bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoassisted Photorecording in Chiral Smectic Azodye Copolymers
Authors: Kozlovsky Mikhail V. , Haase Wolfgang , Rehahn Matthias 
Published: April 2011

ABSTRACTIllumination of photochromic liquid-crystalline (PCLC) copolymer films with polarized light during the mesophase formation has been studied. Both thick pressed and thin spin-coated, the films show prominent increase in photoinduced orientation, as compared with conventional isothermal photorecording. Two methods of the thermoassisted recording have been suggested, one of those with simultaneous cooling of the film and another one after a shock heating and quenching. The photoinduced birefringence, Δnind, and the order parameter of photochromic groups, Sazo, have been measured. The thermally assisted recording produces holographic gratings with high diffraction efficiency, η, up to 20-30%.
Frequency Agile Optical Filters using Nanoscopic Polymer Dispersed Liquid Crystals
Authors: Lewis Keith , Smith Gilbert , Mason Ian , Rochester Kate 
Published: April 2011

ABSTRACTThe ability to realise frequency agile filters has always been a major goal of materials and device scientists. Polymer dispersed liquid crystal materials (PDLCs), in which the droplets are deliberately produced with dimensions smaller than the Rayleigh limit for optical scatter, provide a means of realising this goal. At visible wavelengths the material has the appearance of a phase-homogeneous medium both with and without applied electric field. Refractive indices are an average of those of the liquid crystal and those of its host and can be described on the basis of effective medium approximations using orientationally averaged values for the randomly aligned LC material for the ambient state. On application of electric field, the individual liquid crystal molecules align with a resulting reduction in the effective index of the medium. Extensive studies of the variation of process parameters and their effect on the morphology of the composite have enabled field induced changes in refractive index in excess of 0.05 to be achieved without recourse to the use of polarisers and with little or no hysteresis effects. At wavelengths associated with WDM devices for telecommunication applications, the degree of scatter loss is negligible. Design trade-offs have been assessed for candidate tunable WDM filters based on resonant cavity devices.
Thermal and Liquid Crystalline Properties of a Polymer with Amphiphilic-Mesogenic Side-Chains
Authors: Ujiie Seiji , Yano Yumi , Mori Akira 
Published: April 2011

ABSTRACTA low-molecular-weight liquid crystalline amphiphilic compound (Az6Bu) and a liquid crystalline polymethacrylate [P(Az6Bu)] with amphiphilic-mesogenic side-chains are reported in this present paper. A polyethyleneimine chain with 2-hydroxyethyl side-groups was used as the water-soluble spacer. Az6Bu exhibited a lyotropic columnar phase and no thermotropic mesophase. P(Az6Bu) showed thermotropic and lyotropic liquid crystalline properties. P(Az6Bu) formed thermotropic smectic A and C mesophases on the heating and cooling processes. The lyotropic systems consisting of P(Az6Bu) and water exhibited a smectic C lyomesophase with oilystreak and schlieren textures. The layered structures formed in the thermotropic and lyotropic mesophases are composed of a sublayer produced by the anisotropic alignment of aromatic-mesogenic groups and a sublayer of hydrophilic groups.
Numerical Simulation Of A Voltage-Dependent Surface-Induced Molecular Reorientation In A Confined Nematic Liquid Crystal
Authors: Castro J.J. , Calles A. , Valladares R. M. 
Published: April 2011

ABSTRACTWe present a computer simulation of the voltage-dependent orientational ordering of a nematic liquid crystal within the lattice approximation, confined between two substrates with different anchoring for each surface. The system is studied by analyzing the response of the molecular reorientation near the surfaces as a function of the applied voltage. The model considers a molecular interaction responsible for the nematic phase that includes a superposition of the anisotropic induced-dipole-induced-dipole and isotropic Maier-Saupe interactions, whereas for the nematic-surface intermolecular interaction we assume the Rapini-Papoular form. The response to the external electric field is studied by calculating the dielectric constant tensor, based on a model through the molecular polarizability. We particularly discussed the case for negative dielectric anisotropy that could have relevance for the voltage controlled twist effect. The simulation is carried through a numerical relaxation method for the total energy of the system.
Real-time Study of the Evolution of Anisotropic Phase Separation in H-PDLC’s
Authors: Natarajan Lalgudi V. , Tondiglia V.P. , Sutherland R.L. , Tomlin D.W. , Bunning Timothy J. 
Published: April 2011

