24
The ACF decay function changes as a function of the
size of the particles in solution. As seen on Page 25, two
components come into play here:
1) The intensity of light scattered by a particle at a
given angle; and
2) The speed at which your particle is moving, thus
how quickly the intensity fluctuates
Size affects both intensity and movement— remember
that smaller particles move more quickly, so there
is more fluctuation; however they do not scatter as
intensely, so the absolute intensity is lower.
ACF ACF fit
The autocorrelation function is
obtained from the measurement of
the signal intensity over time.
It is a plot that shows how the signal
changes relative to itself over time.
The autocorrelation function fit is the
mathematical function that describes
the decay rate of the ACF signal.
It allows the so ware to extract a
decay rate, which is directly related
to diffusion coefficient D. With this
information and the Stokes-Einstein
equation, the hydrodynamic radius, r
H
is calculated.
