Dr. Edward L. Quitevis
Joint Professor of Physics
Education: Ph.D., Harvard University, 1981; Postdoctoral Fellow, University of Toronto, 1981-1984
Research Area: Physical Chemistry/Chemical Physics
Office: Chemistry 035
Principal Research Interests
- Ultrafast Nonlinear Optical Spectroscopy of Liquids
- Dynamics of Complex Fluids
- Physical Chemistry of Ionic Liquids
- Supercooled Liquids and the Glass Transition
One of the main techniques used in my laboratory is optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). OHD-RIKES is an ultrafast nonlinear optical time-domain technique that measures the collective polarizability anisotropy dynamics of a liquid. By use of a Fourier-transform deconvolution procedure, the OHD-RIKES transient can be converted to a reduced spectral density or optical Kerr effect (OKE) spectrum, which is directly related to the depolarized Raman spectrum of the liquid and contains information about the low-frequency intermolecular modes of the liquid. To study the ultraslow dynamics in glass-forming liquids, fluorescence recovery after photobleaching (FRAP) techniques are used. In FRAP, the rotational and transitional motions of photobleachable fluorescent probe molecules are used. Since the technique monitors the recovery of the fluorescence of the probe after photobleaching, the timescale of the dynamics that we are measuring is not limited by the fluorescence lifetime of the probe. In translational diffusion measurements, the washing out of a spatially periodic pattern of bleached and unbleached probe molecules is followed, whereas in rotational diffusion measurements, the filling in of an orientational hole is followed.
Ionic Liquids: Room temperature ionic liquids (ILs) are commonly defined as salts with melting points below 373K. An IL is composed of a bulky organic cation and one of a range of common anions, which might be either organic or inorganic, and possesses negligible vapour pressure, low flammability, and a wide liquid range. The vast number of potential ILs (over a million simple ones and over a trillion ternary systems) means that ILs can be designed specifically with tuneable physicochemical properties, leading to their description as “designer” solvents. Because they offer unique sets of properties not achievable with other materials, there is increasing interest in applications beyond solvents in such wide ranging fields as energetic materials, biotechnology, and nanoscience. Despite the great success of this application-driven research, a fundamental understanding of the structure, dynamics, and interactions in these complex fluids is still lacking. A particularly important feature of ILs is that they are structured liquids characterized by nanoscopic polar and nonpolar domains. Understanding the relationship between this nanostructural organization and the intermolecular dynamics in ILs is one of the main themes guiding research in my group.
Supercooled Liquids: The dramatic viscous slow down that accompanies the formation of glasses upon cooling supercooled liquids to below the glass transition temperature Tg is one of the oldest and most extensively studied problems in condensed matter physics and chemistry. The microscopic causes of the viscous slow down responsible for the glass transition however remain an unsolved problem. We are currently studying translational and rotational diffusion in glass-forming liquids above and below Tg. The goal of this research is to further understand the decoupling between translational and rotational diffusion that occurs as Tg is approached from above in the supercooled state and the processes that underlie physical aging when the glass-former is quenched from a temperature above Tg to the glassy state. Current theories of the glass transition are based on the existence of dynamic heterogeneity near Tg. Experiments in my laboratory are aimed at revealing the relationship between decoupling, physical aging, and dynamic heterogeneity. FRAP techniques are being used to measure the ultraslow translational and rotational diffusion near Tg.