Surfactant Fraction Research Articles

The role of the surfactant head group in the emulsification process: Binary (nonionic–ionic) surfactant mixtures

Dilute emulsions of dodecane in water were prepared under constant flow rate conditions with binary surfactant systems. The droplet size distribution was measured as a function of the mixed surfactant composition in solution. The systems studied were (a) the mixture of anionic sodium dodecyl sulfate (SDS) with nonionic hexa(ethyleneglycol) mono n-dodecylether (C 12E 6) and (b) the mixture of cationic dodecyl pyridinium chloride (DPC) with C 12E 6. At a constant concentration of SDS or DPC surfactant in solution (below the CMC) the mean emulsion droplet size decreases with the increase in the amount of C 12E 6 added to the solution. However, a sharp break of this droplet size occurs at a critical concentration and beyond this point the mean droplet size did not significantly change upon further increase of the C 12E 6. This point was found to corresponded to the CMC of the mixed surfactant systems (as previously determined from microcalorimetry measurements) and this result suggested the mixed adsorption layer on the emulsion droplet was similar to the surfactant composition on the mixed micelles. The emulsion droplet size as a function of composition at the interface was also studied. The mean emulsion droplet size in SDS–C 12E 6 solution was found to be lower than that in DPC–C 12E 6 system at the equivalent mole fraction of ionic surfactant at interface. This was explained by the stronger interactions between sulphate and polyoxyethylene head groups at the interface, which facilitate the droplet break-up. Counterion binding parameter ( β) was also determined from zeta-potential of dodecane droplets under the same conditions and it was found that ( β) was independent of the type of the head group and the mole fraction of ionic surfactant at interface.

Thermodynamics of Micelle Asymmetrization in Aqueous Sodium Decyl Sulfate Solution

The process of asymmetrization of spherical micelles in an aqueous sodium decyl sulfate solution is studied by scanning calorimetry. This process represents the intermicellar phase transition with an equilibrium temperature of 300 K occurring at a sodium decyl sulfate concentration of 0.12 mol/kg. The partial molar heat capacities of sodium decyl sulfate in a solution are determined and the thermodynamic functions of the rearrangement of micelles and their temperature dependences are calculated. The regions of the thermodynamic stability of solutions that contain spherical and nonspherical micelles, the former being predominant, are revealed. Equilibrium constants of the process and fractions of surfactant aggregated into spherical and nonspherical micelles are calculated for the model of monomolecular reversible reaction. For nonspherical micelles, the shape of the ellipsoid of revolution is proposed.

Effect of temperature and salt on the phase behavior of nonionic and mixed nonionic–ionic microemulsions with fish-tail diagrams

The phase behavior of Brij-56/1-butanol/n-heptane/water is investigated at 30 °C with α [weight fraction of oil in (oil + water)] =0.5, wherein a 2̲→3→2¯ phase transition occurs with increasing W1 (weight fraction of 1-butanol in total amphiphile) at low X (weight fraction of both the amphiphiles in the mixture) and a 2̲→1→2¯ phase transition occurs at higher X. Addition of an ionic surfactant, sodium dodecylbenzene sulfonate, destroys the three-phase body and decreases the solubilization capacity of the system at different δ (weight fraction of ionic surfactant in total surfactant). A three-phase body appears at α=0.25, but not at α=0.75 for the single system. No three-phase body appears with the mixed system at either α value. Increased temperature increases the solubilization capacity of the Brij-56 system; on the other hand, a negligible effect of temperature on the Brij-56/SDBS mixed system has been observed. Addition of salt (NaCl) produces a three-phase body for both single and mixed systems and increases their solubilization capacities. The monomeric solubility of 1-butanol in oil (S1) and at the interface (S1s) has been calculated using the equation hydrophile–lipophile balance plane for both singles- and mixed-surfactant systems. These parameters have been utilized to explain the increase in solubilization capacity of these systems in the presence of NaCl.

