A First Insight in the Mechanisms Involved in the Self-Assembly of 2D-Hexagonal Templated SiO2 and TiO2 Mesostructured Films During Dip-Coating

Since mesoporous materials can be prepared by combining the sol-gel chemistry and the structuring effect of surfactants, they have attracted attention for application in various high technology fields. The present work deals with the analyses of the mechanisms involved in the formation of SiO₂ and TiO₂ highly organised 2D-hexagonal meso-structured films using Brij 58 as surfactant. The preparation of such films by dip-coating involves rapid evaporation which makes the different steps difficult to control. Simultaneous in-situ SAXS (synchrotron) and interferometry analyses have been performed to get a first understanding of the self-assembly process. SiO₂ and TiO₂ materials have a different chemical reactivity (kinetics and coordination aspects). However, we show that the mechanisms involved during dip-coating are quite similar : the self-assembly leading to the organised phase takes place at a final stage of the drying process, involves the formation of a disorganised intermediate phase and depends also on the presence of micellar interfaces in addition to film/air and film/substrate interfaces.     

SAXS from a poly(amido-amine)-heparin complex in aqueous solutions: a comparison between two analysis methods

Summary Joerchel's method is applied to SAXS spectra of a poly(amido-amine)-heparin complex in aqueous non diluted solutions, showing a noticeable interference effect. The results are compared with those obtained by the classical Guinier analysis applied to diluted solutions of the complex.

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Zusammenfassung SAXS-Spektren eines Poly(amido-amin)-Heparin-Komplexes in nicht verdünnten wäßrigen Lösungen, die bemerkenswerte Interferenzeffekte zeigen, wurden mittels der Joerchel'schen Methode analysiert. Die Ergebnisse wurden mit den durch die klassische Analyse von Guinier an verdünnten wäßrigen Komplexlösungen erhaltenen verglichen.

     

Combined in-situ SAXS/WAXS and HRTEM study on crystallization of (Cu60Co40)1 − xZrx metallic glasses

CuZr as well as CoZr are well known metallic glass-formers in a wide compositional range. Since the binary Cu-Co system exhibits a metastable liquid-liquid miscibility gap, i.e. Cu and Co tend to separate from each other, the ternary Cu-Co-Zr system is a promising candidate to form phase separated glass-glass composites. In this work (Cu₆₀Co₄₀)_1 − xZr_x metallic glasses with relatively low Zr contents of x = 37 and x = 32 were prepared by melt spinning and investigated by in-situ small-angle and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). Certain heat treated samples were additionally investigated by high-resolution transmission electron microscopy (HRTEM). Even for x = 32 there are no indications for any kind of phase separation in the as-quenched state within experimental resolution, i.e. the critical temperature T_c for a liquid-liquid phase separation has already decreased from 1556 K for binary Cu₆₀Co₄₀ to a temperature below the glass transition temperature T_g = 762(5)K found for (Cu₆₀Co₄₀)₆₈Zr₃₂. Combined in-situ SAXS/WAXS and HRTEM investigations reveal that thermal annealing also does not induce an amorphous-amorphous phase separation. Instead the formation of nano crystallites of a so far unknown Cu-rich/Zr-poor phase with relatively low activation energy for crystallization E_a = 116(7) kJ/mol at temperatures far below the crystallization temperature deduced from DSC measurements is observed.     

Permeation of gases through modified polymer films III. Gas permeability and separation characteristics of gamma-irradiated teflon FEP copolymer films

A study has been made of the diffusion, solubility, and separation of nitrogen and methane gases at temperatures ranging from 15° to 50°C in a series of Teflon FEP copolymer films which were irradiated by γ rays in air and under vacuum. The irradiated films were subjected to postirradiation treatment temperatures above and below the glass I transition temperature of the copolymer. The effect of radiation on crystallinity and cross-linking was examined by density, thermal, and tensile strength measurements. Diffusion and permeability coefficients of both gases decreased with irradiation dose but solubility coefficients were not greatly affected. Nitrogen-methane separation factors for vacuum-irradiated films increased with irradiation dose, but little change was observed for the air-irradiated films. Chain scission appeared to be the predominant reaction in air-irradiated films whereas both cross-linking and chain scission occurred in vacuum-irradiated films depending on post-irradiation heat-treatment conditions. The permselectivity of the Teflon FEP films was increased by γ irradiation but this was achieved at the expense of the permeation rate.     

PHASE SEPARATION IN THE MELT OF POLYPROPYLENE–1-DECENE COPOLYMERS

A propylene homopolymer and three copolymers with 1-decene containing 1.82, 3.55, and 7.83 mol% of comonomer units, respectively, were prepared with metallocene catalyst and the phase behavior in the melt of these polymers was studied using simultaneous synchrotron small-angle x-ray scattering and differential scanning calorimetry. The results show that the phase behavior of the melt varies with comonomer content and the copolymers tend to be phase-separated with increasing comonomer content. The phase separation in the melt of the propylene–1-decene copolymers was further confirmed by the fitting of the experimental data with Teubner–Strey micro-emulsion model and a transition from the phase-separated melt to the disordered melt was observed. We tentatively attribute this phenomenon to the inhomogeneous intra-molecular composition distribution at high levels of comonomer and the incompatibility of propylene sequences with different lengths. Such a finding is consistent with the facts of multiple melting peaks and mixed γ and α crystal phases in the polymer solids. Since the phase behavior depends on temperature, the effect of annealing temperature, from which the copolymers were cooled, on the nonisothermal crystallization of the copolymers was also investigated. It is found that higher degree of phase separation accelerates the crystallization but reduces the crystallization enthalpy.     

