Ch 2 - Chemical Structure of Biomaterials Flashcards
1
Q
Crystalline
A
- Periodic pattern of atoms (Long-Range Order)
* i.e. metals, ceramics, polymers
2
Q
Amorphous
A
- Lacking systemic atomic arrangement (like liquid)
* i.e. ceramics, polymers
3
Q
Structure of metals
A
- Non-directional metallic bonding
* Crystal structures (where atoms are located e.g. BCC/FCC, HCP)
4
Q
Unit cell
A
Config. of atoms that is repeated in all 3 dimensions to form final material
5
Q
Coordination number (CN)
A
nearest neighbor atoms
6
Q
Atomic Packing Factor (APF)
A
APF (per unit cell) = V_atoms/V_total
• BCC = 0.68
• FCC/HCP = 0.74
7
Q
Face-centered cubic (FCC)
A
- a = 2r*√(2)
- APF = 0.74
- CN = 12
8
Q
Body-centered cubic (BCC)
A
- a= 4r/√(3)
- APF = 0.68
- CN = 8
- e.g. Ti β-phase = improved \ductility
9
Q
Hexagonal-close packed (HCP)
A
- APF = 0.68
* e.g. Titanium α-phase
10
Q
Ductility
A
Plastic deformation before fracture
11
Q
Lattice structures
A
- Cartesian representation
- Defines unit cell by \lattice parameters e.g. lengths of edges (a,b,c) and angles b/w axes (α, β, γ)
- \lattice points = vertices of unit cell
12
Q
Crystal system
A
Unique combinations of lattice parameters (a,b,c) and (α, β, γ) • BCC 1 . Cubic (3 same lengths) 2. Tetragonal (2 same length) 3. Orthorhombic (all diff lengths) 4. Rhombohedral (//) • HCP 1 . Hexagonal (2 same length) 2. Monoclinic (~rhombohedral) 3. Triclinic (no edges/angles equal)
13
Q
Miller indices
A
Coordinate system to indicate location of points and orientation of planes (i.e. cubic crystals)
1 . Determine plane intersection of x, y, and z axes (if // to axis, "intercept" is ∞) 2. Reciprocal of intercepts 3. Clear fractions (LCD) 4. Record as "(h k l)" 5. Indicate any negative #s w/ bar over integer
14
Q
Defects
A
- \point defects i.e. vacancies & self-interstitials
* \impurities i.e. solid solutions (alloys) & liquid solutions
15
Q
Point defects
A
- Gen’lly occur b/c of thermodynamics of crystal growth
- Creation of defects is favorable b/c it ↑ entropy of system (thermodynamically favorable)
- e.g. \vacancies & \self-interstitials
16
Q
Vacancy
A
Missing atom (expected at lattice site)
17
Q
Self-interstitial
A
- Atom is crowded into interstitial space b/w 2 adjacent atoms
- Occupying what should be “empty” space
18
Q
Why form crystalline structures?
A
Balancing thermodynamic need to form bonds (crystal) and creation of defects (↑ entropy, also ↑ \strain)
19
Q
Lattice strain
A
- Strains in local lattice struc., caused by both vacancies and interstitials
- esp. interstit. defects in metals b/c of large atoms v. small space
20
Q
Solid solution
A
[metals/ceramics]
• Normal crystal structure is maintained + addition of impurity atoms
• e.g. metal alloys (impurity atom improves prop’s of host material)
21
Q
Weight % composition
A
Weight_elem/W_total
22
Q
Atom % composition
A
Moles_elem/Moles_total
23
Q
Liquid solution
A
[metals/ceramics]
• \solute (impurity) mixes in \solvent (host)
• e.g. \interstitial OR \substitutional solutions
* Ceramics: must not affect electroneutrality (solute ion must be similar in size/charge to solvent ion AND simultaneous diffusion for BOTH species)
24
Q
Interstitial solution
A
[metals/ceramics]
• Impurities fill spaces BETWEEN solvent atoms
• Gen’lly when solute smaller than solvent (↓ lattice strain)
25
Substitutional solution
[metals/ceramics]
• Impurity/solute atoms REPLACE solvent atoms
• Gen'lly favored if \Hume-Rothery rules are satisfied
* Typ. for solute anions b/c too large for interstitial space
26
Hume-Rothery rules
* Diff. in size of atomic radii < 15% (min. lattice strain)
* EN are similar (same/bond lengths/strengths)
* Valence charges are similar (same bond lengths/strengths)
* Crystal structures are identical (only if large ~50% solute) → otherwise forms 2 interpenetrating crystals (complex)
27
Structure of ceramics
• Crystal structure (composed of ions, rather than atoms)
* Must be electrically neutral
• Optimal stability when cations have max # anions (and vice versa)
28
AX crystals
* Cation (A) and anion (X) have EQUAL charge
| * Must have equal # of both to be stable ceramic
29
[A]_m*[X]_p crystals
• Cation (A) and anion (X) have DIFFERENT charges
| * # m, p must balance charges to maintain electroneutrality
30
[A]_m*[B]_n*[X]p crystals
* 2 cations (A,B) and 1 anion (X)
| * e.g. ZSCAP and FECAP ceramics
31
Carbon-based materials e.g. graphite
* Sometimes classified as ceramic (loose defin.)
