Solutions Of Cationic Surfactants Research Articles

Different Distributions of Counterions in the Surface Layer of Cationic Surfactant Solutions

We have separately determined the surface tension of pure aqueous solutions of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide and their surface potentials by a Kelvin probe system. With the help of Gibbs equation, the surface excess has been determined through approximating the chemical activity of the surfactant by their dilute bulk concentration. In the following, the surface potential—surface excess isotherms were established. Those potential isotherms evidence that cetyltrimethylammonium chloride solution has a higher value compared to that of cetyltrimethylammonium bromide under equal surface excess. This phenomenon is supposed to be owed to the different distributions of chloride and bromide ions within the adsorption layer of the solutions, which can be attributed to the different properties of those two anions.

Reactivity of phosphorus esters in supramolecular systems based on surfactants containing an uracil residue and polyethylenimine

The reactivity of phosphorus esters with different hydrophobicities was studied in aqueous solutions of cationic surfactants containing an uracil residue, as well as in binary systems based on polyethylenimine. Pronounced substrate specificity was revealed in all supramolecular systems examined; in particular, acceleration of the hydrolysis of more hydrophobic substrate and inhibition of the reaction with less hydrophobic analog were observed. Aggregation in the examined systems was confirmed by tensiometric and conductometric measurements. The aggregation threshold considerably decreased in going from monocationic amphiphile to more hydrophobic dicationic analog due to the presence in the latter of two additional alkyl radicals.

Modeling of the Effects of Ion Specificity on the Onset and Growth of Ionic Micelles in a Solution of Simple Salts

A new version of the molecular thermodynamic model has been developed that takes into account the effect of ion specificity on the free energy of aggregation. The specificity of salt is reflected by differences in the bare ionic sizes and polarizabilities leading to the difference in the dispersion interaction of ions with the aggregate. The model also contains parameters that characterize the compactness of ionic pairs formed between a mobile ion and surfactant's headgroup. The values of these parameters show that more chaotropic heads form tighter pairs with chaotropic ions whereas more cosmotropic heads form more compact pairs with cosmotropic ions. The formation of compact pairs in the micelle corona diminishes the preferable curvature of the aggregates and promotes their growth. The model has been applied to aqueous solutions of cationic (alkyltrimethylammonium, alkyldimethylammonium, and alkylpyridinium) and anionic (alkylsulfate and alkylcarboxylate) surfactants in the presence of simple 1:1 salts. With a single set of parameter values, the model reproduces the critical micelle concentration-salinity curves and the sphere-to-rod transitions or the absence of thereof and describes the aggregate growth for different simple salts, in good agreement with experiment.

Studies on deposition of gold atomic clusters on to polycrystalline gold electrode from aqueous cetyl trimethyl ammonium bromide solutions

Atomic (molecular) clusters, with less than 50–100 atoms (size ⩽1.5nm) are of special interest and exhibit novel and interesting properties due to quantum confinement of electrons and holes. These properties are quite different from those of gold nanoparticles and hence, understanding of electrochemical phase formation of gold atomic clusters assumes importance. In the present study, we report a detailed investigation of deposition of gold atomic clusters on to polycrystalline gold electrode from aqueous cationic surfactant solutions. The studies were undertaken over a wide range of potentials, covering both surface and bulk layer dissolution and deposition processes, by means of cyclic voltammetric and chronoamperometric techniques. Thus, gold atomic clusters are formed in both surface and bulk layer dissolution and deposition processes as evidenced by AFM, MALDI-TOF, XPS and DLS. Electrocatalytic activity has been performed by the electrochemical reduction of oxygen (O2) on AuAC modified gold electrode in 0.1M H2SO4.

Micellar Solubilization of Carbamazepine

Aims: An important property of micelles with particular significance in pharmacy is their ability to increase the solubility of poorly soluble drugs in water thus increasing their bioavailability. It was of interest to increase the solubility of carbamazepine (CBZ) in aqueous media. Therefore, solubilization of carbamazepine (CBZ) in variety of surfactants was investigated. Study Design: In this work the solubilization of carbamazepine (CBZ) was studied in micellar solutions of different anionic and cationic surfactants.

