Permeation of a solvent mixture through an elastomeric membrane—The case of pervaporation

This article presents a model for the permeation of solvent mixtures through an elastomer in the particular case of pervaporation. An analytical expression for each solvent permeation rate is derived, in the limited case of a membrane that undergoes small swelling, without making any assumptions on the solvent diffusion coefficients and their dependence on solvent concentrations. Applying this analytical expression to different situations, we fitted most of the curves previously published on pervaporation experiments. In particular, we correlated the synergy developed by a mixture of two solvents in the permeation process with the sign of their Flory–Huggins interaction parameter χ_AB. This explains why, in most cases (χ_AB > 0), a molecule permeating easily through a membrane is mixed with a molecule permeating much less easily; the latter can see its permeation flux increase by a factor 10 or 100 because the swelling of the polymer induced by the more permeable molecule “opens the meshes of the network” allowing the less permeable molecule to pass through more easily. Within our analysis, the efficiency of the pervaporation process, expressed through the separation factor, is derived very simply as a function of the interaction coefficients and the viscosities of solvents and exhibits an exponential dependence on the volume fraction of either component as seen in most experiments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 183–193, 2003     

Gas-liquid phase transition and singularities

A new model for the space of undercritical states of a gas-liquid system is proposed. Simple, physically motivated mathematical hypotheses among which stsbility plays an essential role, determine differential types of germs of pressure and temperature at the critical point. They are connected with the class D⁺₄ of Arnold's classification. The general configuration of vaporization and condensation curves is examined. As a result, Guggenheim's one-third law is obtained.     

Background-free cars studies of carbon monoxide in a flame

Background-free coherent anti-Stokes Raman spectra (CARS) of carbon monoxide have been obtained in a rich methane-air flat flame. Use of this background rejection method, requiring only two laser frequencies, results in an increase in signal-to-noise of over 200 in the |x⁽³⁾|² spectrum in comparison with normal CARS. In addition, this technique provides a means for determining the symmetry of observed Raman transitions. The principles of background-free CARS are derived, and the capabilities are demonstrated with experimental data.     

Properties of an equilibrium hadron gas subjected to the adiabatic longitudinal expansion

We consider an ideal gas of massive hadrons in thermal and chemical equilibrium. The gas expands longitudinally in an adiabatic way. This evolution for a baryonless gas reduces to a hydrodynamic expansion. Cooling process is parametrized by the sound velocity. The sound velocity is temperature dependent and is strongly influenced by hadron mass spectrum.Work partially supported by the Polish Committee for Scientific Research under contract KBN-200579101     

Films from soft‐core/hard‐shell hydrophobic latexes: Structure and thermomechanical properties

Structured latexes provide a promising route to hard coatings without the use of coalescing aids. We studied the thermomechanical properties of films from structured soft‐core/hard‐shell hydrophobic latexes. We found that the mechanical properties of these films were closely related to their very particular organization. When the rigid phase was continuous, whatever its volume fraction, the films exhibited a high elastic modulus. An analysis of the viscoelastic properties of the films provided a good method for obtaining information about the interphase between the hard shell and soft core of the latex particles. By varying the film structure through annealing or the particle composition (core/shell ratio, core crosslinking, etc.), we were able to tune the mechanical properties of the films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2989–3000, 2000     

An analysis of the reaction–diffusion mechanism governing the chlorination process of poly(vinyl chloride)

Chlorinated poly(vinyl chloride) (CPVC) obtained through a dry chlorination of PVC films or grains can show a heterogeneous repartition of its chlorine atoms because the reaction process is limited by the mass transfer of the chlorine gas in the material. In order to describe the evolution of such a system, a set of coupled equations is derived where only two dimensionless constants have to be determined: K_S, which depends on the solubility of the chlorine gas in the PVC, and K_T, the ratio between the diffusion and the reaction characteristic times. The kinetics of chlorination obtained for the different regimes matches the available experimental data, and the corresponding concentration profiles for the chlorinated PVC chains are displayed to demonstrate how a heterogeneous chlorination can arise from this dual process. In particular, a sharp interface appears in the diffusion‐limited regime that separates the chlorinated region from an unchlorinated core and is shown to progress deeper into the film with the square root of time. To a larger extent, this analysis shows how heterogeneity of reaction and nonlinear effects can arise from a coupling between a diffusive phenomenon and a reactive phenomenon. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3201–3209, 2000     

C80, C86, C88: Semiempirical and ab initio SCF calculations

Three complete sets of the isolated-pentagon-rule fullerene isomers are considered—₈₀ (7 species), C₈₆ (19 species), and C₈₈ (35 species). The interisomeric separation energetics is essentially similar at semiempirical (AM1, SAM1) and ab initio (HF/STO-3G, HF/3-21G, HF/4-31G) levels. For the C₈₀ set, the HF/4-31G computations explain why the lowest-energy isomer is not experimentally observed. The computations also agree with observations on C₈₆ and C₈₈. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 529–535, 1997     

A CASSCF-CASPT2 study of the excited-state intramolecular proton transfer reaction in 1-amino-3-propenal using different active spaces

In this work we analyze how the choice of the active space in the CASSCF (the complete-active-space multiconfiguration self-consistent-field method) and CASPT2 (the second-order perturbation theory based on the CASSCF reference wave function) calculations affects the computed potential energy curves (PECs) for the intramolecular proton transfer reaction in the ground state and the two lowest lying singlet excited states of 1-amino-3-propenal. As anticipated, the results revealed that, qualitatively, the proton transfer in the different states can be correctly described even by minimal active spaces, which include the orbitals involved in the electronic excitation of the considered state and the antibonding sigma orbital corresponding to the bond formed by the molecule with the migrating hydrogen atom. However, quantitatively, the relative energies of the two tautomers and the energy barriers computed at the CASSCF level change when the active space is increased, indicating importance of the dynamic electron correlation. Introducing the dynamic correlation effects via CASPT2 makes the calculated energy parameters more uniform among the different active spaces. The analysis suggested certain optimal active spaces for studying proton transfer reactions in systems similar to 1-amino-3-propenal. The PEC calculations for excited states showed that the results are sensitive to the molecular geometries used in the calculations, particularly near the transition point. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1422–1431 (1999)     

Darwin and mass-velocity relativistic corrections in non-Born-Oppenheimer variational calculations

The Pauli approach to account for the mass-velocity and Darwin relativistic corrections has been applied to the formalism for quantum mechanical molecular calculations that does not assume the Born-Oppenheimer (BO) approximation regarding separability of the electronic and nuclear motions in molecular systems. The corrections are determined using the first order perturbation theory and are derived for the non-BO wave function of a diatomic system expressed in terms of explicitly correlated Gaussian functions with premultipliers in the form of even powers of the internuclear distance. As a numerical example we used calculations of the transition energies for pure vibrational states of the HD(+) ion.