Yuwen Shen

Reversible phase transition between salt-free catanionic vesicles and high-salinity catanionic vesicles

Reversible phase transition between salt-free cationic and anionic (catanionic) tetradecyltrimethylammonium laurate (TTAL) birefringent L-phase solution with uni- and multilamellar vesicles and high-salinity catanionic vesicles was studied. With increasing concentration of NaBr, the salt-free catanionic birefringent Lα-phase formed by cationic tetradecyltrimethylammonium hydroxide (TTAOH) mixing with lauric acid in equimolar ammounts in aqueous solution was transferred into a two-phase precipitate-L-phase, and finally a birefringent L-phase again at much higher salt concentration. The uni- and multilamellar vesicles of birefringent L-phases without salt and with much higher salts were determined by freeze-fracture transmission electron microscopy (FF-TEM) images. The precipitates being the top phase at the two-phase region were also determined by means of FF-TEM images, which consist of densely packed multilamellar vesicles. The phase transition from salt-free catanionic birefringent L-phase to the one with much higher salinity is reversible, which could be achieved by removing the salts through dialysis. Salt-free catanionic birefringent L-phase with uni- and multilamellar vesicles, the densely packed multilamellar vesicles of precipitates that have a lower density than water to another birefringent L-phase at high-salinity, and also the reversible process should improve our understanding of self-assembled structures of surfactants in completely different solvents such as in pure water and ionic liquid media, which may make a significant impact on surfactant sciences.

Reversible phase transition from vesicles to lamellar network structures triggered by chain melting

Reversible phase structural transition from densely packed multilamellar vesicles of cationic and anionic (catanionic) tetradecyltrimethylammonium laurate (TTAL) with an amount of salt (NaBr) to network structures was triggered by chain melting. Phase behavior of catanionic TTAL multilamellar vesicles in aqueous solutions at different concentrations of NaBr with increasing temperature was studied. This phase structural transition is a progressive process and happens at the chain melting, which was monitored by means of Fourier transform infrared (FT-IR) spectroscopy, turbidity and viscosity measurements. Transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) were used to demonstrate the phase structural conversion from vesicles to three-dimensional structures consisting of extended bilayer networks. We found that the phase transition temperature (Tm) was influenced by adding amount of salt but not by being diluted. This is the first time that the phase conversion from catanionic surfactant vesicles to bilayer networks triggered by chain melting has been observed. The phase structural transition should arise from the enhanced membrane elasticity accompanying the catanionic surfactant state fluctuations on chain melting and the solvent-associated interactions including cationic and anionic surfactant electrostatic interaction, which favors a change in membrane curvature. We hope this phase conversion observed in catanionic surfactants in aqueous solution will provide good insight into the nature of the fusion or fission processes and the fluctuation of catanionic vesicular systems.

Phase Transition of Precipitation Cream with Densely Packed Multilamellar Vesicles by the Replacement of Solvent

The swelling of lamellar phase can be induced by the replacement of solvent in a tetradecyltrimethylammonium bromide (TTABr) and sodium laurate (SL) aqueous mixed solution that contains cream floating precipitates on the upper phase and L1-phase (micelles) at the lower phase. The cream floating precipitates contain densely packed multilamellar vesicles, which were determined by freeze-fracture transmission electron microscopy (FF-TEM) images. Phase transition, from cream floating precipitates to swelling birefringent vesicle phase, to two-phase Lalpha/L1, and finally to micelle phase, can be induced by adding glycerin as solvent in the aqueous solution. At first, densely packed multilamellar vesicles of cream floating precipitates on the upper phase swelled throughout the whole phase with increasing content of glycerin. The replacement of solvent lowers the turbidity of the dispersion and swells the interlamellar distance between the bilayers, which is explained by matching of refractive index of the solvent to the refractive index of the bilayers of the surfactant mixtures. With an increasing amount of glycerin, the swelling Lalpha phase turned to two-phase Lalpha/L1, and finally to L1 phase (micelles). This phase transition can also be explained because of the increasing critical micelle concentration of the cationic and anionic (catanionic) surfactant mixture (TTABr and SL) at high glycerin concentration. The phase transition induced by addition of sorbitol can also be studied and compared to the case of adding glycerin. These results may direct toward acquiring an understanding of the phase transition mechanism of catanionic surfactants induced by solvents.

Bilayer swelling of nonionic surfactant and sodium dodecylsulfate mixed system by refractive-index matching

Bilayer swelling behavior of nonionic and anionic surfactant mixed aqueous solution induced by adding glycerin was studied. The phenomenon were performed on a system, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 5 (CH3(CH2)12(OCH2CH2)5OH; abbreviation IT5) and SDS mixed aqueous solution, with white cream of the upper phase and micelles (L1) of the lower phase. White cream containing densely packed multilamellar vesicles was revealed by freeze-fracture transmission electron microscopy and polarized microscope observations. Phase transition from white cream/L1, two-phase, to clear unique vesicle phase can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by refractive-index matching between solvent and bilayers.

