Chemistry and Biochemistry
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Dr. Edward L. Quitevis

Title:

Professor
Joint Professor of Physics

Education:

Ph.D., Harvard University, 1981; Postdoctoral Fellow, University of Toronto, 1981-1984

Research Area:

Physical Chemistry/Chemical Physics

Office:

Phone:

Email:

Chemistry 035

806-742-3066

Edward.Quitevis@ttu.edu

 

Research Group

Personal Web Page

Principle Research Interests

The research of Professor Quitevis is directed toward understanding liquid-state dynamics. Various time-resolved optical spectroscopic techniques are used in this research to probe dynamics from the 10-14 s timescale to the 103 s timescale.  Recently, the focus of our current research has been on the dynamics of complex fluids, in particular liquid crystals (LCs) and room temperature ionic liquids (RTILs), and nanoconfined liquids.

With respect to molecular order, an LC is considered to be an intermediate state of matter between the crystalline and isotropic liquid phase.  The strong anisotropic interactions between the rod-like molecules in an LC lead to long-range orientational order in the nematic and smectic phases.  In the smectic phase the molecules are organized in layers where there is orientational order but no translational order.  In thermotropic LCs, transitions between these phases are induced by temperature changes.  By treating a glass substrate with an alkoxysilane-coupling agent, a surface can be created to align LC molecules along the substrate normal. LCs oriented in this way are said to be homeotropically aligned.  The study of the molecular dynamics of aligned LCs is important not only for technological reasons but in obtaining a fundamental understanding of biomembranes and critical phenomena.  RTILs show great potential as “green” designer solvents for use in catalysis, chemical synthesis, chemical separations, and as electrolytes in batteries and solar cells. Their nonvolatile character makes them highly desirable as solvents, as their adoption in industry would eliminate the health and environmental risks associated with fugitive emissions from the volatile organic compounds (VOCs) currently in use as solvents.  A major stumbling block to the adoption of RTILs as solvents is the lack of established principles to guide the choice of an appropriate solvent for a given task. While much progress has been made in understanding bulk physical properties such as phase transitions, viscosity, and density, the dynamics of RTILs remain poorly understood. The dynamics of these systems are being studied by using optical heterodyne-detected Optical Kerr effect spectroscopy (OHD-OKE) with sub-50 fs pulses from a mode-locked titanium:sapphire laser. OHD-OKE probes the orientational relaxation within the liquid.  By applying a Fourier transform procedure on the OHD-OKE transient, a reduced spectral density is obtained.  The reduced spectral density is directly related to the depolarized Raman spectrum of the liquid and contains information about the low-frequency intermolecular modes of the liquid.

The molecular dynamics of nanoconfined liquids can be quite different than that of the bulk liquid because of finite size effects, size-limited fluctuations, and surface effects.  We are currently interested in understanding the effect confinement on dynamics of glass-forming liquids near the glass transition in porous materials such as sol-gel glasses and cross-linked polymers.  For these studies we are using the technique of fluorescence recovery after fringe-pattern photobleaching (FRAP). In the FRAP technique, crossing two laser beams ("writing beams") in a sample creates a grating.  Photobleachable molecules are selectively destroyed in the regions of constructive interference. Attenuating the writing beams creates a reading grating. The phase of one of the beams is modulated in such a way that the reading grating is swept at constant velocity across the writing grating.  Each time the reading grating is out of phase with the writing grating, a maximum will be observed in the probe fluorescence.  The fluorescence is monitored using a photomultiplier tube, which is fed into a lock-in amplifier referenced to the modulation frequency.  The fluorescence signal decays as a result of the translational motion of the unbleached probes.

Reduced spectral densities of the LC 8CB in the
Smectic A and isotropic liquid phases.

FRAP signal for rubrene in supercooled ortho-terphenyl at 20YC

 

Representative Publications