Small Angle X-ray Spectroscopy Research Articles

Biophysical Characterization of a Recombinant Chromatin-Liposome Aggregates

Self-assembled aggregates of recombinant chromatin and liposomes were characterized by synchrotron small angle x-ray spectroscopy (SAXS) and optical microscopy. Recombinant nucleosome core particles (NCP) and 12-mer nucleosome arrays, where half of the negative DNA charge is neutralized by histone octamers, were used as a chromatin model. Liposomes of different charge and charge density were prepared from the either cationic DOTAP or anionic DOPG lipid molecules mixed with zwitterionic DOPC at different molar percentages.Two distinct phases were identified in aggregates with low and high charge density cationic liposomes. The former appeared as translucent precipitate, probably due to higher water retention, compared to latter appearing compact and opaque, and exhibiting birefringence. Systematic SAXS measurements revealed chromatin-lipid bilayer complexes at 3-10% DOTAP, with lamellar distance around 160 A for NCP, and 200 A for arrays. At 10-100% DOTAP, proteins were displaced from DNA by cationic liposomes forming DNA lamellar phase. Confocal microscopy with triple fluorescent labeling displayed homogeneous distribution of DNA, proteins and lipids in both phases at the resolution scale determined by the diffraction limit.Array adopted compacted 30-nm fiber and NCP formed columnar-hexagonal phase in the aggregates with anionic liposomes at 2-50 [Mg2+] revealed by SAXS. These Mg-induced effects are known to occur in the absence of anionic liposomes. Variations of charge density and lipid concentration were found not to influence the dimensions of NCP columnar phase. Lipid molecules may prevent resolubilization of condensed chromatin by neutralizing excess of Mg ions.Chromatin aggregates with liposomes of different charge may serve as a model of the eukaryotic nucleus where chromatin is surrounded by the nuclear envelope. The current results may demonstrate why cationic lipids destabilizing for chromatin are not prevalent in the nucleus, and how anionic membranes may influence the chromatin aggregation state.

Engineering a Structure Switching Mechanism into a Steroid-Binding Aptamer and Hydrodynamic Analysis of the Ligand Binding Mechanism

The steroid binding mechanism of a DNA aptamer was studied using isothermal titration calorimetry (ITC), NMR spectroscopy, quasi-elastic light scattering (QELS), and small-angle X-ray spectroscopy (SAXS). Binding affinity determination of a series of steroid-binding aptamers derived from a parent cocaine-binding aptamer demonstrates that substituting a GA base pair with a GC base pair governs the switch in binding specificity from cocaine to the steroid deoxycholic acid (DCA). Binding of DCA to all aptamers is an enthalpically driven process with an unfavorable binding entropy. We engineered into the steroid-binding aptamer a ligand-induced folding mechanism by shortening the terminal stem by two base pairs. NMR methods were used to demonstrate that there is a transition from a state where base pairs are formed in one stem of the free aptamer, to where three stems are formed in the DCA-bound aptamer. The ability to generate a ligand-induced folding mechanism into a DNA aptamer architecture based on the three-way junction of the cocaine-binding aptamer opens the door to obtaining a series of aptamers all with ligand-induced folding mechanisms but triggered by different ligands. Hydrodynamic data from diffusion NMR spectroscopy, QELS, and SAXS show that for the aptamer with the full-length terminal stem there is a small amount of structure compaction with DCA binding. For ligand binding by the short terminal stem aptamer, we propose a binding mechanism where secondary structure forms upon DCA binding starting from a free structure where the aptamer exists in a compact form.

