Prof. Thomas A.P. Seery "Dynamic light scattering from light absorbing solutions: Phenomenology and model systems"

Dynamic light scattering (DLS) is a powerful tool for characterizing polymers and colloids in solution.  The ease of sample preparation and in situ, non-perturbative nature are powerful advantages to a technique that is capable of probing 9 to 10 decades of dynamic behavior in a single measurement. However, the application of scattering methods is greatly restricted when the sample of interest absorbs light at the scattering wavelength. Autocorrelation functions obtained from DLS of light absorbing solutions can exhibit decays that are faster than exponential with periodic functions overlaid on the decaying tail, features that are not typical of DLS from quiescent, non-light absorbing samples. These features have been observed in a diverse collection of light absorbing mixtures that include polyaniline, cytochrome-C/cytochrome-C peroxidase, carbon nanotubes and gold clusters.  These different scattering systems possess two common features: aggregation leading to a bimodal size distribution and an absorption spectrum that includes wavelengths used for light scattering.  This talk will discuss our observations of this phenomenon and efforts to fit the data while incorporating an approximation of the underlying physics.  Details of efforts to reproduce this behavior using model systems will also be discussed.