Unusual Stability and Catalytic Activity of Gold Nanoparticles in Polyoxyethylene Cholesteryl Ether.

We report a simple and spontaneous method for creation of extremely stable and catalytically active gold nanoparticles (AuNPs) from polyoxyethylene cholesteryl ether (ChEO) and sodium tetrachloroaurate (III) dihydrate (Na[AuCl₄] · 2H₂O). AuNPs with uniform size and distribution were prepared at 27 °C (AuNPs were formed in <3 h) and at 50 °C (AuNPs were formed in <1 h). Our elucidations propose that creation of well-defined AuNPs is assisted by reductive ChEO surfactant solution via complexation and reduction of AuCl₄ ions in which ChEO acts both as a reducing and consequently a stabilizing (capping) moiety.

Clay-supported novel bimetallic core-shell Co-Pt and Ni-Pt nanocrystals with high catalytic activities.

We demonstrate the striking potential of exfoliated clay (synthetic hectorite; Laponite XLG) platelets to prepare bimetallic (Co-Pt and Ni-Pt) NCs with well-defined structures. Catalytic studies show a strong bimetallic synergistic effect of the core-shell NCs; their catalytic activities are much higher than those of monometallic NCs and other bimetallic core-shell NCs.

Novel bimetallic core-shell nanocrystal-clay composites with superior catalytic activities.

Clay (synthetic hectorite; Laponite XLG) plays a very crucial role in the formation and stabilization of core-shell nanocrystals and affords high stability, large BET surface area and stimulates the exceptional catalytic activity of the core-shell NCs.

Preparation and characterization of highly planar flexible silver crystal belts.

We report a novel simple one-pot strategy for fabricating pure and highly planar silver (Ag) crystal belts. Unique single-crystal Ag belts (high width-to-thickness ratio ~50) were successfully synthesized in high yield (80 wt%) by reducing AgNO3 using N,N,N',N'-tetramethylethylenediamine (TEMED) as a reducing and a structure-determining agent in the presence of polyethylene glycol (PEG) under mild conditions.

Superior CO catalytic oxidation on novel Pt/clay nanocomposites.

Nanostructured novel Pt/Clay nanocomposites consisting of well-defined Pt nanoparticles prepared by clay-mediated in situ reduction displays very high thermal stability, large BET surface area and superior catalytic activity for CO oxidation as compared to a model reference Pt/SiO2 catalysts. CO oxidation has attracted renewed attention because of its technological importance in the area of pollution control. The Pt/Clay system consisting of Pt nanoparticles strongly immobilized between the atomic layers of clay inhibits nanoparticle sintering and loss of catalytic activity even after prolonged heating at high temperatures.

Adsorption, organization, and rheology of catanionic layers at the air/water interface.

We have investigated the adsorption and organization at the air/water interface of catanionic molecules released from a dispersion of solid-like catanionic vesicles composed of myristic acid and cetyl trimethylammonium chloride at the 2:1 ratio. These vesicles were shown recently to be promising foam stabilizers. Using Brewster angle microscopy, we observed the formation of a catanionic monolayer at the air/water interface composed of liquid-condensed domains in a liquid-expanded matrix.

Synthesis of highly active and thermally stable nanostructured Pt/clay materials by clay-mediated in situ reduction.

Novel and intriguing one-pot in situ method for the preparation of nanostructured Pt-clay materials under simple conditions is reported. In this synthesis, an inorganic clay mineral such as synthetic hectorite ("Laponite XLG") or natural montmorillonite ("Kunipia F") serves as a mild and effective reducing agent for Pt ions, which is uncommon for such a clay system, and also acts as an outstanding stabilizer for the resulting Pt nanoparticles. In aqueous solution, exfoliated colloidal clay platelets forms complex with Pt ions in the initial stage of mixing.

Effect of polyol on the structure of nonionic surfactant reverse micelles in glycerol monoisostearate/decane systems.

Using small-angle X-ray scattering (SAXS), effects of different polyols used as polar additives, glycerol (GC), ethylene glycol (EG), and 1,2-butanediol (1,2-BD), on the structure of nonionic surfactant glycerol monoisostearate (iso-C(18)G(1)) reverse micelles in decane have been investigated as a function of polyol concentration and temperature. The real space structural functions of the reverse micelles were obtained by generalized indirect Fourier transformation (GIFT) evaluation of the SAXS data, letting the form factor virtually model-free, and the results were complemented by conventional theoretical model fittings. The iso-C(18)G(1) forms spheroid type or slightly elongated prolate type micelles in n-decane.

Tunable parameters for the structural control of reverse micelles in glycerol monoisostearate/oil systems: a SAXS study.

Formation of reverse micelles in surfactant/oil binary systems without water addition and the tunable parameters for the structure control of such micelles are presented. The small-angle X-ray scattering (SAXS) technique has been used for the structural characterization of micelles. It has been found that the nonionic surfactant glycerol monoisostearate (abbreviated as iso-C18G1) forms reverse micelles in different organic solvents such as cyclohexane, n-decane, and n-hexadecane without the addition of water.

Solubilization of triglycerides in liquid crystals of nonionic surfactant.

