bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanoscale Elastic-Property Mapping with Contact-Resonance-Frequency AFM
Authors: Hurley D. C. , Kos A. B. , Rice P. 
Published: April 2011

ABSTRACTWe describe a dynamic atomic force microscopy (AFM) method to map the nanoscale elastic properties of surfaces, thin films, and nanostructures. Our approach is based on atomic force acoustic microscopy (AFAM) techniques previously used for quantitative measurements of elastic properties at a fixed sample position. AFAM measurements determine the resonant frequencies of an AFM cantilever in contact mode to calculate the tip-sample contact stiffness k*. Local values for elastic properties such as the indentation modulus M can be determined from k* with the appropriate contact-mechanics models. To enable imaging at practical rates, we have developed a frequency-tracking circuit based on digital signal processor architecture to rapidly locate the contact-resonance frequencies at each image position. We present contact-resonance frequency images obtained using both flexural and torsional cantilever images as well as the corresponding vertical contact-stiffness (k*) image calculated from flexural frequency images. Methods to obtain elastic-modulus images of M from vertical contact-stiffness images are also discussed.
Structure and Dynamics of Propylene Oxide and Trimethylene Oxide Clathrate Hydrates
Authors: Peral Inmaculada , Curtis Joseph E. , Chakoumakos Bryan C. , Jones Camille Y. 
Published: April 2011

ABSTRACTWe present results from studies of the structure and dynamics of clathrate hydrates of three cyclic ethers by neutron diffraction and preliminary results on molecular dynamics simulations. Recent results from neutron powder diffraction and quasielastic neutron scattering of studies of propylene oxide (PO, C3H6O) and its isomer trimethyelene oxide (TMO, C3H6O), are compared with structural results obtained previously for tetrahydrofuran (THF, C3H5O). Experimental evidence of distortions of the host structures with temperature is discussed in light of the findings from quasielastic neutron scattering, which indicate distinct regions of high-temperature and low-temperature rotational dynamics and a temperature dependence related to the size of the guest. Preliminary MD results indicate a general expansion of the lattice with temperature resulting in increased volume available to PO.
On The Mechanics of Indentation Induced Lateral Cracking
Authors: Chen Xi 
Published: April 2011

ABSTRACTThe mechanics governing the lateral cracks that form when a hard object plastically penetrates a ceramic is presented. The roles of indentation load, penetration depth and work of indentation are all highlighted, as are the influences of the mechanical properties of the substrate. The three dimensional axisymmetric problem for an annular crack driven by a rigid spherical or conical indenter pushed into a semi-infinite half-space of elastic-perfectly plastic material is solved using numerical methods. The region of highest tensile stress is identified corresponding to the location where a crack is most likely to nucleate. This location coincides with the depth below the surface where the crack will expand parallel to the surface under mode I conditions. The solutions have been validated by comparison with measurements of the cracks that form upon Vickers indentation. The basic formula for the crack radius has been used to predict trends in cracking upon static penetration.
MODELING OF NANOINDENTATION AND MICROSTRUCTURAL DUCTILE BEHAVIOR IN METALLIC MATERIAL SYSTEMS
Authors: Ma Jeong Beom , Ashmawi W. , Zikry M. A. , Schall D. , Brenner D. W. 
Published: April 2011

ABSTRACTSpecialized large-scale computational finite-element and molecular dynamic models have been used to understand and predict how dislocation density emission and contact stress fields due to nanoindentation affect inelastic deformation evolution at scales that span the molecular to the continuum level in ductile crystalline systems. Dislocation density distributions and local stress fields have been obtained for different crystalline slip-system and grain-boundary orientations. The interrelated effects of grain-boundary interfaces and orientations, dislocation density evolution and crystalline structure on indentation inelastic regions have been investigated.
Nanomechanical Testing of Hydrated Biomaterials: Sample Preparation, Data Validation and Analysis
Authors: Kaufman Jessica D. , Klapperich Catherine M. 
Published: April 2011

