Comparison of structures and properties of lyotropic cholesteric phases induced by center and axial chiral compounds

We studied the Phase chirality in disklike lyotropic cholesteric (Ch(D)) ph ases which were obtained by adding center and axial chiral dopants to achir al lyotropic nematic (ND) host phases. In a lyotropic nematic matrix of the ND phase in the hexadecyldimethylethyl-ammonium bromide/water/n-decanol te rnary system, a ChD phase was induced by adding center chiral sterols (chol esterol, prednisolon, taurocholic acid) and the axial optically active comp ound R(-)-1,1'binaphthalene-2,2'-diyl-hydrogen phosphate (BDP). The helical twisting power (HTP) of BDP is generally lower than the HTP of inducing su bstances with center chirality, such as cholesterol, prednisolon, etc. At c onstant composition of the ND phase, the helix lengths were determined from the ordered fingerprint texture, the so-called "spaghetti-like texture" se en in polarizing microscopy. The reciprocal helix lengths change linearly w ith the BDP concentration. The properties of the ChD phase (textures, helix lengths, micelle parameters) induced by the chiral compounds and changed b y the composition of host phases give information on the mechanism of chira lity transfer from the molecular level to that of the micellar aggregates a nd, eventually, to the liquid-crystalline superstructure. The structure in the ChD phase was described in the form of micelle parameters. For helix fo rmation a minimum concentration of the chiral compounds is necessary. Durin g the helix formation the number of micelles per helix length changes as a function of the concentration of the center and axial chiral molecules. The first step during the formation of the ChD phase is the solubilization of dopants into the micelles. Interaction between the optically active molecul es then leads to the formation of hydrogen bridges between adjacent optical ly active molecules in the helical stack.