Associate Professor of Chemical and Biomolecular Engineering
 Education
B.S., ChE Auburn University, 1993
M.S., ChE Massachusetts Institute of Technology, 1996
Ph.D., ChE Massachusetts Institute of Technology, 1998
Contact Information
Dept. of Chemical and Biomolecular Engineering
Vanderbilt University
Box 1604, Station B
Nashville, TN 37235
Phone: (615) 322-2707
FAX: (615) 343-7951
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Group web page
Research
Organic films on metal surfaces are used extensively in materials processing
as mediating layers, ionomers, responsive films, and protective coatings. My
research utilizes a molecular-level approach to design and assemble tailor-made
ultrathin organic films on metal surfaces to impact the processing of advanced
materials. Two fundamentally important systems that we study are
self-assembled monolayers (SAMs) and polymer films grown from surfaces by
surface-initiated and surface-catalyzed approaches. These systems are
prepared by straightforward immersion processes, can coat objects of any shape,
and represent highly uniform films with controlled thickness and
composition. We have used these monolayer and polymer systems to engineer
composition and structure at interfaces of materials and impact energy-related
issues, including solar energy conversion and alternative proton exchange
membrane fuel cells, as well as friction/wear, biological adhesion, and
chemical sensing.
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Biomimetic Solar Energy Conversion with
Photosystem I. The
development of affordable and renewable energy sources that supplant our
reliance on fossil fuels is perhaps the most important challenge facing our
society today. Our research with Prof. David Cliffel is developing
biomimetic solar cells containing Nature’s optimized nanoscale components
harvested from green plants as the active elements. Our chief component
is Photosystem I (PSI), a 10 nm protein complex that functions as a photodiode
and is one of the fundamental machines that powers photosynthesis.
We are preparing monolayer and multilayer films of PSI on electrode
surfaces and using these films to convert light into electrical current.
To date, we have shown that the surface density of a PSI monolayer greatly
affects the amount of photocurrent it produces, and covalent attachment of PSI
to a SAM results in the densest protein films and highest photocurrents.
PSI can be assembled within the pores of nanoporous gold electrodes to increase
interfacial area and further improve measured photocurrents. We have
recently produced a prototype, hand-held photoelectrochemical cell in which micron-thick
films of PSI produce 2 mA/cm2 of current and 65 mV upon irradiation with light
at 95 mW/cm2.
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Nanoscale Lubrication. We are working with Prof. Clare McCabe to develop
new strategies to lubricate microelectromechanical systems (MEMS) and devices.
We are currently using both experimental and computational approaches to
investigate the interfacial behavior and lubricating properties of ionic
liquids and self-assembled monolayers as combined mobile/bound coatings.
Our published results show that nanoscale ionic liquid thin films can be
deposited onto SAMs, provided the surface energy of the monolayer is
sufficiently high or the surface tension of the IL is sufficiently low.
For monolayers in the absence of ionic liquids, a critical chain length of ~8
total carbons is necessary to obtain consistently low coefficients of friction
at low loads. As loads are increased, monolayers with covalent silane
linkages vastly outperform chemisorbed alkanethiolates in tribological
performance, owing to their stronger surface attachment. These results
illustrate the importance of interchain interactions and robust surface
attachments to produce films that are tribologically effective over a range of
loads.
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Interfacial Engineering in
Proton Exchange Membrane Fuel Cells. We are using surface-initiated, ring-opening metathesis
polymerization (ROMP) to prepare new ion-conducting interfaces for
applications in fuel cells. The partially fluorinated ionomer chains
are grown from the surface of pore walls and are designed to encapsulate
catalyst particles to provide a well-defined three-phase boundary for gas,
proton, and electron transfer. By molecular design of the
polymerizing species, we are promoting self-organization of the polymer
chains to create a hydrophobic fluorocarbon matrix for gas transport and
hydrophilic channels for proton conduction. We have reported that
these ionomers can be successfully integrated with catalytic Pt monolayers
for extremely low Pt loading and high utilization efficiency.
