材料化學與生物分子

1. 材料化學與生物分子 『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 11/08/2012

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

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

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

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

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

7. 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.  2009, Prentice-Hall, Inc.

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

9. 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).  2009, Prentice-Hall, Inc.

10. 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.  2009, Prentice-Hall, Inc.

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

12. 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.  2009, Prentice-Hall, Inc.

13. Ceramics (陶瓷材料) 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 Al2O3 SiC Si3N4 TiO2 ZrO2 SiO2  2009, Prentice-Hall, Inc.

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

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

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

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

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

19. Ethylene Polyethylene 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.  2009, Prentice-Hall, Inc.

20. 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.  2009, Prentice-Hall, Inc.

21. Synthesis of Nylon Nylon is one example of a condensation polymer. n H2N(CH2)6NH2 + n HOOC(CH2)4COOH  + n H2O  2009, Prentice-Hall, Inc.

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

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

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

25. 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)  2009, Prentice-Hall, Inc.

26. Biomaterials • Physical Requirements • The properties of the material must mimic the properties of the “real” body part (i.e., flexibility, hardness, etc.). • Biocompatibility • The materials used cannot cause inflammatory responses. • 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.  2009, Prentice-Hall, Inc.

27. Biomaterials -OCH2CH2OC(=O)PhC(=O)- Polyethylene terephthalate (PET) • Heart valvesusing DacronTM • Artificial skin grafts • Using copolymer of glycolic acid (乙醇酸) and lactic acid(乳酸) • Vascular graftsusing DacronTM  2009, Prentice-Hall, Inc.

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

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

30. 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.  2009, Prentice-Hall, Inc.

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

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

33. 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.  2009, Prentice-Hall, Inc.

34. LCDDisplay  2009, Prentice-Hall, Inc.

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

36. Nanoparticles Different sized particles of a semiconductor (like Cd3P2) can emit different wavelengths of light depending on the size of the energy gap between bands.  2009, Prentice-Hall, Inc.

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

38. 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.  2009, Prentice-Hall, Inc.

39. 20 amino acids

40. 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.  2009, Prentice-Hall, Inc.

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

43. 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).  2009, Prentice-Hall, Inc.

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

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

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