Microcapsules are produced by immersing uniform sized droplets of an organic phase into an aqueous solution. The process of polycondensation of terephthaloyldichloride (TDC), dissolved in the organic phase, and diethy...
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Microcapsules are produced by immersing uniform sized droplets of an organic phase into an aqueous solution. The process of polycondensation of terephthaloyldichloride (TDC), dissolved in the organic phase, and diethylenetriamine (DETA) in combination with ethylenediamine (EDA) or hexamethylenediamine (HMDA), dissolved in the aqueous phase, was studied. This process produced the capsule wall at the interface;the capsule diameter varied between 0.5 and 1 mm. The influence of the concentration ratio of TDC and DETA, the addition of EDA or HMDA, their concentration relative to the DETA concentration in the aqueous phase and the kind of the organic phase on the diffusion coefficient of DETA through the polymer produced was measured. The decrease of the TDC concentration in the capsules and the growth of the capsule wall could be described by the same relationship as derived from macrocapsules. Also the influence of the TDC/DETA concentration ratio was in agreement with the results obtained for macrocapsules. Addition of diamine to the aqueous phase reduces the permeability of the capsule wall;an increase of the ratio of the diamine and the triamine concentration also reduces the permeability.
Magnetic nanocomposite powders of Fe x N/BN ( x = 3 or 4) were prepared by thermochemical conversion of a FeBN-containing precomposite synthesized via an aqueous chemical route. Various characterization techniques...
Magnetic nanocomposite powders of Fe x N/BN ( x = 3 or 4) were prepared by thermochemical conversion of a FeBN-containing precomposite synthesized via an aqueous chemical route. Various characterization techniques were used to study the precomposite and composite materials. The results show that the conversion of the precomposite gel to the composite nanostructured material goes to completion around 400°C. Structural, chemical, morphological, and magnetic properties are presented.
作者：
ODIJK, TDepartment of Polymer Technology
Faculty of Chemical Engineering and Materials Science Delft University of Technology P.O. Box 5045 2600 GA Delft The Netherlands
A self-consistent theory is developed for the hexagonal phase of semiflexible polyelectrolytes. The electrostatic interactions analyzed in the Poisson-Bolzmann approximation, couple non-linearly to the undulations of ...
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A self-consistent theory is developed for the hexagonal phase of semiflexible polyelectrolytes. The electrostatic interactions analyzed in the Poisson-Bolzmann approximation, couple non-linearly to the undulations of the polyions so that the intermolecular forces may be enhanced by an order of magnitude. The theory is in good agreement with the osmotic stress measurements on DNA by Podgornik et al. It also seems to bear on unresolved discrepancies arising in stress experiments on tobacco mosaic virus and muscle thin filament.
The effects of addition of glass fiber and HMS4 carbon fiber on the crystallization of nylon 6,6 has been investigated using DSC and polarized optical microscopy (POM). DSC observations indicate that HMS4 fiber lowers...
The effects of addition of glass fiber and HMS4 carbon fiber on the crystallization of nylon 6,6 has been investigated using DSC and polarized optical microscopy (POM). DSC observations indicate that HMS4 fiber lowers the supercooling required to initiate crystallization. A transcrystalline layer is also observed in the near-fiber region of carbon fiber-reinforced composites after DSC. The presence of transcrystallinity and the earlier onset of crystallization for this composite are due to heterogeneous nucleation on carbon fiber surfaces. DSC measurements of nylon 6,6 with glass fibers show supercoolings similar to those of neat nylon 6,6. Transcrystallinity is also absent in the glass-reinforced composites. These glass fibers appear to be weak nucleation catalysts. Different transcrystalline layer thickness is found to be influenced by thermal processing condition. In addition to transcrystallinity, the HMS4 carbon fiber also influences the bulk morphology of the nylon 6,6.
A laser cladding process has been developed and is now in production for the cladding of new aircraft carrier catapult components. The Service Life Extension program (SLEP) Office of Naval Sea Systems Command (NavSea)...
