IN-SITU CHARACTERIZATION OF COLLOIDAL SPHERES BY SYNCHROTRON SMALL-ANGLE X-RAY-SCATTERING

We have performed small-angle X-ray scattering with a synchrotron sour ce on dilute suspensions of colloidal spheres of polystyrene latex, St ober silica, and microemulsion-grown silica, Many interference fringes are observed of the monodisperse particles over a large range of scat tering vectors and more than 5 orders of magnitude in intensity. We pr esent a straightforward method to deduce the radii, the size polydispe rsity, and the interface thickness of the particles from a Pored plot of one and the same in situ measurement. The radii agree very well wit h static light-scattering data. The radii are larger than the electron microscopy data of dry spheres and smaller than the hydrodynamic radi i from dynamic lightscattering data. The size polydispersities are sma ller than those obtained by electron microscopy, which is well explain ed by the intrinsic random errors of electron microscopy. We find that nearly all the particles have a homogeneous internal density and a sh arp interface with the suspending medium of less than 1 nm wide. In on e case of a stepwise synthesized particle, we have discerned a dense c ore and a less-dense shell, without contrast matching with the suspend ing liquid. It is concluded that synchrotron small-angle X-ray scatter ing is a very powerful technique for the in situ study of colloidal sy stems.