Abstract
The relationship between particle dynamics in a suspension drop during drying and final coffee ring patterns was investigated using suspension systems with spherical and non-spherical ellipsoidal particles. Employing multi-speckle diffusing wave spectroscopy (MSDWS), fast particle Brownian motions in suspension drops containing spherical and ellipsoidal particles were quantitatively compared during the drying process in real time. From the autocorrelation function data and characteristic times for β-relaxation, we confirmed that ellipsoidal particles move more slowly than spherical particles in a suspension drop due to their structural factor. The resulting coffee ring patterns by spherical and ellipsoidal particles are clearly distinguishable from one another and are dependent upon particulate concentration, initial drop volume, and particle shape. Notably, ellipsoidal particles in a suspension drop form coffee rings less readily than spherical particles.
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