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Introduction to DYNAMIC LIGHT SCATTERING (DLS)

Introduction to DYNAMIC LIGHT SCATTERING (DLS). or PHOTON CORRELATION SPECTROSCOPY (PCS). Christer Svanberg. Outline. Basic of DLS Experimental set-up Accessible time- and length-scales Applications Size and shape of sub-micron objects Research Glass transition Polymer dynamics.

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Introduction to DYNAMIC LIGHT SCATTERING (DLS)

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  1. Introduction toDYNAMIC LIGHT SCATTERING (DLS) or PHOTON CORRELATION SPECTROSCOPY (PCS) Christer Svanberg

  2. Outline Basic of DLS • Experimental set-up • Accessible time- and length-scales Applications • Size and shape of sub-micron objects Research • Glass transition • Polymer dynamics

  3. correlation Experimental set-up

  4. Scattered Electric Field • DLS probes • density fluctuations • concentration fluctuations

  5. Time range of DLS DLS QENS NMR Raman Brillouin Dielectric -14 -10 -6 -2 2 LOG(TIME (s)) DLS covers a very large time range! Typically: 10-7 - 103 s! => 10 decades in time!

  6. Experimentally accessible wave vectors Q-range: typically 0.6 – 2×10-3 Å-1 DLS is therefore suitable for diffusional studies of macromolecules, such as polymers and large biomolecules!

  7. Wide time range Cheap Simple experimental set-up Advantages and Disadvantages • Only transparent samples • Very clean samples needed • Sensitive for mechanical disturbances + -

  8. Commerically avaliable products

  9. Scientific instruments • More laser power! • Specially designed cryo-furnaces • Polarization options • Vibration isolation table

  10. Scotland, 1827

  11. Brownian Motion • First observed in 1827 by the botanist Robert Brown. He was looking at pollen grains under a microscope. The force of life? • Desaulx in 1877: "In my way of thinking the phenomenon is a result of thermal molecular motion in the liquid environment (of the particles).” • The mathematical theory of Brownian motion was developed by Einstein in 1905. • Jean-Baptiste Perrin verified Einstein's analysis (Nobel Prize 1926).

  12. Stoke-Einstein relation: Brownian Motion Explanation: A suspended particle is constantly and randomly bombarded from all sides by molecules of the liquid. If the particle is very small, the number of hits it takes from one side at a given time will be stronger than the bumps from other side. This make the particle jump. These small random jumps are what make up Brownian motion.

  13. Applications of DLS Size: Using Stoke-Einstein equation DLS can be used to easy, fast and accurate determination of the hydrodynamic radius of particles. Typically range: 1 nm – 1μm. Shape: Ellipsodial particles results in a small fraction depolarized scattered light. Can be used for estimation of ellipticity of the particles. Difficult!

  14. Examples Some examples of sub-micron systems: • Micro-emulsions • peptides • micelles • macromolecules • polymers • paint pigments • bacteria, viruses

  15. Calculated ellipitic shape Lysozome Hydrodynamic size Calculated hard sphere Estimation of Ellipsodial objects

  16. Size Distribution of Insulin Intensity Diameter (nm)

  17. The influence of pH on Insulin Amplitude Diameter (nm)

  18. Research using DLS • Determination of size on complex systems: • “water-in-oil” • bio-molecules • cellulose • Glass transition dynamics • Polymer dynamics

  19. 1.0 0.8 0.6 correlation 0.4 t 0.2 0.0 -2 -1 0 1 2 log[t/t (s)] Glass transition dynamics log  glass liquid -relaxation • cooperative intermolecular motion • stretched exponential decay • non-Arrhenius temp. dep. • freezes at Tg -relaxation • local motion • broad response • Arrhenius temp. dep.   fast 1/T 1/Tg

  20. 1 0,8 0,6 192 K 0,4 Temp. 0,2 221 K 0 -6 -4 -2 0 2 4 10 10 10 10 10 10 Time (s) Poly(propylene glycol)

  21. Arrhenius Plot 4 Polymer Dimer (n=69) (n=2) 0 Oligomer (n=7) Monomer -4 log[ Relaxation time (s)] (n=1) -8 -12 2 2.5 3 3.5 4 4.5 5 5.5 6 1000/T (1/K) Arrhenius Plot Conclusion: Shorter polymer chains relax faster than long chains.

  22. 200 - 500 Å Glass Transition dynamics in Free-standing Polymer Films Polystyrene Tg=369 K DLS can be used to probe the dynamics of thin free-standing polymer films

  23. Glass-to-glass transitions copolymer micellar system SCIENCE 300, 619 (2003)

  24. Multiple Glassy States in a Simple Model System Sterically stabilized PMMA-particles in cis-decalin. SCIENCE 296 104 ( 2002)

  25. Dilute solutions Semi-dilute solutions f* 2xh Entangled dynamics 2Rg Brownian motion Polymer Dynamics

  26. Dynamic Correlation Length ξh

  27. Polymer Gel Electrolytes Poly(methyl methacrylate) + Propylene Carbonate / Ethylene Carbonate + Lithium Perchlorate (LiClO4)

  28. Dynamics in aPolymer Gel Electrolyte

  29. Relaxations and Conductivity in Polymer Gel Electrolytes Nernst-Einstein equation …there is a close connection between the fast diffusive process and the ionic conductivity!

  30. Outlook: X-ray PCS Exemplary correlation functions of colloidal silica suspension measured at q ~ 7.6 × 10-4 Å-1 using three different X-ray energies as indicated.

  31. Summary: DLS technique Probes density and/or concentration fluctuations. Time scales: ~10-6 - 103 s Wave vectors: ~10-3 Å-1 Standard characterisation techniques for particles • Determination of size 1 nm - 1 mm • Estimation of ellipticity and/or swelling Research • Polymer dynamics • Glass transition dynamics

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