Altered lung phospholipid metabolism in mice with targeted deletion of lysosomal-type phospholipase A2

Lung surfactant dipalmitoylphosphatidylcholine (DPPC) is endocytosed by alveolar epithelial cells and degraded by lysosomal-type phospholipase A2 (aiPLA2). This enzyme is identical to peroxiredoxin 6 (Prdx6), a bifunctional protein with PLA2 and GSH peroxidase activities. Lung phospholipid was studied in Prdx6 knockout (Prdx6-/-) mice. The normalized content of total phospholipid, phosphatidylcholine (PC), and disaturated phosphatidylcholine (DSPC) in bronchoalveolar lavage fluid, lung lamellar bodies, and lung homogenate was unchanged with age in wild-type mice but increased progressively in Prdx6-/- animals. Degradation of internalized [3H]DPPC in isolated mouse lungs after endotracheal instillation of unilamellar liposomes labeled with [3H]DPPC was significantly decreased at 2 h in Prdx6-/- mice (13.6 +/- 0.3% vs. 26.8 +/- 0.8% in the wild type), reflected by decreased dpm in the lysophosphatidylcholine and the unsaturated PC fractions. Incorporation of [14C]palmitate into DSPC at 24 h after intravenous injection was decreased by 73% in lamellar bodies and by 54% in alveolar lavage surfactant in Prdx6-/- mice, whereas incorporation of [3H]choline was decreased only slightly. Phospholipid metabolism in Prdx6-/- lungs was similar to that in wild-type lungs treated with MJ33, an inhibitor of aiPLA2 activity. These results confirm an important role for Prdx6 in lung surfactant DPPC degradation and synthesis by the reacylation pathway.

Sorption study of 2,4-dichlorophenol on organoclays constructed for soil bioremediation

The role of the type and amount of cationic surfactant in the sorption behaviour of partially modified clays was studied and the applicability of a partially modified organoclay for bioremediation was demonstrated. Partially modified surfactant/clay complexes (“organoclays”) were prepared from Na-montmorillonite by using monoalkyl-(dodecyltrimethylammonium and octadecyltrimethylammonium) and dialkylammonium (didodecyldimethylammonium and dioctadecyldimethylammonium) bromides. The degree of modification was varied between 35 and 89% of the cation exchange capacity of montmorillonite (MM). The sorption of 2,4-dichlorophenol (DCP) on organoclays was studied by using the batch technique. The intercalation of DCP into the interlayers of organo-MM was detected by X-ray diffraction. The adsorption isotherms found were non-linear indicating that the sorption is not only based on a simple partition mechanism. The adsorption coefficients K d calculated from the initial isotherm slope turned out to be exponential with the organic carbon content of organo-MM ( f oc). In particular, dialkylammonium-modified MM revealed outstanding sorption characteristics for DCP. The comparison of partially modified organo-MMs with similar f oc and volume fraction of surfactant indicated that the surfactant arrangement in the interlayers significantly influences the DCP adsorption. It could be assumed that both the kind and degree of exchanged surfactant play a decisive role in the adsorption of DCP on the organoclays. By performing biodegradation experiments in the presence of dioctadecyldimethylammonium montmorillonite, the complete biodegradation of DCP was achieved demonstrating the applicability of partially modified organoclays for bioremediation.

Surface Properties of Gleditsia Saponin and Synergisms of Its Binary System

A gleditsia saponin (GS) is isolated and purified from the fruits of Gleditsia sinensis Lam. Its surface and thermodynamic properties in aqueous solution at 0, 15, 25, 35, 45, and 60°C have been investigated by surface tension measurement. The major data at 25°C are the critical micelle concentration (cmc), 1.10E‐3 mol · L−1; the surface tension at cmc (γ cmc ), 34.4 mN · m−1; the maximum surface excess concentration (Γmax), 2.33E‐6 mol · m2; the minimum area per molecule (A cmc ), 0.712 nm2; the standard adsorption energy (ΔG ad 0), −32.9 kJ · mol−1; and the standard micellization energy (ΔG m 0), −16.9 kJ · mol−1. The molecular interaction parameters, β s and β m , for the binary systems of GS with a cationic surfactant (C16H33NMe3Br), an anionic surfactant (C12H25SO3Na), and a nonionic surfactant (C8H17Ph(EO)10OH) have been determined. Based on the regular solution treatments of Rubingh, Rosen, and their coworkers, the conditions of synergism in surface tension reduction effectiveness have been extended. The condition to produce this synergism and the corresponding parameters at the maximum synergism point, i.e., the mole fractions of surfactant 1 in the solution phase (α1*), the critical micelle concentration of mixtures (cmc 12*), and the surface tension at this concentration (γ cmc12*), are given. The results show that of the three binary systems, synergism in micelle formation can occur only in the mixture of GS with cationic surfactants; synergism in surface tension reduction efficiency can occur in the mixture of GS with both cationic surfactant and nonionic surfactants, but, all the binary systems of GS with ionic and nonionic surfactants can show remarkable synergism in surface tension reduction effectiveness.

