lecture slides - 8 - Berkeley MSE · structure • Open structure results in ... – Sometimes...

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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

Transcript of lecture slides - 8 - Berkeley MSE · structure • Open structure results in ... – Sometimes...

Page 1: lecture slides - 8 - Berkeley MSE · structure • Open structure results in ... – Sometimes woven into 2d or 3d ... lecture slides - 8.ppt Author:

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

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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

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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++

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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

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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

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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)

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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

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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

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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 =

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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

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

MSE 200A Fall, 2008

The Lipid Bilayer

- NIST

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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

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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

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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

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

MSE 200A Fall, 2008

The Lipid Bilayer

- NIST

Page 16: lecture slides - 8 - Berkeley MSE · structure • Open structure results in ... – Sometimes woven into 2d or 3d ... lecture slides - 8.ppt Author:

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

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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

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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

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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

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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

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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

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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)

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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

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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

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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

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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

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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