Swelling of Lamellar Gel from Catanionic Hydro- and Perfluoro-Carbon Surfactant Mixtures by Refractive-Index Matching

Bilayer swelling behavior of cationic and anionic surfactant mixtures in solution induced by adding glycerin was investigated. The measurements were performed a system, cationic tetradecyltrimetylammonium bromide (TTABr), and anionic sodium perfluorodecanoate (C9F19CO2Na) surfactant mixtures with their stoichiometric mole ratio being exactly 1 in aqueous solution. The non-precipitated phase of cationic and anionic hydro- and perfluoro-carbon surfactant mixtures being the mole ratio of 1:1 could be identified to be lamellar gel phase, which was characterized by freeze-fracture transmission electron microscopy (FF-TEM) and x-ray diffraction (XRD) measurements. Deuterium nuclear magnetic resonance (2H NMR) and rheology were used to characterize the phase transition from the lamellar gel to smaller vesicles. Phase transition from lamellar gel to smaller vesicles can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by matching of refractive index between solvent and bilayers.

Lamellar phase formation in catanionic mixtures of hydrogenated and fluorinated surfactants: a comparative study

The properties and phase behaviors of the catanionic mixtures consisting of tetradecyltrimetylammonium bromide (TTABr) and different anionic surfactants (i.e., sodium docanoate, C10HOONa; sodium laurate, C12HOONa; sodium perfluorodecanoate, C10FOONa) were examined, in particular when the molar mixing ratio in the aqueous solution was exactly 1:1. Although the three inspected systems have identical head groups and counterions, they exhibited very different lamellar (Lα) phases. When using the hydrogenated surfactants, the C10HOONa–TTABr system formed domain-like Lα/L1 two phases and the C12HOONa–TTABr system formed cream-like Lα/L1 two phases, respectively. In the case of the perfluorinated surfactant, the C10FOONa–TTABr system formed interdigitated and tilted Lα gel. The microstructures of the three Lα phases were characterized by polarized microscope, freeze-fracture transmission electron microscope, small angle X-ray scattering, and X-ray diffraction. The phase transition of the lamellar gel at different temperature was studied by differential scanning calorimetry and rheological measurements. The results elucidated the formation of the Lα phase in catanionic mixtures containing hydrogenated or fluorinated anionic surfactants with molar mixing ratio of 1:1.

Formation of Unique Unilamellar Vesicles from Multilamellar Vesicles under High-Pressure Shear Flow

Vesicles in surfactant systems are influenced by a shear field. The high shear flow generated by a homogenizer is expected to affect the size of vesicles. Hence, it should be possible to control the size and dispersion of vesicles by tuning the shear. In this study, the influence of shear on the vesicle phase was studied by measuring the rheology and conductivity of a solution made of the nonionic surfactant trideceth-5, a polyethylene glycol ether of tridecyl alcohol with an average number of ethylene oxide of 5, and the anionic surfactant sodium dodecylsulfate. It was found that when shear was applied by a homogenizer, the bilayers of the multilamellar vesicles were stripped off and became unilamellar vesicles, which decreased the viscoelasticity of the system. However, because of the pressure provided by the homogenizer, the newly formed unilamellar vesicles were small and the relative distance between them was large. As a result, the vesicles were no longer crowded and could easily pass each other under shear. This is why the unilamellar vesicles generated by the homogenizer had low viscoelasticity and flow birefringence. Additionally, it took a long time for the unilamellar vesicles to relax back to the original state.

Effects of Byproduct Amendment on Enzyme Activities and Physicochemical Properties of Acidic Orchard Soil from Jiaodong Peninsula of China

ABSTRACT Application of byproduct amendment containing silicon, calcium, magnesium, and potassium has been shown to improve acidic soil quality in Jiaodong Peninsula of China. In this study, we explored the influences of amendment supplemented with and without urea on the physicochemical properties as well as microbial activities of acidic soil from Jiaodong over a 120-day period. With the amendment, the electronic conductivity and pH of soils changed. The amendment treatment significantly reduced inorganic nitrogen content and increased microbial biomass nitrogen content during the whole incubation period. The microbial biomass, activities of phenol oxidase and dehydrogenase were increased by the addition of amendments, while the soil respiration, catalase and urease activity were declined. Our results indicated that application of byproduct amendment could improve the chemical and biological properties of the acidic orchard soils from Jiaodong over a short time period of investigation.

The phase transition from L3 phase to vesicles and rheological properties of a nonionic surfactant mixture system

A sponge phase (L3 phase) was observed in aqueous solution of a nonionic surfactant polyethylene glycol ether of tridecyl alcohol with the average 3 of ethylene oxide (CH3(CH2)12(OCH2CH2)3OH, abbreviated as Trideceth-3) with tetradecyldimethylamino oxide (CH3CH213N↑OCH32