Structure of a poly(2,5‐benzimidazole)/phosphoric acid complex

As‐cast films of poly(2,5‐benzimidazole) exhibit uniplanar orientation in which the planes of the aromatic rings lie parallel to the film surface. Upon doping with phosphoric acid, the original crystalline order is lost, but the doped film can be stretched to produce films with uniaxial orientation. After thermal annealing at 540 °C, nine Bragg reflections are resolved in the fiber diagram, and these are indexed by an orthorhombic unit cell with the dimensions a = 18.1 Å, b = 3.5 Å, and c = 11.4 Å, containing four monomer units of two chains. The absence of odd‐order 00l reflections points to a 2₁ chain conformation, which is probably planar so that the aromatic units can be stacked along the b axis. The water and phosphoric acid contents of the crystalline structure cannot be determined exactly because of the presence of extensive amorphous regions that probably have different solvation. The best agreement between the observed and calculated intensities is for an idealized structure containing two phosphoric acids and two water molecules per unit cell. However, the phosphoric acid is probably present mainly in the form of pyrophosphoric acid and its higher oligomers. In addition, the X‐ray data are consistent with a more disordered structure containing chains with random (up and down) polarity and a lack of c‐axis registry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2576–2585, 2004     

Determination of the degree of cure under dynamic and isothermal curing conditions with electrical impedance spectroscopy

This article presents a new methodology for the quantitative determination of the progress of the curing reaction of a thermosetting resin, using the results of electrical impedance spectroscopy. The method is an extension of the use of the imaginary impedance maximum as a reaction progress indicator and is based on the demonstration of a close correlation between the reaction rate, as measured by conventional differential scanning calorimetry, and the rate of change of the value of the imaginary impedance spectrum maximum. Tests on a commercial aerospace epoxy resin under both isothermal and dynamic heating conditions with calorimetry and impedance spectroscopy have demonstrated the validity of the method and set the accuracy limits involved. This technique can be used as a real-time online control tool for thermoset composite manufacturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 146–154, 2004     

Solvent‐ and interface‐induced surface segregation in blends of isotactic polypropylene with poly(ethylene‐co‐propylene) rubber

The surface compositions and morphologies of melt‐quenched blends of isotactic polypropylene (iPP) with aspecific poly(ethylene‐co‐propylene) rubber (aEPR) were characterized by atomic force microscopy, optical microscopy, and X‐ray photoelectron spectroscopy. The surface morphologies and compositions formed in the melt are frozen‐in by crystallization of the iPP component and, depending on the processing conditions, are enriched in iPP or aEPR or contain a phase‐separated mix of iPP and aEPR. Enrichment of iPP is observed for blends melted in open air, in agreement with earlier work showing the high surface activity of atactic polypropylene at open interfaces. Surface segregation of iPP is suppressed at confined interfaces. Blends melt‐pressed between hydrophilic and hydrophobic substrates have phase‐separated iPP and aEPR domains present at the surface, which grow in size as the melt time increases. Surface enrichment of aEPR is observed after exposing melt‐pressed blends to n‐hexane vapor, which preferentially solvates aEPR and draws it to the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 421–432, 2004     

Statistical thermodynamics evaluation of polymer–polymer miscibility

The Simha and Somcynsky (S–S) statistical thermodynamics theory was used to compute the solubility parameters as a function of temperature and pressure [δ = δ(T, P)], for a series of polymer melts. The characteristic scaling parameters required for this task, P*, T*, and V*, were extracted from the pressure–temperature–volume (PVT) data. To determine the potential polymer–polymer miscibility, the dependence of δ versus T (at ambient pressure) was computed for 17 polymers. Close proximity of the δ versus T curves for four miscible polymer pairs: PPE/PS, PS/PVME, and PC/PMMA signaled the usefulness of this approach. It is noteworthy, that the tabulated solubility parameters (derived from the solution data under ambient conditions) propounded the immiscibility of the PVC/PVAc pair. The computed values of δ also suggested miscibility for polymer pairs of unknown miscibility, namely PPE/PVC, PPE/PVAc, and PET/PSF. In recognizing the limitations of the solubility parameter approach (the omission of several thermodynamic contributions), these preliminary results are auspicious because they indicate a new route for estimating the miscibility of any polymeric material at a given temperature and pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2909–2915, 2004     

