3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)3.012 Fund of Mat Sci: Structure – Lecture 22POLYMERSPhotos removed for copyright reasons.From day-to-day plastics to light-emitters to artificial muscles3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Homework for Fri Dec 2• Study: Chapter 2 of Allen-Thomas until 2.4.33.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Last time: 1. Curie’s principle2. Amorphous systems: Te-Sb-Ge alloys in readable/writeable CD or DVD, silicon, ice3. Order parameters3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Pair correlation functionsremoved 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.Graphs of the pair-distribution functions for gas, liquid/gas, and monatomic crystalPair correlation function: waterCourtesy 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)3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Pair correlation function: water3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Count thy neighboursZThickness drYXrFigure by MIT OCW.3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Models of disorder: hard spheres• Bernal random close packed sphere modelPhotos of the Bernal random close-packing model removed for copyright reasons.See them at the Science & Society Picture Library: Image 1, Image 2.3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Models of disorder: hard spheres• Voronoi polyhedra (in a crystal: Wigner-Seitz cell)Facial AreaVolumeSolid AngleNormal DistanceQuantitative Definitions of Voronoi PolyhedraFigure by MIT OCW.3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)PolymersFigure by MIT OCW.C=C C_CH HH HH HH HC=CH HH[ ]C_CH HH[ ]Ethylene has two carbon atoms and four hydrogenatoms, and the polyethylene repeat structure has two carbon atoms and four hydrogen atoms. None gained, none lost.StyrenennFree Radical Vinyl PolymerizationPolystyrene3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Polymers• Homopolymers• Copolymers– Random–Block• Graft, branched3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Classification: Tacticity• Isotactic• Syndiotactic• Atactic3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Glass TransitionRubbery StateLiquidGlassy StateGlassy StateSpecific VolumeSpecific VolumeTemperatureTemperatureTg1TgTfTg2Crystalline StateRubbery StateLiquid122Figure 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 rigidity3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Addition vs. Condensation polymerizationCl_C_CH2_CH2_CH2_CH2_C_ClO O+N_CH2_CH2_CH2_CH2_CH2_CH2_NHHHH_C_CH2_CH2_CH2_CH2_C_N_CH2_CH2_CH2_CH2_CH2_CH2_NOOH H+HClThis Chlorine atom and this hydrogen atom don't end up in the polymer.They split off to form HCl gas.[]nFigure by MIT OCW.C=C C_CH HH HH HH H[ ]nFigure by MIT OCW.Chain growth3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)A-:+CH2=CH+HA_CH2_C-:+CH2=CHHA_CH2_C-:HA_CH2_C_HCH2_C-:HA_CH2_C_HCH2_C_HA_CH2_C_HCH2=CHCH2_C-:HCH2_C-:HA_CH2_C_HCH2_C_HCH2_C-:HA_CH2_C_HCH2_C_HCH2_C-:+A 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.Figure by MIT OCW.3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Step growthCl_CC_ClO OCl_CC_O_CH2_CH2_OH + HCLO OHO_CH2_CH2_OH+Terephthoyl chloride and ethylene glycol react to form an ester dimer.Terephthoyl chloride Ethylene glycolDimerFigure by MIT
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