3.012 Fund of Mat Sci: Structure – Lecture 23 GLASSES 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005) Image removed for copyright reasons.A photonic fiber made from polymeric and chalcogenide glasses (Prof. Fink)Homework for Fri Dec 2 • Study: Chapter 2 of Allen-Thomas (2.5 excluded)3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Last time: 1. Pair correlation functions 2. polyhedra 3. Polymers: homo and co-polymers, elastomers-thermosets, addition or step growth Bernal’s model of hard spheres, Voronoi tacticity, glass transition, termoplastics-condensation polymerization, chain or 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Glass transition temperature Fast Slow αg Τg α1 Τ VXL(T) Rate of cooling V (T) Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Glass transition temperature Table removed for copyright reasons. See page 39, Table 2.2 in in Allen, S. M., and E.L. Thomas. The Structure of Materials. New York, NY: J. Wiley & Sons, 1999. 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. Recyclables. • 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)Classification: structure LINEAR (I) 1930's-CROSS-LINKED (II) 1940's-BRANCHED (III) 1960's-x DENDRITIC (IV) 1980's-Flexible Coil Lightly Cross-Linked Random Short Branches Random Hyperbranched Rigid Rod Cyclic (Closed Linear) Densely Cross-Linked Random Long Branches Controlled Hyperbranched (Comb-burstTM) Regular Comb-Branched x Polyrotaxane Interpenetrating Networks Regular Star-Branched Regular Dendrons Dendrimers (StarburstR) Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Random walks: size of polymers 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Mean Square Displacements 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Mean Square Displacements 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Packing Fraction in Polymeric Glasses 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Solvent quality factor 20 20 20 20 10 10 10 10 10 10 10 10 Solvent In Solvent Out α2 = <r2 >θ <r2 > θ − Solvent Poor Solvent Good Solvent Local Picture Global Picture Solvent quality factor Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Theta condition • In a good solvent the chain will expand – interaction between the polymer and the solvent is favored, and solvent-monomer contacts are maximized (and monomer-monomer contacts are minimized). • In a poor solvent the chain will contract, to reduce interactions with the solvent. In practice, difficult to study (polymer will precipitate away). • At the theta condition Į=1 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)-Prof N. Thomas 3.063Self-avoiding random walk RW Figure by MIT OCW. SARW Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding Nicola Marzari (MIT, Fall 2005)Diffusion: Rouse chain • Low molecular weight linear polymers: Figure by MIT OCW. • An elastic string of Brownian particles in a viscous medium: diffusion=1/N 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Large molecular weight: Reptation • Diffusion=1/N2• Diffusion=1/N2• Diffusion=1/N23.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005) Figure by MIT OCW.Monomer Repeating Unit Polymer Name Uses CH 2 = CH 2 _ CH 2 _ CH 2 _ Polyethylene Film, toys, bottles, plastic bags CH 2 = CH _ CH 3 CH 2 = CH Cl Cl _ CH 2 _ CH_ _ CH 2 _ CH _ Poly(vinyl chloride) Polypropylene "squeeze" bottles, pipe, siding, flooring Molded caps, margarine tubs, indoor/outdoor carpeting, upholstery CH 2 = CH _ CH 2 _ CH _ CH 3 Polystyrene Packaging, toys, clear cups, egg cartons, hot drink cups CF 2 = CF 2 _ CF 2 _ CF 2 _ Poly(tetrafluoroethylene) Teflon R Nonsticking surfaces, liners, cable insulation CH 2 = CH C = N= C = N= _ CH 2 _ CH _ Poly(acrylonitrile) Orlon , Acrilan R R Rugs, blankets, yarn, apparel, simulated fur CH 2 = C _ CH 3 COCH 3= O COCH 3= CH 3 CH 2 C Poly(methyl methacrylate) Plexiglas , LuciteR R Lighting fixtures, signs, solar panels, skylights O CH 2 = CH CH 2 CH Poly(vinyl acetate) Latex paints, adhesives OCCH 3= OCCH 3= O O Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Monomer Uses CH2 Cl CH2 Cl + CH2 CH2 C=N + Styrene Acrylonitrile CH2 Styrene = CH2 2 CH2 2 CH3 CH2 C=N Acrylonitrile = CH2 3 CH3 ++ + Saran SAN ABS Isobutylene Isoprene Copolymer Name =CH = CCl Vinyl chloride Vinylidene chloride =CH =CH =CH =CH CH=CH=CHC=CH=CH = CCH1, 3-butadiene Butyl rubber Film for wrapping food. Dishwasher-safe objects, vaccum cleaner parts. Bumpers, crash helmets, telephones, luggage. Inner tubes, balls, inflatable sporting goods. Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Network models: Continuous random network • Monofunctional (dimers), bifunctional (linear chains), trifunctional or more (networks) Images removed for copyright reasons. See page 65, Figure 2.20 in Allen, S. M., and E.L. Thomas. The Structure of Materials. New York, NY: J. Wiley & Sons, 1999. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Oxide glasses • Zachariasen constraints: – Each oxygen linked to not more than 2 cations – Functionality of central cation small – Oxygen polyhedra share corners – At least three corners of each polyhedron shared 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Quartz and silica Figure by MIT OCW. Figure by MIT OCW. 3.012 Fundamentals of Materials Science: Bonding - Nicola Marzari (MIT, Fall 2005)Network modifiers Diagram of the effect of the lead-to-phosophorus ratio on phosphate glass removed for copyright reasons. See page 71, Figure 2.25 in Allen, S. M., and E. L. Thomas. The Structure
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