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Light Scattering Techniques

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Presentation on theme: "Light Scattering Techniques"— Presentation transcript:

1 Light Scattering Techniques
…and what they can do for You! Tom Caremans 24/10/2005

2 Equipment Laser Detector Sample

3 Qué? Scattering Dynamic Light Scattering Static Light Scattering
INTENSITY (and don’t you forget that!) Rh RG Mol Weight (Mw) Relaxation time of the different modes DIFFUSION COEFFICIENT of different modes You measure a collective!!

4 DLS: basic formula’s Remember! : I~m² so: I~D6

5 What can DLS tell you?

6 Be careful with DLS data!

7 DLS and silicalite formation
Occurrence of slow phases?? Twomey, Thompson, Zeolites 14, 1994 Schoeman, Zeolites 18, 1997 In-situ at 105° (full ns, 125°C) Slow phases were systematically cut out!!!

8 However… Diluted CS shows a different story when measured in-situ CS: H2O 1:9

9 Ex-situ vs In-situ; concentrated vs diluted
Undiluted CS In-situ: regular case No slow modes visible Ex-situ: slow modes visible That disappear after a certain moment Slow modes appear upon cooling?? Diluted CS Upon heating at 55-60°C slow modes appear Reversibly disappear when cooling Is this the same process happening? More analysis/measurements needed

10 Books & Texts No “DLS for dummies” available
The DLS Bible: Robert Pecora, Bruce Berne, Dynamic Light Scattering SLS: Charles Johnson, Laser Light Scattering, easy to read


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