Macromolecules, Vol.40, No.23, 8336-8341, 2007
Solution drying and phase separation morphology of polyacrylamide/poly(ethylene glycol)/water system
Blends of two immiscible polymers dissolved in a common solvent exhibit phase separation during drying of the solvent. This leads to different morphologies depending on the physical and physicochemical conditions of the systems. Here we report the final morphology of blend films of a glassy polymer (polyacrylamide, PAAm) and a crystalline polymer (poly(ethylene glycol), PEG) in water, prepared by blade coating with a controlled thickness from several to hundreds of micrometers. By changing the blend composition, we observed the inversion in morphology from mounds to holes via multiscale phase separation. A systematic study of PAAm-rich films having a morphology with holes revealed that two regimes may be distinguished depending on the drying rate: a heterogeneous drying regime where a glassy skin of PAAm is formed at the surface and fixes the morphology and a slow homogeneous drying regime where coalescence of holes is observed. Formation of monolayer of PEG crystals having fingerlike branched patterns at the surface of the PAAm matrix at different drying conditions is discussed.