Smectic C phases and reentrant behavior in cholesterol containing dimer liquid crystals

A series of dodecyloxybiphenylyl and cholesteryl group containing dimers with ethers as spacers have been prepared and their liquid crystalline properties were investigated as a function of spacer length. For short spacers SmA and SmC phases were observed with monolayer ordering. This is aparent from. polarization microscopy and temperature dependent X-ray measurements. With increasing spacer length a N*-phase gradually appears whose liquid crystalline range increases. For the dodecyl spacer no smectic phase is observed anymore. For the nonyl spacer reentrant behavior is found (N*-TGB-SmA-TGB-N*). Reentrant behavior, probably N*-TGB-N*, is also observed for a related compound with an ester spacer.