Function Of Surfactant Concentration Research Articles

Interface Thermodynamic State-Induced High-Performance Memristors

A new class of memristors based on long-range-ordered CeO2 nanocubes with a controlled degree of self-assembly is presented, in which the regularity and range of the nanocubes can be greatly improved with a highly concentrated dispersed surfactant. The magnitudes of the hydrophobicity and surface energy components as functions of surfactant concentration were also investigated. The self-assembled nanostructure was found to demonstrate excellent degradation in device threshold voltage with excellent uniformity in resistive switching parameters, particularly a set voltage distribution of ∼ 0.2 V over 30 successive cycles and a fast response time for writing (0.2 μs) and erasing (1 μs) operations, thus offering great potential for nonvolatile memory applications with high performance at low cost.

Interaction of Surfactants and Polyelectrolyte-Coated Liquid Crystal Droplets

It is known that the adsorption of surfactants at the liquid crystal (LC)/aqueous interface can induce a bipolar-to-radial director configuration of LC droplets dispersed in aqueous solution. In this paper, we study the effect of charged polyelectrolyte-coating on the interaction of surfactants and LC droplet cores by observing the director configuration of the LC droplet cores as a function of surfactant concentrations. It is found that surfactants can penetrate into the polyelectrolyte coating and react with the LC droplet cores to induce the bipolar-to-radial transition of the LC inside the droplet cores. However, the concentration of charged surfactants required to induce the configuration transition of the LC droplet cores is affected by the charged polyelectrolyte coating. The effect is significantly enlarged with decreasing the alkyl chain length of charged surfactants. Our results highlight the possibility of engineering polyelectrolyte coatings to tune the interaction of LC droplets with analysts, which is critical towards designing LC droplet based sensors.

Solid-state intercalation of cationic surfactants into Tunisian smectites

AbstractIntercalation of cationic surfactants hexadecylpyridinium (HDPy+) and hexadecyltrimethylammonium (HDTMA+) into the interlayer space of homoionic (Na-, Ca- and Zn-) smectites by solid-solid reactions was investigated. These reactions were complete within 15 min. Changes in the surface and structure of the smectites modified with different surfactants were characterized using XRD, FTIR and DSC. The intercalation of surfactant is controlled by the exchangeable cation of smectite and monofunctional ammonium cation type. HDPy+ and HDTMA+ surfactants were retained by Zn-exchanged smectite, suggesting important surface properties (CEC = 80 meq/100 g clay, SBET = 116.5 m2/g) and acid-base properties (point of zero proton charge PZC, density charge σH). HDPy cation loading was effective, suggesting that the aromatic polar group is favoured for intercalation. Comparing with original clay, modification with surfactants increased the basal spacings d001. Based on the d001 spacing of modified smectites, different configurations of surfactants within smectite interlayer were proposed as a function of surfactant concentration, which were examined by FTIR and DSC.

Association of sodium dodecyl sulfate in aqueous solutions according to chemical shifts in 1H NMR spectra

Proton chemical shifts of different atomic groups in sodium dodecyl sulfate (SDS) have been studied by 1H NMR spectroscopy as functions of surfactant concentration in aqueous solutions. Three surfactant concentration ranges of the chemical shifts have been revealed. The first range corresponds to the premicellar solutions, the second one is in the vicinity of critical micelle concentration (CMC1), and the third range corresponds to high surfactant concentrations, at which intermicellar interactions play a significant role. The parameters of SDS association (CMC1 and CMC2) determined based on the concentration dependences of the chemical shifts are in satisfactory agreement with the data available from the literature. The concept of critical dimerization concentration (CDC) has been introduced for the first concentration range. The values of CDC and dimerization constant K 2 (210 × 60 dm3/mol) have been estimated within the framework of the two-state model.

