Forces at biological interfaces: insights from neutron reflectometry

Abstract:  

Neutron reflectometry (NR) is a powerful method to interrogate the structure of multilayered thin films at interfaces and has found application in many areas in both hard and soft condensed matter. A key feature of neutron scattering for structural analysis is its isotope sensitivity, which can often be exploited in biological or biomimetic systems just by changing the aqueous medium from H2O to D2O. In many cases, NR is the most direct structural technique to probe interfacial phenomena in these systems; in this talk, following a general introduction to NR, I will discuss two examples in which NR revealed the strong interfacial forces at the surface of lipid bilayer membranes. In the first, https://pubs.acs.org/doi/full/10.1021/jacs.3c12348, counterintuitively, charged membranes are observed to strongly repel neutral nanoscale particles from its surface, creating a water-rich exclusion zone near the membrane surface. I will show that this effect is related to the formation of extremely strong local field gradients in the electric double layer; these repel neutral particles both by dielectrophoresis and counterion pressure. In the second, https://doi.org/10.1021/acs.langmuir.1c00214, I will demonstrate how substrate-supported lipid bilayers can be decoupled from the substrate by tuning the surface charge of the substrate. Finally, I will discuss several recent developments in NR: the new, highly parallelized CANDOR reflectometer at the NIST Center for Neutron Research, and the role that automation and active learning can play in accelerating data collection and discovery with NR.

Michael F Toney, University of Colorado Boulder 

Local atomic structure often differs from the global average structure as measured with diffraction and yet the local structure has a profound impact on properties. This structure-function relationship applies in many materials classes, ranging from organics to Li-ion battery cathodes to oxide and halide perovskites. Accurately characterizing this local structure has proven challenging but recent advances in diffuse scattering (“between” Bragg peaks) has enabled local structure determination.

In this talk, I will discuss the importance of local structure and how this can be quantified and will demonstrate this for organic-inorganic hybrid halide perovskites [1,2]. These materials are a recently re-invigorated class of semiconductors that have demonstrated very high efficiencies for solar cells after just over a decade of research. While the importance of lattice dynamics and dynamical (dis)order have been recognized in these materials, their nature is only poorly known and understood. We used X-ray and neutron diffuse scattering coupled with molecular dynamics to quantify the nature, size, and time scale associated with dynamical local order in CH3NH3PbI3 and CH3NH3PbBr3 perovskites. We observe that the nominally cubic perovskite consists of dynamical, two-dimensional sheets of lower symmetry tetragonal regions of about 3 nm diameter with several picosecond lifetimes. The implications on halide perovskite properties will be discussed. 

[1] NJ Weadock et al., Joule 7, 5, 1051-1066 (2023)

[2] DM Ladd, unpublished.

Abstract:

Farmers and their modern machinery collect prodigious amounts of data while engaging in the critical task of producing food to feed the world. Thinking about agriculture and agricultural data like a physicist is an unusual but very fruitful way of approaching the complex problems of helping farmers maximize their profits and production while managing their environmental impact.  The techniques that physicists regularly use for a wide range of problems have applicability and can lead to interesting discoveries and cultural processes, and this crossing of fields called “agrophysics” is an exciting opportunity for convergent research.  This talk will explore data, data acquisition, modeling and the huge potential for changing how agricultural practitioners and physicists might work together.  We will also explore what is needed for data to revolutionize agriculture in ways that it has yet to do.

Join us for “Bridging Physics and AI: Pioneering Advances in Computational Material Science " a keynote presentation by Dr. Aldo Romero, College of Arts & Science – Physics & Astronomy, MizzouForward faculty candidate.  Dr. Romero will present on his research for approximately 40-minutes with a 20-minute question and answer session to follow.

Prof. Aldo Romero is an Eberly Family Distinguished Professor in the Physics and Astronomy Department at West Virginia University. With expertise in theoretical physics and computational material science, he has significantly contributed to high-performance computing applications, software development, and electronic structure research. Romero's academic journey includes Ph.Ds.  in Theoretical Chemistry and Theoretical Physics from the University of California, San Diego, and a post-doctoral fellowship in Germany. He has published extensively in peer-reviewed journals, co-organized international scientific events, and served as an editor for several academic journals. His work is recognized through various awards and as a fellow of the American Physical Society. As an educator, Romero has developed and taught courses at both undergraduate and graduate levels, integrating innovative methodologies and cutting-edge topics like machine learning and neural networks into his curriculum.

