Bootstrap Dynamic Light Scattering Approach to
Size and Viscosity in Complex Fluids
80th ACS Colloid & Surface Science Symposium
Boulder, Colorado June 19, 2006
Grigor B. Bantchev, Robin L. McCarley, Robert P. Hammer & Paul S. Russo
Louisiana State University
National Science Foundation-Division of Materials Research
National Science Foundation-Chemistry
National Institutes of Health-Aging
Can we start with nothing and get something?
How does DLS work again?
DLS can be dangerously wrong.
Depolarized DLS—often overlooked tool.
Lifting ourselves up by our DLS bootstraps.
Making regular DLS faster and safer.
http://www.mouthmag.com/issues/58/graphics/bootstraps.gif
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
2
Normal DLS works by interference among
multiple scatterers, detected coherently.
g ( 2 ) (t ) 
1
2T I
T
lim
2 T 
 2 t
I
(
t
)
I
(
t

t
'
)
dt
'

1

f
e
coh

T
  q 2D trans
0  fcoh  1
q set by scattering angle,
refractive index,
wavelength
Intensity
q
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
3
In normal DLS, you sometimes can get by
with one angle (q value)—i.e., Dtrans=/q 2.
6
4
Uh-oh!
Campbell, Epand, and RussoBiomacromolecules 2004, 5, 1728-1735
-7
Dapparent / 10 cm s
2 -1
human influenza virus
2
silica-homopolypeptide composite particles
Very good.
0
0
1
2
3
2
4
10
q /10 cm
5
6
Fong and Russo, Langmuir 1999, 15(13); 4421-4426
-2
Size essentially comes from inverting D .
Size would seem to depend on q for influenza virus: not good.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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Depolarized DLS senses rotational motion, in addition
to translational motion.
a
θ
Incident polarizer
Always vertical (v)
a
H
V
H
Detection analyzer
Vertical (V) or
Horizonal (H)
Now we can measure
g (2)Vv(t ) or g (2)Hv(t)
v
• This only happens if the object is
optically anisotropic.
• Many but not all rods qualify.
• Some spheres qualify.
• This rotational motion contributes
fluctuations even when q = 0.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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Which has stronger depolarized signal, and why?
Depolarized signal strength arises from optical
anisotropy, not anisotropy of shape.
TMV: Tobacco Mosaic Virus
PTFE Latex
Shape highly anisotropic
Barely depolarizes at all
Shape barely anisotropic
Depolarizes like crazy!
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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Dynamic Light Scattering: Summary
LASER
Vv = q 2Dtrans
Vv Geometry
(Polarized)
q
v
V
LASER
q
v
Hv = q 2Dtrans + 6Drot
H
Hv Geometry
(Depolarized)
q
4n sinq / 2 
o
Requires optical anisotropy
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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Let’s look at those equations graphically.
Hv
Vv
Dtrans
q2
Dtrans
6Drot
q2
We’ll see real data later.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
8
Probe diffusion, a form of microrheology: invert the
Stokes-Einstein relations. Rather than get a size, know
the size and solve for the (micro)viscosity.
D trans
D rot
kT
kT

 hm 
6hR
6RD trans
kT
kT


h

m
3
3
8hR
8R D rot
Originators: Turner & Hallett, Phillies & coworkers.
Many others since the 1980’s.
Other ways: fluorescence or phosphorescence depolarization.
Mixed opinions about equality of hm and h.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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Bootstrapping:
using two transport measurements
eliminates viscosity. We get size without knowing viscosity,
then we get viscosity anyway.
D trans
D rot
kT
4 2
3 D trans
6hR

