Gilbert Walker

Academic Title: Professor

Phone: 416-946-8401 / fax 416-946-3865

Office: LM 514A

Email:

Research Homepage: http://www.chem.utoronto.ca/~gwalker/

The goal of our research program is to identify and exploit self-assembly processes of polymers that will enable the fabrication of nanostructured materials with useful electromagnetic, mechanical and physiological properties. The work is strongly interdisciplinary and we collaborate with researchers from most branches of science and engineering.

Nanophotonics: Chemical Microscopy: We are developing a new form of extremely high resolution infrared microscopy. This technique will give us the ability to identify chemical components of heterogeneous surfaces at <20nm resolution under ambient conditions. Presently we are concentrating in the mid-IR region, which will enable us to examine the coupling of self-assembly processes in mixed- protein crystal and block-copolymer systems. One significant challenge that we face is to develop a detailed, quantitative model for the coupling of the vibrational transitions to the light field, in the presence of a shaped, light-scattering tip. Nanophotonics for Information Storage: We aim to develop apertures for heat assisted magnetic recording, in collaboration with photonics engineers. The work presently involves cutting apertures of defined shapes and examining the light transmission through them, which feeds back to redesign of the aperture. Nanoaperture Arrays for Sensing Applications: Arrays of nanoapertures can couple efficiently couple narrow spectral regions of visible or infrared light (plasmonic or phononic arrays). Our objective for these materials is to develop device technologies for plasmonic sensor array chips for biochemical analytes.

Single Molecule Assembly Forces: Protein Unfolding: A key component in developing a surface active biological sensor, as is necessary for the protein receptor in the device indicated above, is developing a surface that does not cause the receptor to deactivate. Because the surfaces of bioactive materials can be heterogeneous, one of our key objectives is to develop tools to study their activity at the highest resolution, the single molecule level. Hierachichically Assembled Materials: We are using single polymer chain force spectroscopy to examine the interactions between macromolecules in hierachichically assembled materials. In our example, by chemically linking or embedding self-assembling proteins in structure-forming copolymers, the self-organization of the proteins will be used to affect the evolution of the block copolymers and, similarly, the structural evolution of the copolymers will be used to affect the self-assembly of the proteins. This work connects fundamentally to our efforts to understand the biofouling dynamics on minimally adhesive and topographically textured surfaces by living organisms such as algae and barnacles.

Electrical Properties of Nanostructured Polymeric Materials: We are examining how the interface between charge transport molecules and their environments influences transport rates. We recently observed, for the first time, a bias dependent, nanoscale adhesion force that undergoes transitions when a conducting polymer sample undergoes redox transitions, which opens a new window onto polymer surface chemistry and single molecule electromechanical signal processing. Our work in conducting polymers aims to address the need to engineer materials that will make electrical connections between metal electrodes and molecules in molecular electronics.

S. Zou, R. Hong, T. Emrick and G. C. Walker "Ordered CdSe Nanoparticles within Self-Assembled Block Copolymer Domains on Surfaces", Langmuir, 2007, 23 (4): 1612-1614.

Romanov, V.; Walker, G. C. "Infrared Near-Field Detection of a Narrow Resonance Due to Molecular Vibrations in a Nanoparticle", Langmuir, 2007, 23 (5): 2829-2837.

Zhang, H.; Tumarkin, E.; Sullan, R. M. A.; Walker, G. C.; Kumacheva, E.; "Exploring Microfluidic Routes to Microgels of Biological Polymers," Rapid Macromol. Comm., 2007, 28, 527-538.

Gunari, N; Balazs, A.; Walker, G. C. "Force Induced Globule-Coil Transition in Single Polystyrene and Polymethylmethacrylate Chains in Water", J. Am. Chem. Soc., 2007, 129, 10046-10047

Nie, Z.; Fava, D., Kumacheva, E.; Zou, S.; Walker, G. C, Rubinstein, M. "Self-assembly of Metal-Polymer Analogues of Amphiphilic Triblock Copolymers", Nature Materials, 2007, 6, 609-614

Zhang, H.; Tumarkin, E.; Peerani, R.; Nie, Z.; Sullan, R. M. A.; Walker, G. C.; Kumacheva, E.
Microfluidic Production of Biopolymer Microcapsules with Controlled Morphology J. Am. Chem. Soc. ; 2006 ; 128 , 12205-12210.  

Stebounova, L. Chen, F.; Bain, J.; Schlesinger, T. E.; Ip, S.; Walker, G. C. “Field localization in very small aperture lasers studied by apertureless near-field microscopy” Applied Optics , 2006 , 45 , 6192-6197.

Meadows, P. Y.; Bemis, J. E., Walker, G. C. “ Quantifying Adhesion Bond Parameters to Distinguish Interactions of Hydrophilic and Hydrophobic Blocks of Polystyrene-Poly-2-vinylpyridine with a Silicon Nitride Surface” J. Am. Chem. Soc . 2005, 127 , 4136-4137 .

Tivanski, A. V.; Walker, G. C. “ Ferrocenylundecanethiol Self-Assembled Monolayer Charging Correlates with Negative Differential Resistance Measured by Conducting Probe Atomic Force Microscopy “ J. Am. Chem. Soc. ; 2005 , 127 , 7647-7653.

Chen, J.; Liu, H.; Weimer, W. A.; Halls, M. D.; Waldeck, D. H.; Walker, G. C. “ Noncovalent Engineering of Carbon Nanotube Surfaces by Rigid, Functional Conjugated Polymers “ J. Am. Chem. Soc. 2002 ; 124 , 9034-9035.