Macromolecular Amphiphiles Polymer Synthesis Diblock Copolymers Triblock Copolymers Dendron Copolymers Bio-Inspired Hybrid Materials Mesoporous Materials High-Temperature Ceramics Hybrids from Nanoparticles Mesoporous Metals Thin Films Fuel Cell Materials Functional Core-Shell Silica Particles Fluorescent C Dot Particles Probes for Nanobiotechnology Laboratories on Particles Nanophotonic Materials Complex Polymeric Materials Mobile Hydrogels Complex Fluids filler
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Research Areas of Interest Links
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Nanoparticle-derived Hybrid Materials

Particles larger than the hydrophilic block of the block copolymers segregate into onion cores. If the block copolymer were to mix with the largest particles, the polymer chain would have to elongate in order to mix.   This is entropically unfavorable, as the polymer prefers to exist as a coil, a state in which the number of confirmations is greater.   Instead of taking this entropic penalty, the largest particles segregate into onion cores.

Through the control of nanoparticle size and size distribution, unusual morphologies can be produced from nanoparticle-block copolymer hybrids. For example, when small nano-particles are mixed with a block copolymer, a lamellar morphology is produced.   When using larger nanoparticles, however a change onion-type mesostructures are produced.   This same concept allows large nanoparticles with similar surface chemistry but distinct interior compositions to be isolated in the onion core.

ooh shiny

All images and text Copyright 2008

Wiesner Research Group - Cornell University

tems

A typical onion-type mesostructure is shown at left.   At right, we show the localization of gold-silica core-shell nanoparticles in the onion cores through size effects.   Because the gold particles are larger than the hydrophilic block, these particles also segregate into the onion cores.

Disassembly of Composite Materials

Disassembly of nanoparticle-block copolymer hybrids is also possible, owing to the discrete nature of nanoparticles that make up the hybrids.   Application of the retrosynthetic methodology from organic synthesis to mesostructured materials suggests that an inverse hexagonal hybrid can be disassembled into nanotubes, and that an Inverse Plumber's Nightmare hybrid can be disassembled into a variety of structural building units

disassembly

Indeed, a variety of structures can be produced through this disassembly route, as shown a single unit cell (a "monomer"), two unit cells (a "dimer"), and so on as shown schematically at right and by TEM below

more TEMs

Liquid-like Nanoparticles

We are also interested in studying the assembly of metal nanoparticles with block copolymers.   In order to prepare metal nanoparticles for assembly, the solubility of the particles needed to be drastically increased, as typical metal nanoparticles have extremely low solubility.   We designed a thiol-based ionic liquid, which imparts liquid-like properties to the nanoparticles.

liquid nanoparticles

This synthetic route can be used for preparing liquid nanoparticles of a range of compositions.   Top left: platinum.   Top right: palladium.   Bottom: gold nanoparticles of two different size distributions.

hey! more TEMs

Selected References

S. Warren, F. DiSalvo, U. Wiesner. "Nanoparticle-tuned assembly and disassembly of mesostructured silica hybrids" Nature Materials 6(3), 2007, 156-161

A. Jain, U. Wiesner.   "Silica-Type Mesostructures from Block Copolymer Phases: Formation Mechanism and Generalization to the Dense Nanoparticle Regime."   Macromolecules , 37, 5665, 2004.

* S. C. Warren, M. J. Banholzer, L. S. Slaughter, E. P. Giannelis, F. J. DiSalvo, U. B. Wiesner.   "Generalized route to metal nanocrystals with liquid behavior," J. Am. Chem. Soc. 128, 12074 2006.

*As highlighted in Science 313, Editor's Choice, "Flowing Precious Metals," 1542