ISPyB: an information management system for synchrotron macromolecular crystallography

Individual research groups now analyze thousands of samples per year at synchrotron macromolecular crystallography (MX) resources. The efficient management of experimental data is thus essential if the best possible experiments are to be performed and the best possible data used in downstream processes in structure determination pipelines. Information System for Protein crystallography Beamlines (ISPyB), a Laboratory Information Management System (LIMS) with an underlying data model allowing for the integration of analyses down-stream of the data collection experiment was developed to facilitate such data management. ISPyB is now a multisite, generic LIMS for synchrotron-based MX experiments. Its initial functionality has been enhanced to include improved sample tracking and reporting of experimental protocols, the direct ranking of the diffraction characteristics of individual samples and the archiving of raw data and results from ancillary experiments and post-experiment data processing protocols. This latter feature paves the way for ISPyB to play a central role in future macromolecular structure solution pipelines and validates the application of the approach used in ISPyB to other experimental techniques, such as biological solution Small Angle X-ray Scattering and spectroscopy, which have similar sample tracking and data handling requirements.

Physical Characterization of High-k HfxAl1-xOy Gate Dielectrics Prepared by ALD

This work describes the physical characterization of hafnium aluminates prepared by atomic layer deposition (ALD) and annealed at 1000oC during 60s in N2 or N2+O2(5%) and laser annealing at 1200oC during 1ms. Aerial concentrations of Hf, Al and O were obtained with the aid of Rutherford Backscattering Spectrometry (RBS), Oxygen Resonance using 3.048 MeV (α,α) elastic scattering and Wavelength Dispersive X-Ray Spectroscopy (WDS), respectively. Following, the molar concentration of hafnium was obtained and compared with the nominal value of the Atomic-Layer-Depostion recipes. As a result, a significant difference was observed for films with a higher concentrations of hafnium. In addition, X-ray reflectometry (XRR) was employed to confirm thickness and to obtain surface roughness, which was around 1 nm. Finally, Grazing Incidence Small Angle X-ray Spectroscopy (GISAXS) experiments allowed to characterize composition variations based on a modeling using spherical nanoparticles. Experiments indicated the presence of nanoparticles having an average radius ranging from 0.4 to 0.9 nanometers and a significant composition variation was observed for films with a higher concentrations of hafnium .

Structural Effects of Insulin-Loading into HII Mesophases Monitored by Electron Paramagnetic Resonance (EPR), Small Angle X-ray Spectroscopy (SAXS), and Attenuated Total Reflection Fourier Transform Spectroscopy (ATR-FTIR)

Insulin entrapment within a monoolein-based reverse hexagonal (H(II)) mesophase was investigated under temperature-dependent conditions at acidic (pH 3) and basic (pH 8) conditions. Studying the structure of the host H(II) system and the interactions of insulin under temperature-dependent conditions has great impact on the enhancement of its thermal stabilization and controlled release for the purposes of transdermal delivery. Small angle X-ray spectroscopy (SAXS) measurements show that pH variation and/or insulin entrapment preserve the hexagonal structure and do not influence the lattice parameter. Attenuated total reflection Fourier transform spectroscopy (ATR-FTIR) spectra indicate that, although insulin interacts with hydroxyl groups of GMO in the interface region, it is not affected by pH variations. Hence different microenvironments within the H(II) mesophase were monitored by a computer-aided electron paramagnetic resonance (EPR) analysis using 5-doxylstearic acid (5-DSA) as a pH-dependent probe. The microviscosity, micropolarity, order of systems, and distribution of the probes in different microenvironments were influenced by three factors: temperature, pH, and insulin solubilization. When the temperature is increased, microviscosity and order parameters decreased at both pH 3 and 8, presenting different decrease trends. It was found that, at pH 3, the protein perturbs the lipid structure while "pushing aside" the un-ionized 5-DSA probe to fit into the narrow water cylinders. At the interface region (pH 8), the probe was distributed in two differently structured environments that significantly modifies by increasing temperature. Insulin loading within the H(II) mesophase decreased the order and microviscosity of both the microenvironments and increased their micropolarity. Finally, the EPR analysis also provides information about the unfolding/denaturation of insulin within the channel at high temperatures.

