Larissa Kunz (Cargnello group)
Abstract: Approximating Polychromatic Quantum Yields to Fairly Compare Photocatalytic Heterojunction Systems
With a growing need for sustainable fuels and chemicals, interest in photocatalytic processes has grown in recent decades. Since photocatalytic efficiencies remain prohibitively low--typically believed to be limited by fast electron-hole recombination--much of the work reported in the literature focuses on suppressing recombination by the addition of co-catalysts to help separate electrons and holes. Unfortunately published catalyst materials are difficult to compare and then improve upon due to the common practice of reporting activity on a catalyst-mass-basis. We use a model TiO2/g-C3N4 system to demonstrate that catalyst-mass-normalization not only fails to provide mechanistic insight but can also artificially inflate the apparent activity of heterojunction systems. This artificial enhancement results from the nonlinear absorption of light. We propose a method to approximate a photocatalytic quantum yield, enabling a fair comparison of heterojunction systems under polychromatic light. This method can be applied to evaluate the sensitivity of a system to this artificial enhancement, thereby providing guidelines for reporting photocatalytic activity.
Larissa is a third year PhD student jointly advised by Matteo Cargnello and Arun Majumdar. Passionate about sustainability and the environment, she is interested in photochemical energy systems and light harvesting. Before coming to Stanford, she received her BS and MS in chemical engineering / chemical engineering practice from MIT.
Kolade Adebowale (Chaudhuri group)
Abstract: Substrate stress relaxation regulates cell migration
Cell migration has been implicated in human diseases, including cancer metastasis. A key step in the metastatic cascade is cell migration through the extracellular matrix (ECM). The mechanical and structural properties of the ECM are thought to impact cell migration. Recent studies suggest that tumor tissue is viscoelastic and exhibits stress relaxation, or the relaxation of mechanical stresses resisting a deformation over time.
Here, we examined the impact of substrate stress relaxation on cell migration using substrates with tunable stress relaxation. Interpenetrating networks of alginate and reconstituted basement membrane, were used as viscoelastic substrates for cell migration studies while poly-acrylamide hydrogels were used as elastic substrates. Cell migration characteristics were measured using confocal time-lapse microscopy and image analysis.
Our analyses indicate that faster stress relaxation promotes increased cell migration speeds, rounded morphology and greater persistence in migration. The combination of these results and finite element analysis suggest that the observed migration may represent a previously undescribed mode of migration relevant to viscoelastic substrates with fast stress relaxation.
Kolade completed his undergraduate degree at Illinois Institute of Technology. He is currently a 4th year PhD student in the Chaudhuri lab for cell biophysics and mechanotransduction where he studies the biophysics of cell-extracellular matrix interactions.
Benjamin Dolata (Zia Group)
Abstract: Micromechanical modeling of heterogeneous suspensions
We present a theoretical study of the stress tensor in dilute heterogeneous suspensions. In such flows, the traditional volume averaging approach employed to compute the stress tensor in a statistically homogenous suspension is no longer generally valid; to overcome this limitation, we utilize a point-wise ensemble averaging method. In contrast with heterogeneous suspensions, where the particle stress depends only on the integral of the stress interior to the particle, i.e. the stresslet and torque, the stress in heterogeneous suspensions depends on the first, second, and all higher-order moments of the stress interior to the particle. Using tensor decomposition techniques, we derived differential identities that allow transformation of these volume moments of the stress into surface moments of the hydrodynamic traction and fluid velocity. We show that the stress tensor in heterogeneous suspensions is symmetric in the absence of externally applied torques on the particles, in contrast with prior work. We derive constitutive equations for dilute suspensions of spherical particles, showing that spatial heterogeneity in the suspension breaks the usual isotropy of the constitutive equations, leading to new couplings that are forbidden by symmetry in homogeneous suspensions.
Benjamin is a graduate student working with Professor Roseanna Zia in the Chemical Engineering Department. His general research interests are in the field of transport phenomena, with a specific focus on the microscopic response of colloidal suspensions to imposed macroscopic fluxes. He has a bachelor's degree in Chemical Engineering from the University of Wisconsin-Madison and a masters degree in Chemical Engineering from Cornell University.