Events
The following are events associated with or of interest to the Center for Computation and Theory of Soft Materials community.
UPCOMING Events
Inviting “time” to non-equilibrium thermodynamics:Universal Laws and Design Principles
Zhiyue Lu, Assistant Professor of Chemistry, University of North Carolina Chapel Hill
Thursday, October 24th, 2024
4:00 - 5:00 PM
Ryan Hall, Room 4003
Host: Todd Gingrich
Event Co-hosted with the Department of Chemistry
Living systems behave differently from inert materials, challenging traditional chemical theories. The Lu group at UNC is developing a time-dependent non-equilibrium framework to bridge this gap, connecting non-equilibrium thermodynamics with complex systems. This talk introduces universal laws governing chemical and biological systems far from equilibrium, presenting geometric design principles for time-domain activated catalytic reactions. We reveal how certain catalysts or reaction networks can perform counter-intuitive tasks under dynamically changing environments, impossible in steady states. Extending to arbitrary dynamics, we present universal non-equilibrium response relations beyond linear response theory. This theoretical foundation offers new approaches to understanding and manipulating complex living systems and life-like matter. By integrating time-dependent thermodynamics with chemical complexity, we aim to provide a unified framework for understanding and engineering life-like performances in artificial synthetic materials, potentially revolutionizing fields from medicine to materials science.
Biographical Information
Dr. Zhiyue Lu is an Assistant Professor in the Department of Chemistry at the University of North Carolina, Chapel Hill. He completed his Ph.D. in Chemical Physics at the University of Maryland at College Park in 2016. Dr. Lu served as a postdoctoral scholar at the James Franck Institute at the University of Chicago in the Physical Sciences Division before joining the faculty at the University of North Carolina in 2019.
Past Events
Stretching Polymers: from Hydrogels to Genome
Aykut Erbas, Assistant Professor, National Nanotechnology Research Center & Materials Science Graduate Program, UNAM - Bilkent University
March 1st, 2024
Polymers are ubiquitous, providing practically unlimited industrial applications in the age of plastic, organizing information in a highly functional and complex way in biological systems, as seen in the case of genome and proteins. Due to their complex chemical structure and stimuli-response properties, they can also provide many opportunities for the components required for functional biomimetic material systems, such as artificial muscles or skin. Yet, in most cases of interest, polymers are under external forces, either electrical or mechanical, which renders their equilibrium description relatively invalid. This issue becomes more evident when we consider using them as components in soft biomechanics or trying to correlate mechanobiological aspects of epigenetic regulation in mammalian cell nuclei, which confine one of the longest polymers in our body (DNA). In my talk, I will briefly discuss how forces acting on charged-polymer networks and genomes exhibit rich physical phenomena, many of which cannot be described by mean-field level equilibrium theories. Importantly, these results can inspire the development of new materials or diagnostic systems while offering new research questions on a fundamental level.
Biographical Information
Dr. Aykut Erbas completed his Ph.D. studies at the Technical University Munich (TUM) - Germany. Later, he moved to the Chemistry Department at the University of North Carolina - Chapel Hill to research polymer dynamics. Between 2014-18, Dr. Erbas was a research fellow at the Material Science & Engineering Department and later at the Department of Biomolecular Sciences at Northwestern University under various centers dedicated to designing Bio-inspired Energy Systems. Dr. Erbas has been working on polymer physics and chemistry, spanning a wide range of time and length scales, including polyelectrolytes, hydrogels, ionic liquids, and amphiphilic molecular systems, in collaboration with various experimental and theoretical groups. Dr. Erbas’ recent studies also include DNA-protein interactions and in vivo chromatin conformation in health and disease. Since September 2018, he has been an assistant professor at Bilkent University, Turkey.
Nonequilibrium Thermodynamics of Complex Systems
Massimiliano Esposito, Professor of Theoretical Physics, Department of Physics and Materials Science, University of Luxembourg
Host: Todd Gingrich
February 28th, 2024
I will demonstrate how recent advancements in nonequilibrium thermodynamics can effectively characterize the energetics of a broad spectrum of complex systems. The methodology involves examining the macroscopic behavior of systems governed by thermodynamically consistent stochastic dynamics, such as chemical reaction networks, nonlinear electric circuits, and Potts models. I will explore the novel fundamental insights derived from this approach, along with its practical applications in analyzing the energetics of phenomena like synchronization, active phase separation, and energy transduction within chemical reaction networks.
References:
[1] G. Falasco and M. Esposito, "Macroscopic Stochastic Thermodynamics", arXiv:2307.12406.
[2] N. Freitas and M. Esposito, "Emergent second law for non-equilibrium steady states", arXiv:2109.04906.
[3] J. Meibohm and M. Esposito, "Minimum-dissipation principle for synchronised stochastic oscillators far from equilibrium", arXiv:2401.14982.
[4] T. Aslyamov, F. Avanzini, E. Fodor and M. Esposito, "Non-ideal reaction-diffusion systems: Multiple routes to instability", Phys. Rev. Lett. 131, 138301 (2023)
[5] F. Avanzini, N. Freitas and M. Esposito, "Circuit Theory for Chemical Reaction Networks", Phys. Rev. X 13, 021041 (2023).
Biographical Information
Prof. Dr. Esposito studied Chemistry and obtained his PhD in Physics in 2004 at Université Libre de Bruxelles (ULB) in Belgium. After two postdocs in California at UC Irvine and UC San Diego, he came back as a contract researcher for two years at ULB. In 2012 he was awarded a five year Attract Fellowship by the National Research Fund of Luxembourg to start his own research group "Complex Systems and Statistical Mechanics" in the Physics and Materials Science Research Unit at the University of Luxembourg. In 2016 he became Professor of Theoretical Physics and was awarded a five years Consolidator Grant by the European Research Council. He is currently a member of the editorial board of Physical Review Letters.
CCTSM Distinguished Lecture: The Physics of Active Matter
M. Cristina Marchetti, Distinguished Professor of Physics, University of California Santa Barbara
Host: Michelle Driscoll
May 19th, 2023
Watch the Seminar (Northwestern Credentials Required)
Birds flock, bees swarm and fish school. These are just some of the remarkable examples of collective behavior found in nature. Physicists have been able to capture some of this behavior by modeling organisms as "flying spins’’ that align with their neighbors according to simple but noisy rules. Successes like these have spawned a field devoted to the physics of active matter – matter made not of atom and molecules but of entities that consume energy to generate their own motion and forces. Through interactions, collectives of such active particles organize in emergent structures on scales much larger than that of the individuals. There are many examples of this spontaneous organization in both the living and non-living worlds: motor proteins orchestrate the organization of genetic material inside cells, swarming bacteria self-organize into biofilms, epithelial cells migrate collectively to fill in wounds, engineered microswimmers self-assemble to form smart materials. In this lecture I will introduce the field of active matter and highlight ongoing efforts by physicists, biologists, engineers and mathematicians to model the complex behavior of these systems, with the goal of identifying universal principles.
Biographical Information
Cristina Marchetti is a Distinguished Professor of Physics at the University of California Santa Barbara. She was educated in Italy at the University of Pavia, earned her Ph.D. in the U.S. at the University of Florida, and joined the faculty at UC Santa Barbara in 2018, after thirty years on the faculty at Syracuse University. Marchetti is a theoretical physicist who has worked on a broad range of problems in condensed matter physics, including supercooled fluids, superconductors and driven disordered systems. Currently, she is interested in understanding the emergent behavior of active matter. The name refers to large collections of self-driven agents that exhibit organized behaviors on scales much larger than that of the individuals. Examples range from the flocking of birds to the sorting and organization of cells in morphogenesis, and include synthetic analogues, such as active colloids and engineered microswimmers. Marchetti is currently co-lead editor of the Annual Reviews of Condensed Matter Physics. She is a Fellow of the American Physical Society and of the American Association for the Advancement of Science, and a member of the American Academy of Arts and Sciences and of the US National Academy of Sciences. In 2019 she was awarded the inaugural Leo P. Kadanoff prize by the American Physical Society.
