New shear apparatus for in situ small-angle x-ray scattering experiments

Small-angle scattering is a powerful tool for the investigation of micellar solutions. By applying a shear flow, increased information can be obtained . A new parallel disks shear apparatus for in situ detection of the sheared state by means of small-angle x-ray scattering is described. The steady sh ear rate Gamma may be changed from 0.25 to 200 s(-1). If needed transient s hear rates Gamma having the shape of stop and go, being sinusoidal or a ram p, can be applied. Typical response times of the apparatus are less than 1 s. The path length of the x rays in the shear cell can be continuously chan ged between 0.5 and 5 mm. The angle alpha between the incident x-ray beam a nd the shear gradient vector Gamma may be varied from 0 degrees to approxim ately 55 degrees. As an example, we give a brief report of experiments perf ormed on two sheared aqueous surfactant solutions with differently shaped ( disk-like and rod-like) particles: a 30% by weight solution of tetramethyla mmonium perfluorononanoate in D2O and a 30 mM solution of tetraethylammoniu m perfluorooctanesulfonate in H2O. (C) 1999 American Institute of Physics. [S0034-6748(99)04501-3].