Dynamic Study of Gemini Surfactant and Single-chain Surfactant at Air／Water Interface

Molecular dynamics (MD) simulation are used to study the properties of gemini surfactant of ethyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C2C12) and dodecyl-trimethylammonium bromide (DTAB) at the air/water interface, respectively. In the two systems,t he surfactant concentrations are both 28 wt.%, and other conditions are also the same. After reaching the thermodynamic equilibrium, the concentration profiles, the radial distributions functions (RDF) and the mean squared displacement (MSD) are investigated. The results reveal that the surface activity of C12C2C12 surfactant is higher than DTAB surfactant.     

Preparation of Langmuir-Blodgett Film of Oligophenylenevinylene at the Air/Water Interface and Study on its Fluorescence

Phenylenevinylene polymers and oligomers were widely investigated as active materialsused in emission layer of light emitting diodes (LEDs), recently, due to their conductingand luminescent properties1-3. Comparing with their polymers, oligophenyl ene-vin…     

Effect of Electrolyte on the Interfacial Dilational Properties of Sodium 4,5-Diheptyl-2-propylbenzene Sulfonate at the Oil–Water Interface

The dilational viscoelastic properties of 4,5-diheptyl-2-propylbenzene sulfonate (377) in the presence or absence of electrolyte were investigated by means of two methods: the interfacial tension response to sinusoidal area variations and the relaxation of an applied stress. The higher dilational modulus of 377 than ordinary surfactant indicates that the strength against perturbation of interfacial layer of the former is greater. This may due to the two long and flexible branched alkyl chains, which are easily cross-linked and entangled. Moreover, the results reveal that the added electrolyte results in screening of electrostatic interactions between the ionized groups, which decreased the interfacial dilational modulus.     

Interfacial Behaviors of Azocalixarene Derivatives at the Air/Water Interface and Photochromism in the Langmuir-Blodgett Films

The azocalixarenes is a novel chromogenic compound and their spectra properties have been reported. A number of them have been applied as selective ionophores in extractive process1 or as selective ligands in ion selective electrodes and optical sensors based on spectra changes2. Some amphiphilic azocalixarene derivatives with hydrophobic long alkyl chains were synthesized and their interfacial behaviors at the air / water interface have also been investigated3. However, the photochromism of t…     

Dilational Rheological Properties of Non-Ionic Surfactants at the Water–Decane Interface: Effect of Unsaturated Hydrophobic Group

The interfacial tensions and dilational properties of adsorbed films of two non-ionic surfactants with different hydrophobic groups, polyoxy-ethylene sorbitan stearate (Tween 60) and polyoxy-ethylene sorbitan monooleate (Tween 80), at the water–decane interface have been investigated by the drop-shape analysis method. The effects of dilational frequency and bulk concentration on the interfacial properties were expounded. The influence of low temperature on the interfacial tensions and dilational properties have also been researched. The experiment results show that the interfacial activity of Tween 80 is rather large compared with Tween 60. The minimum area per molecule at the water–decane interface (A_min) value of Tween 80 is little large than that of Tween 60, which is due to the steric effect of unsaturated double bond in Tween 80 molecule. The dilational data show that the ethylene oxide groups of non-ionic surfactant form a stable sub-layer, which results in the increase of modulus and the decrease of phase angle for both Tween 60 and Tween 80 than those of common ionic surfactants. Moreover, the unsaturated hydrophobic group of Tween 80 is much flexible, which is easily crosslinked and entangled. Therefore, dilational modulus of Tween 80 is higher and phase angle is lower than that of Tween 60. Low temperature decreases the flexibility of unsaturated hydrophobic group and lessens the influence on the interaction of saturated hydrophobic group. Saturated surfactant molecules of Tween 60 almost lose temperature response.     

Phase Behavior of n‐Butanol/n‐Octane/Water/Cationic Gemini Surfactant System

Phase diagrams of the n‐butanol/n‐octane/water/(12‐3‐12,2Br^?1) system were determined, where n‐octane usually represents oil (O), 12‐3‐12,2Br^?1 is a gemini cationic surfactant trimethylene‐1,3‐bis(dodecyldimethyl ammonium bromide) abbreviated as S, and n‐butanol is a co‐surfactant written as A. Effects of the weight ratio of gemini surfactant to cosurfactant, S/A, and of temperature on the phase behavior were studied. The microemulsion structures including O/W, bi‐continuous (B.C.), W/O, and liquid crystal were determined by the conductivity method and polarization measurement. Experimental results show that the gemini surfactant, used facilitates the formation of microemulsions compared with its corresponding monomeric surfactant, n‐dodecyl trimethylammonium bromide (DTAB). When S/A=1/1, and the total concentration of gemini surfactant and alcohol is 20–40%, microemulsions with higher water content can form in a wider region. When the temperature increases, the size and position of each type of microemulsion region changes notably.     

