Are Spherulites Spherical? 3D Visualization of Semicrystalline Polymer Morphology Using Optical Tomography*

Spherulites, shish-kebab, cylindrites and other morphological features of bulk semicrystalline polymers have been studied for decades using methods such as polarized optical microscopy, TEM or AFM. For these studies either thin films or thin sections were used, giving 2D but not 3D pictures. The organization in the 3^rd dimension has been implied rather than directly observed. Attempts at 3D imaging have been made with varying success using approaches, notably electron tomography (TEMT) and some other methods. Most studies focussed on polymer blends and block copolymers, relying on contrast produced by the chemically different components, although some remarkable images of crystal lamellae were obtained by TEMT. However 3D images of microstructure on the crucial 10-1000 micron scale, especially of single-component polymers or their nanocomposites, are still missing. Here we present first such images obtained by confocal microscopy using appropriate sample preparation and image processing. Already rather unsuspected features of 3D morphology are emerging, previously being hidden by the limitations of the conventional techniques.