Animating soft materials using molecular programs
REBECCA SCHULMAN, Associate Professor, Dept of Chemical and Biomolecular Engineering, Johns Hopkins University
Materials Science and Engineering Department Fine Lecture
Host: Monica Olvera de la Cruz
Tuesday, October 4th, 2022
Abstract:
Complex cellular behaviors such as motion and division are directed by far-from-equilibrium chemical networks that regulate the assembly and reconfiguration of a cell’s architecture at the molecular scale. We have been asking how one can program the evolution of synthetic materials using designed chemical networks analogous to the biological networks that regulate cell and tissue architecture. In these systems, the dynamical evolution of molecular programs, or reaction processes, drive the evolution of the environment where materials assembly and act. This work thus amounts to controlling the pathways of assembly and reconfiguration. Molecular programs can comprise tens of species whose interactions are kinetically controlled, providing many new levers for controlling material formation and metamorphosis. These methods are thus promising routes toward building radically new materials that could grow into specific shapes, heal, or adapt to their environments. I will describe our recent work focused on controlling the dynamic assembly and shape change of biomolecular materials such as hydrogels and semiflexible polymer networks. Different biomolecular signals can induce different dynamic polymerization and depolymerization processes in these materials and how chemical networks can be coupled to these materials to induce dynamic material behavior. To understand what new behaviors can arise in these systems when the chemical networks that regulate them become large and complex, we have recently developed integrated synthetic in vitro genetic regulatory networks consisting of oligonucleotide templates, T7 RNA polymerase and an RNase. These networks can consist of tens of different interconnected network elements, making it possible to construct synthetic regulatory networks of complexities comparable to those of simple viruses, enabling stepwise, multifaceted regulation of materials and chemistry.
Bio:
Rebecca Schulman is an associate professor in the Departments of Chemical and Biomolecular Engineering, Chemistry and Computer Science and a member of the Institute for Nanobiotechnology, the Hopkins Extreme Materials Institute, the Chemistry-Biology Interface Program, the Center for Cell Dynamics and the Laboratory for Computational Sensing and Robotics at The Johns Hopkins University. She develops intelligent and adaptive biomolecular materials and nanostructures by combining ideas from materials science, circuit design and cell-free synthetic biology. Her work uses techniques from biophysics, biomolecular design, systems design and machine learning. Dr. Schulman joined JHU after working as a Miller Postdoctoral Fellowship in physics at UC Berkeley. She received undergraduate degrees in mathematics and computer science from MIT and a Ph.D. from the California Institute of Technology in computation and neural systems. She is the recipient of a Hartwell Individual Biomolecular Research Award, a President’s Early Career Award in Science and Engineering (PECASE), a DARPA Young Faculty Award and Directors Fellowship, an NSF Career Award, a Turing Scholar Award and a DOE Early Career Award and is currently the co-Director of the Passport to Future Technology Leadership program for Ph.D. students at Johns Hopkins.
Nonequilibrium Interaction between Catalytic Colloids
YITZHAK RABIN, Professor Emeritus, Dept of Physics and Institute of Nantechnology and Advanced Materials, Bar-Ilan University
JULY 22, 2022
Abstract:
Spherical colloids that catalyze the interconversion reaction between solute molecules A and B whose concentration at infinity is maintained away from equilibrium, interact due to the nonuniform fields of solute concentrations. We show that this long range 1/r interaction is suppressed via a mechanism that is superficially reminiscent but qualitatively very different from electrostatic screening: catalytic activity drives the concentrations of solute molecules towards their equilibrium values and reduces the chemical imbalance that drives the interaction between the colloids. The imposed nonequilibrium boundary conditions give rise to a variety of geometry-dependent scenarios; while long range interactions are suppressed (except for a finite penetration depth) in the bulk of the colloid solution in 3D, they can persist in quasi-2D geometry in which the colloids but not the solutes are confined to a surface, resulting in the formation of clusters or Wigner crystals, depending on the sign of the interaction between colloids.
Bio:
Current research interests: Biophysics, Soft Matter, Non-Equilibrium Physics
PhD in Chemistry (Quantum Optics), Tel Aviv University, 1980
Positions: MPI for Quantum Optics (Garching), UCLA (Los Angeles), La Jolla Institute (La Jolla), Weizmann Institute (Rehovot), Bar-Ilan University (Ramat-Gan)
Visiting Professor:
1988: College de France, ESPCI
1989, 2011: KITP Santa Barbara
1990, 2009-2011: University of Chicago
1990-1991: Materials, UC Santa Barbara
1993: Yukawa Inst, Kyoto University
1995-1998, 2002, 2009: Physics and Biology, Rockefeller University
1997: Curie Institute
2003-2004: Rowland Inst, Harvard
2005: Chemistry, Harvard
2009, 2013, 2015: Soft Matter Physics, NYU
2009-2011: Biomedical Engineering, Northwestern University
2017: Physics, NYU Shanghai
Life in a Tight Spot: How Bacteria Swim, Disperse, and Grow in Crowded Spaces
Sujit S. Datta, Princeton University, Department of Chemical and Biological Engineering
JANUARY 31st, 2022
This is a joint seminar offered in partnership with the Department of Engineering Sciences and Applied Mathematics
Abstract:
Bacterial motility and growth play central roles in agriculture, the environment, and medicine. While bacterial behavior is typically studied in bulk liquid or on flat surfaces, many bacterial habitats—e.g., soils, sediments, and biological gels/tissues—are complex and crowded spaces. In this talk, I will describe my group's work using tools from soft matter physics to address this gap in knowledge. In particular, using studies of E. coli in transparent 3D porous media, we demonstrate how confinement in a crowded medium fundamentally alters bacterial behavior. In particular, we show how the paradigm of run-and-tumble motility is dramatically altered by pore-scale confinement, both for cells performing undirected motion and those performing chemotaxis, directed motion in response to a chemical stimulus. Our porous media also enable precisely structured multi-cellular communities to be 3D printed. Using this capability, we show how spatial variations in the ability of cells to perform chemotaxis enable populations to autonomously stabilize large-scale perturbations in their overall morphology. Finally, we show how when the pores are small enough to prevent cells from swimming through the pore space, expansion of a community via cellular growth and division gives rise to distinct, highly-complex, large-scale community morphologies. Together, our work thus reveals new principles to predict and control the organization of bacteria, and active matter in general, in complex and crowded environments.
Bio:
Sujit S. Datta earned his M.S. from the University of Pennslyvania, and his Ph.D. from Harvard University, both in Physics. He is now an Assistant Professor of Chemical and Biological Engineering at Princeton University, where he studies celluar and tissue engineering, complex materials and processing, and energy and environment.
Thermodynamics of chiral active fluids
Ming Han, University of Chicago, Chicago Materials Research Center
Tuesday, JANUARY 25th, 2022
Abstract:
Active materials are characterized by continuous injection of energy at the microscopic level and typically cannot be adequately described by equilibrium thermodynamics. In this talk, I will show how thermodynamics emerges far from equilibrium using, as a case study, an active fluid composed of self-spinning particles. A single effective temperature generated by active rotation of the particles parameterizes both the equation of state and the emergent Boltzmann statistics. The same effective temperature, renormalized by velocity correlations, relates viscosities to steady-state stress fluctuations via a Green-Kubo relation. These equilibrium-like behaviors at both the single-particle and hydrodynamic level can be backed up by a fluctuating hydrodynamic theory derived from first principle. In fact, similar effective thermodynamics can exist in a class of active fluids such as oscillating granular gases and active Brownian rollers, as long as the fluctuating and activated degrees of freedom in the system are statistically decoupled.
Bio:
Ming Han did his Ph.D. in Applied Physics at Northwestern University, working with Prof. Erik Luijten. A major theme of his research is the study of nonequilibrium soft materials by combining statistical mechanics and particle-based simulations. Now, he is a Kadanoff-Rice postdoctoral fellow at the University of Chicago. There, he is working on analytical theories of active matter with Prof. Vincenzo Vitelli and meanwhile developing machine-learning methodologies for polymer informatics with Prof. Juan de Pablo.
The interplay of geometry and kinetics in chemical transformations of nanocrystals
Layne Frechette, National Institute of Health
Tuesday, JANUARY 11th, 2022
Abstract:
Post-synthetic modification is a promising avenue for chemists to tailor the properties of nanocrystals and to guide their assembly into functional materials. Yet, tuning such properties as nanocrystal shape and composition is often difficult because procedures for doing so take place far from equilibrium. In this talk, I will discuss the progress we have made in understanding two such processes using theory and computer simulation: (i) chemical etching, which produces concentration-dependent transformations of nanocrystal shape, and (ii) cation exchange, in which spontaneous swapping of ions of different identities effects compositional change. In both cases, geometry plays a key role in determining the outcomes of these nonequilibrium transformations.
