Liquid crystal

Some things are in the middle.

They flow like water. But they also point one way like a solid. These are called liquid crystals.

They can be found in nature. Some are in living things. They are also in soap. Scientists use them to make screens. This helps you see pictures on a device.

It is amazing how they work!

Some things are in the middle. Liquid crystals are a special state of matter. They act like a liquid and a solid at the same time.

They can flow like water. But their tiny parts, called molecules, often point in one direction. This is like a solid crystal.

There are different kinds of liquid crystals. Some change based on heat. These are called thermotropic liquid crystals. Others change based on heat and how much of a substance is in a liquid. We call these lyotropic liquid crystals.

Many living things use these. Cell membranes are made of them.

Scientists use liquid crystals in many tools. The most common use is in liquid-crystal displays, or LCDs.

These screens help us see pictures on devices. In 1888, Friedrich Reinitzer found them by accident. He saw a substance with two melting points. He found it turned into a cloudy liquid first. Then it became clear. This helped him find this new state of matter.

Liquid crystals are a special state of matter. They sit between a liquid and a solid crystal.

A liquid crystal can flow like a normal liquid. However, its molecules often point in a common direction. This is similar to how molecules act in a solid. These different areas of orientation are called domains. Different domains create different textures when you look at them. This makes the material very interesting to study.

There are three main types of liquid crystals. Thermotropic liquid crystals change based on temperature. Lyotropic liquid crystals change based on temperature and concentration. These are often found in water.

Many living things use these, like cell membranes and proteins. Metallotropic liquid crystals use both organic and inorganic molecules. Their state depends on the ratio of these two parts. The shape of the molecules also matters a lot.

Some molecules are shaped like rods, while others look like discs or bowls.

Scientists discovered this state by accident in 1888. Friedrich Reinitzer was an Austrian scientist studying cholesterol. He noticed a substance called cholesteryl benzoate had two melting points. First, it melted into a cloudy liquid. Then, it melted again into a clear liquid. He wrote to a physicist named Otto Lehmann about this. Lehmann used a special microscope with a heater to study it. He realized this was a brand new phenomenon.

Research grew much larger after World War II. In the 1960s, scientists at RCA Laboratories began working on displays. Richard Williams found that electric fields could create patterns in these crystals. At first, the materials only worked at very high temperatures. This made them hard to use in homes. In 1966, researchers found mixtures that worked at room temperature. This was a huge step for technology. Later, George Gray helped create stable materials for small electronic products.

Today, you see liquid crystals almost everywhere. They are the main part of Liquid-crystal displays, or LCDs. These screens are in many electronic devices. You can find them in televisions and handheld tools. The way they work is like a tiny, controlled dance. The molecules respond to electricity to change how light passes through them. This allows us to see clear pictures on flat screens. It is a wonderful way that science helps us every day.

Liquid crystals represent a unique state of matter. They exist between the properties of conventional liquids and solid crystals.

While a liquid crystal can flow like a liquid, its molecules often maintain a common orientation. This directional alignment is a characteristic usually seen in solid crystals. These materials are categorized by their optical properties, which often appear as distinct textures. These textures occur because molecules in one area, or "domain," point in one direction. Other domains in the same material may have different orientations.

Scientists classify liquid crystals into three primary types based on what triggers their phase changes. Thermotropic liquid crystals change their state based on temperature shifts. Lyotropic liquid crystals change based on both temperature and the concentration of molecules in a solvent, such as water.

Metallotropic liquid crystals consist of both organic and inorganic molecules. Their transition depends on the specific ratio of these two components. Thermotropic and lyotropic types are mostly made of organic molecules. However, some minerals also exhibit these properties. Lyotropic liquid crystals are very common in living systems, including cell membranes, proteins, and the tobacco mosaic virus.

To understand how these materials function, one must look at molecular ordering. Liquid crystals possess orientational order, meaning molecules point in a similar direction. However, they lack the strict positional order found in solid crystals.

In a solid, molecules sit in a fixed, repeating lattice. In a liquid crystal, they can move around while staying aligned. Most thermotropic liquid crystals have an isotropic phase at high temperatures. In this state, thermal motion becomes so high that it destroys the molecular alignment. The material then behaves like a conventional, disordered liquid.

The discovery of this state was largely accidental. In 1888, Austrian botanist Friedrich Reinitzer studied cholesterol derivatives at the Karl-Ferdinands-Universität. He noticed that cholesteryl benzoate did not melt like normal compounds. Instead, it exhibited two distinct melting points. First, it melted into a cloudy, intermediate liquid. Then, it melted again into a clear liquid. Reinitzer shared his findings with physicist Otto Lehmann in March 1888. Lehmann used a microscope with a heated stage to study the cloudy phase. He confirmed the material showed crystalline features despite its ability to flow.

Research into liquid crystals expanded significantly during the 20th century. German chemist Daniel Vorländer synthesized many known liquid crystals until his retirement in 1935. After World War II, researchers like George William Gray in England improved molecular design. In 1965, Glenn H. Brown organized the first international conference on liquid crystals in Ohio. This event helped move the field from a scientific curiosity toward practical technology.

In 1962, scientists at RCA Laboratories began exploring liquid crystals for flat panel electronic displays.

Developing commercial displays required finding materials that worked at room temperature. In 1965, Richard Williams observed that electric fields created patterns called domains in nematic liquid crystals.

However, the substance he used only worked above 116 °C. This was too hot for consumer use. In 1966, researchers Joel E. Goldmacher and Joseph A. Castellano discovered that mixing specific nematic compounds could create a stable range. Their ternary mixture worked between 22 °C and 105 °C. This breakthrough allowed for the first practical display devices. Later, George Gray synthesized stable cyanobiphenyls, which helped small LCDs enter electronic products by 1973.

The physical shape of a molecule determines its liquid crystal behavior. Most successful materials are rod-shaped, meaning they are elongated and thin.

This shape allows them to align along a specific direction. Other molecules can be disc-shaped, which are flat like a coin.

Some are even cone-shaped or shaped like a rice bowl. These shapes allow for different types of molecular ordering. In 1991, Pierre-Gilles de Gennes won the Nobel Prize in physics for his work on these complex systems. Today, liquid crystals are essential to the technology in our televisions and handheld devices.