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Seminars
Composite Nanostructures: Protein and nanoparticle arrays templated in block-copolymer mesophases
Danilo Pozzo
Carnegie Mellon University
When: Thursday, March 9, 2006
Time: 2:30 PM to 3:30 PM
Where: 1070 Duncall Hall
Abstract:
The self-assembly of surfactants and block-copolymers allows for the spontaneous formation of highly ordered, nanometer length scale structures. We have developed a simple, scaleable approach to utilize amphiphilic (hydrophilic – hydrophobic) self-assembly to control the spatial arrangement of nanoparticles at nanometer distances. In this work, inorganic nanoparticles and globular proteins are dispersed in a commercially-available block-copolymer matrix. Aqueous solutions of poly-ether based copolymers (PEO-PPO-PEO) are used to form the structured matrix. These polymers are fully soluble at low temperatures (~5°C) but their middle (PPO) block becomes hydrophobic near room temperature. This drives the aggregation of polymer chains into spherical or cylindrical micelles which, at sufficiently high concentrations, pack into crystals with long range order. The three-dimensional organization of biomolecules and inorganic nanoparticles inside polymer matrices is key to a number of emerging applications such as controlled-release of therapeutic proteins, biomolecule separations in gel electrophoresis and for the design of novel optical and electronic materials.
The thermoreversible nature of these block copolymers allows us to create stable dispersions of hydrophilic proteins or nanoparticles at low temperatures when the viscosity of the samples is low. The structured gel is then formed by increasing the sample temperature and the nanosized additives remain trapped in the free space between the micelles in the crystal. The dispersed particles themselves form an ordered array because the interstitial spaces follow the order of the micelle crystal. The environment around the templated particles and the three dimensional structure of the particle array can therefore be controlled through the choice of an adequate polymer matrix. This process is fully reversible after repeated heating and cooling. In this talk I will quantify the influence of specific design parameters (e.g. nanoparticle size, polymer concentration, temperature and polymer architecture) on the structure and properties of these novel nanocomposite materials. Carefully designed small angle neutron scattering (SANS) experiments allow for the characterization of the long range order and nanometer structure of both phases within the same nanocomposite sample. The influence of the nanosized additives on the mechanical properties of the nanocomposites is also probed using rheology. The results of this work provide the first experimental framework for the design of templated nanocomposites. From this framework, several different applications and novel properties of these nanocomposites are being developed.
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