Dynamic Surface Elasticity of Polyelectrolyte/Surfactant Adsorption Films at the Air/Water Interface: Carboxylmethylchitosan and Cetyltrimethylammonium Bromide

The dynamic surface elasticity of the solution of carboxymethylchitosan (CMCH) and cetyltrimethylammonium bromide (C₁₆TAB) was measured as a function of the surfactant concentration and the surface age by the oscillating drop method. The results showed that the surface layer of the CMCH/C₁₆TAB solution transformed from loose to structured with the increase in the surfactant concentration. The surface elasticity versus the surface pressure curve during the adsorption showed different features at different surfactant concentration ranges, which was connected with the structural transformation of the surface layer. Our results show that the measurement of dynamic surface dilational properties is a powerful tool for studying the surface kinetics, which is helpful for dealing non-equilibrium systems in industry.     

Rheological Study of Interactions between Anionic Guar and Oppositely Charged Surfactant

We have studied the interactions between anionic carboxymethyl guar (CMG) and oppositely charged surfactant: dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), cetyltrimethylammonium bromide (CTAB), and gemini surfactants (16-4-16), using rheological measurements. In the present study, two competing forces, electrostatic interaction and hydrophobic interaction, have been identified as important factors. Various types of structure formed on the anionic CMG chains are qualitatively discussed in comparison. For example, C₁₂TAB and gemini surfactant tend to form polymer-bound aggregates, whereas the C₁₆TAB tend to form the polymer-associated architecture. Furthermore, possible mechanisms based on the experimental results to elucidate these interesting phenomena have been proposed and discussed.     

Interaction of Sodium Dodecyl Sulfate with Poly(ethyleneimine) in Bulk Solution and at the Air-Solution Interface

Interaction of sodium dodecyl sulfate (SDS) with the cationic polyelectrolyte poly(ethyleneimine) (PEI) was investigated in this study. Turbidity measurements were performed in order to analyze the interaction and complex formation in bulk solution as a function of polymer concentration and pH. Surface tension measurements were made to investigate the properties of SDS/PEI/water mixtures at air/solution interface. Results revealed that SDS/PEI complexes form in solution depending on the surfactant and polymer concentration. A decrease was observed in surface tension values in the presence of SDS/PEI mixtures compared to the values of pure SDS solutions. Both solution and interfacial properties exhibited pH dependent behavior. A shift was seen in the critical micelle concentration of SDS solutions as a function of PEI concentration and solution pH. Monovalent and divalent salt additions showed some influence on the interfacial properties of SDS solutions in the presence of PEI.     

Solubilization and Transfer Free Energy of Some Organic Compounds from Bulk Aqueous Phase to Micelle of a New Type of Surfactant

A new type of surfactant, 3‐alkoxyl‐2‐hydroxylpropyltrimethyl ammonium bromide (C_nH_2n+1OCH₂CH(OH)CH₂N(CH₃)₃ ⁺Br^?, abbreviated as R_nTAB, n=8, 12, 14, 16) was synthesized. The solubilization of n‐pentanol, n‐hexanol, n‐heptanol, benzyl alcohol, n‐hexane, benzene, toluene, heptane, and carbon tetrachloride in aqueous solutions of R_nTAB, sodium dodecyl sulfonic(R₁₂SO₃N_a), and in the mixed solution of R₁₆TAB/R₁₂SO₃N_a have been studied by the microtitration method. The experimental results show that the solubilized amounts of the organic compounds increase with the growing of the hydrocarbon chain of R_nTAB, and the solubilizing ability of the binary system is lower for polar substances than for a mono‐surfactant aqueous solution. “V” isothermal curves of the solubilized amount of polar substances have been observed, and the minimum solubilized amount is at the molar ratio 1∶1 of R₁₆TAB/R₁₂SO₃N_a. However, the solubilizing ability of mixed surfactants for non polar substances is higher than that for a mono‐surfactant solution, the solubilizing isotherm curves present a “saddle” shape, and the maximum solubilized amount is at the molar ratio 1∶1 of R₁₆TAB/R₁₂SO₃N_a too. The length of hydrophobic chains of surfactant and the polarity of the organic compound affect the transfer free energy from aqueous to micelle phase. The longer the hydrophobic chain of R_nTAB and the lower the polarity of the organic compound, the more easily will the compound transfer from aqueous phase to micelle phase.     

