Post on 30-Apr-2018
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Macromolecular Solids
• Polymeric solids – Organics – Plastics
• Silicates – Rocks and minerals – Clay
• Fibers – Fabrics – Fiber composites
• Lipid bilayers – Biological membranes
• Quasicrystals
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Silicates
• Are the basis for rocks, clays and minerals
• Common dirt is, in fact, aluminosilicate: Si-Al-Fe oxide
• Other minerals also have complex compositions with many elements
• Study SiO2 as a simple prototype
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Silicates
• SiO4-4 tetrahedra join at corners
to form networks: strong, hard structure
• Open structure results in several crystal structures, glasses
• Glass formation promoted by ions that terminate oxygen bonds
M+--- M++
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Layered Silicates: Clay
• If SiO4-4 join at three
corners, they form sheets
• In clay, two sheets are bound together by ions to form a sandwich
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Layered Silicates: Using Clay
• Clay is soaked – Water molecules fit between
platelets
• Clay is formed – Water separates and lubricates
plates – They slide easily over one another – Can be molded into shapes
• Clay is fired – If clay dries, shape crumbles – Firing reorganizes bonds, creates 3d
network structure ⇒ clay becomes stone
H2O H2O H2O
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Fibers
• Fibers are used in – Woven fabrics – Fiber matrix composites
• Inorganic fibers – Glass (fiberglass: structures) – Graphite (Composites: stiff aircraft parts, sports equipment )
• Organic – Fabrics (nylon, etc.: clothing) – Kevlar (“bullet proof” jackets)
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Glass Fibers
• Glass drawn through a dye to produce thin fibers
• May be – Chopped (cut up) and embedded in epoxy (fiberglass) – Used in long lengths to conduct light (optical fibers)
• Engineering considerations: – Advantages: high strength, stiffness, low density – Disadvantages: brittle
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Graphite Fibers
• Graphite rolled into tube to form strong, stiff fiber
• Happens naturally when certain organic fabrics are “pyrolized”: heated to decompose into graphite
• Used to make strong, stiff composites – Strong but brittle – Weak in perpendicular direction – Sometimes woven into 2d or 3d
structures for multiaxial properties
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Kevlar Fibers
• Kevlar: benzene rings joined to make puckered sheets
• Puckered sheets form fibers – Join edgewise to form star pattern – “Accordion folds” perpendicular to axis of the fiber
• Fibers are strong, but elastic – Behave like elastomers while the accordion folds extend, then strong – Useful for body armor: “catch”projectiles
C = ON
H
NH
CO =
CO =N
H
C = ON
H
NH
CO =
CO =N
H
C = ON
H
NH
CO =
CO =
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Macromolecular Solids
• Polymeric solids – Organics – Plastics
• Silicates – Rocks and minerals – Clay
• Fibers – Fabrics – Fiber composites
• Lipid bilayers – Biological membranes
• Quasicrystals
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
The Lipid Bilayer
- NIST
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Phospholipid Building Block
• Sequence from top – NH3(CH2)2
+
– PO4-
– (CH2)2CHO2(CO)2 – (CH2)n
• Electronic configuration – Polar head (+): hydrophilic (active) – Non-polar CH2 tail: hydrophobic
• Physical configuration – Cis-double bonds may kink tail
• Lubricants have similar features – Head attaches, tail extends out
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Assembly of Bilayer
• In water, phospholipids form a double layer – Polar, hydrophilic heads contact water – Non-polar, hydrophobic tails are sealed in the interior
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Lipid Bilayer Structure
• Physical structure – Phospholipid sandwich – Low T: chains ordered
• semi-crystalline – Normal T: chains disordered
• Glassy
• Chemical structure – Surfaces attract hydrophilic species
• Polar molecules – Bulk attracts hydrophobic species
• Trapped molecules
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
The Lipid Bilayer
- NIST
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Surface and Trans-Membrane Proteins
• Proteins adsorbed on surface – Membrane coating – Catalytic functions
• Proteins that penetrate wall – “Channel proteins”
• Permit ion transport • Participate in “nerve firing”
