Effect of the thickness of the hydrophobic bilayer on the helical twisting power in micellar nematic liquid crystals

Abstract

The effect of the thickness of the hydrophobic bilayer of host nematic phases on the helical twisting power (HTP) of some chiral guests has been investigated. The thickness of the hydrophobic bilayer of the host nematic phases was varied with varying chain length from C₈ to C₁₂ in the alkylammonium chloride series and from C₁₂ to C₁₆ in the alkyltrimethylammonium bromide series. The chiral guests were L-alanine esters with C₄, C₆, C₈ and C₁₀ hydrocarbon chains, mandelic acid (MA) and hexahydromandelic acid (HHMA). In the host chiral nematic phases of the alkylammonium chloride series, the HTPs of the chiral alanine ester guests increased as their chain length was increased and the thickness of the hydrophobic bilayer was extended. In both series, similar behaviour was observed for the chiral guests MA and HHMA, but in general, the HTPs of HHMA were larger than those of MA. Accordingly, the chirality transfer from the chiral guest to the achiral micelle was interpreted to be more effective if the chiral guest has a “certain fitting and orientation” in the micelle.