Confined dynamics, forms and transitions in colloidal systems: from clay to DNA

In this presentation, we show how the slow and confined water dynamics at proximity of a colloidal surface provides an original way to probe colloidal shape and colloidal orientation dynamics. Two topics are presented. First of all, water field-cycling NMR relaxometry is used to probe the glass transition and the strong rotational slowing down of a colloidal system made of plate-like particles, a synthetic clay (laponite). Second, we analyze the case of long colloidal thin rods (either mineral or biologic such as DNA cylinders) dispersed in very diluted suspensions. At large distance and/or long time, these particles appear as a portion of a line. We discuss how the embedded fluid dynamics can be sensitive to this morphological crossover and may provide information about the particle shape. Some comparisons with recent experiments are presented.