1. 材料化學與生物化學 『從原子到宇宙』課程第八週 胡維平 國立中正大學化學暨生物化學系 11/21/2013

2.  2009, Prentice-Hall, Inc. Types of Materials Recall that atomic orbitals mix to give rise to molecular orbitals.

3.  2009, Prentice-Hall, Inc. Types of Materials In very large clusters of atoms, the energy gap between molecular orbitals essentially disappears, and continuous bands of energy states result.

4.  2009, Prentice-Hall, Inc. Types of Materials Rather than having molecular orbitals separated by an energy gap, these substances have energy bands.

5.  2009, Prentice-Hall, Inc. Types of Materials The gap between bands determines whether a substance is a metal, a semiconductor, or an insulator.

6.  2009, Prentice-Hall, Inc. Types of Materials

7.  2009, Prentice-Hall, Inc. Metals Valence electrons are in a partially-filled band. Fe, Cu, Au, Ni There is virtually no energy needed for an electron to go from the lower, occupied part of the band to the higher, unoccupied part. This is how a metal conducts electricity.

8.  2009, Prentice-Hall, Inc. Semiconductors Semiconductors have a gap between the valence band and conduction band of ~50-300 kJ/mol.

9.  2009, Prentice-Hall, Inc. Semiconductors Among elements, only silicon, germanium and graphite (carbon), all of which have 4 valence electrons, are semiconductors. Inorganic semiconductors (like GaAs) tend to have an average of 4 valence electrons (3 for Ga, 5 for As).

10.  2009, Prentice-Hall, Inc. Doping By introducing very small amounts of impurities that have more (n-Type) or fewer (p- Type) valence electrons, one can increase the conductivity of a semiconductor.

11.  2009, Prentice-Hall, Inc. Insulators The energy band gap in insulating materials is generally greater than ~350 kJ/mol. They are not conductive.

12.  2009, Prentice-Hall, Inc. Ceramics These are inorganic solids, usually hard and brittle. They are highly resistant to heat, corrosion and wear. –Ceramics do not deform under stress. –They are much less dense than metals, and so are used in place of metals in many high-temperature applications.

13.  2009, Prentice-Hall, Inc. Ceramics ( 陶瓷材料 ) SiO 2 無機，非金屬性的固體材料 抗熱，抗壓，抗腐蝕， 重量輕，不變形 適合做機械元件 Al 2 O 3 SiC Si 3 N 4 TiO 2 ZrO 2

14.  2009, Prentice-Hall, Inc. Superconductors At very low temperatures, some substances lose virtually all resistance to the flow of electrons.

15.  2009, Prentice-Hall, Inc. Superconductors Much research has been done recently into the development of high- temperature superconductors. ( 許多為陶瓷材料 )

16.  2009, Prentice-Hall, Inc. Superconductors The development of higher and higher temperature superconductors will have a tremendous impact on modern culture.

17.  2009, Prentice-Hall, Inc. Polymers ( 高分子 ) Polymers are molecules of high molecular mass made by sequentially bonding repeating units called monomers.

18. Some Common Polymers 聚苯乙烯 PS 聚氯乙烯 PVC 聚乙烯 PE 寶特 PET 保麗龍

19.  2009, Prentice-Hall, Inc. Addition Polymers ( 聚合高分子 ) Addition polymers are made by coupling the monomers by converting  -bonds within each monomer to  -bonds between monomers. Ethylene Polyethylene

20.  2009, Prentice-Hall, Inc. Condensation Polymers ( 縮和高分子 ) Condensation polymers are made by joining two subunits through a reaction in which a smaller molecule (often water) is also formed as a by- product. These are also called copolymers.

21.  2009, Prentice-Hall, Inc. Synthesis of Nylon Nylon is one example of a condensation polymer. n H 2 N(CH 2 ) 6 NH 2 + n HOOC(CH 2 ) 4 COOH  + n H 2 O

22.  2009, Prentice-Hall, Inc. Properties of Polymers Interactions between chains of a polymer lend elements of order to the structure of polymers. PE

23.  2009, Prentice-Hall, Inc. Properties of Polymers Such differences in crystallinity can lead to polymers of the same substance that have very different physical properties. LDPEHDPE

24.  2009, Prentice-Hall, Inc. Cross-Linking Chemically bonding chains of polymers to each other can stiffen and strengthen the substance.