Bio:
Layne received his Ph.D. in chemistry from UC Berkeley in 2020. There, working with Prof. Phill Geissler, he used statistical mechanics and computer simulation to study chemical transformations of nanocrystals. He is currently a postdoctoral fellow with Dr. Robert Best at NIH, where he is using coevolutionary models to study fold-switching proteins. His research interests are in understanding the assembly, organization, and dynamics of materials.
Building kinetic models for complex systems with arbitrarily long memories
Sun-Ting Tsai, University of Maryland, Department of Physics
Friday, DECEMBER 17th, 2021
Abstract:
Molecular Dynamics (MD) simulations are now broadly accepted as a useful tool to model and predict complicated chemical, material, and biological processes. Unfortunately, many important phenomena such as drug unbinding or crystal nucleation happen at the timescale of minutes or even hours and so are rarely observed in MD due to MD’s timescale limitation of milliseconds. Therefore, many enhanced sampling methods such as metadynamics have been developed to help sampling such rare events. However, it is still challenging to understand kinetics and mechanisms of rare events, as opposed to just static free energies. In this talk, I will show how we have used notions of path entropy (Maximum Caliber) and recurrent neural networks to both enhance MD and also interpret dynamical trajectories, from MD or from experiments, with minimum prior bias. On that basis, we can then build kinetically truthful models for rare events in biology and materials sciences using these reaction coordinates which have the minimally sufficient dimensionality. The insights possible due to these methods include quantifying the role of shape and entropy in nucleation processes, and how small biomolecules fluctuate.
Bio:
Sun-Ting Tsai is PhD candidate in Physics at the University of Maryland, College Park working in the group of Professor Pratyush Tiwary. Prior to this he obtained his BS and MS degrees in Physics from the National Tsing Hua University in Taiwan. His PhD work involves developing and applying computational and theoretical tools to understand the behavior of complex systems with arbitrary memories and interactions. To solve these problems, he has integrated ideas from enhanced sampling, statistical mechanics, and artificial intelligence to develop robust open-source software that can then be used by the broad scientific community. His work has been published in high-impact journals including Nature Communications which highlighted his work as Editors’ choice in two different categories (applied physics and AI).
Polarization of interfacial water
Dmitry Matyushov, Arizona State University, Chemistry and Physics
Friday, NOVEMBER 19th, 2021
Abstract:
Much of chemistry and all molecular biology involve polarized interfacial water. The question that puzzled generations of scientists is how to characterize the interfacial polarization and whether one can come up with simple parameters and functions similar to the dielectric constant of bulk dielectrics. This question is still far from fully resolved, but a recent joint push by computations and experiment has allowed to produce initial insights into an effective dielectric susceptibility of water in the interface. This talk is about the twisted history of the subject, recent progress in the field, and potential consequences of recent findings for solvation and screening of charge in water.
Bio:
Dmitry Matyushov received MS in Chemical Physics from Moscow Institute for Physics and technology and PhD in Theoretical Physics from Kiev State University. He was a Lise Meitner fellow and an invited Professor in Vienna University of Technology and joined Arizona State University in 2000, where he is now a Professor of Chemistry and Physics. His research has focused on charge transfer in chemistry and biology, solvation, and properties of polar liquids, interfaces, and dielectrics.
Physical Mechanisms of Cell Membrane Organization and Shape Deformations
Ahis Shrestha, University of Southern California, Physics and Astronomy
Tuesday, NOVEMBER 16th, 2021
Abstract:
Cell membranes show an intricate organization of lipids and membrane proteins into domains with distinct composition and hydrophobic thickness. Such a spatial organization of cell membranes is thought to be essential for many physiological functions. In the first part of my talk, I will be focusing on local lipid-protein organization and regulation through membrane thickness deformation. Using mechanosensitive ion channels as a model system, we employ the elasticity theory of protein-induced bilayer thickness deformation together with the Landau-Ginzburg theory of lipid domain formation to quantify the energetics of local lipid-protein organization in a heterogeneous lipid bilayer. We show that protein-induced lipid bilayer thickness deformations yield local organization of lipids and membrane proteins according to their preferred hydrophobic thickness, and couple the conformational states of membrane proteins to the local membrane composition. Our work suggests that protein-induced lipid bilayer thickness deformations endow proteins in cell membranes with diverse and controlled mechanical environments that, in turn, allow targeted regulation of membrane proteins.
In the second part of my talk, I will be focusing on the mechanics of caveolae, which are membrane invaginations of size ~ 100 nm found in many mammalian cell types. Caveolae alter their shape in response to changes in membrane tension and are thought to have important biological roles in membrane area and membrane tension homeostasis, mechanotransduction, and signaling. Super-resolution light microscopy and electron microscopy have revealed that caveolae can take a variety of cup-like shapes. We show that the competition between membrane tension and membrane bending yields caveolae with cup-like shapes similar to those observed experimentally. We find that the caveola shape and its sensitivity to changes in membrane tension can depend strongly on the caveola spontaneous curvature and on the size of caveola domains. Our work suggest that heterogeneity in caveola shape produces a staggered response of caveolae to mechanical perturbations of the cell membrane, which may facilitate regulation of membrane tension over the wide range of scales thought to be relevant for cell membranes.
Bio:
Ahis Shrestha is currently a PhD student in the Department of Physics and Astronomy at the University of Southern California, working with Prof. Christoph Haselwandter. Ahis’s PhD thesis focuses on the theoretical physics of cell membrane organization and shape deformations, and their physiological roles in the regulation of membrane protein function and membrane tension. Ahis received his B. S. in physics from the University of California, Los Angeles. Ahis is fascinated by emergent phenomenona at the interface of physics, chemistry, and biology. Ahis has worked on research topics connected to membrane mechanics, mechanochemical lipid-protein organization in cell membranes, the locomotion and neural activity of C. elegans, the electrostatics of charged nanoparticles, and the electric double layer in ionic mixtures.
Mechanics and Dynamics in Soft Matter Systems: From Microscopy to Bulk Phenomena Across Multiple Time Scales
Shih-Yuan Chen, North Carolina State University
October 12th, 2021
Abstract:
Soft matter systems encompass a wide variety of materials, which can often be understood by considering universal properties. In this talk, I will present two projects illustrating how I approach two univeral properties. The first project aimes to differentiate phenomena at particular time schales and develop a general model covering all pheonomena. The second project connects the macroscopic phenomena and teh microstructure in a soft matter system.
The first project focus on elastocapillary partial wetting. I demonstrate how we approach this system via an experiment involving elastocapillarity, viscoelasticity, and swelling. We successfully build a model which describes our experimental measurements of gel deformation under equilibrium conditions. Using these results, I designed a dynamic quasi-static experiment that captures glycerol droplet motion at ultra-slow velocities of microns/hr. This work is a potential candidate to bridge statics and dynamics in elastocapillary research.
In the second project, I will discuss an active granular system, grain mixtures containing living larvae. Microscopically, our group finds that the wiggling larvae introduce particle-scale fluctuations to the mixture, which become faster with more larvae. Macroscopically, we find that the pile flow induced by gravity depends on the larvae fraction, the grain type, and the force between the grain particles. Importantly, we observe that the flow rate is faster with a higher larvae fraction, indicating that the fluctuations cause the pile to flow more easily. This work additionally serves as a motivation for my work here at Northwestern, which will explore trainable materials.
Bio:
Shih-Yuan Chen received his Ph.D. in Dr. Karen Daniels’ lab at North Carolina State University, working on elastocapillarity and active matter. His current project focuses on synthesizing tunable materials using colloids and polymers.
