Volume 52, Issue 4

Predictive models based on artificial neural networks have been developed for the percolation threshold of AOT based microemulsions with addition of either glymes or polyethylene glycols. Models have been built according to the multilayer perceptron architecture, with five input variables (concentration, molecular mass, log P , number of C and O of the additive). Best model for glymes has a topology of five input neurons, five neurons in a single hidden layer and one output neuron. Polyethylene glycol model's architecture consists in five input neurons, three hidden layers with eight neurons in both first two and five in the last, and a neuron in the last output layer. All of them have a good predictive power according to several quality parameters.

Bile acid salts are the most important biological surfactant-like molecules. These compounds play an active role in the cholesterol and lipid solubilization. They are also used as drug carriers. The salts give anionic amphiphilic moiety in aqueous solution and will interact strongly when mixed with cationic amphiphiles. With this aim we have investigated mixed systems of three bile acid salts (sodium cholate (NaC), sodium deoxycholate (NaDC) and sodium taurocholate (NaTC)) with two cationic drugs (adiphenine hydrochloride (ADP) and clomipramine hydrochloride (CLP)) by surface tension measurements. It was found that the two components mix nonideally, i.e., the cmc values of the mixtures decrease with the stoichiometric mole fraction (α 1 ) of bile salts and are lower than cmc* values (cmc at ideal mixing condition). The interaction parameters, β m and β σ , come out to be negative and large in magnitude which is obvious from the fact that the two components are of opposite charge and would experience attractive interactions. The results suggest that the contribution of bile salts in the mixed micelles (X 1 m ) is greater than both the α 1 and X 1 id (the contribution in ideal mixing condition). These components also form mixed interface where the contribution of bile salts is more than α 1 (i.e., X 1 σ > α 1 ). The minimum area occupied by a monomer decreases with increase in the content of bile salts in the solution. This confirms that the opposite charges on the two components decrease the repulsion among the head groups. All the evaluated thermodynamic parameters (i.e., ΔG 0 m , ΔG ex , ΔG° ads and G min ) support the above explanations.

In this study, the first and second critical micelle concentration (FCMC and SCMC) were determined by recording the absorbance at various surfactant concentrations using a dye probe and ultra violet (UV)-visible spectrophotometer. This method could predict the concentrations of hexagonally packed rods and palisade layer structure of ionic surfactants. The UV-visible absorbance graphs were plotted at specific concentrations. Sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) were used as the model surfactants, and methylene blue was used as the dye probe. The FCMC and SCMC were obtained from the concentration vs. absorbance graphs. The results are in good agreement with those obtained from the fluorescence, scattering, conductivity, and surface tension measurements.

Octyl amine, nonyl amine, dodecyl amine, hexadecyl amine and octadecyl amine are propoxylated with propylene oxide at mole ratios 1 : 1 and 1 : 2. The structure of the synthesized compounds has been identified by IR-and NMR-spectroscopy methods. Colloidal-chemical indices of these compounds have also been determined and their surface-active parameters have been measured, including the critical micelle concentration (CMC), the effectiveness of surface tension reduction (π CMC ), the surface excess concentration (Γ max ), area per molecule at the interface (A min ), the changes of Gibbs free energies of adsorption (ΔG ad ) and micellization (ΔG mic ). Petroleum-collecting and petroleum-dispersing capacities of the synthesized compounds on the surface of water of varying mineralization degree have been studied.

In order to find out the influence of dilational rheology on chemical flooding systems, the dilational rheology of Zhuangxi crude oil/NaOH solutions interface was investigated by DSA100 interfacial dilatational rheometer (KRÜSS, Germany). The results show that the alkaline system, which can enhance oil recovery, mainly depends on its interfacial dilational rheology, rather than interfacial tension. The greater the interfacial dilational elasticity, the higher the oil recovery is. The greater the interfacial dilational viscosity, the lower the oil recovery is. The conclusion is consistent with the change of displacement pressure in the macro displacement experiment and the change of sweep efficiency in the microscopic displacement experiment.

