Macromolecular Solids

Macromolecular Solids MSE 200A Fall, 2008 •  Polymeric solids •  Silicates •  Fibers •  Lipid bilayers •  Quasicrystals –  Organics –  Pla...
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Macromolecular Solids

MSE 200A Fall, 2008

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Polymeric solids

• 

Silicates

• 

Fibers

• 

Lipid bilayers

• 

Quasicrystals

–  Organics –  Plastics

–  Rocks and minerals –  Clay –  Fabrics –  Fiber composites –  Biological membranes

J.W. Morris, Jr. University of California, Berkeley

Silicates

MSE 200A Fall, 2008

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Are the basis for rocks, clays and minerals

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Common dirt is, in fact, aluminosilicate: Si-Al-Fe oxide

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Other minerals also have complex compositions with many elements

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Study SiO2 as a simple prototype

J.W. Morris, Jr. University of California, Berkeley

Silicates

-

MSE 200A Fall, 2008

++ -

M

- M+

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SiO4-4 tetrahedra join at corners to form networks: strong, hard structure

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Open structure results in several crystal structures, glasses

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Glass formation promoted by ions that terminate oxygen bonds

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Layered Silicates: Using Clay

H2O

MSE 200A Fall, 2008

H2O

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Clay is soaked

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Clay is formed

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Clay is fired

H2O

–  Water molecules fit between platelets –  Water separates and lubricates plates –  They slide easily over one another –  Can be molded into shapes –  If clay dries, shape crumbles –  Firing reorganizes bonds, creates 3d network structure ⇒  clay becomes stone

J.W. Morris, Jr. University of California, Berkeley

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)

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Graphite Fibers • 

Graphite rolled into tube to form strong, stiff fiber

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Happens naturally when certain organic fabrics are “pyrolized”: heated to decompose into graphite

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Used to make strong, stiff composites –  Strong but brittle –  Weak in perpendicular direction –  Sometimes woven into 2d or 3d structures for multiaxial properties

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Kevlar Fibers N

N

H

H

O= C

O= C

O= C

H

C =O

H

C =O

H

C =O N

N

N

N N N O= C

H

O= C

H

O= C

H

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Kevlar: benzene rings joined to make puckered sheets

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Puckered sheets form fibers –  Join edgewise to form star pattern –  “Accordion folds” perpendicular to axis of the fiber

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Fibers are strong, but elastic –  Behave like elastomers while the accordion folds extend, then strong –  Useful for body armor: “catch”projectiles

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Macromolecular Solids • 

Polymeric solids

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Silicates

• 

Fibers

–  Organics –  Plastics

–  Rocks and minerals –  Clay –  Fabrics –  Fiber composites

MSE 200A Fall, 2008

• 

Lipid bilayers

• 

Quasicrystals

–  Biological membranes

J.W. Morris, Jr. University of California, Berkeley

The Lipid Bilayer

MSE 200A Fall, 2008

- NIST

J.W. Morris, Jr.

University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Assembly of Bilayer

•  In water, phospholipids form a double layer –  Polar, hydrophilic heads contact water –  Non-polar, hydrophobic tails are sealed in the interior

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Lipid Bilayer Structure • 

Physical structure –  Phospholipid sandwich –  Low T: chains ordered •  semi-crystalline

–  Normal T: chains disordered •  Glassy

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Chemical structure –  Surfaces attract hydrophilic species •  Polar molecules

–  Bulk attracts hydrophobic species •  Trapped molecules

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

The Lipid Bilayer

MSE 200A Fall, 2008

- NIST

J.W. Morris, Jr.

University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Embedded Molecules: Cholesterol

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Membrane elasticity –  Critical to integrity

•  No brittle fracture

–  Flexibility in volume change

•  Pulses in blood flow •  Ion exchange through channels

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Cholesterol

–  Molecules imbed in bilayer –  Stiffen membrane –  May be

•  Beneficial: some strengthens wall •  Harmful: too much overhardens wall

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Macromolecular Solids • 

Polymeric solids

• 

Silicates

–  –  –  – 

Organics Plastics

Rocks and minerals Clay

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Fibers

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Lipid bilayers

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Quasicrystals –  Ordered, but non-periodic –  Ex.: semi-infinite spiral

–  –  – 

Fabrics Fiber composites Biological membranes

• 

MSE 200A Fall, 2008

Unique origin of pattern

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

First Law of Thermodynamics

•  Defines “internal energy”, E •  Energy is conserved dE = dW + dQ dW = work done (chemical + mechanical +electromagnetic) dQ = heat transferred (thermal work) –  Energy transferred to one material is taken from another

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

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

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

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

Reversible curve from moving piston

E

•  Paddle work is irreversible

–  System moves to new E-V curve –  System can never return

Irreversible change from paddle wheel

V MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

The Measure of Time in an Adiabatic System Future

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The E-V curve divides states into

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States (E,V) below are the past

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States (E,V) above are in the future

E

Past

Present

–  Past (below current curve) –  Present (on current curve) –  Future (above current curve)

–  System cannot do work on paddle wheel –  These states are unattainable

V

–  Can be reached by paddle + piston –  But system can never return

Reversible curve from moving piston

E

•  Irreversible change from paddle wheel

The current (E,V) curve is the present

–  System can sample these states at will

V MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley

Entropy = Time (State of Evolution)

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States (E,V) on a reversible curve have a common property: call it entropy (S)

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Assign a numerical value of S to each curve such that S is continuous

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Then S = S(E,V) measures the evolutionary time of the state (E,V)

curves of constant “entropy” S

E S

–  S can only increase –  S divides past (S’S)

V

MSE 200A Fall, 2008

J.W. Morris, Jr. University of California, Berkeley