16
Incident light
Wavelength λ
Particle size < λ/10
Not angle dependent
Particle size > λ/10
Angle dependent (increases with increasing particle size)
Both scattering phenomena contribute to the
DLS signal. Note that a detector cannot separate
whether the detected light is a result of Rayleigh
or Mie scattering. When designing an instrument,
the detector angle is o en fixed, which means this
parameter will not change between experiments
or within a single experiment. Because of the Mie
scattering phenomenon, detectors at a "back-
scattering" angle are more sensitive to smaller
particles because there is less interference from
the forward-scattering of large particles.
The second is Mie scattering. In this case, when
particle size starts to grow above 1/10th the
incident light wavelength, the intensity of the
scattered light is greatest in the forward direction,
e.g. as you approach 180
o
from the incident light.
As particles get larger, the intensity increase for
these angles becomes more dramatic.
