Nanostructured Polymers to Direct Nanoparticle Organization

Abstract

A central goal in nanoresearch is to create entirely new materials from nanosized basic units such as nanoparticles which can be engineered according to a vast range of design principles. This promises unprecedented tuning of material properties provided nanoparticles can be spatially organized into useful components such as nanowires. Nanostructured polymeric materials are natural candidates for achieving these delicate arrangements. We developed theories of ultrathin end-tethered polymer films and diblock copolymer materials as organizing media to achieve 2D and 3D nanoparticle arrangements. Ultrathin films can direct aggregation and select final morphologies of elongated aggregates ("stripes") with a brush-selected stripe width. The stripe morphology results from competing short range attractions and long range polymer-induced repulsions, similarly to many other stripey 2D systems. This agrees with recent experiments by Levicky et al at Columbia where elongated gold nanoparticle aggregates developed in polyethylene propylene films. We find similar physical principles govern organization of A/B diblock copolymer phases: interfacial tensions compete with chain stretching to determine morphologies, though a new complexity is annealing of effective A/B surface tensions. We present phase diagrams describing different possible aggregate morphologies.