Use of bulky ligands (BLs) in the synthesis of metal nanoparticles (NPs) gives smaller core sizes, sharpens the size distribution, and alters the discrete sizes. For BLs, the highly curved surface of small NPs may facilitate growth, but as the size increases and the surface flattens, NP growth may terminate when the ligand monolayer blocks BLs from transporting metal atoms to the NP core. Batches of thiolate-stabilized Au NPs were synthesized using equimolar amounts of 1-adamantanethiol (AdSH), cyclohexanethiol (CySH), or n-hexanethiol (C6SH). The bulky CyS- and AdS-stabilized NPs have smaller, more monodisperse sizes than the C6S-stabilized NPs. As the bulkiness increases, the near-infrared luminescence intensity increases, which is characteristic of small Au NPs. Four new discrete sizes were measured by MALDI-TOF mass spectrometry, Au(30)(SAd)(18), Au(39)(SAd)(23), Au(65)(SCy)(30), and Au(67)(SCy)(30). No Au(25)(SAd)(18) was observed, which suggests that this structure would be too sterically crowded. Use of BLs may also lead to the discovery of new discrete sizes in other systems.

Understanding of thedurability of each individual layer and their interfaces in a multilayered photovoltaic (PV)backsheetis critical to the design and selection of materials for making reliable andhigh performance PV modules. In this study, Raman imaging was used to depth profile the chemical degradation of a multilayer commercial backsheetfilm exposed to ultraviolet (UV) radiationat 85°C, 5% relative humidity (RH, dry) and 85°C,60% RH (humid)on the NIST (National Institute of Standards and Technology) SPHERE(Simulated Photodegradation via High Energy Radiant Exposure).The backsheetfilm wasa multipartlaminate comprising of a pigmented polyethylene terephthalate (PET)-based outer layer, PET core layer and three ethylene vinyl acetate (EVA) layers having different vinyl acetate(VA) contents, along with two inner adhesive layers between PET outer and PET core layers, and PET core and EVA layers. Cross-sectional samples were prepared by cryo-microtomyfor various characterizations.The multilayer structureswere examined by laser scanning confocal andatomic force microscopies, while their chemical degradation profiles were obtained by Raman spectroscopic imaging. Non-uniform degradation was observed in the agedbacksheet film, and both UV and moisture appeared tosignificantly affect the degradation profiles of the multilayers.Severe degradation, indicated by high fluorescence,occurredin the outermost region of the pigmented PET outer layer, and the degradation gradient extended to approximately 20 µm to the bulk. It was also found thattheinner adhesive layerswere severelydeterioratedunder moist condition, indicating thatthe long-termadhesion between the layers could be a major area of concern for multilayer backsheets used in a humid environment. The relationship between the sharp 3 (non-uniform) degradation profile, resultant internal stress, and ultimate failures (cracking and delamination)was discussed as well.

Self-assembly is the thermodynamically guided organization of disordered systems into more highly ordered structures. The process of life exemplifi es the power and diversity of selfassembly, and understanding and controlling self-assembly is crucial for engineering advanced materials from molecular and nanoscale precursors. Nature has preceded researchers' efforts in magnetic fi eld-directed self-assembly (MFDSA) in magnetotactic bacteria, which navigate in the earth's magnetic fi eld using magnetically coupled chains of iron oxide nanoparticles (NPs). [ 1 ] Here, we report the MFDSA of magnetic NPs into threedimensional (3D) arrays of chains embedded within bulk poly mers, where no volatile solvent is present during the polymerization process. Application of uniform magnetic fi elds drives formation of magnetic NP chains that repel each other, resulting in their assembly into an array with quasiperiodic ordering. Removing the solvent from a 3D structure would cause collapse due to capillary forces. Therefore, special measures are required to preserve the structure [ 2 ] after removing the fi eld, such as embedding within a polymer. Polymer composites and thin fi lms containing NPs, including magnetic NPs, are well known, [3][4][5][6][7][8][9][10][11][12][13][14][15][16] as are microgels [ 17 ] and microcapsules. [ 18 ] There is signifi cant interest in embedding NP chains within polymers for their potentially anisotropic mechanical, [ 19 ] electrical, optical, magnetic, and thermal properties. Diverse applications are envisioned, including actuators, [ 20,21 ] artifi cial cilia, [ 22,23 ] ferrogels, [24][25][26] sensors, [ 27 ] polymer solar cells, [ 28,29 ] electromagnetic interference (EMI) shielding, [ 30,31 ] and drug delivery. [ 32 ] Several methods have been employed to form NP chains, often utilizing polymer templates to direct the assembly of NPs. [ 33 ] For example, there have been many studies of NP selfassembly at interfaces within [34][35][36][37][38][39][40][41][42][43][44][45][46] and on the surfaces of block copolymers, [47][48][49][50] but these systems are limited by the morphologies of block copolymers. Here, our focus is on template-free self-assembly of magnetic NPs, where MFDSA has potential to provide control and tunability over the self-assembly process without the use of templates.Stellacci and co-workers [ 51 ] have assembled magnetic NP chains in zero fi eld by crosslinking the ligand shells, [ 52 ] but most examples of magnetic NP chaining have utilized magnetic interactions between the NPs: Magnetotactic bacteria synthesize iron oxide NPs that form chains through magnetic interactions. Cryogenic TEM measurements of solutions of iron oxide NPs by Philipse and co-workers [ 53,54 ] showed that magnetic NPs spontaneously form disordered chains in solution in zero applied fi eld, if the NP diameter exceeds a minimum size. Pyun and co-workers [ 55,56 ] have also shown that strongly interacting Co NPs spontaneously form chains, and application of magnetic fi elds causes the chains to straig...

