Surfactant Film Research Articles

Electrochemical Quantification of Corrosion Mitigation on Iron Surfaces with Gallium(III) and Zinc(II) Metallosurfactants.

We have recently described a new potential use for Langmuir-Blodgett films of surfactants containing redox-inert metal ions in the inhibition of corrosion and have shown good qualitative results for both iron and aluminum surfaces. In this study we proceed to quantify electrochemically the viability of gallium(III)- and zinc(II)-containing metallosurfactants [GaIII(LN2O3)] (1) and [ZnII(LN2O2)H2O] (2) as mitigators for iron corrosion in saline and acidic media. We evaluate their charge transfer suppression and then focus on potentiodynamic polarization and impedance spectroscopy studies, including detailed SEM data to interrogate their metal dissolution/oxygen reduction rate mitigation abilities. Both complexes show some degree of mitigation, with a more pronounced activity in saline than in acidic medium.

Molecular and biophysical basis for the disruption of lung surfactant function by chemicals

With the intention to move away from animal testing for the toxicological evaluation of chemicals comes the need to develop new approach methodologies which are mechanism-anchored and target relevant key events leading to an adverse outcome. To date, no validated alternative methods are available for studying the acute inhalation toxicity potential of airborne chemicals but the constrained drop surfactometer measuring the surface tension of a drop of lung surfactant presents as a promising candidate. Indeed, the correlation of the increase in minimum surface tension of lung surfactant in vitro with changes in the breathing patterns of mice after inhalation of test compounds has been shown in multiple studies. However, the causal factors leading to lung surfactant inactivation remain speculative. This paper combines molecular and biophysical methods (constrained drop and captive bubble surfactometers, Langmuir-Blodgett balance, epifluorescence microscopy, cryogenic transmission electron microscopy, and differential scanning calorimetry) applied to purified porcine lung surfactant and dipalmitoylphosphatidylcholine interfacial films to gain insights into the disruption of lung surfactant function by three chemicals known to show acute inhalation toxicity (trimethoxyoctylsilane, methyl 3-oxo-2-pentylcyclopentaneacetate, and diisopentyl ether). The results of this study suggest that the test chemicals intercalate between the phospholipids at the air-liquid interface, reduce the stability of the films, and decrease the cohesivity of interface-associated multilayered structures thereby perturbing the lung surfactant surface activity. These findings contribute to a better understanding of chemically-induced lung surfactant function disruption.

Effect of commonly used EOR polymers on low concentration surfactant phase behaviors

High molecular weight polymers are required for the purpose of mobility and conformance control during surfactant chemical flooding. However, they are usually not incorporated in the process of phase behavior tests to screen surfactant formulations. Literature review shows some particular polymers have a boosting effect on surfactant solubilization efficiency. To gain more insight into this subject, we performed phase behavior tests in the presence of four commonly used EOR polymers for low concentration surfactant systems (0.3%). They were two partially hydrolyzed polyacrylamides (HPAM) with different molecular weights, one xanthan gum, and one hydrophobically associating polymer (HAP). Their influence on the optimal salinity, solubilization ratio, quickness of phase equilibration, and middle phase rheological behavior was assessed. The results showed: (1) a decrease of surfactant solubilization efficiency and the optimal salinity was observed with HPAM polymers. This trend became more pronounced as increase of polymer concentration and molecular weight; (2) xanthan seemed to slightly increase the optimal salinity without significantly affecting middle phase volume; (3) both HPAM and xanthan did not delay or quicken the equilibration of various phases compared to the zero polymer case. The analysis of the oil/water solubilization ratios showed HPAM tended to drag water out of the middle phase, while the presence of xanthan increased the water solubilization in the middle phase; (4) the viscosity and rheology of the middle phase microemulsions were very similar for systems containing HPAM, xanthan, and zero polymer. This confirmed the partitioning of polymer molecules in the middle phase was negligible; (5) the association of HAP with surfactants thickened the surfactant-rich phase, which made the phase separation dramatically slow. These phenomena could be explained well by the nature of their molecular structures. For both water-soluble HPAM and xanthan gum, unlike the reported diblock copolymers, they lack the amphiphilic features, which prevents them from adsorbing in the surfactant film. Conversely, the introduction of hydrophobic group into the backbone renders associating polymers some surfactant-like attributes, enabling them to associate with surfactant molecules and affect the surfactant-rich phase behaviors.

