Physico-chemical and spectroscopic investigation of flavonoid dispersed C n TAB micelles

In this study, kaempferol (0.2 m/mmol kg −1 ) dispersed cationic surfactant micelles were prepared as a function of alkyltrimethylammonium bromide (C n TAB) hydrophobicity (C = 12 to C = 16). The dispersion study of kaempferol in different C n TAB, i.e. dodecyltrimethylammonium bromide (C = 12), tetradecyltrimethylammonium bromide (C = 14) and hexadecyltrimethylammonium bromide (C = 16), was conducted with the physico-chemical properties of density, sound velocity, viscosity, surface tension, isentropic compressibility, acoustic impedance, surface excess concentration and area occupied per molecule and thermodynamic parameters Gibbs free energy, enthalpy and activation energy measured at 298.15 K. These properties were measured with varying concentration of C n TAB from 0.0260 to 0.0305 mol kg −1 in a 10% (w/w) aqueous dimethyl sulfoxide solvent system. The variations in these measured properties have been used to infer the kaempferol dispersion stability via hydrophobic–hydrophilic, hydrophilic–hydrophilic, van der Waals, hydrogen bonding and other non-covalent interactions.

Adsorption Properties of Hydrocarbon and Fluorocarbon Surfactants Ternary Mixture at the Water-Air Interface

Measurements were made of the surface tension of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10 oxyethylene groups in the molecule (Triton X-100, TX100) and cetyltrimethylammonium bromide (CTAB) with Zonyl FSN-100 (FC6EO14, FC1) as well as with Zonyl FSO-100 (FC5EO10, FC2) ternary mixtures. The obtained results were compared to those provided by the Fainerman and Miller equation and to the values of the solution surface tension calculated, based on the contribution of a particular surfactant in the mixture to the reduction of water surface tension. The changes of the aqueous solution ternary surfactants mixture surface tension at the constant concentration of TX100 and CTAB mixture at which the water surface tension was reduced to 60 and 50 mN/m as a function of fluorocarbon surfactant concentration, were considered with regard to the composition of the mixed monolayer at the water-air interface. Next, this composition was applied for the calculation of the concentration of the particular surfactants in the monolayer using the Frumkin equation. On the other hand, the Gibbs surface excess concentration was determined only for the fluorocarbon surfactants. The tendency of the particular surfactants to adsorb at the water-air interface was discussed, based on the Gibbs standard free energy of adsorption which was determined using different methods. This energy was also deduced, based on the surfactant tail surface tension and tail-water interface tension.

Synthesis and Properties of Alkyl Bis-Guanidinium Acetates Surfactants

Novel surfactants with double hydrophilic groups (cocopropane and tallowpropane bis-guanidinium acetates), were synthesized and tested to evaluate both the basic surfactant properties and the unique application performance. Surface tension, conductivity and contact angle measurements were used to study the self-aggregation behavior in aqueous solution. Aggregation parameters were calculated such as adsorption efficiency and effectiveness (pC20 and CAC/C20), the maximum surface excess concentration (Гmax) and minimum surface area permolecule (Amin). The thermodynamic parameters of aggregation based conductivity measurements revealed that the aggregation process was spontaneous and entropy-driven. Compared to DTAC and CTAC, the alkyl bis-guanidinium acetates showed a higher emulsification capacity with both liquid kerosene and soybean oil. The evaluation of antimicrobial activity showed that the alkyl bisguanidinium acetates exhibited strong antibacterial activity against the tested strains at a concentration of 50 ppm.

Theoretical and experimental investigation of effect of salinity and asphaltene on IFT of brine and live oil samples

Several factors influence the IFT of oil and formation water. These factors are rooted in the complex composition of oil, presence of different salts in water, water salinity, temperature, and pressure of reservoir. In the first part of this paper, effect of salinity on IFT between brine and an Iranian live oil sample has been studied experimentally. It is observed that IFT increases almost linearly with brine concentration. Also, linear increasing behavior of IFT with respect to pressure is obviously seen. Then, using thermodynamic properties such as surface excess concentration, chemical potential, chemical activity, and activity coefficient, results were analyzed and observed effect of salinity and pressure were justified thermodynamically. In the second part, the effect of asphaltene on IFT reduction has been studied. In previous works, the investigators extracted resin and asphaltene and then examined their effects on IFT in the absence of other fractions of oil phase. We believe that all fractions play a role in this phenomenon so, in this paper, the effect of natural surfactants of oil phase on IFT has been investigated in presence of all fractions of oil. Hence, SARA test was performed on all samples. Then, IFT between oil samples and brine were measured using captive drop instrument at 25 °C and 3000 psia. Results showed that neither asphaltene content nor asphaltene/resin ratio is a good indicator for effect of asphaltene on IFT, whereas colloidal instability index could be a useful tool to predict asphaltene effect on IFT.

Interfacial and Micellization Behavior of Cetyltrimethylammonium Bromide (CTAB) in Water and Methanol-Water Mixture at 298.15 to 323.15 K

The micellization behavior of cetyltrimethylammonium bromide (CTAB) in water , 0.1, 0.2, 0.3, and 0.4 volume fractions of methanol at 298.15, 308.15, 318.15, and 323.15 K were investigated by surface tension measurements. The effect of methanol on values of critical micelle concentration (cmc), free energies of micellization ΔGmo, and surface properties viz. maximum surface excess concentration Γmax, area occupied by per surfactant molecule Amin, surface pressure πcmc, solution surface tension γcmc, solvent surface tension (γo), free energies of adsorption ΔGadso, the efficiency of adsorption (pC20), effective Gibbs free energy ΔGeffo, and free energy of surface at equilibrium (Gmin) were investigated using surface tension values. Other parameters such as the packing parameter (P), aggregation number (N), concentration of surfactant in the bulk phase (C20), relation between Amin and πcmc, and correlation of slopes dγ/d log C, γo/γcmc, Γ/Γmax, cmc/C20, ΔGadso/ΔGmo, and cmc/pC20 with the volume fraction of methanol are calculated and discussed in the light of the experiment done.

Adsorption of surfactants at liquid interfaces: thermodynamics

The thickness and hence material content of a surface is generally unknown, and there are two common definitions of a surface/interface. In one the surface is treated as a phase distinct from the surrounding bulk phases, and in the other, due to Gibbs, the Gibbs dividing surface is supposed to be a plane, parallel to the physical interface. The former model gives rise to the surface concentrationΓ‎s of a surfactant, and the Gibbs model introduces the surface excess concentration, Γ‎σ‎. Some thermodynamic quantities for surfaces (e.g. surface chemical potential and Gibbs free energy for surfaces) are defined. Adsorption lowers interfacial tension by an amount termed the surface pressure, and the Gibbs adsorption equation allows the calculation of Γ‎s or Γ‎σ‎ for a surfactant from the variation of interfacial tension of a liquid/fluid interface with surfactant concentration in bulk solution.