General Areas of Research:
- Nonlinear optical sum frequency, second harmonic generation
- Linear vibrational spectroscopies – Raman, IR reflection
- Surface Potential measurement and methodology
- Liquid surface imaging
- Interfacial structure, dynamics, and chemistry
- Water Surfaces
- Ion pairing and hydration at surfaces
- Surfactant science
- Lipid – binding mechanisms and ion recognition
- 2D molecular organization
- Electric fields at liquid surfaces
- Physical chemistry of liquid interfaces
- Atmospheric aerosol and ocean surface proxy systems
- Biomembranes, hydration, and organization
- Instrument development – US Patent App. 16/085,21 ; US Patent App. 15/664,425; Pending Patent App. 61/857,511
Ongoing Projects (accepting students for projects 1, 2, 3):
1. Rare Earth Extraction Mechanisms in Confined Interfacial Environments: Separation Science
Rare earth elements (REEs) are critical components for many technologies, yet limited supplies impact technological advancements in myriad areas: electronics, clean energy, space and weapons systems, medicine, and medical technologies. Supply limitations threaten U.S. industries and national security. U.S. mining sites are being considered a possible sources of REEs. The solvent, water or organic/low dielectric phase, and solvation environment in addition to extractant molecular class play key roles in facilitating REE extraction and extraction capacity, and equally important is that the interface is unique in that interfacial transfer can be tuned selectively. We investigate 3 interfacial environments to understand separation mechanisms and thus interfacial binding mechanism(s) and thermodynamic properties of the interfacial extractant-ion-solvent complexes with effects from the solvent(s) and selected co-ions.
2. Controlling Aqueous Interfacial Phenomena of Redox Active Ions (DOE)
Redox ions are an important class of ions in which their multivalent states provide the potential for significant interfacial impact, with and without an externally applied field. There is a critical need to develop a thorough understanding of interfacial hydration of redox ions and solvent organization in externally applied fields, including the effect of ion charge, ion speciation, and the effect of co-solutes. In the absence of such knowledge, opportunities to improve new energy platforms are stunted and narrowly restricted thereby reducing the speed of such developments that might improve our energy infrastructure. Furthering the understanding of geochemical phenomena including mineral dissolution is also a potential outcome of this work.
The organization of, and induced by, redox ions Fe(II) and Fe(III) and externally applied electric fields at the hydrophobic air /water interface is being explored in our laboratory. Surface acidity, co-anion perturbation, ionic strength, electric field and electrode polarity effects, as well as the associated perturbations to hydration and organization to these redox ion interfacial systems are investigated. For these studies, we employ vibrational sum frequency generation spectroscopy, glancing angle Raman spectroscopy, surface tension and surface potential instrumentation. Expected outcomes of this project include instrumentation development and advances in surface-sensitive spectroscopy.
3. N2O4 and N2O5 Charge Stabilization at Liquid Surfaces to Understand NOx Reactivity – Fundamental Physical Chemistry project with varied applications (NSF)
4. Nanoplastic-induced molecular-level structural changes at lung alveolar surfaces (Herbert Hoover Foundation)
5. Surfactant Science and Biological Membrane Mimics
We study a myriad of fundamental phenomena relevant to surfactants, organization, binding and intermolecular interactions to better understand the driving forces behind organization and binding at aqueous and organic interfaces. Studies span applications such as surfactants, aerosols, biological membrane mimics to ocean and fresh water lakes and water bodies. an example of the biomembrane mimic focuses on pulmonary lung surfactant (PS). PS is a surface active lipoprotein formed by alveolar type II cells. PS adsorbs to the air-water interface of the alveoli with the head group (hydrophilic) facing the water, and the tail (hydrophobic) facing the air; hence the reason why some lipids have the ability to decrease the surface tension of water. The main component of PS is the lipid dipalmitoylphosphatidylcholine (DPPC), which can reduce the surface tension of water to near zero values. Deficiencies or inactivation of these lipids at the air-water interface can lead to clinically significant diseases such as Respiratory Distress Syndrome (RDS) and Acute Respiratory Distress Syndrome (ARDS). Our lab interrogates lipid monolayers, submonolayers, and in complex subphases to understand the permeability and electric fields at such interfaces to shed light on driving factors of organization and function.
6. Molecular Recognition in Aqueous Environments
We now have advanced to molecular and, in general, ion recognition with collaborations with Amar Flood at Indiana University and more recently, collaboration with Jovica Badjic at Ohio State. Proteins for example exploit microenvironments of low dielectric constant and partial dehydration. Yet, such biologically inspired environments have rarely been examined in artificial receptors. There is a critical need to understand and discover new recognition modes at bioinspired receptor-water interfaces.
Prior Projects (not accepting students currently for these projects):
