Morphology of adsorbed polymers and solid surface wettability

The adsorption of a polyacrylamide (MW 14600) and two polysaccharides (MW 9260 and 706 x 10(3)) onto model silica surfaces of different hydrophobicities was investigated. In all cases, adsorption adhered to the Freundlich isotherm, reflecting the heterogeneous character of the solid substrates. The latter strongly influenced the character of the adsorbed polymer, with morphologies from chainlike structures to thin films and patches being observed. Surface roughness, polymer type, and molecular weight also play roles in controlling adsorbed polymer morphology. Surface wettability is strongly influenced by the thickness of the adsorbed layer.     

Structural properties and state of the surface layer of zirconium dioxide modified by tungstate anions

A tetragonal metastable phase of zirconium dioxide formed after the addition of tungstate anions (>13 mol %) to the hydroxide precursor by different methods with heating (600–700°C), as revealed by X-ray diffraction analysis and X-ray photoelectron and IR spectroscopy. The W⁶⁺ and W⁵⁺ cations formed a solid solution with ZrO₂. On the surface of the solid solution, the tungsten cations formed tungstate clusters (?WO _x ?)n. The formation of the WO₃ phase was observed at concentrations of tungstate anions higher than 17.6 mol % or at temperatures of 850–870°C.     

The reduction of gold nanoparticles in the surface layer of modified silica

Silicas with deposited hydridepolysiloxane layers were used for the in situ preparation of gold nanoparticles by the reduction of metal ions from a solution of chloroauric acid. The metal-containing silicas obtained were characterized by X-ray powder diffraction, transmission electron microscopy, and UV, IR, and laser correlation spectroscopy.     

Effect of top layer swelling on the oxygen/nitrogen separation by surface modified polyurethane membranes

Cobalt(II) was chelated on the surface of a hydroxyl terminated polybutadiene (HTPB) based polyurethane (PU) membrane. The surface of a HTPB based PU membrane was first modified by ethylenediamine (EA) plasma. The cobalt chelated membrane was prepared by immersing the plasma treated membrane into a cobalt(II)/formamide solution for various length of time. For a fair comparison, the untreated and plasma treated membranes were also immersed in formamide solution. The gas transport properties of all three membranes were compared. Without solvent immersion, the O₂/N₂ selectivity increased from 2.6 to 3.1 after EA plasma treatment. But the permeability decreased from 0.88 GPU to 0.35 GPU. The selectivity was further improved to 4.4 by immersing the plasma treated membrane in a solution of CoCl₂·6H₂O/formamide for 1 h, but the permeability decreased to 0.23 GPU. The solvent immersion had little effect on the transport properties of the untreated membrane. But the transport properties of the plasma treated and cobalt chelated membranes were greatly affected by the formamide immersion. The oxygen and nitrogen permeabilities of the modified top layers could be calculated from a series model for composite membranes. It was found that both the permeability and selectivity of the top layer of the plasma treated membrane increased with the solvent immersing time. For the top layer of the cobalt chelated membrane, the gas permeability first decreased after 1 h immersion and then increased after further immersion in CoCl₂·6H₂O/formamide solution. The selectivity of cobalt chelated membrane increased as the gas permeability decreased and vice versa. These results implied that the EA grafting enhanced the O₂/N₂ selectivity by increasing its oxygen affinity but the cobalt chelating increased the O₂/N₂ selectivity by enhancing the size sieving effect.     

Quantification of fluorine density in the outermost atomic layer

The outermost atomic layer of perfluorinated thiol monolayers on gold and poly(tetrafluoroethylene) (PTFE) is analyzed by low-energy ion scattering. Absolute quantification of fluorine density in this layer was achieved after calibrating the fluorine signal with a freshly cleaved LiF(100) single crystal. The fluorine density of monolayers of a C8F17-thiol on gold was 1.48 x 10(15) F atoms/cm2, whereas for PTFE a value of 1.24 x 1015 F atoms/cm2 was observed. This difference was explained by the different tilt angles of the thiol on gold and PTFE chains with respect to the surface normal. Both a configurational and a molecular interpretation on the perfluorinated thiol monolayer on gold are given.     

