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Science and Mathematics

Dynamic and Rheology of Soft Complex Interfaces and 2D Membranes

March 10, 2020 at 3:30pm5:00pm

Physics Building, 202 / 204

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The Department of Physics is pleased to welcome Dr. Mehdi Molaei for their weekly colloquium. Dr. Molaei is a Postdoctoral Research Associate at University of Pennsylvania. This speaker is a candidate for a faculty position in the Department of Physics, part of the cluster hiring initiative in the BioInspired Institute.

Abstract: Soft interfaces and membranes control many biological processes. They form the complex membranes of living cells, and they are hot spots to adsorb biomolecules and active colloids. In the first part of my talk, I discuss how we characterize the dynamics and mechanics of a 2-d model lipid membrane and the complex plasma membrane of liver cells. The plasma membrane displays time-dependent undulations, which are controlled by its bending modulus, excess area, and membrane tension. Together, these physical characteristics couple to and modulate vesicle trafficking, membrane adhesion, and actin-based motility. While the complex physics of lipid membranes is relatively well understood in reconstituted form, the understanding of the dynamics and mechanics of plasma membranes in living cells remains at an early stage. We have developed a new nanoscale rheology approach, based on angle resolved dark field microscopy, to probe interfacial rheology, tension, and curvature fluctuation of the plasma membrane. The goal of this study is to develop a high throughput assay for identification of cancer cells. In the second part of my talk, I present the new approach to study the mechanics of complex fluid interfaces. Adsorbed surfactant, proteins, and macromolecules on interfaces form thin layers with complex structures and with wide range of viscoelasticities. We have developed a new approach for manipulating fluid interfacial systems that enables simultaneous tensiometry to measure surface pressure and high-performance interfacial shear microrheology. We study an adsorbed layer of protein on the  air-water interfaces as a model system. The power law frequency dependent complex shear modulus at high surface pressure reveals the soft glassy response of protein-laden interfaces. To understand complex flow fields established on fluid interfaces, which depend on interface viscoelasticity, (in)compressibility, and hydrodynamic coupling with bulk fluids, we measure displacement fields induced by the thermal motion of passive particles in interfacial films

This event was first published on January 27, 2020 and last updated on January 28, 2020.


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