Structural Changes in Films of Pulmonary Surfactant Induced by Surfactant Vesicles.

When compressed by the shrinking alveolar surface area during exhalation, films of pulmonary surfactant in situ reduce surface tension to levels at which surfactant monolayers collapse from the surface in vitro. Vesicles of pulmonary surfactant added below these monolayers slow collapse. X-ray scattering here determined the structural changes induced by the added vesicles. Grazing incidence X-ray diffraction on monolayers of extracted calf surfactant detected an ordered phase. Mixtures of dipalmitoyl phosphatidylcholine and cholesterol, but not the phospholipid alone, mimic that structure. At concentrations that stabilize the monolayers, vesicles in the subphase had no effect on the unit cell, and X-ray reflection showed that the film remained monomolecular. The added vesicles, however, produced a concentration-dependent increase in the diffracted intensity. These results suggest that the enhanced resistance to collapse results from enlargement by the additional material of the ordered phase.

Corrigendum: Alveolar Dynamics and Beyond – the Importance of Surfactant Protein C and Cholesterol in Lung Homeostasis and Fibrosis

[This corrects the article DOI: 10.3389/fphys.2020.00386.].

INVESTIGATION OF MORPHOLOGICAL FEATURES OF FILM POLLUTION ON WATER SURFACE BASED ON RADAR SENSING DATA

The article deals with the morphological features of spreading films of surfactants on the surface of the reservoir on the basis of experiments on the Gorky reservoir under various meteorological conditions. The test substances were: oleic acid, vegetable oil, diesel. The registration of film contamination was carried out using X-band digital coherent radar MRS-1000, located on the roof of the lighthouse at the end of the outside harbor. The processing of the obtained radar panoramas made it possible to establish that the physical properties of the pollutant are reflected in the morphological characteristics of the film slicks. In particular, the substance properties are manifested in relation of the slick axes along and across the wind direction, as well as in the effects of growth and saturation of the slick area, all other things being equal. Without claiming to be a method for identifying a substance based on the data obtained, we can conclude that these effects are present and that they can be observed using radar methods.

Electrostatic precipitation of exhaled particles for tensiometric examination of pulmonary surfactant

Collecting exhaled particles that represent small droplets of the alveolar lining fluid shows great promise as a tool for pulmonary surfactant (PS) sampling. In this work we present a setup consisting of two modules, namely, a module for droplet collecting, called an electrostatic aerosol trapping (ESAT) system, and a measurement module for studying PS properties. We also suggest a method to extract numerical values from experimental data. The operating principle of ESAT is based on electrostatic precipitation of exhaled particles. Native material was collected directly on the water surface, where the adsorbed pulmonary surfactant film was investigated by the tensiometric method. The modified capillary wave method proposed in our previous work was adapted for studying small-volume samples. The efficiency of the setup was verified in the experiments involved the participation of healthy subjects. The accumulation of PS components on the water surface in an amount sufficient for tensiometric study was reported. The idea underlying the new concept used in this work may give impetus to the development of point-of-care facilities for collecting PS samples needed to provide their express analysis.

Template-mediated self-assembly of magnetite-gold nanoparticle superstructures at the water-oil interface of AOT reverse microemulsions

