2 Structures of Solid Materials generalStructures of Solid MaterialsCrystalline materialsMaterials which have crystal structure.dense, ordered packing.atoms pack in periodic, 3D long range atomic order.tend to have higher (max.) bond energies.Occurs for: normal solidification conditions.Typical of: metals, many ceramics & certain polymers.Energyrtypical neighbor bond lengthtypical neighbor bond energytypical neighborbond lengthbond energycrystal structureamorphous structurecrystalline SiO2noncrystalline SiO2metalsceramicspolymersSC, BCC, FCC, HCP crystal structuresOthers: silicate, glass, carbon ceramics.AX, AX2 & ABX3 type crystal structures,Linear, branched, cross-linked, network structures (as molecular chains)(refer to atomic arrangement in crystalline materials)Noncrystalline materialsMaterials which have amorphous structure.non dense, random packing.atoms have no periodic short range order.tend to have lower (min.) bond energies.Occurs for: complex rapid cooling.Typical of: polymers, some ceramics & metals.(refer to atomic arrangement in noncrystalline materials)
3 Structures of Solid Materials Characteristics of polymer moleculesmetalsceramicspolymersChemistry (repeat unit composition)Size (molecular weight)Shape (chain, twisting, entanglement, etc)Structure (as polymer molecular chains)In generalAll polymer are made from organicmaterials.natural polymers – plants & animals(organic materials), such as: wood,rubber, cotton, wool, leather, silk etc.synthetic polymers – R&D from organicmaterials, such as: polyethylene,polypropylene, polystyrene, Kevlar,nylon etc.Most polymeric materials are…hydrocarbons (made up of H & C)– organic materials.composed of very large molecularchains (in 2D array) with organicsgroup (methyl, ethyl, sidegroup of various atoms (O, Cl, etc).2 classifications:Thermoplastic polymers.Thermosetting polymers.SC, BCC, FCC, HCP crystal structuresOthers: silicate, glass, carbon ceramics.AX, AX2 & ABX3 type crystal structures,Linear, branched, cross-linked, network structures (as molecular chains)Linear, branched, cross-linked, networkLinearCross-linkedBranchedNetworkIsomeric statesStereo isomersGeometrical isomerscistransIsotacticSyndiotacticAtactic
4 Structures of Solid Materials repeatunitrepeatunitStructures of Solid MaterialsCHPolyethylene (PE)HPolypropylene (PP)CCH3PolymersceramicsMetalsrepeatunitRepeat units:Smaller structural entities that are repeated along the molecular chain.ClCHPoly(vinyl chloride) (PVC)Chemistry of polymer moleculesPolymer molecules (composition & structure)polymer is defined as many repeat unit (in terms ofmolecular chains).these macromolecules are composed of repeat units.2 types of bond exist:intramolecular bonds: covalent (between C – C).intermolecular bonds: hydrogen & van der Waals(between C – H @ C – other atoms (O, Cl etc)).ex: ethane, C2H6Adapted from Fig. 4.2, Callister & Rethwisch 3e.General termsC2H6composition (chemical formula)Intramolecules Covalent bond (strong)structureIntermolecules Hydrogen & van der Waals bonds (weak)
5 Structures of Solid Materials Other organic groups:Methyl, CH3Ethyl, C2H5Phenyl, C6H5Alcohols (methyl alcohol), R – OHEthers (dimethyl ether), R – OH – RAcids (acetic acid), CH3O2HAldehydes (formaldehyde)Aromatic hydrocarbons (phenol)Structure of phenyl groupfree radical, R from organic groupsPolymersceramicsMetalsChemistry of polymer moleculesPolymer molecules (composition & structure)composed of hydrocarbons molecules.saturated & unsaturated hydrocarbons.Unsaturated hydrocarbonsdouble & triple bonds between 2carbon atoms.- unstable & can form new bonds.ex: ethylene or ethene, C2H4Saturated hydrocarbonsalso known as paraffin molecules/compounds.each carbon singly bonded to 4 other atoms.ex: ethane, C2H6double bondex: acetylene or ethyne, C2H2others: methane, CH4, propane, C3H8,butane, C4H10, pentane, C5H10 &hexane, C6H14triple bond
6 Structures of Solid Materials Isomerismhydrocarbon molecules (compounds) with same composition (chemicalformula) can have quite different structures (atomic arrangement).ex: C8H18PolymersceramicsMetalsOctane (normal)2,4-dimethylhexaneChemistry of polymer moleculesPolymer moleculesPolymerization2 steps of polymerization:reaction between R (catalyst species/free radical) & monomer (from unsaturated hydrocarbon) to form solid polymer materials.Monomer:Small molecule from which polymer is synthesized.
