Quetol 812 set

After optical measurements, the BP films were dehydrated with ethanol and embedded in epoxy resin (Quetol 812 set, NisshinEM, 340). The resin was cut along the sheet plane with an ultramicrotome (LEICA, EM UC7) to an approximate thickness of 80 nm. The microtomed sections were collected on 150 μm mesh grids, and observed by a TEM (Hitachi, H-7500) with an accelerating voltage of 80 kV. For the serial sections, a slit grid with a supporting formvar layer was used. Analyses of the TEM images were performed using a commercial data analysis software (Wave Metrics, Igor Pro). The periodicities of the contrast were measured at various locations where the azimuthal orientation of the BP lattice was nearly parallel to the knife mark. Because of the compression along the knife mark, the periodicity appeared shorter along the direction of the cut: the periodicities were 229 nm (N = 25) and 131 nm (N = 25) parallel to the knife mark, and 247 nm (N = 25) and 140 nm (N = 25) perpendicular to the knife mark for BPs I and II, respectively. The values written text are the average along the two directions. In the discussion of the alignment behaviour, the rubbing direction was estimated by acquiring low magnification images such that the whole film could be observed, and then measuring its orientation.

After the cover slide is removed, portions of the sample with BPLC platelets are scratched away. The films obtained were cut into small pieces of 2 × 2 mm in size and embedded in an epoxy resin (Quetol 812 set, NisshinEM, 340). Resins with the embedded PS-BPLCs films were maintained at room temperature. After being fully cured, the resins are cut into thin slices with a thickness of ~50 nm using an ultramicrotome (LEICA, EM UC7). The cuts were made parallel to the film plane, and the resins were deposited using a fishing method on copper grids covered with carbon films^{47 (link)}. The TEM images were recorded on a Hitachi HT7700 and JEM-1011 instrument operating at 200 kV.