Chainlength effects on interactions of polyvinylpyrrolidone with low and high molecular compounds

Very narrow fractions of polyvinylpyrrolidone (PVP) for a range of low molecular weight from 20·10³ to $\text{\&{;10}{}^3$ were prepared by gel filtration using sephadex gel. Interactions between fractions of different M_n and small molecules (iodine and 1-anilinonaphthaline-8-sulphonate) and polymers (polymethacrylic and polyacrylic acids) were studied in aqueous solution. The ability of PVP to form complexes with low molecular weight compounds depends on chainlength. The greatest loss of the ability was observed for PVP with M_n on passing from 5·10³ to $\text{\&{;10}{}^3$. The chainlength effects for PVP are accounted for an unlike dehydration and unlike “local” link concentration near links for these macromolecules in water. For PAA and PMAA. the threshold values of M?_n, below which there is the beginning of weakening of complexation for PVP, are 6·10³ and 2.5·10³ respectively. The difference of the complex formation for these polyacids appears to be related to hydrophobic interactions between the χ-methyl groups of PMAA and nonpolar regions of PVP.     

Dielectric response of modified Hubbard models with neutral-ionic and Peierls transitions

The dipole P(F) of systems with periodic boundary conditions in a static electric field F is applied to one-dimensional Peierls-Hubbard models for organic charge-transfer (CT) salts. Exact results for P(F) are obtained for finite systems of N=14 and 16 sites that are almost converged to infinite chains in deformable lattices subject to a Peierls transition. The electronic polarizability per site, alpha(el)=(partial differential P/partial differential F)0, of rigid stacks with alternating transfer integrals t(1+/-delta) diverges at the neutral-ionic transition for delta=0 but remains finite for delta>0 in dimerized chains. The Peierls or dimerization mode couples to charge fluctuations along the stack and results in large vibrational contributions alpha(vib) that are related to partial differential P/ partial differential delta and that peak sharply at the Peierls transition. The extension of P(F) to correlated electronic states yields the dielectric response kappa of models with neutral-ionic or Peierls transitions, where kappa peaks >100 are found with parameters used previously for variable ionicity rho and vibrational spectra of CT salts. The calculated kappa accounts for the dielectric response of CT salts based on substituted TTF's (tetrathiafulvalene) and substituted CA's (chloranil). The role of lattice stiffness appears clearly in models: soft systems have a Peierls instability at small rho and continuous crossover to large rho, while stiff stacks such as TTF-CA have a first-order transition with discontinuous rho that is both a neutral-ionic and Peierls transition. The transitions are associated with tuning the electronic ground state of insulators via temperature or pressure in experiments, or via model parameters in calculations.     

The Picard Theorem on S-metric spaces

Recently, the notion of an S-metric space is defined and extensively studied as a generalization of a metric space. In this paper, we define the notion of the S∞-space and prove its completeness. We obtain a new generalization of the classical "Picard Theorem".     

Sizing Polydisperse Dispersions by Focused Beam Reflectance and Small Angle Static Light Scattering

In this work, two different methods for particle characterization, namely focused beam reflectance and small angle static light scattering, are quantitatively compared. The results are presented in the form of moment ratios of the particle size distribution, i.e., the number weighted diameter, D_1/0, and the volume weighted diameter, D_4/3, for a broad range of particle size distributions ranging from 20 to 400 μm. Various aqueous dispersions including narrow, broad, and bimodal particle size distributions of spherical shaped ceramic beads were used in the comparison. It was found that the moment ratios obtained by focused beam reflectance measurements and small angle static light scattering correlate well, in the case of spherical particles. Furthermore, it was found that the D_1/0 values obtained by focused beam reflectance measurements are more sensitive to the presence of a small fraction of fine particles in a bimodal distribution than those obtained by small angle static light scattering.     

Giant infrared intensity of the Peierls mode at the neutral-ionic phase transition

We present exact diagonalization results on a modified Peierls-Hubbard model for the neutral-ionic phase transition. The ground state potential energy surface and the infrared intensity of the Peierls mode point to a strong, nonlinear electron-phonon coupling, with effects that are dominated by the proximity to the electronic instability rather than by electronic correlations. The huge infrared intensity of the Peierls mode at the ferroelectric transition is related to the temperature dependence of the dielectric constant of mixed-stack organic crystals.     

Beitr?ge zur Gasanalyse. II. Die Bestimmung des Acetylens.

