Surfactants In Aqueous Media Research Articles

Poly (3,4‐ethylenedioxythiophene) γ‐Fe2O3 polymer composite–super paramagnetic behavior and variable range hopping 1D conduction mechanism–synthesis and characterization

AbstractThe present paper reports the preparation of poly (3,4‐ethylenedioxythiophene) (PEDOT) ferrimagnetic conducting polymer composite by incorporation of ferrite particles in the polymer matrix by emulsion polymerization. Synthesis of PEDOT–γ‐Fe2O3 composite was carried out by chemical oxidative polymerization of EDOT with ferrite particles in the presence of dodecylbenzenesulfonic acid (DBSA) that works as dopant as well as surfactant in aqueous medium. The resulting conducting composite possesses saturation magnetization (Ms) value of 20.56 emu/g with a conductivity of 0.4 Scm−1, which was determined by VSM and four probe technique, respectively. B‐H curve reveals that ferrimagnetic particles of γ‐Fe2O3 show super‐paramagnetic behavior at room temperature which was also observed in PEDOT–γ‐Fe2O3 composite. The resulting conducting ferrimagnetic composite shows microwave absorption loss of 18.7–22.8 dB in the frequency range of 12.4–18 GHz. Thermogravimetric analysis of the composite revealed that the composite is thermally stable up to 230°C. The characterization of the PEDOT–γ‐Fe2O3 composite was carried out using XRD and FTIR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.

Temperature and pH-Responsive Single-Walled Carbon Nanotube Dispersions

Solubilization of single-walled carbon nanotubes (SWNTs) using noncovalently interacting polymer surfactants in aqueous media has opened up a new vista of SWNTs in biology and medicine. In many potential applications, it is desirable to control the dispersion or aggregation of SWNTs in solvents with external stimuli. Here we report two "smart" SWNT dispersions that respond to temperature and pH changes in poly(N-isopropylacrylamide) and poly-L-lysine solutions.

Micellar, interfacial and fluorescence investigation on binary mixtures of dodecyl cationic surfactants in aqueous media

The critical micelle concentration (cmc) of binary mixtures of C 12-triphenyl phosphonium, pyridinium and trimethyl ammonium bromides were determined employing conductometry, surface tensiometry and fluorescence techniques. Binary mixtures of C 12 phosphonium bromide with C 12 trimethyl ammonium and pyridinium bromide surfactants exhibited second breaks due to the structural micellar transition, and are supported by conductometric and flurometric methods. The values of surface excess, minimum area of the C 12 surfactants at the cmc and Gibbs energy of adsorption were evaluated. The ideality/non-ideality of the mixing was analysed using regular solution theory (RST) to obtain the composition of the mixed micelle and the interaction parameter ( β m) to evaluate the strength of interactions of surfactants in the mixed micelles. The tensiometric measurements were also analysed to obtain the interaction parameter ( β σ) for the mixed monolayer at the air/water interface. Activity coefficients and the excess free energy of mixing were also determined.

Spectroscopic Investigations on the Interaction of Crystal Violet with Nonionic Micelles of Brij and Igepal Surfactants in Aqueous Media

The behavior of the triphenylmethane dye crystal violet in aqueous solutions containing polyoxyethylene nonionic surfactants was investigated using absorption and fluorescence spectroscopic techniques. The interactions of the dye were examined in micellar media in order to prevent dye aggregation and to ensure maximum dye and surfactant interaction. The relative fluorescence enhancements and the binding constants of the dye to the surfactant micelles were determined. The micropolarities of the micellar environment sensed by the pyrene probe were estimated from the I 1/I 3 intensity ratios of the fluorescence spectra of pyrene. The fluorescence quenching of pyrene by hexadecylpyridinium chloride was investigated in aqueous surfactant mixtures at a fixed concentration of surfactant in order to determine the aggregation numbers. Attempts were made to correlate the binding constants obtained in this investigation to various micellar parameters.

