bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanomechanical Properties of UV Degraded TiO2/Epoxy Nanocomposites
Authors: Scierka Stephanie , Drzal Peter L. , Forster Amanda L. , Svetlik Stephanie
Published: April 2011

Model epoxy nanocomposite thin films containing one of three types of titanium dioxide (TiO2) particles were degraded using an integrating sphere-based ultraviolet weathering chamber. Instrumental Indentation Testing (IIT) was used to measure nanomechanical changes in the surface region of thin films resulting from UV exposure. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC) were used to support the mechanical results with chemical and thermal data. The unfilled epoxy was the most photosensitive sample tested, exhibiting the highest rates of chemical oxidation, the largest decrease in the glass transition (Tg), and the greatest increase in elastic modulus with increased exposure. Similar trends were observed in the nanocomposite films, but the rates of change were much lower than the unfilled epoxy and decreased with increasing volume fraction of nanoparticles.
Nano Scratching of Clear Coats and Relation to Mechanical Material Properties
Authors: Nothhelfer-Richter Rolf , Klinke Eugen , Eisenbach Claus D.
Published: April 2011

The nano single scratch experiment has been proven to be a suitable method to evaluate the scratch resistance of a coating. Single scratch damage and its recovery have been studied for a variety of clear coats under dry as well as wet conditions; these investigations were complemented by multi-scratch tests. Bulk mechanical materials properties of free standing films of the clear coats were determined by tensile tests and dynamic mechanical analysis (DMA). It was found that the recovery of the scratch groove is inversely related to the maximum value of the loss tangent (tan δ) as obtained from DMA analysis. The results of our comparative experiments and implications for the evaluation of the scratch resistance of organic coatings will be discussed.
The atomic scale removal mechanism during chemomechanical polishing of Silicon: An atomic force microscopy study
Authors: Katsuki Futoshi , Watanabe Junji
Published: April 2011

The pressure dependence of the microwear of an oxidized Si surface under aqueous electrolyte solutions has been investigated using an atomic force microscope with a single crystal Si tip. The removal ratio of Si tip to SiO2 surface is found to be highly sensitive to the contact pressure. We present a microscopic removal mechanism which is determined by an interplay of the diffusion of H2O in Si and SiO2.
Microstructures of LENS™ Deposited Nb-Si Alloys
Authors: Dehoff Ryan R. , Sarosi Peter M. , Collins Peter C. , Fraser Hamish L. , Mills Michael J.
Published: April 2011

Nb-Si “in-situ” metal matrix composites consist of Nb3Si and Nb5Si3 intermetallic phases in a body centered cubic Nb solid solution, and show promising potential for elevated temperature structural applications. Cr and Ti have been shown to increase the oxidation resistance and metal loss rate at elevated temperatures compared to the binary Nb-Si system. In this study, the LENS™ (Laser Engineered Net Shaping) process is being implemented to construct the Nb-Ti-Cr-Si alloy system from elemental powder blends. Fast cooling rates associated with LENS™ processing yield a reduction in microstructural scale over conventional alloy processes such as directional solidification. Other advantages of LENS™ processing include the ability to produce near net shaped components with graded compositions as well as a more uniform microstructure resulting from the negative enthalpy of mixing associated with the silicide phases. Processing parameters can also be varied, resulting in distinct microstructural differences. Deposits were made with varying compositions of Nb, Ti, Cr and Si. The as-deposited as well as heat treated microstructures were examined using SEM and TEM techniques. The influence of composition and subsequent heat treatment on microstructure will be discussed.
Microstructure and Thermo-Mechanical Behavior of NiAl Coatings
Authors: Dehm G. , Riethmüller J. , Wellner P. , Kraft O. , Clemens H. , Arzt E.
Published: April 2011

In this study the thermo-mechanical behavior of a commercial Pt containing NiAl coating deposited on a Ni-base superalloy is compared with a Ni-rich NiAl coating sputter-deposited on a Si substrate. Both types of coatings possess high tensile room temperature stresses after thermal straining. The Pt-NiAl coating shows negligible plasticity as a result of solid solution and dispersion strengthening. In contrast, for the NiAl coatings on Si noticeable plasticity can be obtained if the film thickness exceeds the sub-micrometer range.
Complex Intermetallic Compounds: Defects, Disordering, Details
Authors: Sprengel W. , Baier F. , Sato K. , Zhang X. Y. , Schaefer H.-E.
Published: April 2011

A short overview will be given on the thermodynamics of the formation of thermal defects in intermetallic aluminides. We focus on thermal vacancies studied by the specific techniques of positron annihilation and time-differential dilatometry and discuss the results together with self-diffusion data. We then demonstrate that these techniques can be employed for studying vacancies in compound semiconductors specifically. Furthermore, structural order-disorder phase transitions can be investigated from an atomistic point of view by making use of positron annihilation as shown in the exemplary case of decagonal Al-Ni-Co quasicrystals.
Mechanical Aspects of Structural Optimization in a Bi-Te Thermoelectric Module for Power Generation
Authors: Nakatani Yujiro , Takaku Reki , Hino Takehisa , Shindo Takahiko , Itoh Yoshiyasu
Published: April 2011

