# Liquid crystals for academic outreach?

I am interested in making a Schlieren texture of liquid crystals to show kids at an outreach event (see image below). I have the polarizers and camera for the imaging part, but I don't know of a place to find liquid crystals.

I would prefer something cheap and chemically inert because I don't want to bring anything sensitive or hazardous. I would imagine that it should be really easy to get solutions or powders of liquid crystal materials, but I am having a hard time finding a source.

Any suggestions? I don't have access to a proper chemistry lab, but I can mix basic things in my kitchen.

• Could you disassemble a cheap calculator so that you have access to the LCD display? It comes with polarizers already attached, but if you can remove the top one, you can use your polarizer. It doesn't have Schlieren, though. – Karsten Theis Oct 1 '19 at 1:04
• Did you try right the title in Google? Teachers have wrote about. Don't know if setups are simply enough for you, though. – Alchimista Oct 1 '19 at 12:09
• I don't understand how this question is too broad, no one has given a single example of a purchasable liquid crystal solution. If it was too broad I would expect too many options if anything. – user157879 Oct 2 '19 at 5:16
• Try this site. Merck are a major manufacturer of LCD materials: merckgroup.com/en/expertise/displays/solutions/liquid-crystals/… – matt_black Oct 2 '19 at 12:37

Assuming you already have the optical setup built around, aiming for the least amount of expensive chemicals, you may try semicrystalline extruded polymers, e.g. polyethylene foils, or PET bottles.

The «trick» is that you do not melt them, but that you reach just the glass transition temperature ($$T_g$$) which is below melting. Here, crystalline parts in the polymer break up, rendering the material isotropic and in transmittent observation with crossed polarizer / analyzer black. Depending on material and degree of polymerization, this solid-solid transition already may happen in a range of 60 to 80 Celsius. Put the material on a glass slide which is heated gently from beneath with an low-powered heating plate. With a tooth-pick you may test that the material becomes softer.

Upon cooling you will see how spherulites re-appear, e.g.

(source)

Size and shape of them will depend on the rate of cooling, for example if let cool at air (or on the table of your microscope), or if you cool the glass slide by putting it on an ice bag. If not overheated this may be repeated over and over easily for a dozen of times. Apart from the heating plate, there is little potential danger.

A low-cost set up including a heating stage, where you could continue the observation of the sample's recrystallization was described in the February issue of the Journal of Chemical Education (J. Chem. Educ., 2019, 96, 823-826, doi 10.1021/acs.jchemed.8b00879).

• Thanks, but isn't this an example of a crystal, not a liquid crystal? That is, it is actually on the solid state at the end of the day. In that case, I think salt crystal formation from water drying would be the typically demonstration they use for outreach. What I'm struggling on is the liquid crystal (e.g. nematic, smectic) phase. – user157879 Oct 1 '19 at 7:07