bluuebunny/crossref_metadata_2025 huggingface dataset:
Laminates From The Soy-Based Polyurethanes and Natural and Synthetic Fibers
Authors: Petrovič Zoran S. , Zhang Wei , Javni Ivan , Guo Andrew
Published: April 2011

Two polyols were prepared from soybean oil, one by epoxidation route and the other via hydroformylation. The polyol obtained by epoxidation has secondary groups and has a gel time of more than one hour when reacted with crude MDI to produce polyurethanes. Hydroformylated polyol has a gel time with MDI of several minutes and is more suitable for reinforced reaction injection molding (RRIM). The first group of polyurethanes had a glass transition close to 80 °C while the hydroformylated gave about 30 degrees lower Tg and comparable strength but higher elongation. Adding glycerin as the crosslinker could increase both Tg and strength. Two series of laminates were prepared using several types of glass fabric, carbon fiber, polyester, cotton and jute fabrics r as reinforcements. Hydroformylated polyol based polyurethane composites were softer, with lower Tg, modulus and strength. Composites with organic fibers were lighter and more flexible than the glass reinforced samples. For comparison glass reinforced epoxy and polyester were prepared and tested. Organic fibers gave lower stiffness and strength than the corresponding glass or carbon fiber. Although the neat polyester and epoxy resins had somewhat higher strengths than the polyurethanes from soybean oil, mainly due to the higher crosslinking density, the composites from the soy oil-based resin displayed comparable or better properties. Glass transition and mechanical properties of the soy-based polyurethanes was varied from about 70 °C to 140 °C with added crosslinkers. Processing time of the soy-polyurethanes resins was shorter than that of the other two resins.
The role of the interfaces in the optical effects of large-sized SiCxO1-xN nanocrystallites
Authors: Plucinski K.J. , Kaddouri H. , Kityk I.V.
Published: April 2011

The band energy structure of large-sized (10-25) nm nanocrystallites (NC) of SiCxO1-xN (0.96<x<1.06) was investigated using different band energy approaches, as well as modified Car Parinello molecular dynamics simulations of interfaces. A thin carbon sheet (of about 1 nm) appears, covering the crystallites. This sheet leads to substantial reconstruction of the near-the-interface SiCxO1-xN crystalline layers. Numerical modeling shows that these NC may be treated as quantum dot-like SiCxO1-xN reconstructed crystalline surfaces, covering the appropriate crystallites. All band energy calculation approaches (semi-empirical pseudopotential, fully augmented plane waves and norm-conserving self-consistent pseudopotential approaches) predicted the experimental spectroscopic data. In particular, it was shown that the near-the-surface carbon sheet plays a dominant role in the behavior of the reconstructed band energy structure. Independent evidence for the important role of the dot-like crystalline layers are the excitonic-like states, which are not dependent on the particular structure of the SiC, but are sensitive to the thickness of the carbon layer.
Magic Family of Discretly Sized Ultrabright Si Nanoparticles
Authors: Belomoin G. , Therrien J. , Smith A. , Rao S. , Twesten R. , Chaieb S. , Nayfeh M. H. , Wagner L. , Mitas L.
Published: April 2011

We describe a procedure for dispersion bulk Si into a family discretely sized ultrasmall ultrabright nanoparticles. We demonstrate that electrochemically etched, hydrogen capped SinHx clusters with n larger than 20 are obtained within a family of discrete sizes. These sizes are 1.0 (Si29), 1.67 (Si123), 2.15, 2.9, and 3.7 nm diameter. We characterize the particles via direct electron imaging, excitation and emission optical spectroscopy, chromatography, and colloidal crystallization. The band gaps and emission bands are measured. The smallest four are ultrabright blue, green, yellow, and red luminescent particles. The availability of discrete sizes and distinct emission in the red, green and blue range is useful for biomedical tagging, RGB displays, and flash memories.
Optical Nonlinearity of Sputtered Co3O4-SiO2-TiO2 Thin Films
Authors: Yamamoto Hiroki , Naito Takashi , Hirao Kazuyuki
Published: April 2011

Optical non-linearity of cobalt oxide with SiO2-TiO2 additives was investigated, and the change mechanism of the refractive index (n) and extinction coefficient (k), based on the relation between band structure and optical non-linearity of the thin films, was discussed. Refractive index and extinction coefficient of Co3O4 thin films in the ground state were 3.17 and 0.42, respectively. Both n and k decreased by irradiation from a pulse laser with 650 nm of wavelength (1.91eV). These values in the excited state were 2.91 and 0.41, respectively. n2 estimated from the change of n and k was −2.8 ×10−11 m2/W. The film had a band gap corresponding to 2.06eV, indicating that it was widened by the band filling effect during the laser irradiation at 1.91eV, and this led to the decrease in absorption coefficient and refractive index.
Superconductivity of embedded lead nano particles in metallic and amorphous matrices
Authors: Chattopadhyay K. , Bhattacharya V. , Tsai A. P.
Published: April 2011

Nanodispersed lead in metallic and amorphous matrices was synthesized by rapid solidification processing. The optimum microstructure was tailored to avoid percolation of the particles. With these embedded particles it is possible to study quantitatively the effect of size on the superconducting transition temperature by carrying out quantitative microstructural characterization and magnetic measurements. Our results suggest the role of the matrices in enhancement or depression of superconducting transition temperature of lead. The origin of this difference in behavior with respect to different matrices and sizes is discussed.
Synthesis of Epoxy and Block Oligomer Modified Clay Nanocomposite
Authors: Chen Kang Hung , Yang Sze Ming
Published: April 2011

Acrylic triblock (AxMyBz) and diblock (MyBz) oligomers containing methyl methacrylate (MMA, M), methacrylic acid (MAA, A) and dimethylaminoethyl methacrylate (DMAEMA, B) groups are intercalated into the layers of montmorillonite. The results indicate that the block oligomer lay flatly between the clay layers. ICP analyses of Na+ content indicate no unexchanged sodium ions are left in the intercalated clay.