Molecular interactions of sodium laureth sulfate with N-alkyl-1,3-propanediamine in aqueous solutions, based on potentiometric and photometric data

The role of Coulomb and hydrophobic interactions in association and aggregation in binary solutions of anionic surfactant sodium laureth sulfate and cationic surfactant N-alkyl-1,3-propanediamine is established from the concentration dependences of the pH of the solutions. It is shown that the development of the processes is initiated by the Coulomb interaction of oppositely charged sodium laureth sulfate and N-alkyl-1,3-propanediamine molecules and enhanced by the hydrophobic interaction between the hydrocarbon tails of neutral associates of the surfactant molecules.

Hydrophilic–oleophobic coatings on cellulosic materials by plasma assisted polymerization in liquid phase and fluorosurfactant complexation

Materials with hydrophilic–oleophobic properties are of relevance due to their application to different fields such as self-cleaning coatings, liquid–liquid separation membranes and functional textiles for different technical applications. In this work, hydrophilic–oleophobic coatings have been deposited on cellulosic materials (filter paper and bleached cotton) by means of plasma assisted polymerization of acrylic acid solutions in water followed by cationic fluorosurfactant complexation. Chemical composition of the coatings on cellulosic materials was characterized by means of FTIR–ATR and XPS whereas their morphology was studied by SEM. Hydrophilic–oleophobic behavior was characterized by means of contact angle and wetting time. Additionally wetting properties of cationic, anionic and non-ionic surfactant solutions on the hydrophilic–oleophobic coatings were used to characterize the polyelectrolyte electrostatic forces upon the functionalized layer.

Adsorption of Congo red from solution using cationic surfactant modified wheat straw in column model

An agricultural by-product, wheat straw (NWS), was soaked in 1% a cationic surfactant (hexadecyl trimethyl ammonium bromide, CTAB) solution for 24h (at 293K) and modified wheat straw (MWS) was obtained. Then MWS was used as adsorbent for the removal of Congo red (CR, anionic dye) from aqueous solution. The experiment was performed in column mode at room temperature (293K) and effects of initial CR concentration, flow rate, bed depth and common salt existed in solution on breakthrough curves were presented. The breakthrough curves became flatly at lower flow rate, lower CR concentration and higher bed depth and these conditions were advantageous of CR removal from solution. There is no significant effect of CR adsorption capacity at 0.1mol/L sodium chloride solution. Thomas model and modified dose–response model were used to fit the column data using nonlinear analysis method and the fitted results were presented. Modified dose–response model was better to predict the breakthrough curves. 0.1mol/L sodium hydroxide solution can elute CR adsorbed on MWS in column. The results implied that MWS can be selected as an inexpensive, effective and environmentally friendly adsorbent to remove CR from aqueous solution.

Confining ss-DNA/carbon nanotube complexes in ordered droplets.

In 1/1 mass ratio mixtures made of single strand DNA and single-walled carbon nanotubes lyotropic nematic phases are formed. The process is assisted by segregative phase separation procedures. The liquid crystalline order occurring therein was confirmed by optical polarizing microscopy and zero-shear rheology. The resulting nematic droplets were dispersed in protein or cationic surfactant solutions, under appropriate pH and/or ionic strength conditions. The components of the hosting fluid(s) rapidly adsorb onto the droplets, form a permanent peel on their surface, and confine them. The peel resists osmotic gradients and has significant stability. The distribution of the species in the droplet and in the peel was determined by SEM. Data indicate that the peel contains protein or surfactant, depending on the titrant, when the core is rich in DNA and nanotubes. According to electron microscopy, nematic order in the droplets is partly retained.

