Simple method for accurate measurements of the cholesteric pitch using a “stripe–wedge” Grandjean–Cano cell

Abstract

The classical method for measuring the inherent periodicity, or “pitch”, in the order parameter in a cholesteric liquid crystal implies using a wedge cell with well‐defined boundary conditions. But the error can be large due to difficulties in controlling the wedge angle, α. A modified method is presented that significantly reduces the measurement error. A relief of indium tin oxide stripes on one of the plates shifts the disclination lines a distance proportional to both relief amplitude and to the wedge angle. With this “stripe–wedge Grandjean–Cano cell” the pitch can be accurately determined without a priori knowing α.

Keywords:

• cholesteric liquid crystal
• pitch measurement
• stripe–wedge Grandjean–Cano cell

Acknowledgements

The authors would like to acknowledge Dr P. Jägemalm and Dr Å. Haglund, for performing the AFM measurements. Part of this work was supported by The Swedish Foundation for Strategic Research, Dnr 2005/0257.