Crystallization of Poly(γ-benzyl L-glutamate) in Thin Film Solutions: Structure and Pattern Formation

Abstract

We have investigated the formation of poly(γ-benzyl L-glutamate) (PBLG) crystals from semi-dilute thin film solutions. Crystallization was initiated by adding methanol, a non-solvent. After drying, each PBLG crystal possessed an internal domain structure exhibiting a zig-zag pattern consisting of parallel stripes of alternating orientations between domains. X-ray scattering and electron diffraction revealed within these crystals a pseudo-hexagonal packing of the PBLG α-helices with their axis oriented parallel to the plane of the substrate. Based on optical anisotropy studies, it could be shown that the orientation of the helix axis was parallel to the stripes. While forming in solution, the objects are assumed to consist of a hexagonal columnar liquid crystalline phase. Upon drying, lateral packing density of the helices increased and resulted in a net dilative strain perpendicular to the columns, which is supposed to cause the formation of zig-zag patterns.