Volume 58, Issue 1

Micelles and micellization appeal long lasting interest as promising drug carriers. A conventional parameter providing information about formation of micelles is critical micelle concentration (cmc). Its value roughly separates two states of the surfactant solution – namely states with and without presence of micelles. If concentration of surfactants in water solution approaches cmc some physical quantities abruptly change, and this phenomenon is a key to determine value of the cmc. From numerous approaches for determination of the cmc the paper considers the conductivity-based method. But rather than studying the mechanism of micellization that is primarily carried out by the colloid chemists, the paper is focused on the development of an information rich and optimal dynamical model of the conductivity vs. concentration dependence. The model is derived from the solutions of the 1 st order differential equation. The optimal model parameters are determined by the downhill simplex algorithm and the cmc is computed on the basis of the curvature of the concentration dependence of the conductivity.

In the present study, the interaction of the anionic polymer sodium carboxymethyl cellulose (NaCMC) with the two cationic gemini surfactant (C 12 -(EO)-E-C 12 and C 12 -(EO) 2 -E-C 12 ) has been investigated by surface tension and turbidity measurements. The co-adsorption of the polymer and the surfactants as well as the formation of highly surface-active polymer-surfactant complex was observed. By inserting the surface tension data into the Gibbs equation it could be shown that the surface layers of the mixed solutions have a multi-level adsorption structure. Comparing the critical adsorption concentration (C 1 ), the critical saturation concentration (C 2 ) and the critical micelle formation concentration (C 3 ) of mixtures with different concentrations, it can be seen that all variables increase with the increase in polymer concentration. In addition, the inorganic salt (NaBr) greatly influences the C 1 , C 2 and C 3 . The salt effects depend on the competition between the salt-enhancing effect and the salt-shielding effect.

In the present study, binary mixtures of sodium N-lauroylglutamate (SLG) and dodecyltrimethylammonium chloride (DTAC) or dodecylbetaine (BS-12) were examined for their synergistic effect. The surface chemical properties of the compound systems with different molar ratios were determined by the regular solution theory. Results indicated that both compound systems show synergistic effects of overall synergy, in which the SLG/DTAC system exhibited a better activity than the SLG/BS-12 system. The aggregation number of SLG compound systems was smaller than that of single surfactants, and the difference of the proportion of the two surfactants had little effect on the aggregation number of compound systems.

A surfactant-mediated cloud point extraction (CPE) method using the non-ionic surfactant Triton X-100 (TX-100) has been developed to remove the dye Direct Blue 71 (DB71) from a waste water. Most of the dye molecules are solubilized in the coacervate phase so that the dilute phase remains free of the dye. The effects of surfactant concentration, temperature and salt concentration on the different dye concentrations were studied to determine the optimal conditions for removing DB71. The concentration of DB71 in the dilute phase was measured using UV-Vis spectrophotometer. It was found that the separation of phases was complete and the recovery of DB71 was very effective in the presence of NaCl as an electrolyte. The results showed that up to 25 ppm DB71, i.e. more than 95%, can be quantitatively removed by cloud point extraction procedures in a single extraction at optimal conditions. It was also observed that at a dye concentration of 1 ppm, 100% of the blue dye DB71 can be directly removed with a TX-100 concentration of 12% by weight. At higher dye concentrations of up to 30 ppm, 94.7%-100% dye can be removed. The TX-100 concentration was 12 wt%, the salt concentration (NaCl) 0.005 M and the temperature 75°C. It is concluded that the surfactant mediated cloud point extraction method for dye removal can be an alternative to current dye removal methods.

The sensory properties of cosmetic emulsions are part of the basic properties of products such as face creams and body balms. They are extremely important parameters in the product evaluation by consumers. Cosmetics manufacturers are increasingly introducing ingredients in the form of solid particles (talc, bentonite, clay) into formulations to improve the sensory properties of products. Their addition simplifies the application of the emulsion on the skin, effects faster absorption and leaves a feeling of silky smoothness after application. During the work, we investigated solid particles of plant origin: powder from ground orange peel and oat grain. These ingredients were introduced into the formulation of the model body balms. The antioxidant and physicochemical properties of the obtained emulsions as well as the skin hydration after their application were evaluated. It has been shown that the introduction of solid plant particles increases the antioxidant properties of the emulsions and significantly improves emulsion stability and skin moisture after application.

