Professor, Materials Science Program Director
Optical Spectroscopy in Hard to See Places
Office: Room 57
Chemistry & Biochemistry Building
P.O. Box 173400
Bozeman, MT 59717
- B.A. Chemistry, with high honors, Dartmouth College, 1990
- Ph.D. University of Wisconsin at Madison, 1995
- Post Doctoral Research Associate: University of Oregon, 1995-1998
- Visiting Fellow, Durham University (UK) 2007
- Assistant, Associate, Full Professor, University of Maryland, College Park, 1998-2009
- Associate Chair, Chemical Physics Program, University of Maryland, College Park, 2003-2009
- Montana State University, Professor 2009 - present
- CHMY 373 PHYSICAL CHEMISTRY II
- CHMY 558 CLASSICAL AND STATISTICAL THERMODYNAMICS
Awards and Professional Activities
- Merck Award for Undergraduate Research 1990 Dartmouth College
- Young Investigator Award 1999 Dynamics at Surfaces Gordon Conf.
- NSF CAREER Award 2001 National Science Foundation
- Alfred P. Sloan Fellow 2003 Alfred P. Sloan Foundation
- Undergraduate Research Mentor of the Year 2005 University of Maryland
- Institute of Advanced Study Fast Track Fellow 2007 Durham University (UK)
Our group develops and utilizes optical methods to study chemical structure, organization and reactivity at surfaces. While the systems studied are diverse and far ranging, our goal is always the same: we work hard to understand how asymmetric forces found at surfaces alter interfacial chemistry from bulk material limits. Projects currently underway fall into two general categories: 1) solvation at liquid surfaces and 2) high temperature surface chemistry in electrochemical devices.
Solvation at liquid surfaces I
Measuring the widths of liquid interfaces: “Our original work in the area of surface chemistry was motivated by the simple question, Do oil and water really not mix? A more quantitative way of asking this question is, "Over what lengthscales do the properties of one liquid converge to those of a second, immiscible liquid?" Using custom designed surfactants dubbed "molecular rulers" and resonance enhanced, second harmonic generation (SHG) spectroscopy we have measured the distances required for solvent polarity to transition from the aqueous to the organic limit across a wide variety of immiscible liquid/liquid interfaces. As a result of these studies, we discovered that interfacial asymmetry can force solvent species to organize differently compared to their long range structure in bulk solution. Consequently, liquid surfaces may acquire properties that can not be described simply by extrapolating contributions from the two individual phases. For example, water is a very polar solvent and long-chain alcohols have intermediate polarity based on their respective static dielectric constants. However, water/alcohol interfaces are dominated by a nonpolar, alkane-like region. These findings necessarily force one to reconsider proposed mechanisms of solvent extraction, interfacial electrochemistry and colloid stability.
Solvation at Liquid Surfaces II
Structure and organization at liquid interfaces - Our studies of polarity across liquid/liquid interfaces raise questions about how molecules having different structures organize themselves when constrained to two dimensions. Irregularly shaped, organic molecules are ubiquitous throughout biology, chemistry and environmental science, yet very little is known about how these species assemble spontaneously to form organic films at aqueous interfaces. To answer these questions, we use vibrational sum frequency spectroscopy (VSFS) to acquire vibrational spectra of species adsorbed to the aqueous-vapor interface. These data coupled with careful surface pressure measurements provide the quantitative information needed to model the competing forces that control surfactant concentration and conformation at air/aqueous interfaces.
Optical studies of high temperature surface chemistry
The overall goal of this project is to identify the mechanisms responsible for electrochemical oxidation in solid oxide fuel cells (SOFCs). Due to the high activation energy needed to catalyze molecular oxygen dissociation and the small diffusion constants associated with oxide ion transport through doped, metal-oxide ceramics, SOFCs must operate at elevated temperatures typically 650 C or higher. Traditional studies of SOFC operation use electrochemical techniques to report on system performance, but these data can not differentiate the chemical species responsible for observed behavior. Samples used in these studies are often subjected to exhaustive, ex situ, post mortem analyses. Thus, researchers are left to infer how chemical and structural changes observed after operation correspond to electrochemical performance measured during operation. To overcome the challenges associated with making measurements at high temperatures and under strongly reducing or oxidizing conditions, my group has built and adapted instrumentation to acquire vibrational Raman spectra from metal and metal oxide surfaces at temperatures in excess of 750 C (!).
Recent PublicationsJ. Karnes, E. A. Gobrogge1, R. A. Walker and I. Benjamin “Unusual structure and dynamics at silica/methanol and and silica/ethanol interfaces – A molecular dynamics and nonlinear optical study” J. Phys. Chem. B. 120 (8) 1569-1578 (2016).
