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Davis Research Group
Rapf Lab

Davis Research Group

Fundamental Laboratory Studies of Microenvironments


Focus: Analytical, Physical and Atmospheric Chemistry
Professor: Ryan Davis, Ph.D.
Website: Davis Research Group

Overview: The Davis Research Group utilizes elements of chemistry, physics, engineering, and computer science to develop advanced analytical techniques to study the unique properties of microenvironments and address science questions relevant to atmospheric chemistry, sustainability, climate, human health and indoor air quality. Microenvironments are ubiquitous in nature and science.  Examples include biological cells and atmospheric aerosols.  Understanding the chemistry and physics occurring in these small, isolated compartments is essential to understanding human health and global climate, among other things.  From the sea to the atmosphere to our bodies, these microscopic environments influence our daily lives in ways yet to be understood.  Our research aims to increase our understanding of micro-environmental properties to increase our understanding of the world and how we can improve it. In the Davis Research Group, there will be ample opportunities for students to develop instrumental techniques (such as that shown at right), design and build control electronics, write and develop software, perform experiments, process data, and present their work through presentations and publications.

Currently, there are several ongoing research directions.

Marine polysaccharides are known to self-assemble into ordered aggregates, such as polymer gels, at the ocean surface. Recently, marine polymer gels have also been observed in cloud/fog droplets. Due to their dense, compact nature, self-assembled gels in atmospheric particles are speculated to change the microstructural properties and chemical reactivity of that particle. However, these points remain largely unexplored. One initial project within my research group will study self-assembly of polymer material under the complex conditions relevant to the atmosphere, thus advancing fundamental physical chemistry knowledge and constraining important properties relevant to atmospheric science in terms of understanding air quality and climate.

To date, bridging the gap between atmospheric models and atmospheric observations has proven difficult.  This difficulty is largely due to the extreme chemical complexity of atmospheric particles and the unique but poorly understood properties of microenvironments. In the Davis Research Group, there are opportunities to study how these unique microdroplet properties lead to unique chemistry that cannot be replicated through “beaker synthesis”. One example includes studying the production of reactive oxygen species (ROS), including hydroxyl radical production under atmospheric conditions, as shown in image to the right.

We spend the majority of our time inside a building. However, less is known about indoor air chemistry than the chemistry occurring in the outdoor environment. A recent research push has led to an explosion of information about indoor air quality, but there is much research to be done. In the Davis Research Group, there will be opportunities to pursue research related to indoor air quality in the workspace, studying the types of particulate generated under “blue-collar” labor conditions.

 

More details on the Davis Research Group can be found at https://www.trinity.edu/sites/davis-research-group.

 

Rapf Lab

Photochemistry in Complex Aqueous Environment


Type: Physical Chemistry
Professor: Rebecca Rapf, Ph.D.

Overview: The Sun is the largest source of energy to the planet, and it controls, directly or indirectly, the vast majority of physical, chemical, and biological processes that take place on Earth. Photochemical processing of material drives the engine of atmospheric and environmental chemistry in planetary environments, largely through the formation and subsequent reactions of radical species. The reactivity of these radicals is controlled and mediated by the surrounding environmental conditions under which they were generated. Photochemically-generated organic radicals are particularly interesting because they offer an abiotic pathway to make larger, more complex organic molecules, which has applications to atmospheric chemistry, prebiotic chemistry, and astrobiology. This research is grounded in fundamental physical chemistry but is inherently interdisciplinary, drawing on organic chemistry, environmental chemistry, biophysics, and planetary science.

The Rapf lab examines the direct aqueous photochemistry of organic molecules under conditions relevant to planetary environments, including the modern and ancient Earth as well as other potentially habitable worlds. We conduct detailed photochemical experiments that allow us to examine, mechanistically, changes in reactivity that occur as a function of reaction conditions, including photon flux, atmospheric composition, and solution conditions (e.g. pH and salinity). Using model chemical systems, we can systematically increase the complexity of model systems to investigate the origins of emergent behavior.

In tandem with photochemical studies, we also explore how intermolecular interactions mediate chemistry, both through orientation and concentration at interfaces and through the formation of supramolecular assemblies. This is motivated by the repeated observations that in many cases the chemistry of single species in a bulk environment cannot be used to predict the reactivity of those species either in confined environments or in concert with other molecules. Of particular interest are recent literature reports that molecules at aqueous interfaces can undergo photochemistry that is not seen in the bulk. We explore how photochemistry is mediated by surface films composed of insoluble surfactants, such as long-tailed fatty acids like stearic and palmitic acid, using photochemical-initiator species, such as pyruvic acid.

Students will conduct photochemical experiments, which are analyzed using a combination of mass spectrometry, optical spectroscopy, and surface tension measurements. Students will also have opportunities for instrument development, as we build surface sensitive spectroscopic techniques to probe interfacial photochemistry directly.