Thick Beryllium Coatings by Magnetron Sputtering

ABSTRACTThick (>150 μm) beryllium coatings are studied as an ablator material of interest for fusion fuel capsules for the National Ignition Facility (NIF). As an added complication, the coatings are deposited on mm-scale spherical substrates, as opposed to flats. DC magnetron sputtering is used because of the relative controllability of the processing temperature and energy of the deposits. We used ultra small angle x-ray spectroscopy (USAXS) to characterize the void fraction and distribution along the spherical surface. We investigated the void structure using a combination focused ion beam (FIB) and scanning electron microscope (SEM), along with transmission electron microscopy (TEM). Our results show a few volume percent of voids and a typical void diameter of less than two hundred nanometers. Understanding how the stresses in the deposited material develop with thickness is important so that we can minimize film cracking and delamination. To that end, an in-situ multiple optical beam stress sensor (MOSS) was used to measure the stress behavior of thick Beryllium coatings on flat substrates as the material was being deposited. We will show how the film stress saturates with thickness and changes with pressure.

Tensile behaviour of rubber-modified polyester resin materials

AbstractPolymer blends comprising an unsaturated polyester resin and dispersed particles were prepared. Rubbery particles were synthesized by sequential emulsion polymerization and had core-shell morphology. Curing of materials was carried out at ambient temperature and subsequently post cured at elevated temperatures to obtain materials of consistent properties. Materials made of different particle content were prepared and their tensile properties evaluated. Effect of matrix ductility was investigated by inclusion of ethyl acrylate in the polyester resin composition. Deformation mechanisms involved in these materials were examined using transmission electron microscopy (TEM) and real-time small angle X-ray spectroscopy (RT-SAXS). Incorporation of rubbery particles in the polyester resin was found to generally improve the tensile properties of the materials. Furthermore, the deformation mechanisms were found to involve cavitation/debonding processes as evidenced from stress whitening in the failed specimen and from real-time small angle X-ray scattering experiments.

Alternative hybrid electrolytes based on a series of bis(trialkoxysilyl)alkanes and 3-(trihydroxysilyl)-1-propane sulfonic acid applied in gas diffusion electrodes of proton exchange membrane fuel cells

This study demonstrates a method for improving the electrolyte distribution in catalyst layers and enhancing the utilization of catalyst existing in primary pores. Bis(trialkoxysilyl)alkanes (BTAS-alkanes) and 3-(trihydroxysilyl)-1-propane sulfonic acid (THS)Pro-SO 3H) precursors have been used to prepare a series of hybrid electrolytes with various organic segment lengths of BTAS-alkanes and ratios of organic moiety and sulfonic acid groups. Investigations of BTAS-alkanes series includes bis(triethoxysilyl)octane (BTES-Oct), bis(trimethoxysilyl)hexane (BTMS-Hex), and bis(triethoxysilyl)ethane (BTES-Eth). Small angle X-ray spectroscopy (SAXS) identifies morphological phase separation in BTES-Oct and BTMS-Hex hybrid electrolytes. The results of mercury porosimetry and BET porosimetry show that the hybrid electrolytes have better capability than Nafion ionomer to penetrate into primary pores of the catalyst layers. Electrochemical measurements including electrode polarization, electrochemical active surface (EAS) and electrochemical impedance spectroscopy (EIS) are discussed. The BTES-Oct or BTMS-Hex hybrid electrolytes with higher ratio of organic moiety and sulfonic acid group have achieved better electrode performance. Oxygen benefit current (OBC) results indicate that higher ratios of BTES-Oct/(THS)Pro-SO 3H provides higher hydrophobicity with better gas transport properties. However, the hybrid electrodes exhibit lower cathode performance than Nafion ®-based electrodes due to excessive electrolyte incorporated in the catalyst layer.

