Page 20 - Periodic ISSUE 8

Ba
Looking inside nana-shaped

liquid crystals

Carla Fernández-Rico, TVs and computers. The reason this state of matter is
3rd year DPhil student in a cornerstone of both living and technological materials
the Oxford Colloid Group is inherent to its unique properties: it shows order in a
supervised by Professor preferred direction, like a solid, but it also flows, like a
Roel Dullens, describes the liquid, and as such, it easily responds to external stimuli
development of a new system such as electric fields.
of micrometre sized banana-
shaped particles. With these The shape of the liquid crystal forming building
‘bananas’ the researchers blocks, which are typically elongated molecules, has
Carla Fernández-Rico. an enormous impact on the way they pack into liquid
experimentally confirm the
existence of the so-called ‘splay-bend nematic’ crystals. While simple rod-like molecules form just five
liquid crystal phase, which was predicted 40 liquid crystal phases, banana-shaped molecules form
years ago, but had remained elusive until now. more than fifty phases. These ‘banana phases’ were
These results provide the cornerstone for the discovered 20 years ago and have since then initiated
further development of new banana-shaped liquid a true ‘banana-mania’ in the field of liquid crystals. The
crystals. fact that even a small molecular curvature results in a Fig.2: Bananas in the splay-bend nematic phase colored Fig.3: Confocal microscopy image of the splay-bend nematic
new library of banana phases is not only fascinating from according to the particle orientation as indicated by the white phase. Note the wavy nature of this phase arises from the banana-
Liquid crystals are a fascinating state of matter that a fundamental point of view, but also from an industrial arrows in the inset. shape of the particles when packing close together.
The scale bar is 10 micrometers.
we encounter in our everyday life. For example, the cell perspective, as they can switch their orientation under
membranes in our bodies are in a liquid crystalline state electric fields at ultra-fast speeds, making them ideal
- and so are the functional materials used in displays of candidates for new highly responsive displays. Despite the importance of banana phases, to date Using image analysis techniques, they directly
nobody has managed to look inside them and directly determined the positions and orientations of the banana-
visualize the way the banana particles pack or move. shaped particles, which enabled the identification of a
This is largely due to the fact that molecular systems are range of different banana phases (see Fig.2). Moreover,
extremely small and move very fast, making their direct with their colloidal bananas they experimentally
imaging extremely challenging even when using the most confirmed the existence of the so-called splay-bend
advanced microscopes. nematic LC phase (see Fig.3), which was predicted 40
years ago, but had remained elusive until now.
Carla Fernández-Rico and co-workers used colloidal
bananas and optical microscopy to study and visualize, Publication: C. Fernández-Rico et al, (2020) Science 21
for the first time, the inner details of banana-shaped Aug 2020: Vol. 369, Issue 6506, pp. 950-955. DOI:
liquid crystals with single particle resolution. 10.1126/science.abb4536.

The Dullens/Aarts group.
Professor Dirk Aarts is seated
in the front row, 3rd from left,
next to Professor Roel Dullens
(front row, 4th from left).

Fig. 1. Scanning electron microscopy image of the colloidal bananas. Note the false
colouring emphasizes the shape of the particles. The scale bar is 5 micrometers.

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