ABSTRACTImplants, tissue engineering scaffold materials, drug delivery and bio-micro electromechanical systems (BioMEMs) all use polymer or hydrogel materials. These applications require both mechanical performance and successful integration of the material into a biological environment. Mechanical strength, storage and loss moduli, wear resistance and surface adhesion properties are all critical in biomedical device design and can be determined using nanoindentation. The difficulty of obtaining large samples of specialized materials, and the complexity of testing soft materials in traditional materials testing apparatus, make nanoindentation an attractive alternative. Our previous research using nanoindentation to measure the surface mechanical properties of non-hydrated polymers led to improvement in nanoindentation testing protocols. One of the major challenges in using this technique for hydrogels and tissues is maintaining and controlling hydration of the materials during the test. Here we describe the design of a microfluidic platform for nanoindentation that facilitates continuous hydration of hydrogel samples and high throughput nanomechanical testing. Data from creep experiments on synthetic, hydrated poly-2-hydroxyethyl methacrylate (poly-HEMA) are presented. In addition, we show data to validate the materials properties determined from nanomechanical testing by complementary testing. Finally, the data is fitted to a phenomenological model for viscoelastic materials, specifically the three-element standard linear solid model used by Cheng et al. [1].
Measurements of Viscoelastic Properties of SWNT/Polymer Composite Films Using Nanoindentation
Authors: Lu Hongbing , Huang Gang , Wang Bo , Mamedov Arif , Gupta Sachin 
Published: April 2011

ABSTRACTMethods for measuring the mechanical properties of linear viscoelastic materials in both time and frequency domains have been presented using the nanoindentation technique. In the time domain, the viscoelastic functions of materials were measured through the direct differentiation method using the load-displacement curve or the material parameter extraction method by fitting the load-displacement curve. In the frequency domain, the complex creep functions of materials were measured in terms of dynamic load-displacement data under a harmonic loading superimposed upon a ramp loading. As an application, these methods were used to determine the material properties for single-wall carbon nanotube (SWNT)/polyelectrolyte mutilayer films and the neat resin film made of polyelectrolyte under nanoindentation tests. The uniaxial relaxation moduli as a function of time for both SWNT/polymer composite films and the neat resin film have been obtained from quasi-static nanoindentation tests. The complex compliance as a function of frequency for SWNT/polyelectrolyte composite films has been obtained from dynamic nanoindentation tests.
High Temperature Nanoindentation for the Study of Flow Defects
Authors: Schuh C. A. , Mason J. K. , Lund A. C. , Hodge A. M. 
Published: April 2011

ABSTRACTOur recent progress in elevated temperature nanoindentation is reviewed, with an emphasis on the study of discrete events (i.e., pop-in phenomena) observed during nanoindentation. For crystalline materials the incipient plasticity problem is associated with the nucleation of dislocations, an effect which we show to be significantly temperature dependent. For metallic glasses it is the operation of individual shear bands beneath the indenter that gives rise to pop-in events; here we also show this to be a temperature dependent phenomenon. Approaches to extract the activation volume and energy of defects involved in plastic flow beneath the indenter are also briefly described.
Effects of Surface Stress on the Load-Depth Curves of Depth-Sensing Indentation
Authors: Wang Q. , Ozaki K. 
Published: April 2011

ABSTRACTBased on the effects of residual surface stress on the unloading curves of indentation load-depth responses, an experimental scheme for determination of the residual stress by depth-sensing indentation is proposed. From the point that the elastic unloading portion of the load-depth curves can be expected to be unaffected by the residual stresses, the formula for evaluating surface stress by indentation is derived based on energy method. The proposed formula is verified by using FEM simulated indentation load-depth responses for different surface stress levels. The levels of surface stress evaluated by the proposed formula show a good agreement with the ones used as input parameters in FEM simulation.
Abnormal deformation behavior in Polysynthetically-twinned TiAl crystals with A and N orientations——an AFM study
Authors: Chen Yali , Pope David P. 
Published: April 2011

ABSTRACTPolysynthetically-twinned TiAl crystals were deformed by compression with loading axis parallel and perpendicular to the lamellar interfaces. The deformation structures on the free surfaces were scanned using a dimension AFM with scan directions parallel and perpendicular to the lamellar interfaces. Abnormal deformation behaviors were observed to occur in both orientations. When the compression axis is parallel to the lamellar interfaces, the gamma and alpha lamellae deform primarily by shear in planes inclined with the lamellar interface, while the shear vectors lie in the interface. However, in-plane shear, shear in slip planes parallel to the lamellar interfaces, also occurs along the lamellar interfaces. When the loading axis is perpendicular to the lamellar interface, in-plane shear was found to be dominant at the beginning stage of plastic deformation and contributes more to the macroscopic strain. These behaviors are controversial to the Schmid's Law since the applied resolved shear stress for these deformation systems is zero. The abnormal phenomenon was explained by the large coherency stresses along the lamellar interfaces.
Identification of the chirality of intermetallic compounds by electron diffraction
Authors: Fujio S. , Sakamoto H. , Tanaka K. , Inui H. 
Published: April 2011