Nanocomposites of epoxy and clay modified with block oligomers were synthesized. Glass transition temperature (Tg) of the nanocomposite is 129.6°C (M18B2424+ modified clay) compared to 84.1°C for the physical mixture of epoxy and unmodified clay. Tg increases with decreasing amount of modified clay. When modified clay content are below 2 phr, Tg higher than 131.7 °C can be obtained. Water resistance and light transmittance of the nanocomposite is also improved over composite of epoxy and unmodified clay.
Growth of Highly Oriented ZnO Nanorods by Chemical Vapor Deposition
Authors: Liu Sai-Chang , Wu Jih-Jen
Published: April 2011

Highly-oriented ZnO nanorods were grown on the fused silica substrates by a thermal CVD technique using Zinc acetylacetonate (Zn(C5H7O2)2). The substrate was heated to 500°C and the vaporization temperature of Zn(C5H7O2)2 was keep at around 135°C. X-ray diffraction and TEM analyses reveal that the nanorods are preferentially oriented toward the c-axis direction. Photoluminescence (PL) and absorption measurements show a strong emission at around 380nm which corresponds to the near band-edge emission of the bulk ZnO. Moreover, the negligible green emission band in PL spectrum and the absence of E1(LO) mode of the ZnO crystal in Raman spectrum indicate a low concentration of oxygen vacancy in the highly-oriented ZnO nanorods.
Sol-Gel Processing of Low Dielectric Constant Nanoporous Silica Thin Films
Authors: Kim Deok-Yang , Du Henry , Bhandarkar Suhas , Johnson David W.
Published: April 2011

Tetramethyl ammonium silicate (TMAS) is known as a structuring agent in zeolite synthesis. We report its first use to prepare porous silica films for low k dielectric applications in microelectronics. A solution of TMAS 18.7 wt. % was spin coated on silicon substrates with a 3000 Å thick thermal oxide. The spin coated films were subsequently heat-treated at 450°C to obtain porous silica. The use of TMAS solution without gelation led to films of only moderate porosity value of 10%. The addition of methyl lactate, a gelling agent, significantly increased film porosity and improved the pore size distribution. For example, 50% porosity and uniform pore size distribution (average pore size ∼ 40 Å) has been achieved. Dielectric constants (k) of our porous films are as low as 2.5.
Deposition of Polymer Thin Films on ZnO Nanoparticles by a Plasma Treatment
Authors: He Peng , Lian Jie , Wang L. M. , Ooij Wim J. van , Shi Donglu
Published: April 2011

Ultrathin acrylic acid polymer films have been deposited on the surfaces of nanoparticles of ZnO using a plasma polymerization treatment. The average size of nanoparticles is on the order of 50 nm in irregular shapes. High-resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin film of the acrylic acid layer (15 nm) was uniformly deposited on the surfaces of the nanoparticles. In particular, the particles of all sizes exhibited equally uniform ultrathin films indicating a well-dispersed nanoparticles in the fluidized bed during the plasma treatment. The deposition mechanisms and the effects of plasma treatment parameters are discussed.
Nanostructured Hydroxyapatite Coatings for Improved Adhesion and Corrosion Resistance for Medical Implants
Authors: Zhang Zongtao , Dunn Matthew F. , Xiao T. D. , Tomsia Antoni P. , Saiz E.
Published: April 2011

Hydroxyapetite (HA) coating on medical implant has been used in commercial application for several decades. The coating, commercially made by thermal spray method, functions as a intermediate layer between human tissues and the metal implant. The coating can speed up early stage healing after operation but the life span is much limited by low interfacial bond strength, which comes from the dissolution of amorphous HA in human body fluid during its service. This amorphous phase is formed in coating process under high temperature. To overcome these problems, we have developed a novel room temperature electrophoretic deposition process to fabricate nanostructured HA coating. This nanostructured HA coating significantly improved coating's bond strength up to 50-60 MPa, 2-3 times better than the thermal sprayed HA coating. The nanostructured HA coating also has corrosion resistance 50-100 times higher than the conventional HA coating. X-ray diffraction shows that all the HA coating is fully crystalline phase. It is expected that the implants with the nanostructured HA coating will have much longer service life. Other benefits derived from this process include room temperature deposition, the ability to control the coating microstructure and phases, and low cost for production.
Characterization of Self-Assembled SnO 2 Nanoparticles for Fabrication of a High Sensitivity and High Selectivity Micro-Gas Sensor
Authors: Ghan R.C. , Lvov Y. , Besser R.S.
Published: April 2011

