Surfactant Flux Research Articles

Synthesis of sodalite octahydrate zeolite-clay composite membrane and its use in separation of SDS

A simple two-step process for synthesis of sodalite octahydrate zeolite-clay composite, charged ultrafiltration membrane is described wherein the active layer is obtained by partial plugging of the pore-mouth of macroporous clay support with in situ grown zeolite particles. Dip-coating of zeolite synthesis solution at pH 12 is found to give higher deposition of zeolite on the clay support. Increase in amount of zeolite in the active layer obtained by repeated deposition of zeolite particles on clay-support is quantified using membrane potential measurements and it is found that four cycles of zeolite deposition gives optimum results. The membrane is characterized using SEM for surface morphology, XRD for zeolite characterization, water flux and separation of surfactant (SDS) above cmc concentration. SDS separation results show observed-rejection in the range of 10–45%. The observed-rejection is found to decrease with increase in the applied pressure difference and increase with increase in the surfactant concentration. The permeate flux is found to reduce significantly to about 0.2–0.46 times the pure water flux. The trend is similar to that reported in literature for separation of surfactant micelle by ultrafiltration membrane of pore size much larger than the size of surfactant micelle.

Adsorption Kinetics in a Dual-Inlet Channel Flow Cell: II. Cetyl Pyridinium Chloride on Methyl and Methyl Ether Surfaces

The adsorption of cetyl pyridinium chloride (CPC) in 0.1 M KCl to methyl- and methyl ether-terminated organic monolayers has been studied using a dual-inlet channel flow cell. The surfaces were formed by reaction of H-terminated Si(111) with dodecene and 11-methoxy-1-undecene, respectively. The equilibrium adsorption isotherm, the desorption kinetics, and the adsorption kinetics can be explained self-consistently on the basis of the Frumkin model of adsorption. The equilibrium adsorption isotherms on both surfaces were very close to Langmuirian, indicating that the driving force for adsorption remains roughly constant with coverage. Adsorption was in the mixed diffusion-kinetic regime under the mass transport conditions of the channel flow cell (adsorption times of the order of tens of seconds). Most of the difference in the adsorption energies of the two surfaces appears to be reflected in the adsorption rate constant rather than the desorption rate constant, suggesting a late transition state. Comparing the Frumkin model parameters for the methyl and methyl ether surfaces with those for hydrophilic silica helps clarify and quantify the difference between the surfaces. The nature of the surface has a very-significant effect on the equilibration time for the same initial surfactant distribution because the adsorption rate affects the subsurface concentration and consequently the flux of surfactant to the interface itself. The organic self-assembled monolayers (SAMs) formed by reaction of H-terminated Si(111) with alkenes make robust and versatile substrates for surfactant adsorption experiments. A combination of SAMs with the dual-inlet channel flow cell offers an opportunity for the systematic and quantitative study of the effect of surface chemistry on the adsorption kinetics of surfactants to organic surfaces.

A concentration polarization model for the ultrafiltration of nonionic surfactants

A theoretical model has been developed that describes ultrafiltration of nonionic surfactants. The model takes into account the fact that surfactants start to aggregate and form micelles at the critical micelle concentration. The model can be used to predict the performance of the membrane if the transport properties inside and at the membrane surface as well as the surfactant association behavior, are known. Three hydrophilic ultrafiltration membranes, made of regenerated cellulose, were used in the investigation. The cut-offs of the membranes were 10,000, 20,000, and 30,000 Da. The surfactant used in the investigation was the nonionic surfactant Triton X-100. The influence of the concentration of surfactant, transmembrane pressure and pure water flux were studied theoretically and experimentally. From the results presented in this work it can be concluded that the calculated values are in good agreement with experimental data.

Growing surfactant waves in thin liquid films driven by gravity

The dynamics of a gravity-driven thin film flow with insoluble surfactant are described in the lubrication approximation by a coupled system of nonlinear PDEs. When the total quantity of surfactant is fixed, a traveling wave solution exists. For the case of constant flux of surfactant from an upstream reservoir, global traveling waves no longer exist as the surfactant accumulates at the leading edge of the thin film profile. The dynamics can be described using matched asymptotic expansions for t →∞ . The solution is constructed from quasistatically evolving traveling waves. The rate of growth of the surfactant profile is shown to be O( √ t) and is supported by numerical simulations.