Influence of Interaction Between Heavy Oil Components and Petroleum Sulfonate on the Oil–Water Interfacial Tension

The purpose of this study is to obtain the interaction between heavy oil components and petroleum sulfonate (NPS). In this article, the effects of pH, NaCl concentration, and NPS on the oil–water interfacial tension (IFT) of Gudao crude oil and its polar components were investigated. The results show that the NPS concentration corresponding to turning point of IFT is 0.001 g·mL^?1. This is lower than the CMC of NPS (0.0015 g·mL^?1) as there is a positive synergetic effect between NPS and the active substances of crude and its components, and the strength of their interaction depends on the interfacial activity of crude components. In simulated system of crude and polar components with 0.1 wt% NPS, at basic condition, the acidic substances in the polar components create naphthenates (the component whose acid number is higher creates more naphthenates), leading to lower IFT, so the interaction between heavy oil components and NPS is stronger in the basic condition. Proper concentration of NaCl in the stimulated systems improved the hydrophile-lipophile balance of emulsifier (NPS), accelerated the well-regulated adsorption of NPS in oil–water interface, and increased the interfacial activity of NPS, the interaction between heavy oil components and NPS was also enhanced.     

The Influences of Polymers and Temperature on the Foam Properties of 3‐Dodecylalkoxyl‐2‐hydroxylpropyl Trimethylammonium Chloride

The foam performances of 3‐dodecoxy‐2‐hydroxypropyl trimethylammonium chloride (C₁₂TAC) have been determined in the existence of different relative amount of polymer. The experimental results show that the foaming ability of the mixture systems of the C₁₂TAC/PEG and C₁₂TAC/PVP is stronger than that of the surfactant solutions in the absence of polymer, and with the increase of relative amount of polymer both foaming efficiency and foam stability of the surfactant solutions are evidently enhanced. For the aqueous solution of the surfactant, effect of temperature on foaming properties has also been examined. The results show that both the foaming ability and stability of the foams of the surfactant solutions are highest (or strongest) at 30°C.     

Skin Constituents as Cosmetic Ingredients. Part III: A Molecular Modeling Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface

Tetrakis(4-hydroxylphenyl)porphyrin (THPP) modified multi-walled carbon nanotubes were synthesized. Meanwhile, THPP or tetrakis(4-hydroxylphenyl)porphyrin cobalt(II) (CoTHPP) was introduced on the surface of carboxyl-functionalized multi-walled carbon nanotubes (MWNTs-COOH) and amino-functionalized multi-walled carbon nanotubes (MWNTs-NH₂) to form a series of complexes, respectively. TEM images indicated that the assemblies were made of the short chipping carbon nanotubes and the long assembled carbon nanotubes. The UV-vis spectra and fluorescence spectra were used to investigate the properties of the porphyrins assembled on the carbon nanotubes.     

Skin Constituents as Cosmetic Ingredients. Part II: A Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Dynamic Mode

This work aims at presenting the viscoelastic behavior of bio‐mimetic monoglycerides used as emulsifier in a mixture made of two non‐miscible liquids, squalene and water. The measurement of the interfacial tension, carried out by the “pendant drop” method in “dynamic” mode, made it possible to characterize these amphiphilic molecules according to the value of their elastic modulus, ?, as well as their relaxation time, τ_R.

The analysis of these parameters, as well as those developed in the previous publication [L. Blasco et al. (2006) Skin constituents as cosmetic ingredients. Part I: A Study of bio‐mimetic monoglyceride behavior at the squalene‐water interface by the “pendant drop” method in a static mode. J. Dispers. Sci. Technol., 27(6).] shows that the hydrocarbon chain structure, such as its length, the presence of one or more unsaturations, hydroxyl function, affects the behavior of surfactant molecules at the squalene/water interface.     

UV/Vis Spectral Study of the Self-aggregation of Pinacyanol Chloride in Ethanol–Water Solutions

The concentration dependent self-aggregation of 1,1′-diethyl-2,2′-carbocyanine chloride (pinacyanol chloride dye) in 7.5% (v/v) ethanol + 92.5% water solution in the range of 10⁻⁶–10⁻³ mol⋅dm⁻³ has been investigated by quantitative UV/vis and derivative spectroscopy. Bands with maxima at 601, 546, 522, and 507 nm could be attributed, respectively, to the monomer, a sandwich-type dimer, a vibronic overtone of the dimer, and a higher aggregate, most probably a stacked trimeric form of the dye. Using the PeakFit program, the overlapping bands were separated and analyzed for all concentrations studied. From the spectral fitting routine, extinction coefficients of 192,000, 156,000, and 282,000 cm⁻¹⋅mol⁻¹⋅dm³ were determined for the monomer, dimer and trimer respectively.     