Horseradish Peroxidase Activity in a Reverse Catanionic Microemulsion

In this paper we present the first results of enzymatic activities in a reverse microemulsion medium based on a mixture of an anionic and a cationic surfactant, called catanionic microemulsion. The studied system is composed of sodium dodecyl sulfate (SDS)/dodecyltrimethylammonium bromide (DTAB)/n-hexanol/citrate buffer/n-dodecane, with high SDS/(SDS + DTAB) weight fractions. It turns out that the results are similar to those obtained in classical reverse microemulsions, except that the presence of DTAB exerts an inhibiting effect on the enzyme. Nevertheless, enzymatic superactivities are found even at a DTAB to total surfactant ratio of 15%, corresponding to 3% weight fraction of cationic surfactant in the microemulsion. The influence of pH and hexanol content on the enzymatic activities is also studied.

Water solubilization capacity of mixed reverse micelles: Effect of surfactant component, the nature of the oil, and electrolyte concentration

Solubilization of water in mixed reverse micellar systems with anionic surfactant (AOT) and nonionic surfactants (Brijs, Spans, Tweens, Igepal CO 520), cationic surfactant (DDAB)–nonionic surfactants (Brijs, Spans, Igepal CO 520), and nonionic (Igepal CO 520)–nonionics (Brijs, Spans) in oils of different chemical structures and physical properties (isopropyl myristate, isobutyl benzene, cyclohexane) has been studied at 303 K. The enhancement in water solubilization has been evidenced in these systems with some exceptions. The maximum water solubilization capacity ( ω 0 , max ) in mixed reverse micellar systems occurred at a certain mole fraction of a nonionic surfactant, which is indicated as X nonionic , max . The addition of electrolyte (NaCl or NaBr) in these systems tends to enhance their solubilization capacities further both at a fixed composition of nonionic ( X nonionic ; 0.1) and at X nonionic , max at 303 K. The maximum in solubilization capacity of electrolyte ( ω max ) was obtained at an optimal electrolyte concentration (designated as [NaCl] max or [NaBr] max). All these parameters, ω 0 , max vis-à-vis X nonionic , max and ω max vis-à-vis [NaCl] max, have been found to be dependent on the surfactant component (content, EO chains, and configuration of the polar head group, and the hydrocarbon moiety of the nonionic surfactants) and type of oils. The conductance behavior of these systems has also been investigated, focusing on the influences of water content ( ω), content of nonionics ( X nonionic ), concentration of electrolyte ([NaCl] or [NaBr]), and oil. Percolation of conductance has been observed in some of these systems and explained by considering the influences of the variables on the rigidity of the oil/water interface and attractive interactions of the surfactant aggregates. Percolation zones have been depicted in the solubilization capacity vs X nonionic or [electrolyte] curves in order to correlate with maximum in water or electrolyte solubilization capacity. The overall results, obtained in these studies, have been interpreted in terms of the model proposed by Shah and co-workers (Langmuir 3 (1987) 1086; J. Colloid Interface Sci. 120 (1987) 320 and 330) for the solubility of water in water-in-oil microemulsions, as their model proposed that the two main effects that determine the solubility of these systems are curvature of the surfactant film separating the oil and water and interactions between water droplets.

SURFACTANT PROTEIN C BIOSYNTHESIS AND ITS EMERGING ROLE IN CONFORMATIONAL LUNG DISEASE

Surfactant protein C (SP-C) is a hydrophobic 35-amino acid peptide that co-isolates with the phospholipid fraction of lung surfactant. SP-C represents a structurally and functionally challenging protein for the alveolar type 2 cell, which must synthesize, traffic, and process a 191-197-amino acid precursor protein through the regulated secretory pathway. The current understanding of SP-C biosynthesis considers the SP-C proprotein (proSP-C) as a hybrid molecule that incorporates structural and functional features of both bitopic integral membrane proteins and more classically recognized luminal propeptide hormones, which are subject to post-translational processing and regulated exocytosis. Adding to the importance of a detailed understanding of SP-C biosynthesis has been the recent association of mutations in the proSP-C sequence with chronic interstitial pneumonias in children and adults. Many of these mutations involve either missense or deletion mutations located in a region of the proSP-C molecule that has structural homology to the BRI family of proteins linked to inherited degenerative dementias. This review examines the current state of SP-C biosynthesis with a focus on recent developments related to molecular and cellular mechanisms implicated in the emerging role of SP-C mutations in the pathophysiology of diffuse parenchymal lung disease.

