G.E. Derbyshire

Simultaneous time resolved SAXS and WAXS experiments using synchrotron radiation

Abstract Instrumentation has been developed which offers the possibility of performing simultaneous time resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) experiments in the range from approximately 0.007–0.21 A −1 and 0.31–4.2 A −1 . A synchrotron SAXS beamline is therefore equipped with two gas filled proportional detectors. The ultimate system time resolution will be of the order of 1 μs. Successful test experiments have been performed on block copolymer samples and polyethylene.

Simultaneous SAXS/WAXS and d.s.c. analysis of the melting and recrystallization behaviour of quenched polypropylene

Abstract The behaviour of a quenched ethylene-propylene block copolymer cast film has been investigated during melting and recrystallization experiments carried out at heating and cooling rates of 10°;C min −1 . The experimental techniques used to follow the melting and recrystallization processes were differential scanning calorimetry (d.s.c.) and simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). In particular, the WAXS results show that the melting of the material is preceded by a solid-state transition involving transformation of the quenched structure into the monoclinic α modification. This transition appears as an exotherm in the range 65–120°C on the d.s.c. melting trace. SAXS results show that an increase in the amount of long-range order occurs during this transition. The sample was then found to melt at 162°C. Upon cooling from the melt, recrystallization of the monoclinic α modification was found to occur in the range 123-105°C without any apparent prior formation of the quenched structure.

Simultaneous studies of reaction kinetics and structure development in polymer processing.

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.

The Combination of Thermal Analysis and Time-Resolved X-ray Techniques: a Powerful Method for Materials Characterization

A differential scanning calorimeter with a temperature range of 77 to 873 K has been developed for use in combination with either time-resolved X-ray scattering or high-resolution energy-dispersive powder diffraction studies using synchrotron radiation. The first results of successful experiments are briefly described.

A direct method to determine the degree of crystallinity and lamellar thickness of polymers: application to polyethylene☆

Abstract Time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) patterns have been simultaneously obtained during melting and crystallization of high-density polyethylene using a newly constructed camera at the SRS, Daresbury. The data have been analysed to yield the long spacing, the degree of crystallinity and the lamellar thickness in the context of the two-phase model. The long spacing was obtained from the peak in the Lorentz-corrected SAXS pattern. The degree of crystallinity was obtained from a combination of the SAXS invariant and the integrated WAXS intensity of the crystals. The invariant passes through a maximum at 50% crystallinity and the integrated WAXS intensity is a minimum for the melt. Thus two points in the linear relationship between the WAXS intensity and the degree of crystallinity are known, affording calibration. Calculation of the degree of crystallinity by solving the quadratic in the SAXS invariant gave good agreement with the WAXS result. The long spacing and the degree of crystallinity may be combined in the two-phase model to estimate the lamellar thickness, an important parameter in determining mechanical properties.

Simultaneous monitoring of amorphous and crystalline phases in silicalite precursor gels. An in situ hydrothermal and time-resolved small- and wide-angle X-ray scattering study

The gel transformations and subsequent crystallization that occur in the precursor reaction mixture of silicalite were investigated using simultaneous small- and wide-angle X-ray scattering (SAXS–WAXS). The SAXS–WAXS measurements, together with the use of a high flux of synchrotron radiation and a newly developed high-pressure reaction cell, provide the possibility of in situ hydrothermal and time-resolved monitoring of amorphous gel transformations and crystallization.

Aerodynamic laser-heated contactless furnace for neutron scattering experiments at elevated temperatures

Conventional radiative furnaces require sample containment that encourages contamination at elevated temperatures and generally need windows which restrict the entrance and exit solid angles required for diffraction and scattering measurements. We describe a contactless windowless furnace based on aerodynamic levitation and laser heating which has been designed for high temperature neutron scattering experiments. Data from initial experiments are reported for crystalline and amorphous oxides at temperatures up to 1900 °C, using the spallation neutron source ISIS together with our laser-heated aerodynamic levitator. Accurate reproduction of thermal expansion coefficients and radial distribution functions have been obtained, demonstrating the utility of aerodynamic levitation methods for neutron scattering methods.

A low-profile monolithic multi-element Ge detector for X-ray fluorescence applications

A highly compact and rapid-count-rate multi-element solid-state detector has been designed, built and recently commissioned on the oldest XAFS station of the SRS, station 7.1, which has undergone major refurbishment. The low profile of the detector has been achieved by using the monolithic solution where nine elements with a combined active area of 370 mm2 have been fabricated on Ge of diameter 21.8 mm. A typical energy resolution of 170 eV with a semi-Gaussian shaping time of 0.5 µs has been achieved with X-rays of energy 5.9 keV. The low profile of the detector makes it ideal for several synchrotron radiation applications as it can be easily incorporated into complicated experimental set-ups. These include XAFS of single crystals and samples generated in a stopped flow system, protein crystallography (fluorescence XAFS for MAD or for on-line monitoring), microprobe fluorescence imaging and trace-element analysis.

Combined energy dispersive EXAFS and x‐ray diffraction

An in situ experiment to measure both x‐ray absorption spectroscopy and x‐ray diffraction of aurichalcite is described. The experiment uses position sensitive detectors to enable both data sets to be collected while the sample is slowly decomposed in air and then reduced in hydrogen.

High-performance X-ray detectors for the new powder diffraction beamline I11 at Diamond.

The design and performance characterization of a new light-weight and compact X-ray scintillation detector is presented. The detectors are intended for use on the new I11 powder diffraction beamline at the third-generation Diamond synchrotron facility where X-ray beams of high photon brightness are generated by insertion devices. The performance characteristics of these detection units were measured first using a radioactive source (efficiency of detection and background count rate) and then synchrotron X-rays (peak stability, light yield linearity and response consistency). Here, the results obtained from these tests are reported, and the suitability of the design for the Diamond powder beamline is demonstrated by presenting diffraction data obtained from a silicon powder standard using a prototype multicrystal analyser stage.