In order to refine further the material technology for tin-oxide based gas sensing we are exploring the use of precision nanoparticle deposition for the sensing layer. Layers of SnO2 nanoparticles were grown on Quartz Crystal Microbalance (QCM) resonators using the layer-by-layer self-assembly technique. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electron Diffraction Pattern (EDP) analyses were performed on the self-assembled layers of SnO2 nanoparticles. The results showed that SnO2 nanoparticle films are deposited uniformly across the substrate. The size of the nanoparticles is estimated to be about 3-5 nm. Electrical characterization was done using standard current-voltage measurement technique, which revealed that SnO2 nanoparticle films exhibit ohmic behavior. Calcination experiments have also been carried out by baking the substrate (with self-assembled nanoparticles) in air at 350°C. Results show that 50%-70% of the polymer layers (which are deposited as precursor layers and also alternately in-between SnO2 nanoparticle monolayers) are eliminated during the process.
Topology and Electronic Structure of Onion-Like Carbon and Graphite/Diamond Nanocomposites
Authors: Bulusheva Lyubov G. , Okotrub Alexander V. , Kuznetsov Vladimir L. , Chuvilin Andrew L. , Butenko Yuriy V. , Heggie Malcolm I.
Published: April 2011

Annealing of nanodiamond at moderate temperature makes it possible to produce structures being intermediate in the carbon transformation from sp3- to sp2-state (graphite/diamond nanocomposites) and onion-like carbon (OLC). Electron microscopy shows such structures involve cage shells with spacing close to graphite. X-ray emission spectroscopy has been applied to examine the electronic structure of OLC and graphite/diamond nanocomposites. The CKα-spectra of OLC produced in the temperature range of 1600-1900 K were found to be markedly different from the spectrum of particles formed at 2140 K and characterized by better ordering of graphitic shells. The latter spectrum was shown to be very similar to the CKα-spectrum of polycrystalline graphite, while the former ones exhibited a significant increase of high-energy maximum that might be caused by the holed defect structure of graphitic networks forming at the intermediate annealing temperatures. To interpret experimental spectra, the quantum-chemical semiempirical AM1 calculation of icosahedral C540 cage and that with holed defects was carried out. The lack of at least 22% atoms in an internal carbon cage was found to be essential to provide an increase of density of high-energy electronic states similar to that observed in the spectrum of OLC produced at 1900 K.
Mechanical Properties of Unsaturated Polyester / Montmorillonite Composites
Authors: Inceoglu A. Baran , Yilmazer Ulku
Published: April 2011

Nanocomposites composed of unsaturated polyester matrix and organically modified clay filler were prepared. After the synthesis, XRD patterns showed that the interlayer spacing expanded from 1.25 nm to 4.5 nm. The mechanical properties of the nanocomposites were determined and it was found that adding only 3 w/w % organically modified clay improved the flexural modulus of unsaturated polyester by 35%. From DSC diagrams, it was found that Tgvalues of the nanocomposites also increased with the clay content. It is concluded that partially exfoliated / intercalated nanocomposites were formed at relatively low clay contents.
Cellular Response to Nanoparticles
Authors: Shortkroff Sonya , Turell Mary Beth , Rice Karen , Thornhill Thomas S.
Published: April 2011

Particles of BaSO4 with sizes in nano-scale and micro-scale ranges were investigated for their interactions with fibroblasts in order to determine the biocompatibility of nano-sized particles. Cells were incubated in the presence of particles at 1, 10 and 100 times the particle to cell surface area ratio and at a single concentration of 0.138 mg/ml. Production by the fibroblasts of an inflammatory cytokine in response to the particles was measured and the effect of particle size and volume on cell viability was examined. All particles were cell associated and some agglomeration was visible at all size ranges. Release of interleukin-6 by cells subjected to the same concentration of Ba SO4was similar to control levels, while addition of 1x surface area ratio (SAR) of particles to cells resulted in an increase in IL-6 from 94 pg/ml for 100 nm particles to 218 pg/ml with 2 μm particle diameter. By increasing particle to cell surface area ratios from 1× to 100x, cell viability was compromised for the 2μm particles but was not affected by the nanometer sized BaSO4 particles.
Application of Dispersed Nano Particles
Authors: Oda Masaaki , Abe Tomoyuki , Suzuki Toshihiro , Saito Norimich , Iwashige Hisashi , Kutluk Ghalip
Published: April 2011

Nano-particles can become one of the best materials for forming thin and fine pitch films at low temperature, if particles are individually dispersed densely in a solvent. Individually dispersed metal(gold, silver, copper) nano-particle(d-nano particle) are formed at a state of suspension in an organic solvent by the modified gas evaporation method where formed particles are covered with an organic surfactant just after their formation. The particle formed by the gas evaporation method are metal impurity free and have a narrow size distribution. This suspension is condensed and used as a formed of solution or paste. D-nano particle solution or paste can be baked at 200-300C to form metal thin films. These has been applied to PDP electrode repairing, coloring of car window glass, a filler of electric conductive resin paste and ULSI interconnection formation.
Effect of Particle Size on the Luminescent Properties of Europium Doped Yttrium Oxide Nano-Phosphors
Authors: Copeland Thomas S. , Lee Burtrand I. , Elrod Amanda K.
Published: April 2011