Solubilization by different-sized surfactant mixtures

The solubilization phenomenon was investigated in mixed surfactant systems. The solubilization power of a mixed surfactant reaches its maximum at a particular temperature at each mixing ratio of surfactants. When the mole fraction of C 4E 1 in the total surfactant ( w 1 value) was varied in a water/C 12E 5/C 4E 1/decane system, the minimum mole fraction of total surfactant in the system necessary to obtain a single microemulsion phase ( ξ value) was almost unchanged for w 1 < 0.3 , whereas it increased remarkably for w 1 > 0.8 . The molar solubilization capacity ( C s = ( 1 − ξ ) / ξ ) of the mixed surfactant decreased remarkably for w 1 < 0.3 , whereas it decreased gradually for w 1 > 0.8 . The result | d ξ / d w 1 | w 1 < 0.3 < | d ξ / d w 1 | w 1 > 0.8 is due largely to the characteristic of the function ξ ( C s ) = 1 / ( 1 + C s ) , specifically, | d ξ / d C s | w 1 < 0.3 < | d ξ / d C s | w 1 > 0.8 , where d ξ / d w 1 = ( d ξ / d C s ) ( d C s / d w 1 ) . The partial molar solubilization capacity ( C ¯ s ) of C 4E 1 was negative at almost all w 1 , but the C ¯ s value of C 12E 5 went through a maximum on the addition of C 4E 1. Propanol (a cosurfactant) has the same effect on the solubilization phenomenon in the water/C 12E 6/propanol/heptane system. In the water/C 12E 5/C 12E 7/decane system, the C ¯ s value of each surfactant did not vary greatly as the mixing ratio of surfactants was varied. The C s and ξ values were close to molar additivity for each mixing ratio.

Effect of NaCl and temperature on the water solubilization behavior of AOT/nonionics mixed reverse micellar systems stabilized in IPM oil

Solubilization of water in mixed reverse micellar systems formed with anionic surfactant (AOT) and nonionic surfactants (Brij-30, Brij-35, Brij-52, Brij-56, Brij-58, Brij-76, Tween-20, Tween-40, Span-20, Span-40, Span-60, Span-80) in isopropyl myristate (IPM) oils has been studied. The enhancement in water solubilization (i.e. synergism) has been evidenced by the addition of nonionic surfactants to AOT/IPM system. The maximum water solubilization capacity ( ω 0,max) and the mole fraction of nonionic surfactant at which maximization occurs ( X nonionic,max) in these mixed reverse micellar systems has been found to depend on surfactant component (size and nature of polar group and hydrocarbon moiety of the surfactant). The addition of electrolyte (NaCl) in these systems has been found to enhance the solubilization capacity ( ω max) depending upon the content and their EO chains and type of polar head group of nonionic surfactant used. The maximum solubilization of electrolyte, ω max was obtained at an optimal concentration of it ([NaCl] max), which depends on the content and their EO chains and type of polar heads of the nonionic surfactants. The temperature induced solubilization of water (in absence and presence of additives) for AOT blended with nonionic surfactants (Brijs, Tweens, Spans) at different compositions has been investigated. The stability of these systems with respect to temperature has been found to be dependent on the content and nature of the polar head group as well as the hydrophobic moiety of the nonionics. The energetic parameters ( Δ G ¯ ° , Δ H ¯ ° and Δ S ¯ ° ) of the desolubilization process of water in the mixed systems have been estimated from the solubilization capacity–temperature profile. An attempt has been made to shed more insight into the process of solubilization–desolubilization of water (or aqueous NaCl) in mixed reverse micelles stabilized in IPM oil on the basis of the model proposed by Shah et al. [M.J. Hou, D.O. Shah, Langmuir 3 (1987) 1086; R. Leung, D.O. Shah, J. Colloid Interf. Sci. 120 (1987) 320, 330] and thermodynamic approach.