Morphology of organosilicon ladder polymers

The morphology of organosilicon ladder polymers was studied by various methods, including x-ray techniques, diffraction of monochromatic polarized light, and electron microscopy. The morphology is discussed as a function of the chemical composition, the molecular weight, and the method of preparation.     

Quantitative analysis of gaseous diffusion in glassy polymers

The current theoretical treatment of diffusion of gases in glassy polymers is based on the “dual sorption” model, but also includes certain other important assumptions, at least some of which cannot be fully justified a priori. They require experimental validation, which, however, is not possible by the procedures used or proposed so far. Methods suitable for this purpose are discussed here.     

Recovery of photodegraded polymers by surface treatment

A two-step process has been developed in order to renovate highly photodegraded polymers. It was applied to clear and pigmented commercial PVC plates, which were exposed to accelerated weathering. The brown highly degraded top layer was first removed by sandpapering, which makes the color disappear and restores the original impact resistance of PVC. In a second step, a thin film of a UV-curable acrylic resin was sprayed onto the PVC plate, which thus recovered its initial transparency. After a 1s UV exposure, the coated PVC was found to exhibit an excellent resistance to chemicals, weathering and scratching. One of the distinct advantages of this new low-cost recycling process is that it is based on existing technologies and can be carried out directly on the plastic structures to be renovated.     

Structure and properties of polymers modified by ion implantation

Thin films of oriented polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE) and polyamide (PA6) were modified by the implantation of 150 keV Sb⁺ ions to the fluences 10¹²–10¹⁵ cm⁻². The Sb depth profiles were determined by a standard Rutherford back-scattering technique and the range parameters were found to differ from the theoretical TRIM estimate. The thickness of the ion beam modified surface layer is about 150 nm for all polymers examined. Production of conjugate double bonds and polymer surface oxidation were proved by means of i.r. and u.v. spectroscopies. Surface polarity, obtained by goniometric measurements, is an increasing function of the implanted dose with only the exception of PA6 where a polarity decrease is observed. The measured temperature dependence of the sheet resistivity for PE, PP and PA6 do not correspond to the well known variable range hopping mechanism.     

Adsorption behavior of end-functionalized polymers modified by iminium ion

In order to clarify the end-functionalization effect of polymers modified by iminium ion, a model compound with a modified chain end was prepared by directly reactingn-butyllithium withN-methyl-2-pyrrolidone and then quenching by the addition of methanol. It is shown that the model compound includes the iminium ion group and that the adsorption bands in the IR-spectra of the chemically modified polymer were similar to those of model compoundThe adsorption behavior of end-functionalized polystyrene(PS-X) and diblock copolymer of PS and polybutadiene(PB) which were modified by iminium ion(PS-PB-X), were examined over a wide range of molecular weights of these polymers. It is evident that the amount of adsorption increased significantly by the end-functionalization and this trend was especially strong in the low molecular weight polymers (M _w<-10⁵). The preference for the end-functionalized polymer was also examined by competitive and sequential adsorption experiments between different molecular weight species. It is shown that a prefered adsorption of PS-X with low molecular mass is pronouced over the adsorption of PS or PS-X with high molecular weight and in the combination of high and low molecular weight species of PS-X, a special enhancement of total adsorption can be observed. This enhancement is based on a combination of different adsorption layers formed by these two molecular weight species.     

The polyaniline/MF-4SK composite systems with modified surface layer

Processes of aniline polymerization in perfluorinated polysulfonic acid MF-4SK solution are studied by UV-spectroscopy. Membranes with polyaniline-modified surface layer are synthesized. It is shown by voltammetry and potentiometry that the composite materials demonstrate asymmetric ion transfer with respect to protons and sodium cations.     