HypothesisBimetallic magnetite-gold nanostructures are interesting candidates to combine and enhance individual properties of each metal element in catalytic and analytical applications. Microemulsions have been employed in templated synthesis of nanoparticles, and their combination with different types of nanoparticles can further mediate interactions at the water-oil interface, providing new forms of hybrid nanostructures. ExperimentsReverse water-in-oil microemulsions of droplet sizes below 50 nm were prepared from ternary mixtures of Aerosol-OT (AOT) as surfactant, incorporating 4 nm sized superparamagnetic nanoparticles (MNPs) to the hexane-pentanol oil phase and 5 nm sized polyethyleneimine-stabilized gold nanoparticles (Au(PEI)-NPs) to the water phase. The resulting isotropic L2 phase, Winsor phases and organized nanostructures were investigated using conductometry, calorimetry, UV–Vis spectroscopy, cryo-SEM and HRTEM. FindingsDroplet-droplet interactions, morphology and surfactant film properties of AOT microemulsions could be modulated in different ways by the presence of the different nanoparticles from each liquid phase. Additionally, phase separation into Winsor phases allows the formation upon solvent evaporation of films with bimetallic heterostructures on the micrometer scale. This demonstrates a new way of nanoparticle templated assembly at liquid interfaces by assisted interactions between microemulsions and nanoparticles, as a promising strategy to obtain thin films of small, isotropic nanoparticles with hierarchical ordering.

Atomic Force Microscopy Imaging of Adsorbed Pulmonary Surfactant Films

Pulmonary surfactant (PS) is a lipid-protein complex that adsorbs to the air-water surface of the lung as a thin film. Previous studies have suggested that the adsorbed PS film is composed of an interfacial monolayer, plus a functionally attached vesicular complex, called the surface-associated surfactant reservoir. However, direct visualization of the lateral structure and morphology of adsorbed PS films using atomic force microscopy (AFM) has been proven to be technically challenging. To date, all AFM studies of the PS film have relied on the model of Langmuir monolayers. Here, we showed the first, to our knowledge, AFM imaging of adsorbed PS films under physiologically relevant conditions using a novel, to our knowledge, experimental methodology called constrained drop surfactometry. In conjunction with a series of methodological innovations, including subphase replacement, in situ Langmuir-Blodgett transfer, and real-time surface tension control using closed-loop axisymmetric drop shape analysis, constrained drop surfactometry allowed the study of lateral structure and topography of animal-derived natural PS films at physiologically relevant low surface tensions. Our data suggested that a nucleation-growth model is responsible for the adsorption-induced squeeze-out of the PS film, which likely results in an interfacial monolayer enriched in dipalmitoylphosphatidylcholine with the attached multilayered surface-associated surfactant reservoir. These findings were further supported by frequency-dependent measurements of surface dilational rheology. Our study provides novel, to our knowledge, biophysical insights into the understanding of the mechanisms by which the PS film attains low surface tensions and stabilizes the alveolar surface.

Interfacial rigidity and topology of reverse microemulsions: Influence of alcohol molecules

Using dielectric relaxation spectroscopy and small-angle neutron scattering techniques, we present a quantitative analysis of the influence of short-chain (ethanol) and long-chain (octanol) alcohol molecules on the elastic bending constants of AOT [sodium-1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate]-stabilized reverse microemulsions. A significant increase in the elastic bending rigidity, κ, of the AOT surfactant layer (30.7%) is observed with the inclusion of octanol, whereas a decrease in κ amounting to 11.2% is obtained in the presence of ethanol. The experimentally elusive saddle-splay modulus, κ¯, of alcohol-loaded microemulsions is determined using a novel approach. Notably, the ratio κ¯/κ lies in the range −2<κ¯/κ<0, which is acceptable for spherical microemulsion droplets. Further, the presence of ethanol molecules causes a decrease in the percolation threshold temperature owing to an increase in the fluidity of the surfactant monolayer at the oil–water interface. On the other hand, the addition of octanol molecules shifts the percolation threshold to higher temperatures implying a further reinforcement of the surfactant film.

FULL-SCALE STUDIES OF FLUORESCENCE FEATURES OF SURFACTANT FILMS ON EUTROPHIC WATER WAVY SURFACE

The current paper presents the results of a full-scale study of the fluorescence features of pollutants ( diesel fuel, Urals oil), as well as an alcoholic solution of oleic acid, which imitates oil by visco-elastic characteristics. The experiment was carried out on the Gorky Reservoir under conditions of wind waves. Local areas of artificial slicks were created for multiple intersections at different angles to the wind and waves with continuous lidar sounding of the upper water layer. Signals were recorded by the ninth generation UVL-9 laser ultraviolet fluorescent lidar developed by the Institute of Oceanology of the Russian Academy of Sciences. At signal analysis, spectral intensities and fluorescence features of the studied substances are determined, possibilities of slick detecting as well as film thickness estimation are made, examples of surfactant film detecting behind the oleic slick where visual observation of pollutants does not give a result are showed. The obtained results are useful for the further development of fluorescent methods and devices for operational remote sensing of surface pollution on wave water surface.

