Colloidal liquid crystals

When matter is composed of anisotropically shaped building blocks, such as rod-like particles, additional states of matter between the liquid and crystalline states arise. These states are called liquid crystal phases and originate from the additional orientational degrees of freedom that anisotropic building blocks have. As a result, liquid crystal phases possess orientational but not (long-range) positional order and therefore show properties that are intermediate between those of liquids and crystals. Liquid crystals are a fascinating state of matter that we encounter in our everyday life. For example, the cell membranes in our bodies are in a liquid crystalline state – and so are the functional materials used in displays of TVs and computers.

Among other factors, the shape of the liquid crystal-forming building blocks, which are typically elongated molecules, has an enormous impact on the way they arrange into different phases. While simple rod-like molecules just form a handful of liquid crystal phases, banana-shaped molecules form more than fifty. These ‘banana phases’ were discovered almost 30 years ago and have since then initiated a true ‘banana-mania’ in the field of liquid crystals.

‘Left: Confocal microscopy image of a splay-bend nematic phase formed by colloidal bananas. In the upper part the bananas are coloured according to their orientation.
Right: Confocal images of the vortex phase formed by poly disperse colloidal bananas. In the upper part the bananas are coloured according to their curvature.’

In our group, we recently developed both rod-like and banana-shaped colloidal particles made of the photo-resin SU-8, which we use to study colloidal liquid crystals. Using confocal microscopy and image analysis techniques, we study the impact of the particle shape on the structure and dynamics of different types of colloidal liquid crystals at the single-particle level.