Dynamic transmission electron microscopy of the [1,6-di(N-carbazolyl)-2,4-hexadiyne] diacetylene monomer-polymer phase transformation

The monomer-polymer phase transformation has been directly imaged in [1,6-di(N-carbazolyl)-2-4-hexadiyne] diacetylene crystals by low-dose dynamic transmission electron microscopy. The crystallography of the phase transition has been studied by dynamic selected-area electron diffraction. The polymerization was found to be quasihomogeneous, with the lattice parameters changing continuously through a series of crystalline intermediate states. The solid-state reaction was found to be analogous to a martensitic phase transition with three invariant planes: (001), (220), and (220). The transformation matrix T-mp relating the monomer and polymer crystal reciprocal lattices was determined. Diffraction streaks developed along directions normal to the (200) and (2(2) over bar0$) planes during the phase transformation. These streaks fade away at the end of the polymerization. The microstructural evolution during the polymerization reaction was also examined by dynamic dark-field and high-resolution electron microscopy.