(296a) Characterization of Internal Structure in Composite Latex Dispersions Using Contrast Variation Neutron Scattering

The characterization of phase segregation in composite nanoparticles is of fundamental interest for a number of applications. Our group is developing aqueous dispersions of conjugated polymer/fullerene nanoparticles for organic solar cell applications made from poly(3-hexlythiophene) (P3HT) and [6,6] phenyl-C₆₁-butyric acid methyl ester (PCBM). Composite nanoparticles (CNPs) that incorporate these materials can have complex internal structures depending on how the particles are prepared and on their composition. Due to insufficient contrast, electron microscopy provides little information about their internal phase segregation, which is critical to understanding how such dispersions will perform in devices. Structural information of CNPs can also be obtained from contrast variation Small Angle Neutron Scattering (SANS) measurements. By varying the H₂O/D₂O content in the aqueous phase of these dispersions, scattering profiles are obtained as a function of bulk phase contrast. These profiles are then fit using the Guinier approximation to obtain the radius of gyration of the dispersions as a function of contrast with the bulk solvent. For nanoparticles composed of two or more components, this functional dependence was first described by Stuhrmann.¹The application of the Stuhrmann analysis yields valuable information about the eccentricity, distribution and overall size of inhomogeneities internal to these composite nanoparticles. This approach proves to be a robust method to describe the internal structures of composite nanoparticles.

1.Stuhrmann, H. B. et al. Shape of the 50S subunit of Escherichia coli ribosomes. Proceedings of the National Academy of Sciences of the United States of America 74, 2316–20 (1977).