Small-Angle X-ray Scattering (SAXS) has been used as an analytical tool to study the development of microstructure with increasing Heat Treatment Temperature (HTT) of a carbonized phenolic resin, which is often used a...
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Small-Angle X-ray Scattering (SAXS) has been used as an analytical tool to study the development of microstructure with increasing Heat Treatment Temperature (HTT) of a carbonized phenolic resin, which is often used as matrix in commercial carbon-carbon composites. Processing parameters-heating rate and maximum heat treatment temperature-were the primary variables of interest. Results from SAXS have led to the consideration of a model for microstructure development in carbonized phenolic resins. Local density variations on the 10 angstrom-100 angstrom scale seem to be the predominant feature of these carbonized resins in the temperature range studied (450-900-degrees-C). Heat treatment results in a gradual destruction of crosslinks, which leads to clustering of the aromatic units. These clusters enclose pores, the high concentrations of which give rise to scattering maxima in SAXS data. Concentration and dimensions of pores are sensitive both to the heating rate used and the maximum carbonization temperature.
Polyether-based polyurethane/poly(methyl methacrylate-co-ethyleneglycol dimethacrylate) interpenetrating polymer networks [PU/P (MMA - co - EGDMA) - IPNs] were synthesized and used as adhesives to adhere vulcanized na...
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Polyether-based polyurethane/poly(methyl methacrylate-co-ethyleneglycol dimethacrylate) interpenetrating polymer networks [PU/P (MMA - co - EGDMA) - IPNs] were synthesized and used as adhesives to adhere vulcanized natural rubber (NR) and soft polyvinyl chloride (PVC). The structure and morphology of the IPN adhesives in bulk and near the adhesive/substrate interfaces were investigated. A new mechanism of adhesion called conjugate interpenetration of networks across interfaces, which is suitable for IPN adhesives and polymer substrates, was put forward. According to this mechanism, while forming simultaneous interpenetrating networks in the adhesive, the monomers in the IPN adhesive can permeate polymer substrates and polymerize in situ to form gradient IPNs, thereby producing conjugate three-component IPNs near the adhesive / substrate interfaces. It is the conjugate interpenetration of the networks across the interfaces that strengthens interfacial combination remarkably and results in high bond strength of IPN adhesives. (C) 1994 John Wiley & Sons, Inc.
We formulate an equation for the dynamic sedimentation of linear micelles (both rodlike and flexible) in the limit of local thermodynamic equilibrium when the recombination and scission of micelles are fast processes....
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We formulate an equation for the dynamic sedimentation of linear micelles (both rodlike and flexible) in the limit of local thermodynamic equilibrium when the recombination and scission of micelles are fast processes. A self-similar solution of the first kind is proposed for rodlike micelles in a free-draining approximation. The analytical structure of the associated nonlinear ordinary differential equation is very different from that pertaining to solutions of nonaggregating molecules. The theory may be of use in an experimental determination of the growth parameters by ultracentrifugation.
作者：
JAHROMI, SDepartment of Polymer Technology
Faculty of Chemical Engineering and Materials Science Delft University of Technology 2600 GA Delft P.O. Box 5045 Netherlands
The orientational order for a reactive liquid crystalline epoxy-amine mixture was monitored in real time with the aid of deuterium nuclear magnetic resonance (H-2-NMR) and birefringence (DELTAn) measurements. The orie...
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The orientational order for a reactive liquid crystalline epoxy-amine mixture was monitored in real time with the aid of deuterium nuclear magnetic resonance (H-2-NMR) and birefringence (DELTAn) measurements. The orientational order increased during the chain extension process, and it became irreversibly fixed as a result of the cross-linking reaction. The order parameter of the amine compound was more sensitive to the degree of the polymerization reaction than that of the epoxide. During the isothermal polymerization, the point where DELTAn started to level off corresponded well with the point of gelation as determined by solubility experiments. The relative increase of the orientational order according to H-2-NMR agrees with the value extracted from birefringence measurements. X-ray diffraction measurements revealed that the orientation of the network hardly changes upon heating and cooling in the absence of the magnetic field. The reaction was also measured in quasi-real time by gel permeation chromatography (GPC) and so the nature of various species, formed during the reaction, was determined. There was a good agreement between the reaction kinetics as determined by GPC and H-2-NMR experiments. The conversion (alpha) of the epoxy groups at the gel point agreed well with the value predicted by the statistical theory for network formation in isotropic stoichiometric epoxy-amine mixtures, namely, alpha almost-equal-to 55%. In addition, good agreement was found between the experimentally determined increase in the number-average molecular weight and theoretical predictions.
