Protecting structure analyses of organic molecule-protected nanoscopic noble metal clusters

The stabilizing structure of cationic surfactant-protected platinum clusters in water and tertiary amine-protected rhodium clusters in chloroform, prepared by photo- and hydrogen-reduction, respectively, was investigated. These nanoscopic noble metal clusters present a narrow size distribution and are stable. The structural information of protective organic molecules on the surface of metal clusters was studied by transmission electron microscopy and hydrodynamic radius measurements according to the Taylor dispersion method. The size of the entire cluster with the protective layer surrounding the metal surface, obtained as Stokes' radii by the Taylor dispersion method, is considered to be fairly consistent with the sum of the naked particle size, obtained by transmission electron micrographs, and the size of the adsorbed protective layer, supporting the conformational information.     

Electric Double Layer in Water-Organic Mixed Solvents: Titania in 50% Ethylene Glycol

Ethylene glycol (EG) and its mixtures with water are popular components of nanofluids used as heat transfer fluids. The stability of nanofluids against coagulation is correlated with their zeta potential. The electrophoretic mobility of titania nanoparticles in 50-50 w/w EG was studied as a function of the concentration of various solutes. HCl, NaOH, SDS and CTMABr at concentrations up to 0.01 M are strong electrolytes in 50% EG, that is, the conductance of their solutions is proportional to the concentration. HCl, NaOH and CTMABr were very efficient in inducing a high zeta potential for titania in 50% EG. NaOH induced a negative zeta potential in excess of 70 mV, and HCl and CTMABr induced a positive zeta potential in excess of 70 mV at concentrations below 10⁻⁴ M. Apparently, HCl, NaOH and CTMABr are also more efficient than SDS in terms of nanofluid stabilization against coagulation. An overdose of base (>1 mM) results in depression of the negative zeta potential. This result may be due to the specific adsorption of sodium on titania from 50% EG.     

Role of cationic gemini surfactants toward enhanced ninhydrin–tryptophan reaction

In this paper we report the effect of dicationic ‘gemini’ surfactants (CH₃)₂C₁₆H₃₃N⁺? (CH₂)_m? N⁺C₁₆H₃₃(CH₃)₂, 2Br^? (where m = 4, 5, 6) on the reaction of ninhydrin with DL ‐tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (k_ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing k_ψ at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in ¹H NMR line widths. Quantitative kinetic analysis of the rate constant–[surfactant] data has been performed on the basis of modified pseudophase model. Copyright © 2007 John Wiley & Sons, Ltd.     

利用1H NMR探究混合离子型/非离子型表面活性剂临界胶束浓度降低的实质

利用¹H NMR技术研究了离子/非离子表面活性剂形成的二元混合体系,结果显示表面活性剂的混合导致各组分的临界胶束浓度（CMC）均比各自纯溶液有所降低,用吸附平衡理论清楚地解释了这个现象.通过定量分析,发现不同的表面活性剂混合使得其组分CMC降低的程度各异,可以理解为它们吸附于界面单分子吸附层上的分子之间相互作用的不同（相吸或相斥）引起的.由此揭示了"协同效应"的实质,可以为选择适当的表面活性剂类型和混合比例以达到预期的性能提供有力的参考.     

混合表面活性剂对某些吡啶偶氮试剂显色反应的作用

本文研究了表面活性剂对不同电子结构的三种金属离子(Zn~(2+),Cu~(2+),Pd~(2+))与两种分子结构类似但反应官能团不同的吡啶偶氮染料(PAR和5-Cl-PADAB)间的显色反应的作用。试验证明:(1)表面活性剂对显色反应增敏作用的产生,最根本的是由于金属离子的电子结构和试剂的反应官能团的不同,以及由此引起所成显色络合物的结构的不同。(2)表面活性剂对显色络合物的增敏效应,与单个表面活性剂分子对有色络合物的作用有关,更重要的是形成胶束,改变反应微环境。(3)离子型-非离子型混合表面活性剂对显色反应是否产生协同增敏效应和协同增敏效应的大小,决定于两者形成混合胶束的难易。如果显色络合物的结构有利于此两种表面活性剂同时对它起协同作用,则协同增敏效应可进一步提高。     

Dependence of Colloidal Forces Between Bitumen and Silica on the Chain Lengths of Ammonium Surfactants

Effects of ammonium surfactants with different hydrocarbon chain lengths (C8, C12, C16, and C18) on the colloidal forces between bitumen and silica were studied by atomic force microscopy. The results showed that the chain length of the ammonium surfactants had a significant impact on both the long-range interaction and adhesion forces. With the addition of surfactants with relative short chains of C8 and C12 in the solutions, the long-range repulsive force decreased or even became strong attractive force, while it became repulsive again in solutions of surfactants with long chains of C16 and C18. It was further observed that addition of Ca²⁺ in various surfactants solutions would either depress or enhance the colloidal interactions based on the surfactant chain lengths. It was believed that variation of the interaction behaviors resulted from the mono-layer or bilayer adsorption of various surfactant molecules on the negatively charged surfaces of bitumen and silica, which affected the surface wettability and the surface charge characteristics and then greatly changed the colloidal interactions. The findings indicated that, to have a high bitumen recovery and good froth quality, the surfactant type and concentration of the di-valent metal ions in the oil sand processing slurry must be well considered.     

