Controlled Supramolecular Assembly of Micelle-Like Gold Nanoparticles in PS-<italic>b</italic>-P2VP Diblock Copolymers via Hydrogen Bonding

Ligand molecules tethered on the surface of inorganic nanoparticles play an important role in the synthesis and application of nanoparticles due to their dramatic influence over surface properties. Tailoring of nanoparticle surfaces with ligands is therefore a key factor for stabilizing nanoparticles in various solvents as well as for controlling hierarchical assembly of nanoparticles to give functional materials. The incorporation of inorganic nanoparticles into block copolymer matrices to give self-assembled, microphase-separated periodic structures has been intensively studied to create novel functional hybrid materials, such as high-performance catalysts, photonic crystals, chemical sensors, and electronic devices. 7 Precise control of nanoparticle segregation in A-b-B block copolymers has been achieved by synthesizing nanoparticles with various ligands, including short aliphatic molecules, A or B homopolymers, mixed A and B homopolymers, and A-r-B random copolymers leading to localization of the nanoparticles into either A or B domains or at the A/B interface. 18 These approaches are based on minimizing the enthalphic interaction of mixing of nanoparticles into block copolymer matrices by tailoring the nanoparticle surface with components similar to the respective block copolymer domains. Recently, Kim et al. demonstrated that the segregation of nanoparticles can also be precisely controlled by an attractive secondary interaction between nanoparticle cores and the block copolymer matrix. 17,19 For example, the physical adsorption of poly(2-vinylpyridine) (P2VP) chains on the surface of the gold core (Au), allowed by the low areal chain density (Σ) of PS ligands, has been successfully employed to segregate nanoparticles at the interface of poly(styrene-b-2vinylpyridine) (PS-b-P2VP) diblock copolymers. In examining other attractive, nonbonded interactions, our attention was drawn to hydrogen bonding. Due to its specific, directional, and reversible characteristics, hydrogen bonding has been widely used for supramolecular self-assembly of polymers and inorganic molecules. Although the typical single hydrogen-bond strength (5 30 kJ/mol) is much less than covalent bonds (250 800 kJ/mol), significant favorable interactions can be obtained through the formation of multiple hydrogen bonds. This enables self-healing polymeric materials, which is an emerging goal in materials science. In addition, blending of block copolymers with homopolymers havingmultiple complementary hydrogen bonds has been used to induce interesting order order morphology transitions without macrophase separation of homopolymers from block copolymer domains. 31 Hydrogen bonding also has been used for the selective segregation of nanoparticles in block copolymer domains. Yeh et al.