Liquid+Crystals

= **C6 and C12: Liquid Crystals** =

= = = = =Objectives:=

SL:
Liquid Crystals are basically elements that lie between two states of matter. As the name suggests Liquid Crystals are fluids that have physical property.
 * 1) **Describe the meaning of the term liquid crystals**
 * = [[image:between_state.jpg width="350" height="350"]] ||
 * Liquid Crystals have characteristics of both solids and liquids ||

**Having physical properties means that:**
Are retained even though the object is in a liquid state. (Normally none of those are retained in a liquid form)
 * Electric polarity
 * Optical polarity
 * Elasticity
 * Examples of Liquid Crystals are: (from the book)**
 * Graphite
 * Cellulose
 * An extruded spider solution which will eventually become silk
 * DNA
 * Examples of Liquid Crystals: (not from the book)**
 * Various Polypetides
 * LCD Monitor
 * NOTE:** Liquid Crystals will not always be in a liquid crystal state

**1. Distinguish the difference between thermotropic and lyotropic Liquid Crystals**

 * Thermotropic, ** consists of the word Thermo, which like thermometer means that it has something to do with heat. Therefore a Thermotropic liquid crystal are materials that will act be in a liquid crystal state over a range of temperatures. Examples include:
 * < [[image:0083645300028_215X215.jpg]] || [[image:SIGG-0-5L-Thermo-Bottle-Hot_7FC0392A.jpg]] || [[image:thermometer.jpeg width="175" height="217"]] ||
 * < A Thermal Detonator || Thermal bottle || Infant Thermometer ||

· Biphenyl nitriles used in LDC's (from the book)

· para-azoxyanisole -(a white powder used in the development of LCDs) The Thermotropic liquid crystals goes through a nematic phase when they are exposed to sources of energy.
 * Lyotropic ** liquid crystals are materials that act as liquid crystals when they are in certain concentrations. Examples of lyotropic liquid crystals are: Soap, which at low concentrations in water will not behave like a liquid crystal, i.e. they behave randomly, not have their poles in one direction, and while at higher concentrations they group into larger units called micelles, which are ordered in their orientation

2. Describe the liquid-crystal state in terms of arrangement of the molecules and explain thermotropic behaviour
The Thermotropic liquid crystals goes through a nematic phase when they are exposed to sources of energy. The nematic phase is a phase wherein the molecules of the liquid exists in groups or domains, but flow and are randomly distributed in groups, however they have the same orientation in each group or domain. Therefore as more energy is exposed to the molecules, the molecules become more excited and the orientation is disrupted which then creates the normal liquid state.

3. Outline the principle of the Liquid Crystal display device
The basis of the technology is that: o Liquid Crystals are polar o By applying an electric field the orientation of the molecules can be changed o Different orientations of the molecules will affect the ability of the liquid crystal to emit light || ||
 * Liquid crystals Displays, or as they are more commonly known as LCDs are based on the science of Liquid crystals(no duh)

4. Discuss the properties needed for a substance to be used in a Liquid Crystal display.
Properties that are needed for a Liquid Crystals to be used are:
 * be a chemically stable compound
 * contain polar molecules
 * remain stable in the liquid crystal phase over a suitable range of tempreature
 * be able to oreiantate quickly

HL:

 * 1) ===Identify molecules that are likely to show liquid crystal properties and explain the liquid crystal behavior on molecular level===
 * 2) ===Describe and explain in molecular term the workings of a twisted nematic liquid crystal===
 * 3) ===Describe the liquid crystal property of Kevlar and explain its strength and solubility in concentrated sulfuric acid===