Introduction to DYNAMIC LIGHT SCATTERING (DLS). or PHOTON CORRELATION SPECTROSCOPY (PCS). Christer Svanberg. Outline. Basic of DLS Experimental set-up Accessible time- and length-scales Applications Size and shape of sub-micron objects Research Glass transition Polymer dynamics.
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PHOTON CORRELATION SPECTROSCOPY
Basic of DLS
DLS covers a very large time range!
Typically: 10-7 - 103 s! => 10 decades in time!
Q-range: typically 0.6 – 2×10-3 Å-1
DLS is therefore suitable for diffusional studies of macromolecules, such as polymers and large biomolecules!
A suspended particle is constantly and randomly bombarded from all sides by molecules of the liquid. If the particle is very small, the number of hits it takes from one side at a given time will be stronger than the bumps from other side. This make the particle jump. These small random jumps are what make up Brownian motion.
Using Stoke-Einstein equation DLS can be used to easy, fast and accurate determination of the hydrodynamic radius of particles.
Typically range: 1 nm – 1μm.
Ellipsodial particles results in a small fraction depolarized scattered light. Can be used for estimation of ellipticity of the particles. Difficult!
Some examples of sub-micron systems:
DLS can be used to probe the dynamics of thin free-standing polymer films
copolymer micellar system
SCIENCE 300, 619 (2003)
Sterically stabilized PMMA-particles in cis-decalin.
SCIENCE 296 104 ( 2002)
Propylene Carbonate / Ethylene Carbonate
Lithium Perchlorate (LiClO4)
…there is a close connection between the fast diffusive process and the ionic conductivity!
Exemplary correlation functions of colloidal silica suspension measured at q ~ 7.6 × 10-4 Å-1 using three different X-ray energies as indicated.
Probes density and/or concentration fluctuations.
Time scales: ~10-6 - 103 s
Wave vectors: ~10-3 Å-1
Standard characterisation techniques for particles