Multilayer formation of a series of chiral liquid crystal molecules at the air/water interface

A series of liquid crystal molecules, 4-alkoxy-N-(2-hydroxy-4-(s-2-chloro-3-methylbutanoyloxy)benzylidene) aniline with -C(n)Ha(n+1) as the terminal group (abbreviated as Ln hereafter, n = 2, 4, 6, 8, 10, 12), were spread at the air-water interface and studied by measuring their pi-A isotherms and surface potential-area isotherms. Films of Ln at the air-water interface were transferred onto solid substrates and characterized by polarized microscopes, X-ray diffraction, and FTIR spectroscopy. It was found that L12 and L10 formed tetralayer and bilayer, respectively, on water under the compression of the barriers of a Langmuir trough, while L8, L6, L4, and L2 spontaneously formed smectic multilayers of about 25 molecules thick. FTIR studies confirmed that the molecules in the smectic multilayers were oriented with their long molecular axis preferentially perpendicular to the water surface.