Search results for "Optica"
showing 10 items of 7696 documents
Self-Diffusion in Concentrated Colloid Suspensions Studied by Digital Video Microscopy of Core−Shell Tracer Particles
1998
Optical video microscopy and digital image processing have been used to study the self-diffusion of colloidal particles with a hard-sphere potential. The colloid particles consist of cross-linked polymers and are dispersed in a good solvent to avoid aggregation. To investigate single particle motion in highly concentrated dispersions, a host−tracer system, consisting of two different kinds of polymer particles, has been designed: the host particles are made of poly-t-butylacrylate (with ethanedioldiacrylate as cross-linker) and have the same refractive index as the employed solvent, 4-fluorotoluene. The tracer particles have a core−shell structure with a polystyrene core (cross-linked with…
QENS from polymer aggregates in supercritical CO2
2000
Abstract We report QENS measurements from PS-b-PFOA aggregates in supercritical CO2. Line shapes are dominated by localized diffusive modes and segmental dynamics of the anchored, finite-length PFOA chains. For Q⩽0.6 A−1, we obtain effective diffusion coefficients of ≅0.8 10−6 cm2/s. At higher Q, a single component is not sufficient as shown by excess intensity on the flanks. For Q⩾1.5 A−1, the wings reflect contributions due to a distribution of faster, more localized chain modes.
Low-temperature specific heat of orientational glasses
1992
This review summarizes specific heat data measured at low temperatures (T<1 K) on orientational glasses. Three species of mixed molecular crystals exhibiting orientational disorder are considered, namely (KBr)1−x (KCN) x , (NaCN)1−x (KCN) x (Rb)1−x (NH4) x H2PO4. For intermediate concentrations of the anisotropic components, glass-like excitations have been observed. It is demonstrated that with respect to thermal properties, orientational disorder leads to the same “universal” behaviours than for structural disorder, i.e. a specific heat which varies below 1 K and for times 10−4 s–10 s as:C p(T,t)∞T 1×ln(t). The variation of the glass-like anomaly with compositional disorder is also discus…
Iron(II) Metallomesogens Exhibiting Coupled Spin State and Liquid Crystal Phase Transitions near Room Temperature
2008
Reaction of the ligand 2,2,2-tris(2-aza-3-((5-akloxy)(6-methyl)(2-pyridyl))prop-2-enyl)ethane (C n -tameMe) with Fe(X) 2 . sH 2 O salts afforded a series of spin crossover metallomesogens with general formula [Fe(C n -tame)](X) 2 . sH 2 O (s ≥ 0), with n = 6, 10, 12, 14, 16, 17, 18, or 20 and X =ClO 4 - or BF 4 -. Single crystal X-ray measurements have been performed on the [Fe(C 6 -tameMe)](ClO 4 ) 2 (C 6 -1) derivative at 100 K. The complex C 6 -1 crystallizes in the triclinic system and adopts the Pbca space group. The iron(II) ion is in a distorted octahedral environment shaped by three imine and three pyridine nitrogen atoms of the C n -tameMe ligand. The average Fe-N im and Fe-N py bo…
Supramolecular isomerism in spin crossover networks with aurophilic interactions
2004
Assembly of FeII, 3-cyanopyridine and [Au(CN)2]– affords, in one-pot reaction, three coordination polymers that represent a genuine example of supramolecular isomerism with strong influence in the spin crossover regime of the FeII ions. Real Cabezos, Jose Antonio, Jose.A.Real@uv.es
Deposition and production of highly reproducible hybrid Cu[(tBu)4Pc]-polystyrene thin layers via spin casting
2012
This study focuses on the determination of a protocol for the production of a hybrid material composed of a polymer and a macrocyclic complex, namely polystyrene and a tetra-tert-butyl-copper phthalocyanine (Cu[(tBu)4Pc]), in order to obtain a layer thickness of about 100 nm and a controlled porosity in a highly reproducible way. Several methods were implemented and their reproducibility was evaluated through elements of characterization such as optical microscopy, atomic force microscopy and scanning electron microscopy. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers
Evaluation of interfacial shear strength by tensile tests of impregnated flax fiber yarns
2011
Adhesion of flax fibers and polymer matrix as well as mutual bonding of elementary fibers in a technical fiber are among the principal factors governing the mechanical response of flax fiber-reinforced polymer–matrix composites. A method for evaluation of adhesion is proposed based on tension tests of impregnated fiber yarns, with subsequent characterization by optical microscopy of length distribution of fibers pulled out of the yarn fracture surfaces. An elementary probabilistic model is derived relating aspect ratio distribution of the pulled-out fibers to the fiber tensile strength distribution and the effective interfacial shear strength (IFSS). The method was applied to flax fiber/vi…
Combined thermal evaporated and solution processed organic light emitting diodes
2011
Abstract Highly efficient, partly solution processed phosphorescent red, green and white organic light emitting diodes with small molecular weight host materials are prepared from commercially available starting compounds. Starting from an evaporated reference device, layers are stepwise replaced by solution processed layers. Replacing the evaporated hole transport layer by a solution processed polymer interlayer does not affect the performance and allows spincoating of the emissive layer after annealing of the polymer. Devices with, next to the spincoated hole injection and transport layer, a solution processed emission layer show similar characteristics and efficiencies as the reference d…
Optical Field-Induced Mass Transport in Soft Materials
2013
Abstract The dependence of the surface relief formation in amorphous chalcogenide (As 2 S 3 and As-S-Se) and Disperse Red 1 dye grafted polyurethane polymer films on the polarization state of holographic recording light beams was studied. It is shown that the direction of lateral mass transport on the film surface is determined by the direction of light electric vector and photoinduced anisotropy in the film. We propose a photoinduced dielectropfhoretic model to explain the photoinduced mass transport in amorphous films. Model is based on the photoinduced softening of the matrix, formation of defects with enhanced or decreased polarizability, and their drift under the electrical field gradi…
Functional 3D Photonic Films from Polymer Beads
2007
This paper describes synthesis and properties of polymer opals with a special emphasis on functional opals. Polymer opals are formed from monodisperse polymer colloids by self-assembly. Their potential applications range from coloring pigments, 3D bicontinuous supports for catalysis to photonic materials. This latter application requires especially the controlled creation of defects and the incorporation of fluorescent materials. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)