ABSTRACTWe have investigated the dynamics of formation of a reflection hologram in a photosensitive formulation containing pre-polymer and liquid crystal. Kogelnik’s two beam coupling theory of an isotropic material has previously been expanded to account for variations of refractive index Δn in the x, y, and z directions. This theory predicts a non-zero p-polarized coupling coefficient, κp at 45o internal angle, only when a macroscopic anisotropy in the grating is present. A broadband source was used as a probe to monitor the diffraction efficiencies (DE) during exposure for both s- and p-polarized light. The onset of a macroscopic ordering of the liquid crystal is observed at the same time as the onset of scattering. We report here the effects of laser writing power on the temporal evolution of s- and p-polarized diffraction efficiency and ppolarized scattered intensity.
Liquid Crystalline Nano-Segregated Structures in Hydrogen-Bonded Complexes of Fluoroalkyl Substituted Benzoic Acids
Authors: Nishikawa Etsushi , Yamamoto Jun , Yokoyama Hiroshi 
Published: April 2011

ABSTRACTSeveral new benzoic acid derivatives having perfluorinated substituents were synthesized and their hydrogen-bonded complexes with 4, 4’-dipyridyl were prepared. In these acid/base complexes the incompatibility between perfluoroalkyl moieties and hydrocarbon parts is large, which can lead to organize nano-segregation structures. We have found in one of such complexes, that has a long flexible fluorinated moiety, a thermotropic cubic phase with Ia3d symmetry formed by double gyroid of two interpenetrating jointed rod networks with an estimated cell parameter of 10.9 nm. Furthermore another complex with a branched long perfluoroalkyl terminal chain exhibits a first order smectic A to smectic C phase transition, which is confirmed with thermal analysis detecting a large enthalpy change of 5.3 kJxmol-1, X-ray scattering experiments revealing a tilt angle jump, and polarized optical microscopy observing a remarkable texture change at the phase transition temperature.
Adhesion and Interfaces Involving Polymers, Studied by Electrical Resistance Measurement
Authors: Mei Zhen , Chung D.D.L. 
Published: April 2011

ABSTRACTThe adhesion and interfaces involving polymers were studied by electrical resistance measurement. Adhesive bonding and bond degradation were monitored by measuring the resistance in real time during temperature or stress variation. The resistance measured was either the contact resistance of the joint interface or the apparent volume resistance of one of the two adjoining components in a direction in the plane of the joint interface. The polymers were in the form continuous carbon fiber thermoplastic-matrix composites, due to the importance of these composites for lightweight structures and due to the conductivity of carbon fibers and the necessity of conductivity for electrical resistance measurement. The technique was used for the case of both of the adjoining components being such composites, and for the case of one component being such a composite and the other component being concrete. The concrete case is relevant to the use of the composite to retrofit concrete structures.
Effect of Solvent Quality on the Friction Forces Between Polymer Brushes
Authors: Forster Aaron M. , Kilbey S. Michael 
Published: April 2011

ABSTRACTWe have used the surface forces apparatus to measure the structural and frictional force profiles between opposing, solvated brush layers as a function of temperature. Two different polyvinylpyridine-polystyrene [PVP-PS] diblock copolymers were used to make PS brushes. The molecular weights (in thousands) of these PVP-PS materials were [114/103]k, [30/70]k, respectively. Structural and frictional force profiles in toluene and cyclohexane were measured, and the cyclohexane experiments were conducted at temperatures ranging from the theta-point to 50°C. In toluene the PS brushes needed to be compressed to ∼1/5th of their equilibrium height before frictional forces were measured, but this onset of frictional forces was detected at a much lower level of compression in near-theta cyclohexane. In cyclohexane the structural force profiles were basically insensitive to the temperature change, but the frictional forces depended strongly on the solvent temperature. When the cyclohexane temperature was raised, the onset of frictional forces decreased toward the good-solvent onset. We also discuss the dependence of frictional force on shearing parameters.
In Situ Measurement of the Second Harmonic Signal of Adsorbing Nonlinear Optical Ionically Self-assembled Monolayers
Authors: Brands C. , Neyman P.J. , Guzy M.T. , Shah S. , Van Cott K.E , Davis R.M. , Wang H. , Gibson H.W. , Heflin J.R. 
Published: April 2011

