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Incorporation of nanoparticles into self-assembled block copolymers has been explored as an efficient way for improving the mechanical strength, electrical conductivity, and optical properties of materials at the nanometer scale. Recent computer simulations [1][2][3] predict that the cooperative self-organization of nanoparticles and block copolymers should yield a wide variety of structures with well-controlled particle arrangements. Such nanostructures may make it possible to fabricate novel functional materials, such as photonic bandgap materials, nanostructured solar cells, highly efficient catalysts, and high-density magnetic storage media. In particular, gold nanoparticles have attracted much interest for applications as catalysts [4,5] as well as building blocks for electronic devices that operate at the single-electron level.[6]Over the years, several experimental methods have been developed for incorporating inorganic nanoparticles into polymeric nanostructures. These can be divided into two approaches. The first approach involves synthesizing nanoparticles in situ within preformed block-copolymer structures. Preformed micelles of block copolymers containing metal precursors are used as nanoreactors to synthesize nanoparticles selectively in block copolymers. [7][8][9][10][11][12][13][14] For example, Boontongkong et al. [7] produced micropatterned silver nanoparticles in a poly(styrene-b-acrylic acid) block-copolymer template using this approach. Such an approach is simple and can be easily extended to yield large-area samples. However, controlling the arrangement of the nanoparticles within the periodic structure of the block copolymer is difficult. A second approach, recently proposed as a way to avoid some of the drawbacks of the method described above, [15][16][17] uses cooperative self-organization of nanoparticles and block copolymers. Based on theoretical predictions of the morphology of inorganic-organic hybrid materials by Balazs and coworkers, [3,18] Bockstaller et al. [15] demonstrated hierarchical pattern formation using block copolymers and binary mixtures of different sized hydrophobic nanoparticles. More recently, our previous work [19] showed how grafting different polymers to particle surfaces can be used to precisely control the placement of particles either at the center of one of the block-copolymer domains or at the interface dividing the two block-copolymer domains. This approach exploits enthalpic interactions between the block copolymer and functionalized nanoparticle surfaces to achieve precise particle placement. Such precise control of nanoparticle position in block-copolymer thin films is important for developing highly organized hybrid materials. A particularly interesting example is the work of Russell and co-workers, [20] who showed that the orientation of block-copolymer domains in thin films could be controlled by introducing surface-active nanoparticles that preferentially segregated to the surface of high-surface-energy domains. However, the introduction of particles i...

A simple strategy to tailor the surface of nanoparticles for their specific adsorption to and localization at block copolymer interfaces was explored. Gold nanoparticles coated by a mixture of low molecular weight thiol end-functional polystyrene (PS-SH) (Mn = 1.5 and 3.4 kg/mol) and poly(2-vinylpyridine) homopolymers (P2VP-SH) (Mn = 1.5 and 3.0 kg/mol) were incorporated into a lamellar poly(styrene-b-2-vinylpyridine) diblock copolymer (PS-b-P2VP) (Mn = 196 kg/mol). A library of nanoparticles with varying PS and P2VP surface compositions (FPS) and high polymer ligand areal chain densities was synthesized. The location of the nanoparticles in the PS-b-P2VP block copolymer was determined by transmission electron microscopy. Sharp transitions in particle location from the PS domain to the PS/P2VP interface, and subsequently to the P2VP domain, were observed at FPS = 0.9 and 0.1, respectively. This extremely wide window of FPS values where the polymer-coated gold nanoparticles adsorb to the interface suggests a redistribution of PS and P2VP polymers on the Au surface, inducing the formation of amphiphilic nanoparticles at the PS/P2VP interface. In a second and synthetically more challenging approach, gold nanoparticles were covered with a thiol terminated random copolymer of styrene and 2-vinylpyridine synthesized by RAFT polymerization. Two different random copolymers were considered, where the molecular weight was fixed at 3.5 kg/mol and the relative incorporation of styrene and 2-vinylpyridine repeat units varied (FPS = 0.52 and 0.40). The areal chain density of these random copolymers on Au is unfortunately not high enough to preclude any contact between the P2VP block of the block copolymer and the Au surface. Interestingly, gold nanoparticles coated by the random copolymer with FPS = 0.4 were dispersed in the P2VP domain, while those with FPS = 0.52 were located at the interface. A simple calculation for the adsorption energy to the interface of the nanoparticles with different surface arrangements of PS and P2VP ligands supports evidence for the rearrangement of thiol terminated homopolymers. An upper limit estimate of the adsorption energy of nanoparticles uniformly coated with a random arrangement of PS and P2VP ligands where a 10% surface area was occupied by P2VP -mers or chains was approximately 1 kBT, which indicates that such nanoparticles are unlikely to be segregated along the interface, in contrast to the experimental results for nanoparticles with mixed ligand-coated surfaces.