Red light emitting Eu3+ doped Y2O3 phosphor nano-particles were synthesized by a solgel method combined with a furnace firing. The particle size, measured using dynamic light scattering (DLS), was between36nm and 1 micron depending on the conditions. Final dopant concentrations were measured through inductively coupled plasma (ICP). The ICP results show a dopant loss of 58% during the processing for the europium doped yttria. Red photoluminescence (PL) and cathodoluminescence (CL), at 614nm was observed from the phosphor particles under UV excitation and electron bombardment. Results show that the samples with a mean diameter of 30nm displayed a significant increase in PL brightness over the samples whose mean diameter was 215nm. The lag in PL, and CL intensity behind the commercial reference samples is attributed to the significantly lower dopant levels present in the experimental phosphors. Results also indicate that these processing methods and nanophosphors may be a useful alternative to current materials and methods.
In-situ Gold Coating of Superparamagnetic Nanoparticles by Microemulsion Method
Authors: Kim D. K. , Mikhailova M. , Toprak M. , Zhang Y. , Bjelke B. , Kehr J. , Muhammed M.
Published: April 2011

Monodispersed gold coated Superparamagnetic Iron Oxide Nanoparticles (SPION) were prepared in water-in-oil reverse microemulsion (μE) of CTAB (cetyltrimethyl -ammonium bromide)/octane/butanol/water and Brij@97/cyclohexane/water. Gold coated SPION were obtained in the μE system by coprecipitation of magnetite and subsequent reduction of Au on the surface of the magnetite using NaBH4. The SPION were characterized by TEM with EDX, AFM, TGA, ESA, UV-Vis spectroscopy, and SQUID at intermediate and final stages.
Synthesis and ROMP of Metal Nanocluster Containing Norbornene Derivatives
Authors: Wynne James H. , Lloyd Christopher T. , Bullock Steven E. , Cozzens Robert F.
Published: April 2011

We report the synthesis of a series of highly functional metal chelated silyl- and tert-butyl-protected 2, 3-diaminomethyl norbornene derivatives. Subsequent alterations to the previously synthesized norbornene adducts afford many other derivatives containing such functionalities as alkyl, cyano, esters, and ethers. These derivatives are then subjected to ring-opening metathesis polymerization (ROMP) employing a ruthenium homogeneous catalyst to afford phase separated block polymers. The block polymers formed serve as unique templates for the formation of size controlled metal nanoclusters having a narrow dispersion. These metal nanoclusters containing diblock polymers are evaluated as unique electrical and optical materials.
Electrical Characterization of Nanostructured Carbon Films Produced by Supersonic Cluster Beam Deposition
Authors: Piseri Paolo , Barborini Emanuele , Bruzzi Mara , Miglio Stefania , Bongiorno Gero , Milani Paolo
Published: April 2011

Electrical conduction in nanostructured carbon (ns-C) films produced by deposition of a supersonic beam of neutral carbon clusters has been studied. The d.c. conduction properties of these films have been measured in-situ during the deposition process and ex-situ as a function of the temperature in vacuum and in ambient of different gases (H2, N2, CH4, He). The ns-C films exhibit an ohmic behavior with a room temperature resistivity in the range 10MΩcm-1GΩcm depending on the growth and storage conditions. Conductivity vs. temperature measured in vacuum in the range 300-400K is characterized by activation energies in the range 0.3-0.7eV, the current response does not differ significantly in gas atmosphere.
Structural and Spectroscopic Study of Manganese Silicide Islands on Silicon
Authors: Tanaka Miyoko , Zhang Qi , Takeguchi Masaki , Furuya Kazuo
Published: April 2011

The Mn deposited clean Si (111) substrates were examined with UHV-TEM and STM that are part of an UHV-TEM/STM integrated characterization system. The Mn deposition with coverages of 5-20 ML followed by annealing at 673 K formed MnSi islands with Moire fringes. They showed metallic character. Subsequent annealing at 873 K dissipated the islands instead of transforming them into MnSi1.7. The re-deposition of Mn and re-annealing at 473 K succeeded to transform MnSi islands into MnSi1.7. The islands had several orientation relationships with substrate Si, and were semiconducting. The growth mechanism of MnSi1.7 is inferred.
Micropatterned Vertically Aligned Carbon Nanotube Growth on a Si Surface or inside Trenches for field-emission devices
Authors: Sohn Jung Inn , Lee Seonghoon , Song Yoon-Ho , Choi Sung-Yool , Lee Jin Ho , Kang Young-Il
Published: April 2011

The good field-emission properties of carbon nanotubes coupled with their high mechanical strength, chemical stability, and high aspect ratio, make them ideal candidates for the construction of efficient and inexpensive field-emission electronic devices. The fabrication process reported here has considerable potential for use in the development of integrated radio frequency amplifiers or field emission-controllable cold electron guns for field emission displays. This fabrication process is compatible with currently used semiconductor processing technologies. Micropatterned vertically aligned carbon nanotubes were grown on planar Si surface or inside the trenches, using chemical vapor deposition, photolithography, pulsed-laser deposition, reactive ion etching, and the lift-off method. To control the field-emission current by a 3rd electrode, the gate electrode, we grew carbon nanotubes inside the trenches. This triode-type structure is the best to realize the gray-scale carbon nanotube field emission. This carbon nanotube fabrication process can be widely applied for the development of electronic devices using carbon nanotube field emitters as cold cathodes and could revolutionize the area of field-emitting electronic devices such as RF amplifiers and field emission displays.
Structure of Frilled Carbon Nanowires Synthesized by Sulfur-assisted Chemical Vapor Deposition
Authors: Mitsui Tadashi , Sekiguchi Takashi , Nishitani-Gamo Mikka , Zhang Yafei , Ando Toshihiro
Published: April 2011