Zusammenfassung Die Ergebnisse unserer Untersuchungen zur Bestimmung von Acetylen können wie folgt zusammengefaßt werden:Wenn CO₂ nicht zugegen ist, wendet man beim Verfahren der Volummessung die alkalische QuecksilberII-cyanidlösung in einer Konzentration von 40% an. In diesem Fall stört das Äthylen nicht. In Gegenwart von CO₂ wird 10%ige Silbernitratlösung angewendet.In Abwesenheit von CO₂ wird bei der Methode der Druckmessung das Acetylen durch alkalische 40%ige QuecksilberII-cyanidlösung absorbiert, wenn das Äthylen nicht stört. Wenn CO₂ und C₂H₂ gleichzeitig zugegen sind, wird 40%ige Silbernitratlösung angewendet.     

Neutral and charged excited states in polar organic films: origin of unusual electroluminescence in tri-p-tolylamine-based hole conductors

The photoluminescence (PL) and electroluminescence (EL) of thin films of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) are remarkably different. Similar PL and EL are instead observed in films of the closely related donors tri- p-tolylamine (TTA) and N, N'-diphenyl- N, N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD). Such films show a wide range of hole transport that depends on the morphology and on external parameters such as temperature and electric field. Restricted configuration-interaction calculations performed on TTA, TAPC, TPD, and radical ions of TTA indicate that the unusual EL of TAPC films is due to direct recombination from a low-lying charge-transfer (CT) state. The CT state is strongly stabilized by electrostatic interactions with the polar environment. Theory confirms that TAPC can be considered a dimer of TTA. The charge distributions of TTA (+) and TTA (-) indicate charge localization in the anion that rationalizes low electron mobility as well as a strong charge-induced-dipole stabilization of the CT state.     

Population balance modeling of aggregation and breakage in turbulent Taylor-Couette flow

An experimental and computational study of aggregation and breakage processes for fully destabilized polystyrene latex particles under turbulent-flow conditions in a Taylor-Couette apparatus is presented. To monitor the aggregation and breakage processes, an in situ optical imaging technique was used. Consequently, a computational study using a population balance model was carried out to test the various parameters in the aggregation and breakage models. Very good agreement was found between the time evolution of the cluster size distribution (CSD) calculated with the model and that obtained from experiment. In order to correctly model the left-hand side of the CSD (small clusters), it was necessary to use a highly unsymmetric fragment-distribution function for breakage. As another test of the model, measurements with different solid volume fractions were performed. Within the range of the solid volume fractions considered here, the steady-state CSD was not significantly affected. In order to correctly capture the right-hand side of the CSD (large aggregates) at the higher solid volume fraction, a modified aggregation rate prefactor was used in the population balance model.     

Experimental and modeling study of breakage and restructuring of open and dense colloidal aggregates

In this work we present experimental and simulation analysis of the breakage and restructuring of colloidal aggregates in dilute conditions under shear. In order to cover a broad range of hydrodynamic and interparticle forces, aggregates composed of primary particles with two sizes, d(p) = 90 and 810 nm, were generated. Moreover, to understand the dependence of breakage and restructuring on the cluster structure, aggregates grown under stagnant and turbulent conditions, having substantially different initial internal structures with fractal dimension d(f) equal to 1.7 and 2.7, respectively, were used. The aggregates were broken by exposing them to a well-defined elongational flow produced in a nozzle positioned between two syringes. To investigate the evolution of aggregate size and morphology, respectively, the mean radius of gyration, , and d(f) were monitored during the breakup process using light scattering and confocal laser scanning microscopy. It was found that the evolution of aggregates' fractal dimension during breakage is solely controlled by their initial structure and is independent of the primary particles size. Similarly, the scaling of the steady-state vs the applied hydrodynamic stress is independent of primary particle size, however, depends on the history of aggregate structure. To quantitatively explain these observations, the breakage process was modeled using stokesian dynamics simulations incorporating DLVO and contact interactions among particles. The required flow-field for these simulations was obtained from computational fluid dynamics. The complex flow pattern was simplified by considering a characteristic stream line passing through the zone with the highest hydrodynamic stress inside the nozzle, this being the most critical flow condition experienced by the clusters. As the flow-field along this streamline was found to be neither pure simple shear nor pure extensional flow, the real flow was approximated as an elongational flow followed by a simple shear flow, with a stepwise transition between them. Using this approach, very good agreement between the measured and simulated aggregate size values and structure evolution was obtained. The results of this study show that the process of cluster breakup is very complex and strongly depends on the initial aggregate structure and flow-field conditions.