Coacervation and aggregate transitions of a cationic ammonium gemini surfactant with sodium benzoate in aqueous solution

Coacervation in an aqueous solution of cationic ammonium gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) with sodium benzoate (NaBz) has been investigated at 25 °C by turbidity titration, light microscopy, dynamic light scattering, cryogenic temperature transmission electron microscopy (Cryo-TEM), scanning electron microscopy (SEM), isothermal titration calorimetry, ζ potential and (1)H NMR measurements. There is a critical NaBz concentration of 0.10 M, only above which coacervation can take place. However, if the NaBz concentration is too large, coacervation also becomes difficult. Coacervation takes place at a very low concentration of C12C6C12Br2 and exists in a very wide concentration region of C12C6C12Br2. The phase behavior in the NaBz concentration from 0.15 to 0.50 M includes spherical micelles, threadlike micelles, coacervation, and precipitation. With increasing NaBz concentration, the phase boundaries of coacervation shift to higher C12C6C12Br2 concentration. Moreover, the C12C6C12Br2-NaBz aggregates in the coacervate are found to be close to charge neutralized. The Cryo-TEM and SEM images of the coacervate shows a layer-layer stacking structure consisting of a three-dimensional network formed by the assembly of threadlike micelles. Long, dense and almost uncharged threadlike micelles are the precursors of coacervation in the system.

Is the counterion responsible for the unusual thermodynamic behaviour of the aqueous solutions of gemini bispyridinium surfactants?

Apparent and partial molar enthalpies at 298K of the aqueous solutions of cationic gemini surfactants 1,1′-didodecyl-2,2′-trimethylenebispyridinium dichloride (12-Py(2)-3-(2)Py-12 Cl); 1,1′-didodecyl-2,2′-tetramethylenebispyridinium dichloride (12-Py(2)-4-(2)Py-12 Cl); 1,1′-didodecyl-2,2′-octamethylenebispyridinium dichloride (12-Py(2)-8-(2)Py-12 Cl) and 1,1′-didodecyl-2,2′-dodecamethylenebispyridinium dichloride (12-Py(2)-12-(2)Py-12 Cl) were measured as a function of concentration and are here reported for the first time. The curve of the compound with the four carbon atoms spacer lies above than that of the compound with the three carbon atoms spacer, not below, as expected. We have already found this behaviour for the same compounds here studied, but having methanesulfonate as counterion. It is interpreted as an evidence of a conformation change of the molecule determined by stacking interactions between the two pyridinium rings, appearing at an optimum length of the spacer. The curves of apparent and molar enthalpies vs. concentration and surface tension measurements, here reported, show that this behaviour is independent on the counterion. In fact, the group contribution additivity for the counterion is respected, independently on the spacer length. This behaviour could have interesting effect in biological applications for which this new class of gemini surfactant has been tailored.

Conductometric and spectroscopic study of interaction of cationic surfactants with 3-methyl-1-pentylimidazolium hexafluorophosphate

This paper outlines the effect on micellar behavior of aqueous solutions of cationic surfactants viz. cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) upon addition of ionic liquid 3-methyl-1-pentylimidazolium hexafluorophosphate [C5mim][PF6]. Important physicochemical properties such as conductance, critical micelle concentration (cmc) and aggregation number (Nagg) are observed to change as [C5mim][PF6] is added to aqueous CTAB/CTAC. The conductivity/concentration data of aqueous solutions of CTAB/CTAC with [C5mim][PF6] were determined in the temperature range 298.15, 308.15, 318.15K. These data were used to determine cmc as a function of temperature and concentration and to evaluate degree of ionization. Using temperature dependence of cmc, various thermodynamic parameters have been evaluated. Behavior of fluorescence probe, pyrene, confirms the interaction between [C5mim][PF6] and cationic micellar surface. Further, 1H NMR studies in micelle solutions containing [C5mim][PF6] have also been carried out in order to interpret the preferential solubilization site of [C5mim][PF6] on the studied micellar systems.

Effect of electrolytes on wettability of glass surface using anionic and cationic surfactant solutions

Wetting behavior of a flat glass surface using pure nonionic, anionic, and cationic surfactants solutions has been studied by the dynamic contact angle (Wilhelmy plate) measurement technique. The advancing contact angle increases with the increasing concentration of surfactant and the value is maximum in the presence of cationic surfactant CTAB. The effect of different electrolytes in the presence of ionic surfactants was also studied to see the wetting behavior in the presence of electrolytes. The presence of electrolytes on ionic surfactant solutions significantly enhance the contact angle at very low concentration, which in turn lead to reduction in ionic surfactant requirement by more than 90% to achieve a particular contact angle. The effectiveness of electrolyte highly depends on the valance of counter ion. The reduction of ionic surfactant requirement is mostly useful for different applications such as flotation, and colloidal stability to reduce the production cost as well as environmental pollution.

