SO, now that we know a little about the mechanical properties we can examine strategies for preparing:

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SO, now that we know a little about the
mechanical properties we can
examine strategies for preparing MULTICOMPONENT
POLYMERS There are a number of very different
strategies for combing two (or more) different
contributing properties into a polymer system to
provide a material with specific optimal overall
properties 1) COMPOSITES mechanically
combining different polymer phases 2) POLYMER
BLENDS chemical mixing of different polymers 3)
COPOLYMERS statistical, graft, block. these are
3 very different lengthscales, and 3 different
material types
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Multi-Components Beyond Tensile Properties
Discussion of mechanical properties has focused
mostly on tensile properties. When we look at
other properties, like compressional properties
or flexural properties things can be completely
different. For example, fibers have very high
tensile strength and good flexural strength as
well, but they usually have terrible
compressional strength. They also only have good
tensile strength in the direction of the
fibers. Fibres are very strong
and very weak ALONG their long
axis AGAINST this axis
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Polymer Composites are usually made of a fiber
and matrix. Fibres can be glass (cheap),
Carbon (strong) Kevlar (tough), polyethylene
(good mix) etc. The matrix is usually an epoxy
resin, or a polyimide. The fiber is embedded in
the matrix by repeated layering, the more
intimate the mixing the better. (text 498-501)
Material Elastic Modulus GPa Tensile
Strength GPa Epoxy Matrix 4 0.1
Glass Fibre 86 4.5 Carbon
Fibre 253 4.5 Kevlar 124 3.6 Glass
composite 55 2.0 Carbon
composite 145 2.3 Kevlar composite
80 2.0 Polymer composites are among the best
strength/weight materials
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MATRIX CONSIDERATIONS. The matrix assumes the
role of holding the fibers together. Also,
though fibers are strong, they are usually
brittle, and the matrix can absorb energy by
deforming under stress, adding toughness to the
composite. Thirdly, the matrix is responsible for
providing compressional strength to the
composite. Optimal fibre volume fraction can be
40-75 For very high-tech (read )
applications, Fibres are usually chosen first,
then the matrix material matched chemically (4
mechs) Adhesion too good? Behaves like a single
component, and no energy absorbed at debonding
interfaces too brittle. Adhesion too poor?
Fibres will pull out under stress- too
compliant. Ideally under stress, matrix fractures
first, then debonds from fibres, then lastly
fibre fracture. Max energy absorbed this way.
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FIBRE CONSIDERATIONS. Strength vs Toughness
vs Weight vs Cost per application.
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Case Study Airbus A380 (This is their
ad.)COMPOSITE HIGH- LOAD STRUCTURES
Elements with high load resistance

• Manufactured in Europe, multi-site
• 25 of structure is Carbon Fibre reinforced
  plastic (CFRP).
• Up to 840 passengers (challenges !) Hard to
  build, transport, manage

Better Strength to Weight ratio means better fuel
economy.
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Case Study Airbus A380 (This is their
ad.)COMPOSITE WRAPPING TECHNIQUES
COMPOSITE LARGE, ODD, STRUCTURES
Components with carbon fibre resin infusion

• Large parts and complex shapes
• New tape layering machine built
• First application on A380 large sections also
  stitched.

• Curved components are built by post form
  resin-impregnation
• Application to complex curved parts (example
  pressure bulkhead)