Use of acrylic based surfmers for the preparation of exfoliated polystyrene–clay nanocomposites

Two polymerizable cationic surfactants, (11-acryloyloxyundecyl)dimethyl(2-hydroxyethyl)ammonium bromide (hydroxyethyl surfmer) and (11-acryloyloxyundecyl)dimethylethylammonium bromide (ethyl surfmer), were used for the modification of montmorillonite (MMT) clay. The modification of MMT dispersions was carried out by ion exchange of the sodium ions in Na +-MMT by surfactants in aqueous media. Modified MMT clays were then dispersed in styrene and subsequently polymerized in bulk by a free-radical polymerization reaction to yield polystyrene–clay nanocomposites. An exfoliated structure was obtained using the ethyl surfmer-modified clay, whereas a mixed exfoliated/intercalated structure was obtained using the hydroxyethyl surfmer-modified clay. Nanocomposite structures were confirmed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The nanocomposites exhibited enhanced thermal stability and an increase in glass transition temperature, relative to neat polystyrene. The nanocomposites also exhibited enhanced mechanical properties, which were dependent on the clay loading. Intercalated polystyrene–clay nanocomposites were obtained using the non-polymerizable surfactant-modified clay (cetyltrimethylammonium bromide). Nanocomposites made from mixtures of surfmer-modified and CTAB-modified clays were also prepared, showing intermediate properties. However, when the nanocomposites were prepared in solution only intercalated morphologies were obtained. This was attributed to the competition between the solvent molecules and monomer in penetrating into clay galleries. These nanocomposites also exhibited enhanced thermal stability relative to the virgin polystyrene prepared by the same method. Similar temperatures of degradation (at 50% decomposition) were found for these nanocomposites relative to those prepared by bulk polymerization.

Interaction of Pyrene-1-Carboxaldehyde with micelles and mixed micelles of polyoxyethylene nonyl phenol (Igepal): A spectroscopic study

The absorption and steady-state fluorescence of a non-amphiphilic derivative of pyrene, Pyrene-1-Carboxaldehyde (1-PyCHO) is sensitive to the probe's environment. Association of the surfactants in aqueous medium as micelles and mixed micelles has been studied from the photophysical changes of 1-PyCHO in these media. The physicochemical characteristics of the micelles, i.e. CMC, aggregation number have been determined. The obtained CMC values from different methods are close to each other. The association constants of the 1-PyCHO molecules with the non-ionic micelle of Igepal and location of the fluorophore in the micellar environment have been determined. Micropolarity of Igepal micelle and Igepal/Igepal mixed micelle surrounding 1-PyCHO has been ascertained comparing the shift in fluorescence maximum with E T(30) values of standard solutions.

Mixed Micellar Systems of n-Alkyl-β-D Glucopyranosides with Hexadecyl Cationic Surfactants

Abstract Critical micelle concentrations (cmc) were obtained from tensiometric method on binary mixtures of decyl and dodecyl glucopyranoside nonionic surfactants with hexadecyl-triphenyl and tributyl phosphonium bromide and trimethylammonium bromide surfactants in aqueous media. The cmc data have been analysed in the context of pseudophase separation model. The interaction parameter (b) determined by using the regular solution theory (RST) was found to be negative and composition dependent. The values of interaction parameters were found to be more negative for C10 glucopyranoside mixtures. Employing Maeda's Theory, the chain/chain contribution parameter B1 was obtained and related to the Gibbs free energy of mixed micelle formation. Thermodynamics of adsorption, surface excess and minimum area occupied by surfactant molecules were also evaluated.

