Advanced Powder Technology V
Silicon Carbide and Related Materials 2005
Advances in Materials Processing Technologies, 2006
Residual Stresses VII, ECRS7
High-Temperature Oxidation and Corrosion 2005
Aluminium Alloys 2006 - ICAA10
Recent Developments in Advanced Materials and Processes
Functional Materials and Devices
Advanced Materials Forum III
Advanced Materials and Technologies
Advanced Structural and Functional Materials Design
Eco-Materials Processing & Design VII
Advanced Structural Materials II
Recent Developments in Advanced Materials and Processes
摘要: This paper describes DSC, dielectric and dynamic mechanical behavior of linear and crosslinked liquid crystalline (LC) polyurethanes based on LC diols with a mesogenic group in the side chain, diisocyanates of various flexibility and two triols. From our investigations it follows: a) Linear polymers prepared from diols with simple end side chain substituents (as hydrogen, nitro and nitril group) exhibit only amorphous behavior regardless of the structure of used diisocyanate; generally, the most pronounced LC behavior exhibited polymers prepared from a diol with phenyl substituent. b) Investigation of the curing reaction showed that rheological power-law parameters, which are characteristic of the structure at the gel point, are dependent on the initial ratio of the reactants (amount of LC diol in EANCs). c) Strong physical interactions between the mesogens support the cyclization in the course of crosslinking reaction. d) Introduction of chemical junctions (amount of triols) suppresses LC ordering in the networks.
摘要: A method for predicting XPS C1s binding energies in polymers has been developed previously . The calculation uses partial atomic charges determined quantum chemically (by the semi-empirical AM1 Method), which are found to provide a linear correlation with the binding energies corrected by the so-called Madelung intramolecular potential. We used this method successfully for interpreting XPS spectra of partially degraded fluoropolymers . In the current contribution we investigate the possibility of developing a similar equation to describe siliconcontaining polymers that are medically and technologically important, and also some nanoparticles based on organo-silicon compounds.
摘要: Recently, a new charge percolation mechanism (CPM) of the Ziegler-Natta (ZN) polymerization of olefins by supported transition metal (Mt) complexes has been presented: a macromolecular chain is formed by polymerization of the monomer cluster (nM) adsorbed on the support (S) between two immobilized Mt ions, some in the higher (Mtn+1, i.e. acceptors) and the other in the lower (Mtn-1, i.e. donors) oxidation state: (Mtn-1...nM...Mtn+1)/S → (Mtn Mtn)/S + polymer. A special computer program «Lattice» has been developed to simulate olefin polymerization based on CPM using a Monte Carlo procedure. The effects of reaction conditions (Mt concentration, Mt/S ratio, sequence of chemical components addition and time) of ethylene and propylene polymerization by various Mt precursors (TiCl4/MgCl2, CrOx) and supports (MgCl2, SiO2) on molecular mass and molecular mass distribution can be predicted by simulation and confirmed by published experimental results.
摘要: Optical properties of bilayer organic light-emitting diodes (OLEDs) based on MEH-PPV (2-methoxy, 5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene) and Alq3 (tris(8-hydroxy-quinolinato) aluminum) are investigated in this paper. Numerical method solving 1D model based on driftdiffusion, continuity and Poisson`s equations extended by boundary conditions in treatment of internal organic interface is applied. The obtained space charge densities were employed in the emissive singlet exciton continuity equation resulting in the singlet exciton distribution and the emission zone profile. Dipole methods were utilized for the simulation of light emission in a layered medium. The electroluminescence (EL) spectra of OLED are considered by taking into account dominant interference effects. The exciton quenching near electrodes, allowing for a dominant nonradiative decay, is treated through effective emission zone narrowing.
摘要: Using semi-empirical quantum mechanic (AM1, ZINDO/S) and ab-initio Hartree-Fock (HF) calculations we investigated selected structural, electronic and vibrational properties of phenylene-based oligomers from biphenyl P2P to para-sexiphenil P6P. Special attention is paid to the interplay of electrostatic and conjugation effects on torsion barrier, energy gap, charge distribution and selected vibrational modes, and their dependence on torsion angle and oligomer size.
