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