Nonionic−Anionic Mixed Surfactants Cubic Mesophases. Part I: Structural Chaotropic and Kosmotropic Effect

We prepared and investigated cubic bicontinuous (V) phase from mixtures of nonionic monoolein (GMO) and anionic oleyl lactate (OL) surfactants in the presence of ethanol and water. The isotropic region and the composition of the V phase in the pseudoternary phase diagram vary with the nature of the hydrophilic headgroups and their charge. We examined three anionic species, acidic (HOL), partially neutralized (OL), and totally ionized (NaOL) forms. The largest swollen V region within the phase diagram was formed from the partially neutralized form. The V formation is dependent on the GMO/OL ratio. The largest isotropic region in the phase diagrams was found with GMO/OL at a 70:30 wt % ratio and in the presence of 5.0 and 38.5 wt % ethanol and water, respectively. The structural effect of OL was determined by small-angle X-ray spectroscopy, differential scanning calorimetry, and Fourier transform infrared. The results revealed that the structure is curvature-dependent. Mesophases made from 90:10 wt % GMO/OL showed phase transition from gyroid (G) to diamond (D) symmetry. Preparations made from 30:70 wt % GMO/OL exhibited coexistence of two mesophases, one (of low order) cubic and the other lamellar. Because of the overall gauche deformation growth, the hydrocarbon order decreased with the OL content increase. The GMO, sn(2) and sn(3) headgroups, and water structure vibration bands indicate a chaotropic effect as a result of the interdigitation of OL anions and Na(+) and H(+) counterions.

Imaging of Ionic Channels in Proton Exchange Membranes by the Nickel Replica Method

An imaging method for ionic channels in proton exchange membranes in wet conditions is reported. The ionic channels were replicated by the electrodeposition of nickel and then observed using scanning electron microscopy (SEM). The fidelity of the replica to the channels was confirmed by comparison of the SEM image of the nickel deposit to the transmission electron microscopy and atomic force microscopy image of the ionic channels using a sulfonated hydrocarbon block copolymer membrane, which keeps continuous ionic channels even in dry condition. By use of this method, the morphology of the ionic channels in a Nafion membrane in wet conditions was successfully observed. The nickel replica showed a continuous network of 5−10 nm wide channels, which is close to the reported value estimated using small-angle X-ray spectroscopy.

The role of nitrogen atoms in forming the carbon structure in the carbonization of polymer composites

Data have been used from X-ray photoelectron spectroscopy, small-angle X-ray spectroscopy, nuclear magnetic resonance, IR Fourier spectroscopy, electron spectroscopy, and other current methods for polyacrylonitrile, polypyromellitimide, hydrated cellulose, hard coals, and various model compounds to examine the effects of the nitrogen atoms on carbonization and graphitization. The nitrogen atoms are found to have multiple effects on the thermochemical and thermophysical parameters of the polymer carbonization over a wide temperature range. In the derivation of the carbon structures, the nitrogen acts as a messenger combined agent, which gives rise to heterorings, which are transformed into intermediate aromatic compounds, which form the basis of the matrix synthesis consisting of ordered graphite-type structures.

Metallomics, elementomics, and analytical techniques

AbstractMetallomics is an emerging and promising research field which has attracted more and more attention. However, the term itself might be restrictive. Therefore, the term "elementomics" is suggested to encompass the study of nonmetals as well. In this paper, the application of state-of-the-art analytical techniques with the capabilities of high-throughput quantification, distribution, speciation, identification, and structural characterization for metallomics and elementomics is critically reviewed. High-throughput quantification of multielements can be achieved by inductively coupled plasma-mass spectrometry (ICP-MS) and neutron activation analysis (NAA). High-throughput multielement distribution mapping can be performed by fluorescence-detecting techniques such as synchrotron radiation X-ray fluorescence (SR-XRF), XRF tomography, energy-dispersive X-ray (EDX), proton-induced X-ray emission (PIXE), laser ablation (LA)-ICP-MS, and ion-detecting-based, secondary-ion mass spectrometry (SIMS), while Fourier transform-infrared (FT-IR) and Raman microspectroscopy are excellent tools for molecular mapping. All the techniques for metallome and elementome structural characterization are generally low-throughput, such as X-ray absorption spectroscopy (XAS), NMR, and small-angle X-ray spectroscopy (SAXS). If automation of arraying small samples, rapid data collection of multiple low-volume and -concentration samples together with data reduction and analysis are developed, high-throughput techniques will be available and in fact have partially been achieved.

