Products

Liquid crystal (LC) is a thermodynamic stable phase intermediate between crystalline solids, which are characterized by a regular periodic arrangement of atoms or molecules, and isotropic liquids, which lack any type of order. As LC materials can scatter incident light selectively, they can be used in screen display which is called liquid crystal display (LCD), and it is commonly used in laptops, calculators, digital cameras, digital watches, and other similar devices.

Structure of Liquid Crystal

Liquid crystals are not as disordered as a liquid because the molecules have some degree of alignment. Most substances that exhibit the properties of liquid crystals consist of long, rigid rod- or disk-shaped molecules that are easily polarizable and can orient themselves in one of three different ways, as shown in Figure 1^[1].

Fig. 1 The Arrangement of Molecules in the Nematic, Smectic, and Cholesteric Liquid Crystal Phases

In a nematic phase, the molecules are aligned in the same direction but are free to drift around randomly, as in an ordinary liquid. In the smectic phase, the molecules are arranged in layers with the long molecular axes approximately perpendicular to the laminar planes. The only long-range order extends along this axis, with the result that individual layers can slip over each other in a manner similar to that observed in graphite. Finally, in the cholesteric phase, the molecules are arranged in layers; each layer is rotated with respect to the ones above and below it to give a spiral structure. The molecular order increases from the nematic phase to the smectic phase to the cholesteric phase, and the phases become increasingly opaque.

Application and Working Principle

Because of their anisotropic structures, liquid crystals exhibit unusual optical and electrical properties. The intermolecular forces are rather weak and can be perturbed by an applied electric field. Because the molecules are polar, they interact with an electric field, which causes them to change their orientation slightly. This behavior is ideal for producing dark images on a light or an opalescent background, and it is used in the LCDs.

The configuration of an LCD can be understood from the schematic drawings of Figure 2. Liquid crystals, which are sandwiched between two sheets of glasses (with transparent, electrically conductive coatings) in LCD screen, can switch pixels on and off to reveal a specific color. When it's switched off, it rotates the light passing through it by 90 degrees, effectively allowing light to flow through the two polarizing filters and making the pixel look bright. When it's switched on, it doesn't rotate the light, which is blocked by one of the polarizers, and the pixel looks dark. Each pixel is controlled by a separate transistor (a tiny electronic component) that can switch it on or off many times each second.

Fig. 2 Typical LCD construction

Alfa Chemistry is a leading manufacturer of liquid crystals. We offer various of single liquid crystals, liquid crystal intermediates and mixed liquid crystals. To place an order or request a quote, please don't hesitate to contact us.

Reference

1. General Chemistry: An Atoms First Approach. LibreTexts, Chapter 11.8: Liquid Crystals.