Influence of single wall carbon nanotubes and thermal treatment on the morphology of polymer thin films

Homogeneous and stable thin films of poly(butylene terephthalate) PBT and its nanocomposites based on single wall carbon nanotubes (SWCNTs) were prepared by spin coating. PBT thin films show crystalline structures for thicknesses above 40 nm, consisting of submicrometer size 2D-spherulites. In the case of nanocomposites, carbon nanotubes act as nucleating agents and provide a template for the crystallization of PBT. This gives rise to hybrid shish-kebab structures, even in the thinnest films (∼10 nm thick). Melting and recrystallization provoke the crystallization of PBT and its nanocomposites, and can be used to control morphology. For PBT thin films, the orientation of crystalline lamellae undergoes a transformation, changing from a disposition perpendicular to the substrate (“edge-on”) to a parallel arrangement (“flat-on”) after recrystallization. In the case of the nanocomposites, the CNT influence on the polymer crystallization morphology in thin films is less significant than in the bulk due to the effect of the substrate interactions. Using Raman microscopy it is possible to directly observe both, the degree of dispersion and the location of carbon nanotubes in the films. The results reveal that bigger agglomerates act as more effective nucleating points than isolated bundles of SWCNTs during crystallization of the polymer matrix.