Probing complex fluids with polarization
contrast-matched scattering
Randy Cush & Paul Russo
LSU – Baton Rouge
Chicago
ACS Meeting
August 26, 2001
Study of Complex Fluids
by DLS: Prospects & Problems
+ + + Wide-ranging autocorrelators
> 10 decades of time in one measurement!
– – – Contrast stinks: everything scatters, esp.
in aqueous systems where refractive index
matching cannot hide matrix.
Solution: Use Polarizers to Hide Matrix
Dynamic Light Scattering Setup
LASER
Uv = q2Dtrans

V
LASER

V
H
Hv = q2Dtrans + 6Drot
q
4n sin  / 2 
o
Uv Geometry
(Polarized)
Hv Geometry
(Depolarized)
ZADS
PTFE latex microrheology of polyacrylamide gel
Fraction Frozen by Gelation
2.0
470 s
g(2)()
1.8
1.6
1130 s
1.4
1340 s
1.2
1630 s
1.0
1E-6
2470 s
1E-5
1E-4
1E-3
0.01
/s
0.1
1
1.0
0.8
0.6
0.4
0.2
0.0
10
0
See also: Piazza, Tong, Weitz
1000
Tim
Entanglement in solution?
Collander
To isolate spaghetti in "solution" with a fork is
difficult: hydrodynamic interactions interfere
with entanglement. After solvent is drained to
obtain a "melt" the entire blob is easily handled.
Strategy
•Find polymer that should “entangle”
Dextran
•Random coil
•Polysaccharide
•Invisible in DDLS
•Find polymer that should not “entangle”
•Highly-branched
•Polysaccharide
•Invisible in DDLS
Ficoll
•Find a rodlike probe that is visible in DDLS
TMV
•Rigid rod
•Virus
•Visible in DDLS
•Measure its diffusion in solutions of each polymer separately
Doing our Part to Keep the “A” in LSU A&M
Seedlings
Sick Plants 
And close-up
of mosaic
pattern.
TMV Characterization
Sedimentation, Electron Microscopy and DLS
•Most TMV is intact.
•Some TMV is fragmented
–(weaker, faster mode in CONTIN)
•Intact TMV is easy to identify
–(stronger, slower mode in CONTIN)
nL
0
1
3
6
5
-8
Dr /s
Translation
Dt /10 cm s
-1
500
400
Rotation
3
300
2
Experiments are
in dilute regime.
3
TMV overlap (1/L )
1
200
0
0.0
0.5
1.0
1.5
2.0
c/mg-mL
-1
2.5
3.0
2 -1
4
TMV + Dextran 215 s acquisition
1.3
g
(2)
1.2
1.1
1.0
Dextran >6000 s acquisition
0.9
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
Hv correlation
functions for 14.5%
dextran and 28%
ficoll with and
without added
0.5mg/mL TMV
t/s
g(2)
1.4
TMV + Ficoll 600s aquisition
•The dilute TMV
easily “outscatters”
both matrices.
1.2
Ficoll >6000 s acquisition
1.0
1E-6
1E-5
1E-4
1E-3
0.01
t/s
0.1
1
10
100
4000
3500
/s
-1
3000
Hv TMV / Buffer
2500
2000
Uv TMV / Buffer
1500
1000
Hv TMV / Dextran / Buffer
500
0
0
1
2
3
2
10
4
-2
q /10 cm
5
350
350
300
300
D / s-1
250
250
D / s-1
150
200
rot
rot
200
100
150
100
50
50
0
0
0
2
4
6
8
10
12
14
16
0
2
4
6
8
10
wt% dextran
6
14
16
18
20
22
24
26
28
30
/10-8cm2 s-1
6
5
4
trans
3
2
D
D
trans
/10-8cm2 s-1
12
wt% ficoll
1
0
5
4
3
2
1
0
0
2
4
6
8
10
wt% dextran
12
14
16
0
2
4
6
8
10
12
14
16
18
wt% ficoll
20
22
24
26
28
30
Dextran overlap
5
10
15
20
9
8
80
6
60
4
40
2
20
0
0
0
5
10
wt % dextran
15
20
h/cP
Dr/Dt /10 cm
-2
0
Stokes-Einstein Plots: if SE works, these
would be flat. Instead, deviations in
different directions for Drot and Dtrans
2
4
6
8
10
12
14
16
1.5
-1
4
-9
hDt /10 g-cm-s
hDr /g-cm -s
-1
0
1.0
-2
2
0.5
0
0.0
0
2
4
6
8
wt% Dextran
10
12
14
16
80
9
60
4
40
2
20
0
0
0
5
10
15
20
wt% ficoll
25
30
h/ cP
Drot /Dtrans /10 cm
-2
6
3.5
0.8
2.5
0.6
-1
0.5
2.0
0.4
1.5
0.3
1.0
0.2
0.0
0.0
0
5
10
15
20
wt% ficoll
25
30
-1
0.1
-1
0.5
-9
hDrot /g-cm -s
-1
0.7
hDtrans /10 g-cm -s
3.0
Ficoll
Dextran
9
Drot / Dtrans/ 10 cm
-2
8
7
6
5
4
3
2
1
0
-1
0
10
20
30
h/ cP
40
50
60
Too-Good-to-be-True Conclusion?
