Texture of cholesteric cellulosic gels and films observed by electron microscopy

Abstract

It is now well known that cellulose derivatives form cholesteric liquid crystalline phases in the bulk and in solution. The supramolecular arrangement of the cholesteric materials gives them unique optical properties. Light entering the cholesteric domain is partially reflected. Circularly-polarized light with the same handedness as the helicoidal structure and a wavelength corresponding to the cholesteric pitch will be reflected by the mesophase. Free-standing films displaying a cholesteric order are thus strongly desirable for many different applications.Even though transmission electron microscopy (TEM) seems to be the perfect technique to extend results obtained by optical microscopy, this approach has been used infrequently in the study of liquid crystals. Liquid crystals don't lend themselves to electron microscopy because of their fluidity. Lyotropic systems are destroyed by evaporation of the solvent under high vacuum. However, under specific conditions, solid cellulosic films can retain a helicoidal organization. Classical embedding and ultra-sectioning can thus be applied on such materials as long as they do not dissolve in water.