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The motion of the particles in solution is what ultimately
becomes crucial for determining the particle size. As
particles zip into the detector region, they scatter more
light at the detector; as they move out of the detector
volume, they no longer scatter that light and the detected
intensity decreases. For standard Brownian motion,
small particles will move more quickly than larger ones.
Smaller particles will be moving around more in solution,
which means they will pass in and out of the detector
volume more frequently. There will be more fluctuations in
the scattered light.
Movement of particles affects how the intensity
fluctuates in the detector, and movement is based
on particle size. This phenomenon is what ultimately
allows DLS to give precise particle sizing and distribution
information.
Particle motion
Intensity
Time [s]
Intensity fluctuations
Larger particles
Laser
Intensity
Time [s]
Intensity fluctuations
Smaller particles
Laser
