# Quick question about liquid crystals

1. Dec 17, 2014

### skrat

After some reading, I noticed that everybody likes to mention the order parameter and most of the literature simply adds a graph, for example: http://www.personal.kent.edu/~bisenyuk/liquidcrystals/maintypes2.html

However, many (all of them, to be exact) seem to avoid the exact expression of order parameter S as function of temperature T. This makes me wonder why?
I would like to know the exact $S(T)$, so I can plot it in mathemathica and play with it. Where could I find this? :/

2. Dec 17, 2014

### nasu

So you mean a theoretical formula for the order parameter versus temperature, right?
This will depend on the theoretical model and the specific system. And of course, on how this S is defined for the specific system.
There is no "exact" S(T) that applies to all liquid crystals.
It's more likely to find experimental plots for different materials.

Here you can find results obtained by using Landau's theory of phase transitions applied to liquid crystals (also called Landau-de Gennes in this case).
http://www.shu.ac.uk/research/meri/sites/shu.ac.uk/files/mmg-chapter_2.pdf

But the formula will depend on some parameters which have to be found experimentally.

3. Dec 17, 2014