Helical filamentary growth in liquid crystals consisting of banana-shaped molecules

The formation of coils is common in nature when achiral symmetry breaking o ccurs. Here we describe spectacular examples of single, double and triple c oils observed in smectic liquid crystal phases of achiral banana-shaped mol ecules. Such molecules form chiral smectic phases due to two symmetry-break ing instabilities: polar molecular packing, and molecular tilt. The appeara nce of helical filaments at the isotropic-smectic transition is therefore a direct indication of the achiral symmetry-breaking of the smectic structur es. The number of observed left- and right-handed domains is equal, reflect ing the achiral nature of the constituent molecules. Our studies indicate t hat the helical filaments consist of concentric smectic layers. The coiling stabilizes the growth process and suppresses the penetration of molecules from the isotropic phase, leading to moving of the tip with constant speed.