Recently, the development of bimetallic nanoparticles with functional properties has been attempted extensively but with limited control over their morphological and structural properties. The reason was the inability to control the kinetics of the reduction reaction in most liquid-phase syntheses. However, the alcohol reduction technique has demonstrated the possibility of controlling the reduction reaction and facilitating the incorporation of other phenomena such as diffusion, etching, and galvanic replacement during nanostructure synthesis. In this study, the reduction potential of straight-chain alcohols has been investigated using molecular orbital calculations and experimentally verified by reducing transition metals. The alcohols with a longer chain exhibited higher reduction potential, and 1-octanol was found to be the strongest among alcohols considered. Furthermore, the experimental evaluation carried out via the synthesis of metallic Cu, Ni, and Co particles was consistent with the theoretical predictions. The reaction mechanism of metallic particle formation was also studied in detail in the Ni–1-octanol system, and the metal ions were confirmed to be reduced via the formation of nickel alkoxide. The results of this investigation were successfully implemented to synthesize Cu–Ni bimetallic nanostructures (core–shell, wire, and tube) via the incorporation of diffusion and etching besides the reduction reaction. These results suggest that the designed synthesis of a wide range of bimetallic nanostructures with more refined control has become possible.
The interaction forces between silica surfaces modified to different degrees of hydrophobicity were measured using colloidal probe atomic force microscopy (AFM). A highly hydrophobic silica particle was prepared with octadecyltrichlorosilane (OTS), and the interaction forces were measured against silica substrates modified to produce surfaces of varying hydrophobicity. The interaction forces between the highly hydrophobic particle and a completely hydrophilic silicon wafer surface fitted well to the DLVO theory, indicating that no additional (non-DLVO) forces act between the surfaces. When the silicon wafer surface was treated to produce a contact angle of water on surface of 40°, an additional attractive force that is longer ranged than the van der Waals force was observed between the surfaces. The range and magnitude of the attractive force increase with the contact angle of water on the substrate. Beyond the effect on the contact angle, the hydrocarbon chain length and the terminal groups of hydrophobic layer on the substrate only have a minor effect on the magnitude of the force, even when the substrate is terminated with polar carboxyl groups, provided the hydrophobicity of the other surface is high.
Effects of pressure on thermal Z/E isomerization of substituted N-benzylideneanilines and azobenzenes were studied in 2-methyl-2,4-pentanediol. Pressure dependence of the Z/E isomerization of a substituted azonaphthalene was also studied in glycerol triacetate. From the results in this and earlier papers, the following conclusions were reached. 1) It is possible to cast slow thermal reactions into the state of fluctuation control in highly viscous liquid phase realized by a combination of a viscous liquid and high pressure. 2) The viscosity dependence of the rate constant can be rationalized by the two-dimensional reaction-coordinate model developed by Sumi but not by the Grote–Hynes’ theory of frequency-dependent friction. Namely, the energy-barrier crossing takes place after the solvent molecules are rearranged to accommodate the transition state. 3) Whether the solvent rearrangement involves chemical transformations with appreciable energy increases depends on the nature of the reaction and the solvent.
The effects of the solvent viscosity on the thermal Z/E isomerization of three substituted N-benzylideneanilines were studied in a nonpolar aprotic solvent, 2,4-dicyclohexyl-2-methylpentane. By increasing the pressure to several hundred megapascals, the viscosity of the reaction system was raised high enough to retard the isomerization. The viscosity dependence of the observed rate constant was analyzed by assuming a two-step mechanism based on the two-dimensional reaction-coordinate model proposed by one of the present authors. The rate constant of this mechanism is given by 1/(kTST−1 + kf−1), where kTST represents the rate constant expected from the transition state theory, while kf (>0) represents the part controlled by a solvent rearrangement during thermal fluctuations. The kf values were inversely proportional to a fractional power of the viscosity, in agreement with the theory. It was also found that, compared at the same temperature and viscosity, the kf values in the present solvent are larger than those in a polar aprotic solvent, glycerol triacetate, and in a polar protic solvent, 2-methyl-2,4-pentanediol, reported earlier.
The solution of thermal elastohydrodynamic lubrication of rolling/sliding line contacts has been obtained. The Newton-Raphson technique was used to solve the simultaneous system of Reynolds and elasticity equations. The energy equation with boundary conditions was solved by the finite-difference method. Two models were developed: one with a constant viscosity across the oil film and another with a variable viscosity across the oil film. Different viscosity formulas such as modified WLF, Roelands, and Barus can be used in these models. Viscosity measurements were also performed over wide ranges of pressure and temperature. A very good fitting of experimentally measured viscosity by modified WLF formula was obtained. The oil film shape and minimum film thickness were calculated for pure rolling and high slip. For high slip and high rolling velocity, a tapered wedge shape of EHL film (in the longitudinal direction) was obtained. These results show a good correlation with measurements reported in other papers. They show that there is a significant influence of temperature on the oil film shape.
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