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  • Slide 1
  • Atkins & de Paula: Atkins Physical Chemistry 9e Chapter 18: Materials 1: Macromolecules and Self-Assembly
  • Slide 2
  • polymer, a compound formed by linking together small molecules. naturally occurring polymers; Proteins, Nucleic acids, Cellulose, Rubber synthetic polymers; Nylon, Dacron, Lucite monomer, the small molecules linked together to form a polymer.
  • Slide 3
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly STRUCTURE AND DYNAMICS configuration, the structural features that can be changed only by breaking chemical bonds and forming new ones. conformation, the spatial arrangement of the different parts of a chain. 18.1 The different levels of structure primary structure, the sequence of small molecular residues making up a polymer. polypeptide, a macromolecule formed from amino acids. peptide link, the group CONH. sequencing, the determination of primary structure.
  • Slide 4
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly degradation, a disruption of primary structure. secondary structure, the (often local) spatial arrangement of a chain. denaturation, the loss of secondary structure. tertiary structure, the overall threedimensional structure of a macromolecule. quaternary structure, the manner where large molecules are formed by the aggregation
  • Slide 5
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly protein structure; intermolecular forces in a protein molecule. ionic forces hydrogen bonds dispersion forces dispersion forces dispersion forces dipole-dipole forces
  • Slide 6
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly 18.2 Random coils random coil, a conformation in which neighboring groups adopt random angles to each other. freely jointed chain, the simplest model of a random coil, a conformation in which any bond is free to make any angle with respect to the preceding one. Freely jointed chain Constrained chain
  • Slide 7
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly probability that ends of a long 1-D freely jointed chain (N units of length l) are a distance nl apart (n = N R -N L ), probability that ends of a long 3-D freely jointed chain lie in the range r to r+dr, f(r)dr (Further information 18.1(a) & Problem 18.20) (Further information 18.1(b)) 18.2 (a) Measures of size
  • Slide 8
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly contour length, R c, the length of a macromolecule measured along its backbone: R c = Nl. root mean square separation, R rms, the square root of the mean value of R 2 : R rms = N 1/2 l. radius of gyration, R g, the radius of a thin hollow spherical shell of the same mass and moment of inertia as the molecule: R g = (N) 1/2 l. (Justification 18.1 & Problem 18.16) R g for 3-D random coil: R g = (N/6) 1/2 l. (Problem 18.17)
  • Slide 9
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly 18.2 (b) Conformational entropy conformational entropy, the statistical entropy arising from the arrangement of bonds: S = kNln{(1 + v) 1+v (1 v) 1v }, with v = n/N, when a coil of N bonds of length l is stretched or compressed by nl. (Justification 18.2) 18.2 (c) Constrained chains constrained chains, R rms & R g should be multiplied by F= [(1-cos)/(1 + cos)] 1/2 18.2 (d) Partly rigid coils persistence length, l p ; when first monomer-monomer direction is sustained. (Further information 18.1(c))
  • Slide 10
  • Chapter 18: Materials 1: Macromolecules and Self-Assembly 18.3 The mechanical properties of polymers elastic deformation, strain is proportional to the stress and is reversible. plastic deformation, strain is not proportional to the stress. yield point, turning point from elastic to plastic deformation. elastomer, a polymer with a long elastic range. perfect elastomer, an elastomer where the internal energy is independent of the extension. restoring force of a perfect elastomer extended or compressed by nl is F = (kT/2l) ln {(1 + v)/(1 v)} nkT/Nl when v