ABSTRACTIonically self-assembled monolayers (ISAMs) have recently been shown to spontaneously exhibit a polar ordering that gives rise to substantial second order nonlinear optical response. The deposition of ISAMs has been studied in situ via second harmonic generation. This is a particularly sensitive probe of the growth of nanometer-thick films since the centrosymmetry of the immersion solutions, the substrate, and the container yields no SHG contribution from these bulk components. Upon immersion in the NLO-active polyelectrolyte solution, the SHG rises sharply over the first minute. When a film is immersed into salt water, the SHG decreases significantly only to be restored when the salt solution is replaced with deionized water.
Nanoscratch Behavior of Sputtered Metal Films on PAMAM Dendrimer Monolayers
Authors: Xu Feng-Ting , Curry Mike , Huang Feng , Ye Ping-Ping , Rar Andrei , Street Shane C. , Barnard John A. 
Published: April 2011

ABSTRACTStriking differences have been observed in the deformation modes associated with 2mN constant load nanoscratch events on ultrathin Cr layers deposited on SiOx with and without a dendrimer interlayer. In the absence of the dendrimer distinct ridge formation along the wear track indicative of plowing and wedge formation are observed. By contrast, dendrimer monolayer-mediated films exhibit ridgeless scratches apparently formed in a nearly pure cutting mode. In addition, the width of the scratch trench in the sample without dendrimer is larger than the one with dendrimer.
Molecular Weight Dependence of the Surface Glass Transition of Polystyrene Films Investigated by the Embedding of Gold Nanoclusters
Authors: Erichsen J. , Günther-Schade K. , Dolgner K. , Strunskus T. , Zaporojtchenko V. , Faupel F. 
Published: April 2011

ABSTRACTWe probed the glass transition temperature Tg at the surface of polystyrene (PS) samples with different molecular weights by embedding of gold nanoclusters. The embedding of the nano-clusters was monitored by x-ray photoelectron spectroscopy (XPS). The onset embedding temperature determined by XPS was taken as a measure for the Tg at the surface. We observed a small decrease of Tg at the surface relative to the bulk for all molecular weights (ΔTg= 2.5- 8.5 K). This decrease is small for short chains (MW = 3.6 kg/mol) and grows to a saturation for MW ≥ 44 kg/mol (ΔTg ≍ 8 K). This is in accord with the smaller relative increase in the number of degrees of freedom between bulk and surface for shorter chains.
X-ray Reflectivity Study of Gold Nanoparticles in a Polymer Matrix
Authors: Shin Kwanwoo , Wang Howard , Satija Sushil K. , Han Charles C. , Josell Daniel 
Published: April 2011

ABSTRACTWe have examined the structural evolution of a thin gold layer sandwiched between two polymer films using specular X-ray reflectivity. We used a depth-profiling model consisting of three independent layers, upper and bottom PS layers and an intermediate gold layer. The results show that a well-defined as-deposited Au layer of about 62 ± 3 Å breaks within 10 min of annealing at 120 °C. During the breakage of the Au film, the bottom low-Mw PS flows to fill into the void between the Au particles, causing the reduction of the bottom PS film, while the top polymer layer remains relatively constant.
Diffusion Limited Aggregation of PMMA Stereocomplex in Thin Films
Authors: Grohens Yves , Castelein Gilles , Carriere Pascal , Spevacek Jiri 
Published: April 2011

ABSTRACTThe nanoscale patterns formed by poly(methyl methacrylate) (PMMA) stereocomplexes at the surface of silicon wafers, glass and mica, were investigated by tapping mode atomic force microscopy (TM-AFM). The effects of the solvent nature, PMMA concentration, i/s-ratio (stoechimetry) and surface nature on the morphology of the stereocomplex thin layer at a surface were addressed. The aggregation phenomena are well described by the diffusion limited cluster-cluster aggregation model (DLA) and the fractal exponent D calculated. The i/s-ratio strongly influences the fractal exponent D which is equal to 1.35 for the 1:2 ratio is lower than for the other i:s ratios which are 1.46, 1.61, 1.82 for 1:1, 2:1 and 4:1 ratios, respectively. The low values of the fractal dimension D are indicative of a fast aggregation process and higher values of D correspond to a slow aggregation process.
Near-Interface Structure and Mobility of Polymeric Chains in Polymer-Based Nanocomposites
Authors: Picu Catalin R. , Ozmusul Murat S. 
Published: April 2011