Interaction of Particles with Langmuir Monolayers of 1,2-Dipalmitoyl-Sn-Glycero-3-Phosphocholine: A Matter of Chemistry?

Lipid layers are considered among the first protective barriers of the human body against pollutants, e.g., skin, lung surfactant, or tear film. This makes it necessary to explore the physico-chemical bases underlying the interaction of pollutants and lipid layers. This work evaluates using a pool of surface-sensitive techniques, the impact of carbon black and fumed silica particles on the behavior of Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The results show that the incorporation of particles into the lipid monolayers affects the surface pressure–area isotherm of the DPPC, modifying both the phase behavior and the collapse conditions. This is explained considering that particles occupy a part of the area available for lipid organization, which affects the lateral organization of the lipid molecules, and consequently the cohesion interactions within the monolayer. Furthermore, particles incorporation worsens the mechanical performance of lipid layers, which may impact negatively in different processes presenting biological relevance. The modification induced by the particles has been found to be dependent on their specific chemical nature. This work tries to shed light on some of the most fundamental physico-chemical bases governing the interaction of pollutants with lipid layers, which plays an essential role on the design of strategies for preventing the potential health hazards associated with pollution.

Alveolar Dynamics and Beyond - The Importance of Surfactant Protein C and Cholesterol in Lung Homeostasis and Fibrosis.

Surfactant protein C (SP-C) is an important player in enhancing the interfacial adsorption of lung surfactant lipid films to the alveolar air-liquid interface. Doing so, surface tension drops down enough to stabilize alveoli and the lung, reducing the work of breathing. In addition, it has been shown that SP-C counteracts the deleterious effect of high amounts of cholesterol in the surfactant lipid films. On its side, cholesterol is a well-known modulator of the biophysical properties of biological membranes and it has been proven that it activates the inflammasome pathways in the lung. Even though the molecular mechanism is not known, there are evidences suggesting that these two molecules may interplay with each other in order to keep the proper function of the lung. This review focuses in the role of SP-C and cholesterol in the development of lung fibrosis and the potential pathways in which impairment of both molecules leads to aberrant lung repair, and therefore impaired alveolar dynamics. From molecular to cellular mechanisms to evidences in animal models and human diseases. The evidences revised here highlight a potential SP-C/cholesterol axis as target for the treatment of lung fibrosis.

Characterization of Microbubble-Based Drilling Fluids: Investigating the Role of Surfactants and Polymers

Colloidal Gas Aphrons (CGA), consist of gas bubbles with diameters ranging from 10 to 100 micron, surrounded by a thin aqueous surfactant film. This fluid combines certain surfactants and polymers to create the systems of microbubbles. The function of surfactant in CGAs is to produce the surface tension to contain the aphrons. Also, a biopolymer needs to be considered in the formulation as a viscosifier as well as a stabilizer. The aphron-laden fluid appears to be particularly well suited for drilling through depleted zones. The unique feature of aphron based fluids is to form a solid free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion using air microbubbles. This microenvironment seal readily cleans up with reservoir flow back as production is initiated, thereby reducing the cost associated with stimulation processes. This paper presents a comprehensive, comparative study of rheological behavior and filtration properties of CGA based drilling fluids with various concentrations of polymer and surfactant. Laboratory evaluations showed that the CGA based fluid is one of the ideal engineering materials which can control and kill the loss circulation, save cost and increase productivity in which rheological characteristics and filtration properties of them are greatly influenced by the level of polymer and surfactant concentration.