TIME-RESOLVED SAXS/WAXS STUDY OF PHASE BEHAVIOR AND CRYSTALLIZATION IN POLYMER BLENDS

Real-time SAXS and WAXS patterns have been simultaneously obtained during isothermal melt-crystallization of blends of low-molecular-weight poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA). The analysis of results shows that the originally homogeneous, single-phase polymer blend separates into two phases. The PMMA molecules diffuse from the blend and form completely segregated regions while PEO starts to crystallize. The first and dominating effect at the beginning of crystallization is the formation of unstable lamellae of nonintegrally folded chains (NIF). The real-time crystallinity and density of the PEO crystalline phase in absolute units were obtained from the time-resolved SAXS/WAXS results. The structure development proceeds in two steps. A very fast evolution of PEO crystals from the melt starts to crystallize in disordered NIF lamellae with thick amorphous interlayers and with a lower density of crystalline phase. The steep growth of crystallinity and crystalline density mean quick thickening of crystalline part of lamellae and improvement of their crystalline structure. In the second step, the structure of the crystalline phase gradually improves and crystallinity grows very slowly. The recrystallization of NIF lamellae into extended chain lamellae (EC) and lamellae with once folded chains (1F) proceeds during both stages of crystallization.     

Random Block Copolymers via Segment Interchange Olefin Metathesis

Polycarbonate/polyethylene random block copolymers (RBCs) have been produced using olefin metathesis catalysis in a process termed segment interchange metathesis. An olefin metathesis catalyst tolerant of polar functionality was added to reagent polycarbonate and polyethylene polymers which contained internal unsaturated carbon–carbon bonds. Subsequent metathesis occurred, segmenting the reagent polymers, resulting in RBCs. The block copolymers self-assembled into microphase structures which persisted into the melt state as determined by small angle X-ray scattering (SAXS).

     

Structural and morphological studies on the deformation behavior of polypropylene/multi‐walled carbon nanotubes nanocomposites prepared through ultrasound‐assisted melt extrusion process

Structural and morphological behavior under stress–strain of polypropylene/multi‐walled carbon nanotubes (PP/MWCNTs) nanocomposites prepared through ultrasound‐assisted melt extrusion process was studied by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, small angle X‐ray scattering (SAXS), and wide angle X‐ray scattering (WAXS). A high ductile behavior was observed in the PP/MWCNT nanocomposites with low concentration of MWCNTs. This was related to an energy‐dissipating mechanism, achieved by the formation of an ordered PP‐CNTs interphase zone and crystal oriented structure in the undeformed samples. Different strain‐induced‐phase transformations were observed by ex situ SAXS/WAXS, characterizing the different stages of structure development during the deformation of PP and PP/MWCNTs nanocomposites. The high concentration of CNTs reduced the strain behavior of PP due to the agglomeration of nanoparticles. A structural pathway relating the deformation‐induced phase transitions and the dissipation energy mechanism in the PP/MWCNTs nanocomposites at low concentration of nanoparticles was proposed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 475–491     

Effects of aromatic regularity on the structure and conductivity of polyimide‐poly(ethylene glycol) materials doped with ionic liquid

An understanding of the structure and properties of polymer electrolyte systems can be crucial to a variety of different applications. The current work performs a study of the composition, structure and properties of poly(ethylene glycol) (PEG)‐aromatic polyimide systems incorporating ionic liquids that are relevant to several applications especially fuel cell membranes. Composition was varied through using different aromatic dianhydrides, aromatic diamines and in some cases synthesis solvent. Properties were characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small‐angle x‐ray scattering, electrochemical impedance spectroscopy and cyclic voltammetry. By varying solvent, aromatic regularity and expected rigidity can be tuned, impacting average conductivity by 30%. Varying the aromatic diamine can influence the length scale and amount of aromatic regularity, which can ultimately affect the conductivity by a factor of four. The maximum conductivity reached was 83 mS/cm at 80 °C and 70 %RH. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 509–521     

Versatile gold-polymer nanointerfaces probed by GISAXS

An increasing trend toward integration of polymers in microelectronics and organic electronics has recently boosted research focusing in metal-polymer interfaces. These two materials differ vastly, with the former forming dense, crystalline, cohesive structures and the latter forming open structures bound together by weak van der Waals forces. As a result, there is dire need to assess their surface features (e.g., roughness) and correlate them with corresponding growth parameters, as metal-polymer interfaces are mainly determined by the preparation process. Here, we report a laboratory-based grazing-incidence small-angle x-ray scattering (GISAXS) study on distinct gold-polymer interfaces fabricated with different growth mechanisms, utilizing in-plane and oblique sputter geometries. GISAXS provided an improved analytic scheme for the buried surface in free-standing 2D gold-polymer nanosheets (with 19% porosity) revealing their fractal structure (Porod slope: ?1.71). Two quantitative approaches (Height-Height Correlation and Power Spectral Density functions) were used to describe rough surfaces characterized by Atomic Force Microscopy (AFM) in consort with GISAXS data; different correlation length dependencies on growth time were revealed for gold rough surfaces grown on bare and polymerized Si. The results are considered pertinent to interfacial nanoscience and engineering, enabling statistical data collection from large surface areas, in a fast and nondestructive manner.