Film formation from polymer solution using inkjet printing method

The factors determining the thin-film shape from an evaporating polymer solution droplet are experimentally studied. The polystyrene/xylene droplets, whose diameter is controlled in the range of 30-100 mu m with the mass fraction of 0.5-3.0 wt % are ejected onto a lyophobic substrate. The droplet on the substrate results in an axisymmetric or nonaxisymmetric ring-like/dot-like film. The film configuration is dominated by the evaporation rate and the film symmetry is governed by the local pinning time at the periphery. Various relationships are also found among the evaporation rate, pinning time, wetting diameter, and average solute concentration of which the nondimensionalization pronounces explicit relationships and similarity. (c) 2007 American Institute of Chemical Engineers.