Micelle-forming Surfactants Research Articles

Synthesis of Stable Polystyrene and Poly(methyl methacrylate) Particles in the Presence of Carboxymethyl Cellulose

The synthesis of polystyrene or poly(methyl methacrylate) in the presence of carboxymethyl cellulose (CMC), a cellulose derivative, was carried out by emulsion polymerization using a cationic surfactant, cetyltrimethylammonium bromide (CTAB). First, the complex formation between CTAB and CMC was studied by surface tension measurements. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at 0.25 mmol L-1 CTAB and 1.0 g L-1 CMC. The hybrid particles were characterized by ζ potential and light scattering measurements and scanning electron microscopy. All dispersions were stable in the ionic strength of 2.0 mol L-1 NaCl at least for 4 days. The colloidal stability was attributed to the presence of a hydrated CMC layer around the particles. The present procedure brings the advantage of synthesizing and stabilizing particles with functional groups on the surface in a one-step method using very small amo...

Monte Carlo study of shear-induced alignment of cylindrical micelles in thin films

The behavior of confined cylindrical micelle-forming surfactants under the influence of shear has been investigated using Monte Carlo simulations. The surfactants are modeled as coarse-grained lattice polymers, while the Monte Carlo shear flow is implemented with an externally imposed potential energy field which induces a linear drag velocity on the surfactants. It is shown that, in the absence of shear, cylindrical micelles confined within a monolayer coarsen gradually with Monte Carlo "time" t , the persistence length of the micelles scaling as t(0.24) , in agreement with the scaling obtained experimentally. Under the imposition of shear, the micelles within a monolayer align parallel to the direction of shear, as observed experimentally. Micelles confined within thicker films also align parallel to each other with a hexagonal packing under shear, but assume a finite tilt with respect to the velocity vector within the velocity-velocity gradient plane. We propose a mechanism for this shear-induced alignment of micelles based on breaking up of micelles aligned perpendicular to the shear and their reformation and subsequent growth in the shear direction. It is observed that there exists a "window" of shear rates within which such alignment occurs. A simple theory proposed to explain the above behavior is in good agreement with simulation results. A comparison of simulated and experimental self-diffusivities yields a physical time scale for Monte Carlo moves, which enables an assessment of the physical shear rates employed in our Monte Carlo simulations.

Cerasome as an Organic-Inorganic Vesicular Nanohybrid: Characterization of Cerasome-Forming Lipids having a Single or a Dual Trialkoxysilyl Head

Morphological characterization of the organic-inorganic vesicular nanohybrids, Cerasomes, was performed in aqueous media from two aspects. Firstly, a novel Cerasome-forming lipid having two triethoxysilyl groups in the head moiety was synthesized and the physical property of the Cerasome was investigated. While the morphological stability of the Cerasomes, as evaluated from the vesicular collapse behavior against a micelle-forming nonionic surfactant, Triton-X 100, was extremely higher than that of the conventional phospholipid liposome, the stabilities were comparable to each other for the Cerasomes derived from the dual- and single-head lipids. On the other hand, the surface property of the Cerasome formed with the dual-head lipid more closely resembled the colloidal silica particles rather than that derived from the single-head lipid, as suggested by zeta-potential measurements. Secondly, the effect of the media pH on the morphological stability of the Cerasome formed with the single-head lipid was evaluated and appeared as a time difference in obtaining the morphological stability of the Cerasome. These morphological characteristics of the Cerasomes could be mainly owing to the development of the siloxane network on the vesicular surface.

Thermodynamic Stability of Clusters of Molybdenum Oxide

We show that a single geometrical rule underlies the stability of "polyoxomolybdates", the variety of clusters of molybdenum(VI) oxide in (acidified) aqueous solution that are found experimentally. We predict that upon increasing the proton or total molybdenum oxide concentration, the average size of the clusters increases. We compare our predictions with results from ultracentrifugation experiments and with data in the literature. Finally, it is shown that the formation of metal oxide clusters is thermodynamically equivalent to the formation of surfactant micelles.

