No abstract

Monodisperse spherical Ni nanoparticles with diameters of 2 nm, 5 nm, and 7 nm were synthesized from the thermal decomposition of a Ni–oleylamine complex. Ni nanocrystal superlattices were generated via the controlled evaporation of solvent (see Figure). The nanoparticles were successfully used as catalysts for the Suzuki coupling reaction, and were readily oxidized to produce NiO nanoparticles.

The crystalline structures associated with melting and crystallization behaviors of monodisperse linear polyethylene confined in cylindrical nanopores were investigated by X-ray diffraction and differential scanning calorimetry. The crystalline structures, melting, and crystallization behaviors of PE under the imposed cylindrical confinement were noticeably different from those of the bulk state. The isothermal crystallization experiments showed that the overall crystallization of polyethylene in cylindrical nanopores was dominated by the nucleation rather than the growth of crystallites. The c- and a-axes of orthorhombic PE crystals developed in nanoporous alumina were preferentially oriented perpendicular to the long axis of cylindrical nanopore while the b-axis was parallel to the pore axis. The melting temperature of polyethylene in the nanopores was substantially depressed, and it was analyzed with the Thomson−Gibbs equation. The crystallinity of linear polyethylene in cylindrical nanopores was less than 50%, whereas the bulk value was 71.6%.

The phase transitions in block copolymers (BCPs), like the order-to-disorder transition, occur when the enthalpic term of free energy of mixing is equal to the entropic term. In thin films, interactions at the substrate/polymer and polymer/air interfaces influence this free energy balance, leading to a change in the transition behavior. Here, we report on the transition behavior of BCP thin films on a substrate modified by polymer chains that preferentially interact with one component of the BCP. The thickness dependence of the transition temperature shows that interfacial interactions enhance the orientation of the lamellar microdomain parallel to the film surface even in 40 L0 in thickness, where L0 is the equilibrium period of the BCP in the bulk. This phenomenon can be attributed to the fact that, in a thin film geometry with a preferential interaction of one component with the substrate, a high concentration of one component is pinned at the substrate leading to an amplification of a periodic variation in the composition and a shift of transition temperature.