Crack Formation on a Drying Droplet in the Presence of Static Electric Field

摘要

The formation of crack patterns in a drying droplet of Laponite is studied under a DC (direct current) field. Though in the absence of a field, the droplet produces no crack on drying, it gives remarkable and reproducible results in the presence of a radial field. Cracks always appear from positive electrode and propagate towards the negative electrode and water seeps out from the negative electrode. When the centre electrode is negative, small cracks appear from outer periphery and the central portion remains almost free of crack. The behavior of cracks depends on the strength, direction and duration of application of field. The patterns show a typical memory effect different from 'Nakahara effect'. We name this as 'persistence memory'. From SEM (Scanning Electron Microscopy) images, it is seen that there are some striation marks left on the cracked surface, similar to cracks in larger systems.