Probing complex fluids with polarization contrast-matched scattering Randy Cush & Paul Russo LSU –...
-
Upload
anthony-underwood -
Category
Documents
-
view
215 -
download
0
Transcript of Probing complex fluids with polarization contrast-matched scattering Randy Cush & Paul Russo LSU –...
Probing complex fluids with polarization contrast-matched scattering
Randy Cush & Paul RussoLSU – Baton Rouge
Chicago ACS Meeting
August 26, 2001
Study of Complex Fluidsby 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.
Dynamic Light Scattering Dynamic Light Scattering SetupSetup
Hv = q2Dtrans + 6Drot
LASER
VV HH
PMT
Hv Hv Geometry (Depolarized)
Uv Geometry Uv Geometry (Polarized)(Polarized)
VV
Uv = q2Dtrans
o
nq
2/sin4
PMT
LASER
ZADS PTFE latex microrheology of polyacrylamide gel
1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10
1.0
1.2
1.4
1.6
1.8
2.0
2470 s
1630 s
1340 s
1130 s
470 sg(
2)()
/s0 1000 2000 3000
0.0
0.2
0.4
0.6
0.8
1.0
Time/s
Fra
ctio
n F
roze
n b
y G
ela
tion
See also: Piazza, Tong, Weitz
Entanglement in solution?Entanglement in solution?
To isolate spaghetti in "solution" with a fork is To isolate spaghetti in "solution" with a fork is difficult: hydrodynamic interactions interfere difficult: hydrodynamic interactions interfere with entanglement. After solvent is drained to with entanglement. After solvent is drained to obtain a "melt" the entire blob is easily handled. obtain a "melt" the entire blob is easily handled.
Collander
StrategyStrategy
•Find polymer that should not “entangle”
•Find a rodlike probe that is visible in DDLS
•Measure its diffusion in solutions of each polymer separately
•Random coil
•Polysaccharide
•Invisible in DDLS
•Highly-branched
•Polysaccharide
•Invisible in DDLS
•Rigid rod
•Virus
•Visible in DDLS
Dextran
Ficoll
TMV
•Find polymer that should “entangle”
TMV CharacterizationTMV 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)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
200
300
400
500
Dt /10
-8cm2s
-1D
r /s-1
10 L3
c/mg-mL-1
0
1
2
3
4
5
6
Rotation
Translation
Experiments are in dilute regime. TMV overlap (1/L3)
Hv correlation Hv correlation functions for 14.5% functions for 14.5%
dextran and 28% dextran and 28% ficoll with and ficoll with and without added without added
0.5mg/mL TMV0.5mg/mL TMV
•The dilute TMV The dilute TMV easily “outscatters” easily “outscatters”
both matrices.both matrices.
1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10 100
1.0
1.2
1.4
Ficoll >6000 s acquisition
TMV + Ficoll 600s aquisition
g(2
)
t/s
1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10 1000.9
1.0
1.1
1.2
1.3
Dextran >6000 s acquisition
TMV + Dextran 215 s acquisition
g(2
)
t/s
0 1 2 3 4 5
0
500
1000
1500
2000
2500
3000
3500
4000
Hv TMV / Dextran / Buffer
Uv TMV / Buffer
Hv TMV / Buffer
/s-1
q2/1010 cm-2
0 2 4 6 8 10 12 14 160
1
2
3
4
5
6
Dtr
ans/1
0-8 c
m2
s-1
wt% dextran
0 2 4 6 8 10 12 14 16
0
50
100
150
200
250
300
350
Dro
t/ s-
1
wt% dextran
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300
1
2
3
4
5
6
Dtr
an
s/10-
8 cm
2 s-
1
wt% ficoll
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
0
50
100
150
200
250
300
350
Dro
t/ s-
1
wt% ficoll
0 5 10 15 20
0
2
4
6
8 /cPD
r/Dt /
109 cm
-2
wt % dextran
0 5 10 15 20
0
20
40
60
80
Dextran overlap
Stokes-Einstein Plots: if SE works, thesewould be flat. Instead, deviations in
different directions for Drot and Dtrans
0 2 4 6 8 10 12 14 16
0.0
0.5
1.0
1.5
Dt /10
-9g-cm
-s-2
Dr /
g-cm
-1-s
-1
wt% Dextran
0
2
4
0 2 4 6 8 10 12 14 16
0 5 10 15 20 25 300.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5D
tran
s /10-9g-cm
-1-s-1
Dro
t /g-
cm-1-s
-1
wt% ficoll
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Too-Good-to-be-True Conclusion?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!
LSU
Randy Cush
David Neau
Ding Shih
Holly Ricks
Jonathan Strange
Amanda Brown
Zimei Bu
Zuhal & Savas Kucukyavuz--METU
Seth Fraden—Brandeis
Nancy Thompson—Chapel Hill
NSF
Storage Modulus of Dextran Solutions
0.001
0.01
0.1
1
10
100
1000
10000
1 10 100
/ rad s-1
G'
/ Pa
5% Dextran
10% Dextran
15% Dextran
20% Dextran
25% Dextran
30% Dextran
35% Dextran
40% Dextran
The chiral dextranand ficoll alterpolarization slightly before and after thescattering center.
Sign & magnitude of Stokes-Einstein failuresdepend 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 ProbeConditions 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 ConcentrationEffect 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 Francewho wondered how molecules dance.“They’re like snakes,” he observed, “As they follow a curve, the large onesCan hardly advance.”
D ~ M -2
P.G. de GennesScaling Concepts in Polymer Physics
Cornell University Press, 1979
de Gennes
Ld
1
1
3
3
3
L
L
L
1
1
2
2
2
dL
dL
dL
1
14
2
2
2
2
A
A
dLA
LC formation = 4/A2 5/dL2
Reduced # Density dL2/5
Doi-Edwards-Onsager Reference Volumes for Rods = number density = # of rods per unit volume
OutlineOutline• 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 TMVhas protein subunits (ca. 2130). The protein
subunits enfold a spiral-wound strand of RNA whichwill encode the next generation. TMV is more
extended than an ear of corn.
Effect of Ficoll ConcentrationEffect 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.