Diffusion in polymer—solvent systems. I. Reexamination of the free-volume theory

The free-volume theory describing diffusion in polymer–solvent systems is reexamined. Calculation of the specific free volume for such systems is discussed, and equations are presented for the determination of the self-diffusion coefficients of the polymer and the solvent. Conditions under which the mutual diffusion coefficient can be deduced solely from free-volume considerations are clarified, and a more general version of the free-volume diffusion theory proposed by Fujita is presented. The further restrictions needed for the theory of Fujita are discussed, and it is concluded that these additional restrictions are responsible for failures of the Fujita theory.     

Diffusion of large penetrant molecules in amorphous polymers

A new version of the free-volume theory of diffusion is modified to describe self-diffusion phenomena in polymer + solvent systems for solvents which do not move as single units. The free-volume equations are used to interpret data which appear to illustrate that some large solvent molecules do indeed move in a segmentwise manner. The dependence of the effective activation energy for diffusion on solvent size is examined, and the importance of energy effects on the diffusion process is considered.     

Diffusion in atactic polystyrene above the glass transition point

Diffusivities and solubilities in the system n-pentane-polystyrene were measured for low penetrant concentrations at several temperatures above the glass transition temperature. The relatively sharp changes in the activation energy of diffusion and the heat of solution near 150°C. are interpreted tentatively as indicating that a second-order transition exists in atactic polystyrene above the glass transition temperature. Evidence indicating the existence of this transition has been obtained by other techniques and the effects observed in this study should also be present in the diffusion of other penetrants in polystyrene. Correlation of these and other available data for diffusion in polystyrene as a function of the molecular size of the penetrant indicates that specific thermodynamic interactions between polymer and penetrant have little influence on the diffusion process.     

Dielectric and magnetic permittivities of three new ceramic tungstates MPr2W2O10 (M = Cd,Co, Mn)

Broadband dielectric spectroscopy measurements revealed an anomalously large relative permittivity value (ε _r?=?884) for MnPr₂W₂O₁₀, a smaller value (ε _r?=?156) for CoPr₂W₂O₁₀ and the smallest value (ε _r?=?22) for CdPr₂W₂O₁₀ at low frequency (ν?=?0.1?Hz) and above room temperature in the insulating and paramagnetic state. Below 273?K, the relative permittivity (ε _r?～?24) did not depend significantly on frequency for all the tungstates under study. Electrical resistivity, thermoelectric power, electron paramagnetic resonance, magnetic susceptibility and magnetization provided experimental evidence that the studies tungstates were paramagnetic insulators with low n-type conduction. Only in the case of MnPr₂W₂O₁₀ was a ferrimagnetic order below 45?K observed. These effects are discussed within the framework of Maxwell–Wagner polarization, chemical covalent bonds and porosity mechanism.     

Flow of a newtonian fluid through a sudden contraction

The full Navier-Stokes equations describing flow through a sudden contraction are solved by an explicit finite-difference method. Streamlines, vorticity distributions, velocity profiles, excess pressure drops, and entrance lengths are calculated as functions of Reynolds number and radius ratio. The results are compared with existing experimental data and the limited theoretical work available.     

Surface enhanced Raman scattering of light by ZnO nanostructures

Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E ₂(high) and A ₁(LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 10³) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model.     

Observationally constrained modeling of sound in curved ocean internal waves: examination of deep ducting and surface ducting at short range

A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones).     

Are there “prompt” like-sign dimuons?

From exposures of the CDHS detector at the CERN SPS we have obtained 367μ ⁺ μ ^? events in neutrino beams and 73μ ⁺ μ ⁺ events in an antineutrino beam. The magnitude of a prompt like-sign signal has been controversial in the past and moreover could not be explained by known production mechanisms. A critical discussion of the experimental situation is given. We have tried to reduce the systematic uncertainties of previous experiments and to get more information on the dependence of the signal with energy and the muon momentum cut-off. This experiment yields a signal of 2.8σ (2.4σ) of prompt like-sign dimuon events in the case of neutrinos (antineutrinos). The rate to charged current events is of the order of 10^?4 forp _μ<9GeV andE>100 GeV. The prompt signal has all the properties expected from the production and decay of charm-anticharm events. The magnitude, however, is substantially higher then the prediction of perturbative QCD but lower than some other experiments.     

Specific propagation directions of acoustic waves for piezoelectric and nonpiezoelectric media

I reanalyze the problem of the existence of longitudinal normals inside the symmetry planes of piezoelectric crystals belonging to the symmetry class mm2. The equations determining components of longitudinal normals situated outside the symmetry planes for media of this symmetry are discussed. It is proven that nonpiezoelectric media of rhombic symmetry could have 4 or 8 distinct acoustic axes. Examples of nonpiezoelectric elastic media of monoclinic symmetry without acoustic axes are given. The method of determination of the components of acoustic axes for piezoelectric media of arbitrary symmetry is presented. With the help of this method, I discuss the problem of acoustic axes for piezoelectric media of the symmetry class mm2. The text was submitted by the author in English.     

Phase equilibrium and diffusion of solvents in polybutadiene: A capillary‐column inverse gas chromatography study

The capillary‐column inverse gas chromatography method was used to measure the diffusion and partition coefficients of ethylbenzene, styrene, and acrylonitrile in polybutadiene (PBD) at infinite dilution of the solvents. Experiments were performed over a temperature range of 50–125 °C. At temperatures well above the glass‐transition temperature of PBD, the diffusivities were correlated using an Arrhenius expression. The Arrhenius parameters in turn were intercorrelated and shown to be a function of the occupied volume, thus providing a method for predicting the diffusion of other solvents in the same polymer. Further, the activation energy was predicted using the Duda‐Vrentas free‐volume approach. The activation energy thus obtained was compared with the activation energy of the Arrhenius approach. The weight‐fraction activity coefficient data were compared to the predictions of the group contribution, lattice‐fluid equation‐of‐state, and the UNIquac Functional‐group Activity Coefficient (UNIFAC) free‐volume models. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1046–1055, 2002