Tracer and mutual diffusion of nonionic and ionic mixed micellar systems: octa- and hexa-ethylene glycol monododecyl ether and long-chain ionic surfactants

Tracer diffusion coefficients, D t, for mixed micelles and mutual diffusion coefficients, D m, for mixed surfactants were measured in water at 298.15 K for systems of a nonionic surfactant, octaethylene glycol monododecyl ether (C 12E 8) or hexaethylene glycol monododecyl ether (C 12E 6), and a long-chain ionic surfactant, octadecyltrimethylammonium chloride (C 18TACl) or sodium octadecanesulfonate (C 18SO 3Na) using the Taylor dispersion method. Aggregation numbers of the mixed micelles were determined by measuring the monomer fluorescence decay of pyrene solubilized in the micelles. When C 18TACl or C 18SO 3Na was added to the 10 mM (1 M=1 mol dm −3) solution of C 12E 8, D t values decreased monotonically with increasing fraction of the ionic surfactants. When C 18TACl or C 18SO 3Na was added to the 10 mM solution of C 12E 6, D t values increased first and then decreased with increasing fraction of the ionic surfactants, reflecting the decrease in the aggregation number and increase in the micelle-medium electrostatic interactions with increasing ionic surfactant fraction. When C 18TACl or C 18SO 3Na was added to the 10 mM solution of C 12E 8 or C 12E 6, the D m values increased up to a concentration of 2 mM and then reached plateaus with increasing ionic surfactant concentration. Using surfactant and counter ion selective electrodes, concentrations of free ions were measured and ionic charges of the mixed micelles were calculated. From the D t values of the mixed micelles and counter ions, together with the numbers of free counter ion per micelle, D m values were calculated and compared with those measured.

Clean-up of Oily Wastewater by Froth Flotation: Effect of Microemulsion Formation III: Use of Anionic/Nonionic Surfactant Mixtures and Effect of Relative Volumes of Dissimilar Phases

ABSTRACTFroth flotation, a surfactant-based separation process, can be used to remove emulsified oil from water. In previous work, the maximum removal of ortho-dichlorobenzene from water using froth flotation was achieved when a Winsor Type III microemulsion was formed. However, the exact relationship between the equilibrium microemulsion characteristics and the froth flotation operation is still not clear. In the Winsor Type III microemulsion, three phases are present: an excess water phase containing little surfactant or oil, an excess oil phase containing little water or surfactant, and a middle phase containing almost all of the surfactant and large volume fractions of both oil and water (even equal volumes of oil and water). The Winsor Type III microemulsion also corresponds to a minimum in interfacial tension between liquid phases at equilibrium. In order to elucidate which aspect of the microemulsion is responsible for flotation of oil, flotation experiments were performed with three different combinations of phases: water and middle phases (w-m); water and oil phases (w-o); and water, middle, and oil phases (w-m-o). Since it was deduced that most oil being recovered when in the Winsor Type III microemulsion region is in the excess oil phase (not the middle phase), the reason why the Winsor Type III microemulsion results in excellent oil removal in flotation operation is probably the ultralow interfacial tensions present, and the formation of the middle phase is incidental.

The role of surfactants in Köhler theory reconsidered

Abstract. Atmospheric aerosol particles typically consist of inorganic salts and organic material. The inorganic compounds as well as their hygroscopic properties are well defined, but the effect of organic compounds on cloud droplet activation is still poorly characterized. The focus of the present study is the organic compounds that are surface active i.e. tend to concentrate on droplet surface and decrease the surface tension. Gibbsian surface thermodynamics was used to find out how partitioning between droplet surface and the bulk of the droplet affects the surface tension and the surfactant bulk concentration in droplets large enough to act as cloud condensation nuclei. Sodium dodecyl sulfate (SDS) was used together with sodium chloride to investigate the effect of surfactant partitioning on the Raoult effect (solute effect). While accounting for the surface to bulk partitioning is known to lead to lowered bulk surfactant concentration and thereby to increased surface tension compared to a case in which the partitioning is neglected, the present results show that the partitioning also alters the Raoult effect, and that the change is large enough to further increase the critical supersaturation and hence decrease cloud droplet activation. The fraction of surfactant partitioned to droplet surface increases with decreasing droplet size, which suggests that surfactants might enhance the activation of larger particles relatively more thus leading to less dense clouds. Cis-pinonic acid-ammonium sulfate aqueous solutions were studied in order to study the partitioning with compounds found in the atmosphere and to find out the combined effects of dissolution and partitioning behavior. The results show that the partitioning consideration presented in this paper alters the shape of the Köhler curve when compared to calculations in which the partitioning is neglected either completely or in the Raoult effect. In addition, critical supersaturation was measured for SDS particles with dry radii of 25-60nm using a static parallel plate Cloud Condensation Nucleus Counter. The experimentally determined critical supersaturations agree very well with theoretical calculations taking the surface to bulk partitioning fully into account and are much higher than those calculated neglecting the partitioning.

