New bio-SAXS beamline ID14-3 at the ESRF

Petra Pernot, Adam Round
2009 Acta Crystallographica Section A Foundations of Crystallography  
NSRRC) with a 1.5 GeV storage ring, a small-angle X-ray scattering (SAXS) beamline has been installed. The X-ray beam can be selectively monochromatized by a double Si(111) crystal monochromator (DCM) with high energy resolution (∆E/E ≈2×10 -4 ) in the energy range of 5-23 keV or by a double Mo/B 4 C multilayer monochromator (DMM) for 10-30 times higher flux (~10 11 photons/s) in the 6-15 keV range. A plane mirror is especially installed to the beamline to selectively deflect the beam downwards
more » ... with high precision for grazing-incidence SAXS (GISAXS) with liquid surfaces. Using a grazing incident angle near the critical angle of water with 10 keV X-rays, we have monitored in-situ the growth process of silicate films at the air-water interface. Cetyltrimethylammooium bromide (CTAB) is used as the surfactant template for the tetraethyl orthosilicate (TEOS) in the solution in forming mesoporous silicated films, with the film growth temple controlled by temperature (in the range 25-55 °C) and pH value. The TESO molar ratio is varied from 0.04 ro 0.7 with respect to the molar ratio of H 2 O:HCl:CTAB = 100:2-0.5:0.11. At 25 °C, after an induction period the formation of a lamellar phase and its transformation to a hexagonal mesophase of single-crystal-like reflections can be clearly observed. The layering process of the silicate rods, however, can be suppressed at higher temperatures above 45 °C; namely, the hexagonally-packed silicate rods can be formed near the air-water interface without going through the layering process of the rods, which is due presumably to larger thermal fluctuations. 1 Furthermore, transmission SAXS is used to monitor the evolution of the aggregation structure of the silicate/surfactant complex in the bulk solution. During the induction period, there are mainly complex CTAB/TESO rod-like micelles. Later, randomly oriented domains of lamellarly and hexagonally packed rods appear sequentially in the bulk solution. These results imply that the lamellar-to-hexagonal phase transformation can occur both in the bulk and near the air-water interface. Instead of layer-by-layer formation, it is possible that the silicate films may grow via reorientation-and-attachment of ordered silicate domains that adsorb to the air-water interface, while there is a thin surface layer of one or two micelle thickness stabilized at the air-water interface. [1] S.
doi:10.1107/s010876730909758x fatcat:bolcr4jssjcdrl2trm5d4nficm