The last movie that I posted was of a columnar hexagonal phase. As I noted in that post, these phases are often not all that visually interesting, especially compared to nematic phases. This is partly due to symmetry and alignment effects; in a homeotropic orientation, the hexagonal phase is nonbirefringent. In contrast, columnar oblique phases are highly birefringent. The following movie shows an oblique phase growing in from the higher temperature nematic phase. This transition has been featured in earlier photos on this blog, but the movie tells a more dramatic picture:
Columnar phases are the bread-and-butter of my research. One of the challenges that we often face in identifying these phases is getting them to grow characteristic textures. There's a lot of trial and error in this; how quickly you cool the sample from the isotropic phase matters, as does the slide preparation (we prefer to load our liquids by capillary action between the slide and the cover slip).
One factor that figures into this alignment; homeotropically aligned samples, in which viewer is looking straight down on the columns, appear dark by POM. Only where the columns are tilted do you get color. In the movie below, a columnar phase of a dibenzophenazine derivative emerges upon cooling from the isotropic liquid. But you can't see much; the black areas visible at the end of the video are liquid crystalline, just homeotropically aligned. One of these days, I'll post a video showing a similar video, but viewed through a quarter wave plate.
Continuing with the theme of LC movies, the following is a short clip of the nematic-isotropic transition of bis(4,4'-heptyloxy)azoxybenzene.
As much as I'm a fan of still photography, a static image can't capture the essence of fluid LC phases. To truly understand liquid crystals, you have to see them in motion. I have recently started to experiment with capturing movies of liquid crystals, as viewed by optical microscopy. Below is one of my first efforts: a commercial mixture of PCH derivatives being cooled from the isotropic phase into its nematic phase.
In my last post, I showed several images of the nematic phases of an azoxybenzene derivative. The dibenzoate derivative shown to the left also forms a single liquid crystal phase; in this case it is a smectic A phase. Smectic phases consist of rod-shape molecules arranged in layers.