Polymer-Induced Phase Separation of Nanoparticles in Lamellar Polymers

Abstract

Nanoinclusions in complex polymer phases have been the subject of considerable recent research. An important motivation is that nanoscale arrangements of metallic or seminconducting nanoparticles can produce remarkable new materials with novel electronic or photonic properties. It is a major challenge, however, to achieve such delicate spatial configurations. Nanostructured polymer phases provide potential templates to spontaneously arrange the nanoparticles. We have developed theory of hard core nanoparticles in lamellar polymer phases, typically formed from A-B diblock copolymers. When nanoparticles prefer A energetically, they tend to segregate to the A layers. We find that penetration of nanoparticles into the A lamellae diminishes strongly with increasing particle size b. Above a certain threshold, mixing is only partial with penetration depth scaling as fracNb^3 where N is chain length. The maximum nanoparticle density then scales as frac1b^3, independent of N: excess nanoparticles phase separate into a pure naonoparticle phase. Finally, above a certain maximum size, particles are entirely rejected from the A layer. These effects result from the unusual anisotropically elastic environment provided by the stretched polymer chains in these layered polymer structures.