25.  2009, Prentice-Hall, Inc. Cross-Linking Naturally-occurring rubber (polymer of isoprene, 異戊二烯 ) is too soft and pliable for many applications. In vulcanization, chains are cross-linked by short chains of sulfur atoms, making the rubber stronger and less susceptible to degradation. (Charles Goodyear, 1839)

26.  2009, Prentice-Hall, Inc. Biomaterials Biocompatibility –The materials used cannot cause inflammatory responses. Physical Requirements –The properties of the material must mimic the properties of the “real” body part (i.e., flexibility, hardness, etc.). Chemical Requirements –It cannot contain even small amounts of hazardous impurities. –Also it must not degrade into harmful substances over a long period of time in the body.

27.  2009, Prentice-Hall, Inc. Biomaterials Heart valves using Dacron TM Vascular grafts using Dacron TM  OCH 2 CH 2 OC(=O)PhC(=O)  Polyethylene terephthalate (PET) Artificial skin grafts Using copolymer of glycolic acid ( 乙醇酸 ) and lactic acid ( 乳酸 )

28.  2009, Prentice-Hall, Inc. Electronics Silicon is very abundant, and is a natural semiconductor. This makes it a perfect substrate for transistors, integrated circuits, and chips.

29.  2009, Prentice-Hall, Inc. Electronics Noncrystalline silicon panels can convert visible light into electrical energy.

30.  2009, Prentice-Hall, Inc. Liquid Crystals Some substances do not go directly from the solid state to the liquid state. In this intermediate state, liquid crystals have some traits of solids and some of liquids.

31.  2009, Prentice-Hall, Inc. Liquid Crystals In nematic liquid crystals, molecules are only ordered in one dimension, along the long axis. Unlike liquids, molecules in liquid crystals have some degree of order.

32.  2009, Prentice-Hall, Inc. Liquid Crystals In smectic liquid crystals, molecules are ordered in two dimensions, along the long axis and in layers.

33.  2009, Prentice-Hall, Inc. Liquid Crystals In cholesteryl liquid crystals, nematic-like crystals are layered at angles to each other. These crystals can exhibit color changes with changes in temperature.

34.  2009, Prentice-Hall, Inc. LCD Display

35.  2009, Prentice-Hall, Inc. Light-Emitting Diodes In another type of semiconductor, light can be caused to be emitted (LEDs).

36.  2009, Prentice-Hall, Inc. Nanoparticles Different sized particles of a semiconductor (like Cd 3 P 2 ) can emit different wavelengths of light depending on the size of the energy gap between bands.

37.  2009, Prentice-Hall, Inc. Carbon Nanotubes Carbon nanotubes can be made with metallic or semiconducting properties without doping. Graphene

38.  2009, Prentice-Hall, Inc. Amino Acids and Proteins Proteins are polymers of  - amino acids. A condensation reaction between the amine end of one amino acid and the acid end of another produces a peptide bond.

39. 20 amino acids

40.  2009, Prentice-Hall, Inc. Amino Acids and Proteins Hydrogen bonding in peptide chains causes coils and helices in the chain. Kinking and folding of the coiled chain gives proteins a characteristic shape. Most enzymes are proteins. The shape of the active site complements the shape of the substrate on which the enzyme acts; hence, the “lock- and-key” model.

42.  2009, Prentice-Hall, Inc. Carbohydrates Simple sugars are polyhydroxy aldehydes or ketones. In solution, they form cyclic structures. Starch

43.  2009, Prentice-Hall, Inc. Nucleic Acids Two of the building blocks of RNA and DNA are sugars (ribose or deoxyribose) and cyclic bases (adenine, guanine, cytosine, and thymine or uracil).

44.  2009, Prentice-Hall, Inc. 1953 Watson and Crick discovered the structure of DNA and solve the mystery of genetics

45.  2009, Prentice-Hall, Inc. DNA Replication

46. Protein Synthesis  2009, Prentice-Hall, Inc.

47. Origin of Life Life on earth began ~35 byr ago. Where did the water come from? How were the biomolecules synthesized? How did the first life begin? Is the Universe fine-tuned for life?

48. From RNA World to DNA World RNA can store information and can act as an enzyme