Nanometer-sized cavities and pores can now be routinely generated in sol-gels, supramolecular assemblies, reverse micelles, zeolites, and even proteins, giving strong impetus to improving our understanding of chemistry in confined solvents. These cavities and pores can serve as nanoscale reaction vessels in which a chemical reaction takes place in the small pool of solvent allowed in the restricted space. One ultimate goal is to control the chemistry occurring in these systems by manipulating the properties of the confining framework as well as the species present. This may have important applications for catalysis, sensing, and separations. However, there is currently little understanding about how the confining framework properties affect chemical reactivity, that is
How does a chemical reaction occur differently in a nanoconfined solvent than in a bulk solvent?
We are addressing this question using theoretical and computational approaches, within which the pore properties can be readily varied and the changes in reactivity directly examined. A key focus is understanding chemical reactions in solvents confined within nanoscale frameworks using both simple models and atomistic models of silica pores with diameters of 2.5-5 nm. We are particularly interested in how the pore properties, e.g., the geometric constraints, surface hydrophilicity/hydrophobicity, pore roughness, and pore size, affect the chemistry. These studies will assist in the development of design principles for mesoporous catalysts. We collaborate with chemical engineers at the Center for Environmentally Beneficial Catalysis at KU who synthesize, characterize, and test mesoporous catalysts.
A related issue is
How can one probe the structure and dynamics of a nanoconfined liquid?
Even when the chemistry is dramatically different in confinement compared to the bulk liquid, it can be challenging to understanding the underlying molecular driving forces (e.g., liquid structure, entropic effects, hydrogen bonding). Thus, we are also investigating the molecular-level mechanisms of spectroscopic signatures of nanoconfined liquids, i.e., what information is (or is not) present in the electronic and vibrational spectra of confined liquids. Significant insight can be obtained by comparing simulated spectra, that agree with experimental measurements, to the detailed information in a molecular dynamics simulation. A particular recent focus is on nonlinear spectroscopies for probing liquid dynamics.
Stephane Abel, Nuno Galamba, Esra Karakas, Massimo Marchi, Ward H. Thompson, and Damien Laage, Langmuir 32, 10610-10620 (2016). “On the Structural and Dynamical Properties of DOPC Reverse Micelles”
Paul C. Burris, Damien Laage, and Ward H. Thompson, Journal of Chemical Physics 144, 194709 (2016). "Simulations of the Infrared, Raman, and 2D-IR Photon Echo Spectra of Water in Nanoscale Silica Pores"
Krista G. Steenbergen, Jesse L. Kern, Zhenxing Wang, Ward H. Thompson, and Brian B. Laird,Journal of Physical Chemistry C 120, 5010-5019 (2016). "Tunability of Gas-Expanded Liquids under Confinement: Phase Equilibrium and Transport Properties of Ethylene-expanded Methanol in Mesoporous Silica"
Robert H. Wells and Ward H. Thompson, Journal of Physical Chemistry B 119, 12446-12454 (2015). "What Determines the Location of a Small Solute in a Nanoconfined Liquid?"
Jacob A. Harvey and Ward H. Thompson, Journal of Chemical Physics 143, 044701 (2015). "Solute Location in a Nanoconfined Liquid Depends on Charge Distribution"
Jacob A. Harvey and Ward H. Thompson, Journal of Physical Chemistry B 119, 9150-9159 (2015). "Thermodynamic Driving Forces for Dye Molecule Position and Orientation in Nanoconfined Solvents"
Aoife C. Fogarty, Elise Duboue-Dijon, Damien Laage, and Ward H. Thompson, Journal of Chemical Physics 141, 18C523 (2014). "Origins of the Non-exponential Reorientation Dynamics of Nanoconfined Water"
Cassandra D. Norton and Ward H. Thompson, Journal of Physical Chemistry B 118, 8227-8235 (2014). "Reorientation Dynamics of Nanoconfined Acetonitrile: A Critical Examination of Two-State Models"
Cassandra D. Norton and Ward H. Thompson, Journal of Physical Chemistry C 117, 19107-19114 (2013). "On the Diffusion of Acetonitrile in Nanoscale Amorphous Silica Pores. Understanding Anisotropy and the Effects of Hydrogen Bonding"
Damien Laage and Ward H. Thompson, Journal of Chemical Physics 136, 044513 (2012). "Reorientation Dynamics of Nanoconfined Water: Power-law Decay, Hydrogen-bond Jumps, and Test of a Two-state Model"
Christine M. Morales and Ward H. Thompson, Journal of Physical Chemistry A 113, 1922-1933 (2009). "Simulations of Infrared Spectra of Nanoconfined Liquids: Acetonitrile Confined in Nanoscale, Hydrophilic Silica Pores"
Tolga S. Gulmen and Ward H. Thompson, Langmuir 22, 10919-10923 (2006). "Testing a Two-State Model of Nanoconfined Solvents: The Conformational Equilibrium of Ethylene Glycol in Amorphous Silica Pores"