In this study, two novel resonance light scattering (RLS) methods were developed for the determination of benzalkonium chloride. These methods were based on the formation of inorganic anionic-surfactant aggregates in a Clark-Lubs medium, which increases the resonance light scattering intensity of the reaction system and were also predominantly divided into sodium tungstate-benzalkonium chloride (method A) or phosphomolybdate-benzalkonium chloride (method B). The detection is performed both at 285 nm. Under the established conditions, the limits of quantification ranged from 0.10 mg L –1 to 1.00 mg L –1 with the R values of 0.9994 and from 0.20 mg · L –1 to 3.20 mg · L –1 with the R values of 0.9991, with good precision and accuracy both for method A and method B. The limits of detection were 0.029 mg · L –1 for method A and 0.013 mg · L –1 for method B. These two methods were successfully applied for the assay of benzalkonium chloride for the first time. All validation parameters were in agreement with the International Conference on Harmonization of Requirements for Registration Pharmaceuticals for Human Use (ICH) guidelines. Compared to the classical spectrophotometric method, these two methods take advantages of rapidity, high efficiency and good selectivity.

The most frequently investigated salts in coal flotation are chlorides. However, seawater contains additional salts such as sulfates. In coal flotation, magnesium chlorides showed the best results in terms of higher yield and lower ash content compared to the other magnesium salts studied. Therefore, two magnesium salts were tested in this investigation, namely magnesium chloride and magnesium sulfate. The effect of the magnesium salts as well as the optimization of coal flotation were investigated by statistical design of experiments in terms of pulp density, particle size, conditioning time and different dosages of MgCl 2 and MgSO 4 . The flotation results obtained by statistical design show that the ash content was lowest at 8.2% when a mixture of 2 kg/t MgSO 4 and 2 kg/t MgCl 2 has been used, with pulp density 20%, particle size 400 lm and conditioning time 15 min. The particle size plays an important role in reducing the ash content when the conditioning time has been extended and pulp density has been reduced. The strong interaction between the salts hinders the reduction of the ash content to less than 8.2%.

We have studied the surface dilatational properties of aqueous foaming dispersions containing mixtures of silica nanoparticles (Ludox CL) and sulfobetaine (LHSB) in Tahe formation water. The effects of temperature and pH on the surface dilatational modulus and time shift were studied by oscillating drop module (ODM). The ODM results show that the surface dilatational modulus of mixtures of CL and LHSB is large and increases with the decrease of surface area deformation, which results from hydrophobic interaction between adsorbed mixtures. Under test conditions, the Gibbs stability criterion E > σ/2 against foam coarsening is fulfilled. Results of Brewster angle microscopy (BAM) show that an uniform adsorption layer is established at the air-water interface. Temperature and pH-value influence the dilatation modulus of the surface by hydrophobic interaction or adsorption. Time shift has a similar variation trend. This is a surprising feature. It suggests that LHSB adsorbed on CL can respond to surface tension gradient. The time shift difference results from the response of LHSB at different adsorption sites. In addition, sand pack tests show that compared to LHSB, a finer foam was produced by the mixtures CL/LHSB due to the capillary-induced \snap-off". Thus, higher pressure difference and higher oil recovery could be achieved.

Among the surfactants, dimeric surfactants represent a niche group with multifunctional properties. In this work a modified gemini surfactant was synthesized using symmetrical fatty acids. Due to the spacers used to combine the two symmetrical monomers, the synthesized gemini surfactant is cationic. The structure of the compound was confirmed with 1 H-NMR. The most advantageous property of the gemini surfactant is that it has a lower surface tension, i. e. less than 35 mNm –1 at 25°C, compared to monomeric surfactants. The surface tension was determined with a Kyowa tensiometer. The CMC (critical micelle formation concentration) was calculated according to the pyrene method and detected by UV spectroscopy at 25°C. The very low CMC is another market advantage of the gemini surfactant. Hydrophobicity and hydrophilicity of the synthesized compound were checked by the emulsification method. The ability of the synthesized gemini surfactant to wet and foam and the emulsification index at different pH values were tested. Based on the results, the gemini surfactant was used in formulations for hair and skin care. Conditioners and creams were prepared with the synthesized compound and the properties were analyzed at different concentrations of the gemini surfactant in the respective formulation.

In this work, we report the Nocardia species were initially screened and then tested for their ability to produce biosurfactant. The biosurfactant production from the Nocardia species was determined by qualitative standard methods. The selected bacterial strain had better oil spreading and emulsifying activity and surface tension reduction. The biosurfactant producer strain was identified by 16S rRNA gene sequencing method. Using Fourier transform infrared spectroscopy and comparative analysis, the biosurfactant structure could be detected. Oil spreading tests and blue agar plate tests confirmed the presence of biosurfactant and extracellular anionic glycolipids. The E24% assay using olive oil showed strong emulsifying characteristic of extracted biosurfactant with a 100%. The stability of the biosurfactant produced in different conditions was significant. Nocardia coubleae was identified by biochemical methods and molecular methods.