ABSTRACTA new CBED method is proposed for the identification of the chirality of enantiomorphic crystals, in which asymmetry in the intensity of the reflections of Bijvoet pairs in an experimental symmetrical zone-axis CBED pattern is compared with that of a computer-simulated CBED pattern. The intensity difference for reflections of these Bijvoet pairs results from multiple scattering among relevant Bijvoet pairs of reflections, each pair of which has identical amplitude and different phase angles. With the method, a single CBED pattern is sufficient and chiral identification can be made for all possible enantiomorphic crystals that are allowed to exist in crystallography. The method is successfully applied to some chiral intermetallic compounds.
TEM Analysis of Long-Period Superstructures in TiAl Single Crystal with Composition Gradient
Authors: Hata S. , Shiraishi K. , Kuwano N. , Itakura M. , Tomokiyo Y. , Nakano T. , Umakoshi Y. 
Published: April 2011

ABSTRACTThe ordering mechanism of long-period superstructures (LPSs) in Al-rich Ti-Al alloys was studied using a TiAl single crystal with a composition gradient. A TiAl single crystal with gradient compositions from 55 to 75 at.% Al was prepared by annealing in a molten Al at 1234°C. The single crystal exhibits long-period ordering into different LPSs depending on the Al concentration as follows: an Al5Ti3 type short-range order, h-Al2Ti and one-dimensional antiphase domain structures. These LPSs show an orientation relationship in which Al (002) layers of the LPSs are parallel to those of the TiAl matrix. The atomic arrangements of the LPSs are characterized in common as the alternate stacking of the Al (002) layers and Ti-Al (002) layers. It is thus concluded that the ordering of this type of LPSs and the phase transition between these LPSs are explained as structural changes in Ti-Al (002) layers of the Al-rich L10-TiAl crystal.
Nanomechanical and Microstructural Properties of Bombyx mori Silk Films
Authors: Ebenstein Donna M. , Park Jaehyung , Kaplan David L. , Wahl Kathryn J. 
Published: April 2011

AbstractInstrumented indentation and micro-Raman spectroscopy were used to investigate the mechanical and structural properties of Bombyx mori silk films. Twelve different films were prepared from B. mori silk fibroin protein using a variety of post-deposition processing treatments (e.g. soaking in methanol, soaking in water, stretching, and/or enzymatic etching). The results show that different treatments lead to changes in both the conformation of the silk fibroin protein and the mechanical properties of the films.
Photoinduced Memory Effects based on Poly(3-hexylthiophene) and Al Interface
Authors: Kaneto Keiichi , Ujimoto Mitsuru , Takashima Wataru 
Published: April 2011

ABSTRACTOrganic memory cells have been constructed utilizing conducting polymer, poly(3-hexylthiophene), PHT. The PHT film with Au electrodes at the bottom was coated with ultra thin Al having the thickness of 1 nm on the top. The cell showed the large photoconductivity, which was measured between Au bottom electrodes. The photoconductivity lasted for several hours after turn off the illumination, indicating photo induced memory effect. The phenomenon is discussed in terms of the persistent photoconduction, which is resulted from the electron trapping at Al donor sites in the depletion layer formed near the top of film.
Simulations of Organic-tethered Silsesquioxane Nanocube Assemblies
Authors: Zhang Xi , Chan Elaine R. , Ho Lin C. , Glotzer Sharon C. 
Published: April 2011

