Manipulating the optical properties of pyramidal nanoparticle arrays

This paper reports the orientation-dependent optical properties of two-dimensional arrays of anisotropic metallic nanoparticles. These studies were made possible by our simple procedure to encapsulate and manipulate aligned particles having complex three-dimensional (3D) shapes inside a uniform dielectric environment. Using dark field or scattering spectroscopy, we investigated the plasmon resonances of 250-nm Au pyramidal shells embedded in a poly(dimethylsiloxane) (PDMS) matrix. Interestingly, we discovered that the scattering spectra of these particle arrays depended sensitively on the direction and polarization of the incident white light relative to the orientation of the pyramidal shells. Theoretical calculations using the discrete dipole approximation support the experimentally observed dependence on particle orientation with respect to incident field. This work presents an approach to manipulate--by hand--ordered arrays of particles over cm(2) areas and provides new insight into the relationship between the shape of well-defined, 3D particles and their supported plasmon resonance modes.     

Preparation and properties of waterborne polyurethane–urea anionomers—influences of the type of neutralizing agent and chain extender

Waterborne polyurethane–urea anionomers were prepared by polyaddition reaction using isophorone diisocyanate (IPDI), poly(tetramethylene ether) glycol (PTMG, Mn=1000), dimethylolbutanoic acid (DMBA), and hydrazine monohydrate (HD), ethylene diamine (EDA), 1,4-butane diamine (BDA) as a chain extender, followed by neutralization of pendant COOH groups by NH₄OH/Cu(OH)₂ or triethylamine (TEA) as a neutralizing agent. The effects of the types of neutralizing agent such as NH₄OH/Cu(OH)₂ and TEA with various chain extenders on the properties of waterborne polyurethane–urea ionomers were investigated. Two loss modulus peaks for all samples are observed owing to the glass transition temperature of soft segments (Tg_s) and the glass transition temperature of hard segments (Tg_h). The conductivity, Tg_h, Tg, and tensile strength/modulus of TEA-based samples increased in the order of BDA>EDA>HD; however, those of NH₄OH/Cu(OH)₂-based samples increased in the order of HD>EDA>BDA. TEA-based film samples were found to have higher thermal stability, Tg_h, Tg, tensile strength/modulus, and storage modulus than NH₄OH/Cu(OH)₂-based ones at the same chain extender. On the other hand NH₄OH/Cu(OH)₂-based samples had higher conductivity and stronger antibacterial halo than TEA-based samples.     

On the frequency bandwidth change of a servo system with a gear reducer due to backlash and motor input voltage

Summary The paper analyzes how the frequency bandwidth of a servo system is affected by the input voltage of its motor and the magnitude of the total backlash. The bandwidth of the system is defined as the set of antiresonance frequencies, which appears in the frequency-response characteristic. The change in the frequency-response characteristics is investigated depending on motor input voltage and the magnitude of the total backlash. It is shown that at infinite motor input voltage, the servo system has a bandwidth equivalent to that of a backlash-free system. The amount of the systems bandwidth reduction due to the backlash changes greatly with the motor input voltage. It becomes possible then to determine the necessary maximum input voltage of the motor and the admissible magnitude of the total backlash to satisfy the desired bandwidth for a servo system with a gear reducer.     

Dynamics of water probed with vibrational echo correlation spectroscopy

Vibrational echo correlation spectroscopy experiments on the OD stretch of dilute HOD in H(2)O are used to probe the structural dynamics of water. A method is demonstrated for combining correlation spectra taken with different infrared pulse bandwidths (pulse durations), making it possible to use data collected from many experiments in which the laser pulse properties are not identical. Accurate measurements of the OD stretch anharmonicity (162 cm(-1)) are presented and used in the data analysis. In addition, the recent accurate determination of the OD vibrational lifetime (1.45 ps) and the time scale for the production of vibrational relaxation induced broken hydrogen bond "photoproducts" ( approximately 2 ps) aid in the data analysis. The data are analyzed using time dependent diagrammatic perturbation theory to obtain the frequency time correlation function (FTCF). The results are an improved FTCF compared to that obtained previously with vibrational echo correlation spectroscopy. The experimental data and the experimentally determined FTCF are compared to calculations that employ a polarizable water model (SPC-FQ) to calculate the FTCF. The SPC-FQ derived FTCF is much closer to the experimental results than previously tested nonpolarizable water models which are also presented for comparison.     

Novel families of three-component reversible redox cycles involving cage deformation via intramolecular redox reaction: tetrathiolate-bridged dinuclear molybda- and tungstacarboranes

The synthesis and structural analysis of two novel families of three-component reversible redox cycles [(C(2)B(9)H(11))M(mu-SPh)(2)](2)(n)PPN(n) (M = Mo, n = 2-, 2; 1-, 3; 0, 4; and M = W, n = 2-, 6; 1-, 7; 0, 8), where the cleavage and re-formation of the carborane cage C-C bond is observed during the redox reaction, are reported. Electronic saturation of the metal center (18e center) and the lack of bulky substituents on the carborane cage suggest that the deformed carborane cages in 2.PPN(2), 6.PPN(2), and 7.PPN invoke a new kind of deformed cage ("semicloso" framework). The XPS results show that the unprecedented competition for electron density between the metal center and the carborane cage is involved in the cleavage and formation of the carborane C-C bond.     

Dynamic mechanical and solid-state NMR determination of molecular-scale heterogeneity in a raw elastomer,a microcrystalline polymer,and their blend

Dynamic mechanical and solid-state ¹³C nuclear magnetic resonance (NMR) analyses have been used to assess a molecular-scale heterogeneity in a raw elastomer (butadiene-acrylonitrile copolymer elastomer, NBR), a microcrystalline polymer (poly(vinyl chloride), PVC), and their 50/50 blend. The presence of the microcrystalline heterogeneity in PVC and in the blend was characterized by the temperature dependence of the frequency-swept dynamic mechanical behavior. The NMR T_1ρ relaxation experiments with cross-polarization (CP) and magic-angle spinning (MAS) revealed that (1) NBR contained a substantial fraction (ca. 27%) of a molecular-scale heterogeneity identified as butadiene blocks, (2) the fraction of microcrystallites in PVC was ca. 14%, (3) pure phases of both component polymers were present in the blend, dispersed in the mixed matrix, (4) the upper limit of the heterogeneous domains was estimated to be ca. 2.4 nm, and (5) fractions of heterogeneity tend to increase upon blending, indicating that the solubility of the butadiene block and syndiotactic PVC block decreases in the blend. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 709–716, 1997