The kinetic study of catalytic oxidation of D-lyxose by hexavalent chromium has been investigated spectrophotometrically under pseudo first order condition at temperature 313 K. The rate of oxidation of D-lyxose is very slow. Picolinic acid (PA), 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) are used as promoter to accelerate the rate of the reaction. Phen acts as the most effective promoter in aqueous medium. The rate of the reaction is also increased in presence of nonionic surfactant Triton-X-100 (TX-100) and anionic surfactant sodium dodecyl sulphate (SDS). They are used as catalyst in this reaction. Thus the observed micellar effects have been explained by considering the hydrophobic and electrostatic interactions between the reactants and surfactants in terms of the proposed mechanism. However, the combination of promoter and surfactants produces a better result. The maximum rate enhancement is obtained in presence of the combination of phen and TX-100.

An effort has been made to synthesize, characterize and evaluate the fluorescence and surface active properties of dodecanol based bis-sulfosuccinate anionic gemini surfactants using α,ω-dibromo alkanes (BSGSLA 1,4 ; BSGSLA 1,6 and BSGSLA 1,8 ). The chemical structures of the synthesized surfactants were confirmed by spectroscopic analytical techniques viz. elementary analysis, fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR). Numerous surface active properties viz. surface tension at CMC (Υ CMC ), critical micelle concentration (CMC), efficiency of adsorption of surfactant (pC 20 ), surface pressure at the CMC (π CMC ), adsorption amount of surfactant (Γ max ) and minimum area per molecule (A min ) were determined for synthesized surfactants. Low CMC value, larger pC 20 consequently higher surface activity, higher Γ max value and lower A min values for the surfactants with higher flexible spacer length [(CH 2 ) 8 ] were observed. The experimental data indicated that a gemini surfactant with a larger hydrophobic flexible spacer [(CH 2 ) 8 ] was more readily able to form micelles which leads to a lower CMC value, larger aggregation number, and a more closely packed micelle structure. The results also indicated that a greater aggregation number and a higher micropolarity can be achieved when concentration of gemini surfactants was increased.

The deposition of material at the edge of an evaporating droplet is known as the coffee ring effect. This phenomenon is widespread in various colloidal and bacterial systems. The study has examined the self-assembly and deposition of colloidal rhamnolipid (a natural surfactant) structures on a glass surface. The effects of the rhamnolipid concentration, pH and the addition of cations on the deposition formation and the alteration in coffee ring effect were studied by using in- vitro scanning electron microscope observation. Above the critical micelle concentration, a transition from ring-like deposition to dispersed deposition is observed. Whereas upon the addition of cations, the multi-distribution of aggregates size enhances the non-homogeneity of the drying film and consequently results in multi-nucleation of rhamnolipid aggregates.

An amphiphilic random copolymer was synthesized and applied as a surfactant in seed emulsion polymerization. The composition and structure of the copolymer were confirmed by Fourier transforms infrared spectroscopy (FTIR), 1 H nuclear magnetic resonance spectroscopy ( 1 H NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The effect of the copolymer content on the properties of latexes and their sizing properties was discussed. The average size, size distribution and stability of latexes were measured by quasi-elastic light scattering. The results suggest that the copolymer was a random copolymer, and displayed surface-active properties in water. The copolymer content affected strongly the properties of latex and its sizing performance. Monodisperse and nano-sized latex particles were obtained in the presence of 10.5 % copolymer. The thermal characteristics of latex films could be regulated by controlling the content of the copolymer. Adding an appropriate amount of the copolymer could reduce the surface tension of the latexes and promote their adsorption on the paper surface. Latex-treated paper showed a better water resistance and higher surface strength.

This paper reports on the ethanol assisted ultrasonic extraction of tea saponin from tea seed cake, an agriculture waste product, and on the application of tea saponin in toothpaste after purification of the extract. From the experiment, the tea saponin toothpaste fulfills the requirement of GB8372-2008 with regard to remove tea and coffee stains.