Release behavior of triazine residues in stabilised contaminated soils

This paper reports the release behavior of two triazines (atrazine and simazine) in stabilised soils from a pesticide-contaminated site in South Australia. The soils were contaminated with a range of pesticides, especially with triazine herbicides. With multiple extractions of each soil sample with deionised water (eight in total), 15% of atrazine and 4% of simazine residues were recovered, resulting in very high concentrations of the two herbicides in leachate. The presence of small fractions of surfactants was found to further enhance the release of the residues. Methanol content up to 10% did not substantially influence the concentration of simazine and atrazine released. The study demonstrated that while the stabilisation of contaminated soil with particulate activated carbon (5%) and cement mix (15%) was effective in locking the residues of some pesticides, it failed to immobilise triazine herbicides residues completely. Given the higher water solubility of these herbicides than other compounds more effective strategies to immobilise their residues is needed.

Study on the interaction of anionic dye–nonionic surfactants in a mixture of anionic and nonionic surfactants by absorption spectroscopy

The interaction between an anionic dye C.I. Reactive Orange 16 (RO16) and different surfactants, i.e., the anionic surfactant sodium dodecylsulfate (SDS) and nonionic surfactants polyoxyethylene ethers (C m POE n ; m = 12, 16 and 18, n = 4, 10 and 23) has been researched spectrophotometrically in a certain micellar concentration range. Light absorbances in the visible spectral range are measured as a function of mole fraction of surfactant at four different temperatures and at 24 h over the periodic time intervals. For this reason, a typical system occurred at 1.0 × 10 −2 mol/l for surfactants and at 1.0 × 10 −4 mol/l for dye concentrations. It is evident from the experimental measurements that while nonionic surfactants form a complex with the anionic dye RO16 in aqueous solution in studied concentration range, anionic surfactant does not. The formation of C m POE n –RO16 complex in the SDS solutions of different mole fractions in its micellar concentration range has been determined and compared to those obtained in the dye–surfactant binary mixtures. Spectrophotometric measurements indicated that the value of absorbance of SDS–RO16 is greater than that of nonionic surfactant–RO16 in the binary systems. This state explains that the ionic and hydrophobic interactions between SDS–RO16 are less than that of nonionic surfactant–RO16 interactions. The addition of SDS to the mixture of C m POE n –RO16 causes an increase in the value of absorbance. This increase is due to changed hydrophobic–hydrophilic balance of the studied mixtures. Furthermore, we observed that the alkyl chain length and the number of polyoxyethylene in nonionic surfactants do not have an enormous effect on the values of absorbance.

A Monitoring System for Selective Determination of Alkylphenol Ethoxylates by the Adsorptive Stripping‐Indirect Tensammetric Technique

AbstractA new monitoring system for the adsorptive stripping‐indirect tensammetric technique has been developed. The system responded selectively to alkylphenol ethoxylates having 5–14 oxyethylene subunits (APE) (being a fraction of nonionic surfactants). It consists of 20 ppm of Mannoxol OT and 20 ppb of tetrabutylammonium bromide (TBAB). In the presence of APE a tensammetric peak of the monitoring mixture is growing. A calibration plot has a slightly sigmoidal shape; the dynamic response range is from 0.5 to 2.0 μg and the detection limit is 0.075 μg. APE determination is highly tolerant to alcohol ethoxylates (AE) having a C18 hydrophobic part, however, the tolerance of AE having a C12 hydrophobic part is small (the APE signal is only three times higher than that of AE having a C12 hydrophobic part). An analytical response to a mixture consisting different nonionic surfactants (NS) is approximately additive. The developed monitoring system was applied to the determination of an APE fraction in 14 river water samples. NS were separated from the water matrix by liquid‐liquid extraction with chloroform. The recovery of Triton X‐100 spike was 102% and the precision 6.5%.

