Formation of metal nanoparticles in multilayered poly(octadecylsiloxane) as revealed by anomalous small-angle X-ray scattering

Novel hybrid polymeric systems with noble metal nanoparticles located insid e specific areas of the material were developed. A self-assembled multilaye red polymer, poly(octadecylsiloxane) (PODS), provided a nanostructured matr ix for incorporation of gold and platinum compounds and for metal nanoparti cle formation. The internal structure of PODS and the nanoparticle size dis tributions were examined using anomalous small-angle X-ray scattering. The ordering in PODS was largely preserved after interaction with metal compoun ds and reducing agents. The degree of incorporation of the compounds into P ODS depended on the reaction conditions and on the compound type. For the m etal-containing PODS isolated from the reaction medium before reduction, th e major fraction of the nanoparticles had radii around 2 nm, and the size d istributions depended neither on the compound loading nor on the reducing a gent. This points to a "cage"-controlled particle growth restricted by the cavity size in the siloxy bilayer. This hypothesis is corroborated by the c omputed density profiles across the PODS lamella. Incorporation of cetylpyr idinium chloride in-the hydrophobic layers of PODS promotes formation of na noparticles also between the hydrophobic tails. This location does not rest rict the particle growth so that the nanoparticle sizes strongly depend on the reduction conditions.