Synthesis and Characterization of Silver(I) Complexes with C-Alkyl Functionalized N,N′-Diphenylamidinates: Tetrameric and Trimeric Structural Motifs

N,N–Diphenylamidines and the silver(I) complexes of their deprotonated anions have been synthesized. Previously uncharacterized tetrameric structural motifs were produced by the inclusion of alkyl substituents at the amidinate carbon. The addition of a 2-methoxy functional group to the phenyl ring resulted in a cationic silver trimer in which hydrogen bonding links silver(I)-bound water molecules to the methoxy substituents. The thermal stabilities of the tetrameric species vary with alkyl chain length. The new complexes are: tetrakis(N,N-diphenylpropamidinato) tetra silver(I), 1, tetrakis(N,N-diphenylbutamidinato) tetrasilver(I) 2, tetrakis(N,N-diphenylpentamidinato) tetra silver(I) 3, (N,N-diphenyloctamidinato)silver(I) 4, (tetrakis(N,N-di(4-n-butyl)phenylpropamidinato)tetrasilver(I), 5, bis(N,N-di(2-methoxy)phenylacetamidinato)diaquatrisilver(I) nitrate 6 and tetrakis(N,N-di(4-methoxy)phenylacetamidinato) tetrasilver(I), 7. Compounds 1, 5, 6 and 7 were structurally characterized by X-ray methods.     

CHARACTERIZATION OF NANOSTRUCTURES:TOOLS AND CHALLENGES

Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics,diagnostics,drug delivery, UV-absorbers etc.Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques.Applications of techniques like mass spectroscopy,transmission el...     

Finite element method parametric study on scratch behavior of polymers

Parametric studies were performed using finite element analysis (FEA) to learn how material and surface properties of polypropylene (PP) affect scratch behavior. Three-dimensional FEA modeling of scratching on a PP substrate with a spherical-tipped indenter is presented. Three different loading conditions, that is constant scratch depth, constant normal load, and linearly increasing normal load, are adopted for this parametric study. From the FEA findings, it is learned that Poisson's ratio has a negligible effect on scratch performance, whereas raising the coefficient of adhesive friction induces a significantly larger residual scratch depth and tangential force on the scratch tip. Increasing the Young's modulus of a material does not necessarily improve its overall scratch performance. On the other hand, modifying the yield stress of a material has a major impact on scratch resistance as a higher yield stress reduces the residual scratch depth. From this numerical effort, it is concluded that the yield stress and coefficient of adhesive friction are the most critical parameters to influence the scratch performance of a material. Analyses also suggest that the general trend in the parametric effect of the above four parameters on scratch behavior is independent of the applied normal load level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1435–1447, 2007     

Photochromic and fluorescence properties of coumarin fulgimides

Four new fulgimides possessing a fluorescent coumarin unit were synthesized from the corresponding fulgides, and their photochromic as well as fluorescence properties were investigated. The open-ring forms of coumarin fulgimides were found to exhibit fluorescence in the visible region. Upon exposure to UV light, the fulgimides were transformed into the nonfluorescent closed-ring forms, which can be reverted to the initial fluorescent open-ring forms on exposure to visible light. The efficiency of quenching of fluorescence was as high as 95% at the photostationary state of UV irradiation.     

SERS characterization of metallic silver nanoparticle self‐assembly within thin films

Clusters of silver nanoparticles are generated by the thermally initiated reduction of silver carboxylates (long‐chain fatty acids) in the thin polymer films. The size, shape, and aggregation of these nanoparticles are affected by the reduction reaction in the presence of capping agents. In order to understand the mechanism(s) controlling the silver structure formation, it is essential to understand the surface coordination chemistry occurring during this process. We now report the first application of surface‐enhanced Raman spectroscopy (SERS) to directly characterize adsorbates on the surfaces of silver nanoparticles within a thin film imaging construction containing multiple components. In addition, SERS investigation of model silver substrates was used to confirm the identify of specific adsorbates of silver complexes. This is a powerful tool for revealing the chemistry involved with the control of silver nanoparticle aggregation during thermally induced metallic silver formation within thin films. Both the catechol‐reducing agent and the phthalazinone (PAZ) particle aggregation agent are observed on the metallic silver surface at the initial particle formation and during its crystal growth. However, careful attention to excitation wavelength is required in order to observe all the surface species. PAZ appears to be more effective at stabilizing individual silver particles than other aggregation agents investigated. An understanding of the roles of the aggregation/reducing agents in the growth and aggregation of silver nanoparticles is important for preparing different types of silver particles for specific applications including silver‐based thermal imaging systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Squeezing in the audio gravitational-wave detection band

We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.     