Inhibition of CTAB on the Corrosion of Mild Steel in Hydrochloric Acid

The inhibition effect of cetyl trimethyl ammonium bromide (CTAB) on the corrosion of mild steel in 1.0 mol L^?1 hydrochloric acid (HCl) has been studied at different temperatures (25–60°C) by weight loss and potentiodynamic polarization methods. The results reveal that CTAB behaves as an effective inhibitor in 1.0 mol L^?1 HCl, and the inhibition efficiency increases with the inhibitor concentration. Polarization curves show that CTAB is a mixed-type inhibitor in hydrochloric acid. The results obtained from weight loss and polarizations are in good agreement. The effect of immersion time on corrosion inhibition has also been examined and is discussed. The adsorption of inhibitor on mild steel surface obeys the Langmuir adsorption isotherm equation. Thermodynamic parameters have been obtained by adsorption theory. The inhibition effect is satisfactorily explained by the parameters.     

PHYSICAL STRUCTURE AND PHASE PROPERTIES OF AQUEOUS SYSTEMS OF LIPIDS FROM RYE AND TRITICALE IN RELATION TO WHEAT LIPIDS

In connection with studies of technical functionality of lipids in cereals, the aqueous systems of lipids from rye and tri-ticale flour are described and compared to different wheat culti-vars. Rye lipids give a lamellar liquid-crystalline phase with very small ordered regions, and this phase is continuously changed into an L2-phase with increasing water content. Triticale lipids exhibit phase equilibria in between lipids of wheat and of rye. Evidence is given for a significant role of the lamellar liquid--crystalline phase with regard to technical functionality when the cereal flour is worked in water to give a dough.     

Studies on the Effect of Organic Solvents and Temperature on the Micellar Solution of Pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) Gemini Surfactant

Effects of three organic solvents, viz. methyl cellosolve, acetonitrile, and formamide, on the micellization process of Gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) aqueous solutions, with the volume percentages of the organic solvents up to 50%, have been investigated conductometrically. The studies were made at different temperatures and the data were used to find out different micellization parameters. From the study, it was observed that, although an increment in the amount of the organic solvents delays the micellization, the increase in the critical micelle concentration (cmc) is comparatively less below 20%(v/v) showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Applying equilibrium model for micelle formation, various thermodynamic parameters were also calculated from the temperature dependence of the cmc values and the results show that the micellization process becomes less spontaneous as the volume % of the organic solvent increases in the system due to the action of water-organic solvent mixed media as better solvent than pure water (solvophobic effect) for the studied Gemini molecules.     

Synthesis and Properties of Aromatic Side Chained N‐Acyltaurate Surfactants

A series of anionic N‐acyltaurate surfactants, side chain containing aromatic nucleus (abbreviated as SAATT), were synthesized via Williamson reaction, hydrolyzation, and acylation. Krafft temperatures and surface properties of these surfactants at 30°C, that is, critical micelle concentration, cmc, surface excess concentration, Γ_max, surface area demand per molecule, A _min, efficiency in surface tension reduction, pC₂₀, effectiveness in surface tension reduction, π_cmc, and cmc/C₂₀ parameter were determined. It was shown that these surfactants exhibit good solubility which was confirmed by measuring Krafft temperature. The cmc of SAATT was much smaller than that of conventional surfactants with similar effective carbon numbers, and shifted to lower concentration with increasing hydrocarbon chain length. In addition, the γ_cmc decreased with decrease in Γ_max. The pC₂₀ and the cmc/C₂₀ got larger with the increase in hydrocarbon chain length. From the fluorescence intensity ratios of I ₁ (373 nm) and I ₃ (384 nm) using pyrene as a probe, it was indicated that the molecules of SAATT formed loose micelles with a broad size distribution.     

Rheological Properties of Mixed Aqueous Solutions of Geminis (12‐3‐12,2Br−) and SDS

The rheological properties of surfactant solutions are the main parameter that affects the surfactant application. In this work, the rheology of the mixed system 12‐3‐12,2Br^?/SDS/H₂O was discussed particularly. The relationship between the microstructure of surfactant aggregates and rheology of mixed solutions was explored. It is shown that the rheological properties of solutions have different behaviors at different molar ratio of two surfactants under given total concentration. With the increase of molar ratio (12‐3‐12,2Br^?/SDS), the solution change from Newtonian liquid into positive thixotropy then to negative thixotropy, at last turn to positive thixotropy again, and ATPS becomes the dividing line. The difference of rheological properties is the embodiment of difference for surfactant aggregates' microstructures. The cryo‐TEM results shown that the solutions containing aggregates with big size, such as rodlike micelles, multilamellar micelles, show positive thixotropy. However, the solutions containing lamellar micelles or liquid crystal will show negative thixotropy. The positive thixotropy endows the mixied system a potential application in enhanced oil recovery.