Biocompatible magnetic pathwas for the eradication of malignant cells
Eleftherios Kirkinis
August 23rd, 2021
Abstract:
Societal repercussions, the immense effort expended by researchers and the monetary expenditure invested by worldwide institutions designate cancer as primus inter pares of noncommunicable diseases. In our efforts to eradicate malignant cells we will employ the unique characteristics of magnetism connecting seemingly disparate areas. Three principal directions, through the actuation of magnetic nanoparticles, are identified here: 1. Eradication of malignant cells by liquid viscosity-induced heating (to be raised at the therapeutic temperature of 42-43 degrees Celsius); 2. Tumor stress alleviation (to open up blood vessels enhancing delivery of chemotherapeutic agents), and 3. Propel micro and nanorobot structures (chiral swimmers, surface walkers, flexible swimmers and magnetic nanocapsules) to enhance targeting.
In this talk I will discuss open questions raised by experimental results and clinical observations in these three respective areas. I will then describe the results of our theoretical models advancing our understanding in magnetism-mediated therapies. This includes heating from antisymmetric stresses in the Navier-Stokes equiations switched on by AC magnetic fields and teh magnetic torque-induced migration of droplets.
Bio:
Eleftherios Kirkinis holds advanced degrees in applied mathematics & theoretical physics from the University of Cambridge, England and the University of Washington, Seattle. Most recently, he was awarded a multidisciplinary degree in Ethics, Philosophy and History. He has carried-out research at Northwestern University and Imperial College London and transferred teaching skills in Australia. His interests are in complex fluids and soft matter.
On blood and brain pieces. Origin of low frequency relaxation processes in biological tissues
Francisco J. Solis, Arizona State University
August 10th, 2021
Abstract:
Understanding the response of biological tissues to external electrical stimuli is crucial for the development of technologies such as brain-machine interfaces. The response of macroscopic homogeneous bulk tissue to oscillating electric fields can be characterized by an effective frequency-dependent complex conductivity σ. This conductivity is usually expressed as a sum of Debye-type contributions σ ∼ ( ω -iωα ) -1 with a characteristic frequency ωα . The contributions with lowest frequencies, below 105 Hz, are said to belong to the α -dispersion regime. The origin of this low-frequency behavior is not well understood. This talk will discuss a mechanism for the generation of low characteristic frequencies: the confinement of electrolytes by dielectric walls. For a precise description of these results this talk will discuss the proper definition of macroscopically observed currents. These must contain not only contributions from ionic and electronic motion but also from displacement currents that consist of pure electromagnetic fields. The framework developed allows for qualitative explanations of several important aspects of low-frequency conductivity: justification for the range of observed values of the α – dispersion frequency, an explanation for the high-values of relative permittivity, an explicit description of the Maxwell-Wagner effect, a mechanism for the appearance of anisotropic conductivity, a rationale for the lack of α-relaxation in pure blood and the proper description of effective macroscopic models of brain conduction.
Bio:
Francisco J. Solis is associate professor at the School of Mathematical and Natural Sciences of Arizona State University. His research focuses on the properties of charged interfaces and molecular systems that play a role in synthetic and biological processes.
Understanding Origin of Membrane Morphological Transformations: Modelling of Membrane Budding and Fission
Rikhia Ghosh, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
May 11th, 2021
Abstract:
Owing to their fluid-like behaviour, biomembranes are able to transform into a fascinating variety ofmorphologies. These morphological transformations are essential prerequisites for fundamental biological processes, such as, cell division, membrane trafficking, endo- and exocytosis to name a few. An important intermediate step of these biological processes is budding of the membrane in which the membrane
In the first part of my talk, I will describe modelling of membrane morphological transformation by controlling transbilayer asymmetry. Small changes in the lipid distribution between the two leaflets of the membrane generate different mechanical tensions in them which in turn determine the preferred morphology the membrane would like to acquire. In the second part, I would talk about recent development in our model to explore membrane fission by controlling concentration of solute and quality of the solvent. Examples of such solutes are metal ions which adsorb on both charged and neutral membranes, small sugar molecules, short PEG chains. Our simulations reveal a fundamental and non-trivial mechanism of membrane fission arising from an interplay between membrane elasticity and solute mediated membrane adhesion. As a future outlook, I would discuss how our coarse-grained model of membrane can be further incorporated to understand cellular remodelling during endo- and exocytosis. forms two sub-compartments connected by a narrow membrane neck. Subsequently, the neck is often cleaved by membrane fission which leads to division of the corresponding cell or organelle and formation of two separate membrane compartments. Due to the inherent complexity of these cellular processes, it often remains unclear what drives formation of such unique membrane morphologies and the associated events.
Bio:
Dr. Ghosh is currently working as a postdoctoral associate at Max Planck Institute of Colloids and Interfaces in Potsdam, Germany. She received her masters degree in chemistry from Calcutta University with specialisation in physical chemistry. She received PhD from Indian Institute of Science in 2016 followed by which she moved to Potsdam. As a postdoc at Max Planck Institute of Colloids and Interfaces, she has been working on modelling of membrane polymorphism and possible mechanisms of membrane trafficking. Dr. Ghosh has co-authored 13 peer-reviewed publications so far. Her current research interest is to develop collective understanding of physical mechanisms underlying biophysical nano-devices that control and navigate the stream of complex active networks, using approaches from chemical physics and soft matter.
Supramolecular Assembly:
How Does Local Packing of Identical Molecules Select Equilibrium Complex Crystals?
Abhiram Reddy, University of Massachusetts, Amherst, Polymer Science & Engineering
March 8, 2021
Abstract:
Connecting molecular design to nanostructure formation is one of the grand challenges of material science research in recent times. For a variety of soft matter systems it has been established that hierarchical self-assembly of these macromolecules as a result of microphase separation leads to ordered morphologies with varying symmetry. In this talk, I will focus on double gyroid(DG) morphology which is a composite crystal made up of two non-intersecting triply periodic chiral channels and a matrix phase. Formation of DG in self-assembled block copolymer(BCP) melts, along with understanding molecular-scale mechanisms behind its equilibrium selection, has been a topic of longstanding interest in polymer physics. In this talk, I will revisit equilibrium DG using a geometric theory for block copolymers which is valid in an asymptotic limit of conventional mean field theory used to model this many body problem and study equilibrium phase behavior. I will introduce a new variational method based on tessellations using medial set construction to compute space filling optimal chain packing within DG and show that our approach qualitatively alters the equilibrium phase diagram. Our medial model can also be extended to morphologies beyond networks and is easily adaptable to study packing frustration using simulation or experimental data thereby providing valuable insights to engineer molecular design to target yet unrealized novel self-assembled BCP morphologies.Bio:
Abhiram Reddy is currently a graduate student in the department of Polymer Science & Engineering at University of Massachusetts, Amherst. He is working with Prof. Gregory Grason on his dissertation centered around self-assembly of block copolymers into complex crystals. He has an undergraduate degree in Physics from National Institute of Science Education and Research, Bhubaneswar in India.
Modeling Dynamics of Confined Hydrogels: Focus on Pattern Formation, Degradation and Erosion
Dr. Olga Kuksenok, Associate Professor, Materials Science and Engineering
Clemson University, Clemson, SC
March 3, 2021
Abstract:
Pattern formation and dynamic restructuring plays a critical role in a plethora of natural processes. Understanding and controlling pattern formation in synthetic materials is important for imparting a range of biomimetic functionalities. Further, degradation of polymer networks plays a vital role in applications ranging from regulating growth of complex tissues and neural networks to controlled drug delivery. I will focus on controlling dynamic restructuring in responsive hydrogels on two distinctly different length scales. On a continuum level, we use the three-dimensional gel Lattice Spring Model (gLSM), which allows us to focus on dynamics of pattern formation in mm-sized confined hydrogels under variations in external stimuli (temperature, light, mechanical forcing). We demonstrate dynamic restructuring of patterns under stretching and compression and characterize the hysteresis behavior. Our findings show that mechanical forcing can be harnessed to control the onset of pattern formation and hysteresis in gel-based systems.
In the second part of my talk, I will focus on the modeling of the photodegradation process of the confined hydrogel membrane on the mesoscale. Specifically, we develop a dissipative particle dynamics (DPD) approach that captures degradation and erosion in hydrogels. We focus on hydrogels formed by the end-linking of four-arm polyethylene glycol macromolecular precursors (tetra-PEG gels). We track the progress of the degradation via measuring the fraction of the degradable bonds intact, mass loss from the hydrogel films, and distributions of clusters formed during the degradation process. As the degradation proceeds, the hydrogel film undergoes reverse gelation. The reverse gel point calculated from simulations agrees well with the value obtained from the bond percolation theory. Our approach introduces first mesoscale framework capturing erosion and reverse gelation in degrading polymer networks.
