Test measurements to track the alignment of 3D-Spectrometer

Discussions regarding the use of the 3D LS Spectrometer

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Test measurements to track the alignment of 3D-Spectrometer

Postby FredericCardinaux » Mon Dec 15, 2014 12:54 pm

In order to determine the status of alignment of your instrument, test measurements using standard samples in 10mm cylindrical cells are used. These measurements consist of

• a toluene sample,
• a single scattering dispersion of small particles.

The instrument is considered well aligned when:

1. The scattering intensity of the toluene is constant within 5% over the accessible angles (typically 30°-140°).
2. The intercept measured with the single scattering sample in 3D mod is on average higher than 0.65 (0.17 in 3D cross) and has no results lower than 0.6 (0.16 in 3D cross).

Preparation and measurement protocol:
The toluene needs to be filtered several times to avoid dust and other contaminants. The best is to filter two-three ml of toluene directly in a clean scattering cell, then suck it out using a syringe and filter it again directly in the cell. Repeat these last steps few times and finally fill the scattering cell with 1 ml of toluene. A way to verify if the toluene sample is clean is to measure its correlation function at low angle (20° for example). If you observe a decay, it means you need to filter your toluene again.

For the single scattering dispersion of small particles, we recommend using Ludox TM-50 silica particles (1 L for ~50Euro from Sigma-Aldrich, r = 20nm). Dilute the stock to obtain a single scattering sample (typically one drop of the stock in 4 ml of MiliQ water) and fill a clean scattering cell with 1 ml of the suspension. These small particles have the advantage to produce a relatively flat intensity versus angle and to decay fast. However, one can use any type of suspensions for the tests providing there is no multiple scattering and that the sample is ergodic (it fully decays). While filtering is not necessary, sonication of the sample can help dispersing aggregates present in the stock.

We advise you to use the following protocol for the measurement of the toluene sample:
1. set the laser intensity to its maximum
2. execute a script of this type: from 30°to 140° by step of 10°, 5 runs of 10 s per angle in 3D mod (if not available in 3D cross) correlation mode.

and for the single scattering dispersion of small particles:
4. set the intensity to obtain a scattering of the Ludox dispersion around 200 kHz at 30°.
5. execute a script of this type: from 30°to 140° by step of 10°, 5 runs of 40s per angle, in 3D mod (if not available in 3D cross) correlation mode.

If you choose to work with a single scattering sample of larger particles, you will simply need to increase the measurement time and make sure that the intensity stay between 100kHz and 600kHz as the goniometer moves from 30° to 140°.
FredericCardinaux
 
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