Nonuniformity, chemical reaction dynamics

NMR imaging was used to study the spatial distribution of molecules with chemically induced dynamic nuclear polarization. It is shown that heating of a system during the photolysis can cause a highly nonuniform distribution of reaction products due to a convective effect. 

Dispersion, the tendency for ordered molecules to decrease gradients and local concentration, is caused by both molecular diffusion and nonuniform bulk liquid motion. High dispersion rates may be advantageous for mixing and chemical reactions, but are undesirable in separation and purification applications. For separations, minimizing dispersion improves resolution and sensitivity [3] and yields improved dynamics for concentration and purification [4]. As a consequence, the physical processes that lead to dispersion have been a subject of intense interest for more than a century. In recent years, the development of the concept of the micro-total analysis system (p,TAS) or labs on a chip has motivated further exploration of dispersion in microchannel flows. 

---