Many coatings properties such as mechanical, electrical, and ultra violet (UV) resistance are greatly enhanced by the addition of nanoparticles, which can potentially increase the use of nanocoatings for many outdoor applications. However, because polymers used in all coatings are susceptible to degradation by weathering, nanoparticles in a coating may be brought to the surface and released into the environment during the life cycle of a nanocoating. Therefore, the goal of this study is to investigate the process and mechanism of surface degradation and potential particle release from a commercial nanosilica/polyurethane coating under accelerated UV exposure. Recent research at the National Institute of Standards and Technology (NIST) has shown that the matrix in an epoxy nanocomposite undergoes photodegradation during exposure to UV radiation, resulting in surface accumulation of nanoparticles and subsequent release from the composite. In this study, specimens of a commercial polyurethane (PU) coating, to which a 5 mass % surface treated silica nanoparticles solution was added, were exposed to well-controlled, accelerated UV environments. The nanocoating surface morphological changes and surface accumulation of nanoparticles as a function of UV exposure were measured, along with chemical change and mass loss using a variety of techniques. Particles from the surface of the coating were collected using a simulated rain process developed at NIST, and the collected runoff specimens were measured using inductively coupled plasma-optical emission spectroscopy (ICP-OES) to determine the amount of silicon released from the nanocoatings. The results demonstrated that the added silica nanoparticle solution decreased the photodegradation rate (i.e., stabilization) of the commercial PU nanocoating. Although the degradation was slower than the previous nanosilica epoxy model system, the degradation of the PU matrix resulted in accumulation of silica nanoparticles on the nanocoating surface and release to the environment by simulated rain. These experimental data are valuable for developing models to predict the long-term release of nanosilica from commercial PU nanocoatings used outdoors and, therefore, are essential for assessing the health and environmental risks during the service life of exterior PU nanocoatings.

Laterally patterning magnetic nanoparticles (MNPs) through self-assembly and simple solution processing constitutes an important step toward inexpensive nanoparticle-based devices. In this work, MNPs were laterally patterned on metal thin films using laterally patterned self-assembled monolayers (SAMs) as a template. SAMs of inactive molecules were first patterned on an Au thin film using the soft-lithographic technique, microcontact printing. The active, bifunctional molecules, 1,10decanedithiol or 4-(11-mercaptoundecyl)benzene-1,2-diol, were then patterned through backfilling. The MNPs selectively bind to the terminal thiols or modified catechols when the substrates are submerged into a solution of MNPs. By adjusting the deposition conditions, both monolayers and partial multilayers were controllably formed. Co, Ni, Fe 3 O 4 , and FePt MNPs, as well as Au nonmagnetic nanoparticles were successfully patterned by this process. This generalized approach is anticipated to be adaptable to many other kinds of nanoparticles via judicious selection of the substrates, surfactant ligands (on the nanoparticle), and/or surface-bound monolayers.