Comparative energies of Zn(II) cation localization as a function of the distance between two forming cation position aluminium ions in high-silica zeolites

Periodical calculations of Zn(II) metal cation stabilization in cationic positions with distantly placed aluminium ions has been performed for high-silica ferrierite. It was found that decrease of the stabilization energy at large distances between Al ions (more than 10 Å) is about of 2 eV in comparison with nearest possible position of two Al ions in the zeolite lattice and weekly depended on following increase of the Al-Al distance. Main changes in stabilization energy occured within a 3-Å interval of these distances. Only for the localizations of both Al ions in one zeolite ring zinc cationic form is more stable than hydrogen form.     

EQCM Study of the Couple Thallium(I)/Thallium Amalgam at a Thin Film Mercury Electrode

EQCM and voltammetric data show that thallium(I) ions, which are adsorbed in the region of the positive surface charge, most probably, in the form of the ionic pairs, are not reduced. In this potential region, thallium(I) ions are reduced directly from the solution. At more negative potentials, the previously adsorbed stable ionic pairs slowly undergo transition into the less stable form. From this form, thallium(I) ions can be reduced or desorbed into the solution. The process is best described by a model of one electron, i.e., full charge transfer.     

Radioactive Tracer Study of the Displacement of Iodine Adatoms from Platinized Platinum Electrode by Carbon Monoxide

Radioactive tracer studies confirm the earlier electrochemical results that carbon monoxide can virtually completely displace iodine adatoms. For the first time, it is found that iodine adatoms are not displaced by carbon monoxide when iodide anions are adsorbed in the presence of an upd silver monolayer. The possible reasons for the effect observed are discussed.     

Two-Layered Poly-o-phenylenediamine/Polyaniline Composite: Electrosynthesis and Spectroelectrochemical Properties

Spectroelectrochemical properties of poly-o-phenylenediamine (PPD) and the synthesized composite of PPD and polyaniline—two chemically related polymers containing an amino-substituted benzene ring but having different conduction nature—are studied. The polyaniline synthesis on PPD-modified electrodes involves stages of the reaction initiation, the copolymer formation, and the formation of a polyaniline layer at the copolymer/solution interface.     

Adsorption of Kryptate Complexes of Alkali Metals in Electrolytes of Different Compositions and in the Presence of 1-Adamantanol

Data on the adsorption of kryptates of alkali metals on a mercury electrode are obtained for the first time by a method of the measurement of the differential capacitance as a function of potential and are compared to one another. Shown is that there takes place a deep mutual relationship between the structure of a complex and the regularities of its adsorption. An assumption is put forth about the possibility of adsorption of a free ligand in solutions of lithium kryptate, which possesses relatively low strength. The co-adsorption of sodium kryptate with 1-adamantanol, which forms a two-dimensional condensed layer, is investigated. Established is that the C vs. E curves, obtained in 1 M Na₂SO₄ at a constant activity of 1-adamantanol and a varying concentration of Kryptofix^R 222, exhibit two distinctly pronounced portions, each of which corresponds to predominant adsorption of one of the surface-active components. The region of predominant adsorption of Kryptofix^R 222 expands with its concentration.     

Physicochemical and Acoustic Properties of Water-Based Magnetic Colloid

A velocity and absorption coefficient of sound for magnetic fluid (MF) based on water are studied in the frequency range of 12–132 MHz as a function of the concentration of dispersed phase, the uniform magnetic field, the storage time, and the temperature. The MF dispersed phase consist of magnetite Fe₃O₄ particles stabilized with sodium oleate. The parameters of sound propagation are measured within temperature interval 0–80°C. Densities of MF and sodium oleate are also measured as a function of temperature. Volume concentrations of magnetic fluid components (water, magnetite, and sodium oleate adsorbed on the surface of magnetic particles) are determined. Densities, heat capacities, coefficients of heat conductivity and thermal expansion of aggregates are estimated. Aggregate size distribution in the studied magnetic fluid is described by the log-normal function. Parameters characterizing the aggregate size distribution are determined and their interpretation is given.