Optical dilution and feedback cooling of a gram-scale oscillator to 6.9 mK

We report on the use of a radiation pressure induced restoring force, the optical spring effect, to optically dilute the mechanical damping of a 1 g suspended mirror, which is then cooled by active feedback (cold damping). Optical dilution relaxes the limit on cooling imposed by mechanical losses, allowing the oscillator mode to reach a minimum temperature of 6.9 mK, a factor of approximately 40 000 below the environmental temperature. A further advantage of the optical spring effect is that it can increase the number of oscillations before decoherence by several orders of magnitude. In the present experiment we infer an increase in the dynamical lifetime of the state by a factor of approximately 200.     

An all-optical trap for a gram-scale mirror

We report on a stable optical trap suitable for a macroscopic mirror, wherein the dynamics of the mirror are fully dominated by radiation pressure. The technique employs two frequency-offset laser fields to simultaneously create a stiff optical restoring force and a viscous optical damping force. We show how these forces may be used to optically trap a free mass without introducing thermal noise, and we demonstrate the technique experimentally with a 1 g mirror. The observed optical spring has an inferred Young's modulus of 1.2 TPa, 20% stiffer than diamond. The trap is intrinsically cold and reaches an effective temperature of 0.8 K, limited by technical noise in our apparatus.     

Crystallization of silver carboxylates from sodium carboxylate mixtures

Silver carboxylates can be made by the reaction of silver nitrate and the corresponding sodium carboxylates. The length of the alkyl chain has a significant impact on the product behavior. In this study, 18, 20, and 22 carbon chains (stearate, arachidate, and behenate, respectively) have been selected. All three sodium carboxylates are very insoluble in water at room temperature. Solutions are obtained above the Krafft temperature, which precipitates lamellar crystals if cooled at the proper cooling rate. Depending on the chain length, metastable morphologies, such as vesicles and tiny fibers, can be seen consecutively before hexagonal plates form. The carboxylate with the shorter chain length reaches equilibrium more quickly. All three silver carboxylates also take on a lamellar structure. Small-angle X-ray scattering (SAXS) shows that the d spacing of the crystals increases as the chain length increases. Cryo-TEM illustrates that the crystallites are the result of micelle nucleation and micelle aggregation. In addition, the crystallization process in the presence of silver bromide nanocrystals has been investigated. In the initial stage, an epitaxial interface is formed between the silver carboxylate crystallites and the cubic silver bromide grains. Budlike and strandlike structures grow because of it. The consequent strand enclosure restrains the crystal growth, which reduces the size and changes the morphology of the crystals.     

The molecular structure of [bis-triphenylphosphine-silver(I) stearate], [((C6H5)3P)2Ag(O2C(CH2)16CH3)], solubilization of long alkyl chain silver carboxylates

The crystal and molecular structure of [bis-triphenylphosphine-silver(I) stearate], [((C₆H₅)₃P)₂Ag(O₂C(CH₂)₁₆CH₃)], has been determined by single crystal X-ray analysis: the space group is PT witha=12.021(4),b=13.916(5)1,c=14.678(5) Å, =95.952(5), =101.249(6), =93.259(5)°,V=2388(2) ų, andD _calc=1.293 g/cm³ forZ=2. The silver is four coordinate: the carboxylate symmetrically chelates the silver while the triphenylphosphine ligands occupy the third and fourth coordination sites. The strong bonding nature of the phosphine ligands, as indicated by the Ag–P bond lengths, 2.446(3) and 2.424(3) Å, dominates the coordination sphere of the silver and forces the initial carboxylate ligand to rearrange from bridging to chelating resulting in weaker Ag–O bonds, as indicated by the extended Ag–O bond lengths, 2.399(8) and 2.449(8) Å. Unlike the free acid, the long hydrocarbon chain is not linear, and exhibits disorder in the lattice. The structure of the title complex explains the dramatic shift in solubility properties compared to the starting phosphine free silver carboxylate.