The thermal stress and strain occurring on a Bi-Te thermoelectric module subjected to variable thermal conditions were estimated based on three-dimensional elastic-plastic finite element method (FEM) analysis. The analysis showed that mechanical integrity of the interface between a Bi-Te thermoelement and electrodes of Al and Mo coatings formed by atmospheric plasma spraying was significantly reduced and that shear strain rose to 0.6∼1.1% in the vicinity of the interface. Furthermore, to estimate the sensitivity of configurational parameters of the module to the thermal strain, statistical sensitivity analysis based on the design of experiment (DoE) and response surface method (RSM) was conducted. The statistical analysis revealed that the thickness of electrode coatings of Al and Mo affected the thermal strain and that the thinner Al coating and the thicker Mo coating reduced the thermal strain. In this study, a thermal fatigue test machine was newly developed with a view to verifying these analytical studies.
Effect of Heat Treatment Conditions on Multistage Martensitic Transformation in Aged Ni-rich Ti-Ni Alloys
Authors: Nishida Minoru , Hara Toru , Morizono Yasuhiro , Matsuda Mitsuhiro , Fujishima Kousuke
Published: April 2011

It has been demonstrated with systematic experiments that the appearance and disappearance of multistage martensitic transformation (MMT) in aged Ni-rich Ti-Ni alloys depend on the heat treatment conditions. No multistage transformation occurs when the evaporation of Ti and Ni and/or the preferential oxidation of Ti in the specimen are prevented and the purification of heat treatment atmosphere in an evacuated quartz tube is achieved. The heterogeneity in precipitation morphology of the Ti3Ni4 phase, which is responsible for the multistage transformation can be suppressed with the regulation of heat treatment atmosphere as mentioned above. We have concluded that the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys is extrinsic in nature, and is an artifact during the heat treatment.
B2 Phases and their Defect Structures: Part I. Ab Initio Enthalpy of Formation and Enthalpy of Mixing in the Al-Ni-Pt-Ru System
Authors: Prins Sara , Arroyave Raymundo , Jiang Chao , Liu Zi-Kui
Published: April 2011

The enthalpies of formation of the bcc phases in the Al-Ni-Pt-Ru system, particularly in the Al-Ru binary and Pt-Al-Ru ternary subsystems, were calculated by first principle methods. The enthalpies of formation for stoichiometric bcc-B2 phases have been calculated using both the GGA and LDA approximations, while the enthalpies of formation for B2 phases with large amounts of constitutional defects (both vacancies and anti-site atoms) were calculated using the Special Quasirandom Structures (SQS) approach. The enthalpies of mixing for the disordered bcc-A2 phases have also been calculated with SQS by mimicking the random bcc alloy with the local pair and multisite correlation functions. The calculated B2 lattice parameters for the different defect structures were compared with experimental results. These results are used as input values for the CALPHAD modified sublattice model to describe the A2/B2 phases with one Gibbs energy function.
Microstructure, Mechanical Properties and Wear Resistance of Fe-Al Based Alloys with Various Alloying Elements
Authors: Kim Han-Sol , Yeo In-Dong , Ra Tae-Yeub , Kim Won-Yong
Published: April 2011

We report on microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements. The microstructures were examined using optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscope (EDS). Two types of alloys were prepared using vacuum arc melting; one is Fe-28Al based alloys (D03 structured) with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys (B2 structured) produced with same manner. For both types of alloys, equiaxed microstructures were observed by the addition of Mo, while dendritic structures were observed by the Zr addition. These microstructural features were more evinced with increasing the content of alloying elements. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys with or without Mo addition superior to Fe-28Al based alloys especially in the high temperature region.
Phase Equilibria and Lattice Parameters of Fe2Nb Laves Phase in Fe-Ni-Nb Ternary System at Elevated Temperatures
Authors: Takeyama Masao , Gomi Nobuyuki , Morita Sumio , Matsuo Takashi
Published: April 2011

Phase equilibria in Fe-Ni-Nb ternary system at elevated temperatures have been examined, in order to identify the two-phase region of γ-Fe (austenite) and ε-Fe2Nb (C14). The ε single phase region exists in the range of 27.5 to 35.5 at.% Nb in the Fe-Nb binary system, and it extends toward the equi-niobium concentration direction up to 44 at.% Ni in the ternary system at 1473 K, indicating that more than half of the Fe atoms in Fe2Nb can be replaced with Ni. Thus, the γ+ε two-phase region exists extensively, and the solubility of Nb in γ phase increases from 1.5 to 6.0 at.% with increase in Ni content. The lattice parameters of a and c in the C14 Laves phase decrease with increasing Ni content. The change in a axis is in good agreement with calculation based on Vegard's law, whereas that of c axis is much larger than the calculated value. The result suggests that atomic size effect is responsible for a-axis change and the binding energy is dominant factor for the c-axis change. To extend these findings to development of new class of austenitic steels strengthened by Laves phase, an attempt has been made to control the c/a ratio by alloying. The addition of Cr is effective to make the c/a ratio close to the cubic symmetry value (1.633).
Massive Transformation in High Niobium Containing TiAl-Alloys
Authors: Bartels A. , Bystrzanowski S. , Chladil H. , Leitner H. , Clemens H. , Gerling R. , Schimansky F.-P.
Published: April 2011

Massive transformation in high Nb bearing γ-TiAl-based alloys, Ti-45Al-7.5Nb and Ti-46Al-9Nb (at.%), and the thermal stability of the resulting microstructure were investigated. Using a quenching dilatometer, a nearly complete massive transformation in Ti-45Al-7.5Nb was found at about 1050°C after annealing at 1305°C for 10min and subsequent cooling with a rate of 55K/s. Higher starting temperatures and higher cooling rates lead to incomplete massive transformation and small transformed areas situated at the grain-boundary triple points of the parent α-grains are observed. By means of EBSD only in one case the same orientation of the close-packed planes of parent α-grains and of massively transformed γM-areas was observed.