Interaction of Cationic CTAB Surfactant with Curcumin, an Anticarcinogenic Drug: Spectroscopic Investigation

Abstract Curcumin, the most active polyphenolic constituent of turmeric cucuminoids obtained from rhizome Curcuma longa, holds a high place in ayurvedic medicine but its role in conventional disease management is also established. Unfortunately, the compound has poor aqueous solubility, which results in poor bioavailability following high doses by oral administration. In order to enhance its effectiveness and improve bioavailability, surfactant assemblies as the colloidal drug carriers with desired properties have been largely utilized. The interaction of curcumin with cetyltrimethylammonium bromide (CTAB) surfactant has been investigated by absorption spectroscopy as a function of surfactant concentration in pre-micellar and micellar range at acidic pH of 6.4. The pre-micellar and micellar region of pure CTAB surfactant at acidic pH of 6.4 is examined through tensiometry and conductometry techniques. Spectral data shows that in presence of curcumin at lower CCTAB, the change in absorbance and peak form initially was assigned to attraction of positive head group of CTAB towards the β-diketone group of drug. In micellar region including CMC, the type of interaction corresponds to the attachment of C16 chains of CTAB to nonpolar aryl groups of drug and simultaneously displacement of polar head group from β-diketone group of the drug. Finally at post micellar CCTAB, the encapsulation of the curcumin into micelles, predominantly in intact monomeric form is observed with the sharp peak at λmax = 423 nm.

A Study of Local Anaesthetics. Part 202. Determination of the Critical Micellar Concentration of Carbisocainium Chloride in Water Using Spectral Methods and the Probe Pyrene

The micellization process of the local anaesthetic carbisocainium chloride in water was investigated by two spectral methods using the probe pyrene. First, the absorption spectroscopy in UV/VIS region was based on studying changes in characteristic absorption spectrum of pyrene in presence of surfactant. The resultant plot of the sum of absorbances for all the major pyrene peaks as a function of the total surfactant concentration shows, around the critical micellar concentration, a typical sigmoidal increase. The fluorescence emission spectroscopy in UV/VIS region of spectrum by the probe pyrene, second procedure, was applied for determination of the cmc from the measurements of the pyrene I1 /I3 ratio as a function of the surfactant concentration. The pyrene ratio data were fitted by the Boltzmann-type sigmoid of decreasing character.

Thermodynamics and micellization of cetyltrimethyl ammonium bromide in the presence of lysozyme

To study the structural changes in lysozyme (cationic protein) on the addition of N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB) and to understand the mechanism underlying aggregation of resulting protein–surfactant complex, surface tension, density and sound velocity measurements of lysozyme–CTAB solutions were carried out over a temperature range of 25–40°C. The critical micelle concentration (cmc) of CTAB has been calculated from surface tension measurements and is found to increase with increase in lysozyme concentration as well as with temperature. Surface tension data have been further used to calculate the interfacial parameters; maximum surface excess concentration (Γmax), minimum area per molecule (Amin), standard free energy of adsorption (ΔGoad), surface pressure at cmc (Πcmc) and standard free energy of transfer (ΔGotr), that have direct bearing on the consequences of such interactions at the molecular level. The negative values of standard Gibbs energy changes indicate spontaneity of micellization. Apparent molar volume (ϕv) and apparent molar adiabatic compressibility (ϕκ) have also been calculated using density and velocity of sound. These parameters have been examined as a function of surfactant concentration, lysozyme concentration and temperature to understand the consequences of interactions between these two components. A good qualitative correlation is found to exist with regard to the surfactant–lysozyme interaction obtained from the experimental data from different techniques.

Structure and Conformational Dynamics of DMPC/Dicationic Surfactant and DMPC/Dicationic Surfactant/DNA Systems

Amphiphilic dicationic surfactants, known as gemini surfactants, are currently studied for gene delivery purposes. The gemini surfactant molecule is composed of two hydrophilic “head” groups attached to hydrophobic chains and connected via molecular linker between them. The influence of different concentrations of 1,5-bis (1-imidazolilo-3- decyloxymethyl) pentane chloride (gemini surfactant) on the thermotropic phase behaviour of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers with and without the presence of DNA was investigated using Fourier transformed infrared (FTIR) and circular dichroism (CD) spectroscopies, small angle scattering of synchrotron radiation and differential scanning calorimetry. With increasing concentration of surfactant in DMPC/DNA systems, a disappearance of pretransition and a decrease in the main phase transition enthalpy and temperature were observed. The increasing intensity of diffraction peaks as a function of surfactant concentration also clearly shows the ability of the surfactant to promote the organisation of lipid bilayers in the multilayer lamellar phase.

