Ultra-small-angle X-ray scattering studies of attractive colloidal glass transition

The microstructure of a colloidal system with short-ranged inter-particle interactions is studied by ultra-small-angle X-ray scattering (USAXS). A gas-liquid type transition can be induced when the short-ranged attractive interactions attain sufficient magnitude. The static structure factor revealed a systematic development of attractive interactions prior to the appearance of the liquid-like structure. The interparticle interaction in the close vicinity of the transition can be approximately described by a square-well potential with a hard-sphere repulsion. The colloid-rich phase is structurally similar to a liquid, but dynamically it shows extreme non-ergodic behaviour with a complete kinetic arrest. Furthermore, the USAXS intensity from the colloid-rich phase shows Porod behaviour indicating that the colloidal clusters have non-fractal morphology. The attractive term disappears when the domains develop towards their final size suggesting that particles within the clusters interact like hard spheres.