3.012 Fund of Mat Sci: Structure – Lecture 22 POLYMERS Photos removed for copyright reasons. From day-to-day plastics to light-emitters to artificial muscles 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Homework for Fri Dec 2 • Study: Chapter 2 of Allen-Thomas until 2.4.3 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Last time: 1. Curie’s principle 2. Amorphous systems: Te-Sb-Ge alloys in readable/writeable CD or DVD, silicon, ice 3. Order parameters 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Pair Graphs of the pair-distribution functions for gas, liquid/gas, and monatomic crystal correlation removed for copyright reasons. See page 41, Figure 2.5 in in Allen, S. M., and E.L. Thomas. The Structure of Materials. New York, NY: J. Wiley & Sons, 1999. functions 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Pair correlation function: water Courtesy of Dr. J. Kolafa. Used with Permission. See animation at http://www.icpf.cas.cz/jiri/movies/water.htm. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Pair correlation function: water 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Count thy neighbours ) Z Y X r 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005Thickness dr Figure by MIT OCW.• Photos of the Bernal random close-packing model removed for copyright reasons. See them at the Science & Society Picture Library: Image 1, Image 2. Models of disorder: hard spheres Bernal random close packed sphere model 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Models of disorder: hard spheres • Voronoi polyhedra (in a crystal: Wigner-Seitz cell) Facial Area Volume Solid Angle Normal Distance Quantitative Definitions of Voronoi Polyhedra Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Polymers C=C C_C H H H H C=C H H H [ ] C_C H [ ] Ethylene has two carbon atoms and four hydrogen atoms, and the polyethylene repeat structure has two carbon atoms and four hydrogen atoms. None gained, none lost. Styrene nn Polymerization Polystyrene H H H H H H Free Radical Vinyl Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Polymers • Homopolymers • Copolymers –Random –Block • Graft, branched )3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005Classification: Tacticity • • •Isotactic Syndiotactic Atactic 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Glass Transition 1Tg Tf 2 1 2 2 Rubbery State Liquid Glassy State Glassy State Specific Volume Specific Volume Temperature Temperature TgTgCrystalline State Rubbery State Liquid Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)• • • Classification: mechanical Thermoplastics: (linear, or at most contain branches). Melting temperature, and a glass temperature. Elastomers: low degree of cross-linking (rubbers) Thermosets: high-degree of cross-linking, structural rigidity 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Addition vs. Condensation polymerization H H H H C=C H H [C_C]n H H Figure by MIT OCW. Cl_C_CH2 _CH2 _CH2 _CH2 _C_Cl O O + N_CH2 _CH2 _CH2 _CH2 _CH2 _CH2 _N H H H H _C_CH2 _CH2 _CH2 _CH2 _C_N_CH2 _CH2 _CH2 _CH2 _CH2 _CH2 _N O O H H + HCl This Chlorine atom and this[ ]n hydrogen atom don't end up in the polymer. They split off to form HCl gas. Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Chain growth A -: + 2 H + H A_2 _C -: + 2 HH A_2 _C -: H A_2 _C_ H 2 _C -: H A_2 _C_ H 2 _C_ H A_2 _C_ H 2 H 2 _C -: H 2 _C -: H A_2 _C_ H 2 _C_ H 2 _C -: H A_2 _C_ H 2 _C_ H 2 _C -: + CH =C CHCH =C CHCHCHCH CHCH CH =C CHCHCH CH CHCH CH CHA Chain Growth Polymerization: In the anionic polymerization of styrene, only styrene monomer can react with the growing polystyrene chain. Two growing chains won't react with each other. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005) Figure by MIT OCW.Step growth _C C_O O _C C_O_2 _2 _O O _2 _2 _+ClCl ClCH CH OH + HCL HO CH CH OH Terephthoyl chloride and ethylene glycol react to form an ester dimer. Terephthoyl chloride Ethylene glycol Dimer Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall
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