摘要: Here, as part of our experimental investigations dealing with poly(urethane-isocyanurate) networks, we investigate model irregular networks with increasing amount of dangling chains. In our study such an irregular network topology was obtained by partial substitution of a diol for a monohydroxy component during the preparation of isocyanate terminated precursors. Telechelic diisocyanates were synthesized from aromatic diisocyanate (2,4-TDI), α,ω-dihidroxypoly (oxypropylene) (PPG 2000), and diethyleneglycolmonomethylether (an aliphatic low-molecularweight monool component). The networks in undiluted state were prepared by cyclotrimerisation, in the presence of a catalyst. The network properties were estimated by multiple extraction in solvent, differential scanning calorimetry and photoelastical measurements. Independently of mechanical testing, the fraction and concentration of dangling and elastically active network chains were evaluated by the theory of branching processes (cascade theory). The influence of dangling chains on the mechanical properties was analyzed.
摘要: New functional homopolymeric, semiconducting materials soluble in polar solvents, were synthesized by chemical oxidative polymerization of 4-amino-3-hydroxynaphthalene-1- sulfonic acid (AHNSA) and its salts, using ammonium peroxydisulfate as an oxidant, in water at room temperature. Polymerization products obtained from AHNSA, AHNSA hydrochloride, AHNSA mono-sodium salt and AHNSA di-sodium salt were characterized by elemental analysis, gel-permeation chromatography (GPC), infrared spectroscopy (IR) and conductivity measurements. Polymers of AHNSA salts have increased weight-average molecular weights and polydispersity index values, compared to AHNSA polymer. Molecular weights approach a maximum value of ~25200 for polymers of AHNSA salts. Elemental analysis data of polymeric samples show a decrease of the S/C ratio for all polymeric materials in comparison with the monomer, indicating considerable elimination of sulfonic acid group from the macromolecular structure during the polymerization process. New substitution patterns shown by IR spectroscopic analysis combined with MNDO-PM3 semi-empirical quantum mechanical calculations revealed N─C coupling reactions as dominant, where C belongs to unsubstituted AHNSA ring. Coupling mode N─C1 is also important. Naphthoquinonoid and benzenoid structures were observed by IR spectroscopy. Influence of pH on the AHNSA oxidative chemical polymerization mechanism was examined.
摘要: A huge variety of nano-objects, allowing specific reactions at well-defined positions can be generated using oxo-molybdenum compounds based building blocks and fragments. On the other side, the use of suphur-based interfaces as metal-based organic materials is a new area with many potential applications in medicine, particularly as implants. In that respect, as precursors for building new materials with pronounced characteristics five new dioxomolybdenum(VI) complexes of the general formula [MoO2(Rdtc)2] have been used in the present work. Their predicted geometries optimized by the MO calculations are in excellent agreement with the reported crystal structure data, and therefore can be used as models for docking study between complexes and biomolecules. In silico screening for complex-protein interaction will be able to predict behavior of such materials implanted in living systems.
摘要: Silica fillers are used in rubber composites to modify their dynamic-mechanical properties. Three fillers are used: a commercial filler of precipitated silica type Vulkasil- S and two fillers obtained by its treatment in different ways: thermally and hydrothermally. The purpose is not only to obtain higher hysteresis of the composite at low temperatures and lower hysteresis at elevated temperature (which is optimal for good tire performance), but to understand the reasons of such changes in elastomer materials behavior and also possibilities to increase the corresponding trends. Both modified fillers exhibited required trends in comparison with the original commercial one. More detailed analyses of their dynamical behavior indicate interdependence between of filler particle size, morphology of particle aggregates and ratio of elastic to loss moduli, influencing all together the dynamic properties of products.
摘要: Modern material technology relies increasingly on processes for surface modification and coating. Generally, we are lacking a possibility to monitor the progress of such processes. Thus the outcome can only be analyzed after the end of the whole process cycle. We are proposing to use spectroscopic ellipsometry (SE) as an on-line monitoring tool. SE, as an optical method, is not affected by high temperatures, process gases, plasmas, etc. It can be used as a monitoring tool or a sensor for closed loop control of processes. The main difficulty is the on-line interpretation of SE data. Depending on the nature of the process monitored or controlled, different models are used for the interpretation. These models predict the SE response depending on different parameters describing the surface under investigation. A fitting process is used to solve the inverse problem, i.e. extracting material data from the SE spectra. We expect increased process stability and shorter development time as a practical benefit from the use of SE.