ABSTRACTThe effect of a curved solid wall on the conformations of long, flexible polymer chains is studied in a dense polymer system and in the athermal limit by means of lattice Monte Carlo simulations. It is found that the wall does not perturb the atom number density, which is constant throughout the volume of the polymer, however the chain end density is higher at the wall compared to the bulk. The segregation effect decreases with increasing wall curvature. The bonds are preferentially oriented in the direction tangential to the wall over a two-bond thick layer next to the wall. When probing the preferential orientation on the chain segment length scale, the perturbed region has a thickness on the order of the probing metric considered. The chain mobility is evaluated by computing the bead diffusion coefficient in the direction perpendicular and tangential to the curved wall, and as a function of the distance from the interface. The bead mobility is reduced in a two-bond-thick layer in the vicinity of the wall in both the normal and tangential directions, the reduction being more pronounced in the normal direction. The mobility is seen to decrease with increasing wall curvature. The reduction is most pronounced when the particle size becomes smaller than the chain radius of gyration in the bulk, situation in which the average chain surrounds the particle, which hence becomes an effective entanglement site for the chains. This explains in part the increased strength of polymer-based nanocomposites with small fillers.
Frequency Specific Characterization of Very Soft Polymeric Materials Using Nanoindentation Testing
Authors: Conte Nicolas , Jardret Vincent 
Published: April 2011

ABSTRACTPolymer thin films and surfaces play a major role in the functionality of many components in the microelectronic and automotive industries. The characterization of their mechanical properties at a nanometer scale remains a technological challenge. Instrumented indentation testing with frequency-specific dynamic analysis provides access to viscoelastic measurement of near surface properties of polymeric materials. Development of biomaterials for tissue replacement raises the interest for testing polymers with storage modulus of less than 1 MPa. The development of specific testing methodologies with improved accuracy and precision for evaluating very soft polymeric materials are presented in this work. Results at various frequencies for polyurethane and polydimethylsilane using both Berkovich and Flat punch geometries are compared.
Microprobing of Interfacial Behavior of Solid Polymers by Means of Normal Mechanical Contacts
Authors: Garif Y. S. , Gerberich W. W. , Macosko C. W. , Pocius A. 
Published: April 2011

ABSTRACTAdhesion properties of acrylic pressure sensitive adhesives were examined by means of normal (JKR) contact at room temperature. Cylindrically shaped samples were synthesized in capillary tubes in presence of a cross-linking agent in order to obtain an elastic response. The results reveal power law increase of adhesion at higher rates of interfacial separation. Transition from low- to high-power is revealed and explained as a result of bulk shielding of interfacial fracture mechanism. Further results will be available soon. Bulk viscoelastic dissipation and molecular interactions at the interface are thought to jointly govern this behavior.
Measurement of Polymer-Polymer Adhesion in Thin Multi-Layer Systems by Means of Micro-Scratch Probing
Authors: Garif Y. S. , Gerberich W. W. , Macosko C. W. , Pocius A. V. 
Published: April 2011

ABSTRACTA novel technique called Cross-Sectional Scratch (CSS) has been established. The technique employs a sliding contact of an indenter tip across a polymer stack cross-section. The main advantage of the technique is that it allows to measure/quantify interfacial adhesion in multilayer polymer films that are only a few microns thick. CSS has successfully tested both glassy/glassy and glassy/soft polymer interfaces. Thus, PS/PE, PET/PE, PS/PMMA and PVdF/PMMA co-extruded films were chosen as sample systems and tested at room temperature. It was found that indenter speed has a strong effect on the magnitude of the adhesion energy measured. The dependence has a power law form with indices ∼ 0.1-0.2. More viscoelastic systems have higher power law index, a measure of rate sensitivity.
Bulk Modulus and Density Measurements of Small Compressible and Incompressible Samples
Authors: Hay Jack C. , Lucas Barry N. 
Published: April 2011