Spectroscopic investigations on the interaction of an anionic probe with nonionic micelles of Igepal surfactants in aqueous media

The behaviour of the anionic dye 8-anilino-1-napthalenesulfonic acid ammonium salt, or ANS, in aqueous solutions containing the Igepal series of polyoxyethylene nonionic surfactants was investigated using fluorescence spectroscopic technique. The interactions of the dye with the nonionic surfactants were examined in micellar media, to prevent dye aggregate formation and to ensure maximum dye and surfactant interaction. From the relative fluorescence enhancements, binding constants of the dye to the surfactant micelles and aggregation numbers of the micelles were determined. The aggregation numbers were also separately determined by static fluorescence quenching of pyrene by cetylpyridinium chloride in aqueous surfactant mixtures at a fixed concentration of surfactant, and compared with the value obtained from the present investigation of the interaction of the micelles with the ANS probe. The values of binding constants, micropolarity values sensed by pyrene and the Stern–Volmer constants for quenching of pyrene fluorescence by cetylpyridinium chloride were correlated with the number of ethylene oxide groups in the Igepal series.

Conductometric and fluorometric investigations on the mixed micellar systems of cationic surfactants in aqueous media

Micellar properties of binary mixtures of hexadecyldiethylethanolammonium bromide surfactant with tetradecyldimethylammonium, trimethylammonium, triphenylphosphonium, diethylethanolammonium, and pyridinium bromide surfactants have been characterized employing conductometric and fluorescence techniques. The critical micelle concentration (cmc ∗) and the degree of counter-ion binding values ( δ) of the binary systems were determined from the conductivity measurements. The results were analyzed in light of various existing theories to calculate micellar composition, activity coefficients, and the interaction parameter ( β). Partial contribution of each surfactant, cmc ∗ 1, cmc ∗ 2, to the overall cmc ∗ value was also evaluated. Aggregation numbers and micropolarity of the mixed micelles were determined from fluorescence measurements. The results were discussed in terms of synergetic interactions in these systems on the basis of the head group/head group and tail/tail interactions and the counter-ion binding.

Preparation and characterisation of CoS2 nanomaterial in aqueous cationic surfactant medium of cetyltrimethylammonium bromide (CTAB)

Cobalt disulfide is an important nanomaterial in the field of material chemistry due to its interesting catalytic and electromagnetic properties. We herein report the simple solution phase preparation of nanoparticles of cobalt disulfide in micellar medium of cationic surfactant cetyltrimethylammonium bromide (CTAB) and also by way of capping with thiophenol. The product has been characterized using spectroscopic and electron microscopic and magnetic moment measurements. The presence of disulfide bond is clearly evident from the 480 cm−1 peak in the infrared spectrum. The thiol passivated particles prepared in aqueous and ethanol medium has been found to have different compositions as observed from the ESIMS study.

Block ionomer complexes as prospective nanocontainers for drug delivery

Nanosized environmentally responsive materials are of special interest for various applications, including drug delivery. Block ionomer complexes (BIC) composed of graft-comb copolymers of Pluronic and poly(acrylic acid) (Pluronic–PAA) and a model cationic surfactant, hexadecyltrimethylammonium bromide (HTAB), were synthesized by mixing the polymer and surfactant in aqueous media. According to TEM, the resulting BIC represented spherical particles of nanoscale size (50 to 100 nm). The stability of the BIC in the aqueous dispersion depended on the lengths of the hydrophilic poly(ethylene oxide) and hydrophobic poly(propylene oxide) chains in Pluronic molecules as well as on the surface charge of the resulting complexes. The latter was controlled by changing the ratio of the Pluronic–PAA and HTAB in the BIC and by changing the pH due to reversible ionization of the PAA chains. The acidification of the media below pH 6.0 resulted in the appearance of a strong positive charge on the BIC, which in the intracellular environment can trigger interaction of such BIC with the cell membranes. An efficient solubilization of a model hydrophobic molecule, Sudan III, and a drug, Etoposide, in such BIC was demonstrated with the loading capacities of about 6 to 15% by weight of the dispersed complex. Overall, these BIC wield a promise as environmentally responsive nanocarriers for pharmaceuticals.