Regeneration of process water containing surfactants by nanofiltration - investigation and modelling of mass transport

The mechanisms in nanofiltration of aqueous solutions of different anionic surfactants and of mixture solutions of surfactants and NaCl are investigated. The surfactants used are sodium dodecylether sulfate, sodium dodecyl sulfate and sodium alkyl benzene sulfonate. High retentions in the range of 95% up to 99.9% referring to the feed concentration are found to depend on the solvent flux. If additional salt is present in the solution, the permeate quality is deteriorating because of lower solvent flux and of mass transfer due to the electrical potential. The experimental results show that convective mass transfer of surfactant through the nanofiltration membrane occurs. Consequently, an extended solution-diffusion model is used for modelling of the process. Depending on the feed composition, concentration polarisation has to be considered in the model. The calculated surfactant flux through the membrane is in good agreement with the experimental results.

The propagation of a surfactant laden liquid plug in a capillary tube

This paper considers the propagation of a liquid plug, forced by a driving pressure ΔP, within a rigid tube. The tube is already lined with a liquid precursor film of thickness h̄2. Both the plug and the precursor film, as well as the interface, contain small amounts of surfactant whose concentrations are assumed to be near equilibrium. Since the motions are slow, we seek asymptotic solutions for small capillary number, Ca≪1, and also assume that sorption kinetics control the surfactant flux to the interface compared to bulk diffusion. An additional asymptotic assumption is that the Stanton number, St, is sufficiently large such that β∝Ca1/3/St≪1, which relates the importance of sorption kinetics to convection. The surfactant strength is measured by the surface elasticity, E=M/β where M is the Marangoni number. The results of the analysis are that, for a given plug Ca, ΔP increases with increasing E but decreases with increasing h̄2. The trailing film thickness, h̄1, increases with ΔP, but at a slower rate when E is larger. For h̄1<h̄2, criteria for plug rupture are established. This model is relevant to delivery of surfactants into the lung by direct instillation into the bronchial network as is done in surfactant replacement therapy and the use of surfactant solutions to carry other substances (e.g., genetic material) into the airways.

Adsorption Kinetics and Structural Arrangements of Cationic Surfactants on Silica Surfaces

The adsorption of cetyltrimethylammonium bromide (CTAB) to the silica−aqueous interface has been studied using optical reflectometry. The effect of pH, salt, and surface preparation on the surface excess and adsorption kinetics has been studied. The adsorption kinetics have been measured and compared to the theoretical diffusion limited flux of surfactant, the quotient being the “sticking ratio”. Analysis of the sticking ratio as a function of CTAB concentration reveals that the adsorption process is cooperative above the critical micelle concentration (CMC). At the critical surface aggregation concentration (CSAC), adsorption proceeds slowly in the absence of salt and takes hours to reach an equilibrium value. At all other concentrations and even at the CSAC when salt is present, the adsorption is complete within minutes. These results indicate that, above the CMC, micelles adsorb directly to the silica surface, and this is reflected in the structure of the surface layer. At the CSAC the equilibrium surface structure is analogous to adsorbed micelles, but as only monomers are present in solution, the adsorption proceeds to equilibrium slowly.

Effects of Counterions and Co-Ions on the Surfactant Binding Process in the Charged Polymer Network

Kinetic studies of cationic surfactant uptake in an anionic polymer network have been performed, varying the species of co-ions of the surfactant and counterions of the charged network. It was found that the rate of surfactant uptake is distinctly dependent on both the counterions and co-ions which could be explained in terms of the ion pair diffusion mechanism associated with their mobilities in the network. A simple linear relation between the surfactant flux and the harmonic mean of the molar mobilities of the surfactant ion, its co-ion, and the network counterion has been established experimentally.

Spreading of a surfactant monolayer on a thin liquid film: Onset and evolution of digitated structures.

We describe the response of an insoluble surfactant monolayer spreading on the surface of a thin liquid film to small disturbances in the film thickness and surfactant concentration. The surface shear stress, which derives from variations in surfactant concentration at the air-liquid interface, rapidly drives liquid and surfactant from the source toward the distal region of higher surface tension. A previous linear stability analysis of a quasi-steady state solution describing the spreading of a finite strip of surfactant on a thin Newtonian film has predicted only stable modes. [Dynamics in Small Confining Systems III, Materials Research Society Symposium Proceedings, edited by J. M. Drake, J. Klafter, and E. R. Kopelman (Materials Research Society, Boston, 1996), Vol. 464, p. 237; Phys. Fluids A 9, 3645 (1997); O. K. Matar Ph.D. thesis, Princeton University, Princeton, NJ, 1998]. A perturbation analysis of the transient behavior, however, has revealed the possibility of significant amplification of disturbances in the film thickness within an order one shear time after the onset of flow [Phys. Fluids A 10, 1234 (1998); "Transient response of a surfactant monolayer spreading on a thin liquid film: Mechanism for amplification of disturbances," submitted to Phys. Fluids]. In this paper we describe the linearized transient behavior and interpret which physical parameters most strongly affect the disturbance amplification ratio. We show how the disturbances localize behind the moving front and how the inclusion of van der Waals forces further enhances their growth and lifetime. We also present numerical solutions to the fully nonlinear 2D governing equations. As time evolves, the nonlinear system sustains disturbances of longer and longer wavelength, consistent with the quasi-steady state and transient linearized descriptions. In addition, for the parameter set investigated, disturbances consisting of several harmonics of a fundamental wavenumber do not couple significantly. The system eventually singles out the smallest wavenumber disturbance in the chosen set. The summary of results to date seems to suggest that the fingering process may be a transient response which nonetheless has a dramatic influence on the spreading process since the digitated structures redirect the flux of liquid and surfactant to produce nonuniform surface coverage. (c) 1999 American Institute of Physics.