ABSTRACTA novel system is described for determining physical properties, including bulk modulus and density, of small solid samples. The system consists of a chamber in which the sample weight is measured by a weighing device immersed in a gas of controllable density. Thus, the method of measuring density is based on Archimedes' principle where the weight of an object is reduced by the weight of the displaced fluid. This particular device has been designed for examining the density of disk-shaped samples 3 mm in diameter and 0.4 mm thick. The weighing device has a repeatability of 4 nN and sample densities can be determined to 0.5%.A significant feature of this device is the ability to measure buoyancy forces at a plurality of gas densities, which allows one to capture nonlinear behaviors associated with closed-cell compressible media. Results are presented for a quasi-closed cell foam that experiences volume reduction as the gas pressure is increased. Volumetric strains are determined as the difference between the observed behavior and the linear behavior of incompressible media. Plots of hydrostatic stress versus volumetric strain are initially linear, as described by the bulk modulus, and exhibit a “kink” at high pressures, presumably due to the complete compression of internal cells.
Investigation of the Melting Behavior of the Alternating PEO/PCL Multiblock Copolymer by SAXS and WAXS
Authors: Kim Tae Chul , Kim Jong Ho , Lee Hyun Hwi , Bae You Han , Noh Do Young 
Published: April 2011

ABSTRACTThe melting of the semicrystalline poly(ethylene oxide)(PEO)/ poly(ε -caprolactone) (PCL) multiblock copolymer was investigated by small and wide angle x-ray scattering. The two-stage melting was found in which the PEO block and the PCL block melt independently. The crystalline PEO Bragg peaks disappear at 30.5 °C while the block spacing increases due to the chain relaxation. The PEO crystalline domain size decreases continuously in proportion to the amount of the crystalline part. Above 40 °C, the PCL lamellae domains started to melt and the integrated intensity of the PCL Bragg peak decreases with increasing temperature. In the case of the PCL, however, the crystal domain size decreases only slightly. This indicates that the number of the PCL crystalline domains decreases during the melting.
Assessing Structure-Property Relations of Diseased Tissues Using Nanoindentation and FTIR
Authors: Ebenstein Donna M. , Chapman Joan M. , Li Cheng , Saloner David , Rapp Joseph , Pruitt Lisa A. 
Published: April 2011

ABSTRACTDisease processes are often associated with changes in tissue composition. For example, in atherosclerosis lipid and calcification are often found in the artery wall, whereas in healthy arteries the tissue microstructure is dominated by highly organized collagen. Such variations in composition likely result in changes in the material properties of the tissue. However, this relationship has not been fully investigated in atherosclerotic vessels. Using a combination of nanoindentation and spectroscopic techniques, our goal was to assess how changes in tissue composition affect the tissue's mechanical properties. Fourier Transform Infrared Spectroscopy (FTIR) was used to assess the biochemical composition of the tissue samples, such as the lipid and calcium content of fibrous tissues in diseased arteries. Nanoindentation was used to measure the local mechanical properties of the same tissue samples. This information was then correlated by position in the sample to assess the contributions of different constituents to the overall structure-property relations of these tissues.
Nematic liquid crystalline formation of F-actin displays features of a continuous transition
Authors: Viamontes Jorge , Tang Jay X. 
Published: April 2011

ABSTRACTThe phase transition of solutions of the protein filaments F-actin from the isotropic (I) to the nematic (N) liquid crystalline state was studied by quantitative measurements of optical birefringence and fluorescence. The threshold protein concentration for the transition varies inversely with the average filament length, consistent with the prediction of statistical mechanics of rodlike suspensions based on the excluded volume effect. By measurements of local optical birefringence, a range of actin concentration is identified as the transition region between the isotropic and nematic phases. However, local measurements of the protein concentrations detect no discontinuity within a large number of samples in the transition region, suggesting that the I-N transition for F-actin occurs continuously over a defined concentration range. Thus the I-N transition appears to be of a higher order than the 1st, for F-actin of average filament length 3 μm or longer. Additionally, by mixing a tiny number of labeled actin filaments with the unlabeled ones, we observed thermal motions of individual filaments, thus ruling out an alternative picture, viewing an F-actin solution as an amorphous gel in which long filaments are too entangled or even cross-linked to allow partitioning of filaments into domains of discontinuous concentrations. We propose based on these experimental findings that either the extreme polydispersity of F-actin, or the large average filament length itself, renders the I-N transition to be a continuous one, in terms of both the average alignment of filaments and the protein concentration.