How many times have we heard someone talking about the screens that watches, calculators, laptops or televisions have? What’s the difference (besides the size and image quality) between them? How many times have you noticed what are they made of? How many times have you reached to the same answer to that question? Well, most of the screens of the electronic apparatus that we use (still in this time of HD) are made of liquid crystals and this leads us to the next and last question to this paragraph: haven’t you asked yourself what is a liquid crystal?

The term liquid crystal might sound quite weird if we get ourselves to analyze it by comparing the meanings of both the words that compose it. For instance, we know crystals are solids, which means they possess extremely organized molecular arrangements and extremely strong electrostatic interactions; on the other side, the molecular arrangement that liquids present lack of that extreme organization due to the low intensity of the electrostatic interactions between molecules. By the way, by this point we should remember that electrostatic forces and their interactions constitute the attraction between molecules and together the constitute forces like the force of cohesion which serves in practical terms to differentiate between the different states of matter.

So, if the denomination liquid crystal results so absurd: why was this material named like that? Precisely, it is named liquid crystal because it IS a liquid crystal: this means that we are talking about a crystal whose molecules behave like a liquid, or vice versa a liquid whose molecules behave as those of a crystal. In one way or another, the result is the same because a liquid crystal presents an exotic combination of the properties of both states of matter.

So, what happens with the liquid crystals is that the molecules that compose this material can move, something like the ones existing in any glass of water and besides they all tend to be orientated in the same direction (just like the molecules that form grains and crystals of salt). All of this can be resumed as if the molecules have a partial order, which means the molecules do not have such a rigid organization as a solid but this does not means that they lack of one as the molecules in gases.

If you considered the anterior definition as confusing or even vague, and you are still wondering if the material we are describing in this text is a liquid or a solid just wait and keep reading because it gets much more interesting. Maybe for having a clearer idea of the explanations that follows it would be of great aid if you could draw in a piece of paper the crossing of axis X and Y, like a Cartesian graph.

There is not just one kind of liquid crystal but several of them! Depending of the partial order that the molecules present there are three types of liquid crystals:

o Nematics. This kind of liquid crystal presents a molecular order that only involves that which in mathematics we know as the X axis and no other. This means that the only orientation that maters for the molecules of nematics is the one on the X axis leaving aside if the neighbour molecule is on position 9 or 4 on the Y axis.

o Smectics. This type of liquid crystals encloses other three subtypes that are named after the first three letters of the alphabet. The only difference between the three types of smetics is the inclination of the molecules. Now, speaking of their molecules, the order that the molecules of smectics present is greater compared to the order of the molecules in nematics due to the formation of layers in smectics.

In smectics the order of the molecules not just involves the X axis, but the position of the molecules are also influenced by a Y axis. For example, if we could pour a liquid crystal of this type into a cubic receptacle and if also we could trace the X and the Y axis in one of the sides of the recipient then the coordinates of the molecules of one of the layers of molecules of this kind of liquid crystals would be something like this: molecule 1 (4, 6), molecule 2 (5, 6), molecule 3 (6, 6) and so on until the layer touches the wall on thy contrary side of the container.

o Cholesterics. This type of liquid crystals has structures formed by very particular combinations between the other types of liquid crystals mentioned before. The molecules in cholesteric liquid crystals form layers that go from one side to the other of the material, and each layer of molecules has a different tilt respect to the upper and lower layers. Due to this characteristic cholesteric liquid crystals have colour.

The changes in temperature and pressure create changes of colour in this type of liquid crystals. Both temperature and pressure modify the order of the layers that forms cholesteric liquid crystals affecting the angle in which the light hits and reflects on the molecules.

In conclusion, liquid crystals are a phase or state of matter that is only present in some substances and it can only be observed between a delicate and defined range of pressures and temperatures. When the temperature is very high and the pressure is really low the liquid crystal reverts to its liquid phase because its molecules increase their moving capacity. Using logic, we can deduce that having the contrary conditions of temperature (low) and pressure (high) the liquid crystal will revert to its solid phase.

Though, you might be still be wondering how everything that has been explained until now is related to modern electronic devices. So, here you go. Electromagnetic fields also affect electrostatic interactions of the molecules of liquid crystals. These react in different ways producing the amazing colours and permitting the various uses so that’s why they are includes as part of a great deal of electronic devices such as the ones mentioned at the beginning of this text.