Lecture 4212014.pdf

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Materials Science
MATS 3011
Bharat Jalan

Lecture 4212014Monday April 21 2014226 PMPolymersGlassy region above thisLeatherEtRubberyRubbery flowViscous liquidTmTgGlassy Region TTglong molecular chains are frozen in position as in a glassrigidbrittleE doesnt depend strongly on To3leathery or glass transition region this region is within a DeltaT20 C of T E drops by a factor of 10grubbery plateau the material is both viscous and elastic viscoelastic At a molecular level chains can moverotate easily but not quite independent of each other very high T have viscous liquid modulus decreases dramatically chain can rotate and molecules can freely moveindependently of each otherVULCANISATIONa process of crosslinking polymeric moleculesmake it more rigid by putting cross links btwn changes similar effect as decreasing Tsulfur compounds are added in most vulcanisation processchains of sulfur atoms bond with adjacent polymer backbone chainas a result they cross link themkey idea behind vulcanisation link polymer chains w strong covalent bondsas a result modulus of elasticity goes up also tensile strength of a material goes upresistance to degradation also goes upGraph of amorphous polymer w no cross linkingcrosslinked polymermade via process of vulcanisation MatSci Page 1
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