– Electric field controls – Chemical species
influence – Mixed proteins
• Hydrophobic body pins • Hydrophilic ends react
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Embedded Molecules: Cholesterol
• Membrane elasticity – Critical to integrity
• No brittle fracture – Flexibility in volume change
• Pulses in blood flow • Ion exchange through channels
• Cholesterol – Molecules imbed in bilayer – Stiffen membrane – May be
• Beneficial: some strengthens wall • Harmful: too much overhardens wall
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Macromolecular Solids
• Polymeric solids – Organics – Plastics
• Silicates – Rocks and minerals – Clay
• Fibers – Fabrics – Fiber composites
• Lipid bilayers – Biological membranes
• Quasicrystals – Ordered, but non-periodic – Ex.: semi-infinite spiral
• Unique origin of pattern
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Thermochemical Properties
• Materials respond to – Thermal stimuli (temperature) – Chemical stimuli (composition or environment) – Electromagnetic stimuli (electric or magnetic fields) – Mechanical stimuli (mechanical forces)
• Consider the first two together – Response to thermal or chemical stimuli defines
thermochemical properties
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Thermochemical Properties
• Essential features: – Thermodynamics: what material wants to do (forces) – Kinetics: what it can do, and how quickly
• Study – Thermodynamics
• Properties • Equilibrium phase diagrams
– Kinetics • Continuous: heat and mass diffusion • Structural phase transitions
– Environmental interactions • Wetting and catalysis • Corrosion
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Thermodynamics
• The conditions of equilibrium and stability – Equilibrium ⇒ no desire for change – Deviation from equilibrium ⇒ driving force for change – Beyond limits of stability ⇒ must change
• Internal equilibrium – T, P, {µ} are constant – Deviation drives heat and mass diffusion
• Global equilibrium – Thermodynamic potential is minimum – Deviation drives structural phase transformations
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
First Law of Thermodynamics
• Defines “internal energy”, E
• Energy is conserved
– Energy transferred to one material is taken from another
dE = dW + dQ
dW = work done (chemical + mechanical +electromagnetic)
dQ = heat transferred (thermal work)
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Second Law of Thermodynamics
• Defines “entropy”: S
• Entropy is associated with – Evolutionary time (most fundamental) – Heat – Randomness (information)
• When a system is isolated, S can only increase – Any system is isolated when its surroundings are
included
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
A Simple “Adiabatic” System
• Simple system in thermally insulated container
• Can do mechanical work – Reversibly, with a frictionless piston – Irreversibly, with a paddle wheel – But no thermal interaction because of insulation
• This is called an “adiabatic” system – An isolated system is one example of an adiabatic
system
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Change of State in an Adiabatic System
• Moving piston generates E-V curve
• Turning paddle wheel – Raises E at constant V – Changes the reversible E-V curve
• Paddle work is irreversible – System moves to new E-V curve – System can never return
E
V
Reversible curve from moving piston
Irreversible change from paddle wheel
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
The Measure of Time in an Adiabatic System
• The E-V curve divides states into – Past (below current curve) – Present (on current curve) – Future (above current curve)
• States (E,V) below are the past – System cannot do work on paddle wheel – These states are unattainable
• States (E,V) above are in the future – Can be reached by paddle + piston – But system can never return
• The current (E,V) curve is the present – System can sample these states at will
E
V
Past
Future
Present
E
V
Reversible curve from moving piston
Irreversible change from paddle wheel
J.W. Morris, Jr. University of California, Berkeley
MSE 200A Fall, 2008
Entropy = Time (State of Evolution)
• States (E,V) on a reversible curve have a common property: call it entropy (S)
• Assign a numerical value of S to each curve such that S is continuous
• Then S = S(E,V) measures the evolutionary time of the state (E,V)
– S can only increase – S divides past (S’<S) from future (S’>S)
E
V
S
curves of constant “entropy” S