We demonstrate polymer ligand exchange to be an efficient method to control steric stabilization and compatibilization of nanocrystals. A rational design of polymer binding groups and ligand exchange conditions allows to attach polymer brushes with grafting densities >1 nm(-2) to inorganic nanocrystals for nearly any nanocrystal/polymer combination using only a few types of binding groups. We demonstrate the potential of the method as an alternative to established grafting-from and grafting-to routes in considerably increasing the stabilization of inorganic nanocrystals in solution, to prepare completely miscible polymer nanocomposites with a controllable distance between nanoparticles, and to induce and control aggregation into percolation networks in polymeric matrices for a variety of different nanocrystal/polymer combinations. A dense attachment of very short polymer ligands is possible enabling to prepare ordered nanoparticle monolayers with a distance or pitch of only 7.2 nm, corresponding to a potential magnetic storage density of 12.4 Tb/in(2). Not only end-functionalized homopolymers, but also commercially available copolymers with functional comonomers can be used for stable ligand exchange, demonstrating the versatility and broad potential of the method.

Polymer nanocomposites for optical applications require high optical transparency at high filling ratios of nanoparticles. The nanoparticles provide optical functionality but unfortunately have a strong tendency to aggregate in polymer matrices leading to strong turbidity and reduced optical transmission, particularly at high filling ratios. We report a general route to nonaggregated highly filled, optically transparent polymer nanocomposites. It is based on using nanoparticles that have been coated with polymers forming spherical brushlike layers providing thermodynamic miscibility with the polymer matrix over the complete range of nanoparticle volume fractions. The polymers are attached via a versatile ligand exchange procedure which enables to prepare a wide range of optically transparent polymer nanocomposites up to weight fractions of 45%. This is demonstrated for a broad range of metal and semiconductor nanoparticles in optically transparent polymer matrices relevant for selective light/UV absorption, photoluminescence, and high/low refractive index polymer materials. ■ INTRODUCTIONPolymer nanocomposites are currently of immense interest in fundamental research as well as in a large variety of industrial applications. Nanoparticles provide new or largely enhanced material properties, but unfortunately their agglomeration mostly prevents these enhancements and often deteriorates material properties. Therefore, generally less than 5−10 wt % of nanoparticles can be dispersed into polymer matrices without sacrificing material properties by aggregation. 1 Promising experimental studies 2 and theoretical investigations 3 have been reported to understand or control nanoparticle aggregation. This is a critical issue especially for optical applications that take advantage of the optical properties of nanoparticles. These are integrated into transparent polymers for ease of processing and protection, 4 but often at the cost of agglomeration which causes turbidity and strongly reduces optical transmission and efficiency.Since the first reports of polymer−gold nanocomposites for optical applications, 5,6 nanocomposites consisting of inorganic metal or semiconducting nanoparticles and transparent polymer matrices have been continuously investigated toward applications based on selective light absorption in the UV/vis range, photoluminescence, and high/low refractive index polymeric materials. For nanocomposites used as UV-photoprotective materials, high transparency in the visible range and steep absorption in the near UV-range (λ < 400 nm) are required. The most promising inorganic materials are ZnO and TiO 2 nanoparticles, which have bulk band gap energies of around 3 eV. These nanoparticles are preferably incorporated into poly(methyl methacrylate) (PMMA) or other transparent polymer matrices. 7−9 For photoluminescent materials, semiconductor nanoparticles are particularly attractive, since they show wavelength-tunable light emission due to the quantum size effect and possess high photostability and a narrow emission...

The interfacial activity of self-assembled worm-like crystalline-core micelles (wCCMs) with a patchy polystyrene/poly(methyl methacrylate) (PS/PMMA) corona and a semi-crystalline polyethylene (PE) core is studied at the toluene-water interface. Strikingly, the interfacial activity is comparable to that of Janus cylinders with well-separated PS/PMMA hemishells and comparable length. From this finding an adaptation of the corona chains of the patchy wCCMs to the toluene-water interface is proposed. Surface compartmentalization in nanoparticles leads to a variety of unique elds of application, e.g. the self-assembly into hierarchical superstructures or the selective incorporation of multiple nanoparticles or dyes into dened spatial connement. 1,2 Another fascinating attribute of surface-compartmentalized nanostructures is their outstanding surface activity. The combination of the "Pickering effect" 3-5 valid for particles at interfaces with the amphiphilicity of classical surfactants makes them ideal candidates for a new generation of superior surfactants or to produce functional assemblies. 6 Research on surface-compartmentalized nanostructures until now has mainly focused on Janus particles that, named aer the two-faced Roman god Janus, exhibit exactly two opposing hemishells of different chemistry and/or polarity. 7,8 Dense, solid Janus colloids with sizes ranging in the micrometer region and slightly below have been synthesized using various techniques during the last decade, mainly resulting in spherical geometries. 9-12 Stepping down further in size, block terpolymer based spherical, cylindrical, ribbon-like and disc-like Janus micelles with crosslinked cores were prepared via a template-assisted approach. 13-16

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Reinforcing a micellar organogel by self-complementary hydrogen bonds.