In the past two decades, the field of polymer self-assembly has witnessed an explosive growth. Van der Waals forces, hydrophobic and electrostatic interactions have been used to guide the third-order structure of synthetic polymers into an impressive range of morphologies. Copolymers with subunits designed to drive the self-assembly via molecular recognition, hydrophobic interactions and electrostatic interactions are being designed by Centre researchers. Micelles of small molecules are incorporated into polymers, and then easily removed, to fabricate porous polymers. Functionalized polymer films are created through Langmuir-Blodgett techniques and by the layer-by-layer polyelectrolyte method. Identification of the resulting structures relies on the combined efforts of the characterization experts of the Centre, allowing the exploration of possible applications as biosensors, materials for bioseparations and drug delivery agents.
Self-Assembly of Polymers via Molecular Recognition
A truly novel approach will be to synthesize polymers that are able to use molecular recognition to self-assemble into higher-order morphologies, in the same manner that selective base-pairing organizes DNA into a double helical molecule (Sleiman). Advanced NMR and vibrational spectroscopic methods will be used to characterize the hydrogen bonding interactions. (Reven) The morphologies will be characterized by light scattering and transmission electron microscopy. (Eisenberg)
Self-Assembly of Block Copolymers via Hydrophobic and Hydrophilic Interactions
Considerable effort has been devoted over the past decades to the study of hydrophobically-modified polymers (HM-polymers), in view of their theoretical relevance and practical applications. Such polymers consist of a water-soluble chain carrying a few hydrophobic groups, hydrocarbon or fluorocarbon chains. It is well known that fluorocarbons and hydrocarbons do not mix. The question then arises: What will be the properties of HM-polymers carrying both hydrocarbon and fluorocarbon chains?
Optically Active Self-Assembled Block Copolymers
The synthesis of block copolymers containing photo-switchable groups allows one to address their self-assembled structures for reversible changes in optical, geometric, or mechanical properties. Azobenzene derivatized block copolymer vesicles, photoactive elastomers and optically active polymer films will be produced by the Eisenberg, Zhao and Ritcey groups. Barrett's group will provide the optical expertise to test the functionality of the photo-addressable self-assembled polymeric materials.
Block Copolymer Langmuir Blodgett Films
The spontaneous phase separation of AB diblock copolymers can be exploited for the preparation of patterned surfaces exhibiting periodically ordered domains of molecular dimensions (Ritcey, Eisenberg, Lennox). Such surfaces can serve as templates for directed cell growth. A significant limitation to this approach is the general lack of control over microdomain orientation. Films of asymmetric block co-polymers are always polydomain with periodic ordering being maintained typically over few um.
The alternate adsorption of cationic and anionic polymers has become an increasingly important method for producing uniform thin polymer films. Barrett and Reven have recently deposited simple PEMs on silica colloids and used high resolution solid-state NMR spectroscopy to follow the layer-by-layer growth and polymer complexation. A major goal of this research will be to understand the effect of variation of the preparative parameters on the film properties at a molecular level.