Liquid Crystals: source of life and of technology October 11, 2017

Liquid crystals Liquid crystals are the materials that make up the screens of your computer, your phones, your watches. Even before their technological applications they are the molecules that are responsible for life.

What makes them so desirable for life and technological applications They can be made of molecules that look like pencils or like coins. You can do the following experiment: Join together so that all of you have at least 8 - 10 pencils Join together so that you have at least 8 – 10 coins of the same denomination. Designate one person to hold the pencils. Open your hand and release them close to the floor, not pushing them Do the same thing with the coins. Now, take the pencils and the coins and release them at a distance that is further from the floor and almost push them

What makes them so desirable for life and technological applications These shapes tend to align such that the long axis of the pencils are more or less in the same directions and the coins have their surface aligned in the same direction. This property is what is called the self aligment, because given certain temperatures and/or concentrations they will align as described above. Self-alignment will depend on the temperature (which we did by tossing the coins from a larger distance from the floor and “pushing” them as they were tossed) and /or the concentration of the liquid where they are dispersed in.

Real molecules C8H17 CN Coin shaped Pencil shaped Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, Taylor and Francis, 1997

The arrangement can tell us of at least two phases The nematic or the most disordered of the ordered phases And the isotropic or the disordered phase Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, Taylor and Francis, 1997 N

If you are more careful at putting together the pencils and coins, we get more ordered phases Sm-A Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, Taylor and Francis, 1997

How can self-alignment help in technological applications One can choose a liquid crystal such that at temperatures oscillating between RT (25C or 75F) to the boiling point of water (100C or 212F) they are aligned, but not in the same direction. We can use external fields such as an electrical or magnetic field to manage the self alignment such that if the molecules were originally pointing every which way right when the field is applied they point in a certain direction. These can form numbers (watches, displays) or images (TV’s, computers, telephones)

Real molecules C8H17 CN Coin shaped Pencil shaped The areas in circles are electron-rich. By choosing the appropriate molecules and combining in the right geometry them with other molecules or solid materials one can fabricate a photovoltaic. Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, Taylor and Francis, 1997

The molecules of life are slightly different. They are designed (by nature) to have a hydrophilic head (the nitrogen group at the end) and hydrophobic tail (the carbon chains) They change phases by varying the concentration of liquid in which they are mixed into. These molecules are known as lyotropic molecules A well known biological molecule which is a liquid crystal is DNA Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, Taylor and Francis, 1997

They have different phases but the one favorable for life is the lamellar phase With a change in the concentration one can get the hexagonal phase, which in many ways is not a continuously closed surface, except perpendicular to the edges of the hexagon Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, Taylor and Francis, 1997 Several different illnesses can result if a phase change happens (or there is a change in the concentration of water)

In order for cells to perform their functions…. They must have form and structure There must be mechanisms that allow materials to enter and exit the cells. Liquids do not have form or structure, but do provide a medium for the efficient transportation of materials Solids have form and structure but do not allow for the efficient movement of materials. We need a phase intermediate between solid and liquid that shares properties with both these phases. This is the liquid crystal phase

In other words… Do we want to be made out of steel (like Superman)? Do we want to be blobs of water or any other liquids (like the Blob)?