CLRC Normal Template

EARLY RESULTS FROM MPW 6.2

Nick Terrill

The pattern to the left was taken with RAPID II on MPW 6.2 using an as yet not fully optimised set of optics. It is from Si powder (NBS640b) (l=1.24 Å). The resolution is already approximately 0.08° FWHM.

Below is a phase transition of Gypsum converting to Bassanite. The data was collected with a 3-second time resolution. Each frame equates to 0.01°C. The whole experiment took approximately 10mins. cf. 8 hrs per spectra with a conventional scanning mode system.

Data comparison between MPW 6.2 and the Dutch-Belgian beamline, DUBBLE an excellent user facility for SAXS/WAXS at the ESRF, is promising. The wide-angle component on DUBBLE is based on gas-glass microstrip technology. This has inherently higher count rates than RAPID II but at present poorer angular resolution. Data collected recently by Ellen Heeley and Tony Ryan (Sheffield Univ.) demonstrate this point. The figures opposite show the same polymer data set (Daplen iPP) collected on a) DUBBLE and b) on RAPID2 in approximately one hour. The rather poor appearance of the background for RAPID is due to incomplete determination of the detector resolution function.

The first early test of the SAXS/WAXS combination were carried out by analysing a 0.5% by weight high-density polymer (E76B38) in hexane. This experiment was designed to examine crystallisation in constrained geometries. The block copolymer chains have two hydrophobic amorphous ends and a crystallisable centre. When the ethylene oxide crystallises the micelle ends up with exposed hydrophilic sides to a cubic shaped micelle.

In this plot crystallisation can be clearly seen taking place within the micellar rafts at 2q approx. 19.1 and 23.4° respectively

A 10wt% solution was collected on Station 8.2. This, however, contained both Structure and Form factor. At 0.5wt% the form factor can be isolated giving information on the shape of individual micelles.

Conclusions

Early unoptimised results compare very favourably with ESRF bending magnets

Diffraction data of refineable quality can be obtained in seconds

EXAFS, Small and Wide-angle scattering can be obtained for the same sample

Small and Wide-angle scattering are genuinely simultaneous

The station allows simultaneous measurement of sample properties that can be correlated to structure

The detectors are based on the Rapid design and have been constructed by the Daresbury detector group

The station will be available for users from April 2003


In this plot crystallisation can be clearly seen taking place within the micellar rafts at 2q approx. 19.1 and 23.4° respectively	A 10wt% solution was collected on Station 8.2. This, however, contained both Structure and Form factor. At 0.5wt% the form factor can be isolated giving information on the shape of individual micelles.