Bent-core molecule doped liquid crystalline systems
Bent-core or banana shaped molecules are named after there bent molecular structure. They usually consist of a rigid non-linear core with long carbon chains attached to the ends an example of which can be seen below.
Bent core liquid crystals can themselves posses liquid crystalline phases but my research is concerned with their influence when doped into standard liquid crystals. It has recently been shown that achiral bent-core molecules can increase the inherent chirality of a system when used as dopants, even though they themselves are achiral.
To understand this phenomenon, several systems involving ferroelectric liquid crystals (FLC’s) doped with bent-core molecules were investigated, including varying bent-core concentration and varying host FLC configuration. An experimental method to determine the full Landau potential was employed, allowing the chirality of different systems to be probed directly. Experiments show that the chirality increases with increasing achiral dopant concentration [1]. This effect is independent of host FLC chirality.
Whilst studying these doped materials we observed the appearance of a new SmA* twist state [2] which appeared on cooling from the cholesteric, N*, to the smectic A*, phase. The temperature stability of this as of yet unidentified state was observed to broaden with increasing dopant concentration. Two short movies can be seen here and here of this state. The first movie is of a low dopant concentration mixture oriented so that the SmA* phase appears in the dark state. The second movie shows a higher dopant concentration.
[1] P. Archer, I. Dierking, “Experimental determination of the full Landau potential of bent-core doped ferroelectric liquid crystals” Phys. Rev. E 71, 041713 (2005)
[2] P. Archer, I. Dierking, “A bent-core dopant-induced smectic A* twist state” Liq. Cryst. 33, 257 (2006)