Correlation between structure and stress-strain characteristics of metallic coatings deposited onto a polymer by the method of ionic plasma sputtering

Data on the strength of coatings based on noble metals (Pt, Au) deposited onto PET films by the method of ionic plasma sputtering are analyzed. In addition to precipitation of the metal, this mode of deposition is accompanied by modification of the surface polymer layer due to its interaction with plasma. As a result, a complex three-layered structure near the polymer surface forms. A new method for estimating the strength of coatings deposited onto polymer supports is advanced. This method makes it possible to analyze stress-strain characteristics of the three-layered systems that emerge owing to deposition of nanoscale layers of noble metals on polymer films via ionic plasma sputtering. The proposed relationships are in fair agreement with the experimental data.     

The effect of the physicomechanical characteristics of the polymer matrix and structure of a filler on the stress-strain behavior of polymer-montmorrilonite nanocomposites

The stress-strain behavior of PE-Na⁺-montmorillonite nanocomposites is studied. The stress-strain characteristics of the composites are shown to be controlled by the structure of their nanofiller, which is formed upon melt mixing of the polymer and layered silicate (intercalated or exfoliated), the profile of the stress-strain curve of PE matrix, and the fracture mechanism (either adhesive or cohesive). In nanocomposites with a strong adhesive bonding between matrix and clay particles (under cohesive fracture), both the modulus and yield point are found to be markedly increased. In the case of adhesive fracture, mechanical characteristics are less improved due to debonding between matrix and filler results. For nanocomposites, experimental stress-strain characteristics are compared with theoretical estimates calculated according to the models proposed for predicting the characteristics of filled thermoplastic polymers. In some cases, experimental values of modulus and elongation at break appear to differ appreciably from theoretical estimates. The applied models should take into account the orientation of anisodiametric inclusions in a polymer matrix and the character of separation in the composite (adhesive or cohesive).     

The influence of concentration and anion nature on the support effect

The kinetic of decomposition of copper formate, acetate, propionate and butyrate under non-isothermal conditions was studied. The support materials were carborundum and silica and the concentrations of the supported compounds were 15, 20, 25 and 30 mass%. In order to avoid the effects of thermal gradients and dilution, a series of parallel samples of carboxylate/support mixtures with the same concentration were studied. The support effect was estimated by the difference between the isokinetic temperature of the supported, respectively mixted carboxylate series, and is discussed in connection with the precursor concentration and the nature of the carboxylate anion. The suggestion of considering the thermodynamic activation function instead of the Arrhenius parameters for discussion on compensation effect was argued. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of the nature of a nanoparticle and polymer matrix on the morphological characteristics of polymeric nanostructures

Comparative studies of the morphological characteristics of selenium- and platinum-containing nanostructures were performed by molecular optics methods. The nanostructures were based on an ionogenic polymeric stabilizer, poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate, and a non-ionogenic polymeric stabilizer, oxyethylcellulose. Studies were performed in aqueous solutions at a fixed ratio between components. The adsorption of a considerable number of polymer macromolecules on nanoparticles with the formation of superhigh-molecular-weight nanostructures with shapes close to spherical was observed for all the nanosystems studied. The thermodynamic state of nanosystems was characterized. Certain morphological characteristics of nanostructures were substantially influenced by the nature of both nanoparticles and polymer matrix.     

Nanodiamonds effect on characteristics of copper galvanic coatings

The introduction of nanodiamonds (Technical Specification TU 3974-001-10172699-94) into a sulfuric acid electrolyte of copper plating was shown to result in decreased porosity and the corresponding diminishing of the electric resistance of the copper coatings.     

Investigations of the effect of viscosity of resin on the diffusion of pyrene in silicone polymer coatings using steady state fluorescence technique

The diffusion phenomenon of pyrene in silicone coatings prepared from various commercial silicone resins with different viscosities was investigated using steady state excimer fluorescence technique. The amount of pyrene lost from the coatings by diffusion at different temperatures ranging from 25 to 70 °C was estimated from the excimer emission intensity. The diffusion coefficients (D) and activation energy of diffusion of pyrene in silicone coatings were determined. It was found that the kinetic parameters of pyrene were comparable in all the four silicone coatings and independent of the viscosity of the resin. The D values were lower than those expected for pyrene in PDMS resins in the corresponding viscosity range. This may be attributed to restricted mobility of pyrene due to cross-linking of polymer chains in the cured silicone coatings.     

On the physical nature of mesophases of guanosine gels

The unusual columnar aqueous mesophases of self-assembled guanosine stacks, such as 2'-deoxyguanosine 5'-monophosphate and 2'-deoxyguanosine 3'-monophosphate, are analyzed in terms of a general theory of azimuthal correlations between the charged helices. This theory considers forces, specific to the helical structure of each macromolecule, which depend on the azimuthal orientations of the molecules about their long axes. More specifically, in determining the magnitudes and decay lengths of these helix specific forces we utilize the Kornyshev-Leikin theory of electrostatic interaction between helical macromolecules and quantitatively fit experimental data. Together with explaining a number of the observed features of these mesophases, several new effects are predicted. Possible limitations and developments of our theoretical model are discussed, as well as new experiments to test the implications of the theory.     