* Crystalline structure, but no standard unit cell
* Ability to adsorb gases e.g. CV devices
32
Schottky defect
[ceramics]
• Vacancies of BOTH cation and anion (must balance ratio to maintain electroneutrality)
• Created based on same thermo. principles for ceramics as in metals (↑ entropy)
33
Frenkel defect
[ceramics]
• Vacancy/interstitial pair is created to maintain electroneutrality
• Typ. only w/ cations b/c anions are too large for interstitial spaces (→ lattice strain)
34
Macromolecules
* Scale: xE5-xE6 g/mol
* e.g. polymeric mat'ls
* Typ. CH covalent bonds = main constituent
35
Mer
\repeat unit (fixed # of atoms) of polymers
36
Monomer
1 mer
37
Oligomer
2-10 mers
38
Polymer
"many" mers
39
Saturated
∀ carbon in the mer has 4 other atoms
40
Unsaturated
* <=3 atoms per carbon, allows for double bonds
| * May affect X-talinity and crosslinking
41
Bifunctional
\repeat units can bond w/ mers on BOTH ends (most polymers)
42
Trifunctional
\repeat units can bond w/ THREE (3) other mers → polymer network
43
Degree of polymerization
"n" = # repeat units in polymer
44
Number-average molecular weight
[ M_n = (ΣNM)/(ΣN) ]
• N = # chains of single MW
• M = avg. molec weight for chosen MW range
* Treats all polymer chains equally
45
Weight-average molecular weight
[ M_w = (ΣNM^2)/(ΣNM) ]
* Weight larger chains as larger contribution to final value
46
Polydispersity Index (PI)
[ PI = M_w/M_n ]
* Min. value = 1 (all polymers have same MW = \monodispersed; ideal for predicting prop's)
* Shows MW distrib. (PI ↑ as MW broadens)
47
Conformation
* ROTATION of single (σ) bonds
• Impaired by bulky side groups
• Frozen by rigid C==C (double bonds)
48
Configuration (tacticity)
* BREAKING/REFORMING primary bonds
| • \isotactic, \syndiotactic and \atactic config.'s
49
Isotactic configuration
R groups on same side of chain
50
Syndiotactic configuration
R groups on alternate sides of chain
51
Atactic configuration
R groups randomly distributed
52
Special case: repeat unit contains C==C bond
* \cis = constituents on same side
| * \trans = constituents on opposite sides
53
Linear polymers
\repeat units joined end-to-end
54
Branched polymers
Synthesis conditions produce side reactions, which produce chains that branch off main polymer chain
55
Crosslinked polymers
• ("ladder") adjacent chains joined at certain points via covalent bonds → 3D polymer network
• May be induced during synthesis or afterwards via nonreversible chemical rxn
• ↑ MW of polymer chains as they are bonded together
* ↓ X-talinity when crosslinked (b/c need movement)
56
Polymerization
* Synthesis of polymers through repeated chemical rxns, which join individual mer units into a chain
* \addition & \condensation
57
Addition polymerization
• "chain reaction" - bifunctional monomers required; product contains same chemical structure as mer unit
1 . \initiation - initiator species activates monomer (radical or ionic species)
2. \propagation - monomers successively join polymer; active site con't transfer to new monomer
3. \termination - destruction of active site via rxn (of 2 propag. chains, free radical or ionic solvent)
58
Free radical polymerization
[addition polymerization]
1 . \initiation: free radical activates monomer
2. \propagation: monomers join polymer chain
3. \termination: free radical reacts w/ active carbon
59
Ionic polymerization
[addition polymerization] * Gen'lly less polydisperse
1 . \initiation: cat/an-ionic species activates monomer
2. \propagation: monomers join polymer chain
3. \termination: charged active site reacts w/ solvent/water or side reactions
60
Condensation polymerization
* "step reaction" involving mult. monomer species
* Occurs thru elim. of one molec. (typ. water) ∴ product does not have same chem. formula as either mer
* Need long reaction times and near depletion of monomer → high MW
* PI values similar to addition polym.
