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