Small changes to the structure of banana-shaped mesogens have unexpectedly large effects on their phase behaviour, say German researchers.

Wolfgang Weissflog and co-workers from the Martin-Luther-Universität Halle-Wittenberg have linked phenyl rings together using carboxyl groups to create a variety of banana-shaped mesogens. These are compounds that can exist in semi-ordered phases in which the molecules are less ordered than in a crystal.

They found that small changes in the orientation of the linkage groups have a large effect on the stability and type of phase formed by these materials. They believe that the relative directions in which the carboxyl groups point affects the flexibility of the arms of the mesogens, which affects their phase behaviour. This type of behaviour has been seen before in mesogens shaped like rigid rods, but never to such a large degree.

'Banana-shaped liquid crystals represent a new and fascinating topic, because they can form new mesophases with chiral superstructures and ferroelectric properties, although the molecules are not chiral,' said Weissflog.  

It is hoped that understanding the effects of such small structural differences will in the future help with the designing of application-specific materials.

Madelaine A Chapman