Liquid crystalline phases given by helical biological polymers (DNA, PBLG and xanthan). Columnar textures

Abstract

Highly concentrated solutions of helical polymers of biological interest, namely DNA and PBLG, have been found to form hexagonal liquid crystalline phases. Most of the classic textures of hexagonal phases are shown by these polymers (fan-shaped textures, textures with numerous disclinations). In addition there are other new textures such as the undulating patterns and the helical stacking of hexagonal domains. These new textures are probably a consequence of the helical nature of the molecules. However, perfect extended helicoidal organization and hexagonal order are incompatible. We shall discuss the way in which these new textures allow a relaxation of the twist which occurs spontaneously between helical molecules (and which is incompatible with extended hexagonal order) in a continuous or abrupt manner. Finally, the nucleation and growth of the hexagonal phase within the cholesteric phase were observed in the polarizing microscope. The cores of the defect lines which exist in the cholesteric phase act as nucleation centres and the hexagonal textures formed depend on the nature of the cholesteric textures surrounding them