61
Polymer synthesis via genetic engineering
* Potential for greater control over polymer weight distrib./geom.
* Expression of gene within host (protein polymer of interest, PPOI) → isolated → introduced into host
62
Copolymers
* Mult. repeat unit types
* Formed by addition polym. or condensation polym., using a blend of monomer types as reactant species
* \random, \alternating, or \block
63
Homopoolymers
1 type of repeat unit
64
Random copolymers
2 mer units distrib. along chain w/o specif. pattern
65
Alternating copolymers
2 mer units alternate
66
Block copolymers
Each type of repeat unit is clustered (blocks)
67
Graft copolymer
Homopolymer chains attached as side chains to main homopolymer chain of different repeat unit
68
Polymeric crystal structures
• More complex unit cells and contain more atoms
• Depends on tactility and degree of branching (e.g. more branching/bulky side groups reduces X-talinity of polymeric material)
∴ most polymers are semicrystalline
69
Polymeric point defects
* Vacancies = spaces b/w chain ends
* Impurities may be intentional e.g. copolymers
* Less impact in polymers (than metals/ceramics)
70
Spectroscopy
* Excitation of electrons (absorption of energy)
| * Measures how compounds differ in % absorp.
71
Chromatography
• Physical separation of molec's based on chem char
• e.g. MW or charge
* Does not indic chem composition of mat'l
72
Mass spectrometry
• Determines atomic/molec mass of species in mat'l
1 . \ionization chamber (high energy particles)
2. \mass analyzer: Magnetic fieldm
3. Deflection based on mass (lighter = more deflection, only want target mass to hit \detector)
• Can control magnetic field to direct ions of specif. mass to detector
• Computer plot: relative intensity/absorption v. mass
* Highest molec ion ≈ MW of entire molec (all else = fragments of molec)
** App: chem compos of polymers and relative strength/stability of bonds
73
Size-exclusion chromatography (SEC)
* Column w/ beads w/ pores inside
* Small particles can enter the pores, whereas large particles will float around the pores
* Larger species elute first b/c they cannot be trapped; smaller particles = longer (\retention time)
* Pores in beads allow mobile phase to pass thru
* i.e. either gravity feed (large columns) or pump (small columns) → circulates \mobile phase
74
Stationary phase
= column + polymer beads (or small porous silica)
75
Mobile phase
= liquid solvent + dissolved sample
76
Retention time
• Time retained in porous structure, before elution
| * Anything larger than pores cannot enter ∴ only smaller analyte can penetrate network
77
Gel filtration chromatography (GFC)
(polar) aqueous solvents + hydrophilic stationary beads
78
Gel permeation chromatography (GPC)
(nonpolar) organic solvents + hydrophobic stationary phase
79
High performance liquid chromatography (HPLC) SEC instrumentation
1 . Pump (circulation of mobile phase)
2. Injector (of sample into mobile phase)
3. Column (separates molec's based on retention time)
4. Detector/spectrophotometer (converts amount of analyte in mobile phase to electrical signal)
5. Processor/computer (converts electrical signal to graph)
* Must match column w/ expected MW (start w/ broad range of beads, then more distinct beads)
* * App: used to determ. MW of polymers (compared w/ \reference mat'ls to produce \standards of MW v. elution time)
