Nucleation and Growth of Poly(E-caprolactone) on Poly(tetrafluoroethylene) by In-Situ AFM

The nucleation behavior of poly(ε-caprolactone) (PCL) on friction-deposited poly(tetrafluoroethylene) (PTFE) was investigated by means of atomic force microscopy (AFM). This technique allows for imaging of the nucleation and crystallization processes in real time. An estimation of the PCL crystal orientation on the PTFE substrate is made by evaluating the growth rates and the growth geometry of the lamellar crystals formed on PTFE. On the basis of the data collected, it is proposed that PCL crystallizes on PTFE predominantly via a (100)_PCL contact plane (∼80%). The crystals adopt an orientation that minimizes the lattice mismatch at the interface between the nucleating PTFE and PCL. A (010)_PCL||(100)_PTFE contact plane was simultaneously observed at a lower occurrence of approximately 20%. Visualization of the PTFE fibrillar morphology at higher resolution during isothermal crystallization revealed the appearance of a third PCL crystal orientation which developed later in time. The corresponding crystals were observed to develop from grooves on the PTFE substrate, indicating a graphoepitaxial nucleation mechanism.