Late Stages of the “Pearling" Instability in Lipid Bilayers

Applying laser tweezers to cylindrical vesicles of lipid bilayers produces an instability which propagates down the vesicle leaving behind it a peristaltic state, which appears under the microscope as pearls on a string. We investigate the late stages of this “pearling” instability, where the pearls are observed to drift slowly towards the laser trap (the spot at which the tweezers are applied, into which the surfactant is drawn) where they jam up. We model the hydrodynamics of the drifting pearls as a combination of translation of the string of pearls, and “slipping” of the bilayer skin over the pearls, to relate the speed of the pearls to the underlying flux of surfactant into the trap. We find that the pearl drift is slower than the skin-slip speed by a factor of order a/R where a is the radius of the tethers connecting the pearls, and R is the pearl radius.

The role of alpha 1-antitrypsin in the control of extracellular surfactant metabolism

Alveolar surfactant exists in several structural forms that are believed to be secular products of the secreted form, lamellar bodies. The conversion of tubular myelin to the small vesicular form appears to require the action of a novel serine protease, surfactant convertase. As the in vitro activity of this enzyme is quite sensitive to inhibition by the serine protease inhibitor alpha 1-antitrypsin, a normal constituent of the alveolar fluid lining layer, we explored the possibility that the alveolar level of alpha 1-antitrypsin might affect the rate of subtype conversion in vivo. When the alveolar alpha 1-antitrypsin level was augmented by tracheal instillation of exogenous alpha 1-antitrypsin, the newly synthesized surfactant phospholipids of spontaneously breathing mice accumulated in the heavy subtype, and virtually none was found in the light subtype form up to 72 h later. An in vivo turnover study suggested that when the alveolar alpha 1-antitrypsin level was raised by the same means, the flux of surfactant through the light (small vesicular) compartment was virtually shut off, despite the availability of abundant amounts of its precursor, heavy subtype (tubular myelin). Finally, mouse lungs that were lavaged to remove resident surfactant and mechanically ventilated for 1-5 h released surfactant that progressed through heavy and light subtype compartments as in vivo. But in mice whose lung alpha 1-antitrypsin might affect the metabolism of alveolar surfactant in addition to its well-known role in lung defense.

Dynamics and transport of a localized soluble surfactant on a thin film

The flow induced by a localized droplet of soluble surfactant on the surface of a thin film is analysed, motivated by an interest in the interaction between inhaled droplets and the lung's thin liquid lining after an aerosol lands on its surface. The spreading is driven by gradients of surface tension and results in flow of the droplet and underlying liquid film. This induced flow field plays an important role in the transport of dissolved species from the droplet, through the film, and to the tissue for absorption.Evolution equations for the film thickness, surface and bulk liquid concentrations are derived using lubrication theory, since the depth of the film is much smaller than the characteristic radius of the droplet. Solutions are obtained numerically using the method of lines for a variety of surface Péclet numbers.We find that the effect of solubility is to decrease both film disturbances and surface concentrations, and to induce an absorption-driven backflow. In addition, there is a gravity-driven backflow from hydrostatics. At large surface Péclet numbers, large film disturbances are obtained and more surfactant is able to diffuse across the rigid permeable wall, while surface diffusion causes more rapid spreading and decreases film disturbances. Gravity acts as a restoring force by creating a bidirectional flow, and hence disenhances the vertical flux of surfactant across the air-liquid interface. This model may have implications for the delivery of drugs by aerosol inhalation.