Study of the inhibiting effect of a quaternary ammonium surfactants mixture synthesized from petroleum fraction (reformate) against the carbon steel corrosion in HCl 1 M

Quaternary ammonium cationic surfactants were synthesized from reformate, a liquid mixture of hydrocarbons (aromatics, naphthenes and paraffins), via chloromethylation/quaternization sequences. The petroleum surfactants thus obtained were evaluated as corrosion inhibitors for carbon steel in 1 M HCl, by gravimetry, potentiodynamic polarization and electrochemical impedance spectroscopy. The corrosion inhibiting efficiency was assessed as functions of surfactant concentration. The results showed that the inhibiting efficiency increased with surfactant concentration; its optimal value of 70 % was for a surfactant concentration of 320 mg/L at 25 °C. Potentiodynamic polarization measurements showed that the mixture acts as a mixed type inhibitor. The corrosion inhibiting mechanism is thought to proceed via an adsorption of the surfactant molecules on the steel surface, generating a film and hindering the active sites. Our experimental adsorption data were found to obey the Langmuir adsorption isotherm. SEM images of the treated specimens, revealing the likely formation of a protective film, demonstrated the inhibiting capacity of the petroleum quaternary ammonium surfactants against the carbon steel corrosion.

Drop impact on surfactant films and solutions

Drops impacting on horizontal aqueous surfactant films have been analyzed using a high-speed camera. Drops of either water or aqueous surfactant solutions had a diameter of 2.4 ± 0.4 mm and impacted with a velocity of 0.1 to 1.3 m/s. As surfactants, anionic sodium dodecyl sulfate and cationic cetyltrimethyl ammonium bromide were used. Pure water drops impacting on freestanding surfactant films showed coalescence, bouncing, partial bouncing, passing, and partial passing. For bouncing, the concentration of surfactant in the surfactant film must exceed the critical micelle concentration. When surfactant was added to the drop, coalescence and partial passing were suppressed. We attribute the different behavior to different hydrodynamic boundary conditions at the surface of pure water and surfactant solution, leading to different repulsive hydrodynamic forces arising when the air has to flow out of the closing gap between the two liquid surfaces. The boundary condition changes as a function of surfactant concentration from a slip to no-slip, leading to stronger hydrodynamic repulsion. In addition, estimates of the characteristic velocities show that diffusion of air into the water is slow and can only account for the very last thinning of the air gap before coalescence.

Study of Local Anaesthetics. Part 203*. Micellization of Heptacainium Chloride Studied By Spectral Methods in Aqueous Solution

The formation of micelles of the local anaesthetic heptacainium chloride (substance, XIX) in aqueous solution was investigated by the pyrene absorption and the pyrene I 1 /I 3 ratio methods, respectively by optical density (OD) method for surface curvature measurement. First, the absorption spectroscopy in UV/VIS region was based on studying changes in characteristic absorption spectrum of pyrene in presence of surfactant. The resultant plot of the sum of absorbances for the entire key pyrene maximum as a function of the total surfactant concentration showed, in the region of the critical micellar concentration, a usual sigmoidal increase. The fluorescence emission spectroscopy in UV/VIS region of spectrum by the probe pyrene, second procedure, was applied for determination of the cmc from the detections of the pyrene I 1 /I 3 ratio as a function of the surfactant concentration. The pyrene ratio data were fitted by the Boltzmann-type sigmoid of declining progress. The third (OD) method used required microliters of surfactant solutions and standard microplate absorbance measurements.