The thermal stability of the microstructure of massively transformed Ti-46Al-9Nb sheet material was tested by annealing samples for 1 hour between 400 and 1200°C. Above 800°C a drop of hardness was measured and X-ray diffraction patterns show an increasing separation of (200)γ and (002)γ reflections as expected from a tetragonal γ-TiAl lattice. After annealing at 1100°C α2-phase segregates at grain boundaries and after 1200°C α2-lamellae appear insides the γM-grains parallel to all four {111}γ-planes.
Mechanical Behavior of a Pt-Cr Jewelry Alloy Hardened by Nano-Sized Ordered Particles
Authors: Jackson Kamili M. , Nzula Miyelani P. , Nxumalo Silethelwe , Lang Candace I.
Published: April 2011

The materials engineering of platinum jewelry is interesting because only 5wt% can be used for alloying in order to maintain hallmarking. However, pure platinum is very soft and must be alloyed in order to be used effectively as jewelry. In several binary systems an increase in hardness has been found after cold working and annealing at low temperatures. The hardening in these alloys has shown to be a result of nano-sized ordered particles. In particular, the existence of the ordered particles has previously been confirmed for a Pt-Cr alloy by TEM. Extensive work has been done on the Pt-Cr alloy to understand the crystal structure and mechanisms of the ordered phase. Hardness tests were performed to measure mechanical properties after various heat treatments. In addition, tensile tests were conducted using a small-scale tensile testing machine. An 8mm long specimen is used, which significantly reduces the cost of the specimens while providing necessary properties. Tensile tests on the Pt-Cr alloys at various post deformation heat treatments show an increase in tensile strength with no effect on ductility. They confirm results of the hardness tests while providing additional properties data. In addition, the results show a fairly good relationship between strength and hardness.
The Correlation of Slip between Adjacent Lamellae in TiAl.
Authors: Molénat G. , Couret A. , Sundararaman M. , Singh J. B. , Saada G. , Veyssière P.
Published: April 2011

In lamellar TiAl, concerted deformation occurs in adjacent true-twin related variants (O/OT). When deformation takes place in a given variant, O, by activation of the slip system with highest shear stress, slip proceeds in the companion variant, OT, by operation of a slip system of the same family in mirror orientation, including the slip direction. Depending on load orientation, the latter system may not necessarily exhibit the highest resolved shear stress. The correlation does not depend upon Burgers vector orientation with respect to the interface.

This property applies to ordinary dislocations and twinning. The variant that conforms the Schmid law is referred to as the pilot variant, the twin-related variant is dubbed driven.
Examination of the Dynamic Mechanical Properties of Tissue Engineering Scaffolds
Authors: Kauth Heather , Klapperich Catherine
Published: April 2011

Scaffolds of both natural and synthetic materials have been widely utilized to provide a three dimensional environment for cell growth. The characteristics of these scaffolds play a vital, but sometimes ambiguous, role in tissue engineering constructs. Collagen-glycosaminoglycan matrices have been used clinically as artificial skin implants. Previous research in our laboratory on this model has shown that gene expression is regulated by mechanical stress applied to the matrix. In this work we begin the process of quantifying the effects of mechanical stress and preparation technique on a matrix comprised of type I collagen and chondroitin-6-sulfate. Compressive loads were applied to the matrices using a dynamic mechanical analyzer at 37 degrees Celsius and retrofitted with 5% carbon dioxide gas flow. All samples were tested hydrated in either simulated body fluid or PBS. Storage and loss modulus data are presented. Mechanical tests were performed on collagen-GAG meshes both seeded with humandermal fibroblasts and not seeded with cells. Continuing work includes gene expression analysis of the cells on the seeded matrices in order to identify differential gene expression induced by mechanicalloading.
Nanoscale Measurements of Water Loss during Desiccation of Biological Cell Suspensions
Authors: Mittal S. , Devireddy R.V.
Published: April 2011

There is an urgent need to protect and conserve the endangered species of the world. Desiccation, or the phenomenon of anhydrobiosis, offers the attractive possibility of low cost, long term storage of reproductive tissues and cells from endangered species at ambient temperatures. Biophysical optimization of anhydrobiosis procedures requires dynamic and accurate quantification of the rate of moisture loss during a prescribed desiccation protocol. Engineered microstructures can serve as a multifunctional and highly sensitive method to measure the rate of moisture loss. This study presents a novel ultrasound based (resonant) mass sensor to quantify water loss during a drying process by measuring the corresponding shift in the resonant frequency of a micromachined vibrating structure. To model the proposed ultrasound based sensor, we performed a static (stress) and dynamic (frequency change with change in imposed mass) analysis. The results suggest that by tailoring the dimension of the vibrating element appropriate sensitivity can be achieved.
Finite Element Modeling of Bone Ultrastructure as a Two-phase Composite
Authors: Oyen Michelle L. , Ko Ching-Chang
Published: April 2011

