Aurora Nogales

Molecular dynamics and microstructure development during cold crystallization in poly(ether-ether-ketone) as revealed by real time dielectric and x-ray methods

The isothermal crystallization process of poly(ether-ether-ketone) from the glass has been studied in real time by dielectric spectroscopy and x-ray scattering experiments. The combination of these two techniques revealed a complete picture of the crystallization processes from the point of view of both amorphous and crystalline phases. Analysis of results shows that the sample morphology consists of lamellar stacks, separated by rather broad amorphous regions. The lamellar stacks are highly crystalline (∼70%), as obtained from both dielectric and x-ray scattering measurements, and the amorphous phase within the stacks is constrained up to a level where no segmental relaxation is possible. The remaining amorphous phase, after completion of the primary crystallization process, still has a certain mobility, but it is significantly slower than the initial amorphous mobility. Dielectric data and x-ray results are found to be highly congruent.

Applications of synchrotron light to scattering and diffraction in materials and life sciences

Bases of Synchrotron Radiation, Light Sources, and Features of X-Ray Scattering Beamlines.- Scattering of Soft Condensed Matter: From Fundaments to Application.- A Basic Introduction to Grazing Incidence Small-Angle X-Ray Scattering.- Fundaments of Soft Condensed Matter Scattering and Diffraction with Microfocus Techniques.- The Use of Scattering and Spectroscopic Synchrotron Radiation Methods in Materials Science.- Synchrotron Small-Angle X-Ray Scattering Studies of Colloidal Suspensions.- Applications of Synchrotron X-Ray Diffraction to the Study of the Phase Behavior in Liquid Crystalline Polymers.- Structural Analysis of Biological and Technical Nanocomposites by X-Ray Scattering.- Application of Non-crystalline Diffraction with Microfocus to Carbon Fibres.- Simultaneous Calorimetric, Dielectric, and SAXS/WAXS Experiments During Polymer Crystallization.- Discovering New Features of Protein Complexes Structures by Small-Angle X-Ray Scattering.- Protein Shape and Assembly Studied with X-Ray Solution Scattering: Fundaments and Practice.- Diagnosis Applications of Non-Crystalline Diffraction of Collagen Fibres: Breast Cancer and Skin Diseases.- X-Ray Diffraction from Live Muscle Fibres.

On the Origin of the Multiple Melting Behavior in Poly(ethylene naphthalene-2,6-dicarboxylate): Microstructural Study as Revealed by Differential Scanning Calorimetry and X-ray Scattering

In this article a study on the melting behavior and microstructure of semicrystalline poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) prepared by crystallization from the glass under different annealing conditions is presented. The influence of the annealing temperature (Ta), annealing time (ta), and the heating rate (Rh) at which Ta is reached on the endothermic behavior of the samples was investigated by means of differential scanning calorimetry (DSC). A dual melting behavior appeared for low Rh values (2 deg · min−1) within the range of 145 °C < Ta < 250 °C and 1 min ≤ ta. ≤ 16 h. Samples subjected to fast heating rates (Rh = 200 deg · min−1) to reach a Ta ≥ 230 °C showed DSC traces in which a transition is observed from three peaks to a single melting peak when ta increases in the 30–240 min range. On the basis of the DSC results, PEN samples were prepared displaying single or dual endothermic behavior. The microstructure of these samples was studied by wide (WAXS) and small-angle X-Ray scattering (SAXS) techniques. The SAXS data were analyzed using the correlation function and interface distribution function formalisms, respectively. In samples with a single melting behavior, microstructural parameters such as the long spacing, the amorphous and the crystalline phase thicknesses are consistent with a lamellar stacking model in which the thickness distributions of both phases are almost the same. For samples exhibiting two melting endotherms, a dual lamellar model, which is in agreement with the experimental results is proposed.

Structure-dynamics relationships of the α-relaxation in flexible copolyesters during crystallization as revealed by real-time methods

DGICYT (Grant PB 94-0049), Spain, and to NEDO’s International Joint Research Program, Japan. FPI program of the Spanish Ministry of Science. program Human Capital and Mobility

Structure and Morphology of Thin Films of Linear Aliphatic Polyesters Prepared by Spin-Coating

Thin films, with thicknesses from 10 to 400 nm of linear aliphatic polyesters (X, Y), based on propylenediol (X = 3) and on dicarboxylic acid of different chain length (Y = 2, 3, and 4 CH(2) units) were prepared by spin coating of CHCl(3) polymer solutions with different polymer concentrations. Morphology and structure of the spin coated thin films were investigated by atomic force microscopy (AFM) and by grazing incidence X-ray scattering techniques at small, (GISAXS) and wide angles (GIWAXS). AFM revealed a strong dewetting for all three polymers for coatings thinner than 100 nm. The polymer films are clearly semicrystalline for thicknesses higher than 50 nm. GIWAXS of the thicker films revealed their oriented crystalline nature. An edge-on-lamellae morphology is clearly shown by the AFM-phase images even for relatively thin films. SAXS with the beam parallel to the sample plane also support the presence of lamellae perpendicular to the substrate. The use of a mu-beam helped to interpret the GIWAXS patterns and allowed to obtain oriented WAXS patterns from melt solidified filaments. Thus, a crystal chain packing is proposed for the three polymers and consequently the indexing of the observed reflections. Accordingly, the polymer chains lie parallel to the substrate being the bc plane of the monoclinic crystal unit cell parallel to the substrate.