Three‐Component Langmuir–Blodgett Films Consisting of Surfactant,Clay Mineral,and Lysozyme: Construction and Characterization

The Langmuir–Blodgett (L–B) technique has been employed for the construction of hybrid films consisting of three components: surfactant, clay, and lysozyme (Lys). The surfactants are octadecylammonium chloride (ODAH) and octadecyl ester of rhodamine B (RhB18). The clays include saponite and laponite. Surface pressure versus area isotherms indicate that lysozyme is adsorbed by the surfactant–clay L–B film at the air–water interface without phase transition. The UV‐visible spectra of the hybrid film ODAH–saponite–Lys show that the amount of immobilized lysozyme in the hybrid film is (1.3±0.2) ng mm^?2. The average surface area (Ω) per molecule of lysozyme is approximately 18.2 nm² in the saponite layer. For the multilayer film (ODAH–saponite–Lys)_n, the average amount of lysozyme per layer is (1.0±0.1) ng mm^?2. The amount of lysozyme found in the hybrid films of ODAH–laponite–Lys is at the detection limit of about 0.4 ng mm^?2. Attenuated total reflectance (ATR) FTIR spectra give evidence for clay layers, ODAH, lysozyme, and water in the hybrid film. The octadecylammonium cations are partially oxidized to the corresponding carbamate. A weak 1620 cm^?1 band of lysozyme in the hybrid films is reminiscent of the presence of lysozyme aggregates. AFM reveals evidence of randomly oriented saponite layers of various sizes and shapes. Individual lysozyme molecules are not resolved, but aggregates of about 20 nm in diameter are clearly seen. Some aggregates are in contact with the clay mineral layers, others are not. These aggregates are aligned in films deposited at a surface pressure of 20 mN m^?1.     

Comparison between two anionic reverse micelle interfaces: the role of water-surfactant interactions in interfacial properties

The water/sodium bis(2-ethylhexyl) phosphate (NaDEHP) reverse micelle (RM) system is revisited by using, for the first time, molecular probes to investigate interface properties. The solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB) and 6-propionyl-2-(N,N-dimethyl)aminonaphthalene (PRODAN) in the water/NaDEHP/toluene system is studied, and the results are compared with those obtained in water/sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT)/toluene RM media. The results demonstrate that the micropolarity, microviscosity, interfacial water structure, molecular probe partition, and intramolecular electron-transfer processes are dramatically altered for NaDEHP RM interfaces in comparison to the AOT systems. Because of organic nonpolar solvent penetration into the interface, NaDEHP RM media offer an interface with lower micropolarity and microviscosity than AOT media. Also, the interfacial water in the NaDEHP system shows enhanced water-water hydrogen-bond interaction in comparison with bulk water. The AOT RM interface represents a unique environment for PRODAN to undergo dual emission.     

Micellar Effects on Alkaline Hydrolysis of 3,5-Dinitro-2-chloro Benzotriflouride and 2,4-Dinitrochloro Benzene in Aqueous-Acetonitrile Mixtures

Reaction rate for alkaline hydrolysis of the substrates 3,5-dinitro-2-chloro benzotriflouride (DNCBTF) (1) at 30°C and 2,4-dinitrochloro benzene (DNCB) (2) at 50°C separetely with NaOH as nucleophile is carried out spectrophotometrically in mixed aqueous-acetonitrile solvents. In each system, cationic surfactant as dodecyltrimethyl ammonium bromide (DoTAB), or anionic one as sodium dodecyle sulfate (SDS) is used in wide range of concentrations to study the effect of micelle on the reaction rate. The micellar effect is explained in term of modified pseudo phase ion exchange model. Pseudo first order rate constant, k_obs is obtained for each of the nucleophile and for both substrates 1 and 2 at all range of X_AN · k_obs at given [OH^?] and in presence of any substrate is found to increase with the increase of DoTAB,while decrease with the increase of SDS as micellar phases. Critical micelle concentrations (CMCs) in similar trend are observed to increase in DoTAB while decrease in SDS systems by increasing acetonitrile (AN) content. Micellar binding constant (K_S) between any type of given substrate and the formed micelle, is found to decrease in presence of DoTAB and increase in SDS micellar phases by increasing AN content. Finally, the ratios between pseudo first order rate constants for hydrolysis in micellar phase k_M to that in the bulk phase k_w for DoTAB and SDS systems are found to be greater than and smaller than unity respectively at any given X_AN where the data indicated for (1) is always higher than those for (2). The results concluded that micelle DoTAB is working as a catalyst for the reaction rate, while that for SDS is considered as an inhibitor.     

Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach

On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic surfactants investigated were alkylsulphonates (ASS) with alkylchain lengths comprised between 8 and 16 carbon atoms. The critical hydrochloric acid concentration (minimal acid concentration required to separation in two liquid phases) was found to increase as alkylchain length of the anionic surfactant increased from 10 to 14. Non-acid-induced liquid-liquid phase separation was observed for sodium octanesulphonate (SOS) or sodium hexadecyl sulphonate (SHS) in the hydrochloric concentration range 0-10 M. Acid aqueous solutions of sodium decylsulphonate (SDeS) and sodium dodecylsulphonate (SDoS) separated into two liquid phases at temperatures ranging between 10 and 80 °C, while temperatures >35 °C were required for sodium tetradecylsulphonate. The influence on extraction efficiency and concentrating ability of experimental variables such as hydrophobicity and concentration of surfactant, nature and concentration of analyte, hydrochloric acid concentration, time and temperature of extraction and time of equilibration and centrifugation was examined. Advantages provided by anionic surfactant-mediated extractions over the use of non-ionic surfactants (cloud point extractions) are discussed.