Bone is a composite material with a mineral hydroxyapatite (HA) phase and an organic collagen-based phase. Each phase represents about half the material by volume. The precise arrangement of these components at the ultrastructural level is unclear but of great interest in understanding the mechanical functionality of bone. Nanoindentation tests show that the elastic modulus of bone is primarily distributed between 10 GPa and 30 GPa. In this study we examine different ultrastructural arrangements of collagen and apatite phases, to test different proposed models for bone composite ultrastructure within the same finite element modeling framework. Different configurations of the composite are considered, including (a) a compliant phase with stiff reinforcing particles, (b) a stiff phase with compliant reinforcing particles, and (c) an interpenetrating two-phase (co-continuous) composite. An elastic modulus of 100 GPa is used for the mineral phase and 100 MPa for the organic phase, with volume fraction of each phase fixed at 0.5. Stiff phase continuity (as the only continuous phase in 2D and 3D or as one of two continuous phases in 3D) gives rise to effective composite elastic modulus values of 25–35 GPa, similar to the experimental results for bone modulus. Isotropic models with compliant phase continuity only give rise to moduli around 300 MPa, far below experimental results. Anisotropy was evaluated by calculating effective moduli in parallel and transverse directions relative to the primary axes of rectangular particles. High aspect ratio, stiff particles embedded in a compliant matrix do result in a substantially stiffened composite in the direction of the particles when compared to symmetric particles. However, this configuration results in a material with an effective elastic modulus of 2 GPa along the particle direction but a transverse modulus of only 250 MPa. Decreased interparticle spacing in the direction of loading was the mechanism for stiffening parallel to the particle long axis, demonstrating an indirect effect of particle aspect ratio. Although many bone models have considered the mineral as a particle reinforcement phase, the current results suggest this arrangement would not give rise to a material with bonelike properties, particularly when transverse modulus is considered, regardless of the particle geometry. Some degree of continuity of the mineral phase is required for bone-like elastic modulus values and thus a partially to fully co-continuous ultrastructural arrangement of phases is supported.
Theoretical Study on Open-Shell Nonlinear Optical Systems
Authors: Nakano Masayoshi , Kishi Ryohei , Nakagawa Nozomi , Nitta Tomoshige , Kubo Takashi , Nakasuji Kazuhiro , Kamada Kenji , Ohta Koji , Champagne Benoît , Botek Edith , Yamada Satoru , Yamaguchi Kizashi
Published: April 2011

The static second hyperpolarizabilities (γ) of open-shell organic nonlinear optical (NLO) systems composed of singlet diradical molecules are investigated using ab initio molecular orbital (MO) and density functional theory (DFT) methods. It is found that neutral singlet diradical systems with intermediate diradical characters tend to enhance γ as compared to those with small and large diradical characters. This suggests that the diradical character is a novel control parameter of γ for singlet diradical systems.
Strong Enhancement of the Two Photon Absorption Cross Section of Porphyrin J-Aggregates in water
Authors: Collini Elisabetta , Ferrante Camilla , Bozio Renato
Published: April 2011

Strong enhancement of the two photon absorption (TPA) cross section at 812 nm is observed for tetrakis(4-sulphonatophenyl)porphyrin diacid (H4TPPS2-) when a J-type aggregate is formed in water, in comparison to the one observed for the H4TPPS2- monomer in mixture of water, DMSO and urea. Open aperture Z-scan experiments, performed with ultra-short laser pulses, are employed to measure the TPA absorption cross section. The observed enhancement is discussed in terms of possible electronic cooperative effects in the aggregate.
Novel iridium complexes with polymer side-chains
Authors: Holder Elisabeth , Marin Veronica , Tekin Emine , Kozodaev Dmitry , Meier Michael A. R. , Lohmeijer Bas G. G. , Schubert Ulrich S.
Published: April 2011

The focus of the presented research lies on the synthesis of novel charged iridium(III) compounds with potential applications in light-emitting electrochemical cells. The design involves iridium(III)-based materials with polymer side-chains leading to linear light-emitting polymer arrangements.

To study the electro-optical properties of such light-emitting polymers conventional and combinatorial deposition methods are used. Straightforward screening approaches are introduced. The combinatorial efforts engage the processing via inkjet printing and the screening of the optical properties using plate reader technologies based on steady state UV-vis and fluorescence. Furthermore, the morphological properties are investigated using optical interferometry and atomic force microscopy (AFM). Overall it can be shown that novel materials can be deposited revealing high-quality thin films, which allow the screening of electro-optical features using combinatorial methods. Some initial local current density studies by AFM have also been performed to characterize the current injection and transport properties of the novel materials.
Size-dependence of the Linear and Nonlinear Optical Properties of GaN Nanoclusters
Authors: Pineda Andrew C. , Karna Shashi P.
Published: April 2011

In this paper, we present the results of our first-principles quantum mechanical studies of the electronic structure, geometry, and linear and nonlinear optical (NLO) properties of tetrahedral Gam Nm (m=1, 4, 7, 17) atomic clusters. Our calculated results suggest that the linear and NLO properties both exhibit a strong dependence upon cluster size and shape (geometry). However, the size- and the geometry-dependences are more pronounced for the NLO properties than for the linear optical properties. For clusters containing equal numbers of Ga and N atoms, an open-structure with no network-forming ring has a much larger second-order NLO coefficient than a cluster with a closed ring structure.
Photoelectrochemical Behaviors of Pt/TiO2 Nanocomposite thin films Electrodes Prepared by PLD/Sputtering Combined System
Authors: Sasaki Takeshi , Nichols William T. , Yoon Jong-Won , Koshizaki Naoto
Published: April 2011

