SAXS data analysis of a lamellar two-phase system. Layer statistics and compansion

An analysis of small angle x-ray scattering (SAXS) data from three injection molded poly(ethylene terephthalate) (PET) samples is carried out. Two of the samples are annealed at different temperatures. The chosen concept of data analysis is that of Ruland's interface distribution function (IDF) of lamellar two-phase systems. The IDF can be expanded into a series of distance distributions, containing the information on the topological properties of the ensemble of lamellar stacks in the semicrystalline sample.The paper describes the stepwise refinement of a topological model. The final model is described by only few parameters of physical meaning. It unifies the well-known concepts of an ensemble of non-uniform stacks, finite stack size and one-dimensional paracrystalline disorder in an analytical expression. In order to deduce this expression, the concept of inhomogeneity (imagine a variation of the long period from stack to stack) is generally treated in terms of compansion, a suggested superposition principle. Its mathematical equivalent in one dimension is the Mellin convolution.     

CRYSTALLIZATION OF BLENDS OF AN ASYMMETRIC POLY（OXYETHYLENE）-b-POLY（OXYBUTYLENE） BLOCK COPOLYMER WITH POLY（OXYBUTYLENE）

An oxyethylene/oxybutylene block copolymer with asymmetric volume fraction (E115B103) was blended with oxybutylene homopolymer (Bh) at different volume fractions of the block (φE). Crystallization behavior of the blends was studied and was compared with that of the blends from a symmetric block copolymer (E114B56). It was found that the crystallization temperature of E115B103/B28 blend is lower than that of the blends from symmetric block copolymer. For the blend with φE= 0.30 breakout crystallization with an Avrami exponent n ≈ 3.0 is observed. At φE = 0.22 the blend exhibits a variable crystallization behavior: confined crystallization with n ≈ 1.0 at lower crystallization temperatures but breakout crystallization at high crystallization temperatures. For the blend with φE = 0.14 and sphere morphology confined crystallization occurs at all crystallization temperatures studied. When compared with the blends from symmetric block copolymer, confined crystallization occurs more easily in the E115B103/B28 blends. The SAXS results agree with the isothermal crystallization kinetics. Deformation of the confined crystalline block is observed in the blend with φE = 0.14 and mixed lamellar and cylinder morphologies in the blend with φE = 0.22.     

Plasticity in Aerogels

When gently stressed, aerogels show an elastic response. However it was found that under isostatic pressure aerogels display an irreversible shrinkage which may be attributed to plastic behaviour. As a consequence of this plastic shrinkage it is possible to densify and modify the elastic properties of aerogels at room temperature.The structural evolution is followed by Small Angle X ray Scattering and the increase of the connectivity is revealed by the evolution of the elastic properties of the material.The SAXS data show that the densification mechanism is different from that obtained by sintering at high temperature. The densification mechanism induces a textural change at the periphery of the constitutive clusters but not inside, conversely to a sintering effect. We also show that the elasticity of the material is strongly influenced by this structural transformation. The power law evolution of the elastic modulus as a function of the density, usually observed on as-prepared and sintered aerogels, is not valid for compressed material.     

Effect of miscible polymer diluents on the development of lamellar morphology in poly(oxymethylene) blends

The development of lamellar morphology in poly(oxymethylene) (POM) and its miscible blends was studied by synchrotron time-resolved small-angle X-ray scattering (SAXS), during primary and secondary crystallization at temperatures near 150°C. The blends contained two different diluents: poly(vinyl 4-hydroxy styrene) [common name poly(vinyl phenol), (PVP)], which had a high glass temperature (T_g = 150°C), and styrene-co-hydroxy styrene oligomer (PhSO), which had a low glass temperature (T_g = −37°C). The SAXS data were analyzed by correlation function analysis to extract several lamellar parameters: long period (L), lamellar crystalline thickness (lc), amorphous layer thickness (la), and invariant (Q). The variation in Q defined the region where spherulites quickly grew and filled the entire space, and was referred to as the primary crystallization dominant regime. A rapid drop in L and lc was observed at early times, and this can be explained by defective lamellar stacks filling in space between primary stacks, as secondary crystals form during the nominal primary crystallization dominant regime. Lamellar thickening with time in the long-time secondary crystallization region was observed in neat POM and the blend with 10 % low T_g diluent, while this process was inhibited with the high T_g diluent due to the higher T_g of the interlamellar species. A decrease in la at long times confirmed the lamellar thickening. We refer to the lamellar thickening process as a type of secondary crystallization. Interlamellar inclusion or trapping was detected to different degrees with the high T_g diluent, while exclusion was found for the low T_g diluent. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3115–3122, 1999     

Synthesis,structure, and morphology of polymer–silica hybrid nanocomposites based on hydroxyethyl methacrylate

Two types of polymer–silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO₂ nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol–gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis conditions, chemical structure, and resulting morphology have been studied. Type 1 systems exhibit a classical particle-matrix morphology, but where particles tend to form aggregates. Type 2 systems possess a finer morphology characterized by a very open mass-fractal silicate structure, which is believed to be bicontinuous with the organic phase at a molecular level. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3172–3187, 1999     

Crystallization and structure formation in polymer blends with strong intermodular interactions: blends of poly(ethylene oxide) and styrene-hydroxystyrene copolymers

Time-resolved synchrotron wide- and small-angle X-ray scattering experiments were used to investigate crystallization behavior and microstructure development of a nearly monodisperse poly(ethylene oxide) [PEO] (M_w = 53,500), and its melt-miscible blends with two fractionated styrene - hydroxystyrene random copolymers [SHS]. PEO crystallization rates decrease significantly in the presence of the melt-miscible SHS copolymers. All low and high molecular weight SHS blends exhibit a crystallization process at relatively short times characterized by large Avrami exponents (n), followed by a dominant process with n near that of neat PEO. A model for the crystallization of these blends is proposed.     