7 Structures of Solid Materials A listing of 10 common polymeric materialsPolymeric materials Structure repeat unitPolymersceramicsMetalsChemistry of polymer moleculesPolymer molecules
8 Structures of Solid Materials A listing of 10 common polymeric materialsPolymeric materials Structure repeat unitPolymersceramicsMetalsChemistry of polymer moleculesPolymer molecules
9 Structures of Solid Materials Molecular size- not all chains in a polymer are of the same length.i.e., there is a distribution of molecular weights.short molecule chainsPolymersceramicsMetalsLow Mlong molecule chainshigh M- molecular weight, M: Mass of a mole of chains.Size of polymer moleculesMolecular weight distributionMi = mean (middle) molecular weight of size range ixi = number fraction of chains in size range iwi = weight fraction of chains in size range i
10 Structures of Solid Materials Molecular sizeStudentWeightmass (lb)11042116314041435180618271918220922510380Molecule weight calculationex: average mass of a classPolymersceramicsMetalsWhat is the average weight of the students inthis class:Based on the number fraction of students in each mass range?Based on the weight fraction of students in each mass range?answer:The first step is to sort the students into weight ranges. Using 40 lb ranges gives the following table:Size of polymer moleculesCalculate the number and weight fraction of students in each weight range as follows:total numbertotal weight
11 Structures of Solid Materials chainPolymersceramicsMetalsShape of polymer moleculesMolecular shapeTwistingalso known as conformation.chain bending and twisting are possible byrotation of carbon atoms around their chainbonds.note: not necessary to break chain bonds toalter molecular shape.Entanglement
12 Structures of Solid Materials (1) Linear structures(2) Branched structurespolymers are synthesized in which…repeat units are joined togetherend to end in single chains.flexible & spaghetti like.common polymers:PolyethylenePoly(vinyl chloride)PolystyrenePoly(methyl methacrylate)NylonFluorocarbonspolymers are synthesized in which…side-branch chains are connected tothe main chains.the branches may…result from side reactions thatoccur during synthesis.reduced the packing efficiency &lowered the polymer density.- common polymers:high-density polyethylene (HDPE)low-density polyethylene (LDPE)PolymersceramicsMetalsStructure of polymer moleculesMolecular chains structures(3) Cross-linked structures(4) Network structurespolymers are synthesized in which…adjacent linear chains are joined oneto another at various positions bycovalent bonds.accomplished by additive atoms thatare covalently bonded to the chains.common polymers:rubber elastic materials.polymers are synthesized in which…multifunctional monomers forming 3@ more active covalent bonds make3D networks.polymer that is highly cross-linkedmay also be classified as a networkpolymer.these polymers have distinctivemechanical & thermal properties.common polymers:epoxiespolyurethanesphenol-formaldehydeshows the structureof the molecularchains.all structures containvan der Waals &hydrogen bondingbetween the chains.BranchedCross-LinkedNetworkLinearsecondarybonding
13 Structures of Solid Materials Stereo isomersStereoisomers are mirror images – can’tsuperimpose without breaking a bond.ex:EBADCmirror planePolymersceramicsMetals- Tacticity – stereoregularity or spatial arrangement of R units along chain.- It can be isotactic, syndiotactic & atactic.Isotactic configurationStructure of polymer molecules- all R groups on same side of chain.Molecular chains structures – isomeric statesshows the molecular configurations for polymers.to change configurations, it must break bonds.Syndiotactic configuration- R groups alternate sides.Geometrical isomers- either trans isomerism.cistransH atom and CH3 group on same side of chain.- H atom and CH3 group on opposite sides of chain.Atactic configuration- R groups randomly positioned.ex: cis-isopreneex: trans-isoprene
14 Structures of Solid Materials Thermoplastic polymerssoften when heated (eventually liquefy) &harden when cooled.processes that are reversible & repeated.structures: most linear polymers & somebranched polymers with flexible chains.properties: soft & less dimensional stability.common polymers:polyethylene.poly(vinyl chloride).polystyrene.poly(ethylene terephthalate).PolymersceramicsMetalsClassification of polymeric materialsPolymers classificationCopolymersrandomblockgraftalternating- more monomers polymerizedtogether.- 4 types:random – A and B randomly positioned along chain.alternating – A and B alternate in polymer chain.block – large blocks of A units alternate with large blocks of B units.graft – chains of B units grafted onto A backbone.A – B –Thermosetting polymerspermanently hard during their formation& do not soften when heated.processes that are not reversible &repeated.structures: most network polymers &cross-linked polymers.properties: hard, strong & highdimensional stability.common polymers:epoxies.phenolics.polyester resins.
15 Structures of Solid Materials Polymer crystallinityordered atomic arrangements involvingmolecular chains.crystal structures in terms of unit cells.ex: thin platelets with chain folds atfaces.polyethylene unit cell.PolymersceramicsMetals10 nmAdapted from Fig. 4.12, Callister & Rethwisch 3e.Polymer crystallinitychain folded structurepolyethylene unit cellcrystallineregionamorphous- polymers rarely 100% crystalline.difficult for all regions of all chainsto become aligned.degree of crystallinity expressed as% crystallinity.some physical properties dependon % crystallinity.heat treating causes crystallineregions to grow & % crystallinity toincrease.Adapted from Fig , Callister 6e.(Fig is from H.W. Hayden, W.G. Moffatt,and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)
16 Structures of Solid Materials Polymer single crystalsingle crystals – only for slow andcarefully controlled growth rates.electron micrograph – multilayeredsingle crystals (chain-folded layers) ofpolyethylene.PolymersceramicsMetalsPolymer crystallinityPolymer semi crystalsome semicrystalline polymers formspherulite structures.alternating chain-folder crystallites andamorphous regions.spherulite structure for relatively rapidgrowth rates.Cross-polarized light used - a maltese cross appears in each spherulitePhotomicrograph – Spherulites in polyethylene