Evidence at last for long-awaited new liquid crystal phase

Curved rods in nematic phaseCurved rods in nematic phase

Fifty years after scientists predicted a new liquid crystalline phase, it has been observed by Utrecht researchers. The observations were made in model systems of colloidal rods, rod-like particles that are larger than molecules and therefore easier to study. The researchers provide guidance on a way to realize the material with rod-shaped molecules as well. The new phase gives the material properties that are interesting for the further development of displays and reflective coatings, for example. The team was led by Utrecht professors Marjolein Dijkstra and Alfons van Blaaderen. The results appear on 1 December in Nature Communications.

LCDs

A liquid crystal is a material whose properties lie between those of a liquid and a solid. A very well-known example of such a liquid crystal is a nematic liquid crystal. This material is widely used in LCDs (liquid crystal displays) of computers, telephones and TVs. Another application of liquid crystals are coatings. Coatings made of liquid crystal have special reflective properties, so they can be used, for example, to passively cool buildings.

New applications

The phase that the researchers have now observed experimentally for the first time is the splay-bend nematic phase. This is a more complicated version of nematic liquid crystals. It is characterized by a wave-like character in the orientation of the curved colloidal rods from which the phase was formed. If scientists succeed in realizing the material also with molecules, all kinds of new application possibilities will arise. This is because the new phase has different properties from the phases we know so far. The splay-bend nematic phase reacts differently to electric fields, for example, than nematic liquid crystals. This makes the materials suitable for the further development of, for example, screens and other displays, sensors and coatings.

If scientists succeed in realizing the material also with molecules, all kinds of new application possibilities will arise

Frustrations

The researchers observed the new phase through several "frustrations": disruptive operations of the material. The rod shape of particles is responsible for forming a liquid crystal, and when you make them less straight, it becomes harder for the particles to point in the same direction. It was already predicted that this frustration results in the new phase. By then further frustrating the particles by polydispersity (giving the particles different lengths), the material became stable and the predicted phase could be observed.

Publication

Splay-bend nematic phases of bent colloidal silica rods induced by polydispersity
Ramakrishna Kotni, Albert Grau-Carbonell, Massimiliano Chiappini, Marjolein Dijkstra & Alfons van Blaaderen 
Nature Communications volume 13, Article number: 7264 (2022)