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The nucleation behavior of poly( -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.

In studies of spherulitic crystallization in polymers, many questions pertaining to the mechanism of the crystallization process have remained unanswered. A currently accepted view describes the development of spherulites from a framework of individual dominant lamellae that splay apart and branch (e.g., by a dislocation mechanism). This model, in addition, assumes that the space between the dominant lamellae is filled by subsidiary lamellae. In the center of a spherulitic entity, there is a hedritic core that occupies a relative volume that depends on the level of maturity of the spherulitic development. Typical hedritic views consist of lamellae that have a flat stack, or sheaflike, splaying appearance depending on the angle and depth of observation with respect to the central stack of lamellae. Visualization of the three-dimensional appearance of these hedrites by atomic force microscopy (AFM) and the observation of their growth in situ are the subjects of this article. First, we describe AFM studies of hedrites observed at etched surfaces of p-isotactic polypropylene 492 VANCSO ET AL.porting splaying, branching via dislocations, and development of curved lamellae is presented. In the second part, we describe real-time hot-stage AFM in situ observations of the hedritic growth in poly(ethy1ene oxide) (PEO) and poly-(E-caprolactone) (PCL).

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