ABSTRACTPolyhedral oligomeric silsesquioxane (POSS) based materials are a class of organic/inorganic hybrid nanomaterials with many interesting properties. Recent experiments have demonstrated that self-assembly of tethered POSS nanocubes is a promising route to the synthesis of novel materials with highly ordered, complex nanostructures. Using a coarsegrained model developed for tethered POSS, we perform molecular simulations of POSS molecules tethered by short polymers to investigate how the novel architecture of these hybrid building blocks can be exploited to achieve useful structures via self-assembly. We systematically explore the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tethered POSS molecular topology, and solvent conditions. We report preliminary results of lamellar and cylindrical structures that are typically found in conventional block copolymer and surfactant systems, but with interesting modifications of the phase behavior caused by the bulkiness and cubic geometry of the POSS molecules.
Characterization of Dendrimer-Gold Nanocomposite Materials
Authors: Balogh Lajos P. , Rose Ganser T. , Shi Xiangyang 
Published: April 2011

ABSTRACTGold-dendrimer nanocomposite materials have various applications in catalysis, optics, biological sensing, cancer therapeutics, as well as building blocks to assemble functional films. Primary amine-terminated poly(amidoamine) (PAMAM) dendrimers of different generations (generation 2 through 6) were used as templates to synthesize gold-dendrimer hybrid nanocomposites. UV-Vis spectrometry, fluorescence, transmission electron microscope (TEM), zeta-potential, and polyacrylamide gel electrophoresis (PAGE) were used to extensively characterize these nanocomposite materials. Results indicate that the structure of gold-dendrimer nanocomposites changes as the function of generation and their size decreases with the increase of the generation number of dendrimer templates. TEM shows that aggregated gold-dendrimer nanocomposites are polycrystalline. These nanocomposites are fluorescent and display a stronger emission intensity (458 nm) than commercially available gold nanoparticles of similar size do. PAGE analysis shows that the gold-dendrimer nanocomposites have electrophoretic migration patterns that are similar to those of the corresponding dendrimer templates. The combination of applied different analytical techniques provides new insights into the structure and properties of gold-dendrimer nanocomposite materials.
Pentacene Transistors with Polymer Gate Dielectrics on Metallized Optical Fibers
Authors: Granstrom Jimmy , Katz Howard E. 
Published: April 2011

ABSTRACTIt is difficult to deposit a very thin polymer layer onto a fiber-shaped substrate from solution because the high interfacial energy can lead to dewetting. This difficulty presents itself when attempting to apply a gate dielectric to conductive fiber substrates during the fabrication of fiber transistors for use in applications such as “electrotextiles” and optical switches. We present a dip coating process that applies a gate dielectric to metal-coated optical fibers with high uniformity and reproducibility, resulting in pentacene field-effect transistors (FETs) with excellent transistor characteristics including mobilities up to 0.4 cm2/Vs and on/off ratios up to 7000. In one case, a memory effect was demonstrated. Several gate dielectrics were successfully applied to the optical fibers, suggesting a baseline set of suitable materials for this purpose. A thorough study of the dip coating conditions is presented, including proposed explanations of the effects of different coating procedures and solution physical properties.
Self-Extinguishing Polymer Nanocomposites
Authors: Si Mayu , Chu Hsinchou , Hefter Daniel , Sokolov Aryeh , Hefter Jonathan , Smith Michael , Sokolov Jonathan , Rafailovich Miriam 
Published: April 2011

ABSTRACTSelf-extinguishing PMMA/Clay nanocomposites with conventional flame retardant agents, decabromodiphenyl oxide (DB) and antimony trioxide (AO) have been prepared by melt blending using Brabender. The combustion behavior was first investigated by subjecting slabs of the polymer to UL-94 V0 testing. We found that the polymers with only the retardant agents or the clay could not pass. On the other hand all polymers with both components were self-extinguishing. DMA results show that the introduction of 5 wt% clay improves PMMA bending modulus by 28 % and increases Tg by 8 °C. the addition of clay can effectively avoid dripping during burning test. Based on the cone calorimeter data, the general mechanism is proposed that the synergy between the char formation promoted by the clay in condense phase and free radical capture in gas phase due to the DB and AO makes the material become self-extinguishing.
Air-Liquid Foams, Concentrated Direct Emulsion and Soft Chemistry Toward Hierarchically Organized Porous Silica Monoliths
Authors: Carn F. , Colin A. , Achard M.-F. , Backov R. 
Published: April 2011