C. A. Gobrogge1, V. A. Kong2 and R. A. Walker, “Unusual Temperature Dependent Solvation and Partitioning in Phospholipid Membranes” J. Phys. Chem. B 120 (8) 1805-1812 (2016).
S. M. Burrows, E. A. Gobrogge1, L. Fu, K. A. Link1, S. M. Elliott, H. F. Wang, and R. A. Walker “OCEANFILMS-2: Representing co-adsorption of saccharides in marine films improves agreement of modelled and observed marine aerosol chemistry” Geophys. Res. Lett.143 (15) 8306-8313 (2016).
R. E. Latterman1, S. Birrell, P. A. Sullivan, and R. A. Walker “Improved pulsed laser operation with engineered nanomaterials” ACS Applied Materials and Interfaces 8 (30) 19724-19731 (2016).
M. L. Traulsen, M. D. McIntyre1, K. Norrman, S. Sanna, M. Mogensen, and R. A. Walker “Reversible Decomposition of Secondary Phases in BaO Infiltrated LSM Electrodes – Polarization Effects” Advanced Materials-Interfaces 3 (24) Article 1600750 (2016).
Bruce J. Berne, John T. Fourkas, Robert A. Walker and John D. Weeks, “Nitriles at Silica Interfaces Resemble Supported Lipid Bilayers” Accounts of Chemical Research 49 (9) 1605-1613 (2016).
D. R. Driscoll, M. D. McIntyre1, M. M. Welander1, S. W. Sofie and R. A. Walker, “Enhancement of High Temperature Metallic Catalysts: Aluminum Titanate in the Nickel-Zirconia System”Applied Catalysis A 527 36-44 (2016).
K. A. Burbank1, R. A. Walker, and B. M. Peyton, “A molecular basis of metal toxicity by Uranium(VI) in bacterial dehydrogenase enzymes” J. Inorganic Biochem.149 59-67 (2015).
*J. D. Kirtley1, M. B. Pomfret, D. A. Steinhurst, J. C. Owrutsky, and R. A. Walker, “Towards a working mechanism of fuel oxidation in SOFCs: In operando optical studies of simulated biogas and methane” J. Phys. Chem. C 119 (23) 12781-12791 (2015).
*Melissa D. McIntyre1, John, D. Kirtley1, Anand Singh, S. Islam, J. M. Hill, and R. A. Walker, “Comparing in situ carbon tolerances of Sn-infiltrated and BaO-infiltrated Ni-YSZ cermet anodes in solid oxide fuel cells exposed to methane” J. Phys. Chem. C. 119 (14) 7637-7647 (2015).
M. D. McIntyre1, M. L. Traulsen, K. Norrman, S. Sanna, and R. A. Walker, “Polarization induced changes in LSM thin film electrode composition observed by in operando Raman spectroscopy and TOF-SIMS” Electrochemical Society Transactions, 66 (2) 47-59 (2015).
B. L. Woods1, J. K. George2, A. M. Sherman2, P. R. Callis, and R. A. Walker, “Optical studies of adsorption and aggregation at silica methanol interfaces: the role of solute structure” J. Phys. Chem. C 119 (25) 14230-14238 (2015).
J. D. Kirtley1, M. B. Pomfret, D. A. Steinhurst, J. C. Owrutsky, and R. A Walker “In operando optical studies of SOFCs operating with butanol” Electrochemical Society Transactions (SOFC XIV) 68 (1) 1091-1102(2015).
M. D. McIntyre1, D. M. Neuberger1, and R. A. Walker, “In Situ Optical Studies of Carbon Accumulation with Different Molecular Weight Alkanes on Solid Oxide Fuel Cell Ni Anodes” Electrochemical Society Transactions, 66 (32) 11-19 (2015).
K. W. Reeping1 and R. A. Walker “In operando vibrational Raman studies of chlorine contamination in solid oxide fuel cells” J. Electrochem. Soc. 162 (12) F1310-F1315 (2015).
K. W. Reeping1, D. M. Halat2, J. D. Kirtley1, M. D. McIntyre1, and R. A. Walker, “In situ optical and electrochemical studies of SOFC carbon tolerance” Electrochemical Society Trans. (Ionic and Mixed Conducting Ceramics 9), 61 57‑63 (2014)
B. C. Eigenbrodt and R. A. Walker, “In situ Raman measurements of solid oxide fuel cell devices” Spectroscopy 29 (12) 24-30 (2014).