Director, Materials Characterization Lab
The Brookhaven 90plus dynamic light scattering spectrometer (DLS) is used to measure the size of particles in solution. The technique, also called quasi-elastic light scattering or photon correlation spectroscopy, functions by measuring the time-dependent intensity of a scattered laser beam to produce a correlation function. Larger particles transit the laser beam more slowly and scatter more of the laser light into the detector, smaller particles less so. The resulting correlation function is then transformed into a log normal size distribution using the Stokes-Einstein relation. Assumptions are made that the particle is spherical and that the sample is monodisperse. Sample temperature can be controlled using a built-in Peltier device. Typical size limits are 50 nm for organic materials and 10-20 nm for inorganic materials in aqueous solutions.