Polymer melt and recrystallization

Melting and recrystallization of a sPP-PS polymer film 

This movie shows a polymer thin film consisting of syndiotactic polypropylene (sPP) and polystyrene (PS) that was imaged as a function of changing temperature on the Cypher ES AFM using blueDrive photothermal excitation. The scan size is 3 µm and the data channel shown is phase because it shows the most contrast. The round, isolated domains are PS and the continuous matrix around them is the sPP. Note that the melting temperature of sPP is ~ 130-170°C while the melting temperature of PS is ~240°C. The movie starts with the sample at ~60°C. It is then slowly heated to ~135°C, during which time you can observe the PP crystallites melt, diminishing in size and forming a melted layer. You can actually see the high motility of the crystallites in the melt. Notably the heating is stopped before the sPP is fully melted and the sample is then slowly cooled. The remaining crystallites act as nucleation sites, recrystallizing and growing. Once the temperature has returned to 60°C, you see larger features appear. Note that the recrystallization occurs much differently if the sPP is fully melted.