Thermodynamic Investigation on Micellization of Cationic Gemini Surfactants with Nitrophenoxy Groups in Hydrophobic Chains

Isothermal titration microcalorimetry (ITC) is a powerful technique for acquiring thermodynamic information on the micellization process of surfactants. In typical ITC experiments, consecutive injections of small volume of a surfactant micellar solution into water contained in a sample cell are performed. The sample cell is maintained at a constant temperature and the heat of processes occurring during dilution is monitored for each injection and plotted as a function of surfactant concentration in the cell. The interpretation of experimental data obtained by ITC is necessarily based on models describing micellization process. So far, there are two main models to the thermodynamic analysis of the micellization process: the mass action model, considering micelles and unassociated monomers to be in an association-dissociation equilibrium and the phase separation model, which regards micelles as a separate phase at critical micelle concentration (CMC) and assumes that the micellization process is strongly cooperative. The phase separation model is the simplest model for describing micelle forma- tion assuming that this process is akin to a separate phase-precipitation. Based on these two models, an ITC curve of observed enthalpy change versus surfactant concentration allows the determination of CMC and the enthalpy of micellization (ΔHmic) of a surfactant. Other thermodynamic parameters related to micellization, namely the free energy (ΔGmic), the entropy (ΔSmic) and the heat capacity of micellization (ΔCp,mic) can be calculated from the experimentally determined CMC and ΔHmic. In this paper, ITC and electrical conductivity were employed to investigate the micellization process of cationic gemini surfactants, N,N,N',N'-tetramethyl-N,N'-bis(10-(4-nitrophenoxy)alkyl)-1,6-hexanediammonium dibromide (Nm-6-mN, with m=8, 10 and 12, which are the numbers of carbon in the hydrocarbon chains), in aqueous solutions. Both phase separation model and mass action model were used to obtain a series of thermodynamic parameters. The results show that the obtained ΔHmic values based on the two models are very close, however, the obtained ΔGmic values based on the two models are not consistent. In addition, the ΔCp,mic of the micellization process is mainly from the dehydration contribution of hydrophobic alkyl chains of the surfactants, which means the nitrophenoxy group located in the hydrophobic chain still contacts with water after the mi- cellization. Furthermore, the micellar aggregation number n can be obtained by employing the mass action model. The mi- cellar aggregation number n decreases with the increase of the hydrophobic chain length. The reason is that the surfactant with longer hydrophobic chains prefers to form premicelles, leading to the decrease of the average aggregation number. Keywords Gemini surfactant; micellization; isothermal titration microcalorimetry; phase separation model; mass action model

Solution Properties of Gemini Surfactant of Decanediyl-1-10-bis (dimethyltetradecylammonium bromide) in Aqueous Medium

The solution properties of a typical gemini surfactant of decanediyl-1-10-bis (dimethyltetradecylammonium bromide) (abbrev. 14-10-14,2Br(-)) were examined in an aqueous medium at temperatures of 288.2, 298.2, and 308.2 K. The characterization was performed by employing surface tension measurements, electrical conductivity measurements, steady-state fluorescence quenching (SSFQ), and dynamic light scattering (DLS). The surface tension was measured with the drop volume method, in which an improved tensiometer was used and the experimental operation was modified. The resultant data were well reproducible and the equilibrium adsorption time after producing the droplet onto the tip of the capillary was on the order of minutes. In addition, the critical micelle concentration obtained from the surface tension data is in good agreement with that obtained from the conductivity data. Using the conductivity variation as a function of surfactant concentration, the thermodynamic parameters of micellization were calculated. Furthermore, the SSFQ method suggests a small and constant aggregation number, irrespective of temperature. The formation of small-size micelles was also confirmed by DLS measurements.

How specific are ion specificities? A pilot NMR study

NMR quadruple splitting measurements are a useful technique to investigate the adsorption behaviour of ions near to charged surfaces in liquid crystals made of surfactants of different headgroups. In the present paper we show the differences in lithium and sodium adsorption on dodecyl carboxylate and dodecyl sulphate bilayers as a function of surfactant concentration and for two temperatures. To this purpose we mixed the pure surfactants and also mixtures of the lithium and sodium surfactants with octanol as a cosurfactant in appropriate ratios and concentrations to obtain liquid crystals. It turned out that the measured specific ion effects are much more pronounced in the case of carboxylates than for sulphates.

