Small-angle X-ray scattering from solutions of flow-oriented colloidal particles

The amount of information which can be obtained from a small-angle X-ray experiment can be considerably increased by orienting the solute particles with external forces during the scattering experiment. In this paper it is shown that orientation by flow, for instance through a capillary tube, gives additional information about size, shape, flexibility and rotational diffusion of the particles. The only requirement, in order to obtain flow-oriented samples, is that the solute particles must be relatively large and asymmetric. On the other hand, if the scattering curve is dependent on the flow rate through the capillary, it can immediately be concluded that the solute particles are asymmetric (or they are deformed in the hydrodynamic field). Equations describing the relationship between flow rate, molecular shape and scattered intensity are given, and theoretical intensity patterns for some representative cases are presented. It follows that there is a fundamental difference in scattering patterns for oblate and prolate ellipsoids of revolution. This difference can be used to differentiate between these two cases. Some experimental results obtained using inorganic model colloids are presented.