A General Method for Measurement of Enantiomeric Excess by Using Electrooptics in Ferroelectric Liquid Crystals

Chirality Detection Using Nematic Liquid Crystal Droplets on Anisotropic Surfaces

Nematic liquid crystals (NLCs) form helical macroscopic structures through chiral induction when doped with chiral species. We describe a very simple, though highly sensitive method for determination of handedness and pitch of the induced twist in the case of very weak twisting powers of such chiral dopants. A tiny drop-typically less than 10 nL-of the chiral doped NLC is placed on a plate promoting a uniform planar surface anchoring of the liquid crystal director. At the curved NLC-air interface the anchoring is homeotropic and in the sessile droplets we get a locally twisted hybrid director structure with a disclination line extending across the droplet. The configuration of the disclination line (S-like or backwards S-like) reveals the sign of twisting power and extremely large pitch values in the range of 10 mm can easily be measured. We demonstrate the method using the standard NLC 4-cyano-4'-pentylbiphenyl (5CB), weakly doped with the chiral material 2-hydroxy-2-phenylacetic acid (mandelic acid).