Effects of hydrogen sulfide on the structure of carbon nanotubes (CNTs) were studied using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). The CNTs were synthesized with an iron thin-film catalyst by microwave plasma-assisted CVD on the diamond substrate. The HRTEM images revealed that essentially all of the CNTs obtained in this study were multiwall (MWCNT). The addition of H2S resulted in nanotubes with split skins as cornhusks and/or frills. Electron energy loss spectra of the cornhusks indicated that they consist of sp2, sp3 and amorphous carbon phase. The spectra revealed that the sp3 to sp2 ratio at the points where cornhusks divide from the main stem was more than that at the edge of the cornhusks. No evidence of sulfur incorporation into the MWCNTs grown with the H2S addition was found. We speculate that the chemical nature of sulfur on the CNT growth yields such anomalous structure.
Controlling the Aligned Growth of Carbon Nanotubes by Substrate Selection and Patterning
Authors: Jung Y. , Wei B. Q. , Vajtai R. , Ward J. , Zhang R. , Ramanath G. , Ajayan P. M.
Published: April 2011

To build nanotube based nanodevices, controlling the growth of aligned carbon nanotubes will be essential. Our group reported a method for growing aligned nanotube selectively on SiO2 surfaces by thermal chemical vapor deposition (CVD) method from xylene-metallocene mixtures. Here we will describe further studies on the roles of shape and thickness of patterned oxide structures for the controlled growth of aligned carbon nanotubes. By designing the shapes and the thickness of silicon oxide patterns with conventional micro fabrication techniques like lithography and dry & wet etching we could control the growth position as well as orientation of aligned carbon nanotubes precisely.
Dependence of the Second-order G'-band Profile on the Electronic Structure of Single-wal Nanotubes
Authors: Filho A. G. Souza , Joribo A. , Dresselhaus G. , Dresselhaus M. S. , Swan A. K. , Ünlü M. S. , Goldberg B. B. , Hafner J. H. , Lieber C. M. , Pimenta M. A. , Saito R.
Published: April 2011

We analyze the dependence of the second-order G'-band profile in terms of their (n,m) indices by measuring the resonance Raman spectra of several semiconducting and metalic isolated single wal carbon nanotubes. We show that this profile is very sensitive to the electronic structure, thus making it possible to get structural (n,m) information and to probe the splitting of the van Hove singularities in the electronic density of states due to the trigona warping effect.
Injection of Polarized Spins and Anti-Localization Caused by Slight Doping of Heavy Impurities into One End of Carbon Nanotubes
Authors: Haruyama Junji , Takesue Izumi , Hasegawa Tetsuro
Published: April 2011

Electrode atoms are slightly diffused, with only about 5% volume-ratio, into the top end of multi-walled carbon nanotubes (MWNTs), standing in nano-pores of porous Alumina membranes. Diffusion of light-mass materials (carbon and aluminum) leads to weak localization in the Altshuler-Aronov-Spivak (AAS) oscillations, which is qualitatively consistent with previous works on MWNTs. In contrast, we find that diffusion of heavy materials (gold and platinum) changes this weak localization into an anti-localization in the MWNT bulk. This effect is only observable when electrons are injected through the diffusion region, and undergo a φ-phase shift in their electron waves, caused by polarized injection of spin-flipped electrons due to spin-orbit interaction in the diffusion-region of the MWNT bulk.
Production and Characterization of MoSe2 Nanotubes by Electron Irradiation
Authors: Galván D. H. , Rangel R. , Adem E.
Published: April 2011

In this work, we report the production of MoSe2 (molybdenum diselenide) nanotubes formed by irradiating the samples with high doses of electron irradiation. The irradiation was performed on a 2 MeV Van de Graaff accelerator at the following conditions: voltage 1.3 MeV, current 5μA current, dose rate 25 kGy/min, and total dosage 1 MGy. We observed well-defined nanotubes of several nm long and few nm wide, which suppose to be hollow and capped at one end. As the level of irradiation was increased to 1 MGy, elongated onion-like structures were observed.
Interactions in Carbon Nanotubes and Polymer/Nanotubes Composites as Evidenced by Raman Spectroscopy (Invited)
Authors: Lefrant Serge , Buisson Jean-Pierre , Chauvet Olivier , Benoit Jean-Michel , Baibarac M. , Baltog I. , Bernier P.
Published: April 2011

Carbon nanotubes systems have revealed large potentialities in terms of applications, especially at a nanometric scale. As a consequence, the different interactions which can take place can be of primary importance. In this paper, we report studies carried out on different carbon systems such as single-walled or multi-walled nanotubes and polymer/nanotubes composites. By using Raman spectroscopy, apart from the expected interactions between tubes in bundles which have initiated experiments on individual entities, we put in evidence strong chemical reactions at the interface metal/nanotubes when Ag or Au surfaces are used to carry out Surface Enhanced Raman Scattering experiments. We show in particular that a different behavior is observed for metallic and semiconducting tubes. Also, a high state of disorder is observed, together with the transformation of nanotubes to other carbon compounds. In the case of multi-walled nanotubes, theoretical calculations allow us to interpret the low frequency Raman modes by introducing interactions in concentric tubes, in rather good agreement with experiments. Finally, in polymer/nanotubes composites, an upshift of the radial breathing mode is observed and we show in this case that it originates from the dynamical stress applied by the polymer on the bundles in response to the breathing vibration.
Study in the Dispersion of Carbon Nanotubes
Authors: Bratcher Matthew , Gersten Bonnie , Ji Helen , Mays Jimmy
Published: April 2011