Cell Biological and Biophysical Aspects of Lipid-mediated Gene Delivery

Cationic lipids are conceptually and methodologically simple tools to deliver nucleic acids into the cells. Strategies based on cationic lipids are viable alternatives to viral vectors and are becoming increasingly popular owing to their minimal toxicity. The first-generation cationic lipids were built around the quaternary nitrogen primarily for binding and condensing DNA. A large number of lipids with variations in the hydrophobic and hydrophilic region were generated with excellent transfection efficiencies in vitro. These cationic lipids had reduced efficiencies when tested for gene delivery in vivo. Efforts in the last decade delineated the cell biological basis of the cationic lipid gene delivery to a significant detail. The application of techniques such as small angle X-ray spectroscopy (SAXS) and fluorescence microscopy, helped in linking the physical properties of lipid:DNA complex (lipoplex) with its intracellular fate. This biological knowledge has been incorporated in the design of the second-generation cationic lipids. Lipid-peptide conjugates (peptoids) are effective strategies to overcome the various cellular barriers along with the lipoplex formulations methodologies. In this context, cationic lipid-mediated gene delivery is considerably benefited by the methodologies of liposome-mediated drug delivery. Lipid mediated gene delivery has an intrinsic advantage of being a biomimetic platform on which considerable variations could be built to develop efficient in vivo gene delivery protocols.

Formation of ordered cobalt nanowire arrays in the mesoporous silica channels

Abstract Here we report the synthesis and investigation of cobalt nanowire arrays using mesoporous silica as a host material. In the present work, a novel variant of synthesis of ordered magnetic nanowires in the mesoporous silica matrix was suggested. The method is based on incorporation of a hydrophobic metal compound Co2(CO)8 into the hydrophobic part of the silica-surfactant composite. The amount of cobalt intercalated into the mesoporous matrix was measured by chemical analysis (~5 wt %). Additional thermal modification was performed in order to provide a crystallization process of the cobalt nanowires. The prepared nanocomposites were characterized by X-ray diffraction (XRD), small-angle X-ray spectroscopy (SAXS), transmission electron microscopy (TEM), nitrogen capillary adsorption method (BET and BJH), and magnetic measurements. The anisotropy parameters of nanowires were determined using temperature dependence of magnetic susceptibility. For cobalt-containing sample annealed at 300 °C (form factor of nanowire higher than 16), the coercive force at room temperature was found to be 42.2 kA/m at saturation magnetization of 0.5 A.m2/kg, which is nearly sufficient for modern information recording media. According to TEM studies, cobalt particles are uniform and well ordered in the silica matrix. Thus, the suggested method leads to one-dimensional anisotropic nanostructures, which could find an application in high-density data storage devices.

Chemical Clusters in Polyurethane Networks. SAXS, Photoelastic and Dynamic Mechanical Behavior of Networks from Poly(Oxypropylene)Diol, Diisocyanate, and Trimethylolpropane Prepared One‐Stage and Two‐Stage Process

