Recent Developments in Polymer Characterization

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Recent Developments in Polymer Characterization

• And how we may have to modify them for
  nanoparticles

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Obligatory Equation
SEC GPC GFC
Size Exclusion Chromatography Gel Permeation
Chromatography Gel Filtration Chromatography
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A riddle

• After a hurricane, many trees fall over and bend
  into a river. Also, a cow and a dog fall into a
  flooded river. Which one reaches the ocean
  first, cow or dog?

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GPC

• Solvent flow carries molecules from left to
  right big ones come
• out first while small ones get caught in the
  pores.
• It is thought that particle volume controls the
  order of elution.
• But what about shape?

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Simple SEC
log10M
Ve
pump
injector
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Osmometry Real Science
Semipermeable membrane stops polymers, passes
solvent.
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Light Scattering Osmometer without the membrane
100,000 ?
x
q
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LS adds optical effects ? Size
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SEC/MALLS
DRI
pump
injector
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SEC/MALLS
Scattered intensity
Scattering angle
Ve
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Scattering Envelope for a Single Slice
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SEC/MALLS in the Hands of a Real Expert
Macromolecules, 29, 7323-7328 (1996)
ap ? 15 nm Much less than PBLG
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Midpoint
The new power of SEC/Something Else experiments
is very real. SEC is now a method that even the
most skeptical physical chemist should embrace.
For example, our results (not shown) favor higher
rather than lower values for persistence length
of one polymer (PBLG). This helps to settle
about 30 years of uncertainty. So, SEC is good
enough for physical measurements, but is it still
good enough for polymer analysis? What about
nanoparticles, especially large ones, in GPC?
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They were young when GPC was.
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Small Subset of GPC Spare Parts
To say nothing of unions, adapters, ferrules,
tubing (low pressure and high pressure), filters
and their internal parts, frits, degassers,
injector spare parts, solvent inlet manifold
parts, columns, pre-columns, pressure
transducers, sapphire plunger, and on it goes
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Other SEC Deficiencies

• 0.05 M salt at 10 am, 0.1 M salt at 2 pm?
• 45oC at 8 am and 50oC at noon?
• Non-size exclusion mechanisms binding.
• Big, bulky and slow (typically 30
  minutes/sample).
• Temperature/harsh solvents no fun.
• You learn nothing by calibrating.

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Must we separate em to size em?Your local
constabulary probably doesnt think so.
Atlanta, Georgia I-85N at Shallowford Rd. Sat.
1/27/01 4 pm
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• Sizing by Dynamic Light Scatteringa 1970s
  advance in measuring motion, driven by need to
  measure sizes, esp. for small particles.

Is
Its fluctuations again, but now fluctuations
over time! DLS diffusion coefficient, inversely
proportional to size.
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Molecular Weight Distribution by DLS/Inverse
Laplace Transform--B.Chu, C. Wu, c.
Where G(g) cMP(qRg) g q2D
q2kT/(6phRh) Rh XRg
ILT
MAP
CALIBRATE
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Hot Ben Chu / Chi Wu Example
Macromolecules, 21, 397-402 (1988)
MWD of PTFE Special solvents at 330oC

• Problems
• Only works because MWD is broad
• Poor resolution.
• Low M part goofy.
• Some assumptions required.

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• Reptation inspired enormous advances in
  measuring polymer speedand predicts
• More favorable results for polymers in a matrix.

There once was a theorist from France Who
wondered how molecules dance. "They're like
snakes," he observed, "as they follow a
curve, the large ones can hardly advance."
More generally, we could write D M-b where b
increases as entanglements strengthen
With apologies to Walter Stockmayer
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Matrix Diffusion/Inverse Laplace
Transformation Goal Increase magnitude of b

• Difficult in DLS because matrix scatters, except
  special cases.
• Difficult anyway dust-free matrix not fun!
• Still nothing you can do about visibility of
  small scatterers
• DOSY not much better

Solution b -1/2
log10D

• Replace DLS with FPR.
• Selectivity supplied by dye.
• Matrix same polymer as analyzed, except no
  label.
• No compatibility problems.
• G(g) c (sidechain labeling)
• G(g) n (end-labeling)

log10M
Stretching b
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Painting Molecules Makes Life Easier
R. S. Stein
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Fluorescence Photobleaching Recovery
3. An exponential decay is produced by
monitoring the amplitude of the decaying sine
wave. Fitting this curve produces G, from which
D can be calculated.
2. A decaying sine wave is produced by moving
the illumination pattern over the pattern written
into the solution.
1. An intense laser pulse photobleaches a
striped pattern in the fluorescently tagged
sample.
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FPR for Pullulan (a polysaccharide)
Probe Diffusion Polymer physics
Calibration polymer analysis
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FPR Chromatogram

• Indicates targeted M.

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GPC vs. FPR for a Nontrivial Case
User-chosen CONTIN 25 Matrix
PL Aquagel 40A 50A
20,000 70,000 Dextran
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• Indicates targeted M.

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Examples of Separation Results from Simulation
Data

• Indicates targeted M.

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What about separating cows and elephants? Either
will float around the trees. How do you
separate them then?
Moo!
Eeee!
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Field Flow Fractionation, thats how!
In FFF, large nanoparticles are made to flow
between plates.
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One plate is porous, and a cross-flow is
arranged.
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What happens?
Little nanoparticles come out first!
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Potential Advantages of FFF

• Handles a wider range of particles.
• May be easier for some aggressive solvents.

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Conclusion

• GPC is essential in any Nano Lab
• GPC may eventually get replaced.
• Matrix FPR
• FFF

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Thank you!