The solubilization of triglycerides [1,2,3-tributanoylglycerol (TBG) and 1,2,3-trihexanoylglycerol (THG)] in water/octa(oxyethylene) dodecyl ether (C(12)EO(8)) systems has been investigated. Oil-induced changes in the structure of liquid crystals in water/C(12)EO(8) system have been studied by optical observation and small-angle X-ray scattering (SAXS) measurements. In the water/C(12)EO(8)/oil systems, solubilization of THG and TBG induces a transition between H(1) (hexagonal) and L(alpha) (lamellar) liquid crystals at high C(12)EO(8) concentrations, whereas at low surfactant concentrations a H(1)-I(1) (discontinuous micellar cubic phase) transition occurs.

Formation and properties of reverse micellar cubic liquid crystals and derived emulsions.

The structure of the reverse micellar cubic (I2) liquid crystal and the adjacent micellar phase in amphiphilic block copolymer/water/oil systems has been studied by small-angle X-ray scattering (SAXS), rheometry, and differential scanning calorimetry (DSC). Upon addition of water to the copolymer/oil mixture, spherical micelles are formed and grow in size until a disorder-order transition takes place, which is related to a sudden increase in the viscosity and shear modulus. The transition is driven by the packing of the spherical micelles into a Fd3m cubic lattice.

Wormlike micelles in mixed surfactant systems: effect of cosolvents.

We have studied the structure and rheological behavior of viscoelastic wormlike micellar solutions in the mixed nonionic surfactants poly(oxyethylene) cholesteryl ether (ChEO15)-trioxyethylene monododecyl ether (C12EO3) and anionic sodium dodecyl sulfate (SDS)-C12EO3 using a series of glycerol/water and formamide/water mixed solvents. The obtained results are compared with those reported in pure water for the corresponding mixed surfactant systems. The zero-shear viscosity first sharply increases with C12EO3 addition and then decreases; i.

Effect of temperature on the rheology of wormlike micelles in a mixed surfactant system.

The formation and rheological behavior of a viscoelastic wormlike micellar solution in an aqueous solution of a mixed surfactant system of alkyl ethoxylate sulfate (AES), C(12)H(25)(OCH(2)CH(2))(3)OSO(-)(3)Na(+), and polyoxyethylene dodecyl ether, C(12)EO(3), and the unusual effect of temperature on the rheological behavior have been studied. Upon successive addition of C(12)EO(3) to the dilute micellar solution of AES, viscosity increases swiftly and reaches its peak where a viscoelastic solution with nearly Maxwellian behavior is formed. With the further addition of C(12)EO(3), viscosity decreases sharply, which is attributed to the formation of micellar joints.

Viscoelastic behavior of surfactants worm-like micellar solution in the presence of alkanolamide.

A study of the phase and rheological behavior of anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) and nonionic polyoxyethylene sorbitan monooleate (Tween-80) with alkanoyl-N-methylethanolamide (C(12), NMEA-12; and C(16), NMEA-16) in aqueous system is presented. Upon addition of NMEA to the semi-dilute solution of SDES or Tween-80, induces micellar growth leading to the formation of a gel-like highly viscoelastic solution in the maximum viscosity region. These solutions obey the Maxwell model of a viscoelastic fluid.

Wormlike micelles in Tween-80/CmEO3 mixed nonionic surfactant systems in aqueous media.

Formation and rheological behaviour of viscoelastic wormlike micellar solution in aqueous mixed system of nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween-80) and trioxyethylene alkyl ether (C(m)EO(3), m=12, 14, and 16) was studied. The semi-dilute aqueous solution of Tween-80, in presence of C(m)EO(3) shows a sharp increase in viscosity leading to the formation of a gel-like highly viscoelastic solution reaching a maximum, but decreases beyond an intermediate concentration and finally phase separates. When C(12)EO(3) is replaced by C(14)EO(3) the micellar growth occurs more effectively.

Disconnected lamellar phases (Lalpha) in pseudobinary water-non-ionic surfactant systems: a general phenomenon.

This study provides new experimental evidence for the disconnection of the lamellar phase (L(alpha)) in pseudobinary water-non-ionic surfactant systems. To prove that the disconnection is indeed a general phenomenon the phase behavior of the pseudobinary system water-pentaethylene glycol dodecyl ether/hexaethylene glycol dodecyl ether (H(2)O-C(12)E(5)/C(12)E(6)) was investigated as a function of the surfactant composition delta and the total surfactant concentration gamma. At a fixed gamma of 0.

Mixed micelles of cationic surfactants and sodium cholate in water.

Critical micelle concentrations (CMCs) of cationic surfactant (alkyltrimethylammonium bromides, CnTABr, where n = 10, 12, 14, 16 and 18), and a bile salt sodium cholate (NaC) were determined from surface tension, conductance and dye solubilization methods, while of their equimolar mixtures from surface tension and dye solubilization methods. The interaction parameter (beta) obtained from analysis of data, using Rubingh's theory showed strong interaction between NaC and cationic surfactant. Time-resolved fluorescence-quenching results revealed small-sized mixed spherical micelle with aggregation number much less than micelles of cationic surfactant.