The effect of the initial ratio of components and of the one‐ or two‐stage process of formation of polyurethane networks prepared from poly(oxypropylene)diol (PD, M n=2100), 4,4′‐diisocyanatodiphenylmethane (MDI) and trimethylolpropane (TMP) on their extraction, swelling, small‐angle X‐ray spectroscopy (SAXS), photoelastic, and dynamic mechanical behavior was investigated. The networks were prepared at various ratios of hydroxy (OH) to isocyanate (NCO) groups, r HT=[OH]TMP/(0.5[NCO])=1–1.5, by a one‐ or two‐stage process (in the first step [OH]PD/[NCO]=1/2) up to the full conversion of NCO groups. Due to decreasing reactivity of OH groups on TMP a nonuniform distribution of hard (TMP‐MDI‐TMP) segments (chemical clusters) was developed in both network series. The SAXS experiments proved that one‐stage networks exhibit a more heterogeneous structure than two‐stage ones. As expected, the weight fraction of the gel, w g, and equilibrium modulus, G e, decrease with increasing deviation from stoichiometry; the G e and w g values of one‐stage networks at constant r HT are always higher than those of two‐stage networks. The frequency‐temperature (f‐T) superposition of both components of the complex compliance J* (=J′–iJ″) was performed and the horizontal shift factor, log a T, satisfied the WLF equation for all networks. From the dependence of superimposed storage, J′p, and loss, J″p compliances on reduced frequency f.a T, three contributions could be determined from the Cole‐Cole distribution; each process was characterized by the relaxation strength, ΔJ i, relaxation time, τi and distribution broadness, b i. The broadness b and strength ΔJ of the high and medium frequency process (i=1,2), which correspond to the glass‐rubber transition, are roughly independent of r HT and the preparation method. The τ3 and ΔJ 3 values of the low‐frequency process in networks prepared by the two‐stage process are always greater than those in networks prepared by the one‐stage process. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Self-assembly of biocidal nanotubes from a single-chain diacetylene amine salt.

We describe the facile two-step synthesis of nanotubes that form pure, well-defined, nanostructured materials. We have synthesized a secondary amine HBr salt as the headgroup of a single-chain diacetylenic lipid. This molecule can form a number of different self-assembled nanostructures in aqueous or organic solvents. In water, this lipid forms a monodisperse preparation of nanotubes at high yields. Partially dissolving a preparation of nanotubes dried from aqueous solution results in a remarkably organized structure that resembles a nanocarpet. Details of the nanotube structure were investigated by scanning electron microscopy, transmission electron microscopy, and small-angle X-ray spectroscopy. The aqueous nanotubes have a cross-sectional diameter of 89 nm. The walls of the tubes are an exquisitely uniform 27 nm thick and are shown to consist of five lipid bilayers with a repeat spacing of 57.8 A. The chemical structure of the material shows no chiral centers, but suspensions of the nanotubes in an aqueous medium show an unexpected circular dichroism signal. The versatility of this new material as a platform for nanostructure design and synthesis is enhanced by its biocidal activity. This antimicrobial activity along with the regularity the nanostructures will enhance the development of a range of applications from biosensors to artificial retinas.

Studies on dodecyl betainate in combination with its degradation products or with phosphatidyl choline-phase behavior and hemolytic activity.

Surface active betaine esters contain a hydrolysable bond and give naturally occurring products (fatty alcohol and the amino acid betaine) on degradation. They are therefore interesting candidates for use as cationic surfactants in pharmaceutical applications. In this work the phase behavior of two systems of relevance for the utilization of dodecyl betainate as a pharmaceutical excipient is studied, namely dodecyl betainate/dodecanol/betaine hydrochloride/D2O and dodecyl betainate/phosphatidyl choline (PC)/ethanol/D2O. The techniques used for phase characterisation were 2H NMR measured on the solvent, small angle X-ray spectroscopy and optical microscopy. Dilute dodecyl betainate/PC dispersions were characterized using laser diffraction. It is shown that introduction of relatively small amounts of the hydrolysis products of dodecyl betainate, i.e., dodecanol and betaine (used in the form of betaine hydrochloride), has a strong effect on the phase behavior of the binary dodecyl betainate/D2O system. The degradation products change the average curvature of the surfactant film so that, instead of a hexagonal phase at concentrations above the micellar phase, a probably defective, lamellar phase seems to form. The dodecyl betainate/PC/ethanol/D2O system shows a large region of a highly swelling lamellar phase. Dispersions of dodecyl betainate/PC/ethanol in water can be prepared with low energy input; i.e., the preconcentrate can be regarded as a self-dispersing solution. Introduction of dodecyl betainate and its degradation products does not impair the ability of PC to form vesicles. Experiments for evaluating the toxicity of surface active betaine esters to erythrocytes were also performed. There are indications that the hemolytic activity of dodecyl betainate is lower than that of the stable surfactant tetradecyltrimethylammonium chloride, which has similar critical micelle concentration. A combination of dodecyl betainate and PC gives very low hemolytic activity.