Self aggregation of binary surfactant mixtures of a cationic dimeric (gemini) surfactant with nonionic surfactants in aqueous medium

Solubility, tensiometric, fluorometric and dynamic light scattering (DLS) measurements have been used to elucidate the self aggregation of a mixture of alkanediyl-α,ω type cationic gemini surfactant [(C 16H 33N +(CH 3) 2 (CH 2) 10N +(CH 3) 2C 16H 33)2Br −], 16-10-16, 2Br − with POE nonionic surfactants [CH 3(CH 2) 10CH 2-(OCH 2CH 2) 6OH], C 12E 6 and [(CH 3) 3CCH 2C(CH 3) 2C 6H 4-(OCH 2CH 2) 9.5OH] Triton X-100. The critical micelle concentrations (cmc) of the binary mixtures have been investigated at well above their Krafft temperatures in aqueous medium by tensiometric (at different temperatures at 5 °C interval) measurements. Surprisingly it was observed that the Krafft temperatures of binary mixtures were higher than the pure gemini surfactant. Application of the regular solution model to the experimental data yield the interaction parameter at mixed micelles ( β m), and at the air–water interfaces ( β σ), which indicate an attractive interaction and reflect the synergistic behavior in both 16-10-16, 2Br −/C 12E 6 and 16-10-16, 2Br −/TX 100 systems. The micelle aggregation numbers ( N agg) of the binary combinations fall between those of constituent surfactants. The micropolarity values of various combinations and the binding constants ( K sv) were determined from the ratio of intensity of peaks ( I 1/ I 3) of pyrene fluorescence emission spectrum and its quenching, respectively. The micellar interiors were found to be reasonably polar. By using Maeda's concept, it was observed that the chain–chain interactions were very important for stability of mixed micelles in these systems. The hydrodynamic radius ( R h) of TX 100 was higher than that of 16-10-16, 2Br − while the mixed aggregates have intermediate values of R h.

Calorimetric investigation of the thermodynamic basis of the effect of maltodextrins on the foaming ability of legumin in the presence of small-molecule surfactant

In this investigation, using a combination of mixing and differential scanning calorimetry, the relationships have been clarified between thermodynamics of the intermolecular interactions, the conformational stability of the protein globule and foaming ability of the protein in the ternary mixtures: neutral polysaccharide (maltodextrins with different dextrose equivalent (DE=2, 6, 10))+globular protein-legumin (11 S globulin from broad beans)+water-dispersible ionic small-molecule surfactant that represents generally the mixture of the esters of stearic and palmitic acids with a citric acid (CITREM). In addition, it was also shown that the found peculiarities of the intermolecular interactions in the ternary mixtures are also determined by the aggregation states (monomolecular or micellar) of the small-molecule surfactant in aqueous medium. The combined calorimetric data suggest that the role of the unadsorbed maltodextrin in the foaming ability of its mixture with legumin in the presence of CITREM is principally governed, on the one hand, by the marked addition of hydrophilicity from both maltodextrins and CITREM to the protein as a result of the formation of the ternary complex, maltodextrin+CITREM+legumin, and, on the other hand, by the partial protein unfolding of the protein in the ternary (maltodextrin+CITREM+legumin) complex.

