the problem of complex interaction between oil and water in the oil-water interface, especially heavy oil and water, this study investigated the effects of complex surfactants on the interaction of two phases and their aggregation characteristics by molecular dynamics simulation. The results showed that increasing the content of sodium lauryl polyether carboxylate (AEC-9Na) was beneficial to the coordination between it and alkyl glycoside (APG-10), improved the interfacial activity, and enhanced the interfacial stability of the composite system, and the best effect was achieved when AEC-9Na:APG-10 = 8:2. The thickness of the oil and water film on the oil-water interface was irregular. When the concentration of AEC-9Na was lower than that of APG-10, the total thickness of the interfacial film (ttotal) first increased. When the content of AEC-9Na is higher, a large number of sodium ions were adsorbed near the -COO- group of AEC-9Na, which will polarize out of the hydration layer structure and attract water molecules from the second hydration layer on the heavy oil surface to the first hydration layer through electrostatic interaction. Then, the thickness of the interface film was compressed, and the interface film was reduced. When the ratio increased to 10:0, the oil and water phase competed to adsorb surfactant molecules, and the headgroup tended to lay on the interface. Moreover, the hydrophilicity of the surfactant layer was weakened, and the thickness of the water film decreased. The distribution of surfactant was looser than 8:2, the light components of heavy oil molecules (saturated and aromatic hydrocarbons) entered the gap between surfactants in large quantities, and the hydrophobic tail chain tended to be laid on the oil-water interface. The oleophilicity of the surfactant layer increased, and the thickness of the oil film remarkably increased, so the total thickness of the interface film increased again.

Experimental investigation on the effect of interfacial properties of chemical flooding for enhanced heavy oil recovery

Chemical compound flooding has demonstrated its efficacy in enhancing light oil recovery through ultra-low interfacial tension (IFT). However, the optimization of chemical systems properties for displacing heavy oil has not been clarified. This research aims to address this problem by designing common polymer and three surfactant-polymer (SP) systems with varying IFT and interfacial viscoelasticity behaviors, and comparing their ability to recover heavy oil. The findings of core flooding tests indicate that the system with low IFT and high interfacial viscoelasticity simultaneously has a better displacement efficiency for heavy oil than other flood systems, which could enhance heavy oil recovery by 21.94%. Micro-model tests reveal the underlying mechanisms driving the enhanced macro-scale oil recovery. The emulsion formation and interface expansion facilitated by low IFT, as well as increased emulsion stability and reduced snap-off of oil droplets due to the presence of an elastic oil-water interfacial film. These phenomena is more capable of driving microscopic heterogeneous remaining oil and film remaining oil than other solution. The comparative experiment analysis shows that the difference in chemical flooding between heavy oil and light oil is caused by the discrepant distributions of surfactants at the oil-water interface. The light oil interface is a monolayer surfactant molecular film, the heavy components and surfactant moleculars exhibit both competitive and cooperative adsorption phenomena at the oil-water interface. The occurrence of viscosity reduction and increased emulsion stability are more influential factors in the process of heavy oil displacement than those of conventional ultra-low IFT systems used for light oil recovery.

Unraveling the effect of surfactant on the preparation of 40 nm Cu2O nanofluids for enhanced thermal conductivity

The state of the adsorbed surfactant molecules significantly impacts the formation of nanoparticles and their application. In this study, using sodium dodecyl sulfate (SDS) as an anion surfactant, the size and size distribution of Cu2O nanocubes were well regulated through simply altering the introduced concentration of SDS. Moreover, the state of the surfactant on the surface of Cu2O nanocubes was systematically characterized by HRXPS and Ar ion etching. It found that SDS and dehydroascorbic acid are co-adsorbed on the surface of Cu2O nanocubes, and the percentage of SDS is in accord with the concentration of SDS used. Compared to water and refrigerant fluid, the typical 40 nm Cu2O nanofluids displayed an enhanced percentage of 11% and 13% for thermal conductivity and cooling rate, respectively.

