Static Light Scattering
Static Light Scattering (SLS) is an optical technique that measures the intensity of the scattered light in dependence of the scattering angle to obtain information on the scattering source:
A typical application is the determination of the weight average molecular weight Mw of a macromolecule like a polymer or a protein. Measurement of the scattering intensity at many angles allows calculation of the root mean square radius, also called the radius of gyration Rg. By measuring the scattering intensity for many samples of various concentrations, the second virial coefficient A2, can be calculated.
For static light scattering experiments a laser is used to illuminate a cuvette containing the sample to be analyzed. One or many detectors are used to measure the scattering intensity in dependence of the scattering angle θ. This so-called scattering curve Is(θ) contains information about the scattering particle's size, its shape and molar mass. In order to measure the average molecular weight SLS instruments are calibrated using a strong, known scatterer like toluene, since the Rayleigh Ratio of toluene and a few other solvents can be checked in existing tables.
Static light scattering is an in-situ technique where, as opposed to direct imaging techniques such SEM or TEM, the sample can be measured in its natural state as long as the particle concentration is small enough to avoid multiple scattering effects. False measurement due to multiple scattering result in significant errors in both SLS and DLS measurements, often without ever being noticed. They can only be avoided if special techniques such as cross-correlation are used to suppres the multiple scattering.