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.

Solution: Use Polarizers to 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”

Seedlings

Sick Plants And close-up of mosaic pattern.

Doing our Part to Keep the “A” in LSU A&M

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

2

4

6D

rot /

Dtr

ans

/109 cm

-2

wt% ficoll

0

20

40

60

80/ cP

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

0 10 20 30 40 50 60

-1

0

1

2

3

4

5

6

7

8 Ficoll Dextran

Dro

t / D

tran

s/ 1

09 cm-2

/ cP

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.