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In this paper, solid blends of HPC/PVP obtained by polymerization in situ of NVP are analyzed. These blends retain the initial organization of HPC in NVP in terms of liquid crystalline structure and banded texture. It is also demonstrated that the banded texture may be stabilized with respect to thermal cycles by crosslinking the samples.

A simple method is reported allowing the fast evaluation of the athermal limit that is implicitly present within the set of equations recently proposed by Jonah, Brostow and Hess, dealing with the anisotropic-isotropic equilibria of single monodisperse or nearly monodisperse semirigid liquid polymers, including polymer liquid crystals. We have found an athermal limit dependent on the degree of rigidity 0 of the given semirigid liquid polymer (θ being the fraction of its monomeric units belonging to rigid rodlike sequences within each semiflexible polymeric chain) and marked off by critical lengths η al of the rigid sequences, giving rise to non-finite asymptotic values of the anisotropic-isotropic temperatures.

Long-range dispersion and induction coefficients for the homodimers of Li2, Na2, K2 are evaluated in the LALBM scheme using explicit formulae presented previously and numerical values of moments, polarizabilities and dispersion constants obtained from 2-term reduced spectra of the Kaiserslautern group. While induction coefficients are 5–8 times smaller than dispersion, induction anisotropies are always larger than the corresponding dispersion anisotropies for all homodimers.

The C 8 and C 10 long-range induction coefficients for two like centrosymmetric linear molecules are derived explicitly using the irreducible properties of spherical tensor operators. An application to the H 2 –H 2 system shows that whereas the isotropic induction coefficients are 50–100 times smaller than dispersion, the induction anisotropies γ n are always larger than the corresponding dispersion anisotropies.

The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angledependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (1, 1′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, c10, and numerical results are presented for H2H2 using two-term reduced spectra values from the Kaiserlautern group.

The ternary diagram involving a rigid polymer [poly(p-benzamide) (PBA)], a flexible polymer [poly(2-phenylene(5-benzimidazole)isophthalamide) b) (PABI)] and a diluent composed of dimethylacetamide plus 3 wt.-% LiCl (DMAc/3LiCl) was investigated. Addition of PABI to PBA solutions increases the critical volume fraction value at which a nematic phase is observed. The line connecting these values at different PBA/PABI ratios divides a region of isotropic solutions from a biphasic area. No case of a single anisotropic phase was observed. A peculiarity of the diagram is that the composition of the anisotropic phase in the biphasic region lies on the PBA-diluent axis when the molecular weight of PABI is relatively high, whereas it shows a small content of PABI when its molecular weight is low. This result has recently been theoretically predicted by considering the existence of anisotropic interactions in the mesophase. The agreement between theoretical and experimental phase diagrams is fairly good.

It has been found that a method allowing the calculation of an anisotropic-isotropic transition volume fraction for a given semirigid polymer can be derived from the equations recently proposed by Blonski and coworkers to evaluate the equilibrium compositions of isotropic and anisotropic phases coexisting within ternary systems semirigid polymer/flexible polymer/solvent. By using the term anisotropic-isotropic transition volume fraction of a semirigid polymer we will refer to its smallest volume fraction giving an anisotropic character to liquid ternary phases also including a flexible polymer and a solvent. Its evaluation simplifies the construction of the corresponding ternary diagram and can also be seen as a fast and quantitative way of estimating the influence exerted by the semirigid polymer, through its intrinsic anisotropy, on ternary phases.

Results of an interlaboratory comparison on size characterization of SiO2 airborne nanoparticles using on-line and off-line measurement techniques are discussed. This study was performed in the framework of Technical Working Area (TWA) 34 - "Properties of Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS) in the project no. 3 "Techniques for characterizing size distribution of airborne nanoparticles". Two types of nano-aerosols, consisting of (1) one population of nanoparticles with a mean diameter between 30.3 and 39.0 nm and (2) two populations of non-agglomerated nanoparticles with mean diameters between, respectively, 36.2-46.6 nm and 80.2-89.8 nm, were generated for characterization measurements. Scanning mobility particle size spectrometers (SMPS) were used for on-line measurements of size distributions of the produced nano-aerosols. Transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were used as off-line measurement techniques for nanoparticles characterization. Samples were deposited on appropriate supports such as grids, filters, and mica plates by electrostatic precipitation and a filtration technique using SMPS controlled generation upstream. The results of the main size distribution parameters (mean and mode diameters), obtained from several laboratories, were compared based on metrological approaches including metrological traceability, calibration, and evaluation of the measurement uncertainty. Internationally harmonized measurement procedures for airborne SiO2 nanoparticles characterization are proposed. © 2013 Springer Science+Business Media Dordrecht.