Bio:
Dr. Kuksenok is currently an Associate Professor at the Materials Science and Engineering Department at Clemson University in Clemson, SC. Prior to joining Clemson University in 2015, she was appointed as a Research Associate Professor at the Chemical Engineering Department at the University of Pittsburgh, Pittsburgh, PA. Dr. Kuksenok received her PhD in Physics and Mathematics from the Institute of Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine, in 1997, then she was appointed as a research scientist in Theoretical Physics Department, Institute for Nuclear Research, Kiev, Ukraine, and as a postdoctoral research associate at the University of Pittsburgh. Dr. Kuksenok’s research interests and accomplishments span the following areas of computational materials science: elastodynamics of responsive polymer gels, dynamics of multi-component polymer blends, biomimetic and biological materials, pattern formation in non-equilibrium chemical systems, complex fluids dynamics, and theory of heterogeneous liquid crystalline systems. Dr. Kuksenok has co-authored over 90 peer-reviewed publications and 9 book chapters.
Dielectric Response of Confined Polar Liquids: From Atomistic to Continuum Modeling
Dr. Mohammad Hossein Motevaselian,
University of Illinois at Urbana-Champaign
February 17, 2021
Abstract:
Understanding the physics of the confined fluids and obtaining atomic-level insights into their unusual properties is essential to develop and design novel nanofluidic applications related to energy, water, and health. One of the most important properties of any polar liquid is the dielectric permittivity, as it affects the long-range electrostatic interactions. In this talk, molecular dynamics simulations, statistical-mechanical theories, and multiscale methods are adopted to unravel the effects of confinement on the dielectric response of polar liquids. Depending on the degree of confinement and different spatial directions (e.g., perpendicular, ε_⊥, or parallel, ε_∥, to a flat interface), polar liquids experience a universal reduction in the perpendicular permittivity, abnormally low out-of-plane screening ability and planar supper permittivity under extreme confinement of a few molecular diameters in width. Such effects have important consequences in developing accurate coarse-grained force fields, improving the solvent-implicit approaches often used in biology and continuum theories such as the Poisson-Boltzmann equation for accurate prediction of capacitance in the electric double-layer capacitors.
Bio:
Mohammad Hossein Motevaselian received his B.S. in mechanical engineering from University of Tehran in 2012, M.Sc. in mechanical engineering from University of Illinois at Urbana-Champaign in 2015 and Ph.D. in mechanical engineering from University of Illinois at Urbana-Champaign in 2020. His Ph.D. thesis was titled “Bridging the Gap Between Atomistic and Continuum Models to Predict Dielectric and Thermodynamic Properties of Confined Fluids” under the supervision of Dr. Narayana Aluru. His research activity is focused on developing multiscale methods using coarse-graining techniques, statistical mechanical theories, and atomistic simulations to develop force-fields and study the physics of interfacial molecular fluids, with the primary focus on the role of dielectric permittivity in altering the electrostatic interactions between charged species. Applications of his research include energy storage devices such as supercapacitors, ionic liquids, electrochemical reduction of carbon dioxide, ion transport across desalination membranes and biophysics.
Active particles with aligning interactions: aggregation vs. flocking
Dr. Demian Levis
Assistant Professor, Condensed Matter Physics
University of Barcelona, Spain
October 14, 2020
10: 00 - 11: 00 am CST
Abstract:
Unlike passive systems, active systems, made of interacting self-propelled particles, are driven out-of-equilibrium at the level of each constituent. As such, they exhibit rich and novel collective behaviours. In particular, activity may trigger clustering and phase separation in the absence of cohesive forces, or the spontaneous emergence of collective directed motion.
To gain an understanding of the general mechanisms underlying such phenomena, simplified model systems have been introduced and analyzed in-depth. Among them, the Active Brownian Particle (ABP) and Vicsek model has become paradigmatic systems to elucidate the role played by the nature (or symmetry) of the interactions between agents. ABP accounts for the competition between excluded volume interactions and self-propulsion, giving rise to the so-called Motility-Induced Phase Separation (MIPS), while the Vicsek model describes particles tending to align towards the mean direction of its neighbours, triggering a flocking phase transition.
Here I'll discuss the interplay between these different interaction's mechanisms: excluded volume and velocity alignment. I'll show how different kind of alignment affects the stability of the Motility-Induced Phase Separated state, and, conversely, the role played by steric effects in the emergence of coherently moving structures. If time allows I'll also mention how different self-propulsion strategies, in particular circle swimming, provide different routes to non-equilibrium pattern formation.
Bio:
Demian Levis earned a master's degree in Condensed Matter Physics in 2009 from the University of Orsay, France and a PhD in 2012 in Statistical Mechanics from the University of Pierre et Marie Curie, France. During his doctorate, under the supervision of Prof. L. Cugliandolo, he worked on the role played by hard constraints in the critical phenomena and out-of-equilibrium dynamics of a geometrically frustrated magnet, spin-ice. After that, he joined the group of Dr L. Berthier at the University of Montpellier 2, France where he started to work on active matter using simple particle models. In 2015 he obtained the Marie Curie Individual Fellow to continue studies in the collective behaviour of chiral active matter. Recently he has been appointed as Lecturer (Assistant Professor) Condensed Matter Physics Department at the University of Barcelona, Spain.
CCTSM Distinguished Lecturer Co-sponsored with CBES: Surprises in the Self-assembly of Particles in Spherical Confinement
Alfons van Blaaderen
Professor, Soft Condensed Matter
Debye Institute for Nanomaterials Science
Utrecht University
Monday, July 1, 2019
Abstract: About 6 years ago our group started research at developing methodologies to structure matter at multiple length scales by Self-Assembly (SA). Presently, we see the induced SA of particles inside slowly drying droplets dispersed in an emulsion system and the resulting supraparticles (SPs) as a powerful generally applicable methodology of hierarchical SA. We found that making the shape of the particles the dominant factor in the SA is the most versatile way to use this route also for complex particle shapes and mixtures of particles. One of our first findings by both experiments and computer simulations was that spherical particles self-assembled inside a spherical confinement do not have their equilibrium bulk face centered cubic, close packed, crystal arrangement, but instead adopt an icosahedral symmetry. In recent work, we have extended our results to include the effects of particles shape (e.g. using rounded cube shaped particles), rod-shaped particles, plate-shaped and binary particle systems. We will discuss how these changes affect the SA and how such SPs can be analyzed quantitatively on the single particle level in 3D by electron microscopy tomography. We will also show our first more applied work on creating SPs with tunable light emission.
Computer Simulations of Heterochromatin Segregation in Eukaryotic Cell Nucleus
Aykut Erbas
Assistant Professor, Material Science and Nanotechnology Program
Bilkent University, Ankara, Turkey
Wednesday, June 19, 2019Abstract:One of the unresolved puzzles in biological sciences is the 3D packing of the meters-long DNA molecule in the confinement of micron-scale cell nucleus while regulating fundamental cellular activities, from protein transcription to replication. Although the underlying 3D conformation of the genome is a complex phenomenon resulting from the dynamic interactions between nuclear proteins and negatively charged DNA, relatively simple computational models can guide us about the large-scale and long-time behavior of the nuclear ingredient. For instance, extensive computer simulations can provide an explanation of how changes in heterochromatin (a histone rich version of the chromosome) content of the nucleus can alter global nuclear organization. Similarly, the model system can allow us to manipulate the interactions between confining nuclear shell and chromatin, thus, help us elucidate the rules of genomic organization. Furthermore, activities of structural-maintenance-of-chromosomes proteins such as topoisomerase II can be considered by relaxing of certain topological constraints in computational models.
Biography: Dr. Aykut Erbas received his Ph.D. in Physics from Technical University Munich (TUM) - Germany in 2011. During his graduate studies, he worked on peptide-surface interactions, modeled single-molecule experiments. Later for his postdoctoral studies, he moved to the University of North Carolina - Chapel Hill, Chemistry Department, to focus on polymer dynamics. Between 2014 and 2018, he was a research fellow at Northwestern University, Material Science & Engineering Department and Biomolecular Sciences. Dr. Erbas has recently accepted a faculty position at Bilkent University, Material Science and Nanotechnology Program (UNAM) in Ankara-Turkey and explores complex phenomena in polymeric systems, including hydrogels, ionic liquids, and amphiphilic peptides and DNA-protein interactions.