Prof. Aldo Romero is a distinguished researcher in theoretical condensed matter physics, particularly in computational material science. With a profound understanding of high-performance computing applications and expertise in various programming languages, he has significantly contributed to developing electronic structures and computational packages. His research is marked by a strong publication record in peer-reviewed journals, highlighting his expertise in diverse areas like computational nano magnetism, materials prediction, and the theoretical characterization of materials. Additionally, Romero's experience as an academic editor and involvement in various invited talks and keynotes demonstrate his commitment to advancing the field through research and scholarly communication.

The Nobel Prize in Physics 2023 was awarded to three physicists, Pierre Agostini, Ferenc Krausz, and Anne L’Huillier, for “experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter”. Prof. Carsten Ullrich, MU Dept. of Physics & Astronomy, will present a colloquium discussing how these discoveries have given humanity new tools for exploring the incredibly fast processes that rule the quantum world of electrons.

This talk is for faculty, graduate, and undergraduate students alike from all disciplines. Light refreshments will be served at 3:40 pm in Rm 223 A.

Abstract: Epithelial tissues are the first and most abundant tissue type in animals. They can be found in basal organisms like sponges, and they perform a wide range of important biological functions (including gas exchange and nutrient absorption) in humans. These tissues are most typically arranged as monolayers, or “pseudo-2D” sheets of cells. We want to understand how epithelial monolayers develop and maintain that arrangement. Why don’t cells just pile up on top of each other after they divide? I will discuss our lab’s work on this fundamental problem.

Bio: The Finegan-Bergstralh lab studies the question of how cells divide in the context of a developing epithelial tissue, which is usually a fairly crowded environment. We combine approaches from experimental biology (especially microscopy), with approaches from physics and mathematics (especially computational modeling). Dan earned his bachelor’s degree at the University of Maryland, was a postbac at NIH, earned a PhD at the University of North Carolina, and was a postdoc at the University of Cambridge and fellow of Clare Hall during that time. In 2016 he started his lab at the University of Rochester, where he held appointments in both the Department of Biology and the Department of Physics & Astronomy. The lab moved to Mizzou in May of this year and is now run jointly with Tara Finegan. Dan and Tara are excited to be here at Mizzou and eager to work with its physics community! 

Matthew Brahlek, Materials Science and Technology Division, Oak Ridge National Laboratory

The current challenge to realizing continuously tunable magnetism lies in our inability to systematically change properties such as valence, spin, and orbital degrees of freedom as well as crystallographic geometry. In this talk I will discuss how ferromagnetism can be externally turned on with the application of low-energy helium implantation and subsequently erased and returned to the pristine state via annealing. This high level of continuous control is made possible by targeting magnetic metastability in the ultra-high conductivity, non-magnetic layered oxide PdCoO2 where local lattice distortions generated by helium implantation induce emergence of a net moment on the surrounding transition metal octahedral sites. These highly-localized moments communicate through the itinerant metal states which triggers the onset of percolated long-range ferromagnetism. The ability to continuously tune competing interactions enables tailoring precise magnetic and magnetotransport responses in an ultra-high conductivity film and will be critical to applications across spintronics.

Abstract:

Long-standing common lore in fundamental physics insists that the problem of developing a high-energy theory of quantum gravity (QG) is a job for the theoretical physicist, which is largely unconstrained by empirical data. But QG phenomenology --- focused on the link between QG research and the world --- is a field of research with its own long history. So, it is probably not the case that contemporary currents within theoretical QG research are simply detached from the data-oriented focus of the wider discipline. Why, then, does the lore say theoretical QG research is “largely unconstrained by empirical data”? Part of the difficulty in answering this question is that the claim is ambiguous: is it saying something about our current theories of fundamental physics already accounting for nearly everything we may empirically access? Or is it saying something about the “problem” at the heart of QG research being underspecified? Or is it saying something else entirely --- perhaps merely that the relevant community has come to regard articles in QG research with only superficial contact with data as, nonetheless, satisfying standards of “good scholarship”? In this talk, I will critically reflect on the standard lore, which ultimately has to do with the relationship between QG phenomenology and contemporary currents within theoretical QG research. Toward that end, I will draw on phenomenological research done in the context of both large-scale astrophysics and cosmology, as well as QG experiments performed 'on the tabletop'. Note that my perspective throughout will be that of foundations, i.e. the philosophy of physics. Consequently, this talk will not be a review of results obtained in QG phenomenology that might or would bear on explicit proposals within QG research (in the sense of numerical constraints on possible novel microscopic physics, e.g. Lorentz violations or fundamental stochasticity).