Monomer‐micelle equilibrium in the diffusion of surfactants in binary systems through collagen films

Three different binary systems (two anionic/nonionic and one anionic/amphoteric) were selected to study the behavior of these mixtures in their diffusion through a collagen film and the formation of micelle aggregates in such systems. The inhibition observed in the surfactant diffusion of anionic/nonionic and anionic/amphoteric binary mixtures through a collagen film, in comparison with that of single surfactants, has been related to the behavior of these binary systems in the micellization process. The surfactant flux in these systems is mainly determined by the monomeric species. The modification of the equilibrium monomers‐micelle aggregates shown by these surfactant binary systems could be also associated with the reduction of the irritancy power for such binary systems.

The importance of direct measurement of dynamic contact angles during the wetting of solids by surfactant solutions

The dynamic contact angle serves as an appropriate measure of wettability in industrial and laboratory processes that involve moving contact lines. This angle can be obtained from a capillary force measurement, provided the local surface tension at the contact line is known a priori. Even when the liquid contains surface active contaminants, this value is commonly assumed equal to the equilibrium surface tension. Wilhemy plate experiments conducted here show that such an assumption may be invalid under certain operating conditions. The primary reason for this is that surfactant transport by flow and diffusional interchange with the bulk phase can cause a transient surfactant concentration at the contact line or a steady dynamic value. In either case this concentration as well as the corresponding surface tension need not be the equilibrium value. The key dimensionless group impacting this behavior is the Peclet number, arising from the dimensionless surfactant flux balance at the liquid-vapor interface. If it is small, it is safe to assume that the dynamic surface tension at the contact line is equal to the equilibrium value. Liquids involved in practically relevant wetting processes quite commonly contain surfactants, either because they are deliberately added or because of inadvertent contamination. In order to make conclusions about wettability in such systems, it may be necessary to measure dynamic contact angles directly.

The Surfactant Flux—A New Flux for the Ozone Age

The development of a new type of flux—the surfactant flux—is described. This flux is applied in a very thin layer and must be totally dry before soldering. It is not necessary to clean PWBs after soldering for functional or aesthetic reasons. Even the results of the surface insulation resistance (SIR) test suggest no need for cleaning. The flux allows a very high soldering speed, at least double that of normal fluxes. Thus the heat input into the materials involved is minimised, with the consequence of less damage. It is not the chemicals which make the flux highly active but the concept. This new concept makes it possible to design non or low corrosive fluxes in a wide range for purposes where highly corrosive fluxes must be used today.

316 FETAL RAT SURFACTANT AT THE ONSET OF AIR BREATHING

Morphometric and biochemical measures of type II cell surfactant stores were combined to define late gestational maturation of the alveolar epithelium in its preparation for transition to air breathing. Fetal (G20, G22) and newborn (+10min) lung tissue was obtained from pathogen-free timed pregnant rats. Morphometric analyses of type II cells & their organelles was done using a stratified sample. Lamellar body (LB) fractions were obtained by sucrose density gradients & disaturated phosphatldylcholine (DSPC) was quantitated. The table gives the results of the volume fraction (Vv,%) of type II cell organelle content and the LB fraction and whole lung (WL) DSPC content. There was an increase in LB Vv from day 20 of gestation, with a parallel increase in LB DSPC. Within 10 min after birth, we found a significant increase in intracellular LB by morphologic and biochemical measures. This postnatal accumulation of intracellular surfactant could represent recycling of previously secreted phospholipid from the airspaces. Such an occurrence might supplement de novo pathways of surfactant production by newborn rat type II cells providing an additional source of surfactant flux. Supported by NHLBI R0132188 and by the VA research fund.

The pulmonary macrophage population of human smokers.

The lungs of human smokers contain many more pulmonary macrophages than the lungs of non-smokers, probably owing to both enhanced recruitment and diminished efflux; smokers' macrophages exhibit altered morphologic and functional characteristics. Phagocytosis, particularly of relatively indigestible paniculate matter, leads to enzyme release. The potential of cathepsins, particularly elastase and collagenase, to promote local lung damage in smokers is discussed. The enzyme aryl hydrocarbon hydroxylase may yet be of relevance to the epidemiology of human bronchial cancer and PAM levels of this enzyme are raised in smokers. Altered surfactant flux occurs in smokers and PAM play a part in this turnover. Although the analogy is strong, the relevance of pulmonary macrophages to the occupational lung diseases is as yet poorly understood, as is their role in any exacerbation of these dust diseases in tobacco smokers.

Inhibitors of prostaglandin synthesis, tracheal fluid, and surfactant in fetal lambs.

