LIQUID CRYSTAL POLYMERS

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06 ADITI DAMLE07 MAYURI REWATKAR 08 KOMAL SHINGADE 09 MRUNALI MIRASHE 10 NIKHITA MIRCHANDANI

WHAT ARE LIQUID CRYSTALS? Liquid crystals can be defined as,condensed liquid phases with spontaneous anisotropy. State of matter that is intermediate between the solid crystalline & ordinary liquid phases is known as mesomorphic state or liquid crystal.

Clear liquidLiquid crystal(turbid)(turSolid crystal

WHAT ARE LIQUID CRYSTAL POLYMERS? Liquid crystalline polymers or LCPs are a class of advanced polymers combining properties of polymers & liquid crystals. They were discovered in 1984 after injection moulding came into picture. LCPs are basically a class of aromatic polymers which flow maintaining the crystalline properties.

HOW ARE LCPs FORMED? They are formed by dissolving a polymer in a solvent (lyotropically) or by heating a polymer above Tg or Tm(thermotropically). Rod-like or disc-like components called mesogens must be incorporated into the main chains of the polymers for making it LCP. They by altering the intermolecular forces induce liquid crystal phase. These mesogens can be attached directly to the main chain or to the side chain with flexible spacers. The placement of mesogen is very important in determining the type of LCP formed ; as type fixes all properties.

TYPES OF LCPs FORMED ARE:- NEMATIC:If rigid sections tend to point along a preffered direction.They lack positional & orientational order. CHOLESTERIC:If preffered direction of orientation tends to rotate in form of helix.Twisted nematic, chiral structure. SMECTIC:If rigid sections position themselves in layers.Soap like structure.

FACTORS AFFECTING PROPERTIES:-The structure of LCP has two parts1. Central rigid part & flexible ends.2. Polymeric main chain to which substituents are attached.3. Molecular weight.Rigid part maintains orientation while flexible part causes to lose positional order.

WHY TO GO FOR LCPs? LCPs standout the class of polymers due to its remarkable features stated below. They are capable of forming regions of highly ordered,dense structure even in molten state,however the degree of order is somewhat less than regular solid crystals. This morphology results in very good properties in direction of flow.

PROPERTIES OF LCPs:-1. High mechanical properties at high temp. Microdomain morphology & ability to orient in direction of flow imparts excellent mechanical properties at even elevated temp. Some of them are high strength, stiffness, high impact strength which is retained even on cooling, dimensional stability, sp. Gravity(1.38-1.95), thermal stability(2300),modulus of elasticity(8350-17200 MPa),tensile strength(52.8-185 MPa),etc.2. Optical properties Selective reflection of circular polarized light from surface of LCPs pitch,like the banana shaped achiral molecules gives screen effect.When voltage is applied, LCP molecules darken due to transportstion of charge via change in direction of orientation.They also respond to applied magnetic & electric fields leading to induction of optical properties.3. Inherent flame retardancy Due to delocalized aromatic backbones & strong intermolecular attractions,self-reinforcement is provided to M.P.,raising it & retarding the flame.4. Resistance to stress cracking Stress cracking is resisted in presence of most chemicals at high temp. including aromatic & halogenated HCs, strong acids, bases, ketones,etc. This is due to the large relaxation time taken by them on application of stress.It is the time taken to reorient themselves after stress tends to disorient them.5. Weldability,weatherability,inertness,6. Adhesion,Viscosity

DISADAVNTAGES OF LCPs LCPs can be welded but those lines are weak points in products. Highly anisotropic nature. High value of along +Z axis. Req. to be dry before processing. Boiling caustic material,high temp. steam damage the LCPs.

APPLICATIONS OF LCPs Because of the above properties, LCPs have wide range of applications in 1. High strength fibers Stiffness of some LCPs competes that of traditional materials like steel,which ordinary polymers fail to.Mostly mainchain LCPs are used.for making fibers.

Kevlar is used for making bullet proof vests, helmets,etc. Eg.Kevlar,Vectran,Spider silk,Zenite 5145,etc. 2. Optical applications LCPs demonstrate very low response time to electric & magnetic fields & due to optical properties, they are used in displays where the screen needs to change frequently.Twisted nematic PLC makes energy-efficient displays.Here laser is used to selectively melt the portions of display into LC phase, where by applying field the orientation is chosen & the configuration is locked & hardened.3. wave frequency electronics Due to low dissipation factor,availability of laminates they are used here.4. MEMS5. Electrical & automotive parts6. Food containers & appliances.

Thus LCPs are still a matter of research & may replace many traditional materials in coming years.

REFERENCES:-1. Textbook of Engg. Chemistry-Shashi Chawla2. Encyclopedia of Ploymer Science & technology-website3. PLC macromesogens-University of Birmingham4. Advanced polymers-William De Callister5. Textbook of Engg. Chemistry-S.S.Dara