7 research outputs found
Lanthanum Strontium Manganite/Yttria-Stabilized Zirconia Nanocomposites Derived from a Surfactant Assisted, Co-assembled Mesoporous Phase
Spatially Confined Redox Chemistry in Periodic Mesoporous Hydridosilica–Nanosilver Grown in Reducing Nanopores
Periodic mesoporous hydridosilica, PMHS, is shown for the first time to function as both a host and a mild reducing agent toward noble metal ions. In this archetypical study, PMHS microspheres react with aqueous Ag(I) solutions to form Ag(0) nanoparticles housed in different pore locations of the mesostructure. The dominant reductive nucleation and growth process involves SiH groups located within the pore walls and yields molecular scale Ag(0) nanoclusters trapped and stabilized in the pore walls of the PMHS microspheres that emit orange-red photoluminescence. Lesser processes initiated with pore surface SiH groups produce some larger spherical and worm-shaped Ag(0) nanoparticles within the pore voids and on the outer surfaces of the PMHS microspheres. The intrinsic reducing power demonstrated in this work for the pore walls of PMHS speaks well for a new genre of chemistry that benefits from the mesoscopic confinement of Si–H groups
Organometallic–Polypeptide Diblock Copolymers: Synthesis by Diels–Alder Coupling and Crystallization-Driven Self-Assembly to Uniform Truncated Elliptical Lamellae
This
paper reports a new synthetic strategy for the preparation
of polyferrocenylsilane (PFS) block copolymers (BCPs), by conjugation
of two independently prepared homopolymers using Diels–Alder
cycloaddition. The PFS blocks were synthesized by photocontrolled
ring-opening polymerization, yielding polymers with a cyclopentadienyl
end group that serves as a diene in the conjugation reaction. In this
initial study we focused on the synthesis of organometallic–polypeptide
block copolymers PFS-<i>b</i>-PBLG (PBLG = polyÂ(γ-benzyl-l-glutamate) using PBLG polymers with a terminal maleimide attached
by one-step postpolymerization modification. Five PFS-<i>b</i>-PBLG copolymers with different degrees of polymerization were synthesized
and purified by a series of selective precipitations. The self-assembly
of these samples was studied in <i><i>N,N</i></i>-dimethylformamide, a solvent selective for PBLG. The BCPs with a
PFS block longer than the PBLG block after annealing at 90 °C
formed highly uniform platelet micelles with a truncated elliptical
shape. Experiments at 75 °C showed that disordered elongated
structures formed initially, with fiber-like protrusions from the
ends. Over time, the structures became shorter and wider, evolving
into uniform truncated elliptical micelles. The process was monitored
by X-ray diffraction (XRD) measurements and by <sup>1</sup>H NMR spectroscopy.
AFM analysis showed that the micelles were flat and that their thickness
increased with the overall chain length of the BCP. Self-assembly
of these BCPs in the presence of PFS homopolymer led to formation
of flower-like mesostructures consisting of stacks of lamellar petals