In the past, the dispersion of carbon nanotubes (CNTs) in both liquids and solids has been difficult due to the high surface interactions between the tubes. Dispersion of polymer CNT composites is important for such benefits as structural reinforcement of composites, the percolation threshold of CNT based conducting materials, and the thermal properties with the exploitation of the high surface area of CNTs. Here we discuss two approaches towards addressing dispersion of multiwalled nanotubes (MWNTs). One approach is the use of surfactant chemicals selected on the basis that they interact with CNT chemical groups. The second approach is the functionalization through covalent bonding of the CNTs with various polymers including polyethylenimine (PEI), and poly(methyl methacrylate) (PMMA). The two approaches were evaluated to determine whether covalent functionalization was more beneficial than the use of surfactants. Characterization of the dispersion was performed using various microscopy techniques.
Structural Characterization of Segmented Polyurethanes by Small Angle Neutron Scattering
Authors: Espada Loren I. , Mang Joseph T. , Orler E. Bruce , Wrobleski Debra A. , Langlois David A. , Hjelm Rex P.
Published: April 2011

The beneficial mechanical properties of segmented polyurethanes derive from microphase separation of immiscible hard and soft segment-rich domains at room temperature. We are interested in the structure of the domains, how these are affected by hydrolytic aging, and how the structure is modified by low molecular weight plasticizers. To assessed the distribution of the plasticizer in polyurethane, we did small-angle neutron scattering measurements on mixtures of 23% hard segment poly(esterurethane) with different amounts of either non-deuterated or deuterated plasticizer. We analyzed the results using a simple model in which the contrast, Δ=H-, between the hard and soft segment-rich domains is varied by the amount of deuterated or hydrogenated plasticizer, using the fact that I(Q) ∼ Δ2. The result demonstrated that the plasticizer is largely associated with the soft segment rich domains. The structure of PESU with the chain extender of the hard segment was assessed after aging under hydrolytic conditions. The results show that the microphase structure coarsens and segregates and that the hard and soft segments segregated as a result of the loss of constraints from hydrolytic soft segment chain scission. The results on plasticizer distribution and the effects of hydrolytic aging give insight on the loss of mechanical properties that occur in each case.
Electrochemical Self-Assembled of Copper/Copper Oxide Nanowires
Authors: Kenane S. , Piraux L.
Published: April 2011

Arrays of Cu/Cu 2 O nanowires are electrodeposited at room temperature from alkaline solutions of copper lactate in the nanopores of track-etched polymer membranes. Using the appropriate solution, the electrode potential spontaneously oscillates during the application of a constant cathodic current. Both the period of the oscillations and the composition of the nanowires can be controlled by varying the applied current density. A nanocomposite of copper and cuprous oxide is deposited at an applied current over which oscillations occur. In contrast, pure Cu or Cu 2O nanowires are obtained at deposition current out of the range of oscillation.
Formation of Supramolecular Assemblies by Modulating Self-Assembling Properties of Diacetylenic Phosphocholines
Authors: Singh Alok , Wong Eva M. , Spector Mark S. , Schnur Joel M.
Published: April 2011

Diacetylenic phospholipid dispersions in water produce tubules (500 nm diameter) and helices from their initial vesicular morphology as a function of temperature and concentration. A binary mixture consisting of diacetylenic phospholipid, 1,2 bis (tricosa-10, 12-diynoyl)-sn-glycero-3-phosphocholine and a short chain phospholipid, 1,2-dinonanoyl –sn-glycero-3-phosphocholine was studied to explore the morphological transformation of lipids into tubules to develop an approach to control and produce tubules of different diameters. Circular dichroic spectra not only indicated the chiral nature of these tubules, but also provided distinct spectral signatures differentiating micro- and nanotubules. The effects of temperature and lipid concentration on the formation and stability of tubules were also explored. An equimolar lipid mixture provided structures with uniform morphology, which were stable for several hours up to 36°C. The thermal stability of nanotubules makes them an attractive candidate for many practical applications including controlled release technology.
Shape Transition in Self-Organized InAs/InP Nanostructures
Authors: Gutiérrez H.R. , Cotta M.A. , de Carvalho M.M.G.
Published: April 2011

In this letter we report the transition from self-assembled InAs quantum-wires to quantum-dots grown on (100) InP substrates. This transition is obtained when the wires are annealed at the growth temperature. Our results suggest that the quantum-wires are a metastable shape originated from the anisotropic diffusion over the InP buffer layer during the formation of the first InAs monolayer. The wires evolve to a more stable shape (dot) during the annealing. The driving force for the transition is associated with variations in the elastic energy and hence in the chemical potential produced by height fluctuations along the wire. The regions along the wires with no height variations are more stable allowing the formation of complex, self-assembled nanostructures such as dots interconnected by wires.
Imprinting the Quasi Bookshelf Texture of a Ferroelectric Liquid Crystal into Nano-scaled Polymer Fibrils
Authors: Kim S. H. , Suresh S. , Chien L.-C.
Published: April 2011