Highly ordered networks were produced by copolymerization of a low molecular weight liquid crystalline (LC) diepoxide with an aromatic diamine. A series of aromatic diamines was synthesized and their polymerization re...
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Highly ordered networks were produced by copolymerization of a low molecular weight liquid crystalline (LC) diepoxide with an aromatic diamine. A series of aromatic diamines was synthesized and their polymerization reaction with the LC-diepoxide was studied by means of differential scanning calorimetry. By adjusting the melting point of the crosslinking agents an eutectic LC mixture was found on which all the physical measurements were carried out. The degree of order of a certain dye guest in the polymer networks as determined by UV-dichroism was 0.76. Birefringence measurements have confirmed that about the same level of ordering can be maintained up to the thermal degradation point (i.e., 300 degrees C). Microscopy and X-ray studies have revealed that the epoxy-amine mixture is transformed from a nematic to a smectic phase, as a result of the polymerization reaction at 120 degrees C.
Thermal stability of [(CH3SiH)30(C6H5SiCH3)70]n a hydropolysilane copolymer, in vacuum and its crosslinking reactions with vinylic silanes as crosslinking agents was evaluated in order to obtain high yields of oxygen-...
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A nanostructured FeCrMoVM50 type steel was prepared via a chemical route. The process involved the thermal decomposition of organometallic precursors Fe(CO) 5 , Cr(CO) 6 , Mo(CO) 6 and V(CO) 6 , at 150°C ...
A nanostructured FeCrMoVM50 type steel was prepared via a chemical route. The process involved the thermal decomposition of organometallic precursors Fe(CO) 5 , Cr(CO) 6 , Mo(CO) 6 and V(CO) 6 , at 150°C for the formation of nanostructured M50 type steel powders. In addition to the thermal decomposition of these carbonyls, the results of the reduction of respective metal halides for the production of the same steel are also presented. The nanostructured steel powders obtained were also consolidated samples, were characterized using x-ray synthesized powders, as well as the consolidated samples, were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution electron microscopy (HRTEM). Possible mechanisms for the formation of nanostructured particles are also discussed.
In an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length nu and one of length nu+1 at any density (Kumar et al., 1991, Kumar, 1992a, 199...
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In an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length nu and one of length nu+1 at any density (Kumar et al., 1991, Kumar, 1992a, 1992b). In this paper we begin by formally proving that the chemical potential of a whole chain of length nu can be obtained by sequentially summing the incremental chemical potentials of all chains whose lengths are smaller than nu under the same conditions. It was found that the incremental chemical potentials defined in this manner had a well defined chain length dependence, and that they were essentially independent of chain length in polymer melt systems. This allows us, in principle, to enumerate the phase diagrams for polymer blends using the incremental chemical potentials alone.
In an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length nu and one of length nu+1 at any density. (Ref.9) In this paper we begin by for...
In an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length nu and one of length nu+1 at any density. (Ref.9) In this paper we begin by formally proving that the chemical potential of a whole chain of length nu can be obtained by sequentially summing the incremental chemical potentials of all chains whose lengths are smaller than nu under the same conditions. We then compare the numerical value of chain chemical potentials computed in this fashion to those obtained by inserting whole chains into the simulation cell following the configurational bias procedure proposed by Smit and Frenkel. (Ref.5) It is found, for the two cases considered here, that die results obtained from the two different calculations agree within simulation uncertainty, thus verifying the validity of the proposed arguments.
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