Theres a lot of free volume

1
Theres a lot of free volume!
Density of carbon (as diamond) 3 g/mL Density
of 12C nucleus Rnucleus (protons
neutrons)1/3 1.2 ? 10-13 cm Socarbon could
be compressed to about 1 ? 1014 g/mL
WOW! I guess those electrons do a great job of
repelling each other to fill the volume.
2
Wiggle Room as important to polymers as to
Hitler.
Crystal of a small alkane
3
Transitions can be followed through thermodynamic
state variables.
Melting temperature implies a transition from
left to right. We could just as well call it the
freezing point for the transition going from
right to left.
4
Equilibrium is highly overrated!

• Slow-cooled SiO2 Quartz
• Fast-cooled SiO2 window glass
• You can also glass water! Just cool it really,
  really fast.

Practical application of water glass
Freeze-fracture TEM image of aqueous gel.
Water in the gel is just stopped dead in its
tracks without forming ice crystals that would
distort the structure.
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Stopping polymers dead in their tracks is easy.

• Amorphous Polymers
• Polymers that just cant crystallize, ever.
• Polymers that could crystallize,
• but werent given enough
• time. (Frustrated polymers).
• Semicrystalline
• Polymers that partially crystallized,
• but contain amorphous regions.

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Do polymer glasses or crystals shatter?
Does it hurt to dive into water? Do bookcases
sag? Do glaciers flow?
In all cases, the answer is.it depends. Still,
it is easy to identify water as a liquid. Wooden
bookshelves and glaciers are clearly solid for
most practical purposes.
7
Near Chamonix, France, is a flowing ice tunnel.
8
There are at least three general types of polymer
volume-temperature behavior.
9
Remember! Tg is for the down-going transition,
but we often care more about the stuff above Tg.

• That stuff can be melt or tough stuff, depending
  on crystallinity.

Even melty, non-crystallizable polymers can
acquire toughness if covalent crosslinks
substitute for the crystalline zones. Example?
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Above Tg.
Completely amorphous polymer ? Viscous fluid
Frustrated, crystallizable polymer ? lets
return to that later.
Semicrystalline polymer ? Tough solid
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Heres a phase diagram for behavior (no
crosslinks).
? Amorphous
? Semicrystalline
From Rudin The Elements of Polymer Science
Engineering
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A molecular level view shows more local volume at
temperatures exceeding Tg .
Greater local motion
Restricted local motion
V
Tg
T
Can be sticky or pliant/tough
Brittle glass
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Below Tg .
Polymer is certainly more brittle. Polymer might
not be completely brittle, because some motions
remain that permit the chains to dissipate
energy. These correspond to other transitions
that may or may not produce much of a volume
change. Transitions usually called a, b, g
Example Nylon is always used below its Tg, yet
is not brittle
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The various transitions are classified according
to their thermodynamic signatures.
This isnt a thermo class, but you must
recall this golden oldie from PCHEM dG Vdp -
SdT i.e.,
? Volume is related to a first derivative of G.
? So is entropy.
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Crystals melt, glasses librate.
First order transition
Second order transition
Discontinuity in volume, i.e., discontinuity in a
1st derivative of G
Discontinuity in derivative of volume, i.e.,
discontinuity in a 2nd derivative of G
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Measuring Volume Stinks!
Remember that Work -pdV System would have to
gain some energy, as heat, to perform that work.
It might be easier to measure heat instead.
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Entropy trends parallel volume.
DH T DS 1st order transition with latent
heat At transition, you have to suddenly put in
more heat.
DH 0 2nd order transition no latent heat.
After transition, the rate at which heat must be
supplied changes
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Differential scanning calorimetry compares heat
flow of sample and inert reference while heating
or cooling.
Primitive Power Supplies
Thermometers
Sample
Reference
Suppose we keep track of RPMs needed to maintain
sample and inert reference at same temperature as
both are heated.
Orwe could keep track of current.
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1st 2nd order DSC transitions look peaky or
winkly respectively.
Differential heat the extra heat it takes to get
sample through transitions that the inert
reference does not have.
Sample --
Reference
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Heres a DSC of a reversible gel from our
research.
Sarah wanna buy a vowel? Schmidtke
Thermoreversible Gelation of Isotropic and
Liquid Crystalline Solutions of a "Sticky"
Rodlike Polymer Sarah Schmidtke, Paul Russo,
Javier Nakamatsu, Ebru Buyuktanir, Bilge Turfan,
and Elena Temyanko Macromolecules, 33 (12), 4427
-4432, 2000.
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The DSC of plastic pop bottles is a classic
example of melt crystallization.
The DSC of plastic pop bottles illustrates a
classic example of melt crystallization.
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Many other Tg methods have been devised.

• NMR T1, T2, 2H etc.
• Dielectric spectroscopy
• Viscoelastic methods, which can directly probe
  the entire mechanical spectrum as function of
  frequency.

• All these have characteristic frequencies
• Tg ? as frequency ?
• you really have to chill something before it
  cannot slowly deform.

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Some typical Tgs mnemonic, the Tg of PS is
numerically similar to its Mo.
From Campbell Introduction to Synthetic Polymers
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Tg Trends are more or less sensible.
Tg ? as stiffness ? Tg ? as steric bulk ?
Tg ? as M ? i.e., Tg Tg,? -
(K/Mn)?
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Tm and Tg are correlated, but
From Billmeyer
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Caveats

• A lot about this lecture is schematic the real
  picture is more complex.
• A lot depends on rate!

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It really, really matters!
Challenger space shuttle. Feynmann
http//www.feynman.org/
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Plasticizers can change polymer bricks into
polymer pillows by modifying Tg.
Di-sec-octylphthalate (DOP)
Other uses lubricant for textiles rocket
propellant insect repellant perfume solvent
nail polish to prevent chipping
http//www.chemicalland21.com/industrialchem/plast
icizer/DOP.htm
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There has been some concern for phthalates in
kids toys (e.g., rubber duckies).
DINPis one substitute Di-isononyl
phthalatehttp//www.greenfacts.org/glossary/def/D
INP-di-isononyl-phthalate.htm Is this the same
as BASF Hexamoll DINCH? http//www.specialchem4po
lymers.com/tc/phthalate-free-plasticizers/
Citrates are also used (these sound safer)