Characterization of a miniemulsion by DLS and SANS

Dynamic light scattering (DLS), small angle neutron scattering (SANS) and transmission electronic microscopy (TEM) were used for the size determination of the poly(trifluoropropylmethyl)siloxane (PTFPMS) nanoparticles obtained by miniemulsion polymerization. The presence of large particles with a narrow size distribution as deduced from the DLS experiments on the latex sample was taken into account in the SANS data analysis by the introduction of a bimodal size distribution including a small particle population. It was shown that the contribution to scattering of the large particle component consistent with the SANS data should be less than about 45% of the total particle volume fraction. These results were corroborated by the spherical particle shape and the quite large particle size distribution observed on the TEM images. The DLS experimental procedures exploiting merely the cumulant analysis of the autocorrelation function for size determination in routine usage in the field of miniemulsions should thus be practiced with caution.

Latex SANS spectrum best fit (full line) according to the polydisperse homogeneous core–shell sphere model and the corresponding S(Q) (dashed line).Figure optionsDownload as PowerPoint slideHighlights
► DLS and SANS were used for the size determination of the polysiloxane obtained in miniemulsion media.
► The mean size obtained from SANS is about an order of magnitude smaller than the one deduced from DLS.
► the analysis of the SANS data by a bimodal population leads to a better understanding of the structure of the system.
► The presence of two coexistent populations has been explained on the basis of Ostwald ripening.