Transmission X-ray scattering as a probe for complex liquid-surface structures

• Published in: Journal of synchrotron radiation 2016-03, Vol.23 (2), p.519-531
• Main Authors: Fukuto, Masafumi, Yang, Lin, Nykypanchuk, Dmytro, Kuzmenko, Ivan
• Format: Article
• Language: English
• Subjects: air/water interface; liquid surface scattering; MATERIALS SCIENCE; SAXS; transmission X-ray scattering; WAXS
• ISSN: 1600-5775; 1600-5775
• DOI: 10.1107/S1600577515023103

The need for functional materials calls for increasing complexity in self‐assembly systems. As a result, the ability to probe both local structure and heterogeneities, such as phase‐coexistence and domain morphologies, has become increasingly important to controlling self‐assembly processes, including those at liquid surfaces. The traditional X‐ray scattering methods for liquid surfaces, such as specular reflectivity and grazing‐incidence diffraction, are not well suited to spatially resolving lateral heterogeneities due to large illuminated footprint. A possible alternative approach is to use scanning transmission X‐ray scattering to simultaneously probe local intermolecular structures and heterogeneous domain morphologies on liquid surfaces. To test the feasibility of this approach, transmission small‐ and wide‐angle X‐ray scattering (TSAXS/TWAXS) studies of Langmuir films formed on water meniscus against a vertically immersed hydrophilic Si substrate were recently carried out. First‐order diffraction rings were observed in TSAXS patterns from a monolayer of hexagonally packed gold nanoparticles and in TWAXS patterns from a monolayer of fluorinated fatty acids, both as a Langmuir monolayer on water meniscus and as a Langmuir–Blodgett monolayer on the substrate. The patterns taken at multiple spots have been analyzed to extract the shape of the meniscus surface and the ordered‐monolayer coverage as a function of spot position. These results, together with continual improvement in the brightness and spot size of X‐ray beams available at synchrotron facilities, support the possibility of using scanning‐probe TSAXS/TWAXS to characterize heterogeneous structures at liquid surfaces. The potential of scanning transmission X‐ray scattering as a position‐sensitive probe for structures at liquid surfaces is explored.