Highly Methyl-Branched Hydrocarbon Surfactant as a CO2-philic Solubilizer for Water/Supercritical CO2 Microemulsion

To develop an efficient and fluorine-free solubilizer for a water/supercritical CO₂ microemulsion (W/CO₂ μE), in this study, a highly methyl-branched alkyl, isostearyl group was focused on as a CO₂-philic tail, and the custom-made isostearyl surfactant, sodium 2-(4,4-dimethylpentan-2-yl)-5,7,7-trimethyloctyl sulfate (SIS1) was synthesized. The surface tension (γ) of an aqueous SIS1 solution was measured at ambient pressure as a function of surfactant concentration, and it was found to be 25 mN/m at concentrations of > 1.5 mM. A low γ value can generally be reached only by a fluorocarbon surfactant, which implies that SIS1 has an excellent solubilizing power for the W/CO₂ μE, similar to some fluorocarbon surfactants reported previously. Visual observations of the SIS1/W/CO₂ mixtures revealed the formation of transparent single phases without separated water, identified as W/CO₂ μE. The μE was well-stabilized at pressures > 210 bar and temperatures > 55 °C. At 75 °C and 370 bar, SIS1 was found by spectral measurements using a water-soluble UV-light absorber to solubilize water contents up to a maximum water-to-surfactant molar ratio (W0) = 50. The achievement of W0 = 50 in a W/CO₂ μE system has not been reported previously in similar hydrocarbon surfactant/W/CO₂ systems, and this demonstrates that a highly methyl-branched alkyl group can act as a good CO₂-philic group for a W/CO₂ -type surfactant.

Surfactant mediated charging of polymer particles in a nonpolar liquid

We study the charging behavior of polystyrene and polymethyl methacrylate particles with different functional surface groups in water and in decane containing either ionic (AOT) or nonionic surfactant (Span 85). Electrophoretic mobilities in the nonpolar media are measured as a function of surfactant concentration and the applied electric field strength by phase analysis light scattering (PALS); acid–base characteristics of the particles and the surfactant are investigated via contact angle measurement and interfacial tensiometry, and the residual water content of the non-aqueous dispersions is assessed by Karl Fischer titration. The results suggest a competition of several mechanisms for particle charging in nonpolar media. At high concentrations of the nonionic surfactant, particle charging becomes insensitive to the functional surface groups responsible for charging in aqueous dispersions, but consistent with a charge transfer between the polymer surface and the surfactant due to acid–base interactions, which can be rationalized in terms of measurable acid–base parameters. By contrast, particle charging in nonpolar solutions of the ionic surfactant (with significantly larger amounts of residual water) suggests a strong influence of surface headgroup ionization, and of dissociated surfactants adsorbed to the particle surface.

Physico-chemical studies of oppositely charged protein–surfactant system in aqueous solutions: Sodium dodecyl sulphate (SDS)–lysozyme

Sound velocities (v) and densities (d) of sodium dodecyl sulphate (SDS) in various aqueous solutions of lysozyme have been measured over a temperature range of 25–40°C. The data was used to calculate apparent molar volume (ϕv) and apparent molar adiabatic compressibility (ϕk). These parameters have been examined as a function of surfactant concentration, lysozyme concentration and temperature to understand the consequences of interactions between these two components. Surface tension (γ) measurements were also carried out for the same systems using Man Singh Survismeter. The surface tension data have been used further to calculate the interfacial parameters like, maximum surface excess concentration (Γmax), minimum area per molecule (Amin), standard free energy of adsorption (ΔGad°), surface pressure at CMC (Πcmc) and standard free energy of transfer (ΔGtr°), that have direct bearing on the consequences of such interactions at the molecular level. The work has been extended to include UV-studies for different SDS–lysozyme solutions. A reasonably good qualitative correlation is found to exist with regard to the surfactant–lysozyme interaction obtained from the experimental data, from different techniques.