Enhanced electrocapacitive performance of graphene oxide polypyrrole nanocomposites

Graphene oxide/polypyrrole nanocomposites (PNCs) with enhanced electrocapacitive performance were prepared through a cationic surfactant assisted dilute solution polymerization of pyrrole in presence of GO at various concentrations (%, w/w) ranging 10.0–40.0 and ferric chloride as oxidant. PNCs has been characterized through Fourier transformed infrared spectra, X-ray diffraction, scanning electron microscopy and simultaneous thermogravimetric-differential scanning caloriemetry. Electrochemical capacitance (Cs, F/g) of electrodes fabricated from PNCs over 316 stainless steel in presence of sulphonated polysulphone as binder has been investigated in KOH solution (1.0 M) with reference to Ag/AgCl at scan rate (V/s) ranging 0.2–0.001. PNCs with 20.0%, w/w of GO have shown highest Cs of 1073.64 as compared to 92.33 for pure PPy at a scan rate of 0.001 V/s. PNCs rendered a low electrocapacitive decrease during the first 500 cycles at scan rate of 0.1 V/s indicating their appreciable electrochemical performance for fabrication of supercapacitor electrodes.

The Response of Carbon Black Stabilized Oil-in-Water Emulsions to the Addition of Surfactant Solutions

We use carboxyl-terminated, negatively charged, carbon black (CB) particles suspended in water to create CB-stabilized octane-in-water emulsions, and examine the consequences of adding aqueous anionic (SOS, SDS), cationic (OTAB, DTAB), and nonionic (Triton X-100) surfactant solutions to these emulsions. Depending upon the amphiphile's interaction with particles, interfacial activity, and bulk concentration, some CB particles get displaced from the octane-water interfaces and are replaced by surfactants. The emulsions remain stable through this exchange. Particles leave the octane-water interfaces by two distinct modes that depend on the nature of particle-surfactant interactions. Both happen over time scales of the order of seconds. For anionic and nonionic surfactants that bind to the CB through hydrophobic interactions, individual particles or small agglomerates stream away steadily from the interface. Cationic surfactants bind strongly to the carboxylate groups, reduce the magnitude of the surface potential, and cause the CB particles to agglomerate into easily visible chunks at the droplet interfaces. These chunks then leave the interfaces at discrete intervals, rather than in a steady stream. For the longer chain cationic surfactant, DTAB, the particle ejection mode reverts back to a steady stream as the concentration is increased beyond a threshold. This change from chunks of particles leaving intermittently to steady streaming is because of the formation of a surfactant bilayer on the particles that reverses the particle surface charge and makes them highly hydrophilic. The charge reversal also suppresses agglomeration. Zeta potentials of CB particles measured after exposure to surfactant solutions support this hypothesis. These results are the first systematic observations of different particle release modes from oil-water interfaces produced by variations in interactions between surfactants and particles. They can be generalized to other particle-surfactant systems and exploited for materials synthesis.

Fine Control Over the Size of Surfactant–Polyelectrolyte Nanoparticles by Hydrodynamic Flow Focusing

Synthesis of surfactant-polyelectrolyte nanoparticles was carried out in a microfluidic device with a fine control over the size and the polydispersity. An anionic polysaccharide (sodium carboxymethylcellulose, CMC) solution was focused using a cationic surfactant (dodecyl trimethylammonium bromide, DTAB) solution in a microfluidic channel at selected ratios of flow rates and reagent concentrations. The methodology ensured a controlled mixing kinetics and a uniform distribution of charges at the mixing interface. The resulting nanoparticles exhibited remarkably well-defined and repeatable size distributions, with hydrodynamic diameters tunable from 50 up to 300 nm and polydispersity index around 0.1 in most cases. Microfluidic-assisted self-assembly may be an efficient way to produce well-controlled polyelectrolyte-based nanoparticles suitable for colloidal science as well as for gene delivery applications.

