Materials Literature
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Crystallization and solidification in polymers is a problem of great importance to the polymer processing industry. In these processes, the melt is subjected to deformation while being cooled into the desired shape. The properties of the final product are strongly influenced by the deformation and thermal histories an…
The sub-glass-transition viscoelastic and physical aging responses of an amorphous poly(ethylene naphthalate) (PEN) have been studied using uniaxial tension stress relaxation experiments. It is known that PEN exhibits a strong β relaxation that overlaps the α relaxation in the experimental time and temperature ranges…
Aromatic polyamide dendrons (HOOC-G1 ( 6 ), Br-G2 ( 7 ), HOOC-G3 ( 8 ), and Br-G4 ( 9 )) were synthesized by an orthogonal approach, which utilizes the direct condensation reaction and palladium-catalyzed carbon monoxide insertion reaction in an alternating fashion to form amide linkages. G1, possessing four amino gro…
We investigated the nature and the range of interactions between negatively charged polyelectrolyte-coated surfaces as a function of salt concentration using the surface forces apparatus. The measured force profiles (interaction forces versus separation distance) are purely repulsive and show long-range electrostatic…
ζ potential measurements were used to determine the adsorbed layer thickness of poly(ethylene oxide)−polypropylene oxide−poly(ethylene oxide) (PEO−PPO−PEO) block copolymers at the surfaces of poly(dimethylsiloxane) emulsion droplets, silica particles, and polystyrene latex particles. The adsorbed layer thickness (δ) w…
Three hyperbranched aromatic polyamides were synthesized by the direct polycondensation of 3,5-diaminobenzoic acid 2 (AB 2 monomer), G1 dendron 4 (AB 4 monomer), and G2 dendron 6 (AB 8 monomer). The weight-average molecular weights ( M w ) of the resulting polymers were 100 000−200 000 with a polydispersity (PDI) of c…
The photophysical and hydrodynamic properties of dendrimers (G n PZn and G n TPPH 2 ) with zinc porphyrin (PZn) and tetraphenylporphyrin (TPP) cores are studied in tetrahydrofuran (THF) and dimethylformamide (DMF). UV−vis absorption spectra of G n PZn exhibit a small red shift of the Soret band upon increasing the gen…
The alkaline hydrolysis of a polyimide (PMDA-ODA) surface was studied as a function of time, temperature and hydroxide ion concentration. Quantification of the number of carboxylic acid groups formed on the modified polyimide surface was accomplished by analysis of data from contact angle titration experiments. Using…
Micrometer-sized polystyrene (PS) particles coated with poly(3,4-ethylenedioxythiophene) (PEDOT), an air-stable organic conducting polymer, have been described previously ( Langmuir 1999, 15, 3469). X-ray photoelectron spectroscopy (XPS) was used to examine the surface of these coated particles. For the first time, bo…
An oxalate-bridged 3d−5f compound, K2MnU(C2O4)4·9H2O, is the product of the reaction of K4U(C2O4)4 with a Mn(II) salt. Single-crystal structure analysis shows a three-dimensional network with a diamond-type architecture. The magnetic properties have been examined.
Electrical conductivity measurements on a 2D packing of metallic beads have been performed to study internal rearrangements in weakly pertubed granular materials. Small thermal perturbations lead to large non gaussian conductance fluctuations. These fluctuations are found to be intermittent and gathered in bursts. The…
In sonochemical processes, the physical and chemical effects are attributed to the phenomenon of cavitation, which is the formation, growth, and collapse of the cavities termed as activity of cavities. Energy analysis of a single cavity has been considered in order to explain, qualitatively, the effects of acoustic pa…
ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTSpeciation and Thermal Transformation in Alumina Sols: Structures of the Polyhydroxyoxoaluminum Cluster [Al30O8(OH)56(H2O)26]18+ and Its δ-Keggin MoietéJ. Rowsell and L. F. NazarView Author Information Department of Chemistry, University of Waterloo Waterloo, Ontario,…
Multilayer mirrors that maintain or increase their reflectivity with increasing incidence angle can be constructed using polymers that exhibit large birefringence in their indices of refraction. The most important feature of these multilayer interference stacks is the index difference in the thickness direction (z axi…
The crystal structure of Ba 3 Co 2 O 6 (CO 3 ) 0.60 has been determined by means of X-ray, neutron and electron diffraction, and high-resolution electron microscopy. This compound has a hexagonal symmetry (space group P 6̄) and lattice parameters a = 0.9683(1) and c = 0.95180(8) nm related to the 2H−ABO 3 by means of…
The symmetry of CaFe x Ti 1- x O 3- x /2 perovskites (0 x 0.40) has been studied by means of room temperature and high temperature x-ray powder diffraction. At room temperature the perovskites undergo at least two displacive phase transitions with increasing Fe content: from the CaTiO 3 Pbnm structure to the tetragona…
The synthesis and isolation of unsymmetrical porphyrazines bearing two, four, and six bis-(dimethylamino) functionalities has been achieved via the base-catalyzed cross-condensation of 1,2-dicyanobenzene 8 and bis(dimethylamino)maleonitrile 7. In addition, the benzo-fused hexaaminoporphyrazine dimer 10 was prepared fr…
Sodium dodecyl sulfate (SDS)-templated sol−gel films formed by the rapid dip-coating method possess highly ordered lamellar phase structure. Thin film morphology allows both the chemistry and the dynamics of the assembly process to be traced in real time because the steps involved in the formation of the mesostructure…
Microcalorimetric and infrared spectroscopic studies of CO adsorption on Pt/SiO 2 were conducted at temperatures from 298 to 673 K. The adsorption of CO on silica-supported Pt is equilibrated at 673 K, and the microcalorimetric and spectroscopic results obtained at this elevated temperature are in agreement with resul…
The structural properties and the band structures of the charge-transfer insulating oxides SrO, MgO and SrTiO 3 are computed both within density functional theory in the local density approximation (LDA) and in Hedin's GW -scheme for self-energy corrections, by using a model dielectric function, which approximately in…