Surfactant-aided size exclusion chromatography

The flexibility and selectivity of size exclusion chromatography (SEC) for protein purification can be modified by adding non-ionic micelle-forming surfactants to the mobile phase. The micelles exclude proteins from a liquid phase similar to the exclusion effect of the polymer fibers of the size exclusion resin. This surfactant-aided size exclusion chromatography technology (SASEC) is demonstrated on the separation of two model proteins; bovine serum albumin (BSA) and myoglobin (Myo). The effect of the added surfactants on the distribution behavior of the proteins is predicted adequately by a size exclusion model presented in this paper.

Basic Hydrolysis of Crystal Violet in β-Cyclodextrin/Surfactant Mixed Systems

The basic hydrolysis of crystal violet (CV) in mixed systems consisting of beta-cyclodextrin (beta-CD) and a micelle-forming surfactant, cetyltrimethylammonium chloride (CTACl), has been studied. beta-CD was found to catalyze the basic hydrolysis of CV through the interaction of its hydroxyl group, in its deprotonated form, with the carbocation in the complexed substrate. The addition of small amounts of CTACl, with [CTACl] below the critical micelle concentration, to beta-CD solutions does not have an effect upon the observed rate constant for the basic hydrolysis of CV. This behavior is different from that observed for the alkaline hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide and nitrophenyl acetates in mixed beta-CD/cationic surfactant systems. The proposed mechanism allows us to explain the experimental results on the basis of the high percentage of uncomplexed beta-CD in equilibrium with the micellar system, the low CV concentration, and the high value for the binding constant of CV by beta-CD.

Rheology of Mixed Solutions of an Associating Polymer with a Surfactant. Why Are Different Surfactants Different?

The effects of nine different anionic and cationic micelle-forming surfactants on the viscosity and viscoelasticity of semidilute solutions of hydrophobically modified hydroxyethyl cellulose (HMHEC) were studied. All added surfactants gave rise to the well-established viscosity maximum with increasing surfactant concentration, but the total surfactant concentration at the maximum, as well as the magnitude of the viscosity enhancement, varied wide y between the different surfactants. A detailed analysis of the oscillatory shear data for the most viscous samples showed that added surfactant affects both the lifetime and the structure of the transient HMHEC-surfactant network, due to mixed micellization between surfactant molecules and the hydrophobic side chains of HMHEC. The viscosity maximum is the result of two opposing effects of increasing surfactant concentration: an increase in the lifetime of mixed micellar cross-links and a decrease in the number of cross-links. All data indicate that the structure of the HMHEC-surfactant network and the compositions of the mixed micellar cross-links are quite similar for the various surfactants, when the mixtures are compared at their respective viscosity maxima. The shifts of the viscosity versus surfactant concentration curves between the various surfactants may thus be rationalized in terms of differences in lifetimes of the mixed micellar junctions and in the proportions of free (monomeric) surfactant. T e free surfactant concentration at a given degree of surfactant binding is proportional to the critical micelle concentration of the surfactant. The lifetime of a mixed micellar cross-link increases with surfactant chain length and with the nature of the hydrophilic headgroup according to the series trimethylammonium < ammonium approximate to diethoxysulfate < sulfate. (Less)

Estimation of polymer/water interfacial tensions: hydrophobic homopolymer/water interfaces

In this study, quantitative models for monomer/water and the corresponding polymer/water interfaces were developed. The monomer/water interface was modeled within the framework proposed by Fu and Li (Chem. Eng. Sci. 44 (1989) 1519) for organic liquid/water interfaces. We took a similar approach with that which others used to simulate micelle formation of surfactants and block polymers in developing the model for the polymer/water interface. In this model, the Gibbs free energy of interfacial formation was decomposed into two components: transfer free energy of a polymer segment to the interface and mixing free energy within the interface. Interfacial tensions were then estimated using concentration gradient theory. The ratio of the number of total nearest neighbors of a site in a lattice within the interface to that located in each of the adjacent planes was found to be the important correlating factor. It was shown that this ratio for monomer/water interfaces and that for polymer/water interfaces are linearly related. The polymer in the interface is likely to be in the form of short polymer segments (2–4 monomer units) rather than dangling chain ends. The estimation of polymer/water interfacial tension from the models established in this work is in reasonable agreement with experimental observation.

