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Organized arrays of anisotropic nanoparticles show electronic and optical properties that originate from the coupling of shape-dependent properties of the individual nanorods. The organization of nanorods in a controllable and predictable way provides a route to the fabrication of new materials and functional devices. So far, significant progress has been achieved in the self-assembly of nanorod arrays, yet the realization of a range of different structures requires changing the surface chemistry of the nanoparticles. We organized metal nanorods in structures with varying geometries by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polymer chains at both ends. The self-assembly was tuneable and reversible and it was achieved solely by changing the solvent quality for the constituent blocks. This approach provides a new route to the organization of anisotropic nanoparticles by using the strategies that are established for the self-assembly of block copolymers. [ABSTRACT FROM AUTHOR]

The mechanical properties of the adhesive produced by spores of the green, marine, fouling alga Ulva linza are reported. Atomic force microscopy studies were performed and nanoindentation data were analyzed using a model for an asymmetric indenter. Freshly secreted adhesive is characterized by multiple layers. We found that the modulus of the outer ∼⃒600-nm thick layer was about 0.2 ± 0.1 MPa, whereas the modulus of the inner layer was about 3 ± 1 MPa. Older adhesive showed the formation of a “crust” of harder material with a yield strength of ∼⃒20 MPa at a loading rate of 2.5 × 10 -6 N · s -1 . Mechanical properties under tension are also described, and extension profiles that showed either constant or nonlinear force changes with tip-sample separation were observed. Models for both kinds of behavior are described. The work of adhesion between poly-dimethylsiloxane (PDMS)-coated AFM tips and the adhesive was determined to be less than 1.5 mJ · m -2 . [ABSTRACT FROM AUTHOR]

Single-molecule studies under poor solvent conditions show that atomic force microscopy (AFM) measurements of contour lengths of polystyrene 12K and 17K relate well to gel permeation chromatography (GPC) data when grafting concentrations are low (not greater than 0.7 mM). Contact angles and ellipsometry have been used to characterize the surfaces and indicate low grafting densities at this grafting concentration. Persistence lengths ( p ) of different length polystyrene chains, when fitted to a WLC (worm-like chain) model, show values of p = 0.23 nm±0.10 nm and p = 0.25 nm±0.13 nm, for 12 K and 17 K polystyrene, respectively, when the persistence lengths are fitted to log-normal distributions. These values are close to the expected theoretical value of 0.23 nm and further confirm that mostly single molecules were studied on these polystyrene surfaces. Higher grafting concentrations (≥1 mM) resulted in pulling multiple molecules. [ABSTRACT FROM AUTHOR]

Solution-based linearself-assembly of metal nanoparticles offersa powerful strategy for creating plasmonic polymers, which, so far,have been formed from spherical nanoparticles and cylindrical nanorods.Here we report linear solution-based self-assembly of metal nanocubes(NCs), examine the structural characteristics of the NC chains, anddemonstrate their advanced optical characteristics. In comparisonwith chains of nanospheres with similar dimensions, composition, andsurface chemistry, predominant face-to-face assembly of large NCscoated with short polymer ligands led to a larger volume of hot spotsin the chains, a nearly uniform E-field enhancement in the gaps betweencolinear NCs, and a new coupling mode for NC chains due to the formationof a Fabry–Perot resonatorstructure formed by face-to-face bonded NCs. The NC chains exhibitedstronger surface-enhanced Raman scattering in comparison with linearassemblies of nanospheres. The experimental results were in agreementwith finite difference time domain simulations. [ABSTRACT FROM AUTHOR]