Reorganization of molecular alignment in naphthalene and methyl-naphthalene derived pitches

Molecular alignment in methyl-naphthalene and naphthalene-derived mesophase pitch materials was studied at different levels of resolution by means of optical microscopy, X-ray, and TEM using the 002 lattice fringe technique, to determine the influence of different solidification procedures on the molecular alignment in the solidified pitches. Rapid resolidification procedures -quenching in liquid nitrogen or extraction -were found to reduce domain size and molecular alignment in the solidified pitch materials, whereas annealing followed by a slow cooling step produced better alignment, larger domains, or Brooks and Taylor type spheres, depending upon the composition of the pitch. Such rearrangement can be compared to a rate-controlled process such as recrystallization. Quite different molecular rearrangement behavior was found for naphthalene and methyl-naphthalene pitches, reflecting variations in their molecular stacking heights. The degree of liquid crystal alignment and the limitations of TEM in examining these types of structures are discussed.