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Average diameters of colloids

by kasse
Tags: average, colloids, diameters
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kasse
#1
Jan22-09, 08:17 PM
P: 463
A dispersion of spherical polymer particles contains Np = 4•1013 particles/dm3. The total surface of the particles in 1 dm3 is Asp = 820 m2.

a) What kind of average diameter can we calculate. Calculate this average diameter.

b) If we know that the dispersion contains 60 vol% water, we can calculate another type of average diameter. Which? Find it!


a) Surface average.

[tex]\bar{d_s} = \sqrt{\frac{\Sigma n_i d_i^2}{\Sigma n_i}}[/tex]

b) Volume average.

[tex]\bar{d_s} = \sqrt{\frac{\Sigma n_i d_i^3}{\Sigma n_i}}[/tex]

I don't know how to incorporate the data into the formulas.
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Simon_Moore
#2
Jan23-09, 05:44 AM
P: 19
Can't you just work it out by taking the surface area of a sphere and working back to get the radius?

You know the total surface area of the total particles in 1 litre, and you know how many particles there are in 1 litre, so from that you can work out the surface area of 1 particle.


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