Dynamic Light Scattering

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Dynamic light scattering (DLS) is a technique that can be used to determine the size distribution profile of small particles in suspension or polymers in solution. When light (even monochromatic laser light) hits small particles, it is scattered (Rayleigh scattering) provided particles are small compared to the wavelength (below 250nm).

The scattering intensity fluctuates over time and is due to small molecules in solutions undergoing Brownian motion, and so the distance between the scatterers in the solution is constantly changing with time. This scattered light undergoes either constructive or destructive interference by the surrounding particles, and within this intensity fluctuation, information is contained about the time scale of movement of the scatterers.

DLS can be used to characterise the size of particles including proteins, polymers, micelles, vesicles, carbohydrates, nanoparticles, biological cells and gels. If the system is not dispersed in size, the mean effective diameter of the particles can be determined. This measurement depends on the size of the particle core, the size of surface structures, particle concentration, and the type of ions in the medium.

ICAM equipment includes:

  • Malvern Zetasizer Nano-S90 at the University of Cambridge, a particle and molecular size analyser for the detection of aggregates and measurement of small or dilute samples.
  • Malvern Nanosizer Z (NIBS) at The University of Manchester for the determination of particle size and distribution covering the broad size range 1nm to 250μm. Zeta potential can also be determined.
  • Droplet Measurement Technologies (DMT) Single Particle Soot Photometer (SP2) at The University of Manchester capable of sizing and determining the soot content of individual particles in the size range 200 to 1500nm.
  • Brookhaven Instruments ZetaPals at Imperial College London for the measurement of mobility, zeta potential and particle size.
  • Malvern Zetasizer Nano ZSP at the University of Cambridge for the measurement of zeta potential and electrophoretic mobility in aqueous and non-aqueous dispersions.