Sputtering of TiO2 and pulse laser deposition (PLD) of Pt were performed simultaneously to build the nanocomposite with homogenous dispersion of Pt in TiO2 matrix. The films exhibited a pronounced decrease in the optical band gap energy with increasing Pt content indicating the formation of new energy states in the optical gap of TiO2 matrix. As-deposited nanocomposite films were amorphous and crystallized to Pt metal and rutile type of TiO2 after post-annealing at 600 °C. Pt nanoparticle size in the annealed nanocomposite films increased from 6 to 9 nm with the repetition rate of the laser. The photoelectrochemical measurements of the Pt/TiO2 nanocomposite films in aqueous 0.1 M Na2SO4 solution indicate that a dramatic increase in anodic photocurrent at 1.0 V vs. Ag/AgCl at the wavelength region of visible light occurred in annealed films. Pt nanoparticles in the matrix of TiO2 can play an important role in the optical and photoelectrochemical proprieties of Pt/TiO2 nanocomposite thin films.
Organic/Inorganic Hybrid Silicate Materials for Optical Applications; Highly Fluorinated Hybrid Glasses Doped with (Erbium-ions/CdSe nanoparticles) for Laser Amplifier Material
Authors: Choi Kyung M. , Rogers John A.
Published: April 2011

A new family of organic/inorganic hybrid silicate materials, bridged polysilsesquioxanes, was designed and synthesized through a molecular-level mixing technique. Since hybrid materials in the molecular-composite level, whose domain sizes are in the nanometer-scale, and whose constituents often lose individual identities and thus create new properties, we obtained a set of improved properties from those organically modified glasses. By modifying the Si-O-Si polymeric network, in this study, we produced controllable, porous hybrid glasses for facile and uniform doping of various ions, metals or semiconductor particles. By taking advantage of void volume created in those molecularly modified silicate systems, novel optical materials with designed properties can thus be achieved. Via a chemical strategy, we designed hexylene- or fluoroalkylene-bridged hybrid glasses doped with both Er+3 ions and CdSe nano-particles for the development of new laser amplifier materials. In photoluminescence experiments, a significant enhancement in fluorescence intensity at 1540 nm has been obtained from the fluoroalkylene-bridged glass. The presence of CdSe nano-particles, by virtue of their low phonon energy, also appears to significantly influence the nature of the surrounding environment of Er+3 ions in those modified silicate systems, resulting in the increased fluorescence intensity.
From Raspberry-like to Dumbbell-like Hybrid Colloids through Surface-assisted Nucleation and Growth of Polystyrene Nodules onto Macromonomer-modified Silica Nanoparticles
Authors: Duguet Etienne , Reculusa Stéphane , Perro Adeline , Poncet-Legrand Céline , Ravaine Serge , Bourgeat-Lami Elodie , Mingotaud Christophe
Published: April 2011

Colloidal particles with a controlled morphology combining both organic and inorganic parts were synthesized through a seeded emulsion polymerization process. Silica seed particles (from 50 to 150 nm in diameter) were first surface-modified by the adsorption of an oxyethylene-based macromonomer. Then, emulsion polymerization of styrene was carried out in presence of these particles, the formation of polystyrene nodules being highly favored at the silica surface in such conditions. The ratio between the number of silica seeds and the number of growing polystyrene nodules appeared to be one of the key parameters to control the morphology of the final hybrid nanoparticles. When this ratio is close to 1, original hybrid dumbbell-like nanoparticles were mainly obtained.
Novel Organosilanes for the Preparation of High Refractive Index Silicone Coatings
Authors: Chevalier Pierre M. , Ou Duan L.
Published: April 2011

Synthetic routes to high refractive index curable polyaromatics and halogenated aromatic functional silicone resins were developed. Organo silanes containing anthracenylmethyl-, naphthylmethyl- and iodobenzyl- groups were synthesized and used as precursors for the preparation of stable and soluble aryl-functional silicone resins. Alternatively the direct iodination of pre-formed aromatic-functional resins was investigated. We demonstrated the preparation of coatings with RI as high as 1.770 at 633 nm representing a significant optical enhancement as compared to traditional silicone and organic coatings.
Affinity Control of Aminopropylsiloxane-based Organic/Inorganic Hybrids for Optical Sensors
Authors: Katayama Shingo , Yamada Noriko , Awano Masanobu
Published: April 2011

The aminopropylsiloxane-based organic/inorganic hybrid is known as a sensitive material toward NO2gas for optical sensing systems but it has the irreversible detection. The affinity of the aminopropylsiloxane-based organic/inorganic hybrid toward NO2gas was controlled by incorporating an Nb inorganic component derived from Nb(OC2H5)5into the hybrid structure. The amino groups had a strong coordination bond with hydrolyzed Nb(OC2H5)5and/or an acid-base pair with an oxoanion formed by hydrolysis of Nb(OC2H5)5. Thus, the strong solid-basicity of the aminopropylsiloxane-based organic/inorganic hybrid was weakened. The aminopropylsiloxane-based organic/inorganic hybrid containing an Nb inorganic component provided reversible sensing toward NO2gas in an optical sensing system. NO2is thought to be more weakly adsorbed because of the weakened basicity of the amino groups.
Modification and Characterization of Si-Based Nanobuilding Blocks Precursors for Hybrid Materials
Authors: Mammeri Fayna , Douja Najiba , Bonhomme Christian , Ribot François , Babonneau Florence , Dirè Sandra
Published: April 2011

