Crystallization of ultrathin poly(ε-caprolactone) films in the presence of residual solvent, an in situ atomic force microscopy study

The influence of minute amounts of residual tetrahydrofuran on the crystallization of ultrathin poly(ε-caprolactone) (PCL) films has been investigated in real-time by atomic force microscopy. Crystallizations were performed at 30 °C, after melting at 64 °C, for different periods of time; both the morphology and growth rate of the crystals were found to depend on the thermal history of the sample, i.e. on the heating time, due to the evaporation of the residual solvent trapped in the spin-coated polymer. The residual solvent, acting as a plasticizer, facilitates the diffusion of the polymer chains to the crystal growth front; its elimination slows down the growth rates and leads to a decrease of the width of the dendrites. Growth rates were measured for the edge-on and for the flat-on lamellae, which are nucleated from them. Edge-on lamellae were found to crystallize 15 times faster than flat-on lamellae. Finally, spinodal dewetting was observed in the melt left between dendrites grown at 30 °C, after evaporation of the residual solvent, on a substrate of lower wettability. These observations are discussed in terms of the mobility of polymer chains in the melt.