C11 Liquid Crystals (HL) C11.1 Identify molecules that are likely to show liquid-crystal properties, and explain their liquid-crystal behavior on a molecular level. C11.2 Describe and explain in molecular terms the workings of a twisted nematic liquid crystal C11.3 Describe the liquid-crystal properties of Kevlar, and explain its strength and its solubility in concentrated sulfuric acid.

C11.1 Identify molecules that are likely to show liquid-crystal properties, and explain their liquid- crystal behavior on a molecular level. Molecules that display liquid crystal behavior –biphenyl nitriles Nitrile groups make molecules polar Biphenyl groups have rigid rod shaped structures Long alkaline chains ensure molecule spacing

C11.2 Describe and explain in molecular terms the workings of a twisted nematic liquid crystal Twisted Nematic Liquid crystals are the basics of LCD Displays Composition of LCD Screen –Polarizing filter –Glass layer –electrodes –Liquid crystal layer –electrodes –Glass layer –Polarizing filter Helix Structure of liquid crystals

C11.3 Describe the liquid-crystal properties of Kevlar, and explain its strength and its solubility in concentrated sulfuric acid. Kevlar is lyotropic liquid crystal Within Kevlar Molecules are Hydrogen Bonds Kevlar molecules form strong ring like structures Kevlar has a rod-like shape Kevlar molecules form extra hydrogen bonds between molecules