21
To begin with, we have to look at the mathematical relationship
between particle diffusion and its size. The key relationship needed to
do this is the Stokes-Einstein equation:
D = k
B
T/6πɳr
H
D = diffusion coefficient
k
B
= Boltzmann constant 1.380649 × 10
-23
-2 m
2
kg s
-2
K
-1
T = temp (Kelvin)
ɳ = dynamic viscosity
r
H
= hydrodynamic radius of particle
The information researchers are interested in is the
radius of the particle r
H
. For any system of particles
in a solution, generally both D and r
H
are unknown.
However, D can be calculated with the use of the
scattered light, which allows this equation to be solved.
This is done using the autocorrelation function, which
relates the changes in scattered intensity over time with
diffusion coefficient D.
