Comparative study on surface morphology by photo- and thermal-polymerization of a diacetylene with a tapping-mode AFM

Morphology changes in thermal- and photo-polymerization were studied with a tapping-mode atomic force microscope on the (1 0 0) surface of 2,4-hexadiyne-1,6-diol-bis(p-toluenesulfonate) by careful tuning of force. In the thermal-polymerization, the surface exhibits nodules with 50 nm size which become to align as ridges along the b-axis of crystal after full polymerization. This may be resulted from the stress relaxation on the surface. In the photo-polymerization, a different feature was observed in addition to the nodules; rod-like polymer crystallites with smooth crystallographic surfaces were formed mainly at surface steps especially at low conversion. These polymer crystallites are grown at steps as preferred polymerization sites by being controlled presumably due to the surface diffusion of monomers.