Our interdisciplinary research group focuses on the exploration of new and advanced polymer, inorganic, and hybrid nanostructured materials. Our interests embrace materials with the following applications:
Polymeric Materials for Spinal Cord Repair
We work at the interface between polymer design, synthesis, and the creation of scaffolds for biomedical applications. Our major interest is tissue regeneration, for example, to repair spinal cord injury or repair bone tissue. To solve this difficult problem, we try to create polymer scaffolds that promote and guide cell growth. Our successes have involved creating open structures of the right size and shape for the cells to grow, and to control the nature of the surface of the polymers employed as the scaffold material. We created a series of macroporous polymer foams that support the growth of bone cells. Some of these polymers are resorbable, so that one anticipates that the scaffold will eventually disappear leaving intact bone in place. We also developed a novel synthesis of hollow polymer tubes that seem to promote the growth of nerve fibers (i.e., axons).
Planarized Optically Integrated Microphotonic Crystal Chips
We develop new methods for the synthesis and colloidal assembly of silica microspheres in the form of well-ordered crystals and films. We use a spectrum of methodologies, including micro-fluidics, spin coating and micro-fabrication to make functional colloidal crystals integrated into wafers. These kinds of silica-based colloidal crystals may prove useful for diverse kinds of 3D diffractive optical components coupled to waveguides in photonic chips. The application that has received the greatest attention in the public eye is the use of these structures as templates for making periodic structures composed of high refractive index substances like silicon and germanium that have 3-D photonic band gaps in exactly the wavelength range needed (1.5-2.5 microns) for optical telecommunications. Such silicon-based 3D photonic crystals are expected to find utility as semiconductors for light.
We develop novel methods for the co-assembly of organic and inorganic molecular precursors to create new organic-inorganic nanocomposite or hybrid materials with chemical and physical properties that are superior to the component parts. A recent breakthrough in our group concerns the surfactant or triblock copolymer templated synthesis of periodic mesoporous organosilicas, PMOs, a new class of materials with crystalline mesoporosity, pore sizes in the range 2-30 nm, surface areas around 1000 m2/g and a variety of bridging organic groups like methyne, methylene, ethane, ethene, benzene and thiophene, uniformly incorporated within the silica framework. Nanocomposite materials of this genre have perceived utility in application areas diverse as a chiral stationary phase for separations of enantiomers and asymmetric catalysis, low dielectric constant film for microelectronic packaging, and a proton exchange membrane for H2-O2 fuel cell membrane.
Novel Metal-Organic Polymers with Unique Conducting or Magnetic Properties
We develop routes to new classes of inorganic polymers with highly novel structures. These include materials with transition metals such as iron in the backbone and also polymers with chains constructed from atoms such as sulfur, boron, nitrogen, and phosphorus. New methods were developed for preparing crosslinked polymer microspheres made of polyferrocenylsilane, a new class of polymers invented in the Department of Chemistry, UofT. New creative methods were developed to assemble the microspheres and transform them with shape retention to ordered arrays of magnetic ceramic microspheres. Both of these discoveries establish platforms for new directions in future work. For example, with better control over the synthesis, with control of particle properties, these materials will have important potential applications in magnetic data storage.
Develop New Knowledge about Interfaces in Polymer Blends
We have a strong interest in the types of films that are formed from latex nanospheres. We use fluorescence techniques (fluorescence decay, energy transfer, laser confocal fluorescence microscopy, atomic force microscopy, and scanning and transmission electron microscopy for the study of latex films. Many of these films are prepared from a blend in water of several different types of particles, and their ultimate performance depends in an often-unknown way on where the individual components end up. We develop the principles that allow control over the structure of the blends and achieve remarkable new materials.
Create New Optical Limiters and Switches and Storage Devices
We use photo-responsive core-shell polymer microspheres assembled into a 3D structure with perfect crystalline order to produce materials for 3D optical data storage. In a different application, materials prepared from 2D and 3D colloidal crystalline assemblies of the core-shell are transparent to low intensity light but opaque at high incident intensities. Other projects in her group in the area of optoelectronics will involve the synthesis of nm- and micron-sized hybrid particles with both organic polymer and inorganic mineral components.
Make Miniature Catalytic Arrays
We are interested in proteomics and in chiral catalysts. The human genome project has unveiled genes that code for proteins with no known function. To unravel this function, researchers seek oligopeptides that bind specifically to individual proteins. We are developing combinatorial approaches to synthesizing libraries of oligopeptides in which fluorescent dyes are attached as markers. We are also developing strategies to employ changes in fluorescence intensity or lifetime as indications of binding. We also have a strong research effort in developing spatially addressable arrays for electrosynthesis. These arrays are based on thin films of conducting polymers to which electroactive functional groups are attached to specific locations on the film.
Develop New Techniques to Characterize the Elasticity of Complex Fluids
We carry out research on a class of materials that the physicists call "complex fluids." The most basic challenge is to understand the relationship between molecular architecture and flow properties of these fluids. We study the response to shear and extensional flow of liquid crystals and associative polymers and examine diffusion in biomaterials. In addition, we have specific interests in understanding the origin of the elasticity of solutions of associative polymers, and how this property affects specific applications of these polymer solutions. It remains a major challenge to understand how the chemical structure and the architecture of these polymers in solution lead to their useful properties as rheology modifiers.
Synthesis and Assembly of Nano- and Microspheres and Cylinders into Functional 2d and 3d Architectures
We study block copolymers with the iron-containing polymer as the insoluble block. These materials form remarkable wire-like (20-40 nm thick) flexible micelles in which the core can be oxidized to a semi-conducting state. Under other conditions, these objects can serve as ceramic precursors. A very exciting recent discovery is that certain polyferrocenylsilane (PFS) block copolymers self-assemble to form flexible hollow nanotubes with dimensions comparable to carbon nanotubes. It appears that the unusual morphology of these micelles is a consequence of the crystallinity of the PFS block. This discovery opens the door to many years of exciting research. One aspect involves preparing and studying oriented 2D arrays of these micelles. Another major challenge in future work is to learn how to connect these tiny wires and to integrate them into devices.