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Patterning Nanoparticles via Polymer/Polymer Phase Separation

This project applies recent advances in structural control in immiscible polymer blends to the spatial organization of metal and semiconducting nanoparticles (e.g. Ag, CdS, CdS/ZnS) in composite films. Simple spin-coating of blends of various homopolymers and polymer-stabilized nanoparticles is used to produce controllable patterns with structural hierarchy via spinodal decomposition. Control can be exerted on different length scales by varying the spin rate, blend composition, and length of the stabilizing polymer chains. New routes to specific functional structures combine top-down and bottom-up methods: directing phase separation via spin-coating onto surfaces with patterned hydrophilic/hydrophobic regions.

Self-Assembly of Amphiphilic Block Copolymers at the Air-Water Interface Amphiphilic block copolymers such as polystyrene-b-poly(ethylene oxide) (PS-b-PEO) self-assemble into a wide range of nanoscale surface features when deposited at the air-water interface, driven by an interplay of repulsive PS-water and PS-PEO interactions and thermodynamically favourable spreading of PEO on the water surface. Though these driving forces are thermodynamic in origin, kinetic factors such as chain entanglements and the rate of evaporation of the spreading solvent play a critical role in the final structures. Our work has explored methods of tuning the surface features by varying the concentration of the spreading solvent, controlling the extent of chain entanglements in order to "freeze in" a particular morphology. Along with producing novel "chain and ring" structures at low spreading concentrations, this strategy has provided new insights into the origin and evolution of the various surface aggregate morphologies. Amphiphilic block copolymer self-assembly at the air-water interface is also explored as a route to patterning and ordering inorganic nanoparticles within functional composite surface features.

AFM images of a PS-b-PEO copolymer (MW = 141k, 11.4 wt% PEO) deposited at the air-water interface using different spreading concentrations in chloroform.

Photonic Bandgap (PBG) Colloidal Crystals PBG materials have periodic dielectric structures with periodicity on the order of visible wavelengths. Possible applications include low-loss waveguides, optical switches, and optical cavities. PBG materials containing quantum dots represent novel materials in which light emission depends on both quantum and photon confinement. The challenges of assembling nanometer-sized particles into structures with periodicities on the order of hundreds of nanometers are met by a number of strategies, including self-assembly of large compound micelles (LCMs) into colloidal crystals. These water-soluble LCMs are also interesting as highly structured photoluminescent bio-labels, in which nanoparticles are isolated within discrete hydrophilic compartments in a hydrophobic polymer matrix, preventing toxic leaching of metal ions into the biological system.

For more information on these and other projects, please contact:

Dr. Matthew Moffitt, Department of Chemistry, University of Victoria

email: mmoffitt@uvic.ca phone: (250) 721-7162