Dynamic LS

Dynamic light scattering ( DLS ) is where we probe particles in suspension with a fixed laser and collate the rate of light flashes at one angle.

Typical applications of DLS (sometimes called quasi elastic light scattering) are the characterization of particles, emulsions or molecules, which have been dispersed or dissolved in a liquid. The Brownian motion of particles or molecules in suspension causes laser light to be scattered at different intensities. Analysis of these intensity fluctuations yields the velocity of the Brownian motion and hence the particle size using the Stokes-Einstein relationship.

The graphic below left shows a representation of Brownian Motion (from Wikipedia) with small particles randomly moving quickly and a larger particle slowly moving. Illuminated by a laser we will see fluctuations with time that can be correlated as in the second and third graphics to calculate Z average mean diameters and from NNLS maths we can plot the distributions. The rather extreme example of very small and large particles together shown below was captured using a Zetasizer Nano ZSP in the now famous backscatter NIBS mode.

DLS - Brownian_motion_large    light fluctuations     glyphosate correlogramglyphosate by intensity     NIBS



Using the new ultra-small volume cell in the Zetasizer Pro or Ultra you can now measure from sub-nano to 10 microns using DLS!.

Capillary dynamic light scattering: Continuous hydrodynamic particle size from the nano to the micro-scale by