Membrane Perturbation by Surfactant Candidates for STD Prevention

We studied surfactant-induced leakage of vesicles, comparing the efficacy of four surfactants with current or potential application in contraception and the prevention of sexually transmitted diseases: nonoxynol-9 (N-9); the amphoteric mixture known as C31G; benzalkonium chloride (BZK); sodium dodecyl sulfate (SDS). Several features are generic to the membrane leakage process independent of the surfactant used. The kinetics of the leakage process is well-characterized by a single exponential rate of release, and the rate constant increases with surfactant concentration according to a power-law dependence. Notably, however, the formation of surfactant micelles serves to enhance the rate of vesicle leakage. A method for quickly changing the effective surfactant concentration in situ, and thus the rate of vesicle leakage, is presented. Specifically, methyl-β-cyclodextrin is added to the external aqueous solution and forms inclusion complexes with surfactant, effectively reducing the concentration of soluble...

Effect of solubilization in bitemplate synthesis of a homologous series of organosilica mesophases and mesoporous molecular sieves

Peculiarities of bitemplate synthesis of a homologous series of organosilica mesophases (precursors of mesoporous molecular sieves of MCM-41 type) were studied, and an influence of a nature of templating substances and a solubilization on a perfection of their spatial structure was found. n-alkyl(C8–C18)pyridinium halides as solubilizers (micelle-forming surfactants) and monoethanolamides of saturated n-(C10–C16)aliphatic acids as solubilizate were used. Some physicochemical factors promoting a spatial ordering of organosilica mesophases and mesoporous molecular sieves were considered.

Studies on surfactant–biopolymer interaction. I. Microcalorimetric investigation on the interaction of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) with gelatin (Gn), lysozyme (Lz) and deoxyribonucleic acid (DNA)

The interaction of the surfactants cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with the biopolymers gelatin (Gn), lysozyme (Lz) and deoxyribonucleic acid (DNA) was studied by isothermal titration microcalorimetry at varied biopolymer concentration, pH and temperature. The nature of interaction of the surfactants with the biopolymers was assessed from the observed enthalpy–[surfactant] profiles. The biopolymer-induced aggregation of the surfactants was observed. The enthalpies of aggregation of amphiphiles, binding of aggregates with macromolecules, organisational change of bound aggregates, and threshold concentrations for micelle formation of surfactants in the presence of biopolymers were estimated. The results collected on the three biopolymers were analysed and compared.

The Effect of Fatty Alcohols and Valeric Acid on the Regions of Existence of a Three-Phase System Containing Water, Oil, and Surfactant

For different water–oil–surfactant systems with added aliphatic alcohols and valeric acid, conditions for the formation of the microemulsion (third) phase containing approximately equal amounts of oil and water were determined. It was established that the microemulsion phases are formed in the initial two-phase system (oil-in-water microemulsion–oil) on adding alcohols or the acid, which can be more hydrophilic or more hydrophobic than micelle-forming surfactants. Concentrations of alcohols necessary for the transformation of the three-phase system into the two-phase one were determined. The influence of energy parameters of surfactants and structural characteristics of the alcohol and basic micelle-forming surfactant on the stability of the three-phase system is discussed.

Effects of non-ionic micelles on transient chaos in an unstirred Belousov-Zhabotinsky reaction.

The behaviour of the Ce(IV)-catalyzed Belousov-Zhabotinsky (BZ) system has been monitored at 20.0 degrees C in unstirred batch conditions in the absence and presence of different amounts of the non-ionic micelle-forming surfactants hexaethylene glycol monodecyl ether (C10E6) and hexaethylene glycol monotetradecyl ether (C14E6). The influence of the non-ionic surfactants on both the kinetics of the oxidation of malonic acid (MA) by Ce(IV) species and the behaviour of the BZ reaction in stirred batch conditions has also been studied over a wide surfactant concentration range. The experimental results have shown that, in unstirred batch conditions, at surfactant concentrations below the critical micelle concentration (c.m.c.) no significant change in the dynamics of the Belousov-Zhabotinsky system occurs. Beyond this critical concentration the presence of micelles forces the BZ system to undergo a chaos-->quasi-periodicity-->period-1 transition. Thus, the surfactant concentration has been considered as a bifurcation parameter for a Ruelle-Takens-Newhouse (RTN) scenario. Addition of increasing amounts of non-ionic surfactants has no significant effect on the kinetics of the reaction between MA and Ce(IV), but it influences the oscillatory parameters of the stirred BZ system. At surfactant concentrations below the c.m.c. all the oscillatory parameters are practically unaffected by the presence of surfactant, while beyond this critical value the induction period is the same as in aqueous solution but both the oscillation period and the duration of the rising portion of the oscillatory cycle decrease. In all cases, the experimental trends have been ascribed to the enhancement in the medium viscosity due to the presence of micelles.

