Crystallization of Polypeptides in Thin Films: Structures and Patterns

In This work, I have shown the process of nucleation and growth of large scale PBLG birefringent crystals from semidilute thin film solutions. In solution, these birefringent objects show a single domain structure and are assumed to be in a hexagonal columnar liquid crystalline state. After drying, this single domain splits up into multiple almost parallel domains, each consisting of perfectly aligned parallel stripes. Between adjacent domains, the orientation of the stripes conjointly changed by a certain kink angle with respect to each other. Scattering experiments indicate a pseudo-hexagonal internal order within these domains, quite consistent with previous observations for bulk samples. Furthermore, I have correlated the optical anisotropy of the crystals with the orientation of the PBLG helix axis. The helix axis of PBLG was found to be parallel to the stripes of each domain. The formation of zig-zag patterns, often observed in hexagonal columnar liquid crystals, is proposed to be a result of a mechanical instability, caused by the increase of the lateral packing density during the process of drying, and a corresponding net dilative strain perpendicular to the columns.