Synergistic and Antagonistic Effects of Aromatics on the Agglomeration of Gas Hydrates

Surfactants are often used to stabilize aqueous dispersions. For example, surfactants can be used to prevent hydrate particles from forming large plugs that can clog, and sometimes rupture pipelines. Changes in oil composition, however dramatically affect the performance of said surfactants. In this work we demonstrate that aromatic compounds, dissolved in the hydrocarbon phase, can have both synergistic and antagonistic effects, depending on their molecular structure, with respect to surfactants developed to prevent hydrate agglomerations. While monocyclic aromatics such as benzene were found to disrupt the structure of surfactant films at low surfactant density, they are expelled from the interfacial film at high surfactant density. On the other hand, polycyclic aromatics, in particular pyrene, are found to induce order and stabilize the surfactant films both at low and high surfactant density. Based on our simulation results, polycyclic aromatics could behave as natural anti-agglomerants and enhance the performance of the specific surfactants considered here, while monocyclic aromatics could, in some cases, negatively affect performance. Although limited to the conditions chosen for the present simulations, the results, explained in terms of molecular features, could be valuable for better understanding synergistic and antagonistic effects relevant for stabilizing aqueous dispersions used in diverse applications, ranging from foodstuff to processing of nanomaterials and advanced manufacturing.

Effect of Triton X-100 surfactant on thiol-amine cosolvents assisted facile synthesized CdS thin films on glass substrate by spin coating method

In this article, the effect of Triton X-100 surfactant on the spin coated and vacuum annealed CdS thin films on glass substrates using thiol-amine cosolvents have been explored in details. The SEM study reveals that the surfactant assisted CdS films are uniform, homogeneous and smooth having less cracks, voids, pinholes compared to CdS films synthesized without surfactant. The X-ray diffraction spectra indicate the hexagonal structure of the surfactant-added films with (002) and (100) planes having relatively high intensity whereas a weak hexagonal (002) peak appears for the films deposited without surfactant. Two prominent Raman peaks of CdS thin films are observed at the wavenumber 207 and 212 cm−1 due to the multi-phonon vibration of hexagonal CdS. A relatively strong and broad FTIR peaks at 1647 and 670 cm−1 were observed due to the Cd-S bending and stretching vibration in the surfactant mediated films. Surfactant induced CdS films are nearly stoichiometric as manifested by the energy dispersive X-ray report. Finally, higher optical transmission and band gap have been achieved for the CdS thin films deposited with Triton X-100 surfactant. This study reveals that surfactant mediated CdS thin films with thiol-amine cosolvents can be exploited effectively in higher efficiency thin film solar cell technologies with low cost.

Pulmonary Surfactant Lipid Reorganization Induced by the Adsorption of the Oligomeric Surfactant Protein B Complex

Surfactant protein B (SP-B) is essential in transferring surface-active phospholipids from membrane-based surfactant complexes into the alveolar air–liquid interface. This allows maintaining the mechanical stability of the surfactant film under high pressure at the end of expiration; therefore, SP-B is crucial in lung function. Despite its necessity, the structure and the mechanism of lipid transfer by SP-B have remained poorly characterized. Earlier, we proposed higher-order oligomerization of SP-B into ring-like supramolecular assemblies. In the present work, we used coarse-grained molecular dynamics simulations to elucidate how the ring-like oligomeric structure of SP-B determines its membrane binding and lipid transfer. In particular, we explored how SP-B interacts with specific surfactant lipids, and how consequently SP-B reorganizes its lipid environment to modulate the pulmonary surfactant structure and function. Based on these studies, there are specific lipid–protein interactions leading to perturbation and reorganization of pulmonary surfactant layers. Especially, we found compelling evidence that anionic phospholipids and cholesterol are needed or even crucial in the membrane binding and lipid transfer function of SP-B. Also, on the basis of the simulations, larger oligomers of SP-B catalyze lipid transfer between adjacent surfactant layers. Better understanding of the molecular mechanism of SP-B will help in the design of therapeutic SP-B-based preparations and novel treatments for fatal respiratory complications, such as the acute respiratory distress syndrome.

