3D-Positioning of Nanoparticles in High-Curvature Block Copolymer Domains.

The defined assembly of nanoparticles in polymer matrices is an important precondition for next-generation functional materials. Here we demonstrate that a defined three-dimensional nanoparticle assembly within the unit cells can be realized by directly linking the nanoparticles to block copolymers. We show that for a range of nearly symmetric to unsymmetric block copolymers there are only two formed structures, a hexagonal lattice of P6/mmm-symmetry, where the nanoparticles are located in 1D-arrays within the cylindrical domains, and a cubic lattice of Im3m-symmetry, where the nanoparticles are located in the octahedral voids of a BCC-lattice, corresponding to the structure of ferrite steel. We observe the block length ratio and thus the interfacial curvature to be the most important parameter determining the lattice type. This is rationalized in terms of minimal chain extension such that domain topologies with large positive curvature are highly preferred. Already volume fractions of only one percent are sufficient to destabilize a lamellar structure and favor the formation of highly curved interfaces. The study thus demonstrates how nanoparticles can be located on well-defined positions in three-dimensional unit cells of block copolymer nanocomposites. This opens the way to functional 3D-nanocomposites where the nanoparticles need to be located on defined matrix positions.

Controlled Assembly of Block Copolymer Coated Nanoparticles in 2D Arrays.

The defined assembly of nanoparticles (NPs) in polymer matrices is an important prerequisite for next-generation functional materials. A promising approach to control NP positions in polymer matrices at the nanometer scale is the use of block copolymers. It allows the selective deposition of NPs in nanodomains, but the final defined and ordered positioning of the NPs within the domains has not been possible. This can now be achieved by coating NPs with block copolymers. The self-assembly of block copolymer-coated NPs directly leads to ordered microdomains containing ordered NP arrays with exactly one NP per unit cell. By variation of the grafting density, the inter-nanoparticle distance can be controlled from direct NP surface contact to surface separations of several nanometers, determined by the thickness of the polymer shell. The method can be applied to a wide variety of block copolymers and NPs and is thus suitable for a broad range of applications.