EXAFS, SAXS and Eu3+ Luminescence Spectroscopy of Sol-Gel Derived Siloxane-Polyethyleneoxide Hybrids

Hybrid Eu³⁺-doped silica-poliethyleneoxide (PEO) nanocomposites with covalent bonds between the inorganic (siloxane) and organic (PEO) phases have been obtained by sol-gel process. These materials are transparent, flexible and present high Eu³⁺ luminescence output. Their luminescence properties, local environment around europium ions and structure have been investigated as a function of europium content. EXAFS measurements indicate that the increase in Eu-doping induces a decrease in Eu³⁺ coordination number. An increase in symmetry degree around the metal ion is also observed for increasing Eu³⁺ concentration, while non radiative decay paths from the ⁵D₀ excited state become more important. SAXS results suggest the preferential interaction of europium ions with ether-type oxygens of the polymer chains. However, the existence of interactions between the cations and the carbonyl groups from urea bridges located at the siloxane-PEO interface can not be excluded.     

Morphology of homogeneous copolymers of ethylene and 1‐octene. III. Structural changes during heating as revealed by time‐resolved SAXS and WAXD

The structural changes of two linear polyethylenes, LPEs, with different molar mass and of two homogeneous copolymers of ethylene and 1‐octene with comparable comonomer content but different molar mass were monitored during heating at 10 °C per minute using synchrotron radiation SAXS. Two sets of samples, cooled at 0.1 °C per minute and quenched in liquid nitrogen, respectively, were studied. All LPEs display surface melting between room temperature and the end melting temperature, whereas complete melting, according to lamellar thickness, only occurs at the highest temperatures where DSC displays a pronounced melting peak. There is recrystallization followed by isothermal lamellar thickening if annealing steps are inserted. The lamellar crystals of slowly cooled homogeneous copolymers melt in the reverse order of their formation, that is, crystals melt according to their thickness. Quenching creates unstable crystals through the cocrystallization of ethylene sequences with different length. These crystals repeatedly melt and co‐recrystallize during heating. The exothermic heat due to recrystallization partially compensates the endothermic heat due to melting resulting in a narrow overall DSC melting peak with its maximum at a higher temperature than the melting peak of slowly cooled copolymers. With increasing temperature, the crystallinity of quenched copolymers overtakes the one of slowly cooled samples due to co‐recrystallization by which an overcrowding of leaving chains at the crystal surfaces is avoided. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1975–1991, 2000     

Macromolecules at surfaces: Research challenges and opportunities from tribology to biology

A comprehensive review of ongoing and recommended research directions concerning the structure, dynamics, and interfacial activity of synthetic and naturally occurring macromolecules at the solid–liquid interface is presented. Many new developments stem from the ability to target new size regimes of 1–100 nm. These rapid developments are reviewed critically with respect to chemical synthesis, processing, structural characterization, dynamic processes, and theoretical and computational analysis. The common problems shared by flat and particulate surfaces are emphasized. A broad spectrum of material properties are discussed, from the control of interfacial friction between surfaces in moving contact, to the mechanical strength and durability of the interfaces in hybrid materials, to optical and electronic properties. Future research opportunities are identified that involve (1) the emergence of nanoscale material properties, (2) polymer‐assisted nanostructures, and (3) the crossroads between interfacial science and biological and bioinspired applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2755–2793, 2003     

Mechanical properties and the two-phase structure inside the heterophase domains of blends from HDPE and SBS star block copolymers

Blends from polyethylene (PE) and polystyrene-b-polybutadiene-b-polystyrene star block copolymers (SBS) (thermoplastic elastomers) are studied with polyolefine recycling in view. Each component, dispersed in a heterogeneous blend, exhibits a two-phase morphology. This structure is investigated by small angle X-ray scattering (SAXS) and compared to mechanical properties as a function of SBS grade and content. Increasing the SBS content one observes a vanishing PE-related long period reflection, while an SBS-related peak emerges. Best mechanical properties are obtained at concentrations, where the width of the observed long period reflection is broadest. For a quantitative analysis of the SAXS, the interface distribution function (IDF) analysis is employed. Data are fitted with a function modeling arrangement as well as disorder of domains inside the two different kinds of dispersed grains. The analysis yields that the observed broadening of the long spacing peak is caused only by an increased fluctuation of the thicknesses of amorphous layers in the PE stacks. This fluctuation again decreases for SBS concentrations beyond 15 wt %. The effect is strongest for blends containing the SBS grade with the lowest molecular weight and is discussed in terms of its compatibilization effect. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1423–1432, 1998