Rapid quantitative determination and assessment of insulin in oil formulation by micellar electrokinetic capillary chromatography.

A rapid, simple and precise micellar electrokinetic capillary chromatrography (MEKC) with diode array detector had been developed to the determination of insulin in oil formulation. As the micelle-forming ampholytic surfactant, Labrasol was chosen for the separation and analysis of the hydrophobic insulin in oil formulation in this experiment. A buffer containing 10 mmol/ml Tris-HCl plus 10% acetonitrile (ACN) at pH 8.2 was used for running buffer. Samples and tested samples were successfully separated during 8 min with a good linear range(r>0.99) and a concentration detection limit of 0.01 mg/ml. Furthermore, quantitative determinations of insulin in oil formulation had been described and assessed after handled with different pre-treatment conditions to reveal the effect of pH, temperature and tryptic digestion.

Adsorption and Electrochemical Oxidation on Carbon of Micelle-Forming Cationic Surfactants Derived from Pyrrole

The adsorption onto glassy carbon electrodes and the electrochemical oxidation in aqueous sodium tosylate or potassium nitrate electrolyte of micelle-forming cationic surfactants derived from pyrrole is described. Electrode coating by nonelectroactive, thin anion-exchanger films was observed, along with the formation of degradation products following reaction between oxidized pyrrole and water. The best film deposition efficiency was obtained with the more hydrophobic pyrrole−surfactant, which is characterized by the lower critical micelle concentration. The formation of conducting polymer films was successfully achieved by electro-oxidation of adsorbed layers of surfactant in electrolytes containing tetrafluoroborate or perchlorate anions, which decrease the solubility of the surfactant in water, thus increasing the hydrophobic character of the monomer layer.

Film Formation and Redispersion of Waterborne Latex Coatings

Poly(vinyl acetate-co-ethylene) latex dispersions are prepared and their films investigated with a focus on the effect of composition upon redispersion. Films of dispersions containing sufficient amounts of poly(vinyl alcohol) (PVA) can be redispersed in water. This property is lost in the presence of surfactant, a fact which suggests a procedure to control film formation. It is demonstrated that redispersion is due to a PVA-membrane which separates the particles. Loss of redispersibility in the presence of surfactant proceeds with the breakup of the membranes and a corresponding change of film properties. Experimental data is provided by light microscopy, mechanical testing, and TEM in conjunction with a staining method new to the field. The hypothesis is developed that interaction with surfactant leads to imperfect PVA-membranes that are no longer able to prevent latex polymer interdiffusion. Fluorescence correlation spectroscopy demonstrates the formation of surfactant micelles, as well as the simultaneous adsorption and aggregation of PVA onto the micelles. It is concluded that the competing surface of the surfactant micelles traps enough PVA to cause thinning and fragmentation of the membranes surrounding the particles, which enables interdiffusion of latex polymer. This effect can be used to convert the system from one forming a redispersible coating to one forming a nonredispersible (permanent) film.

Formation of Hierarchical Pore Structure in Silica Gel

By inducing a phase separation parallel to the sol-gel transition of alkoxy-derived silicate systems, gels with well-defined macroporous structure can be prepared. Depending on the post-gelation treatment such as aging and solvent exchange, the final pore structure in the nanometer range of dried and heat-treated gels exhibits a considerable variation. With an aim of completely controlling the hierarchical pore structure in the discrete size ranges of nanometers and micrometers, systematic experimental studies have been performed. The macroporous nature of the wet gels allows an efficient solvent exchange process compared with conventional gels only with mesopores. In addition, the surface chemistry of the wet gel skeleton affects the mesopore formation process by the solvent exchange to a great extent. The median size of mesopores larger than 5 nm can be controlled by adjusting the basic solvent exchange conditions such as pH value, temperature and bath ratio for any kind of macroporous silica gel. On the other hand, the control of pore volume independent of the mesopore size is possible only in the system incorporated with the micelle-forming surfactant. Some examples of the effects of controlled mesopores on the analytical performance of monolithic-type chromatographic columns are also presented.

