• Question: How do liqud crystals work

    Asked by neck485ref on 28 Jun 2023.
    • Photo: Alexander De Bruin

      Alexander De Bruin answered on 28 Jun 2023:

      they are molecules with a special shape that means they line up in a specific way. When the molecules line up together they form a “liquid crystal” with some properties of a liquid (can flow) and some of a crystal (very ordered structure). This crystal structure can do interesting things to light, such as affecting the polarisation. This polarisation is what is used to make LCD (liquid crystal display) screens work

    • Photo: John Grasmeder

      John Grasmeder answered on 28 Jun 2023:

      Liquid crystals (LCs) are typically rod-shaped molecules which have 2 melting points. Think of a box of matches, where all the matches are LCs and they are all lined up neatly. This is the crystalline phase, it’s all neatly ordered. Imagine the box is longer than the matches. The first melting point happens when the LCs slide over each other – they can move up and down the length of the box but they do not have room to turn around. This is the liquid crystalline phase – there is some order like in a crystal (the LCs are still all lined up) but there is some disorder like in a liquid (the LCs can move up and down the box. The second melting point is like tipping the matches out of the box – the LCs are free to move in any direction, any orientation, and are completely disordered. This is the liquid phase.
      LC displays have a backlight and use the liquid crystalline phase in a pixel to rotate polarised light by 90° so that the light can get through. Switching the LCs on and off gives the appearance of the pixel switching on and off even though the backlight is on all the time.

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