ABSTRACTHierarchically organized matter appears today a strong and highly competitive field of research mainly induced by the wide scope of applications expected. In this context, chemistry of shapes appears as a strong interdisciplinary field of research combining soft chemistry and soft matter. Hierarchical inorganic porous monoliths can be obtained using either air-liquid foams or biliquid foams as macroscopic patterns while lyotropic mesophases are employed to promote porosity at the mesoscale. By controlling the air-liquid foam's water liquid fraction or the emulsions oil fraction we can design the inorganic porous texture at the macroscale (i.e. cell sizes and shapes as well as the Plateau borders thickness). Those stategies lead to the formation of materials with characteristics that resemble aerogels.
COLLAPSE OF POROSITY DURING DRYING OF ALKYLENE-BRIDGED POLYSILSESQUIOXANE GELS. INFLUENCE OF THE BRIDGING GROUP LENGTH
Authors: Loy Douglas A. , Small James H. , DeFriend Kimberly A. , Wilson Kennard V. , Minke McKenzie , Baugher Brigitta M. , Baugher Colleen R. , Schneider Duane A. , Shea Kenneth J. 
Published: April 2011

ABSTRACTThe introduction of organic substituents into sol-gel materials can often result in networks that collapse during drying to afford non-porous xerogels. This can prove useful if non-porous coatings or membranes are the ultimate objectives. Collapse of porosity is also manifested in bridged polysilsesquioxanes with flexible bridging groups. Alkylene-bridged polysilsesquioxanes are hybrid xerogels whose organic bridging group is an integral constituent of the network polymer that can be systematically varied to probe the influence of its length on the xerogels' porosity and morphology. Our previous studies have shown that hexylene-bridged polysilsesquioxane xerogels prepared from 1, 6-bis(triethoxysilyl)hexane under acidic conditions are nonporous while the pentylene-bridged polysilsesquioxanes prepared under the same conditions are porous. We also discovered that the more reactive 1, 6-bis(trimethoxysilyl)hexane monomer could polymerize under acidic conditions to afford porous xerogels. Here, we have extended our study of bis(trimethoxysilyl)alkanes to include the heptylene (C7), octylene (C8), nonylene(C9) and decylene (C10) bridges so as to ascertain at what bridging group length the porosity collapses. The morphology of the resulting xerogels was characterized by nitrogen sorption porosimetry and electron microscopy. Solid state NMR was used to structurally characterize the materials.
Suppression of Reaction between Si Substrate and Obliquely Deposited Fe Atoms
Authors: Jomori S. , Suzuki M. , Nakajima K. , Kimura K. 
Published: April 2011

ABSTRACTWe have investigated the initial stage of the growth of obliquely deposited Fe on a Si substrate held at 470 °C with atomic force microscopy (AFM) and high resolution Rutherford backscattering spectroscopy (HRBS). During the deposition from the normal direction, many Si atoms are displaced from their lattice position due to the reaction with the deposited Fe. On the contrary, the number of displaced Si atoms decreases significantly, and the nanoislands of a few 10 nm in diameter grow selectively when Fe is deposited at 85°. This is clear evidence that the local nucleation processes for the Fe silicide formation is modified by the geometrical deposition conditions.
Solid State NMR Measurements for Preliminary Lifetime Assessments in λ-Irradiated and Thermally Aged Siloxane Elastomers
Authors: Chinn Sarah C. , Herberg Julie L. , Sawvel April M. , Maxwell Robert S. 
Published: April 2011

ABSTRACTSiloxanes have a wide variety of applications throughout the aerospace industry which take advantage of their exceptional insulating and adhesive properties and general resilience. They also offer a wide range of tailorable engineering properties with changes in composition and filler content. They are, however, subject to degradation in radiatively and thermally harsh environments. We are using solid state nuclear magnetic resonance techniques to investigate changes in network and interfacial structure in siloxane elastomers and their correlations to changes in engineering performance in a series of degraded materials. Nuclear magnetic resonance (NMR) parameters such as transverse (T2) relaxation times, cross relaxation rates, and residual dipolar coupling constants provide excellent probes of changes crosslink density and motional dynamics of the polymers caused by multi-mechanism degradation. The results of NMR studies on aged siloxanes are being used in conjunction with other mechanical tests to provide insight into component failure and degradation kinetics necessary for preliminary lifetime assessments of these materials as well as into the structure-property relationships of the polymers. NMR and magnetic resonance imaging (MRI) results obtained both from high resolution NMR spectrometers as well as low resolution benchtop NMR screening tools will be presented.