Water At Nanoscale solid-liquid interfaces
Pietro Asinari
Professor, Energy Department and Director, Multiscale modeling Laboratory, Politecnico Di Torino, Italy
Wednesday, May 8, 2019
Abstract: In this talk, we will discuss three applications, where the behavior of water at nanoscale solid-liquid interfaces has a prominent significance to predict the performance of biomedical phenomena or to guide the rational design of engineering devices.
First, we use molecular dynamics simulations to compute the self-diffusion coefficient of water within na-nopores, around nanoparticles, carbon nanotubes and proteins. For almost 60 different cases, the diffusion coefficient is found to scale linearly with a dimensionless parameter, which represents the confinement degree of the water molecules [1]. Such relationship has accurately predicted the response of contrast agents for magnetic resonance imaging [1]. Later on, the Oak Ridge National Laboratory (ORNL) has validated experi-mentally and independently this relationship, beyond biomedical applications [2].
Second, experiments and atomistic simulations are used to elucidate the non-trivial interplay between na-nopore hydrophilicity and the overall water transport through zeolite crystals. A poor correspondence between the experiments and simulations has revealed the presence of a surface diffusion resistance at the interface between the zeolite porous matrix and water [3]. This suggests future experimental works to address these surface imperfections, as an essential prerequisite for improving water permeability of such membranes.
Finally, the complexity of water-solid interfaces is fully revealed by surfactants wrapping nanoparticle (NP) in aqueous solutions. Despite the large use of nanoparticle suspensions, tuning NP interactions and identifying desired NP assembly processes, in presence of surfactants, still represent a challenge for the design of nano-suspensions. We present a multiscale model for investigating nanoscale interfacial phenomena, stability, and aggregation of nanoparticles in aqueous solutions, including the dynamics of realistic surfactants [4]. The key idea is to combine the traditional DLVO (by Derjaguin-Landau-Verwey-Overbeek) theory with the kinetic theo-ry of aggregation. As a future perspective, we plan now to apply such approach for studying the aggregation of engineered nanomaterials and hence to get insights for their risk management (http://www.nanoinformatix.eu).
The Architecture of Biological Matter: Amino Acids, Proteins and Nucleic Acids
Jean-Louis Sikorav
High Council for Economy & Sorbonne Université
Tuesday, December 4, 2018
Abstract: DNA is the solution found by Nature for the storage and transmission of hereditary information. Why is DNA such as it is and not otherwise? This question will be addressed through a theoretical construction of the genetic material, using the language and the methods introduced in order to build the foundations of biology (1). The construction shows the necessity of molecular chirality for living processes; it establishes the unique and ideal character of DNA and improves our understanding of the structure of amino acids and proteins (2).
Linking the Colloidal Cluster Morphology With the Extended Law of Corresponding States
Nestor Valadez-Perez
Postdoc, Illinois Institute of Technology
Monday, November 26, 2018
Abstract: The clustering of spherical particles interacting with a short-range attraction has been extensively studied due to its relevance to many applications, such as the large-scale structure in amorphous materials, protein crystallization, aggregation and phase separation of protein inside cells, among others. The parameters that determine the interaction potential among particles affect the way they assemble and the morphology of clusters. It was widely accepted that the range of the attraction solely controls the fractal dimension of clusters, however recent experimental results challenged this concept by also showing the importance of the strength of attraction. In this talk it is presented a quick review of the applications of the extended law of corresponding states in colloidal systems, including the relation of local properties to this law. This physical escenario is confirmed with the reanalysis of experimental results on colloidal-polymer mixtures, previously reported in the literature.
Asymmetric Breathing Motions of Nucleosomal DNA and the Role of Histone Tails
Sharon M. Loverde
Associate Professor, Chemistry Department,
CUNY - Staten Island, New York
Wednesday, October 10, 2018
Abstract: Being the basic packaging unit of DNA, the nucleosome core particle (NCP) stabilizes as well as controls DNA accessibility during vital cellular processes. Recently reported structures of the NCP suggest that the histone octamer undergoes conformational changes during the process of DNA translocation (Bilokapic, Nature Communications, 2018). The mechanism of repositioning of the DNA around the histone octamer has been suggested to be sequence-dependent. Furthermore, the histone talks have been suggested to play a key role in this repositioning. We demonstrate with long-time all-atomistic molecular dynamics simulations (5 microseconds) that the histone tails do indeed play a critical role in nucleosome repositioning through formation of a loop of nucleosomal DNA around the histone core at high salt concentrations (2 M NaCl) (Chakraborty, Kang, and Loverde, in review).
Biography: Sharon M. Loverde, PhD, is an Associate Professor in the Chemistry department at College of Staten Island, a senior campus at the City University of New York (CUNY). She is also a faculty member of the Graduate Center of CUNY in the areas of Chemistry, Biochemistry, and Physics. Dr. Loverde’s research focuses on molecular dynamics simulations of soft and biological systems. In 2014, she received an ACS PRF New Investigator Award and in 2018 she received an NSF CAREER Award. Dr. Loverde was an NIH NRSA Postdoctoral Fellow who worked with Dennis E. Discher (UPenn) and Michael L. Klein (Temple). She received her PhD in Materials Science and Engineering from Northwestern University working with Monica Olvera de la Cruz.
Soft Matter Physics at the Nanoscale
John T. King
Center for Soft and Living Matter, Institute for Basic Science,
South Korea
Friday, September 28, 2018
Abstract: A significant challenge in experimental soft matter physics is overcoming the reliance on bulk-level measurements that average over spatial and temporal heterogeneities. Rapidly advancing microscopy and spectroscopy techniques, including super-resolution fluorescence microscopy, provide access to the spatial and temporal dimensions that often govern macroscopic structure and dynamics. In this talk, two examples will be discussed: 1) nanoscale molecular transport inside protein-DNA liquid-liquid phase separated droplets, and 2) interfacial dynamics of polymers at a non-adsorbing wall.
Biography: John King leads a group at the Institute for Basic Science, Center for Soft and Living Matter (S. Korea), which focuses on understanding how molecular and macromolecular structure and dynamics manifest in the bulk-level behavior of soft materials. He joined the Institute for Basic Science following a post-doc at the University of Illinois, Urbana-Champaign (2013-2016), where he worked on super-resolution microscopy and its application to polymer physics. He received a PhD in chemistry from the University of Michigan (2009-2013) studying ultrafast multidimensional spectroscopy of liquids.
Assembly engineering of soft-matter-based nanomaterials using molecular dynamics simulations
Vikram Jadhao
Professor, Intellegent Systems Engineering -
School of Informatics, Computing and Engineering at Indiana University, Bloomington
Abstract: Self-assembly is a common process in generating biological materials and provides inspiration for engineering synthetic materials with tailored structure and functionality. I will present results from coarse-grained molecular dynamics simulations of the self-assembly of soft-matter-based nanoparticles (NPs); these systems have important applications in nanomedicine and in the design of active functional materials. In the first part of this talk, I will discuss the results on the assembly of bacteriophage P22 virus-like particles (VLPs) into three-dimensional ordered array materials in the presence of oppositely-charged dendrimers via electrostatic control. Equilibrium structures (including VLP-bound dendrimer distributions) as a function of the ionic strength and VLP surface charge will be identified and correlated with experiments. I will then present results on controlling the shape of deformable nanocontainers via the modulation of surface design patterns and ionic environment, which show that surface tension modulates the relative favorability of oblate disk to prolate rod morphologies. Finally, I will present some preliminary results on the nanoscale self-assembly of deformable building blocks, in which we explore the self-assembly of Hepatitis B viral capsids based on a model involving soft capsomeres in order to understand the role of deformability in the capsid assembly and overgrowth.
Biography: Vikram Jadhao is an assistant professor in Intelligent Systems Engineering at the School of Informatics, Computing, and Engineering at Indiana University in Bloomington. Prior to joining IU, he held postdoctoral fellowships in the Department of Physics and Astronomy at Johns Hopkins University as well as the Department of Materials Science and Engineering at Northwestern University. He received his Ph.D. and M.S. in Physics from the University of Illinois at Urbana-Champaign, and his B.S. in Physics from the Indian Institute of Technology at Kharagpur. His current research interests are in soft materials, self-assembled nanostructures, bio-inspired systems, ionic solutions, and flow of polymeric materials, with applications in nanomedicine, energy devices, and electronics. He is a recipient of the NSF CAREER award.
