Physics Colloquia

Entanglements, i.e. topological constraints, are known to dominate the rheological properties of long chain polymer melts and dense solutions. Their properties and consequences led to the generally accepted and well established reptation/tube model, which is at the basis of our understanding of many properties and processes. However, one also can take the approach to use them to manipulate and structure materials, either by avoiding or explicitly using/introducing them. The talk will give a few such examples ranging from melts of non-entangled to very long, highly entangled polymer systems to new entanglement stabilized nanoporous films or topological glasses in active systems. Furthermore, we applied a new data driven approach to determine the glass transition temperature of polymer melts and (ultra) thin films.
[1] HP Hsu, KK, Macromolecules 57, 2998 (2024)
[2} H. P. Hsu, M. K. Singh, Y. Cang, H. Thérien-Aubin, M. Mezger, R. Berger, I. Lieberwirth, G. Fytas, and KK, Adv. Sci. 10, 2207472 (2023).
[3] M. K. Singh, M. Hu, Y. Cang, H. P. Hsu, H. Thérien -Aubin, K. Koynov, G. Fytas, K. Landfester, and KK, Macromolecules 53, 7312 (2020).
[4] J. Smrek, I. Chubak, C.N. Likos, KK Nature communications 11 (1), 26 (2020), J Smrek, K Kremer Physical review letters 118 (9), 098002 (2017)
[5] A. Banerjee, H. P. Hsu, KK, and O. Kukharenko, ACS Macro Lett. 12, 679 (2023).

Quantum materials provide responses and states of matter with no classical analogs. As such, they offer opportunities to create various platforms for future devices crucial to human health, energy efficiency, communications, and imaging. I will describe the physics challenges and sensing opportunities these materials offer. I will then focus on using the relativistic electrons in graphene for biosensing. Specifically, we have developed a new platform for multiplexed, rapid, easy-to-use detectors of biological analytes. I will discuss the unique aspects of graphene involved, resulting in our demonstration of a handheld device that detects antibiotic-resistant bacteria, decease biomarkers, opioids, and respiratory infections in saliva and wastewater at concentrations an order of magnitude better than mass-spectroscopy. Time permitting, I will briefly mention other efforts in our group to study novel quasi-particles in these systems.

Polymeric materials comprising mechano-chemically active components are able to undergo spontaneous structural rearrangements that generate internal stresses and motion. These stresses can be particularly large in the case of liquid crystalline polymers, where elasticity plays an important role on the structure of the underlying materials. Understanding how internal activity leads to specific behaviors could be useful for design of autonomous materials with desirable functionalities. This lecture will focus on the relationship between structure, activity, and motion in liquid crystalline systems. More specifically, results will be presented for two classes of systems: actin and tubulin biopolymer suspensions, where activity is generated by protein motors, and standard thermotropic materials where activity is generated through the application of external fields. In the case of biopolymers, a distinctive feature is that characteristic molecular contour lengths can range from hundreds of nanometers to tens of microns, thereby making them amenable for study by optical microscopy. By relying on molecular and meso-scale models, it is possible to arrive at a comprehensive description of these suspensions that helps explain the connections between molecular structure, the formation and shape of distinct topological defects, activity, and defect dynamics. One of the outcomes of such a description is the realization that hydrodynamic interactions can in some cases exacerbate or mitigate the elasticity of the underlying materials, leading to non-intuitive phenomena that do not arise at equilibrium. By balancing such effects, these findings raise the possibility of designing functional materials where specific, macroscopic dynamical responses are engineered into a system to create function. In the case of thermotropic liquid crystals, recent work has shown that through the application of external fields it is possible to generate structures such as skyrmions and solitons that have generated considerable interest. This presentation will summarize recent advances in this area, and discuss emerging opportunities to harness the formation and motion of solitons for a variety of applications.

Sports occupy an important part of our lives. It is often difficult to flip through the TV channels without encountering sports shows. Surprisingly, a large fraction of the intriguing and often spectacular sports actions and feats can be explained using relatively basic physics concepts. In this talk I will present and discuss the physics behind some remarkably creative innovations in popular sports (baseball, soccer/football, volleyball, basketball, high Jump, gymnastics and swimming) using basic concepts in classical physics. The talk will feature exquisite and exclusive videos created by the New York Times graphics/multimedia team for sports that capture innovative feats of athletes like Simone Biles. The main part of this presentation was initially created in collaboration with Bedel Saget, a New York Times graphics/multimedia editor for sports. Bedel Saget received a 2nd place award for his team's work, titled, "The Fine Line: Simone Biles Gymnastics" at the prestigious 2017 World Press Photo Digital Storytelling contest in the Immersive Storytelling category.

Apologies for the grandiose title, but I’m presenting an approach to gene delivery and immunotherapy that is based on the physics of self-assembly of virus-like particles. By gene delivery I mean the in vivo delivery of genes in messengerRNA (mRNA) form, to targeted cells; and by immunotherapy I mean the in vivo transformation of immune cells – either antigen-presenting cells for vaccination, or killer-T cells for clearing virus-infected or cancerous cells. The virus-like particles are each nothing more than a single mRNA molecule packaged inside an icosahedrally-symmetric protein shell, with or without a lipid bilayer envelope containing a second shell of icosahedrally-ordered proteins. These particles are either synthesized in vitro from purified RNA and protein components, or in cellulo; they are functionalized with antibodies targeting them to specific cells; and they are thermodynamically stable and resistant to nuclease digestion of their mRNA content. Because they contain therapeutic mRNA rather than a viral genome, they are not infectious. But in essentially every other way they resemble – in structure and in gene-delivery function – the highly-evolved virus particles on which their design is modeled. Indeed, our aim is to learn from a billion years of evolution about how viruses have perfected the art of protecting their genes and targeting them to the right cells.