The Structural Basis for Stabilization of Pulmonary Surfactant Films by Subphase Material

Pulmonary surfactant is the mixture of lipids and proteins that lowers surface tension in the lungs. The material forms a thin film on the aqueous layer that lines the alveolar air-sacks. When compressed by the shrinking alveolar surface area during exhalation, the surfactant film achieves surface tensions < 5 mN/m. The molecular arrangement of the film that sustains these low tensions remains obscure. Vesicles of pulmonary surfactant adsorb as collective packets, delivering their complete set of constituents that initially form monolayers at the interface. At physiological temperatures, such monomolecular films readily collapse from the surface. Additional vesicles added below these initial monolayers substantially increase their stability at low surface tensions. The studies here focus on the structural changes that produce that improved stability. Two divergent models attempt to explain how the additional material enhances the resistance to collapse: enrichment of dipalmitoyl phosphatidylcholine (DPPC) in the interfacial monolayer to form a crystalline film; and formation of a multilayered structure. Surface X-ray scattering determined how calf lung surfactant extract added below monolayers of that material affects the structure of the film. The ordered structure within the initial monolayer differed from the DPPC packing motif, but fit with the hexagonal lattice of a binary mixture with DPPC and cholesterol at a ratio of 4:1 (mol%). Vesicles added to the subphase had no effect on the local structure of the film, which remained monomolecular in thickness with an unchanged hexagonal lattice. The vesicles, however, produced a concentration-dependent increase in the size of individual ordered regions, and in their total area. Our results suggest that the functional film contains cholesterol:DPPC rather than DPPC alone, and that vesicles in the subphase provide a reservoir of additional DPPC that allows the ordered phase to grow.

Functional and Structural Characterization of a Lyophilized Pulmonary Surfactant Directly Applied onto the Air-Liquid Interface

Lung surfactant is a lipoproteic complex which main function is to stabilize the air-liquid interface in the alveolous. Its absence or inactivation leads to severe lung damage which can cause death. Up to now, clinical treatments have consisted in the intratraqueal application of a dense aqueous suspension, an invasive procedure that requires intubation of the patient. In an attempt to explore new ways of administration such as powder aerosolization, we have evaluated the functional behavior and structural features of the films formed by lyophilized membranes of porcine lung surfactant directly applied onto the air-liquid interface. Captive Bubble Surfactometry experiments have demonstrated that lyophilization preserves the main characteristics of a functional surfactant such as a fast adsorption and a rapid extension along the interface. Even more, it was demonstrated that less amount of material is needed to obtain the same results compared to an aqueous suspension. This more active material exerts also a higher resistance to the inactivation of the surfactant function that is produced by serum components. The effect of the freezing temperature previous to the sublimation process was also evaluated to stablish the proper conditions needed to observe such results. Surfactant films formed from the direct application of lyophilized fluorescent labeled surfactant complexes at the interface of a Langmuir balance, provided some light upon the possible mechanism that underlies this behavior.

Nanoparticle translocation across the lung surfactant film regulated by grafting polymers.

Nanoparticle-based pulmonary drug delivery has gained significant attention due to its ease of administration, increased bioavailability, and reduced side effects caused by a high systemic dosage. After being delivered into the deep lung, the inhaled nanoparticles first interact with the lung surfactant lining layer composed of phospholipids and surfactant proteins and then potentially cause the dysfunction of the lung surfactant. Conditioning the surface properties of nanoparticles with grafting polymers to avoid these side effects is of crucial importance to the efficiency and safety of pulmonary drug delivery. Herein, we perform coarse-grained molecular simulations to decipher the involved mechanism responsible for the translocation of the polymer-grafted Au nanoparticles across the lung surfactant film. The simulations illustrate that conditioning of the grafting polymers, including their length, terminal charge, and grafting density, can result in different translocation processes. Based on the energy analysis, we find that these discrepancies in translocation stem from the affinity of the nanoparticles with the lipid tails and heads and their contact with the proteins, which can be tuned by the surface polarity and surface charge of the nanoparticles. We further demonstrate that the interaction between the nanoparticles and the lung surfactant is related to the depletion of the lipids and proteins during translocation, which affects the surface tension of the surfactant film. The change in the surface tension in turn affects the nanoparticle translocation and the collapse of the surfactant film. These results can help understand the adverse effects of the nanoparticles on the lung surfactant film and provide guidance to the design of inhaled nanomedicines for improved permeability and targeting.