New functional nanobuilding blocks have been successfully synthesized by hydrosilylation of unsaturated alcohols with dimethylsiloxy isobutyl-POSS and further acylation with methacryloylchloride. The solvent influence on the reaction pathway has been studied, and reaction steps and final nano-objects have been characterized using multinuclear NMR and FTIR spectroscopy. The organic spacer chain length between the inorganic cage and the reactive methacrylate function has been changed in order to modify the reactivity of the final functional nanobuilding block in the polymerization process.
Evaluation of Polypyrrole Coating on Fe3O4 and Its Effect on Nanocomposite Properties
Authors: Liong S. , Harter A. W. , Moore R. L. , Rees W. S.
Published: April 2011

Magnetite (Fe3O4) nanoparticles were synthesized by chemical coprecipitation and were characterized using TEM, XRD, and VSM. XRD and TEM measurements indicate that the average particle size was approximately 10 nm. The nanoparticles were coated with polypyrrole using oxidative polymerization. TGA results show that the polypyrrole coating is 28.5wt%. TEM images indicate that the nanoparticles are bound in clusters by polypyrrole. Measurements show that nanoparticles may hinder curing of the polymer matrix, but they can be effective in producing composites with higher modulus and magnetic permeability at lower frequencies.
ORMOCER®s (Organic-Inorganic Hybrid Polymers) for Telecom Applications: Structure/Property Correlations
Authors: Kahlenberg Frank , Popall Michael
Published: April 2011

The development and characterization of fluoroaryl functionalized organic-inorganic hybrid polymers for optical waveguide applications is presented. The materials are prepared from organoalkoxysilanes in a two-step process. The first step is the formation of the inorganic polysiloxane network by hydrolysis and polycondensation in order to obtain a soluble resin. This can be mixed with a photo initiator and applied onto a substrate as a photo-sensitive film. Micro patterns (waveguides with core and cladding) are then manufactured in a second step by exposure to UV-light through a mask. The polymers are characterized with respect to application in the fabrication of telecom optical waveguide devices. Thus, special attention is turned to optical losses in the telecom wavelengths at 1310 nm and 1550 nm as well as to refractive indices. During all stages of ORMOCER® preparation, structure-property correlations are deduced from presented characterization data.Various spectroscopic tools give an insight into network structures of polycondensate resins and cured hybrid polymer samples. 29Si-NMR in particular is used for the quantitative analysis of siloxane species. With the aid of molecular modeling, structural characteristics of oligomeric intermediates as determined by experiment are visualized. ORMOCER® resins with low optical losses of 0.28 dB/cm at 1310 nm and 0.42 dB/cm at 1550 nm, respectively, are prepared. Subsequent micropatterning by means of photolithography results in waveguide and other test patterns. A low optical loss of 0.51 dB/cm at 1550 nm is measured on a waveguide manufactured from a photopatternable fluoroaryl functionalized ORMOCER®.
Silica and Hybrid Silica Gels Revisited: New Insight by Solid State Nuclear Magnetic Resonance
Authors: Bonhomme Christian , Camus Lydie
Published: April 2011

The “old” 1H→29Si CP MAS (Cross Polarization Magic Angle Spinning) experiment is revisited in the frame of silica hybrid gels and silsesquioxanes. It is proved that the analysis of the CP curves can lead to erroneous interpretation in terms of quantification. We show that this results from false assumptions concerning the dynamical CP parameters THSi (cross relaxation time constant) and T1ρH (1H relaxation time in the rotating frame). In other words, at least one parameter must be measured independently, in order to constrain the fits of the CP curves. Moreover, we demonstrate that the well-known (and universally used…) “spin bath” assumption is not always valid in the frame of 1H→29Si CP MAS NMR. This point is clearly demonstrated on model silsesquioxanes exhibiting short Si-H bonds. In this case, the transfer of magnetization (called coherent transfer) presents clearly oscillations, which can lead to the precise measurement of Si-H distances by solid state NMR! Curiously, the coherent transfer of magnetization is also demonstrated for weakly coupled spin systems, encountered in the silsesquioxane (SiO1.5CH3)8 or T units gels. In this case, a numerical simulation of the CP curves gives a deep insight in the chemical environment of the 29Si sites in terms of Si-H distances and local molecular reorientations. For weakly coupled systems, 1H-1H spin diffusion must be suppressed, in order to reveal the coherent character of the transfer: the quenching of spin diffusion is demonstrated by using a modified version of the CP MAS experiment. We introduce here the Lee-Goldburg CP MAS experiment (CPLG MAS) for that purpose. The “off resonance” 1H irradiation (at the magic angle) ensures the strong suppression of the 1H-1H homonuclear dipolar interaction and therefore the efficient quenching of spin diffusion during the CP transfer.
The use of multinuclear solid state NMR for the characterization of siloxane-oxide hybrid nanocomposites
Authors: Gervais Christel , Julián Beatriz , Cordoncillo Eloisa , Escribano Purificación , Smith Mark E. , Babonneau Florence , Sanchez Clément
Published: April 2011

