Influence of lateral confinement an phase separation in thin film polymer blends

Thin films of polymer blends are molded into strips for investigating the i nfluence of lateral confinement on phase separation. The strip has a width and thickness of 17 mu m and 1.0 mu m, respectively, and contains a 50/50 b lend of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile ) (SAN). Upon annealing, the strip profile rapidly becomes bell-shaped, for ming a contact angle of 3 degrees with the substrate. The dynamics of phase separation is investigated using confocal microscopy and atomic force micr oscopy. The early stage is characterized by an interconnected morphology an d symmetric wetting of the PMMA-rich phase at the substrate and surface. Th e PMMA-rich domains grow from the surface toward the substrate during the e arly intermediate stage and eventually connect with the wetting layer cover ing the substrate to begin the late intermediate stage. The domain diameter increases rapidly (early), slows down (intermediate), and then decreases(l ate) during phase separation. During the late stage the PMMA-rich domains h eal,leaving behind an elliptical SAN-rich core encapsulated by PMMA-rich we tting layers. These studies demonstrate, that confinement directs the forma tion of a self-assembled core/shell morphology, which has potential applica tions for encapsulating drugs or creating microwires.