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1.
Pawan K. Agarwal Richard T. Garner William W. Graessley 《Journal of Polymer Science.Polymer Physics》1987,25(10):2095-2111
We present an analysis of data on the intrinsic viscosity [η] of sulfo-polystyrene ionomers in several solvents for a variety of sulfonation levels and counterions. For solvents of low dielectric constant, 2 < ε < 18, [η] decreases from the base polymer value [η]0 with increasing substitution level. This behavior was attributed to intramolecular association of ionic dipoles. The ratio [η]/[η]0 was found to depend on a single reduced variable αAαSx, where x is the fractional substitution, αA depends only on the counterion, and αS ∝ ε?1 depends only on the solvent. For solvents of high dielectric constant, 36 < ε < 47, [η] increases approximately as x3, and counterion effects are small. This behavior was attributed to ionic dissociation, giving rise to a polyelectrolyte effect. Implications of the low ε results are discussed in relation to association-induced gelation behavior and possible generalizations of the reduced variables approach. 相似文献
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Electrophoresis of lambda phage DNA was carried out in solutions at various concentrations of uncrosslinked polyacrylamide of 0.6, 1, 5 and 9 x 10(6) molecular weight (Mw) with narrow Mw distribution. By inspection of mobilities in the various concentration ranges, it appears that mobilities decrease, and retardation increases, with increasing Mw. The relation between electrophoretic retardation and the Mw of the polymer was also interpreted (i) in the manner previously applied to nonlinear Ferguson plots and compatible with the Ogston model; and (ii) empirically, on the basis of the first derivatives of the functions describing the Ferguson plots at the polymer concentrations used. Interpretation (i) shows that the retardation increases linearly in the order of 0.6, 1, 5 and 9 x 10(6) Mw of polyacrylamide. Interpretation (ii) shows a nonlinear increase of retardation in the Mw range 5 to 9 x 10(6), and a decrease in retardation as Mw is raised from 0.6 to 5.0 x 10(6). Hypothetically, interpretation (ii) can be explained mechanistically by a progressive change, as the polymer size is increased, from a collision with the surface of the polymer fiber to one occurring after permeation in the interior of a random-coiled fiber. Interpretation (i) may fail to detect that change due to the large difference between DNA mobility in solutions of the smallest polymer and the free mobility. DNA peak detection in all of the four size classes of polyacrylamide in solution is limited to relatively narrow ranges of polymer concentration.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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The MSR (muonium spin rotation) technique was used to measure the chemical reaction rate for Mu + F2 → MuF + F in N2 moderator at ≈ 1 atm from 295 to 383 K giving the Arrhenius expression: log10k (?/mole s) = (10.83 ± 0.20) - (200 ± 50)/T, with k = (1.46 ± 0.11) × 1010 ?/mole s at 300 K. This is at least 6.8 times the room temperature rate constant for the analogous H atom reaction. The measured activation energy and enhancement over the H reaction rate are indicative of significant tunnelling in the Mu reaction, in agreement with the recent collinear quantum mechanical calculations of Connor et al. 相似文献
7.
The preparation of some new cationic aryldiazo complexes of platinum of formula trans-[Pt(N2Ar)(PEt3)2L]+, where N2Ar = N2C6H4F-m or -p and L = NH3, Py, Et3P or EtNC, is described. Protonation of these complexes gives the corresponding aryldiimide complexes trans-[Pt(NHNAr)(PEt3)2L]+, and reduction of the protonated complexes with molecular hydrogen in the presence of a catalyst gives the arylhydrazine complexes trans-[Pt(NH2NHAr)(PEt3)2L]+. Some of the spectroscopic properties of these new complexes are reported and discussed. 相似文献
8.
J. R. Kempton M. Senba D. J. Arseneau A. C. Gonzalez J. J. Pan A. Tempelmann D. M. Garner D. G. Fleming 《Hyperfine Interactions》1991,65(1-4):801-809
Results of muon polarization studies in xenon and argon up to 60 atm are reported. In argon for pressures up to 10 atm, the
muon polarization is best explained by an epithermalcharge exchange model. Above this pressure, the decrease inP
D and increase inP
L are ascribed to charge neutralization and spin exchange reactions, respectively, in the radiolysis track. Measurements with
Xe/He mixtures with a xenon pressure of 1 atm indicate that the lost polarization in the pure xenon at this pressure is due
to inefficient moderation of the muon. As the pressure in pure xenon is increased above 10 atm, we find thatP
L remains roughly constant andP
D begins to increase. The lost fraction may be due to the formation of a XeMu Van der Waals type complex, whileP
D is ascribed to XeMu+ formation. This suggests that spur processes appear to be less important in xenon than in argon. 相似文献
9.
Abstract A review is presented of a very general aspect of the response of all metals subjected to displacive irradiation. This aspect is referred to as «persistence» and describes the tendency of both radiation-induced microstructural evolution and the associated changes in material properties or dimensional stability to evolve to saturation states that resist further change upon continued irradiation. It is shown that new persistent states can develop on a longer time frame associated with the late-term loss of existing microstructural components or the gain of new components, especially when transmutation and/or segregation occurs. The persistent states are often dependent on the irradiation conditions, and if these are changed, the material usually adjusts to form the persistent state characteristic of the new conditions, with the memory of the former state often lost, and sometimes leaving no visible record of the former state in the new microstructure. Depending on the microstructural components involved, the transition toward the new persistent state can occur quickly or very slowly. 相似文献
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