Lost?! Follow the orientation of a liquid crystal!

In the field of condensed matter physics, liquid crystals have a particular relevance due to their complex phase behaviour, their role as functional states of matter and particularly also because of their relevance for technological applications. Actually, the antithetic and apparently contradictory name “liquid crystal” reflects well the complex and fascinating properties of these systems. On one hand, we can think of a liquid crystal as a collection of molecules able to flow like a liquid. But on the other hand, they can show a certain local order, if we take into account the molecular orientation. Under some conditions, these molecules tend to be locally aligned. This kind of order is similar to the ordered lattice which characterizes the solid structure (a crystal). In Figure 1, I have given just a simple view of the molecular organization comparing a liquid and a liquid crystal. So, the liquid crystal has this singular characteristic that it can be considered neither a proper liquid nor a solid organised in a crystal lattice, but rather something in between.

Figure 1: Schematic view of molecules in a liquid and in a liquid crystal, respectively.

Roughly speaking, we can image our molecules like fish in the sea. Sometimes they go alone in every direction, other times they aggregate together in swarms moving in the same direction. Actually, they have created a local order with respect to the usually unordered state when they are not part of a swarm. Hence, in this meaning, we can think of liquid crystals as a school of fish in the sea! This comparison makes it clear how complex the dynamics of such a system is. How can we realize that these molecules behave like fish in the sea? By means of polarized light it is possible to observe the elaborate defect structure in a liquid crystal that emerges because of their locally imperfect alignment [1]. Figure 2 shows an experimental result of Oleg D. Lavrentovich, director of the Liquid Crystal Institute: the mixing of regions with different local orientation creates fancy patterns and gives us an idea of the global evolution of the system.

Figure 2: Polarizing microscope texture of a thin film of liquid crystal. [1]

As already indicated by the title of my project,  Looking inside a Liquid Crystal Display with Paraview, my project during the SoHPC involves studying the dynamics of a liquid crystal. In particular, we are interested in analysing two important quantities. The first one is the local average orientation of the molecules, the so-called director field. The second one is the scalar order parameter which measures the variation of the molecular orientation. Large systems like those we study require visualisation in three dimensions in order to promote understanding among the scientific community. The aim of my work is to implement a suitable post-processing analysis procedure by using advanced features of Paraview. More specifically, I am using the batch mode and run Paraview in parallel.

Actually, I have been working for about a week now. I have completed the preliminary work on the post-processing scripts which analyse the output data of the simulations and write them in a suitable file format for Paraview. As I tend to say: it is never too late to start!

Reference

[1] redorbit.com – Polarization microscope image of liquid crystals image