LS Instruments

Static Light Scattering (SLS) is an optical technique that measures the intensity of the scattered light as a function of the scattering angle to obtain information on the scattering source. The most common application is the determination of the weight average molecular weight M_w of a macromolecule such as a polymer, a protein, or a virus. It can also be used to measure the radius of gyration R_g, or the form and structure factor. By measuring the scattering intensity for one macromolecule at various concentrations, the second virial coefficient A₂, can be calculated. Special analysis techniques such as the Zimm or Guinier Plot can be used to obtain the optimum result from the measured data.

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 as a function of the scattering angle θ. This so-called scattering curve I_s⁽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 well known reference such as toluene. The Rayleigh Ratio of toluene can be checked in existing tables.

Static light scattering is an in-situ technique where, as opposed to direct imaging techniques such as 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 measurements 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 suppress multiple scattering.

Learn more about static light scattering by following our online technology section step by step.

It is advisable to read the different sections in the suggested order if you want to understand all the details. For a quick reference, you can also jump to each section individually.

• Rayleigh-Gans-Debye Scattering
• Form Factor
• Structure Factor
• Scattering from Macromolecules
• Excess Rayleigh Ratio 
• Radius of Gyration 
• Guinier Plot
• Zimm Plot

A very detailed source of information is the slide show "Light Scattering Fundamentals".

Links

• Wikipedia: Static Light Scattering 
• Slide Show "Light Scattering: Fundamentals"