The objective of this paper is to review various solid state NMR techniques that have been, or can be used for the structural characterization of siloxane—oxide hybrid systems prepared by sol-gel process, and to discuss the type of information they provide, as well as their limitations. More precisely, this paper focuses on NMR techniques to probe and quantify the different types of oxo-bridges (M–O–M of oxide network, Si–O–Si of siloxane chains and Si–O–M siloxane–MxOy interface) in siloxane-oxide nanocomposites prepared through hydrolysis and condensation of organosilanes and M(OR)n alkoxides. In addition the influence of the functionality of the silicon alkoxides and the nature of the MxOy oxides on the extent of the Si-O-M interface will be examined.
A Novel Method for Rapid Formation of High-ordered Self-Assembled Monolayer
Authors: Fujita Yoshitaka , Nakamoto Norifumi , Takeda Hiroyuki , Hidaka Tomoya , Kimura Nobuo , Suzuki Hiroshi , Yoshimoto Noriyuki , Ogawa Satoshi
Published: April 2011

We have discovered a novel chemisorption method using octadecyltrimethoxysilane (ODMS), titanium tetraisopropoxide (TTIP), water, and toluene [1] to form highly-ordered self-assembled monolayers (SAM) of ODMS. The SAMs were formed rapidly from the active solution even when it was kept for three months. The solution and layers were characterized by several methods. We propose a mechanism for the rapid formation of the ODMS-SAM.
Vanadium Oxide Nanotubes: New Synthesis Route and Mechanism of Formation.
Authors: Jaber Maguy , Steunou Nathalie , Azaïs Thierry , Livage Jacques
Published: April 2011

The synthesis of vanadium oxide nanotubes containing phosphorus (VPOx-NT) is described. A mixture of V2O5.nH2O gels, phosphoric acid and hexadecylamine was heated under hydrothermal conditions at 180°C for 7 days. The VPOx nanotubes were characterized by X-ray diffraction, scanning and transmission electron microscopy, 51V and 31P solid state NMR. In-situ experiments were performed in order to get a better understanding of the mechanism of these nanotubes formation.
Macrocellular Silica Monoliths Hierarchically Textured: Mesostructured Si-HIPE Materials
Authors: Carn F. , Colin A. , Backov R.
Published: April 2011

Interface between sol-gel process and soft matter appears recently as a very nice tool to generate new materials with complex textures or/and structures extended at various length scales. In this general context, hierarchical inorganic porous monoliths have been prepared using a double templates procedure, namely concentrated emulsion as a macroscopic pattern and mesoscopic micellar templates. The texture of those monoliths can vary dramatically playing either with the oil volume fraction, synthetic pH conditions or the emulsification process. These materials show interconnected macroporosity associated to vermicular-type mesostructuration with an average mesoporosity of 800 m2/g associated to bulk density as low as 0.08 g cm-3 which is comparable to values obtained for silica aerogel.
Molybdenum and Tungsten Oxide Nanowires Prepared by Electrospinning
Authors: Sawicka Katarzyna M. , Karadge Mallikarjun , Gouma Pelagia-Irene
Published: April 2011

Tungsten oxide (WO3) and molybdenum oxide (MoO3) nanowires were synthesized through utilizing sol gel and electrospinning methods. Mixtures of metal oxide sol gel and polyvinylpyrrolidone (PVP) in ethanol solution were electrospun and resulted in metal oxide composite nanofiber mats. Precise annealing process removed all organic material, and pure metal oxide single crystal nanowires remained. Both the as-spun nanocomposite mats and the heat-treated nanofiborous materials were characterized using Scanning and Transmission Electron Microscopes. The average diameter of the nanofibers was concluded to be proportional to the flow rate used and inversely proportional to the metal oxide concentration in the solution.
Hierarchical Macro-Mesoporous Silica Monolith
Authors: Amatani Tomohiko , Nakanishi Kazuki , Hirao Kazuyuki , Kodaira Tetsuya
Published: April 2011

Monolithic pure silica gels with hierarchical macro-mesoporous structure have been synthesized via spontaneous sol-gel process from silicon alkoxide using a structure-directing agent and a micelle-swelling agent. Monolithic body with well-defined co-continuous macropores is a result of concurrent phase separation and sol-gel transition induced by the polymerization reaction, whereas the mesopores are templated by the cooperative self-assembly of inorganic species, a structure-directing agent and a micelle-swelling agent. The following removal of surfactants by heat-treatment gives silica gels with hierarchical and fully accessible pores in discrete size ranges of micrometers and nanometers. The highly ordered 2D-hexagonal arrays of mesopores have been confirmed by X-ray diffraction measurements and FE-SEM observations. Furthermore, by further additions of the micelle-swelling agent, the mesostructural transition from well-ordered 2D-hexagonal arrays to mesostructured cellular foams (MCF) have been induced accompanied by minor modifications of the micrometer-range structure.
Dichroism of Thin Films Containing Aligned Ag Nanoparticles Prepared by Multi-Source Dynamic Oblique Deposition.
Authors: Maekita Wataru , Suzuki Motofumi , Kishimoto Kazuaki , Nakajima Kaoru , Kimura Kenji
Published: April 2011

