Last week, I was contacted by Christian Gollwitzer (author of this excellent paper) about something posted here (and in particular detailed in this document) a while ago. It concerns the behaviour of the Guinier approxiation for polydisperse systems, and it looks like I made a mistake when writing that document. This post is open to read and review on The Winnower.
Dear readers, Unfortunately, this week I do not have anything ready for you. It is with great regret that I must therefore skip this week, and break my “once-a-week” posting schedule. Regular scheduling should return next week. Just a quick note, however. Thanks to Sylvain Prévost bringing this back to my attention; Brûlet et al. derived a very similar equation to what was derived in last week’s post. Additionally, Strunz et al.  have some additional considerations for transmission factors that may need to be considered in X-ray scattering as well (in particular for ultra-small angle X-ray scattering). Hopefully I will have the time to look into these things in the near future and give you some more insight on the magnitude of these problems. As suggested by Sylvain, it may be a good idea to adapt the “imp2” data reduction software to be able to handle a more general consideration of transmission factors (then supporting both SAXS and SANS). A bit of thought is needed on how to enable fancy background subtraction while keeping the modular, flexible nature of the program. : Annie Brûlet, Didier Lairez, Alain Lapp and Jean-Pierre Cotton, “Improvement of data treatment in small-angle neutron scattering”, J. Appl. Cryst. 40 (2007), 165–177. [journal link], [free link] : P. Strunz, J. Scoversheet.dviaroun, U. Keiderling, A. Wiedenmann and R. Przenioslo, “General formula for determination of cross-section from measured SANS intensities”, J. Appl. Cryst. 33 (2000) 829–833. [journal link]
The long wait is over! A new publication is out, this one written by Martin Hollamby over the course of three tough years. For those who haven’t seen his one-minute intro video, Martin is investigating the behaviour of molecules in solvents. In his excellent paper, he shows how his range of molecules can self-assemble in (hydrophobic) solvents to form a variety of shapes and forms.
One paper I managed to miss for my review paper on data corrections is a paper by M. H. J. Koch from Hamburg. The paper is written in a nice informal way, replete with good quotes, where he talks about his experiences in instrument development for SAXS and WAXS beamlines. In particular the paper details the development of delay line (wire) detectors, and may form a good introduction into this topic. It seems that wire detectors may still have their uses: their rapid response to incoming photons still puts them among the fastest 2D detectors out there.
This news has also been covered by Birmingham University, Martin Hollamby and The Schnepp Group, and may appear in other news outlets soon. [update: like at azonano.com, nanowerk.com, the Mumbai mirror, FuelCellsWorks, supergen fuel cells, green car congress and phys.org. update2: Some more selected outlets: Ars Technica, the Conversation, World of Chemicals, Renewables Europe, Hydrogen and Fuel Cell letter (paywalled), and The Himalayan Mirror ] Imagine you could turn pigs into catalysts. You’d think that that would take quite some work, but it turns out to be surprisingly easy as long as you have a good oven and some salts lying around. This has been demonstrated by Zoe Schnepp (of the newly formed Schnepp Group at the U. of Birmingham) in collaboration with Yuanjian Zhang, Martin Hollamby and others during her time here at NIMS, and has just been published here. So what did we do?…
By the way, my topical review paper on SAXS data collection and correction has been published and is available open access here! Ensuring that a measurement gets you the right values is quite important for any scientist. One way of finding out what the quality of your machine is, is to compare your results for a standard sample with those measured by others on their instruments. Exactly this has been done by Adrian R. Rennie and coworkers: their publication (also open-access arXiv version or institutional repository version) details the results from analysis of a sample of polystyrene measured at a variety of neutron scattering instruments as well as an X-ray scattering instrument. The analysis and conclusions reveal a few telling issues with small-angle scattering measurements and instrumentation.
Following my previous work in progress detailing the data correction steps to obtain good data, I finally had the chance to write this down in a review article. This review article (open access) has been submitted on Monday. After it has been reviewed and (hopefully) published in the journal, I will ensure that that latest version is available as an open access paper (thanks to funds from NIMS/ICYS). Until then, please enjoy the pre-submission version and as always feel free to comment! [Sep. 22 edit: the ArXiv link has been replaced with a link to the journal, where the paper is available under an open-access license]
Small-angle scattering analysis has never been easy for those working with oriented nanostructures (e.g. fibres, processed polymers, rolled metal alloys), whose structure may lead to anisotropic small-angle scattering. Upon the collection of such 2D scattering patterns, one can integrate thin pie-slices of the data to obtain 1D curves and analyse them in the same way as “normal”, isotropic scattering patterns. This way, however, important cross-correlation information is lost. Alternative full-pattern fitting methods have been developed (amongst others during my Ph.D. studies), but they are complicated to tune to the system at hand and can be quite unstable in least-squares optimisations.