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80 th ACS Colloid & Surface Science Symposium Boulder, Colorado June 19, 2006 Grigor B. Bantchev, Robin L. McCarley, Robert P. Hammer & Paul S. Russo Louisiana.

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Presentation on theme: "80 th ACS Colloid & Surface Science Symposium Boulder, Colorado June 19, 2006 Grigor B. Bantchev, Robin L. McCarley, Robert P. Hammer & Paul S. Russo Louisiana."— Presentation transcript:

1 80 th 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 Bootstrap Dynamic Light Scattering Approach to Size and Viscosity in Complex Fluids

2 2 Can we start with nothing and get something? How does DLS work again? Depolarized DLS—often overlooked tool. Lifting ourselves up by our DLS bootstraps. DLS can be dangerously wrong. Making regular DLS faster and safer. Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits

3 3 Normal DLS works by interference among multiple scatterers, detected coherently.  Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits q set by scattering angle, refractive index, wavelength Intensity

4 4 In normal DLS, you sometimes can get by with one angle (q value)—i.e., D trans =  /q 2.  Uh-oh!  Very good. Size essentially comes from inverting D. Size would seem to depend on q for influenza virus: not good. Fong and Russo, Langmuir 1999, 15(13); Campbell, Epand, and RussoBiomacromolecules 2004, 5, Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits

5 5 Depolarized DLS senses rotational motion, in addition to translational motion. θ V H Now we can measure g (2) Vv (t ) or g (2) Hv (t) 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. Incident polarizer Always vertical (v) Detection analyzer Vertical (V) or Horizonal (H) Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits v H   

6 6 Which has stronger depolarized signal, and why? Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits PTFE Latex TMV: Tobacco Mosaic Virus Shape highly anisotropic Barely depolarizes at all Shape barely anisotropic Depolarizes like crazy! Depolarized signal strength arises from optical anisotropy, not anisotropy of shape.

7 7 Dynamic Light Scattering: Summary  Hv = q 2 D trans + 6D rot LASERv H  PMT Hv Geometry (Depolarized) Vv Geometry (Polarized) v   Vv = q 2 D trans PMT LASER Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits V Requires optical anisotropy

8 8 Let’s look at those equations graphically.  Vv q 2q 2 6 D rot  Hv D trans q 2q 2 Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits We’ll see real data later.

9 9 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. Originators: Turner & Hallett, Phillies & coworkers. Many others since the 1980’s. Other ways: fluorescence or phosphorescence depolarization. Mixed opinions about equality of   and . Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits

10 10 Bootstrapping : using two transport measurements eliminates viscosity. We get size without knowing viscosity, then we get viscosity anyway. Look, ma! No viscosity! Then: Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits archives/issue/images/22_22/large_bike0594.jpg Review of Scientific Instruments (2006), 77(4), / /6

11 11 MADLS=MultiAngle DLS How fast? How much?  x 2π/q2π/q Laser Multiple Correlator 4-8 angles at once. Depends on  Typically 1 minute $20,000 Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits

12 12 We built MADLS because we need it. 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 ALV BI9000 LSU’s Malvern zetasizer LSU’s Wyatt Rex/Heleos- QELS/Viscostar/Eclipse-AF4/GPC

13 13 Low-resolution Movie of MADLS instrument in action. Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits

14 14 Glycerin-water depolarized (Hv) MADLS results Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits

15 15 MADLS compares well to a conventional instrument. Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits  Only 6 Hz

16 16 Bootstrapping the size and viscosity for PTFE latex in various glycerin-water mixtures, with comparison to conventional instrument, looks promising. 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

17 17 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.  Microviscosities from TMV translation and rotation through 15% dextran solution follow the same trend as conventional rheology. Cush, Dorman & Russo Macromolecules 2004, 37(25);

18 18 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

19 19 Fringe benefits of multiple-angle, multiple- correlator techniques for normal, polarized DLS. Find out quickly if you can get away with a simple, commercially available instrument operating at just one angle. Normal DLS  Depolarized DLS  Bootstrapping  Applications  Fringe Benefits Aggregating or responsive systems, such as amyloid fibrils. You can follow in real-time in a meaningful way. Combine with multi- angle SLS: get R h /R g ratios in real time  shape. Very torpid systems: measure the lowest angle right and the others are done already and waiting for you.

20 20 Boulder Canyon 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…

21 21 Monday, 19 June :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)Rheology and Dynamics of Complex Fluids I: New ProbesThe 80th ACS Colloid and Surface Science Symposium (June 18-21, 2006)


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