The following is general advice on how important the choice of presentation is:
.
If the ratio of the refractive index of the particle and the refractive index of
the dispersant is greater that 1.2 and the size of the particles are over 10 mi-
crons then the choice of presentation is not important.
.
If the ratio of the refractive indices is between 1.1 and 1.2 and the particle
size is over 1 micron then the presentation is important.
.
If the ratio of the refractive indices is under 1.1 or the size of the particles is
under 1 micron then the presentation is critical. Contact Malvern for an ap-
propriate model matrix.
.
If the ratio of the refractive indices is under 1.1 and the size of the particles
is under 1 micron then the presentation is critical. Contact Malvern for ad-
vice.
The absorption of the particles also plays a role, the higher the absorption, the less
critical is the optical model. However the above advice is good for any absorption.
It should be clear to the user that for liquid sprays in gaseous atmospheres, and for
dry powders the optical model dependence is not strong due to the high
differential of the refractive indices involved. For these types of experiments the
user will not find the choice of presentation is not critical and the “standard”
presentation will be entirely adequate.
It is worth pointing out in many cases it is possible to choose a different
dispersant to create a high differential refractive index where difficulties are being
experienced with the normal choice.
Selecting a presentation
For this demonstration we will assume that the system presentations are adequate.
Details on selecting a custom presentation can be found in the Software reference
manual.
$
To select a presentation
.
Select Presentation from the Setup menu. The dialogue below will ap-
pear.
.
The sample you have just measured is dispersed in water so you will select
the Standard - Wet system presentation À.
.
Select Load from the dialogue box Á.
The software will load the selected presentation and return to the main screen.
CHAPTER 5
GETTING STARTED
Page 5.7
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