To study their effects on tracheal fluid (TF) production and surfactant flux, we gave 12-h infusions of prostaglandin synthetase inhibitors (PGSI) on 16 occasions to 10 fetal lambs at gestational ages (GA) of 125--141 days. Results were similar with both sodium meclofenamate (13.9 +/- 3.4 mg.kg-1, 12 studies) and indomethacin (33.6 +/- 8.0 mg.kg-1, 4 studies). All studies were done at least 6 days after surgery and 4 days before spontaneous birth. During infusions of PGSI, there were no changes in fetal arterial blood pressure, pH, PaO2, PaCO2, TF production or its concentration of sodium, potassium, and chloride; calcium concentration in TF increased slightly. We expressed tracheal surfactant flux as micrograms.kg-1.h-1 of saturated phosphatidylcholine (SPC). If control SPC flux was less than 5 micrograms.kg-1.h-1 (10 studies at GA of 125--141 days), it did not change during infusion of PGSI; however, if control was greater than 5 micrograms.kg-1.h-1 (6 studies at GA 132--140 days), SPC flux decreased during the infusions in all studies. The results suggest that prostaglandins do not strongly influence TF production up to 4 days before birth and that prostaglandins are involved in the increased flux of surfactant which occurs in late gestation.

Analysis of labeling and clearance of lung surfactant phospholipids in rabbit. Evidence of bidirectional surfactant flux between lamellar bodies and alveolar lavage.

Turnover and clearance of lung surfactant phospholipids were studied with particular reference to myoinositol-induced perturbation in the acidic phospholipids. Administration of myoinositol decreased [(3)H]palmitate and [(32)P]phosphate incorporation into phosphatidylglycerol by 80-90% in whole lung, and by 94-99% in lamellar bodies and in alveolar lavage. The increased incorporation of radioactive isotopes into phosphatidylinositol following myoinositol, was inverse to the decrease in phosphatidyl-glycerol incorporation. Myoinositol treatment affected neither content nor labeling of phosphatidylcholine or disaturated phosphatidylcholine as studied within 50 h of administration. Phosphatidylglycerol was pulse labeled by intravenous [(32)P]phosphate and [(3)H]palmitate, followed by myoinositol. The biological half-lives of phosphatidylglycerol in the microsomal fraction, lamellar bodies, and alveolar lavage were 1.6, 4.6, 5.4 h (with (3)H), and 2.8, 6.5, 7.0 h (with (32)P), respectively.(32)P-labeled lung surfactant tracer was applied to the airways in saline suspension and the clearance of phospholipid radioactivity was measured in alveolar lavage, alveolar macrophages, lamellar bodies and lung homogenates. The clearance rates of phosphatidylcholine, disaturated phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol as studied in whole lung over 6 h were 3.4-5.8% h. Only a small amount of phospholipid radioactivity was recovered in the alveolar macrophage fraction (including bis-[monoacylglycerol]phosphate). Phospholipid radioactivity in alveolar lavage fell to 40-70% of the maximum during the 1st h, and to 5-18% over the next 6 h. During 2 h after the application of phospholipids, the radioactivity in the lamellar body fraction increased, and the specific radioactivities approached those in alveolar lavage. The association of phosphatidylglycerol with lamellar bodies was unaffected by myoinositol. Phosphatidylinositol entered more slowly than did phosphatidylglycerol from microsomes to the alveolar lavage fraction, and from alveolar lavage to lamellar bodies. These differences may be of importance regarding the poor performance of phosphatidylinositol-containing surfactant at birth. Further investigations are needed to clarify the possible role for the postulated bidirectional surfactant flux between the lamellar body and alveolar lavage fractions in maintaining the activity of surfactant.

Surfactant in the Lung and Tracheal Fluid of the Fetal Lamb and Acceleration of Its Appearance by Dexamethasone

We measured tracheal fluid production rate and pulmonary surfactant flux in 12 sets of twin fetal lambs of 102 to 135 days' gestation. In nine of these sets we also measured surfactant flux and the concentration of saturated lecithin in the lungs before and during dexamethasone infusion into one of the twins. The average tracheal fluid flow rate was 3.25 ml/kg/hr (SD 1.6) and, relative to body weight, did not change between 103 and 135 days' gestation or during the infusion of dexamethasone. In untreated fetuses, surfactant was detected between 108 and 130 days and its flux gradually increased but remained less than 150mug/kg/hr at 135 days' gestation; the amount of disaturated lecithin in the lung relative to body weight increased 13-fold from 108 to 134 days. From these data we calculated that the minimal rate of synthesis of disaturated lecithin was increased about 4-fold by dexamethasone from 108 to 120 days; this enhancement fell to about 1.8-fold by 135 days. The rate of secretion of disaturated lecithin, as estimated by surfactant flux in tracheal fluid, was increased by dexamethasone throughout the interval of the study.