Studies in Bio-Inspired Physics
Yitzhak Rabin
Professor, Physics Department; Institute for Nanotechnology and Advanced materials (BINA), Bar Ilan University, Israel
Thursday, August 16, 2018
Abstract:
We devise and study simple physical models that address several questions inspired by biology:
- Do non-specific interactions assist or hinder the formation of specific complexes?
- How can one suppress aggregation of intrinsically disordered proteins?
- How do active processes affect polymer (DNA) dynamics?
Starting With Copolymer Phase Behavior and Moving Away From Equilibrium
Wei Li 
Center for Nanophase Materials Sciences Oak Ridge National Laboratory
Monday, April 16, 2018
Abstract: The abundant phase behaviors make block copolymer systems quite intriguing for theoretical and simulation studies. According to the combination of different numbers and types of the constituting blocks, block copolymer can have unlimited varieties. How the architecture at the molecular scale affects the self-assembly morphology at the meso-scale remains an interesting question. We present a conceptual framework to describe and categorize the phase behavior of two-component block copolymer systems. Based on self-consistent field theory studies, three major universality classes for the topology of the equilibrium phase diagram are identified. Following a bottom-up approach, we analyze the relationship between chain architecture and copolymer mean-field phase behavior.
The precise control of self-assembly over morphology and size at the nanoscale brings a new era for the applications of block copolymers. Combining with other properties, the versality of block copolymers offers a unique platform for material design. To achieve rational design, many fundamental problems need to be addressed. We will present two case studies based on coarse-grained molecular dynamics simulations. In one study, we examined effects of dipolar interactions on the thermosdynamics of microphase separation in diblock copolymer melts and compared the results with the prediction from a field theory approach. In the other study, we investigated responses of thin films containing microphase separated ionic diblock copolymers to applied electric fields. A plausible picture was provided to interpret the experimental findings from neutron reflectometry measurements.
Mechanics of a Bacterial Biofilm Formed at the Air-Liquid Interface
Dr. Eric Raspaud 
Laboratoire de Physique des Solides, Université Paris
Friday, November 10, 2017
Abstract: Bacterial biofilms consist of a complex network of biopolymers embedded with microorganisms, and together these components form a physically robust structure that enables bacteria to grow in a protected environment. This structure can help unwanted biofilms persist in situations ranging from chronic infection to the biofouling of industrial equipment, but under certain circumstances can allow the biofilm to disperse and colonize new niches. Mechanical properties are therefore a key aspect of biofilm life. We study the physical forces acting on the floating pellicles at the air-liquid interface formed by a wild type strain of Bacillus subtilis. We have recently discovered the existence of a growth-induced compressive stress present within the biofilm and we have performed mechanical experiments in which Bacillus subtilis pellicles were subjected to elongational deformations using a custom built apparatus while simultaneously tracking the force response and macroscopic structural changes. Overall, our results indicate that we must consider not only the viscoelastic, but also the viscoplastic and mechanically heterogeneous nature of these structures to understand biofilm dispersal and removal.
Hydrophobic Hydration and the Effect of NaCI Salt in the Adsorption of Surfactants on Clathrate Hydrates
Felipe Jimenez Angeles
Reservoir Engineering Research Institute
Wednesday, September 20, 2017
Abstract: Clathrate hydrates are crystalline structures of water forming cages with guest molecules. Adsorption of hydrocarbons and functional molecules on the surface of hydrates is a key in the mechanisms of hydrate inhibition. The thinking in the literature is that hydrocarbons may not adsorb at the hydrate interface, surfactants adsorb through the headgroup, and ionic surfactants adsorb more strongly than non-ionic surfactants. Hydrophobic hydration is the ordering of water molecules around hydrophobic molecules in structures similar to clathrate hydrates. Here we establish a connection between hydrophobic hydration and the affinity of molecules such as n-decane, a non-ionic surfactant, and an ionic surfactant at the surface of hydrates. The hydrophobic hydration is investigated by means of hydrogen bonding and tetra-hedral structure of water. The affinity for the hydrate surface is investigated through the free energy profile of adsorption on the hydrate surface. We observe the molecules that are favor-ably adsorbed on the surface of hydrates induce hydrophobic hydration in the bulk. On the other hand, the hydrophilic ionic surfactants disrupt hydrophobic hydration and are not favora-bly adsorbed on hydrate surfaces. We show that the idea often presented in the literature that the ionic ammonium groups are hydratephilic may not be correct. We also find that salt disrupts the hydrophobic hydration of hydrocarbons and urfactants in the aqueous phase and increases the propensity of these molecules to be adsorbed on hydrate surfaces. We find a major difference in the adsorption of ionic and non-ionic surfactants on hydrate surfaces. The non-ionic surfactants can be adsorbed by headgroup and tail while the ionic surfactants have less affinity for adsorption and cannot adsorb through the head. Our study is performed by means of molecular dynamics and steered simulations.
Salt Entropy Effects on Protein Solubility and the Hofmeister Series
Wednesday, June 21, 2017Dr. Yuba Dahal
Department of Physics, Kansas State University
Instabilities at Soft Interfaces: From Elastocapillary Snap-Through to Wetting Dynamics on Elastomers
Aurelie Hourlier-Fargette
PhD student at the Université Pierre et Marie Curie in Paris
Thursday, November 17, 2016
Abstract: Capillary forces are often too weak to deform a substrate, but are able to dominate elasticity at small scales, on soft materials. A water droplet can interact in a spectacular way with slender flexible structures such as thin elastic sheets or beams, inducing wrinkling, static or dynamic folding, aggregation of fibers, or buckling. On thicker but softer materials, a droplet that does not deform macroscopically the substrate can raise a microscopic ridge at the triple line.
The role of surface tension in the mechanics of deformable solids is a question raising a growing interest in the soft matter community. In this context, we will present two examples of instabilities featuring liquids on soft materials.
We will begin by revisiting the snap-through instability from an elastocapillary point of view. Snap-through, which is present in systems ranging from carnivorous plants to MEMS, is a well-known phenomenon in solid mechanics: when a buckled elastic beam is subjected to a transverse force, above a critical load value the buckling mode is switched. We show that capillary forces are strong enough to trigger a snap-through instability at small scales, and even counterbalance gravity for a droplet deposited below a downward buckled elastic strip. We investigate the statics and dynamics of this phenomenon, and compare droplet-induced snap-through to dry point force indentation on a buckled thin strip.
In a second part, we will focus on the dynamics of droplet sliding on elastomers. The motion of droplets on stiff surfaces has been investigated for a long time, both experimentally and theoretically, while recent studies have shown the interesting physics underlying the sliding of droplets on soft surfaces. We focus on the dynamics of water-glycerol mixture droplets sliding down vertical plates of commercial silicone elastomers, highlighting an unexpected behavior: the droplet dynamics on such a surface includes two regimes with different constant speeds. Different candidates can be responsible for the sudden speed change: bistability, chemical interaction with the substrate, softness of the material, etc. Our experiments reveal an unexpected link between microscopic phenomena at the scale of the polymer matrix and the macroscopic dynamics of a droplet.
Short Bio: Aurelie Hourlier-Fargette is a last year PhD student at the Université Pierre et Marie Curie in Paris (Institut Jean Le Rond d’Alembert), and has a teaching position in the Physics Department at the Ecole Normale Supérieure in Paris. Her research interests are mainly experimental soft matter physics, and her PhD work focuses on elastocapillarity and wetting at soft interfaces.
Structure Prediction in Nanoparticle Superlattices
Alex Travesset, professor in the Department of Physics and Astronomy at Iowa State University
Date: Friday, July 22, 2016
Abstract: Materials whose fundamental units are nanoparticles instead of atoms or molecules offer major opportunities to overcome many of the technological challenges of our century. They display unique structures and properties that are not found in other types of materials, usually exhibiting deep underlying geometry and topological constraints. In this talk, I will focus on crystalline assemblies of nanoparticles, i.e. supercrystals. I will discuss the efforts in my group to predict the structure and dynamics of three very successful experimental strategies for the rational design of nanoparticle materials: DNA programmable self-assembly, Evaporation of solvent in nanoparticles with hydrocarbon capping ligands, and more recently, a new technique developed at Ames lab consisting in electrostatic crystallization of nanoparticles with grafted neutral (uncharged) polymers.