• Below 6.5% dextran the diffusion of the rodlike
TMV probe is controlled mostly by viscosity.
• Above 6.5% dextran a sharp transition suggests
topological constraint for TMV rotation while
translation is not much affected.
• The transition is more gradual in ficoll.
• The TMV probe senses something different for
linear vs. highly branched polymers in solution.
• Looks good for topological models!
Alternate Conclusion?
• The systems studied so far place (impossibly?)
strict demands on geometric & polarization
alignment.
– Revised polarization placement
– Difficult zero angle measurements requiring even
more TMV
• New systems must be studied:
– TMV is OK
– Dextran/Ficoll must go!
• Depolarized probe diffusion has the potential,
as yet unrealized, to assess strength of
hydrodynamic vs. topological effects.
Thank
you!
Randy Cush
David Neau
Ding Shih
Holly Ricks
L
S
U
Jonathan Strange
Amanda Brown
Zimei Bu
Zuhal & Savas Kucukyavuz--METU
Seth Fraden—Brandeis
Nancy Thompson—Chapel Hill
NSF
Storage Modulus of Dextran Solutions
10000
1000
G' / Pa
100
10
1
5%Dextran
10%Dextran
15%Dextran
0.1
20%Dextran
25%Dextran
0.01
30%Dextran
35%Dextran
40%Dextran
0.001
1
10
w / rad s
100
-1
The chiral dextran
and ficoll alter
polarization slightly
before and after the
scattering center.
Sign & magnitude of
Stokes-Einstein failures
depend on how one
handles this tiny effect.
Misalignment from thick polarizer in “active” part of
detector train, exacerbated by tiny cells
used to squelch optical rotation & conserve TMV
shifted by thick polarizer element
correctly aligned scattered beam
Conditions for use as a Probe
•Is the TMV Probe Dilute?
A TMV concentration of 0.5 mg/mL, well below the
theoretical overlap concentration, was chosen. See Figure 2.
•Does dilute TMV overwhelm the matrix scattering?
At 0.5 mg/mL the TMV easily “outscatters” both
matrices. See Figure 3.
•Is the probe compatible with the matrix?
-Solutions stable months after preparation
-Angle dependent Hv SLS
-Dtrans goes up, not down (Figures 6 & 8)
Effect of Dextran Concentration
• The dependence of Drot and Dtrans upon added dextran
is shown in Figure 4.
• The quotient Drot/Dtrans is plotted against viscosity in
Figure 5. By combining both transport coefficients, each
inversely proportional to viscosity in dilute solution, we
can remove the effect of solution viscosity.
• Figure 6 reveals like positive deviations from the
Stokes-Einstein continuum expectation that diffusion be
inversely proportional to viscosity (below 6.5%).
•Above 6.5% the deviations become greater for both Drot
and Dtrans but in opposite directions
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.”
D ~ M -2
de Gennes
P.G. de Gennes
Scaling Concepts in Polymer Physics
Cornell University Press, 1979
Doi-Edwards-Onsager Reference Volumes for Rods
n = number density = # of rods per unit volume
d
LC formation
n* = 4/A2  5/dL2
L
Reduced # Density
n/n*  ndL2/5
2
3
dL
L
n
1
3
L
nL3  1
n
A2 
1
2
dL
ndL2  1
n
dL2
1
A2
nA2  1
4
Outline
• Characterize the TMV
– Is it intact and behaving properly?
• Establish conditions for use of TMV as probe
– Can the probe be dilute and still overwhelm the
matrix scattering?
– Will the probe stay mixed with the matrix solutions
without aggregating?
• Show the effect of the dextran and ficoll
matrices on TMV diffusion
An ear of corn has about as many kernels as TMV
has protein subunits (ca. 2130). The protein
subunits enfold a spiral-wound strand of RNA which
will encode the next generation. TMV is more
extended than an ear of corn.
Effect of Ficoll Concentration
• The dependence of Drot and Dtrans upon added dextran
is shown in Figure 4.
• The quotient Drot/Dtrans is plotted against viscosity in
Figure 7.
• Figure 8 shows slight like positive deviations from the
Stokes-Einstein continuum expectation (below 11%).
• Above about 11% ficoll the deviation slowly becomes
greater for Drot and slightly greater for Dtrans but in
opposite directions
• Figure 9 compares TMV behavior in ficoll to that in
dextran.