The effect of the steric hindrance on metallic cation conduction in polymer electrolytes

2,6-Di-t-butylphenol and oligo(ethylene oxide) bound covalently to polyisocyanate were synthesized and characterized. The ionic conductivities of their Li, Na, and K phenolates were studied at various temperatures. The conductivities were in the range of 10^?7?10^?5 S/cm at 30°C. The conductivity of Na and K salts was approximately 10² greater than that of the Li salts. The t-butyl groups serve to dissociate K and Na ions from the phenoxide. The cations, therefore, are more mobile as a result increasing the conductivity. The temperature dependence of ionic conductivity suggests that the migration of ions is controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel–Tammann–Fulchere plots. The polyisocyanate backbone is a rather stiff structure, however, a flexible oligo(ethylene oxide) side chain forms complexes with metal ion. Since the ion transport is associated with the local movement of polymer segments, the rigidity of the polymer backbone does not have much influence on the ion mobility.     

The effect of physical state on the drug dissolution rate

In this work, the enhancement of drug dissolution rate through the preparation of new formulations containing Nimodipine in molecular level dispersion or in nanodispersion into poly(vinyl pyrrolidone) (PVP) matrix, was investigated. Differential scanning calorimetry (DSC) and modulated-temperature differential scanning calorimetry (MTDSC) in combination with X-ray powder diffractometry (XRPD) and scanning electron microscopy (SEM) studies showed that Nimodipine was amorphous in solid dispersions of 10 or 20 mass%, and mainly dispersed on a molecular level. This behaviour is attributed to the strong interactions taking place between the amine group of Nimodipine and carbonyl group of PVP. At higher drug loadings, crystal reflections in XRPD patterns and melting peaks of Nimodipine in DSC traces, indicated presence of drug in crystalline form. Micro-Raman studies in combination with SEM micrographs showed that the mean particle size increases with drug content in the formulations, up to 10 μm. Moreover, both XRPD patterns and micro-Raman spectra seem to indicate that Nimodipine crystallized in a second, thermodynamically stable, crystal modification II. The physicochemical characteristics of Nimodipine and the particle size distribution directly affect the dissolution rate enhancement, which is higher in amorphous dispersions.     

On the equation of state of polymer solutions

The theory formulated for single and multicomponent systems is applied to polymer solutions. This follows earlier investigations on mixtures of low molecular weight compounds and a binary compatible polymer mixture. The requisite analysis of the polymer constituents, namely polyisobutylene and poly(dimethylsiloxane) shows good agreement between experiment and theory. Similar conclusions apply to the solvents, namely cyclohexane, benzene and hexa(methyl disiloxane). For the solutions, the theory makes predictions at elevated pressures, based on the equation of state of the constituents and low pressure experimentation for the mixtures. Satisfactory results obtain in this manner with deviations increasing with temperature and pressure (maximally 1 kbar). At low pressures, the agreement between experiment and theory is good for all temperatures and compositions.     

On the nature of the anomeric effect

Calculations of the interaction energies of heteroatoms X and Y unshared electron pairs in structures (I) and (II) have been performed for molecules of 2-methoxytetrahydropyran and fluoromethanol, by semi-empirical EHMO and CNDO/2 methods, as well as by classical dipole-dipole approximation. This type of interaction was shown not to be a factor responsible for the stability of the gauche structure (II). The current interpretation that the anomeric effect is an electrostatic interaction of heteroatom unshared electron pairs (the “rabbit ears” effect) is, therefore, groundless.     

On the nature of the multivalency effect: a thermodynamic model

A quantitative model is proposed for the analysis of the thermodynamic parameters of multivalent interactions in dilute solutions or with immobilized multimeric receptor. The model takes into account all bound species and describes multivalent binding via two microscopic binding energies corresponding to inter- and intramolecular interactions (Delta G(o)inter and Delta G(o)intra), the relative contributions of which depend on the distribution of complexes with different numbers of occupied binding sites. The third component of the overall free energy, which we call the "avidity entropy" term, is a function of the degeneracy of bound states, Omega(i), which is calculated on the basis of the topology of interaction and the distribution of all bound species. This term grows rapidly with the number of receptor sites and ligand multivalency, it always favors binding, and explains why multivalency can overcome the loss of conformational entropy when ligands displayed at the ends of long tethers are bound. The microscopic parameters and may be determined from the observed binding energies for a set of oligovalent ligands by nonlinear fitting with the theoretical model. Here binding data obtained from two series of oligovalent carbohydrate inhibitors for Shiga-like toxins were used to verify the theory. The decavalent and octavalent inhibitors exhibit subnanomolar activity and are the most active soluble inhibitors yet seen that block Shiga-like toxin binding to its native receptor. The theory developed here in conjunction with our protocol for the optimization of tether length provides a predictive approach to design and maximize the avidity of multivalent ligands.     