Short Bio: Alex Travesset is professor in the Department of Physics and Astronomy at Iowa State University and Associate Research scientist at the Ames Lab. His research interests are in the area of theoretical and computational soft condensed matter. He received his PhD from Universitat de Barcelona and had postdoc positions at Syracuse University and the University of Illinois at Urbana-Champaign.
The maximally crumpled state: crumpling dynamics and the evolution of damage networks
Shmuel Rubinstein, Ph.D.,
Physics Department, Harvard University
Monday, May 23, 2016, 4:00pm,
For further information see http://esam.northwestern.edu
When describing the dynamics of a sheet of paper being crumpled one may be tempted to only take the elastic response of the thin sheet into account and consider only those deformations which minimize the elastic energy of the crumpled sheet. However, most materials yield and deform plastically, leaving permanent scars in the thin sheet. Indeed, the simple process of crumpling a sheet of paper with our hands results in a complex network of interconnected permanent creases of many sizes and orientations, along which the sheet preferentially bends. Thereby, history dependence is introduced into the process. I will present an experimental study of the dynamics of crumpling. Specifically, we investigate how a crease network evolves when a thin elastoplastic sheet is repeatedly crumpled, opened up and then re-crumpled. Is there a maximally crumpled state after which the sheet can be deformed into a sphere without further plastic deformations?
Effective Electrostatic Interaction
Pedro González Mozuelos, Ph.D.,
Physics Department, Cinvestav Av. Instituto Poletécnico Nacional
Monday, April 18, 2016
We discuss the general theory applicable to the determination of the parameters regulating the screened Coulomb interactions among spherical macroions immersed in an electrolyte. This approach comes from implementing the precise methodology of the dressed ion theory to the proper definition of the effective direct correlation functions, which emerge from tracing-out the degrees of freedom of the microscopic ions, and thus provides rigorous definitions for the corresponding screening length, effective permittivity, and renormalized charges. Moreover, it can be profitably employed for precise and reliable calculations of these effective parameters within any practical scheme for the determination of the bulk correlations among the components of an ionic solution.
Chemical Microswimmers: From Cargo Delivery to Motion Control
Mykola Tasinkevych, Max Planck Institute for Intelligent Systems
Monday, April 4, 2016
Microscopic agents which can self-propel through confined, liquid-filled spaces are envisioned as a key component of future lab-on-a-chip and drug delivery systems. Chemically active Janus colloids offer a realization of such agents. A Janus microswimmer works by catalytically activating, over a fraction of its surface, chemical reactions in the surrounding solution. The resulting anisotropic distribution of reactants and products drives a surface flow in a thin layer surrounding the particle leading to a directed motion. Depending on the systems, various self-propulsion mechanisms emerge such as self-electrophoresis or self-diffusiophoresis. Here only the last mechanism shall be considered.
First, the self-propulsion of a spheroidal particle which is covered by a catalyst over a cap-like region will be discussed. I will describe how the velocity of the particle depends on its shape and on the size of the catalytic cap. Next, I will show how such particles can be used as carriers of microcargo. As a model for a carrier-cargo system, I will consider a microswimmer connected by a thin rod to an inert cargo particle. It turns out that the velocity of such composite strongly depends on the relative orientation of the carrier-cargo link. Accordingly, there is an optimal configuration for the linkage. The subtlety of such carriers is underscored by the observation that a spherical particle completely covered by catalyst, which is motionless when isolated, acts as a carrier once attached to a cargo.
Finally, I will demonstrate that a chemical microswimmer approaching a planar wall reveals novel motion scenarios, including a steady “sliding” at fixed orientation and height above the wall, and motionless steady “hovering”. Hovering particles create recirculating regions of flow, and can be used to mix fluid or to trap other particles. Sliding states, on the contrary, provide a starting point to engineer a stable and predictable motion of microswimmers. Thus, for topographically patterned walls, novel states of guided motion along the edges of the patterns emerge when the parameters of the microswimmers are such that a sliding state occurs in the absence of the patterns. Such topography-guided states emerge from a complex interplay between chemical activity of the particle, hydrodynamic interactions and the confinement of the chemical and hydrodynamic fields by the topography.
Co-sponsored by CBES
Co(non)solvency or the puzzle of polymer properties in mixed good or poor solvents
Professor Kurt Kremer
Director, Max Planck Institute for Polymer Research
Wednesday, February 17, 2016
The relation between atomistic structure, architecture, molecular weight and material properties is of basic concern of modern soft matter science. Here computer simulations on different levels of resolution play an increasingly important role. To progress further adaptive schemes are being developed, which allow for a free exchange of particles (atoms, molecules) between the different levels of resolution.
The extension to open systems MD (grand canonical MD) as well as recent Hamiltonian based molecular dynamics and Monte Carlo adaptive resolution methods will be explained. Typical examples include the solvation of polymers in mixed solvents, especially PNIPAM in water alcohol mixtures, which reveals an interesting coil-globule-coil transition. This conformational transition cannot be explained within the classical Flory-Huggins picture, which is the standard mean field theory for polymer solutions and mixtures. The results point towards a general design of 'smart stimuli responsive polymers'.
This work has been performed in collaboration with D. Mukherji and C. Marques.
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S. Fritsch et al. Phys. Rev. Lett. 108, 170602 (2012)
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D. Mukherji and K. Kremer Macrom. 46, 9158 (2013)
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D. Mukherji, C. M. Marques, T. Stuehn, K. Kremer, J. Chem. Phys. 142, 114903 (2015)
Self-Consistent Field Modeling of the Polyelectrolyte Charged Nanoparticles Mixtures
Monday, October 19, 2015
The effective interactions between charged hydrophilic nanoparticles (CNP) in polyelectrolyte (PE) solutions are computed using a Self-Consistent Field model. The electrostatic interactions are described within the Poisson-Boltzmann approximation. The dielectric constant is chosen to be a function of the local composition of the species. Local PE and CNP’s charges are dependent on the local concentration of ionizable groups and local degrees of dissociation. A hierarchy of two- , three- and multi-body interactions between CNP’s are computed. By reducing interactions to pairwise only one can access the phase diagram of such PE/CNP systems. For such systems only gas and crystal like phases are thermodynamically stable; the fluid-like phase is metastable. MC modelling demonstrates the suppression of the phase segregation by the formation of highly anisotropic clusters of CNPs.
Victor A. Pryamitsyn (born in 1961) obtained his M.S. in Physics in 1984 from Leningrad State University, USSR and PhD in Physics and Mechanics of Polymers in 1987 from the Institute of Macromolecular Compounds, Russian Academy of Sciences. From 2002 to present he has worked as a research associate in the Department of Chemical Engineering of the University of Texas at Austin. Before coming to Texas he was working at the Department of Chemistry and Institute of Theoretical Science at University of Oregon; IRC in Polymer Science and Technology, Department of Physics and Astronomy, University of Leeds, UK; School of Chemistry University of Bristol, UK; Institute of Problems of Mechanical Engineering and Institute of Macromolecular Compounds of Russian Academy of Sciences.
The Geometry and Assembly of the Rough Endoplasmic Reticulum
Jemal Guven
The rough endoplasmic reticulum (RER) is a large intracellular membrane consisting of a number of more or less regular stacks, an architecture that reflects its function as the principal site of protein synthesis within the cell. Recently it was discovered that adjacent sheets within these stacks are connected by helicoidal ramps. Guven will argue that stacks are organized about a number of dipole defects, or “parking garages”, formed by two parallel gently-pitched ramps of opposite chiralities. Viewed more closely, individual sheets are composed of a pair of lipid bilayers enclosing a lumen. Membrane-shaping proteins are concentrated along the bilayer fold which forms the inner boundary of a ramp. These same proteins also play a role in establishing the tubular geometry of the adjoining smooth ER (SER).
This coincidence suggests a mechanism for parking garage assembly via the nucleation of dipoles at the center of three-way tubular junctions within the SER.