Study on the Deactivation Kinetics of Pd（PPh3）2Cl2 in the Monocarbonylation of Benzyl Chloride

The deactivation kinetics of Pd(PPh3)2Cl2 in the monocarbonylation of benzyl chloride to synthesize phenylacetic acid is studied in this paper. Solid 1-(2-pyridylazo)-2-naphthol (PAN) is used as the colouring agent, and the concentration of Pd(PPh3)2Cl2 in the system is measured through absorptiometry. The result shows that the optimum condition of the chromogenic reaction between Pd2+ and PAN is: 0.5 ml of 0.04% PAN added to 10 ml of Pd2+ solution (1.0×10-6-2.0×10-5 mol/L), and heated in a constant temperature water bath at 40℃ for about 30 min, with pH of the solution being about 3.0. The molar coefficient of absorption is 1.384×104 L/(mol·cm); the orders of the hydrolytic reaction to the concentration of Pd(PPh3)2Cl2, PPh3, phenylacetic acid and NaOH are 0.5, minus 0.8, 2 and 1.2, respectively. The activation energy (E) of the hydrolytic reaction is 75.59 kJ/mol, and the pre-exponential factor is 1.68×1012.     

Temperature Effect on the Phase Behavior of the Systems Water/Sucrose Laurate/Ethoxylated‐mono‐di‐glyceride/Oil

The phase behavior of the systems water/sucrose laurate/ethoxylated mono‐di‐glyceride/oil was investigated as function of temperature and the weight ratio of EMDG in the mixed surfactants. The oils were R (+)‐limonene, isopropylmyristate, and caprylic‐capric triglyceride. This study demonstrates that the phase inversion temperature (PIT) decreases and the efficiency of the mixed surfactants (γ¯) increase as the weight ratio of the EMDG in the mixed surfactants increases. R (+)‐limonene gave lower phase inversion temperatures and higher efficiencies compared to isopropylmyristate, and caprylic‐capric triglyceride. The solubilization capacity of the system water/sucrose laurate/oil increased upon the addition of ethoxylated mono‐di‐ glyceride which stabilize the surfactant layer and increase the interfacial area.     

Theoretical Study on Photoisomerization of 2-Methylfuran to 3-Methylfuran

1 INTRODUCTION 2-Methylfuran belongs to the basic heteroaromatic compounds relevant to many fields of modern che- mistry, ranging from the study of natural products and biologically active substances to the develop- ment of building blocks for organic synthesis and conducting polymers[1]. Since the photochemistry ofR-furan was gradually recognized in 1960s[2～7], lots of interest has been aroused. Herein we only study one branch of photoche- mistry of R-furan: the isomerization of 2-methy…     

Study of Hydrogen Adsorption on Pt/WO3-ZrO2 through Pt Sites

The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO_3- ZrO_2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WO_3-ZrO_2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr.The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K.The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures,indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms,the spillover of hydrogen atoms onto the surface of the WO_3-ZrO2 catalyst,the diffusion of spiltover hydrogen atom over the surface of the WO_3-ZrO_2 catalyst,and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site.The rate determining step was the spillover with the activation energy of 12.3 kJ/mol.The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion.The activity of Pt/WO_3-ZrO_2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.     

Interfacial Behavior of Naphthenic Acids and Multivalent Cations in Systems with Oil and Water. I. A Pendant Drop Study of Interactions Between n‐Dodecyl Benzoic Acid and Divalent Cations

Abstract

Dynamic interfacial tension (IFT) measurements were used to investigate the interactions between a dissociated model naphthenic acid (p‐(n‐dodecyl) benzoic acid) and various divalent metallic cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) across a toluene/hexadecane–water interface. The measurements were performed by using the pendant drop technique. The results obtained, plotted as IFT vs. time gave curves with similar shapes but different slopes and levels of the equilibrium IFT, depending upon the acid and salt concentrations and the type of cation added. Due to differences in degree of hydration of the various cations, the products of the reaction between dissociated acid monomers and the cations showed differences in solubility, which, in turn, affected the IFT. Based on the shapes of the curves, the mechanisms of the reactions involved in the process are discussed.     