Solid Lipid Nanoparticles Bearing Flurbiprofen for Transdermal Delivery

Topical application of the drugs at the pathological sites offer potential advantages of delivering the drug directly to the site of action and thus producing high tissue concentrations of the drug. The solid lipid nanoparticles (SLN) bearing flurbiprofen were prepared by microemulsion method by dispersing o/w microemulsion in a cold aqueous surfactant medium under mechanical stirring. The SLN gel was prepared by adding SLN dispersion to polyacrylamide gel prepared by using polyacrylamide (0.5%), glycerol (10%), and water (69.5%). Shape and surface morphology was determined by scanning electron microscopy that revealed fairly spherical shape of the formulation. Percent drug entrapment was higher in SLN dispersion in comparison to SLN gel formulations. In vitro drug release, determined using cellophane membrane, showed that SLN dispersion exhibited higher drug release compared with SLN gel formulations. Both the SLN dispersion and SLN-gel formulation possessed a sustained drug release over a 24-hr period, but this sustained effect was more pronounced with SLN-gel formulations. The percent inhibition of edema after 8 hr was 55.51 ± 0.26% in case of SLN-T4-gel, whereas flurbiprofen and SLN-T4 dispersion exhibited 28.81 ± 0.46 and 31.89 ± 0.82 inhibition of edema. The SLN-T4-gel not only decreased the inflammation to larger magnitude, but also sustained its effect.

Aggregation Behavior of Sodium Mono-n-Dodecyl Phosphate Surfactant in Aqueous Media, and Function in Catalytic Activity. I. Multi-Step Aggregates Formation and Catalytic Activity for Hydrolysis of p-Nitrophenyl Acetate in Aqueous Solution

Aggregation behavior of sodium salt of mono-n-dodecyl phosphoric acid ester i.e. a species of mono-alkyl phosphate (MAP) surfactants, in pure water was investigated as a function of surfactant concentration (CS) by means of surface tension (γ), electroconductivity (measuring both specific (κ) and molar (Λ) conductivities), pH and UV-Vis spectra measurements. The Krafft temperature was determined as 40°C by observing the change of κ with raised temperature. Although the curve of γ vs. log CS plot gave only one break which corresponds to critical micellization concentration(CMC) in common theory, different relations of κ vs. CS, Λ vs. √CS, or κ vs. log CS, and pH vs. CS resulted in several breaks suggesting the occurrence of various transitions of aggregates or micelles over the concentration range not only above, but also below CMC. The CMC determined by surface tension measurement was referred to as the first CMC (CMC1). The critical concentrations of the transitions observed by various methods were termed as CACi (i=1,2,3) for three-step aggregate formation below CMC1 and as CMCj (j=1-5) for five-step transitions in micellar form. From the temperature study on CACi and CMCj, the estimated standard Gibbs energy changes were estimated, which showed us that the primary driving force of aggregate/micelle formation at any step comes from the entropy term, since the energy term (enthalpy) in this case was found to be positive. This supports our interpretation that the aggregates/micelles are mainly composed of hydrolyzed (protonated) mono-dodecyl phosphate molecules so that they behave as if they were nonionic surfactant micelles. A light scattering measurement verified the existence of aggregates formed below CMC. The experiment of catalytic activity assay revealed that SMDP aggregates formed in the low concentration range (ten times lower than CMC1) were found to act as catalysts for the hydrolysis reaction of p-nitrophenyl acetate (pNPA).

Cloud point formation based on mixed micelles in the presence of electrolytes for cobalt extraction and preconcentration

A new micelle-mediated phase separation of metal ions, applied for preconcentrating trace levels of cobalt as a prior step to its determination by flame atomic spectroscopy, has been developed. Two methods were proposed employing both Triton X-100 and sodium dodecyl sulfate (SDS) as a mixed micellar system while the phase separation was induced by HCl or NaCl addition. Cobalt was complexed with pyridylazo compounds (PAN, PAR, 5-Br-PADAP) in an aqueous surfactant medium and it was concentrated in the surfactant rich phase after phase separation. The chemical variables affecting the cloud point extraction were evaluated, optimized and successfully applied to cobalt determination in pharmaceutical samples. Under the optimized conditions, the preconcentration system permitted limits of detection as 1.1 and 1.6 μg l −1 cobalt, respectively, when HCl and NaCl were used. Both proposed methods showed linear calibration within a 25–200 μg l −1 cobalt range. The extraction efficiency was investigated at different cobalt concentrations (40–185 μg l −1) and good recoveries (98–102%) were obtained by using NaCl as electrolyte. The results obtained were compared with those observed with ET AAS.

