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Atkins & de Paula:

Atkins Physical Chemistry 9e

Chapter 18: Materials 1: Macromolecules and Self-Assembly

Chapter 18: Materials 1: Macromolecules and Self-Assembly

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.

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.

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

Chapter 18: Materials 1: Macromolecules and Self-Assembly

protein structure; intermolecular forces in a protein molecule.

ionic forces

ionic forces

hydrogen

bonds

dispersion

forces

dispersion

forces

dispersion

forces

dipole-dipole

forces

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

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 = NR-NL),

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

Chapter 18: Materials 1: Macromolecules and Self-Assembly

contour length, Rc, the length of a macromolecule measured along its backbone: Rc = Nl.

root mean square separation, Rrms, the square root of the mean value of R2: Rrms = N1/2l.

radius of gyration, Rg, the radius of a thin hollow spherical shell of the same mass and moment of inertia as the molecule: Rg = (N)1/2l. (Justification 18.1 & Problem 18.16)

Rg for 3-D random coil: Rg = (N/6)1/2l. (Problem 18.17)

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, Rrms & Rg should be multiplied by F= [(1-cos)/(1 + cos)]1/2

18.2 (d) Partly rigid coils

persistence length, lp; when first monomer-monomer direction is sustained.

(Further information 18.1(c))

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