The metallic orbital and the nature of metals

In 1938 it was noticed (L. Pauling, Phys. Rev.54, 899, 1938) that about 0.72 of the nine outer spd orbitals per atom of a transition metal remain unoccupied by bonding electrons, unpaired ferromagnetic electrons, or unshared electron pairs. In 1948 this 0.72 orbital per atom was identified (L. Pauling, Nature (London)161, 1019, 1948; Proc. Roy. Soc. A196, 343, 1949) as required for the unsynchronized resonance that confers metallic properties on a substance, and it was named the metallic orbital. A statistical theory of unsynchronized resonance of covalent bonds in a metal with atoms restricted by the electroneutrality principle to forming bonds only in number v ? 1, v, and v + 1, with v the metallic valence, has now been developed. This theory leads directly to the value 0.70 ± 0.02 for the number of metallic orbitals per atom, in reasonable agreement with the empirical value, and to the conclusion that M⁺, M⁰, and M^? occur in the ratios near 28:44:28. It leads also to the conclusions that stability of a metal or alloy increases with increase in the ligancy and for a given value of the ligancy is a maximum for valence equal to half the ligancy. These results with consideration of the repulsion of unshared electron pairs on adjacent atoms go far toward explaining the selection of different structures by different elemental metals and intermetallic compounds.     

Hypercrosslinked polystyrene: A polymer in a non‐classical physical state

Deformation and relaxation properties of hypercrosslinked polystyrene networks have been studied by thermomechanical method at a uniaxial compression using individual spherical beads of the polymer. The networks examined were prepared by postcrosslinking of highly swollen beads of a styrene‐0.3% DVB copolymer with 0.3–0.75 mole of monochlorodimethyl ether, which results in the introduction of 0.6–1.5 methylene bridges between each two polystyrene phenyl rings. The polymers obtained are shown to belong neither to typical glassy materials, nor to typical elastomers. Though no characteristic plateau of rubberlike elasticity was observed on the deformation curves of the beads, the polymers exhibit two fundamentally important features of the rubberlike state: The deformations are large (up to 30–40% of the initial diameter) and reversible. Relaxation of residual deformations, however, requires prolonged heating of the sample, or a cycle of swelling and drying. The deformation can start in the temperature range from −70 to +150°C depending on pressure applied. The crosslinking degree in the range from 40–100% and higher does not affect noticeably the behavior of the hypercrosslinked polystyrene. Nature of the high mobility of the hypercrosslinked network is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2324–2333, 1999     

On the nature of the fluorescent state of methylated indole derivatives

A quantitative study has been made of the solvent effects on the fluorescence properties of 1- and 3-methyl indole, with the aim of further understanding the origin of the unusually large Stokes shift in polar solvents. For the derivatives considered here the fluorescence transition probability is decreased in solvents of moderate and high polarities, and the spectrum shifts to the red. The data (in two-component, solute and solvent, systems) can be interpreted on the basis of the stabilisation, by solvent-solute relaxation, of a state with an increased charge-transfer character, relative to the initially excited state. Å consideration of the decay data for other indole derivatives suggests that this state has its origin in the ¹L₄ state (S₂ in non-polar media). Thus we conclude that the appropriate label of the fluorescent state of many substituted indoles in polar solvents is ¹L_a/CT. This is consistent with the observed solvent, temperature, time and substituent dependence of the decay kinetics of these derivatives.     

The effect of the nature and the state of the surface of highly dispersed silicon, aluminum, and titanium oxides on their sorption characteristics

The results of investigations into the surface of highly dispersed oxides and their interaction with water and certain other adsorbates by experimental (NMR, OS, LCS, TPD, etc.) and theoretical methods are reviewed. Institute of Surface Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 03028, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 1, pp. 1–29, January–February, 2000.     

The synthesis of oligodeoxyprimidines on a polymer support

A polymer supported method for synthesizing deoxypolynucleotides is described. Two non-anucleotides were synthesized. Yields exceeding 90% were obtained for each condensation. The time per nucleotide addition was four hours.     

Solid state NMR of a polymer composite and of a polymer blend

Although nuclear magnetic resonance may not seem the technique of choice to study interfaces between components in a polymer composite or polymer blend because of its inherent low sensitivity, for certain systems solid state NMR techniques can emphasize the signals from these interfaces. In case of a composite material with an inorganic filler (particles, fibers) cross-polarization or dipolar dephasing techniques from protons in the organic matrix or in the interphase to nuclei in the filler can be used to selectively observe the nuclei in the surface of the filler. Any changes at the filler surface caused by the presence of the matrix or coupling agent can then be detected. An example of glass reinforced nylon modelcomposites is discussed. The same techniques can also be used to study interphases in polymer blends when one of the components contains a NMR nucleus that is not present in the other component. As an example the blend poly(vinylidene fluoride)-poly(methyl methacrylate) is studied and it is shown that such techniques can provide very detailed information about the miscibility at a molecular scale.