A synthetic concept of preparing dense polymer brushes on planar surfaces is described, in which a self-assembled monolayer (SAM) of biphenyllithium moieties on gold substrates is used to initiate anionic polymerization of styrene. The thickness of the resulting dry polystyrene brush, as estimated by ellipsometry and atomic force microscopy (AFM), is 18 ( 0.2 nm. These techniques also reveal a smooth, homogeneous polymer surface throughout the entire substrate on the macroscopic, as well as on the microscopic, scale, with a roughness of 0.3-0.5 nm (rms). On the basis of results from in situ swelling experiments, monitored by ellipsometry, a polymerization degree of N ) 382 and a grafting density of approximately 7-8 chains/R g 2 , or 3.2-3.6 nm 2 /chain, were calculated with use of mean-field theory. Polarized external reflection (ER) FTIR spectra of the grafted layer confirm highly stretched preferentially oriented polystyrene chains. Upon annealing, spin-coated polystyrene films dewet immediately the brush surface to give polymer droplets with a contact angle of 3°. All obtained results indicate that the described synthetic approach yields densely grafted polymer brushes whose experimental investigations were till now very limited.

We have measured the diffusion of deuterated polystyrene of molecular weight 90 3 10 3 in various matrices of hydrogenated polystyrene as a function of distance from an attractive interface, oxide-covered silicon. Surprisingly long-range effects are observed. Diffusion rates an order of magnitude slower than bulk persist up to 10R g (radius of gyration) from the interface of either the diffusant or matrix polymers. The slowdown is independent of matrix molecular weight over a broad range. However, mixing of polymers within the matrix strongly influences the rates of diffusion.[S0031-9007(97)

Nanoscale engineering is one of the most dynamically growing areas at the interface between electronics, physics, biology, and medicine. As there are no safety regulations yet, concerns about future health problems are rising. We investigated the effects of citrate/gold nanoparticles at different concentrations and exposure times on human dermal fibroblasts. We found that, as a result of intracellular nanoparticle presence, actin stress fibers disappeared, thereby inducing major adverse effects on cell viability. Thus, properties such as cell spreading and adhesion, cell growth, and protein synthesis to form the extracellular matrix were altered dramatically. These results suggest that the internal cell activities have been damaged.

A new, facile, general one-phase synthesis for thiol-functionalized gold, palladium, and iridium nanoparticles, using tetrahydrofuran (THF) as the solvent and lithium triethylborohydride (Superhydride) as the reducing agent, is presented. For octadecanethiol-functionalized gold (Au/ODT) nanoparticles, HRTEM of drop-cast particle-films revealed the formation of spherical particles of d = 4 ± 0.3 nm average size. Electron diffraction shows fcc packing arrangement, similar to that of bulk gold. The crystalline gold cores are surrounded with closely packed n-alkyl chains mainly in an all-trans conformation, adopting orthorhombic packing as confirmed by FTIR spectroscopy. Particles are arranged in a discrete solidlike assembly with a correlation length of ∼5 nm, as the interparticle distance (center-to-center) and a constant edge-to-edge distance of 1 nm as shown by FFT analysis. Using the same synthetic procedure gold nanoparticles functionalized with 11-hydroxyundecane-1-thiol and with 4‘-bromo-4-mercaptobiphenyl were prepared. TEM images of drop-cast Pd/ODT and Ir/ODT nanoparticles show an average size of 2.25 nm for the former, while for the latter the distribution is broader with the majority of particles between 2.25 and 4.25 nm. Both nanoparticles are crystalline with fcc packing. FTIR spectroscopy reveals that octadecyl chains are close-packed in all-trans conformation, and that there is presumably one chain in unit cell.

We have studied the morphology of blends of PS/PMMA, PC/SAN24, and PMMA/EVA and compared the morphologies with and without modified organoclay Cloisite 20A or Cloisite 6A clays. In each case we found a large reduction in domains size and the localization of the clay platelets along the interfaces of the components. The increased miscibility was accompanied in some cases, with the reduction of the system from multiple values of the glass transition temperatures to one. In addition, the modulus of all the systems increased significantly. A model was proposed where it was proposed that in-situ grafts were forming on the clay surfaces during blending and the grafts then had to be localized at the interfaces. This blending mechanism reflects the composition of the blend and is fairly nonspecific. As a result, this may be a promising technology for use in processing recycled blends where the composition is often uncertain and price is of general concern.

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We have functionalized amorphous Fe2O3 nanoparticles with alkanesulfonic and octadecanephosphonic acids. TEM reveals nanoparticles 5−10 nm in diameter. FTIR spectra suggest that while in all cases the alkyl chains are packed in a solid-like arrangement, packing disorder increased with decreasing chain length. TGA of the sulfonic acid-functionalized Fe2O3 nanoparticles shows that moieties started to decompose and desorb from the iron oxide surface at about 260 °C. In the case of the octadecanephosphonic acid (OPA)-functionalized Fe2O3, moieties started to decompose and desorb at 340 °C. It is suggested that free Fe−OH groups can serve as proton donors to assist in the sulfonic acid desorption process and that because of the diprotic nature of the phosphonic acid these free surface Fe−OH groups may no longer be available. Among all, the octadecanesulfonic acid coating displays the lowest magnetization, which may be explained by the high packing and ordering of the alkyl chains on the particle surface. The saturation curve of the OPA case gives the smallest value of magnetization we have ever measured for functionalized Fe2O3 nanoparticles. It is suggested that the spin state of surface Fe3+ ions is affected by the bonded surfactant, through a mechanism of pπ−dπ P−O, and dπ−dπ Fe−P interactions and that the phosphonate empty d orbitals increase magnetic interactions between neighboring Fe3+ spins.