229 Effect of Perfluorocarbon on Pulmonary Surfactant. An Electron Microscopical and Stereological Study

Background: Partial liquid ventilation (PLV) represents an alternative therapy of severe respiratory insufficiency, caused by disturbances of the pulmonary surfactant. To wean patients from PLV an intact surfactant system is required. Data concerning the interaction of perfluorocarbons (PFC) with surfactant metabolism are controversial. According to in vitro data we hypothesized that intracellular surfactant pool is reduced in PLV treated animals.Methods: Prospective, randomized animal study on male wistar rats. Surfactant depleted rats were treated with either PLV (Lavaged-PFC, n=5) or conventional mechanical ventilation (Lavaged-Air, n=5) for 1 hour. For control, 10 healthy animals with air (Healthy-Air, n=5) or PFC filled lungs (Healthy-PFC, n=5) were studied. A design-based stereological approach was used for quantification of lung parenchyma and the intracellular and intraalveolar surfactant pool at the light and electron microscopic level.Results: Compared to Healthy-lungs, Lavaged-animals had more type II cells with lamellar bodies in the process of secretion and freshly secreted lamellar body like surfactant in the alveoli. Fraction of surfactant covered alveolar epithelial surface area and total intraalveolar surfactant content were significantly smaller in Lavaged-animals. Compared with Air-filled lungs, both PFC-groups had a significantly higher total lung volume, but no other differences.Conclusion: In contrast to the hypothesis, short term PLV in surfactant depleted animals neither affects the intracellular and intraalveolar surfactant composition nor the surfactant content.

Study of the electrostatic and steric contributions to the free energy of ionic/nonionic mixed micellization

We have investigated mixed micelle formation in mixtures of ionic and nonionic surfactants. Three types of ionic surfactant were used: CTAB (hexadecyltrimethylammonium bromide), CPC (hexadecylpyridinium chloride) and CPB (hexadecylpyridinium bromide). These surfactants all have a hexadecyl chain but contain different head groups. The use of CPC and CPB, which differ only in counter ion, allowed investigation of counter ion effects. TritonX-100 ( p-(1,1,3,3-tetramethylbutyl) polyoxyethylene) was used as the nonionic surfactant in all experiments. PFG-NMR was used to measure the self-diffusion coefficients of the mixed micelles as a function of solution composition and total surfactant concentration. The aggregation number and hydrodynamic radius of each type of mixed micelle were determined by combining viscosity and self-diffusion coefficient measurements. The electrostatic and steric contributions to the free energy of mixed micellization, which are considered to be the most important contributions for mixtures of ionic and nonionic surfactants with different head groups, were determined. The electrostatic free energy was determined by solving an analytical approximation to the Poisson–Boltzmann equation. The electrostatic free energy varied dramatically with increasing mole fraction of ionic surfactant in the CTAB/TritonX-100 system but increased more gradually in the CPC/TritonX-100 and CPB/TritonX-100 systems. The more pronounced change for CTAB/TritonX-100 system can be attributed to the trimethylammonium headgroup of CTAB, which confers a high surface charge density and thus a high electrostatic free energy.

Observation of two diffusive relaxation modes in microemulsions by dynamic light scattering.

Water-in-oil microemulsions stabilized by AOT and dispersed in n-alkane oils with a constant molar water-to-surfactant ratio were studied by dynamic light scattering. A dilution series (in the range of volume fraction of water plus surfactant, phi approximately 0.02-0.52) was used, which allowed us to extract information about droplet sizes, diffusion coefficients, interactions, and polydispersity from experimental data. We report the observation of two diffusive relaxation modes in a concentrated microemulsion (0.20 < phi < 0.5) due to density (collective diffusion) and concentration or polydispersity (self-diffusion) fluctuations. Below this concentration it was difficult to resolve two exponentials unambiguously, and in this case one apparent relaxation mode was observed. It was found that for a given composition self-diffusion is more pronounced in apparent relaxation mode for a shorter chain length alkane. The concentration dependence of these diffusion coefficients reflects the effect of hard sphere and the supplementary attractive interactions. It was observed that the attractive part becomes more pronounced in the case of a large alkane chain oil at a given temperature. This explains the shift of the region of microemulsion stability to lower temperatures for higher chain length alkanes. Increase in hydrodynamic radius, Rh, obtained from the diffusion coefficient extrapolated to infinite dilution was observed with increase of alkane chain length. The polydispersity in microemulsion systems is dynamic in origin. Results indicate that the time scale for local polydispersity fluctuations is at least 3 orders of magnitude longer than the estimated time between droplet collisions.