Crystal morphologies in thin films of PEO/PMMA blends

Crystallization in thin films of poly(ethylene oxide) in blends with poly(methyl methacrylate) has been studied. The film thickness is fixed at 120 nm, while the blend composition, PMMA molar mass, and crystallization temperature are varied. Blends with a composition of 50/50 (wt% PEO/wt% PMMA) exhibit a variety of morphologies that are highly dependent on PMMA molar mass and crystallization temperature. A needle morphology not previously reported in this system is also observed. For 40/60 blends, dendrites and DBM are observed at high PMMA molar mass. At low PMMA molar mass, a number of morphologies are observed over small changes in the experimental controls. In 35/65 blends, dendritic growth is observed with sidebranches at 45° and 90° to the dendrite trunk at low undercooling and only at 90° for larger undercooling. For 30/70 blends, dendritic growth is observed over a large range of PMMA molar mass and crystallization temperature. Maps demonstrating the role of the control parameters on morphological development are reported. The observed morphologies are believed to result from the combined effects of the lack of crystallizable chains at the growth front, low dimensionality, rejection of non-crystallizable chains, and variation of the effective levels of noise and/or anisotropy.