Mechanistic Studies of Particulate Soil Detergency: II: Hydrophilic Soil Removal

AbstractIn this work, the removal mechanism of kaolinite and ferric oxide (model hydrophilic particulate soils) from hydrophilic (cotton) and hydrophobic (polyester) fabrics was studied using three surfactant types: sodium dodecyl sulfate (SDS), octylphenol ethoxylate (OP(EO)10), and cetyltrimethylammonium bromide (CTAB). This work investigated the relations between zeta potential, surfactant adsorption, contact angle, solid/liquid spreading pressure, and dispersion stability in washing solutions as compared to detergency performance and antiredeposition as a function of surfactant concentration and pH level. The SDS showed the best detergency for both particulate soils, followed by OP(EO)10, with CTAB being the least effective surfactant. For SDS, the electrostatic repulsion between fabric and soil was found to be the dominant force for hydrophilic particulate soil removal. For the nonionic surfactant OP(EO)10, electrostatics are also important and steric effects aid particulate soil detergency. Electrostatic forces and solid/liquid interfacial tension reduction aids CTAB detergency. These same detergency mechanisms have previously been found for the case of hydrophobic soil removal from fabrics. Dispersion stability did not prove to be a dominant mechanism governing particulate soil detergency. From the SEM photos of soiled fabric, ferric oxide attaches to the fabric surface with no entrapment between fabric yarns; moreover, ferric oxide tends to form larger aggregates on cotton compared to polyester fabric. The adhesion of larger particles is hypothesized to be weaker than the smaller ones. Therefore ferric oxide can be more easily removed from cotton fabric than polyester. The SEM photos for kaolinite show little visual difference in particle agglomeration on polyester compared to cotton. Removal of kaolinite from cotton was found to be higher than from polyester, but there is less difference than for ferric oxide.

Structural Characterizations of Diglycerol Monomyristate Reverse Micelles in Aromatic Solvent Ethylbenzene

Using small-angle X-ray scattering (SAXS) we have investigated the shape and size of diglycerol monomyristate (designated as C14G2) nonionic surfactant reverse micelles in aromatic solvent ethylbenzene as a function of surfactant concentration, temperature, and water. When C14G2 is added into ethylbenzene globular type reverse micelles with maximum core diameter ca. 4.5 nm are formed under ambient conditions. The micellar structure (shape and size) did not change with the surfactant concentration. However, an increase in temperature decreased the micellar size due to an increase in the critical packing parameter (cpp). Surfactant becomes more lipophilic upon heating and the micellar curvature tends to become more negative at higher temperature. Addition of a small amount of water caused a significant micellar growth. For instance, incorporation of 0.3% water in the 5% C14G2/ethylbenzene system resulted in the formation of 2.1 time bigger micelles with a small water pool in the micellar core. Besides the micellar shape is modified into an ellipsoidal prolate, whose scenario can be understood in terms of hydration of the surfactant's headgroup. Hydration decreases the cpp and favors micellar growth. An increase of temperature of a water incorporated system decreased the micellar size due to dehydration, which is equivalent to rod-to-sphere type transition.

Effect of Pharmaceutically Important Cosolvents on the Interaction of Promethazine and Trifluopromazine Hydrochloride with Sodium Dodecyl Sulfate Micelles

The present study is an attempt to gain a better understanding of the characteristics of binding of phenothiazine drugs; promethazine hydrochloride, and triflupromazine hydrochloride to sodium dodecyl sulfate micellar system in the presence of pharmaceutically important cosolvents, such as ethanol, ethyleneglycol, and propyleneglycol. The interactions of promethazine and triflupromazine hydrochloride with anionic surfactant sodium dodecyl sulfate in the absence and presence of various concentrations of cosolvents have been studied by absorption spectroscopy as a function of surfactant concentration ranging from the premicellar to postmicellar region at 298 K. The binding tendency of promethazine and triflupromazine hydrochloride to sodium dodecyl sulfate micelles decreased with the concentration of cosolvents increased. The addition of cosolvents increased the CMC of sodium dodecyl sulfate and at a certain concentration totally inhibited the micellization. The inhibitory effect of cosolvents on binding of promethazine and triflupromazine hydrochloride to micelles followed the order as; water > ethyleneglycol > propyleneglycol > ethanol. Polarity of the micellar microenvironment and probable location of promethazine and triflupromazine hydrochloride were also discussed in different micellar media.