The present chapter deals with multi-phase catalytic membrane reactors where the reactants distributed in different fluid phases meet on catalytic sites located in the structure of a catalytic membrane. The aim of the chapter is to summarize the features of catalytic membrane reactors applied to gas - liquid and liquid – liquid systems in order to show the capabilities, advantages and limitations of this class of emerging multi-phase reactors. In multi-phase systems, the catalytic membrane is usually used as an interface between two fluid phases and allows strict control of the reactant mass transfer with enhancement of the overall heterogeneous kinetics. Moreover, the particular features of the catalyst structured as a membrane can improve the intrinsic kinetics and the catalyst’s effectiveness. This chapter, by discussing some relevant points of catalytic membranes applied to multi-phase systems, aims at being a simple starting point for researchers who would like to begin their investigation in this fascinating field. After an introduction devoted to a first general description of multi-phase reactor systems, the chapter illustrates several contact modalities between reactants distributed in two different phases and the catalytic membrane. The role of mass transfer phenomena and reaction kinetics in multi-phase catalytic membrane reactors is discussed on the basis of simple well-known chemical engineering principles and modelling examples. Typical materials for multi-phase membrane reactors are briefly listed. Finally, some typical applications (e.g., hydrogenation and oxidation reactions) are reported.

The improvement in the convergence rate of the damped multipole expansion for the second order H-H+ induction energy due to the inclusion into the first-order function of a term satisfying the electron-proton cusp condition is quantitatively investigated. Following a technique suggested by Schwartz, the multipole contributions to the energy are put in the form of series ordered by inverse powers of the quantum number l. It is shown that, for high values of l, the dependence of the leading terms is raised from l -4 to l -6 by the cusp correction.

Following early work by Kutzelnigg on the correlation cusp, we have attempted to improve convergence of the damped multipole expansion of the second-order induction energy for H+ + by including a separately determined cusp correction of the form φ = f(r B)ψ0 into the first-order function in order to avoid divergency at the proton position when r B = 0. Three different cusp wavefunctions, all derived from the Taylor expansion of f(r B) into positive powers of r B have been examined, and the best compromise between simplicity and accuracy is found for the function φ = -r Bψ0. Few residual multipoles, variationally approximated in terms of one-centre linear pseudostates, are then found necessary to reproduce accurately the induction energy at the distance of the chemical bond.

Novel proton exchange membranes have been prepared by in synthesis functionalization of a polyurethane matrix with a sulfonic group containing chain terminals. The synthesis procedure was based on the use of two polyethylene glycols with nominal molecular weight of 300 and 1 k and 4,4′ dicyclohexylmethane diisocyanate in presence of the sodium salt of isethionic acid as a donor of the sulfonic group. Glycerol was added in order to improve by reticulation the stability of the cast films. The membranes were characterized in terms of swelling, morphology, methanol permeability, proton conductivity, and ion exchange capacity. The best H2/air cell performance was achieved at 80 °C with a maximum power density of 16.9 mW/cm2 at a voltage of about 0.35 V. Polyurethane based ionomeric membranes have proved to be interesting candidates for proton exchange membrane fuel cells (PEMFC) applications.

The aim of this work was to offer a state-of-the-art critical survey for characterizing airborne nano- and microparticles by means of electron microscopy (EM) techniques and to highlight advantages and limits of different possible operation modes. Procedures of collection and sample preparation are revisited and improved to analyse airborne particles deposited on filtering membranes by using various sampling methods. Three kinds of electron microscopes are used to this end: scanning electron microscope (SEM), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). Following and extending previous studies, we optimized procedures by varying both the sample collection/preparation and the operational parameters of the microscopes. In particular, we diversified the sampling methods applied, using ad hoc filters as well as common filters for standard gravimetric measures. This approach enabled us to achieve a simple and clean procedure allowing direct SEM or TEM observation of the collected particulate matter.

The bonding in van der Waals complexes is examined in the light of the physical nature of the components of the intermolecular energy. Attraction due to electrostatic, dispersion and induction contributions offsets the Pauli repulsion due to the exchange overlap of the closed-shell electron-charge distributions. Spherical tensor expansion of the intermolecular potential in the long range allows the attractive energy components to be related to the electric properties of the molecules, whose relative values explain the main features of the bonding in the van der Waals region. General formulae are derived for the dispersion coefficients of two linear molecules, showing explicitly the anisotropy of the interaction.

The N-term representation of the H atom static propagator in terms of a finite discrete set of linear excited pseudostates involving positive powers of the radial variable is used to calculate multipole components of nonexpanded induction and dispersion interactions at the bond length for H+ 2 and H2, nonexpanded dispersion coefficients for H2, and hydrogenic second-order energy for the He sequence. Even if convergence is sensibly slower than that observed for expanded perturbations, the N = 20 approximation is found to give results at worst within 1% of the accurate reference values from the literature.

The linear pseudo-spectrum giving exact polarizabilities and dispersion coefficients for H atoms is used as such in the hydrogenic perturbation-theory calculation of the partial-wave expansion of the second-order energy for the ground state of the He sequence. The results for the first six partial waves are highly accurate.

