Papers by Keyword: Size-Dependent

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Authors: Hyo Sim Kang, Sun Wha Oh, Young Soo Kang
Abstract: We prepared various pyrazoline derivatives which possess dimethylamino-, ethoxy-, isopropyl-phenyl ring at the 5-position of pyrazoline. The nanoparticles of pyrazoline derivative ranging from tens to hundreds of nanometers by the reprecipitation method have been successfully prepared and their optical size-dependent properties have been investigated with UV-vis, fluorescence spectroscopy, DLS (Dynamic Light Scattering) and SEM. The size-dependent optical properties of pyrazoline organic nanoparticles have been observed in the order of dimethylamino- > ethoxy- > isopropyl- in electro-donating characters.
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Authors: Ali Nakhaei Pour, Seyed Majed Modaresi
Abstract: Concepts of the surface excess energy in the present work have been applied to explain the methane formation in Fischer-Tropsch synthesis by iron catalysts. A series of iron oxide particles doped by adding copper and lanthanum were prepared as a catalyst via precipitation by microemulsion method. Size dependent kinetic expressions for methane formation were derived and evaluated using experimental results. Experimental results show that the methane formation is increased by decreasing the catalyst particle size. The value of surface tension energy (σ) for iron catalyst is calculated in range of 0.047-0.015 J/m2 in methane formation mechanism. This value is lower than iron metal and is referred to the presence of iron carbide and gas phase in this catalytic reaction. With a series of complicated mechanisms, methane is produced on the surface of catalyst and in the gas phase as well, this would be elaborated by following paragraphs, thus we can conclude that surface tension of catalyst has less effect on these reactions.
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Authors: Hui Li, Hao Jie Xiao, Jiang Wang, Hai Xia Zhang, Hai Cheng Xuan, Qing Liang Ma
Abstract: In this study, size-dependent bond length of metallic clusters is established by introducing bond number. This model, free of any adjustable parameters, can be utilized to predict the change rule of bond length with size. If the atomic structure of a cluster is known, the size and shape-dependent bond number are obtained. The cubooctahedral structure is taken for simplicity to describe the shape and geometric characteristics of metallic clusters. It is found that the bond length decreases with the decreased size of metallic clusters, which is due to the structure relaxation and enhanced single bond energy. The theoretical predictions are consistent with the evidences of the simulations for Au and Ag clusters. This confirms the validity of taking cubooctahedron structure, even if the simulated Au and Ag clusters are not cuboctahedron ones. This can be expected to other metallic clusters even with other atomic structures.
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Authors: Jun Feng Zhao, Shen Jie Zhou, Bing Lei Wang
Abstract: A modified continuum model of electro-statically actuated micro-beam is presented based on the modified couple stress theory. The new model contains a material length scale parameter and can capture the size effect, unlike the classical Bernoulli-Euler beam theory. The governing equation of the micro-beam is derived based on the Hamilton’s principle, which accounts for the effects of the moderately large deflection, the residual stress and the fringing electrostatic field. The numerical analysis of mechanical characterization is performed by the Analog Equation Method (AEM). The effects of the couple stress on the static and dynamic responses, pull-in voltage and pull-in time are discussed.
633
Authors: Ming Zhao, Qing Jiang
Abstract: An extension of the classical thermodynamics to nanometer scale has been conducted to elucidate information regarding size dependence of phase transition functions and binary phase diagrams. The theoretical basis of the extension is Lindemanns criterion for solid melting, Motts expression for vibrational melting entropy, and Shis model for size dependent melting temperature. These models are combined into a unified one without adjustable parameters for melting temperatures of nanocrystals. It is shown that the melting temperature of nanocrystals may drop or rise depending on interface conditions and dimensions. The model has been extended and applied to size dependences of melting enthalpy, melting entropy, atomic cohesive energy. Moreover, the above modeling has been utilized to determine the size-dependent continuous binary solution phase diagrams. These thermodynamic approachs have extended the capability of the classical thermodynamics to the thermodynamic phenomena in the nanometer regime.
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Authors: S. Zhang
Abstract: A simple model, without any free parameter, is introduced to predict the size-dependent diffusion coefficient of nanocrystalline materials in this contribution. It is found that as the size of the nanocrystals decreases, the diffusion activation energy of atoms decreases and the corresponding diffusion coefficient strongly increases due to the Arrhenius relationship between them, which leads to evident diffusion at the room temperature. The model prediction is in agreement with the experimental diffusion results of Cu and Ag diffusion in Cu nanocrystalline materials.
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Authors: Shuai Zhang, Lei Chen
Abstract: Size-dependent piezoelectric coefficient d33(D) (D shows particle diameter) for small ferroelectrics is modeled in this paper. It is found that taking account of size effect is essential in understanding piezoelectric characteristics of nanoferroelectrics. The model prediction is in good agreement with the experimental results for PbTiO3 nanoparticles, where d33(D) increases correspondingly as D decreases.
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Authors: Yuan Na Zhu, Yong Qiang Cao, Ai Yu Zhang, Ping Yang
Abstract: Properties of Au nanoparticles (NPs) caused by various sizes (5-12 nm) were studied in this article. Au NPs capped with citrate of various sizes were synthesized by two methods including trisodium citrate dihydrate reduction of chloroauric acid tetrahydrate and sodium borohydride reducion of chloroauric acid tetrahydrate. Au NPs were characterized and measured by using transmission electron microscope (TEM), UV-vis-NIR absorption spectroscopy, and surface Raman scattering. The results of experiment indicated that the size of Au NPs was related to the type of reducing agent and molar ratio of reducing agent and chloroauric acid. The weaker the reducing capacity of the reducing agent or the lower the molar ratio, the bigger the size of Au NPs is. The max wavelength of absorption peak for the citrate-capped Au NPs is red-shifted with the increase of particle diameter. Raman scattering observed from Au NPs of various sizes is found to be NP size-dependent. It is clear that the bigger Au NPs are more apparent in the Raman scattering determination. Size-tunable Au NPs should be crucial for biosensors, particularly as Raman-tag particles.
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