X-ray microscopy studies of aqueous colloid systems

Abstract

X-ray microscopy is capable of imaging objects with a higher resolution than light microscopy. The reason is the shorter wavelength of x-rays compared to visible light. Up to now, the smallest structures that can be visualized are about 30 nm in size. It is possible to image objects directly in their aqueous environment without preparational procedures like drying, staining, etc. In the wavelength range of 2.4 nm ⩽ λ ⩽ 4.5 nm water absorbs x-radiation weakly compared to the absorption of other materials like alumino silicates, iron oxides or organic materials. This yields a natural contrast mechanism for the imaging of structures in their aqueous environment. Studies of aqueous colloidal systems demonstrate the abilities of x-ray microscopy. The aggregation of hematite particles under the influence of divalent cations (Ca²⁺) is investigated. The dependence of the size and the shape of the aggregates on the amount of added Ca²⁺ is directly visualized.