We have demonstrated the direct formation of elongated Ag particles with a quasi-parallel major axis on SiO2 template layer by using dynamic oblique deposition (DOD). The peculiar nanomorphology of the particles and template is physically self-organized owing to the self-shadowing in the oblique vacuum deposition. The resulting films exhibit anisotropic optical absorption due to plasma resonance sensitive to the shape of the Ag particles on the template. Since our method can be applied to any combination of thin film materials, it is useful for enabling the plasmon-mediated optical phenomena and to apply them for the development of various photonic devices such as thin film polarizers.
Kinetic Limitations in Two-and Three-Dimensional Growth
Authors: Man K. L. , Tang W. X. , Huang Hanchen , Altman M. S.
Published: April 2011

Kinetic limitations related to the Schwoebel-Ehrlich (SE) diffusion barrier are examined in two-(2D) and three-dimensional (3D) growth. It is shown that the realization of step instabilities in 2D growth, possibly caused by the SE barrier, may be hindered by other factors such as step permeability and the relative importance of diffusion and step attachment. Growth shapes of Ag crystallites are also determined that reveal the impact of kinetic limitations. Dramatic changes of growth shape caused by In codeposition suggest that surfactants can modify the 3D SE barrier.
Magnetic nanoparticles for space applications
Authors: Sharma S. K. , Kumar Ravi , Dolia S. N. , Siva Kumar V. V. , Singh Mahavir
Published: April 2011

Radiation resistant ferrite materials have potential applications in space station. Mg-Mn spinel ferrite was choosen for this study because of its radiation resistance and potential for use as an insulator in radiation environments. The radiation damage expected in these environments can be quickly and conveniently simulated using ion irradiation. The results of swift heavy ion irradiation induced modifications in the magnetization behavior of the Mg-Mn ferrite nanoparticles have been investigated using 100 MeV Ni8+ ion irradiation. To ensure the singlephase spinel structure of the system powder x-ray diffraction patterns has been performed. The powder samples were irradiated at three different fluences in the range 1×1012-5×1013 ions/cm2. Isothermal dc magnetization studies have been performed using SQUID and vibration sample magnetometer (VSM) on the pristine as well as on the irradiated samples at 20 K and 300 K. With irradiation saturation magnetization remains almost constant with ions irradiation. The coercivity values of the materials decreased about 5% with the fluence 1×1013 ions/cm2 as compare to the pristine nanoparticles. The results have been explained on the basis of the existence of surface defects produced by swift heavy ions, which generate orientational disorder of surface spins. The behavior of saturation magnetization with irradiations makes these nanoparticles suitable for memory devices in the space research.
Polymer Degradation from the Thermal Analysis Point of View
Authors: Artiaga Ramón , Cao Ricardo , Naya Salvador , García Ana
Published: April 2011

This work applies different thermal analysis methods to polymer based materials degradation, studying the degradation process itself and evaluating the degree of material damage as a consequence of chemical degradation by thermal or radiation effects. On the one hand, thermal degradation in varied atmospheres is investigated by means of thermogravimetric analysis (TGA) in dynamic experiments. The authors find that the evolution of the sample mass follows a mixture of logistics models, and these can fit an overall TGA curve. The fitting parameters have important physical meaning related to the kinetics of the different processes involved and to the relative amount of each component in the sample. The method itself entails separating overlapping processes. Other improvements made by the authors are related to reducing the noise and smoothing the TGA and differential scanning calorimetry (DSC) data, particularly when estimating TGA derivatives through logistic regression.

Analyzing many materials by means of TGA results in more or less complex traces that do not allow a simple parametric fit like the one described above. Although it reproduces asymptoticity at the beginning and end of the reaction, there are times when many processes overlap, resulting in a complex trace that would need a high number of logistic components to be adequately fitted. However, it is possible to use a local polynomial regression model instead. This is also applicable to DSC traces, whose shapes are totally different from those found in TGA. The authors propose a model based on a nonparametric estimation, where the fit's suitability very much depends on the bandwidth selection, especially where derivatives are concerned. The proposed model gives a satisfactory fitting. It smoothes noise and always provides reliable values, different from those obtained by other methods strongly dependent on user choice.

On the other hand, to evaluate the degree of damage by thermal analysis methods, dynamic mechanical analysis (DMA) is applied to polyamides. The glass transition temperature is measured before and after exposure to varying doses of proton radiation, emulating the space environment. Other examples show how exposure over long periods at moderately elevated temperatures results in reduction of some mechanical properties. Additionally, the effect of different nanofillers on styrene-isoprene-styrene block copolymers is evaluated by DMA. A shift in the glass transition temperature seems to be dependent on nanofiller content. The degradation of some materials suitable for space applications, such as polyethylene and polyamide, are also briefly reviewed.
Aerothermal analysis of an advanced hot structure for hypersonic flight tests
Authors: Savino Raffaele , Fumo Mario De Stefano , Marino Giuliano , Tului Mario
Published: April 2011

This paper deals with the aerothemodynamic analysis of an advanced concept of hot structure to be investigated in the Expert flight test programme.

Three-dimensional fluid dynamic computations have been carried out at the flight conditions of the reference Expert trajectory to evaluate the aerothermodynamic field and the thermal loads on the winglet. The physical model includes viscous effects, real gas properties, non equilibrium chemical reactions and surface catalytic effects. The unsteady aerothermal analysis has been carried out considering different thermal boundary conditions (adiabatic wall or thermal coupling with the capsule metallic skin).

The results are discussed with particular attention to the temperature distributions in the Ultra High Temperature Ceramics (UHTC) and in the structural support.