Hierarchical nanoparticle clusters induced by block copolymer self-assembly

Abstract

The hierarchical relation of microscale structures with those of zoomed-in nanoscale in a composite material is one of the challenging issues. In terms of multiscale regional analogy of fractal, identical motifs are repeated on different size scales. However, idealized packing schemes are typically known to break down beyond a length scale of a few clusters. Here, we propose a new packing scheme – the structural analogy investigated by gold nanoparticle (AuNP) clusters describes a deformed self-similarity in multiscales. The clusters are directly imaged in microscale and in submicroscale using X-ray microscopy (XM) and X-ray nanoscopy (XN) without sample distortion in the hierarchical field-of-view up to 600 μm. We show that the broad-range ordering has the characteristics of a fractal with a dimension (D) between 1 and 2. This D value is smaller in XN scale than in XM scale, indicating dense cluster formation in large scale. The D values are independent from the pathways of cluster growth and compatibility of AuNPs with the polymer template. The nanoparticle cluster growth induced by block copolymer self-assembly is characteristically different from those occurring in free-space where the conventional diffusion- or reaction-limited aggregations are dominant. Our findings provide a new perspective in organic-inorganic hybrid nanomaterials and has broad implications in understanding their structure–property relationship for various applications.