Viscoelastic Properties of Crude Oil Components at Oil‐Water Interfaces. 2: Comparison of 30 Oils

The dilational properties of diluted (0.7 vol/vol in toluene) and undiluted crude oil‐water interfaces have been studied using the oscillation drop method with the objective of understanding the properties contributing to the overall stability of crude oil emulsions. The importance of working with undiluted crude oils instead of model systems when dilational properties of real oil‐water systems are going to be reproduced in the laboratory setting has been discussed. For such studies, molecular exchange mechanisms and the aggregation state of asphaltenes are too dependent on concentration to justify the use of model compounds, i.e. fractionated asphaltenes diluted in a solvent. As expected in the low frequency range (0.01–1 Hz), molecular exchange from the bulk oil phase strongly affected the measured dilational parameters. For the diluted crude oils, the frequency dependence of the dilational modulus increased with its magnitude. The systems that exhibited particularly low magnitude of the dilational modulus were of the heaviest crude oils in the sample set, whereas the systems with greatest dilational modulus were among the lightest crude oils. The overall characteristic time of relaxation of the crude oil‐water interfaces was in the range below 10 seconds. The undiluted crude oil‐water interfaces had similar interfacial properties as the diluted samples except for slightly reduced magnitude of the dilational modulus. The crude oil‐water interfaces appeared to be soluble, but some observations pointed to intrinsic rheological properties of the interfaces. Intrinsic elasticity and viscosity of the films should be studied outside the frequency range used here at low (ω～0 Hz) and high (ω→500 Hz), respectively.     

Spectrophotometric Determination of Nitrite in Water Samples with 4‐(1‐Methyl‐1‐Mesitylcyclobutane‐3‐yl)‐2‐Aminothiazole

Abstract

A simple, sensitive, and specific spectrophotometric method for the measurement of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. The azo dye, 4‐(1‐methyl‐1‐mesitylcylobutane‐3‐yl)‐2‐(p‐N,N‐dimethylazobenzene)‐1,3‐thiazole was synthesized with the reaction of 4‐(1‐methyl‐1‐mesitylcylobutane‐3‐yl)‐2‐aminothiazole and N,N‐dimethyl aniline in acidic medium. Obtained azo dye has been characterized by infrared (IR), ¹H nuclear magnetic resonance (NMR), and microanalysis methods. The dye shows an absorption maximum at 482 nm. The method is optimized for acid concentration, pH, amount of reagents required, time, and interfering species. All the determinations were carried out at this wavelength throughout the work. At an analytical wavelength of 482 nm, Beer's law is obeyed over the concentration range 0.05 to 2.00 µg nitrite per mL analyte. The molar absorptivity, Sandell's sensitivity, and relative standard deviation are 2.03×10⁴ L mol^?1 cm^?1±251.3 (95%), 2.28×10^?3 µg cm^?2, and 2.74% (n=10), respectively. The detection limit of the method is 0.012 µg ml^?1 of nitrite ion. The method was succesfully applied to the determination of nitrite in tap water and lake water.     

Skin Constituents as Cosmetic Ingredients. Part I: A Study of Bio‐mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Static Mode

This work presents the behavior of bio‐mimetic monoglycerides at the squalene/water interface. The study was done in the so‐called “static” mode using the “pendant drop method”, enabling us to characterize these molecules according to the value of their critical efficiency concentration (CEC), their maximum surface excess concentration (Γ_∞), the efficiency of the surface tension reduction parameter (pC20), and the minimum value of their interfacial tension (γ_min). It also permitted the study of the influence of the structure of the carbon chain of those monoglycerides on their interfacial behavior.

The analysis of the different parameters shows that monoglycerides with small hydrocarbon chains, monoglycerides with one or more double bonds, and monoglycerides possessing a hydroxyl function grafted in the middle of the chain constitute excellent surfactants. Two different groups can be found: one group composed of short saturated hydrocarbon chain monoglycerides (C12∶0 to C16∶0) and long hydrocarbon chain monoglycerides (C18∶0 to C22∶0); the second group, composed of unsaturated hydrocarbon chain monoglycerides, also includes hydroxystearate and isostearate monoglycerides. The first group could be used for the formulation of “hydrating” cosmetic products having secondary droplets, the second group for W/O emulsions.     

Microemulsion of Tween‐80/n‐Butylalcohol/H2O System and Its Entrapment Efficiency of ATRA

Microemulsion of Tween‐80/n‐butylalcohol/H₂O system was prepared, and the microemulsion region as well as the influence of temperature and concentration of NaCl on the region were determined with ternary diagrams. The O/W, W/O, and B.C. regions were divided by the conductance method. The particle diameters of microemulsions with different NaCl concentrations or microemulsion‐enveloping all‐trans retinoic acid (ATRA) were measured with dynamic light scattering in O/W region. The release rate of ATRA was studied with dialysis a bag‐ultraviolet spectrophotometers and the anticancer activity of ATRA in microemulsion was investigated with cancer cells H446. Results showed that O/W microemulsion forms when water content is over 64% in the mixture. The influences of temperature and salinity on microemulsion region were very slight, and even the particle diameter decreased very little with increasing salt and ATRA concentrations. The microemulsion‐enveloping ATRA possessed eminent sustaining release efficiencys and the efficiency was further confirmed with the growth inhibitory effect test on human cancer cells H446.