It could be shown that by a simple casting process from solution two-dimens
ionally ordered arrays of mesoscopic (i.e., in the range of submicrometer t
o micrometer) polymer aggregates on solid substrates can be formed. Pattern
s were investigated by optical microscopy and atomic force microscopy. The
pattern formation was observed in situ by optical and fluorescence microsco
py and it was found that a "fingering instability'' at the three-phase-line
of a solution droplet is the crucial process for pattern formation. (C) 19
99 American Institute of Physics. [S1054-1500(99)00902-7].