SAXS

This review aims at highlighting on recent developments in preparation, characterization, properties, crystallization behaviors, melt rheology, processing, and future applications possibilities of biodegradable polymers and their layered silicate nanocomposites. These materials are attracting considerable interest in materials science research. Montmorillonite and hectorite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into biodegradable polymer matrices. The most common strategy to overcome this difficulty is to replace the interlayer clay cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains.A wide range of biodegradable polymer matrices is described in this review with a special emphasis on polylactide because of more eco-friendliness from its origin as contrast to the fully petroleum-based biodegradable polymers and control of carbon dioxide balance after their composting.Preparative techniques include (i) intercalation of polymers or prepolymers from solution, (ii) in situ intercalative polymerization method, and (iii) melt intercalation method.This new family of composite materials frequently exhibits remarkable improvements of mechanical and material properties when compared with virgin polymers or conventional micro- and macro-composites. Improvements can include a high storage modulus both in solid and molten states, increased tensile and flexural properties, a decrease in gas permeability and flammability, increased heat distortion temperature and thermal stability, increase in the biodegradation rate, and so forth.

Troponin is a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle by participating in a series of conformational events within the actin-based thin filament. Troponin is a heterotrimeric complex consisting of a Ca2+-binding subunit (TnC), an inhibitory subunit (TnI), and a tropomyosin-binding subunit (TnT). Ternary troponin complexes have been produced by assembling recombinant chicken skeletal muscle TnC, TnI and the C-terminal portion of TnT known as TnT2. A full set of small-angle neutron scattering data has been collected from TnC-TnI-TnT2 ternary complexes, in which all possible combinations of the subunits have been deuterated, in both the +Ca2+ and -Ca2+ states. Small-angle X-ray scattering data were also collected from the same troponin TnC-TnI-TnT2 complex. Guinier analysis shows that the complex is monomeric in solution and that there is a large change in the radius of gyration of TnI when it goes from the +Ca2+ to the -Ca2+ state. Starting w...

Many research topics in the fields of condensed matter and the life sciences are based on small-angle X-ray and neutron scattering techniques. With the current rapid progress in source brilliance and detector technology, high data fluxes of ever-increasing quality are produced. In order to exploit such a huge quantity of data and richness of information, wider and more sophisticated approaches to data analysis are needed. Presented here is GENFIT, a new software tool able to fit small-angle scattering data of randomly oriented macromolecular or nanosized systems according to a wide list of models, including form and structure factors. Batches of curves can be analysed simultaneously in terms of common fitting parameters or by expressing the model parameters via physical or phenomenological link functions. The models can also be combined, enabling the user to describe complex heterogeneous systems.

Small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and other techniques were combined in a study of segmented thermoplastic elastomers (Pebax) containing poly(tetramethylene oxide) soft segments and hard blocks of nylon-12. AFM was used to provide real-space resolution of the morphology during tensile elongation and after subsequent relaxation. Nanofibril formation, starting at strains of about 1.5×, was characterized in detail, showing the evolution of the number, orientation, and size of these highly stressed load-bearing fibrils that dominated the mechanical properties. AFM results were combined with two-dimensional SAXS data to develop a model considering the breakup of the original ribbonlike nylon-12 lamellae in combination with progressive reformation and orientation of highly stressed fibrils. The complex changes in the two-dimensional SAXS images included a distorted arc pattern due to increased spacing of the lamellae in the stretch direction at low strains, with an evolution to completely different patterns dominated mainly by intrafibrillar and interfibrillar scattering contributions. Between stretch ratios of 1.5 and 2.3× original lamellae were progressively broken up, and by 3.2×, all lamellae independent of the initial orientation were broken into smaller crystals with low aspect ratios. The results were combined with differential scanning calorimetry and birefringence data taken on films under strain to obtain insight into the microscopic basis for strain softening and plastic deformation in Pebax and related segmented polymers. Birefringence cycling with strain provided a consistent picture with the other techniques for understanding the redistribution of stress on a nanoscopic scale during deformation and relaxation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1727–1740, 2002

The morphology of poly(aryl-ether-ether-ketone) (PEEK) has been studied using optical microscopy (at room temperature and at elevated temperatures), small-angle light scattering (H v and V v ), transmission electron microscopy (bright field, dark field, and selected area electron ...