Dynamic Membranes Based on Poly(N-Isopropylacrylamide-co-Heptadecyl Vinyl Ketone): Preparation and Properties

Dynamic membranes were prepared from poly(N-isopropylacrylamide-co-heptadecyl vinyl ketone) having a lower critical solution temperature in an aqueous solution and being a micelle-forming surfactant. The dependence of the critical concentration of the copolymer micellization on temperature was shown to have an extreme character, with a minimum at the lower critical solution temperature of the copolymer. The dynamic membranes are formed on both the hydrophilic (cellulose) and hydrophobic (polyacrylonitrile) supports. For the penetrants studied, it was found that the dynamic membrane formed on the hydrophobic support favors the rejection of a PEG6000, while that formed on the hydrophilic support rejects more effectively albumin and sodium cellulose sulfoacetate. We failed to realize a completely reversible thermal control of transport properties of the dynamic membranes obtained, while it was readily accomplished for the membranes obtained by grafting N-isopropylamide onto a cellulose matrix.

DNA Complexed with Oppositely Charged Amphiphile in Low-Polar Organic Solvents

The stoichiometric complexes of the DNA samples of rather different molecular masses: 300−500 b.p. (DNA1) and 5000−10000 b.p. (DNA2) with dodecyldimethylammonium (DODA) chloride as a cationic amphiphile were prepared. DNA1−DODA and DNA2−DODA complexes are soluble in low polar organic solvents, in particular, in chloroform, as well as the complexes of ordinary linear polyelectrolytes with micelle-forming ionic surfactants. The solution behavior of the DNA−DODA complexes was studied by ultracentrifugation, viscometry, isothermal diffusion, and electrical birefringence techniques. It has been found that the DNA−DODA complex species in their dilute solutions in chloroform and a chloroform−acetone mixture (2:1) are represented by individual complex macromolecules retaining a double spirality, but strongly compacted. The latter is contrasting with other polyelectrolyte−surfactant complexes, which behave in chloroform as in a good solvent, taking expanded random coil conformations. The possible reason of such a...

Kinetic model of biosurfactant-enhanced hexadecane biodegradation by Pseudomonas aeruginosa.

Many sites of environmental concern contain groundwater contaminated with nonaqueous phase liquids (NAPL). In such sites interfacial processes may affect both the equilibrium and kinetic behavior of the system. In particular, insoluble hydrocarbon partitioning and microbial biodegradation of insoluble hydrocarbon are influenced by the physicochemical and interfacial characteristics of the system. A mechanistic model describing the influence of biological surfactants on microbial biodegradation of liquid-phase insoluble hydrocarbon and subsequent reduction of nonaqueous-phase liquid hydrocarbon is presented. The model consists of six coupled differential equations which use lumped kinetic parameters to describe surfactant micelle formation and diffusion to the microbial cell, nonlinear kinetic expressions for microbial growth and degradation of insoluble hydrocarbon, kinetic spatial descriptions of the change in NAPL-phase droplet size and the organic phase volume fraction with time, as well as equilibrium partitioning expressions for hydrophobic organic contaminant partioning into the surfactant micelle. The model is validated by comparison to data obtained for hexadecane degradation in a well-mixed batch system by the biosurfactant producing microorganism Pseudomonas aeruginosa strain PG201 as well as for nonproducing mutants' growth and hexadecane biodegradation in the presence of exogenously added biosurfactant. Experimentally determined biological growth parameters, as well as physical parameters such as hydrocarbon droplet size, were applied in the kinetic model. Parameter sensitivity analysis was performed on the physical and biological parameters in the model. The parameter sensitivity analysis indicates that for the biological system examined the rate of hydrocarbon solubilization and micellar transport to the cell controls the rate at which cellular uptake and biodegradation of insoluble hydrocarbon occurs. Practical aspects relating to use of the model for support of surfactant-based bioremediation efforts are discussed.