Polymer-stabilized ferroelectric liquid crystals (PSFLCs) are made by photopolymerizing 3% reactive mesogenic monomer on a quasi bookshelf texture of a ferroelectric liquid crystal (FLC). We observe the formation of nano-scaled polymer fibrils templated by the two dimensionally ordered host. The polymer fibrils capture the orientation of the host with thin polymer fibrils interweaving the smectic layers. The SEM study highlights the difference in morphology of the polymer fibrils depending on polymerization conditions; that is, polymerizing with or without the presence of an electric field. The polymer networks suppress the cone of rotation of FLC and thus, facilitate the switching and shorten the response time of the PSFLCs. We observed the threshold-less switching behavior in PSFLCs from samples polymerized with and without the field.
Carrier Transport Properties in Crosslinked Polymer / Liquid Crystalline Semiconductor Composite
Authors: Yoshimoto Naoki , Funahashi Masahiro , Hanna Jun-ichi
Published: April 2011

A novel composite system containing of liquid crystalline semiconductor and crosslinked polymer exhibited high hole mobilities with comparison of that of pure liquid crystalline molecules. The carrier transport properties were influenced by the polymerized conditions. The mobilities were independent on temperature and electric field in the case of mesophases polymerized samples. These carrier transport properties were essentially different of those of well-known molecularly doped polymers.
Synthesis, characterisation and liquid-crystalline phase transition studies on two higher homologues of 4O.m (m=14 and 16) series
Authors: Prabhu C. Rama Chandra , Pisipati V.G.K.M.
Published: April 2011

The synthesis, characterization and phase transition studies of higher homologues of N(p-nbutoxybenzylidene)p-n-alkylanilines, Viz., 4O.m series (m=14 and 16) are carried out by thermal microscopy, differential scanning calorimetry and density. The compounds exhibit a phase variant of nematic and smectic-A. Density studies reveal a first order nature of IN transitions and a weak first order NA transitions. An estimate of pressure dependence of the phase transition temperatures using the volume and enthalpy data are presented. A comparison of these results with other reported results in nO.m and other compounds are presented.
Molecular Design Strategies for High Birefringence Liquid Crystals
Authors: Wu Shin-Tson
Published: April 2011

Some linearly conjugated liquid crystals with birefringence greater than 0.4 are discussed. UV stability of these high birefringence liquid crystals was systematically investigated. Both electronic conjugation and molecular structure make essential contributions to the observed degradation phenomena. Guidelines for designing stable high birefringence liquid crystals for displays and optical communications are discussed.
Multipodal Liquid-Crystalline Materials based on Ferrocene Cores
Authors: Meyer T. , Elsäßer R. , Shepperson K. J. , Vos D. , Donnio B. , Guillon D. , Goodby J. W. , Jutzi P. , Mehl G. H.
Published: April 2011

The synthesis of multipodes based on substituted ferrocene groups and the results of the investigations of the liquid-crystalline phase properties of these materials, determined by optical polarising microscopy DSC and X-ray diffraction studies as central cores is reported.
Photopolymerization of Lyotropic Liquid Crystalline Systems: A New Route to Nanostructured Materials
Authors: Colson Colleen D. , Lester Christopher L. , Guymon C. Allan
Published: April 2011

In recent years, a considerable amount of research has been dedicated to synthesizing highly ordered nanostructured materials. One way to achieve this is through templated polymerizations. A novel route to fabricating such materials is through the use of lyotropic liquid crystals (LLCs) that possess highly ordered nanostructures. However, LLC phases lack the necessary physical robustness. So, templating LLC phase morphology onto other materials such as organic polymers would give a nanostructure retained as part of a robust polymeric matrix. This study focuses on the photopolymerization behavior and structure retention of hydroxyethyl acrylate (HEA) / dodecyltrimethyl ammonium bromide (DTAB) / water system in a select LC phase. The results suggest that the polymerization behavior is heavily dependent on the type of LLC structure. Specifically, lamellar aggregates polymerize faster than either cubic or isotropic morphologies due to diffusional limitations on the growing polymer chain. Monomer segregation also plays a role in determining the polymerization rates. Results also indicate that the original LLC order of these systems is largely retained upon photopolymerization although some LLC phases do change upon cure. This order would be useful in applications such as ultrafiltration membranes, separation media, and drug delivery systems.
Polymer Dispersed Liquid Crystals as Mesoscale 2D and 3D Lattices
Authors: Escuti Michael J. , Crawford Gregory P.
Published: April 2011

We introduce and explore two- and three-dimensional lattices formed in Holographic-Polymer Dispersed Liquid Crystals (H-PDLC) materials, which exhibit an electrically controllable index modulation in multiple dimensions. As electro-optically active holograms, these materials exhibit fast dynamic switching phenomena (~100 microseconds), and are simple to fabricate. While many applications have been proposed for these materials, almost all are based on one-dimensional index modulations in various grating regimes. However, constraints in additional dimensions lead to a much greater sensitivity of the polymer morphology to monomer functionality, exposure irradiance, and grating pitch. In an effort to begin to understand this relationship, two-dimensional triangle lattices were created using two monomeric blends exposed over a range of powers. Final diffraction efficiency (Bragg regime), saturation voltage, and polymer morphology were examined from the resulting triangle lattices. Three-dimensional lattices are discussed and a six-beam holographic method is proposed. Photonic crystal applications are envisioned where the pseudo-bandgap can be electrically controlled.
Structural Characterization of Segmented Polyurethanes by Small Angle Neutron Scattering
Authors: Espada Loren I. , Mang Joseph T. , Bruce Orler E. , Wrobleski Debra A. , Langlois David A. , Hjelm Rex P.
Published: April 2011