Structural organization of iron oxide nanoparticles synthesized inside hybrid polymer gels derived from alginate studied with small-angle X-ray scattering

The structural organization of iron oxide nanoparticles (NPs) obtained through in situ coprecipitation of iron salts in semi-interpenetrating polymer networks (semi-IPNs) constituted of alginate (Alg) and poly(N-isopropylacrylamide) (PNiPAAm) has been investigated by means of small-angle X-ray scattering and transmission electron microscopy. The oxidation reaction was repeated up to two times to increase the amount of iron oxide NPs formed. The results were compared to the synthesis of iron oxide nanoparticles in an alginate solution. It has been demonstrated that the polymeric gel acts as a spatial framework for iron oxide nanoparticles that controls their particle size distribution and that the application of repeating oxidation cycles does not increase the polydispersity of the iron oxide nanoparticles.

Gene vectors based on DOEPC/DOPE mixed cationic liposomes: a physicochemical study

A double approach, experimental and theoretical, has been followed to characterize from a physicochemical standpoint the compaction process of DNA by means of cationic colloidal aggregates. The colloidal vectors are cationic liposomes constituted by a mixture of a novel cationic lipid, 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (chloride salt) (DOEPC) and a zwitterionic lipid, the 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE). A wide variety of high precision experimental techniques have been used to carry out the analysis: electrophoretic mobility, small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM) and fluorescence spectroscopy (ethidium bromide intercalation assays). On the other hand, a theoretical model that considers the renormalization of charges of both the polyelectrolyte and the colloidal aggregates sheds light as well on the characteristics of the compaction process. This global information reveals that the compaction of DNA by the cationic liposomes is mostly driven by the strong electrostatic interaction among the positively charged surfaces of the colloidal aggregates and the negatively charged DNA, with a potent entropic component. DOEPC/DOPE liposomes are mostly spherical, with a mean diameter of around 100 nm and a bilayer thickness of 4.4 nm. From a morphological viewpoint, an appreciable amount of multilamellar structures has been found not only on the lipoplexes but also on the parent liposomes. The isoneutrality of the lipoplexes is found at liposome/DNA mass ratios that decrease with the molar fraction of cationic lipid in the mixed liposome (α). This liposome composition has a clear effect as well on the lipoplex structure, which goes from an inverted hexagonal phase (HII), usually related to improved cell transfection efficiency, at low cationic lipid molar fraction (α ≈ 0.2), to a lamellar structure (Lα) when the cationic lipid content in the mixed liposomes increases (α ≥ 0.4), irrespective of the lipoplex charge ratio. On the other hand, a theoretical complexation model is employed to determine the net charge of the lipoplexes studied in this work, by using renormalized charges. The model allows us to confirm and predict the experimental isoneutrality conditions as well as to determine the maximum magnitude of this charge as a function of the composition of the resulting lipoplexes.

Cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) by simultaneous measurements of X-ray scattering and dielectric spectroscopy

The isothermal cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) was investigated by simultaneous small and wide angle X-ray scattering and dielectric spectroscopy (DS). By this experimental approach, simultaneously collected information was obtained about the specific changes occurring in both crystalline and amorphous phases during crystallization, namely about the chain ordering through wide angle X-ray scattering, about the lamellar crystals arrangement by means of small angle X-ray scattering, and about the amorphous phase evolution by means of DS. The results indicate that average mobility of the amorphous phase suffers a discontinuous decrease upon passing from the primary to the secondary crystallization regime. We interpret these results assuming that the restriction to the mobility of the amorphous phase occurs mainly in the amorphous regions between the lamellar stacks and not in the amorphous regions within the lamellar stacks.

Simultaneous measurements of small angle x-ray scattering, wide angle x-ray scattering, and dielectric spectroscopy during crystallization of polymers

A novel experimental setup is described which allows one to obtain detailed information on structural and dynamical changes in polymers during crystallization. This technique includes simultaneous measurements of small angle-wide angle x-ray scattering and dielectric spectroscopy (SWD). The capabilities of the technique have been probed by following in real time the crystallization process of a model crystallizable polymer: poly(ethylene terephthalate). By performing these experiments, simultaneous information from both, the amorphous and the crystalline phase is obtained providing a complete description of changes occurring during a crystallization process. The SWD technique opens up new promising perspectives for the experimental study of the relation between structure and dynamics in materials science.

Three-dimensional Model of Human Platelet Integrin αIIbβ3 in Solution Obtained by Small Angle Neutron Scattering

Integrin αIIbβ3 is the major membrane protein and adhesion receptor at the surface of blood platelets, which after activation plays a key role in platelet plug formation in hemostasis and thrombosis. Small angle neutron scattering (SANS) and shape reconstruction algorithms allowed formation of a low resolution three-dimensional model of whole αIIbβ3 in Ca2+/detergent solutions. Model projections after 90° rotation along its long axis show an elongated and “arched” form (135°) not observed before and a “handgun” form. This 20-nm-long structure is well defined, despite αIIbβ3 multidomain nature and expected segmental flexibility, with the largest region at the top, followed by two narrower and smaller regions at the bottom. Docking of this SANS envelope into the high resolution structure of αIIbβ3, reconstructed from crystallographic and NMR data, shows that the solution structure is less constrained, allows tentative assignment of the disposition of the αIIb and β3 subunits and their domains within the model, and points out the structural analogies and differences of the SANS model with the crystallographic models of the recombinant ectodomains of αIIbβ3 and αVβ3 and with the cryo-electron microscopy model of whole αIIbβ3. The ectodomain is in the bent configuration at the top of the model, where αIIb and β3 occupy the concave and convex sides, respectively, at the arched projection, with their bent knees at its apex. It follows the narrower transmembrane region and the cytoplasmic domains at the bottom end. αIIbβ3 aggregated in Mn2+/detergent solutions, which impeded to get its SANS model.