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Superhydrophobic Polymer
Films. Typically, superhydrophobic
films, those that cause impinging water droplets to bounce away, are
prepared through a multi-step process that involves patterning both micro-
and nanometer roughness. We have introduced the use of surface-bound
borane sites to grow polymer films from various surfaces by using
diazomethane as a precursor. Through a single-step, surface-initiated
polymerization, we are able to produce micron-thick polymethylene films
with a combination of nano- and micro-scale roughnesses that exhibit
superhydrophobic behavior. Drops of water literally bounce off the
surface of these films with little loss of shape. The ionic
resistance of the thickest films exceeds 1012W·cm2, the largest value ever
reported for surface-initiated polymer film, and is buoyed by the poor
interfacial wettability at the rough, hydrophobic surface. Current
research is focused on the development of a model that describes the
effect of entrapped air at the water/polymer interface on measured film capacitances.
Selected Publications
M. Ciobanu, H. A. Kincaid, V. Lo, G. K. Jennings, and D. E. Cliffel,
“Voltammetric Studies of PSI Direct Electrochemistry,” J. Electroanal. Chem.,
599, 72-78, 2007.
D. Bai, Z. Ibrahim, and G. K. Jennings, “pH-Responsive Random Copolymer
Films with Amine Side Chains,” J. Phys. Chem. C., 111, 461-466, 2007.
R. D. Weinstein, J. Richards, S. D. Thai, C. A. Bessel, D. M. Omiatek, C. J.
Faulkner, S. Othman, G. K. Jennings, “Characterization of Self-Assembled Monolayers
from Lithium Dialkyldithiocarbamate Salts,” Langmuir, 23, 2887-2891, 2007.
D. Bai, C. L. Hardwick, B. J. Berron, and G. K. Jennings, “Kinetics of pH
Response for Copolymer Films with Dilute Carboxylate Functionality,” J. Phys.
Chem. B., 111, 11400-11406, 2007.
B. J. Berron, E. P. Graybill, and G. K. Jennings, “Growth and Structure of
Surface-Initiated Poly(n-alkylnorbornene) Films,” Langmuir, 23, 11651-11655,
2007.
B. J. Berron, P. A. Payne, and G. K. Jennings, “Sulfonation of
Surface-Initiated Polynorbornene Films,” Ind. Eng. Chem. Res., 47, 7707–7714,
2008.
C. J. Faulkner, S. Lees, D. Cliffel, and G. K. Jennings, “Rapid Assembly of
Photosystem I Monolayers on Gold Electrodes,” Langmuir, 24, 8409-8412, 2008.
P. N. Ciesielski, A. Scott, C. J. Faulkner, B. J. Berron, D. E. Cliffel, and
G. K. Jennings, “Functionalized Nanoporous Gold Leaf Films for the
Immobilization of Photosystem I,” ACS Nano, 2, 2465–2472, 2008.
A. M. Cione, O. A. Mazyar, B. D. Booth, C. McCabe, and G. K. Jennings,
“Deposition and Wettability of [bmim] [triflate] on Self-Assembled Monolayers,”
J. Phys. Chem. C, 113, 2384-2392, 2009.
O. A. Mazyar, G. K. Jennings, and C. McCabe, “Frictional Dynamics of
Alkylsilane Monolayers on SiO2: Effect of 1-n-Butyl-3-methylimidazolium Nitrate
as a Lubricant,”Langmuir, 25, 5103-5110, 2009.
S. G. Vilt, Z. Leng, B. D. Booth, C. McCabe, and G. K. Jennings, “Surface
and Frictional Properties of Two-Component Alkylsilane Monolayers and
Hydroxyl-Terminated Monolayers on Silicon,” J. Phys. Chem. C, 2009, 113,
14972-14977.
B. D. Booth, S. G. Vilt, C. McCabe, and G. K. Jennings, “Tribology of
Monolayer Films: Comparison between n-Alkanethiols on Gold and n-Alkyl
Trichlorosilanes on Silicon,” Langmuir, 2009, in press.
B. J. Berron, C. J. Faulkner, R. E. Fischer, P. A. Payne, and G. K.
Jennings, “Surface-Initiated Growth of Ionomer Films from Pt-Modified Gold
Electrodes,” Langmuir, 2009, in press.
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Faculty and Research 