 R R 
kT
3
4 D rot
8hR 3
kT
kT

Then: h m 
3
8R D rot 6RD trans
Look, ma!
No viscosity!
http://admin.urel.washington.edu/uweek/
archives/issue/images/22_22/large_bike0594.jpg
Review of Scientific Instruments (2006), 77(4), 043902/1-043902/6
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
10
MADLS=MultiAngle DLS
How fast? How much?
2π/q
x
Laser
q
4-8 angles at once.
Depends on h
Typically 1 minute
$20,000
Multiple
Correlator
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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We built MADLS because we need it.
LSU’s Malvern zetasizer
LSU’s Wyatt Rex/HeleosQELS/Viscostar/Eclipse-AF4/GPC
Other LSU DLS equipment
Conventional LSU-constructed DLS/SLS system #1
Conventional LSU-constructed DLS/SLS system #2
Union Carbide-Dow Prodigal DLS/SLS System
Wyatt Dawn-Aqueous
Wyatt Dawn-Organic
2 ALV5000
1 BI9000
12
Low-resolution Movie of MADLS instrument in action.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
13
Glycerin-water depolarized (Hv) MADLS results
2200
0.92 cp
1.8 cp
2.2 cp
2.9 cp
85 cp
2000
1800
1600
/s
-1
1400
1200
1000
800
600
400
200
0
0
1
2
3
2
4
10
q / 10 cm
5
6
-2
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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MADLS compares well to a conventional instrument.
1500
-1
1000
MA / s
25
20
15
500
10
 Only 6 Hz
5
0
4 points
0
0
0
500
1000
5
10
15
20
25
1500
-1
Conv / s
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
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Bootstrapping the size and viscosity for PTFE latex in various
glycerin-water mixtures, with comparison to conventional
instrument, looks promising.
h / cP
0.92
1.8
2.2
2.9
83
MADLS
121 ± 6
143 ± 8
146 ± 5
137 ± 2
149 ± 3
Conventional 114 ± 5
Instrument.
RI / nm
121 ± 3
n/a
n/a
128 ± 9
RI / nm
The viscosities were within 25% of cone-and-plate values in the range 1.8 to 83 cP.
OK, but there is room for improvement:
• better polarizers (coming soon).
• better probes (smaller, more monodisperse, more spherical
and also rodlike)
• simultaneous monitoring of SLS as probe aggregation check
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
16
So far, it may seem we have only made the rheology
of simple fluids more complex. Depolarized DLS can
do rheology of complex fluids, though.
h mT
h mR
100
h
h/cP
0.76 ± 0.01
10
(C)
1
100
1000
10000
100000
1000000
1E7
Microviscosities
from TMV
translation
and rotation
through 15%
dextran
solution follow
the same
trend as
conventional
rheology.
Dextran MW
Cush, Dorman & Russo Macromolecules 2004, 37(25); 9577-9584
17
The Main Bootstrap Applications include:
Particle size in a fluid of unknown viscosity.
Particle size in a fluid of changing viscosity.
Viscosities that are difficult to measure, where precision may be more
important than accuracy:
• Supercritical fluids
• Confined fluids
• Zero gravity
Probe diffusion when the probe may aggregate—this will have a minor
effect if the aggregation is moderate.
Only in transparent fluids!
You still need to know the refractive index.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
18
Fringe benefits of multiple-angle, multiplecorrelator techniques for normal, polarized DLS.
Find out quickly if you can get away with a
simple, commercially available
instrument operating at just one angle.
50000
Addition of 5mL of 500mM
Murphy Peptide dissolved
in water
40000
 -Amyloid1-40 incubated
R h,app / Å
30000
in 100% DMSO followed
by dilution in PBS pH 7.4
20000
Aggregating or
responsive systems, such
as amyloid fibrils. You
can follow in real-time
in a meaningful way.
10000
Sonicate in water bath
for 10 mins with probe sonicator
0
0
10000
20000
30000
40000
50000
60000
70000
Time/s
Combine with multiangle SLS: get Rh/Rg
ratios in real time 
shape.
Very torpid systems: measure the lowest angle right and
the others are done already and waiting for you.
Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits
19
A new wrinkle in the fabric of DLS.
Something new from the Stokes-Einstein relations (!)
If the particle depolarizes, you can get size without viscosity.
Then you can go back and get the (micro) viscosity.
We find that microviscosity is generally pretty close to viscosity for probes
of reasonable size.
Accuracy/precision are already respectable for log-log work, but…
Much development work remains:
Better probes, better polarizers, better alignment.
A multiple-angle, multiple-correlator is a helpful appliance for normal DLS, too.
I welcome your questions, but address the deep technical ones to
Dr. Grigor Bantchev, who is at this meeting. If you need a talented designer…
Boulder Canyon
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Monday, 19 June 2006 - 10:10 AM
Eng Ctr 105 (University of Colorado at Boulder)
92
Bootstrap Dynamic Light Scattering Approach to Size and Viscosity in Complex
Fluids
Grigor B. Bantchev, Paul S. Russo, Pavan Bellamkonda, Robin L. McCarley, and Robert P.
Hammer. Louisiana State University, Baton Rouge, LA
Commercial dynamic light scattering instruments are widely available, but at any one time
most of them can only measure the signal from a single detector positioned at a particular
angle. A real-time, multiple-angle, multiple-correlator system will be described. It is
equipped for the measurement of the depolarized signal. Such a system can rapidly
measure the size of optically anisotropic particles without knowledge of the fluid viscosity.
Once the size is known, the viscosity can be obtained in the continuum limit. This capability
may be useful in regular or complex fluids that can be probed by visible light, including
systems that pose difficulty to conventional mechanical rheometers. Another potential
application is to particle growth in complex media. Supported by NSF and NIH.
Back to Rheology and Dynamics of Complex Fluids I: New Probes
Back to The 80th ACS Colloid and Surface Science Symposium (June 18-21, 2006)
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