Phase Behavior and Phase Structure of a Cationic Fluorosurfactant in Water

The phase behavior of the cationic fluorocarbon surfactant 1,1,2,2-tetrahydroperfluorodecylpyridinium chloride in water has been studied using small-angle X-ray and 2H NMR spectroscopy as the main techniques. The following phase sequence was found: micellar (L1), hexagonal (HI), centered rectangular (R; spacegroup c2mm) and centered trigonal (T, spacegroup R3m) with increasing surfactant concentration. At higher concentrations evidence for random mesh phase and a lamellar phase was found, at high temperatures a bicontinuous cubic phase was found. Compared to a cationic hydrocarbon surfactant of similar hydrophobicity, the occurrence of the intermediate phases is more extensive in the phase diagram, and the fluorocarbon surfactant prefers to form intermediate phases instead of a cubic phase. The surface curvature of the aggregates changes from highly curved cylindrical structures of the hexagonal phase to the planar bilayer structure of the lamellar phase over a sequence of geometries that allow the aver...

Sol-Gel Formation of Reticular Methyl-Silicate Materials by Hydrogen Peroxide Decomposition

A new method for the formation of reticular silicate and organically modified silicate is introduced. Monoliths were prepared by incorporating a few percent hydrogen peroxide in the sol-gel starting solution. For example, incorporation of 6–10% (v) hydrogen peroxide in base catalyzed sol-gel precursors of methyl-Ormosil yielded macroporous monoliths with a bi-modal pore size distribution. The average characteristic pore diameters were approximately 1.2 nm and 0.7 μm, depending on the sol-gel precursors used and the preparation protocol. The specific surface area was approximately 160 m2/g, contributed mainly by the microporous structure. A similar preparation procedure without hydrogen peroxide yielded only fractured or powdery materials. Presumably, the decomposition of the hydrogen peroxide yielded microbubbles, which formed templates for the polycondensation reaction. SEM, nitrogen adsorption isotherms and small angle X-ray spectroscopy were used to characterize the reticular materials.

Morphology in binary blends of poly(vinyl methyl ether) and ϵ-caprolactone-trimethylene carbonate diblock copolymer

The morphology of symmetric diblock copolymer of ϵ-caprolactone (PCL) and trimethylene carbonate (PTMC), in blends with poly(vinyl methyl ether) (PVME) is investigated with (modulated) differential scanning calorimetry (d.s.c.), time resolved small angle (SAXS) and wide angle (WAXS) X-ray spectroscopy and optical microscopy. In the melt the crystallizable block PCL is immiscible with the amorphous PTMC block. PCL is melt miscible with PVME, whereas PTMC and PVME are immiscible. Despite the much higher molecular weight of PVME, the favourable interaction between PVME and PCL results in a microphase separated morphology with PVME residing inside the PCL domains, In the melt, PVME is for up to 20 wt%, almost homogeneously mixed with PCL. Above 20 wt%, PVME partly segregate inside the PCL domains. In all cases, PCL starts to crystallize from a microphase separated melt. During the crystallization a characteristic small angle scattering peak together with the corresponding wide angle peaks develops. The long period of the crystalline morphology increases as a function of the amount of PVME.