Temperature dependence of the helical period in the ferrielectric smectic phases of MHPOBC and 10OTBBB1M7

We have measured the temperature dependence of the helical period in the ferroelectric, ferrielectric and antiferroelectric phases of ( R )-MHPOBC and ( R )-10OTBBB1M7. A combination of polarizing microscopy, measurements of optical rotation and the frequency dispersion of the electro-optic linear response has been used to determine both the magnitude and sense of the helical period.