General formulae for the coefficients Cn shaping the long-range behaviour of electrostatic, induction and dispersion interactions between molecular systems, are given in terms of the spherical tensor theory in its real form. The coefficients depend on a function P, describing in a compact way the relative orientation of the partners, and the permanent and induced moments of the individual molecules. Use of a hypergeneralized London formula allows the molecular dispersion coefficients to be expressed in terms of static multipole polarizabilities and their related excitation energies. Explicit formulae are presented for the first few coefficients of the linear water dimer (H2O2)2. The transformation properties of the real spherical tensors under rotation and translation of the origin of the body-fixed reference frame are given in appendices, together with tables containing the coefficients needed in the expansion of the electric potential due to a non-uniform external field as well as the explicit relations connecting real spherical and cartesian forms for molecular moments and polarizabilities up to l = 3.

The k-dependent multipole expansion of rab−1 based on a Fourier transform allows for a compact analytical evaluation in Roothaan closed form of the general two-centre Coulomb integrals over STOs using the finite representation of spherical Bessel functions followed by contour integration in the complex plane.

A fast and simple method has been found to solve the set of equations recently proposed by Jonah, Brostow and Hess [Macromolecules 26, 76 (1993)], allowing the evaluation of the anisotropic-isotropic transition temperature for a semirigid liquid polymer. Starting with given values of η (average length of the rigid sequences coexisting with flexible sequences inside the semiflexible polymer chains) and θ (degree of rigidity of the semirigid polymer), a reduced transition temperature τ is readily obtained, together with the transition values of the anisotropic order parameters s and γ.

The Flory-Huggins equations concerning equilibria of two phases within ternary systems polymer/polymer/solvent are rewritten using a new set of variables. This allows the easy elimination of one of the unknowns of the problem, which can be further simplified, through the elimination of a second unknown, within regions of the diagram sufficiently near to a critical point.

A simple electrostatic model based on the characterization of a molecule by its first two observable electric moments is proposed for van der Waals dimers of polar molecules. The relative stability of different angular geometries of the complexes is deduced from a pictorial analysis of the first few electrostatic interactions between these moments. The predictions resulting for 67 angular geometries of 35 van der Waals dimers of small molecules are in agreement with experiment.

In the one-determinant approximation to the general theory of intermolecular interactions, the single interchange term describing penetration of slightly overlapping closed-shell molecules is shown to be equivalent to order S 2 to the overlap energy resulting from suitably defined overlap densities of the individual molecules, supplemented by a term which vanishes exactly for Hartree-Fock wavefunctions of the separate molecules.

The perturbative configuration interaction approach based on non-orthogonal bond-orbitals previously used for dealing with rotational barriers is applied to the study of the hydrogen bonding in the linear water dimer. First and second-order interaction energies are obtained in terms of static and transition charge distributions fully accounting for intermolecular overlap. Neglecting electron correlation, the second-order calculations include all single excitations from bonding to antibonding orbitals accounting for induction including exchange and giving results close to the corresponding supermolecular SCF-MOs in the same basis. Ab initio calculations using different gaussian minimal bases show that Clementi's GTO basis MEDIUM is the most suitable for describing molecular interactions. Detailed component analysis of the energy up to second order is possible and reveals the main features of the intermolecular hydrogen bonding occurring between the water molecules.

Direct ab initio calculation of long-range induction and dispersion interactions expended up to R−8 and evaluated at the SCF intermolecular separation for the complexes of He and Ne with HF shows that the angular shapes of such van der Waals atom-dipolar molecule dimers are determined by the absolute minima of the induction interaction.

The variational addition of polarization functions to energy-optimum scaled single-zeta SCF bond-orbitals gives second order results close to those obtained by full SCF calculations in a DZ + P basis. Ab initio bond-orbital calculations on the ground state of the water molecule using Clementi's GTO basis MEDIUM show that the introduction of 3d-polarization functions on the O atom (MEDIUM*) is essential to give a correct description of the equilibrium geometry, while the further addition of 2p-polarization functions on H (MEDIUM**) gives, to second order, a molecular energy which is within 26.6 mEh of the estimated Hartree—Fock limit. The resulting dipole moment is, however, too large even after correcting for the first-order distortion in the bond-orbital wavefunction, being as good as can be expected with an energy- optimized basis set of this quality.

In this paper we analyze the angular dependence of the expanded electrostatic interaction in seven van der Waals complexes made by dipolar molecules (HF, H 2 O, NH 3 ) giving H-bonding and homonuclear diatomics (H 2 , N 2 ) having a permanent quadrupole moment in their ground state. It is found that including terms up to R −5 the absolute minima of the expanded electrostatic interaction evaluated at the experimental intermolecular separation converge to a reasonably accurate estimate of the angular shape actually observed for such van der Waals dimers.

Ab initio calculations on twenty van der Waals dimers of small polar molecules at the experimentally observed intermolecular separation R, using Hartree-Fock molecular moments, show that the minima in the electrostatic interaction expanded up to R−6 converges to angular structures which are close to those observed experimentally for such complexes.