Liquid Crystals Lecture 1 PDF

Unit 1: Liquid Crystals-Part B Introduction to liquid crystals Types of liquid crystals Applications in LCDs  Liquid Crystal Polymers (LCPs) Liquid crystal polymers (LCPs) consist of repeated monomer units but which are linked to form extended chain-like molecules...

Unit 1: Liquid Crystals-Part B Introduction to liquid crystals Types of liquid crystals Applications in LCDs  Liquid Crystal Polymers (LCPs) Liquid crystal polymers (LCPs) consist of repeated monomer units but which are linked to form extended chain-like molecules. The primary units of the polymeric chain are attached to one another via a flexible linker which can be of varying lengths (Fig). These polymeric chains aggregate to form LCPs just as single mesogen molecules do to form liquid crystals. The extended chain length of the polymeric units, however, affects enhanced intermolecular interactions between the polymeric chains  Liquid Crystal Polymers (LCPs) Polymer liquid crystals (PLCs) are a class of materials that combine the properties of polymers with those of liquid crystals. These “hybrids” show the same mesophases characteristic of ordinary liquid crystals, yet retain many of the useful and versatile properties of polymers. Types of liquid crystal polymers; 1.Main chain liquid crystal polymers (MCLCPs) 2.Side chain liquid crystal polymers (SCLCPs)  Main-chain polymer liquid crystals or MC-PLCs are formed when the mesogens are themselves part of the main chain of a polymer. Side chain polymer liquid crystals or SC-PLCs are formed when the mesogens are connected as side chains to the polymer by a flexible "bridge" (called the spacer.) Liquid Crystal and Its Applications  Liquid Crystal and Its Applications Liquid crystals are a unique state of matter that exhibit properties of both liquids and solids. They have a distinct molecular arrangement that allows them to flow like a liquid while maintaining some degree of order like a solid. This unique behavior makes them useful in various applications. Here are some common applications of liquid crystals: Liquid Crystal Displays (LCDs): LCDs are widely used in electronic devices such as televisions, computer monitors, smartphones, and digital watches. In LCDs, liquid crystals are sandwiched between two glass plates and controlled by an electric field. By manipulating the alignment of liquid crystal molecules, LCDs can selectively block or allow light to pass through, creating images or text. Optical Devices: Liquid crystals are used in various optical devices, including polarizers, optical shutters, and variable optical attenuators. By applying an electric field, the orientation of liquid crystal molecules can be controlled, allowing the manipulation of light polarization, transmission, and intensity. Thermometers: Liquid crystals can be used in thermometers to indicate temperature changes. The liquid crystal material changes color at specific temperature ranges, providing a visual indication of the temperature. Smart Windows: Liquid crystals can be incorporated into windows to control the  Liquid Crystal and Its Applications Biomedical Applications: Liquid crystals have been used in various biomedical applications, including drug delivery systems, biosensors, and tissue engineering. They can be used to encapsulate and release drugs at specific locations, detect biological molecules, and provide scaffolds for tissue growth. Electro-Optical Devices: Liquid crystals are used in electro-optical devices such as modulators, switches, and beam deflectors. By applying an electric field, the refractive index of liquid crystals can be changed, allowing for the manipulation of light propagation and beam steering. These are just a few examples of the wide range of applications of liquid crystals. Their unique properties make them versatile materials in various fields, including electronics, optics, thermodynamics, and biomedicine. Liquid Crystal Display (LCD) OFF state ON state https://www.youtube.com/watch? v=F0aeFniieB8&list=PPSV https://www.youtube.com/watch?v=Gt0vRVVlV- I&list=PPSV  Applications of LCs in optical switches What Is Optical Switch? As the name implies, the optical switch uses light induction to trigger the switches. The most direct understanding of optical switch is a device used to open or close an optical circuit. It consists of mechanical, optomechanical, or electronic types. It works with the mechanical switch to block the light beam. When the switch is pressed, the stem of the switch moves downward, triggering the light sensor on the PCB and activating the key. That’s why optical switches are faster than the traditional switch as no physical contact is needed to send an electrical signal; eliminating the need for a debounce delay. Also, because there is no physical contact, these switches are usually more durable. The lifespan of the traditional switch is 50 million key presses while the optical switch can double that life span and can last 100 million.  Applications of LCs in optical switches In the past few years, LC cells appear as one of the promising technologies to achieve optical switching in telecommunications networks as these devices do not need moving parts to switch, but a control voltage. Also, optical switching employs liquid crystal (LC) materials due to their extreme sensitivity to applied fields, low power consumption, long lifetime and to their low cost. Optical switches are based on twisted nematic (TN) LCs and surface-stabilized ferroelectric liquid crystals (SSFLC). More recently, systems based on polymer-dispersed liquid crystal (PDLC) have also been developed.  Applications of LCs in optical switches Optical switches based on nematic (N) LCs Homogeneous planar alignment (that is, Nematic LC molecular axis parallel to glass substrate plane) and perpendicular rubbing directions in both alignment layers are used. As a consequence, the LC molecules perform a 90º twist through the thickness of the LC cell (PolRot cell). Through such a cell the polarization state of a linearly polarized light is modified and finally goes out at 90º of incoming direction. In most displays applications, two crossed polarisers are placed on the outside of the substrates, with the transmissive axis of each polarizer parallel to the rubbing direction of each alignment layer. The basic operation of a TN device working in this mode, know as normally white (NW) mode, are roughly depicted in Fig. When no voltage is applied (OFF state) the incident light is transmitted. In the ON state, the Questions??