Destabilization of sol of aerosil OX-50 in solutions of surfactants. II. Aerosil OX-25 in solutions of cationic and nonionic surfactants

The aggregate stability of the sol of Aerosil OX-50 in solutions of cationic surfactants (SAS) of cetyldimethylethylammonium bromide (CDEAB) and cetyltrimethylammonium bromide (CTAB), as well as nonionic SAS alkylphenyl ethers of ethylene glycol, has been studied. Destabilization of the sol in the solutions of SAS was considered in the terms of the balance of surface forces and with regard to the hydrophobic effects.

TAML Activator/Peroxide-Catalyzed Facile Oxidative Degradation of the Persistent Explosives Trinitrotoluene and Trinitrobenzene in Micellar Solutions

TAML activators are well-known for their ability to activate hydrogen peroxide to oxidize persistent pollutants in water. The trinitroaromatic explosives, 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB), are often encountered together as persistent, toxic pollutants. Here we show that an aggressive TAML activator with peroxides boosts the effectiveness of the known surfactant/base promoted breakdown of TNT and transforms the surfactant induced nondestructive binding of base to TNB into an extensive multistep degradation process. Treatment of basic cationic surfactant solutions of either TNT or TNB with TAML/peroxide (hydrogen peroxide and tert-butylhydroperoxide, TBHP) gave complete pollutant removal for both in <1 h with >75% of the nitrogen and ≥20% of the carbon converted to nitrite/nitrate and formate, respectively. For TNT, the TAML advantage is to advance the process toward mineralization. Basic surfactant solutions of TNB gave the colored solutions typical of known Meisenheimer complexes which did not progress to degradation products over many hours. However with added TAML activator, the color was bleached quickly and the TNB starting compound was degraded extensively toward minerals within an hour. A slower surfactant-free TAML activator/peroxide process also degrades TNT/TNB effectively. Thus, TAML/peroxide amplification effectively advances TNT and TNB water treatment giving reason to explore the environmental applicability of the approach.

PIV and DNS analyses of viscoelastic turbulent flows behind a rectangular orifice

We performed PIV (particle image velocimetry) measurements and DNS (direct numerical simulations) on turbulent orifice flows for the Newtonian fluid and viscoelastic fluids, and compared their results with emphasis on turbulence statistics and vortical motions just behind the orifice rib. In the experiment, a cationic surfactant solution of CTAC (cetyltrimethyl ammonium chloride) was chosen as the viscoelastic fluid that is known to provide substantial drag reduction in the case of smooth-wall turbulence. In the viscoelastic flows, the formation of the Kelvin–Helmholtz vortices emanating from the orifice edge was found to be attenuated compared to the Newtonian case, resulting in the suppression of turbulent eddies and Reynolds shear stress behind the orifice. However, the variation of the drag depended on the Reynolds number and the surfactant concentration (or the Weissenberg number): that is, the drag-reducing effect can be achieved only in limited conditions or low Reynolds-number flows. Although DNS results was found to be in qualitative agreement with the experimental data, we discussed also inconsistency between the experimental and DNS results.

Micellar properties of β-casein–cationic surfactant solutions

The micellar properties of b-casein in solution with a homologous series of cationic surfactants have been investigated using turbidity, fluorescence spectroscopy, and quenching fluorescence measurements. Turbidity mea- surements indicated that monomeric cationic surfactants initially bind cooperatively with a site on the b-casein micelle in negatively charged amino acids. This leads to the formation of low-soluble b-casein micelle-monomeric surfactants complexes. Further addition of surfactant leads to the formation of more highly soluble complexes of b- casein micelle-cationic surfactant. The fluorescence experiments were also used to study the formation of b- casein-cationic surfactant complexes and to determine critical micelle concentration of surfactants and b-casein. The mean aggregation number of b-casein and cationic surfactant micelles at various experimental conditions and the dependence of aggregation phenomenon on the chain length of cationic surfactants were investigated. The mean aggregation number for b-casein micelle has been deter- mined to be 45.70 using quenching fluorescence.