[This post takes 2-4 min. to read]
So, this is the much awaited chem post. Now, by looking at the title, you’re probably imagining this-
Well, it’s more like this-
To satisfy your insatiable curiousity[it doesn’t matter if you don’t actually care. Go with the flow.], let’s just get straight to it.
What are liquid crystals?
A liquid crystal, by definition, is a phase of matter that flows like liquid but has some arrangment of molecules. The study of it began in 1888, when Friedrich Reinitzer noticed that a material called cholestryl benzoate possesed not one, but two melting points. When the first melting point had been passed, a hazy liquid substance had formed. When the second melting point had been crossed, only then did a proper, clear, distinct liquid form. Reinitzer, due to his early work, is almost always accredited with discovering this phase of matter.
Properties of Liquid Crystals ->
Liquid crystals are an interesting and complex phase of matter. They have many unusual properties, some of which are listed down below.
- Anisotropy- Isotropy means that the properties of any substance are, in all ways, uniform. A liquid or solid is isotropic. Anisotropy is the exact opposite of isotropy. It is when the properties of any object are not uniform or constant. A liquid crystal is anisotropic.
- Light Scattering- LCs always scatter light, which gives them a cloudy appearance. This scattering of light occurs due to their anisotropy. The light is scattered when small groups of molecules form and disperse.
- Director- Liquid crystals are made of molecules called mesogens. Mesogens are long and elongated, tapering at both ends. All these mesogens have a tendency to point along a common axis and direction, called the director.
LC Phases ->
Liquid crystals, like teens, go through phases[I apologize for the bad joke.] There are three distinct phases that an LC can pass through. Phases are often formed due to a change in the mesogen structures.
- Nematic Phase- The nematic phase is [obviously] the first phase in the above diagram. In this phase, the mesogens all point along a particular axis, but that’s where the organization ends. There is no positional order or structure, except that all the mesogens [in this case] point vertically.
- Smectic Phase- The smectic and nematic phases are extremely similar. The only major difference between the smectic and nematic phases are that in the smectic phase, there is some degree of positional structure as the mesogen all point along a common axis and arrange themseves in layers and sheets.
- Cholesteric Phase-The cholesteric phase is a complicated little thing. The mesogens all arrange themselves in layers. The mesogens in each layer, however, point in a different direction as they have different directors.
Liquid Crystals Replacing/Mimicking Human Tissue->
Yep, you read correct. LCs could, very soon, be the easier solution to cumbersome prosthetic limbs!
When you apply pressure on a piece of silicone, it wil change shape. Once you leave it alone, it will return to its original shape.
However, Rice University’s scientists have discovered that the LC phase of silicone is 90% stiffer once it has gently and repeatdly been compressed. The LC phase of silicone is called liquid crystal elastomer.
The structure of silicone is very similar to a bowl of spaghetti- messy, entangled rods that prevent silicone from changing shapes. In a liquid crystal elastomer, all the rods point in one direction after repeated compression, which keeps it stiff for weeks. This stiffnes can also be eased out after the liquid crystal elastomer has been heated above 70 degrees celsius. This desirable flexibility of material is perfect for mimcking and replacing human tissues!
That’s it for today.
Here’s your Space Bonus- https://www.youtube.com/watch?v=9P6rdqiybaw
Bye, and thanks!