A laser cladding process has been developed and is now in production for the cladding of new aircraft carrier catapult components. The Service Life Extension program (SLEP) Office of Naval Sea Systems Command (NavSea) suggested that this process be utilized for the refurbishment of catapult tracks. Early experiments were conducted by the Naval Surface Warfare Center in conjunction with the IIT Research Institute. The program was then transitioned to the Applied Research Laboratory, Pennsylvania State University (ARL Penn State) under the sponsorship of the Naval Air Systems Command (NavAir)/Navy MANTECH program, thus providing an effective solution to a NavSea/NavAir interface hardware problem. ARL Penn State was responsible for the production and evaluation of six laser clad aircraft carrier catapult tracks as part of a program sponsored and funded by NavAir Code 5512. Six catapult tracks that had been taken out of service because of excessive wear were laser clad at the Westinghouse Electric Research and Development Center (Now ''science and technology Center'') for ARL Penn State. The composition of the clads was Inconel 625, Stellite 6/Stainless Steel 304, and Ferrelium 255. The tracks were machined and installed on the USS Constellation. Wear measurements were taken for the laser clad tracks and standard tracks ahead and behind the clad tracks. After 7,161 launches, the tracks were removed and returned to ARL Penn State for evaluation. The evaluation indicated that impact damage was observed on one track. No additional defects related to operations were found. Wear data indicated that the wear rate for it was 25%-50% less than non-clad. The results indicated that rejectable tracks (and one piece trough covers) could be successfully laser clad for extended operating life at acceptable costs. With emphasis for the future on a more affordable Navy, the need for viable refurbishment processes will be necessary for extending life and performance for the 21st century
The CO2 permeability of uniaxially drawn high-density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free...
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The CO2 permeability of uniaxially drawn high-density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free volume of the amorphous component in the drawn polymers was made on the basis of experimental data. The dramatic variations in permeability resulting from drawing were shown to be the consequence of changes of fractional free volume in the amorphous phase of the drawn polymer. Good correlation exists between measured solubility and diffusion coefficients of drawn samples and the estimated fractional free volume;this correlation agrees with the existing free volume theory for diffusion in polymers.
We propose a new technique, which is a combination of the test and real particle methods proposed originally by Widom, for the calculation of the chemical potentials of molecular systems from computer simulation. The ...
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We propose a new technique, which is a combination of the test and real particle methods proposed originally by Widom, for the calculation of the chemical potentials of molecular systems from computer simulation. The technique involves the creation of a hole in the fluid by removing a particle from the simulated system, and subsequently reinserting it as a test bead. The equations for the calculation of chemical potentials are derived, and it is shown that the results obtained by this method for Lennard-Jones fluids are accurate over larger ranges in temperature and density than other traditional methods. In spite of these advantages for simple systems, the proposed technique is expected to be of greatest value when dealing with complex systems containing ionic or polymeric molecules.
In this paper we explore the crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and miscible blends of PBT with a polyarylate based on Bisphenol A and a 75/25 mole rati...
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In this paper we explore the crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and miscible blends of PBT with a polyarylate based on Bisphenol A and a 75/25 mole ratio of isophthalic and terephthalic acids. For PBT, a regime II --> III transition is indicated near 210-degrees-C (DELTA-T approximately 30-degrees-C) and the fold surface free energy (sigma(e)) was found to be in the range of 57-75 erg/cm2. This leads to a work of chain folding (q) of approximately 3-5 kcal/mol folds. Analysis of the crystallization data of van Antwerpen and van Krevelen for PET shows that crystallization occurs in regime II across a wide range of T(c). Sigma(e) was estimated to be approximately 140 erg/cm2 and q approximately 10 kcal/mol from their data. These values are roughly twice that of PBT, consistent with the longer flexible segments in the PBT repeat unit. Crystallization data for three PBT/PAr blends was analyzed using a modified Lauritzen-Hoffman method and compared to that of pure PBT.
In a previous paper we illustrated a Monte Carlo method to calculate the incremental chemical potential between polymer chains of length nu and nu + 1 at all densities. In this document we present a statistical mechan...
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In a previous paper we illustrated a Monte Carlo method to calculate the incremental chemical potential between polymer chains of length nu and nu + 1 at all densities. In this document we present a statistical mechanics model that allows for its quantitative evaluation as a function of chain length and temperature for macromolecular systems at zero density. Through this approach the incremental chemical potential at zero density is shown to be a strong function of chain length at low temperatures, but becomes chain length independent even for short chains (nu greater-than-or-equal-to 3) at higher temperatures. The temperature where the chemical potential becomes essentially chain length independent is a definition of the Boyle transition for finite chain length polymers, and we show that this transition temperature has a well defined chain length dependence. Chain dimensions and incremental entropies associated with chain segments are also found to decrease significantly when the temperature is reduced below this theta-temperature thus providing that chain segments are localized in the vicinity of other segments in the collapsed state. The consequences of these results on the modeling of the phase equilibria of polymer solutions are also examined.
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