Catalyzed Radical Polymerization of Styrene Vapor on Nanoparticle Surfaces and the Incorporation of Metal and Metal Oxide Nanoparticles within Polystyrene Polymers

We present a novel approach to polymerize olefin vapors on the surfaces of metallic and semiconductor nanoparticles. In this approach, a free radical initiator such as AIBN is dissolved in a volatile solvent such as acetone. Selected nanoparticles (prepared separately using the laser vaporization-controlled condensation method) are used to form initiator-coated nanoparticles placed on a glass substrate. The olefin (styrene) vapor is polymerized by the thermally activated initiator on the nanoparticle surfaces. Our approach also provides structural and mechanistic information on the early stages of catalyzed gas-phase polymerization, which can be used to correlate the gas-phase structural properties with the bulk properties and the performance of the polymer nanocomposites. This correlation is the key step in controlling the properties of the polymer nanocomposites. Our results clearly demonstrate the success of this method in preparing polymer coated nanoparticles for a variety of interesting applications. The precise control of the chemical functionality, thickness, and morphology of the polymer film and the size, size distribution, and properties of the core nanoparticles (photoluminescence, magnetic) may lead to major technological breakthroughs in a variety of applications including drug delivery, ultrasensitive detectors, and chemical and biological sensors

Vapor Phase Growth and Assembly of Metallic, Intermetallic, Carbon, and Silicon Nanoparticle Filaments

A new class of nanoparticle filaments and tree-like aggregates is assembled by the influence of an electric field during the synthesis of metallic, intermetallic, silicon, and carbon nanoparticles from the vapor phase. Enormous electrostatic aggregation due to dipole forces is observed between the nanoparticles to form chain filaments, and between the chain filaments to form tree-like fibers. The filaments and tree-like fibers can grow to lengths exceeding several centimeters. The filaments display stretch and contraction properties depending on the strength of the applied field

Stepwise Hydration and Multibody Deprotonation with Steep Negative Temperature Dependence in the Benzene^•+−Water System

We studied the stepwise hydration and solvent-mediated deprotonation of the benzene•+ cation (Bz•+) and found several unusual features. The solvent binding energies ΔH on-1,n for the reactions Bz•+(H2O)n-1 + H2O → Bz•+(H2O)n are nearly constant at 9 ± 1 kcal mol-1 for n = 1 to 8. We observed a remarkable sudden decrease in the entropy of association accompanying the formation of Bz•+(H2O)7 and Bz•+(H2O)8, indicating strong orientational restraint in the hydration shells of these clusters consistent with the formation of cagelike structures. We observed the size-dependent deprotonation of Bz•+ in a cooperative multibody process, where n H2O molecules (n ≥ 4) can remove a proton from Bz•+ to form protonated water clusters. We measured, for the first time, the temperature dependence of such a process and found a negative temperature coefficient of a magnitude unprecedented in any chemical reaction, of the form k = AT-67± 4, or in an Arrhenius form having an activation energy of −34 ± 1 kcal mol-1. The temperature effect may be explained by Bz•+ and four H2O molecules needing to be assembled from gas-phase components to form the reactive species. Such large temperature effects may be therefore general in solvent cluster-mediated reactions