Weight savings less fuel consumption less
emissions
Extension of Carbon Fibre Manufacturing
technologies to new components reduces aircraft
weight.
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POLYMER BLENDS, a) immiscible and b) miscible
(text 578-585) Firstly, what is miscibility, how
can we tell, and why should we care ? For small
molecules, if we try to mix two components
together which are not thermodynamically
favourable, 2 distinct phases are formed, over
any size sample (oil and water separate and
gather together). For polymers, we can mix two
unfavourable chains together, they will want to
separate, but a small-scale microstructure
results instead. This is good. The resulting
structure depends on the blend ratio
more POLY A 5050
more POLY B
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POLYMER BLENDS, a) immiscible more POLY A
5050 more POLY B this
microphase separation provides interfaces,
combined properties. For example, PS
Polybutadiene (spheres) HIPS (high impact)
the spheres can be 5-10 microns (function of
ratio and miscibility) PET PVA (lamellae) pop
bottles. The PET imparts strength, while the PVA
resists carbon dioxide gas diffusion
depressurization. Car tires are SBR blended with
some cis-Polybutadiene. Glassy Rubber blends
are the most common theme. Desired orientation
can often be controlled through processing.
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POLYMER BLENDS, b) miscible Secondly, the
thermodynamics can be such between the two that
they are always miscible (like water and alcohol
in any proportion). Such materials are single
phase, but display combined and intermediate
properties such as Tg, modulus,
strength/toughness ratio examples Polystyrene
Poly(vinyl methyl ether) Poly(vinyl
chloride) Poly(butylene terepthalate) PMMA
Poly(vinylidene fluoride) Poly(acrylic
acid) Poly(ethylene oxide) Successful
blending assessed by calorimitry (1 Tg) or NMR (1
T1 rho) Easy way to fine-tune a Tg or an
extension under given load.
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COPOLYMERS in one page Along the same lines as
miscible polymer blends, desirable properties can
be brought together by co-polymerizing 2
difference monomers. This is a real pain, but
very few polymers can be blended so its done
when one really doesnt have a choice. The more
dissimilar the mers in many cases, the more
interesting the final resulting
properties. Copolymers can be STATISTICAL (add
both mers then initiator), or BLOCK (add the
2 mers sequentially to a growing chain) (more
later) One trouble is that the more chemically
dissimilar the two mers are, the less random the
distribution the mers are in the chain
(blocky). Another related trouble is that the low
MW fractions can be very dissimilar to the high
MW fractions, and one end of a growing chain can
be unlike the other end, as co-monomer is used up
in the reaction.
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BLOCK COPOLYMERS in more than one page The
immiscible blend approach is a really good one in
theory, but in practice its hard to control the
size and position of the phases. For low-tech
applications when youre not too fussy its OK,
but the phase segregation process depends
strongly on time and temperature. There is
always a RANGE of morphologies and domain sizes,
they can grow over time (collect), and you have
little control of size and spacing. One
variation on this approach requires much more
synthetic effort and cost, but leads to materials
with VERY well defined, stable phase segregation,
of a VERY narrow and reproducible size
distribution.
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ie the well defined material (right) is superior
to the blend at left polymer
blend block copolymer VERY well
defined, stable multi-component materials with
narrow and reproducible size distribution and
morphology spacing can be achieved using phase
segregated BLOCK COPOLYMERS, where the 2
component polymers are covalently tied together
at one end each Interesting materials can be
achieved simply by varying the lengths (and
ratio) of the A and B blocks, and the identity of
the two polymers
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The structures produced are reproducible and
reversible with temp. At 10-100nm, the
lengthscale is also VERY appealing, larger than a
molecule (bigger than chemistry), but smaller
than current nanofabrication methods (smaller
than engineering or biology)
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Multiple morphologies can be accessed by
controlling Na, Nb, and ? the interaction
parameter. Just heat up the sample for a few
hours
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Multiple morphologies can be accessed by
controlling Na, Nb, and ? spheres ? rods
? gyroids ? lamealle ? gyroids ? rods ?
spheres The gyroid phase is bi-continuous, and
has been applied as contact lenses Other phases
can be used as templates for structures, or pore
chemistry
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phase diagrams can be constructed for each pair
of polymers, PS-PMMA
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We will say more about nanotechnology and
patterning later, but in principle, block
copolymers provide an appealing route to
controlled patterning in a very challenging (and
desirable) lengthscale In practice however,
Mother Nature is really the one in
control Spheres (left) and lamealle
(right) are well ordered on the SHORT lengthscale
(a few microns), but disordered on the LONG
lengthscale Much clever work has been done to try
and coax the patterns regular.
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Working in SOLUTION now affords even more
parameters for self assembly, as there are now
three interactions to consider, not one
For a system that is hydrophylic-hydrophobic such
as PAA-PS, the polymer-solvent interaction
parameters can be changed by using a water-THF
mix A wide range of new morphologies is
possible (Eisenberg Group, McGill)
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The usual ones (spheres, rods, ) are now
available in solution As an easy and
clean method to produce small particles for
applications, And again that can be used as
templates for making other structures.
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There are also some unusual ones now available
in solution too Like hollow
vessicles that can be applied as capsules for
drug delivery, or Hexagonally Packed Hollow
Hoops (HHH), which, um, are interesting
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COPOLYMERS in one page Along the same lines as
miscible polymer blends, desirable properties can
be brought together by co-polymerizing 2
difference monomers. This is a real pain, but
very few polymers can be blended so its done
when one really doesnt have a choice. The more
dissimilar the mers in many cases, the more
interesting the final resulting
properties. Copolymers can be STATISTICAL (add
both mers then initiator), or BLOCK (add the
2 mers sequentially to a growing chain) (more
later) One trouble is that the more chemically
dissimilar the two mers are, the less random the
distribution the mers are in the chain
(blocky). Another related trouble is that the low
MW fractions can be very dissimilar to the high
MW fractions, and one end of a growing chain can
be unlike the other end, as co-monomer is used up
in the reaction.