Molecular simulation of the regulation mechanism of the hydrophilic structure of surfactant on the wettability of bituminous coal surface

The regulation of surfactant on the wettability of bituminous coal surface is influenced by its hydrophilic structure. Based on the water absorption simulation and contact angle experiment of bituminous coal under different surfactants, the wetting effect of different surfactants with different hydrophilic structures on bituminous coal was obtained. The mechanism of different surfactants at the coal-water interface was analyzed by molecular dynamics simulation. The frontier orbital distribution and surface electrostatic potential distribution of surfactants and bituminous coal molecules were calculated by quantum chemistry method. The results showed that the wetting effect of surfactants on bituminous coal was APG1214 > OA-12 > SDBS > DTAB. The structure of hydroxyl and amine oxide made surfactants more conducive to promoting the interaction between coal and water molecules. The more oxygen and nitrogen elements the hydrophilic structure contains, the more favorable the surfactant is to modulate the wettability of the bituminous coal surface.

Laminar drag reduction in surfactant-contaminated superhydrophobic channels

Although superhydrophobic surfaces (SHSs) show promise for drag reduction applications, their performance can be compromised by traces of surfactant, which generate Marangoni stresses that increase drag. This question is addressed for soluble surfactant in a three-dimensional laminar channel flow, with periodic SHSs made of long finite-length longitudinal grooves located on both walls. We assume that bulk diffusion is sufficiently strong for cross-channel concentration gradients to be small. Exploiting long-wave theory and accounting for the difference between the rapid transverse and slower longitudinal Marangoni flows, we derive a one-dimensional model for surfactant transport from the full three-dimensional transport equations. Our one-dimensional model allows us to predict the drag reduction and surfactant distribution across the parameter space. The system exhibits multiple regimes, involving competition between Marangoni effects, bulk and interfacial diffusion, bulk and interfacial advection, shear dispersion and surfactant exchange between the bulk and the interface. We map out asymptotic regions in the high-dimensional parameter space, and derive explicit closed-form approximations of the drag reduction, without any fitting or empirical parameters. The physics underpinning the drag reduction effect and the negative effect of surfactant is discussed through analysis of the velocity field and surfactant concentrations, which show both uniform and non-uniform stress distributions. Our theoretical predictions of the drag reduction compare well with results from the literature solving numerically the full three-dimensional transport problem. Our atlas of maps provides a comprehensive analytical guide for designing surfactant-contaminated channels with SHSs, to maximise the drag reduction in applications.

Oscillatory Marangoni flow in a deep layer of a Carreau fluid

We study the spreading dynamics of an insoluble and non-diffusive surfactant on the free surface of a deep layer of a Carreau fluid. When a non-uniform distribution of surfactant is imposed on the free surface of an initially motionless fluid, variations in surface tension are induced, causing the fluid motion from regions of lower surface tension to those of higher tension. Such movement redistributes the surfactant concentration until a uniform condition is reached. The two-dimensional momentum and convection–diffusion equations are employed to determine the hydrodynamics in the deep fluid layer and the evolution of the surfactant on the fluid surface. The modified vorticity-stream function formulation is used to solve numerically the hydrodynamic field, where the non-Newtonian dependent variables of the problem are decomposed into a Newtonian part and a non-Newtonian contribution. One of the most critical variables in practical applications regarding this phenomenon concerns the time required for the surfactant to reach a uniform distribution over the interface. The results show that the dimensionless parameters that control the decay of the variations in surfactant concentration in time are the Reynolds number Re, the fluid behavior index n, and ε, reflecting the influence of the inertia of the fluid. The results show that the temporal decay of the surfactant concentration on the fluid surface increases significantly for high values of the Reynolds number, it is more attenuated in pseudoplastic fluids than in Newtonian fluids, and the surfactant concentration decay exhibits asymmetric oscillations when inertial effects increase.

Emulsification mechanism of surfactants in different oil phases: A dissipative particle dynamics study

The type of oil component affects the emulsification behaviors of surfactants while the underlying mechanism remains vague. In this work, the dissipative particle dynamics (DPD) method is conducted to analyze the behaviors of polyoxyethylated alcohols non-ionic surfactant at different water/oil (W/O) interfaces. Towards this end, the benzene and dodecane molecules are chosen as representatives of aromatic and alkane, respectively. The density distribution of surfactants, the radial distribution functions between different pairs of components, and the diffusion coefficient of surfactants are investigated, along with the morphological analysis. The phenomenon of similarity and intermiscibility is observed at the nanoscale between the hydrophobic chain of the surfactant and the oil phase, and in addition, it is found that the diffusion constant of surfactant molecules in water/benzene systems is nearly three times larger than that in water/dodecane systems, and a local maximum value of diffusion coefficient appears near the critical micelle concentration. This work provides a theoretical guidance for the screening and use of surfactants under different external environments.