Evidence for Ionic Interaction between Cationic Surfactant and Anionic Intermediate Generated in Cathodic Reduction of Acetophenone

Abstract The cathodic reduction of acetophenone in the presence of a chiral cationic surfactant in aqueous media gave S- or R-1-phenylethanol with 8–12 % ee. The observed enantioselectivity clearly suggests the interaction between the cationic surfactants and the anionic intermediate generated from the one-electron reduction of acetophenone.

Novel mathematical description of surfactants macroaggregates

Molecular organization of surfactants in aqueous media is a key element in biochemical research and provides furthermore novel application in biomolecular materials design. Here is shown a novel mathematical representation for the interconversions within very complex and huge aggregates like vesicles, liquid crystals and colloidal dispersions. The resulting equations are able to fully represent the morphology, the symmetry and the topology of extended lipid bilayer. Furthermore, only one parameter is needed to describe the whole transition, regardless of changes in symmetry or topology. The existence of a unique parameter is the most important property of this mathematical treatment. In fact the Gaussian and the mean curvature can be easily derived and consequently bending energy and several geometrical properties can be derived by this ancestor parameter. This parameter, describing curvature and symmetry for the whole transition can be considered as a sort of natural intrinsic indication of the transformation evolution. The mathematical description of these transformations can highlight new aspects of the dynamics of colloidal systems.

Application of the supercritical CO 2 extraction technology on the recovery of natural fat from the sheepskin degreasing process

The content of natural fat in sheepskins can amount up to 50% on the dry skin weight. In order to have skins in good conditions to be adequately processed afterwards, it is necessary to degrease them to a some extent. One of the degreasing methods is carried out with non ionic surfactants in aqueous medium. At the end of this degreasing process a highly pollutant emulsion consisting of natural fat and surfactant in water is obtained. In order to reduce the high contamination load of this emulsion, this is heated to 90°C, at which temperature the emulsion breaks. In this way, water with a reduced contamination load and a fatty phase made up of water, salt, natural fat and non ionic surfactant are obtained separately. Given the nature of this fatty phase, no suitable use has been found up to now. This study deals with the feasibility of the supercritical CO 2 extraction technology to separate the fatty phase obtained from the residual bath of sheepskin aqueous degreasing into its components, natural fat and non ionic surfactant. On the other hand, the natural fat of sheepskins consists of different components: lanoline, waxes, triglycerides, fatty acids, cholesterol, mono- and diglycerides. The fractionation of the different components of the natural fat as a function of the CO 2 pressure and temperature has also been studied. Supercritical fluid extraction technology allows the recovery of natural fat present in the fatty waste obtained from the residual bath of sheepskin degreasing. An increase in the CO 2 density leads to the extraction of a larger number of components of natural fat. All the components of natural fat are extracted at an extraction temperature of 45°C and at CO 2 density of 0.70–0.75 g/ml. The non ionic surfactant is not extracted under these conditions.

Cloud point preconcentration of germanium and determination by hydride generation atomic absorption spectrometry

Cloud point methodology has been successfully employed for the preconcentration of germanium at trace levels from aqueous samples prior to hydride generation flame atomic absorption spectrometry (HGAAS). Germanium was taken into complex with quercetin in aqueous non-ionic surfactant (Triton X-114) medium and concentrated in the surfactant rich phase by bringing the solution to the cloud point temperature (19°C). The preconcentration of only 50 ml of solution with 0.1% Triton X-114 and 2×10 −5 M quercetin at pH 6.4 gives a preconcentration factor of 200. Under these conditions, the detection limit (3 s) and the sensitivity of the cloud-point extraction-HGAAS system were 0.59 and 0.0620 μg l −1, respectively. The extraction efficiency was investigated at low germanium concentrations (10–30 μg l −1) and satisfactory recoveries (93–105%) were obtained.