Microstructure of variable pitch cholesteric films and its relationship with the optical properties
A. Boudet - C. Binet - M. Mitov - C. Bourgerette - E. Boucher
CEMES-CNRS, BP 4347, 31055 Toulouse cedex 4, France
alain.boudet@cemes.fr
Received 14 September 1999 and Received in final form 24 November 1999
Abstract
A way to make cholesteric films reflecting in a broad wavelength
band consists in associating different cholesteric pitches in the
same film. In two previous papers, we proposed an efficient method
to produce variable pitch films, based on a thermal processing, and
we studied the optical properties of these films with respect to
the time of processing. In the present paper, we study the
microstructure of such films with respect to the processing time by
means of transmission electron microscopy. The cholesteric phase is
shown to be very well ordered. Within a wide range of annealing
times, its periodicity is progressive from one face to the other of
the film. A description of the evolution of the structure with
respect to the processing time is given, and classified in three
stages, corresponding to the three stages already stated from the
optical properties. The relationship between the evolution of the
structure and the optical properties is discussed.
PACS
61.30.Eb Experimental determinations of smectic, nematic,
cholesteric, and other structures
- 61.30.-v Liquid crystals
- 61.16.BgTransmission, reflection and scanning electron
microscopy (including EBIC)
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