The beneficial mechanical properties of segmented polyurethanes derive from microphase separation of immiscible hard and soft segment-rich domains at room temperature. We are interested in the structure of the domains, how these are affected by hydrolytic aging, and how the structure is modified by low molecular weight plasticizers. To assessed the distribution of the plasticizer in polyurethane, we did small-angle neutron scattering measurements on mixtures of 23% hard segment poly(esterurethane) with different amounts of either non-deuterated or deuterated plasticizer. We analyzed the results using a simple model in which the contrast, Δρ = ρH Š ρ, between the hard and soft segment-rich domains is varied by the amount of deuterated or hydrogenated plasticizer, using the fact that I(Q) ∼ Δρ2. The result demonstrated that the plasticizer is largely associated with the soft segment rich domains. The structure of PESU with the chain extender of the hard segment was assessed after aging under hydrolytic conditions. The results show that the microphase structure coarsens and segregates and that the hard and soft segments segregated as a result of the loss of constraints from hydrolytic soft segment chain scission. The results on plasticizer distribution and the effects of hydrolytic aging give insight on the loss of mechanical properties that occur in each case.
Polymerization of Poly(Itaconic Acid) on Surfaces by Atom Transfer Radical Polymerization in Aqueous Solution
Authors: Sankhe Amit Y. , Husson Scott M. , Kilbey S. Michael
Published: April 2011

Poly(itaconic acid) (PIA) was grown from surface-tethered initiator sites via atom transfer radical polymerization (ATRP). The surface-tethered PIA layers were grown from hydroxyl-terminated SAMs capped with initiator molecules of 4-(chloromethyl)-benzoylchloride. This polymerization initiator molecule and a copper-based organometallic catalyst allowed tethered PIA chains to be grown via ATRP at room temperature in aqueous solutions. Ellipsometric studies and external-reflection, Fourier-transform infrared spectroscopy (ER-FTIR) confirm the presence and growth of the surface-tethered PIA layer. We describe here how changing the temperature of polymerization alters the layer growth and kinetics of the process, and demonstrate, via ER-FTIR spectroscopy, that these surface-tethered layers do bind cationic dyes through ion-exchange mechanisms.
Mesophases of Regularly Branched Copolymers
Authors: Pickett Galen T.
Published: April 2011

The phase diagram of A/B block copolymers is determined when the A block is a flexible, linear homopolymer, and the B block has a regularly branched tree structure with G generations. The predictions of a classical-path analysis and a lattice self-consistent mean field calculation are in general agreement. The phase diagram is considerably skewed toward keeping the A blocks inside cylindrical or spherical cores with the branched block forming a corona. There is little, if any, tendency for the branched arms to fold back to facilitate packing.
Stick-Slip Fracture of Polymer/Metal Interfaces
Authors: Toivola Y. , Somerday B.P. , Shediac R. , Ivill M.P.
Published: April 2011

The adhesion of a thin-film of PMMA to substrates consisting of Ti or Al was measured using a four-point bend technique. Initial results revealed that cracks propagated along the PMMA/metal interfaces at stable rates. Subsequent experiments showed intermittent (“stick-slip”) interfacial crack propagation consisting of cycles of crack initiation, unstable propagation, and arrest. To investigate the origin of stick-slip fracture behavior at PMMA/metal interfaces the effect of water uptake by PMMA on fracture behavior was studied. Four-point bend sandwich specimens were stored in vacuum or deionized water environments at either 25 °C or 65 °C for a period of 7 days prior to testing. The PMMA/Al system stored at 25 °C showed a transition from stable to stick-slip crack propagation when the exposure environment was changed from vacuum to water. Interface crack propagation was stable for both the PMMA/Ti and PMMA/Al systems on exposure to 65 °C water, but the critical strain energy release rate, GC was markedly reduced, indicating that water uptake promoted stick-slip fracture up to some critical degree of hydration. No change in stick-slip behavior was observed from a variation in imposed load-point displacement rate.
Using Rheology to Probe the Mechanism of Joint Lubrication: Polyelectrolyte/protein interactions in Synovial Fluid
Authors: Oates Katherine M. N. , Krause Wendy E. , Colby Ralph H.
Published: April 2011

The outstanding lubricating properties of synovial fluid, found in freely moving mammalian joints, may be due to intermolecular associations between hyaluronic acid, an anionic polysaccharide, and the plasma proteins. A synovial fluid model comprised of hyaluronic acid and the plasma proteins albumin and γ-globulins, was constructed. Rheological measurements reveal a pronounced viscoelasticity with a strong shear history dependence for the synovial fluid model and the plasma protein solutions at low shear rates. The addition of the anti-inflammatory drug D-Penicillamine to the solution alters the rheology of the synovial fluid model. We present two ideas about the structural features of synovial fluid that may explain this viscoelasticity and suggest further experimental techniques that can be used to test these ideas.
Assemblies of Polymerized Phospholipid Vesicle Structures Chemisorbed on Au Films Visualized in situ by Environmental Scanning Electron Microscopy
Authors: Stanish Ivan , Ray Richard I. , Singh Alok
Published: April 2011

Submicron vesicles immobilized on gold films were visualized in situ using environmental scanning electron microscopy (ESEM). Electron micrographs show that surface immobilized vesicles composed of diacetylenic phospholipids with 1 mole percent disulfide functionality and that encapsulate NaCl are structurally stable for at least three days. Furthermore, energy dispersive spectroscopy (EDS) provides compositional evidence supporting the formation of surface immobilized vesicles. Using ESEM coupled with EDS, a two-layer vesicle structure was imaged and found to contain NaCl and lipid elements sulfur and phosphorous.