Structural change in smectic liquid crystal nanofilm under molecular-scale confinement measured by synchrotron X-ray diffraction

The determination of liquid structures under nanometer-scale confinement is important in advanced sciences and technologies. Synchrotron X-ray diffraction measurement was performed to investigate the structure of a smectic liquid crystal, 4-cyano-40-octylbiphenyl (8CB), nanofilm (thickness: 1.7 ± 0.5 nm) confined between mica surfaces. A diffraction peak at q = 1.99nm ^-1, corresponding to the lamellar spacing of 8CB, appeared immediately after 8CB was injected between the surfaces. This diffraction peak gradually decreased with time, indicating the structural change in 8CB from the ordered to the disordered state. The relaxation time was ca. 60 min and the diffraction peak almost disappeared at 100 min after 8CB injection. We could directly monitor the time course of the structural change in the smectic liquid crystal under molecular-scale confinement.