Liquid crystal Facts for Kids

A special pattern called a Schlieren texture, seen in a liquid crystal. This picture was taken using a microscope and a special filter that blocks certain light waves.

Liquid crystals are amazing substances that are usually liquid, like water, but they also have some cool features of a solid crystal. Imagine a liquid that can flow, but its tiny parts (called molecules) can also line up in a very organized way, just like in a solid.

There are many different kinds of liquid crystals, and each type acts a bit differently, especially when it comes to how they interact with light. If you look at them under a microscope with a special polarized light source, you'll see unique patterns, or textures. The picture above shows one of these patterns! The different areas in the picture show where the liquid crystal molecules are lined up in different directions. But within each area, the molecules are very neatly arranged. Just like water can be liquid, solid (ice), or gas (steam), liquid crystals can also change their form depending on the temperature.

How We Use Liquid Crystals
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How We Use Liquid Crystals

Liquid Crystal Displays (LCDs)

How an LCD screen is built: 1 – a filter for vertical light, 2 and 4 – glass with electrical parts, 3 – the liquid crystals, 5 – a filter for horizontal light, 6 – a mirror.

The word "Wikipedia" shown on a small LCD screen.

One of the most common places you'll find liquid crystals is in your TV, phone, or computer screen! These are called Liquid Crystal Displays, or LCDs. They use the special light-bending abilities of liquid crystals.

Here's how they generally work:

A thin layer of liquid crystal sits between two special filters called polarizers. These filters are usually turned 90 degrees from each other.
Normally, the liquid crystal twists the light that passes through the first filter, allowing it to go through the second filter. This makes the screen look clear or bright.
When a small electric charge is applied to the liquid crystal, its molecules straighten up. This stops them from twisting the light.
Because the light isn't twisted anymore, the second filter blocks it. This makes that part of the screen look dark or opaque.
By turning the electricity on and off, each tiny spot (called a pixel) on the screen can switch between light and dark.
For color screens, tiny red, green, and blue filters are added to these pixels. This lets them create all the colors you see!

Liquid Crystal Thermometers

Some special liquid crystals change color when their temperature changes. This is because their internal structure changes, which affects how they reflect light. You might have seen these on:

Aquarium or swimming pool thermometers.
Thermometers for babies or bathwater.

These liquid crystals are a simple way to see temperature changes just by looking at the color!

Finding Hot Spots and Stress

Liquid crystals can also change color when they are stretched or put under stress. Because of this, industries use sheets of liquid crystals to:

Find hot spots in machines or electronics.
See how heat flows through materials.
Measure how stress is spread out on a surface.
Even find tiny electrical hot spots in computer chips to fix problems.

Liquid Crystal Lenses

Imagine glasses that can change their focus automatically! Liquid crystal lenses can do this. They can bend light differently by changing the way their molecules are lined up with electricity or heat.

These lenses can change their focal length (how much they magnify or shrink things) just by adjusting the electricity.
They are a type of adaptive optics, meaning they can adjust themselves.
Scientists are looking into using them for vision correction, like for people with nearsightedness or presbyopia (difficulty focusing up close as you get older). This could lead to smart glasses or contact lenses!

Liquid Crystal Lasers

Some lasers use liquid crystals inside them instead of mirrors to create the laser light. These lasers can be very small and produce a very pure color of light.

Smart Glass for Privacy

Polymer dispersed liquid crystal (PDLC) is used to make special "smart film" that you can stick on windows.

This film can switch from being clear (transparent) to cloudy (opaque) with just a flick of a switch.
It's a great way to get instant privacy in homes or offices!

Liquid Crystals in Everyday Life

You might be surprised to know that many common fluids are actually liquid crystals! For example, soapy water can form different liquid crystal phases depending on how much soap is mixed with the water.

Images for kids

Otto Lehmann, a scientist who studied liquid crystals.
How molecules line up in a nematic liquid crystal.
A change from nematic (left) to smectic A (right) liquid crystal phases, seen under polarized light. The black areas are where the material is not ordered.
A diagram showing how molecules are arranged in smectic liquid crystals. In smectic A (left), molecules form layers. In smectic C (right), they are tilted within the layers.
A diagram showing how molecules are ordered in chiral liquid crystals. This includes the chiral nematic (left) and smectic C* (right) phases.
A chiral nematic liquid crystal phase, showing its twisted structure.
A test screen showing how a liquid crystal material can twist light.
The "nematic director" shows the average direction of the long molecules in a liquid crystal.