# Diffusion vs. size

1. Feb 23, 2009

### superwolf

1. The problem statement, all variables and given/known data

Eq. 4.14:

$$\zeta = 6 \pi \eta R$$ (Stokes formula)

2. The attempt at a solution

In my plot, collagen, hemoglobin and lactoglobulin give a straight line, while ribonuclease is a bit above the others.

I don't know which diffusion law I'm supposed to use. Fick's? Anyway, here's what I've done:

$$\zeta = 6 \pi \eta R$$

$$\eta = 10^-3 kgm^{-1}s^{-1}$$

$$k_BT = 4.1E-21 J$$

$$\zeta D = k_BT \Rightarrow D = \frac{k_BT}{\zeta} = \frac{k_BT}{6\pi \eta}\cdot\frac{1}{R} \Rightarrow D = 2.2E-19 \cdot \frac{1}{R}$$

Am I on the right track? I'm not sure what the problem asks me to do, really...

Last edited: Feb 23, 2009
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