Energy release in the reaction of metal powders with fluorine containing polymers

Fluorine and its derivatives have been used as a substitute to oxygen-containing oxidizers in higher performing propellants and other energetic materials. They typically react rapidly with metals or thin oxide layers of the metals to produce metal fluorides, generally in the gaseous state.Thermal reactions of stoichiometric mixtures of metal (M=Al, Ti) -F containing polymers have been studied using thermal analyzers and their energetics are compared with the metals in other halogen element containing oxidizers. The experimental results indicated that thermal reaction becomes more exothermic as the bond strength between Al-X (X=F, Br, I) becomes stronger. It was also found that oxidation of metal powders is largely affected by the size of metal powders as well as the nature of existing oxide layer.     

Morphology of modified hydrolysis lignin

The morphology of hydrolysis lignin was studied. The effect of dimethyl sulfoxide, temperature, and activating additives on the surface characteristics of lignin was examined.     

NMR shielding in helium-3 atoms modified by gaseous nitrogen and oxygen

Helium-3 nuclear magnetic resonance (³He NMR) measurements were carried out for the gaseous mixtures of helium-3 with pure nitrogen and synthetic air as the solvents. It was found that ³He shielding is linearly dependent on solvent density up to approx. 6 mol/L. At higher density of the gaseous solvent, the change of ³He shielding is nonlinear and especially distinct when helium-3 atoms can interact with two O₂ molecules. The interaction with paramagnetic oxygen molecules can induce two kinds of ³He shielding changes: (1) due to the isotropic Fermi contact interaction and (2) from the dipolar magnetic interaction between unpaired O₂ electrons and ³He nuclear magnetic dipole moment. The two paramagnetic effects in helium-3 shielding cannot be experimentally separated, although for such small molecular objects, they could be presumably modeled by advanced theoretical calculations.     

Estimation of fluorine in microgramme quantities a modified procedure

A procedure is described for the estimation of fluorine in microgramme quantities by the steam-distillation of the samples with sulphuric or phosphoric acid. Traces of the acid carried over are precipitated from the distillate as silver or barium salts, in order to eliminate their interference in the subsequent titration of fluorine. The results obtained compare favourably with those of the conventional perchloric acid method. By avoiding the latter, the present method offers the advantage of both safety and simplicity.     

Gas chromatographic properties of methacrylate polymers modified by silver nanoparticles

Russian Chemical Bulletin - The gas chromatographic properties of the porous methacrylate polymers, copolymers of 2,3-epoxypropyl methacrylate (2,3-EPMA) and ethylenedimethacrylate (EDMA), modified...     

Hydrogen form of faujasite modified with Al-cations and fluorine

Hydrogen form of faujasite is nonresistant to further treatment with fluorine compounds. Introduction of Al-cations into zeolite HY before the fluorination protects the crystallinity and increases the catalytic activity of the modified sample.

---

. Al- HY .

     

Barrier effects of polyaniline layer in surface modified MF-4SK/Polyaniline membranes

An express method of synthesis of surface-modified membrane composites is suggested that allows obtaining heterogeneous materials featuring effects of the blocking of the transport of solvent ions and molecules. Studies using the methods of atomic force microscopy (AFM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and IR spectroscopy show that polyaniline is in the form of emeraldine and water at the interface of polyaniline aromatic chains and initial membrane sulfogroups is in a structured state due to formation of interpolymer complexes. This determines higher thermal stability of composites and specific morphology of the polyaniline layer. Measurement of electroosmotic and diffusion permeability and also membrane conductivity in HCl solutions (with the concentration of 0.01 to 2 M) shows the blocking effect of the polyaniline layer causing a significant decrease in transport characteristics in a wide range of concentrations of equilibrium solutions. A model of structural heterogeneity of composites is offered that takes into account the presence of an additional structural element, polyaniline, in the basic polymer matrix. Mechanisms of the observed barrier effects are discussed. Comparison of the transport-structural parameters of the MF-4SK membrane and MF-4SK/PAn composites allows elucidating the role of polyaniline in formation of transport routes for ion and solvent fluxes.