Faculty of Physics University of Warsaw > Events > Seminars > Soft Matter and Complex Systems Seminar

Soft Matter and Complex Systems Seminar

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room 1.40, Pasteura 5 at 09:30

(UW)

Student flash talks via Zoom https://us04web.zoom.us/j/73262981794?pwd=UkVwUTNEMDFJOTd5aVVML3NYOWZxQT09 (meeting ID: 732 6298 1794, password: statsoft)

The seminar will feature student flash talks from:

Jacek Gębala "Polymer-polymer miscibility"
I will shortly discuss the thermodynamics of polymer-polymer and polymer-solvent systems. Then, I will procede to describe the dependence of viscosity of such solutions on the concentration of elements. I will also introduce the Huggins equation. Finally, I will mention the experimental technique (viscometry) used to determine the polymer-polymer miscibility.

Stanisław Żukowski "Spatial Iterated Prisoner's Dilemma"
Prisoner's Dillema is a well known game, in which two individuals may cooperate or defect in order to gain points (or years in prison). In iterated case we let individuals play with each other many times, which enables them to invent different tactics based on previous moves. Putting them on a grid, letting play with nearest neighbours and stealing best tactic from neighbourhood let us study stability of different tactics in spatial case.

Michał Zmyślony "Liquid Crystal Elastomers and Wright brothers plane"
The presentation will start with a short introduction into the concept of the LCE and give an explanation how they work. Then I will talk about the experimental results and how they are created in the lab and their possible applications. I will try to give an overview of some of the more interesting examples created in the recent years.

Tomasz Necio "Random matrix theory"
In this talk I will present random matrix theory. I will describe its application in explaining the distribution of atomic energy levels. I will also talk about Bohigas-Giannoni-Schmit conjecture, which relates random matrices with chaotic systems in the quantum limit.

Bartosz Greń “Handcuff topology in proteins and phantom polymers”

room 1.40, Pasteura 5 at 09:30

Tomasz Skóra (Chemical Physics of Complex Systems group, Institute of Physical Chemistry, Polish Academy of Sciences)

[CANCELLED] Macromolecular Crowding: How the Shape of Macromolecules Affects Diffusion?

Significant fraction of cell’s volume is occupied by various proteins, polysaccharides, RNAs etc. Such crowding substantially reduces the mobility of macromolecules, and affects both thermodynamics and kinetics of intracellular processes. While prior research has mainly focused on the dependence of translational mobility on occupied volume fraction, studies of the effect of crowder shape are still scarce. In this work, we fill this gap by investigating self-diffusion in mixtures of spherical and elongated macromolecules with Fluorescence Correlation Spectroscopy (FCS) and Brownian Dynamics (BD) simulations. Our results emphasize that diffusion in crowded systems is determined not merely by the occupied volume fraction, but that the shape of crowders matters, which is relevant to diverse intracellular environments.

room 1.40, Pasteura 5 at 09:30

Piotr Wasylczyk (FUW)

[CANCELLED] Actuators and robots in milli- and micro-scale based on photoresponsive polymers

In my group for a few years we have been using liquid crystal elastomers (LCEs) to make various moving elements and systems driven by light. By controlling the molecular arrangement in a polymer structure we can design the light-induced deformation which can be reversible and fast. I will present a few recent designs and outline our current and future projects.

room 1.40, Pasteura 5 at 09:30

Robert Hołyst (IChF PAN)

Diffusion in living cells: 100 years after Albert Einstein

Stokes-Einstein and Debye-Einstein equation for translational and rotational diffusion of particles disagrees by orders of magnitude with experiments performed in complex liquids . I will explain the discrepancy and generalize these equations. The seminar is a 45 minutes summary of 15 years of experiments performed in my group on complex liquids and living cells.

1. Tabaka M et al. Nucleic Acids Research, 42, 727–738, 2014.
2. Kalwarczyk T et al. Bioinformatics, 28, 2971–2978, 2012.
3. Kalwarczyk T et al. Nano Lett. 11, 52157-2163, 2011.
4. Kwapiszewska K et al., Scientific Reports, 9, 5906, 2019.
5. Wisniewska A et al., Marcomolecules 50, 4555-4561, 2017.
6. Sozanski K et al., Phys.Rev.Lett. 115, 218102, 2015.
7. Makuch K et al, Soft Matter, 16,114, 2020.

room 1.40, Pasteura 5 at 09:30

Bogdan Cichocki & Piotr Szymczak (IFT UW)

Diffusion coefficients of elastic macromolecules

In elastic macromolecules, the value of the short-time diffusion coefficient depends on the choice of the point the displacement of which is tracked. On the other hand, the experimentally more relevant long-time diffusion coefficient isindependent of the reference point, but its estimation usually requires computationally expensive Brownian dynamics simulations. We present an efficient method allowing for a precise estimate of the long-time diffusion coefficient of elastic macromolecules in a fast and robust manner, without invoking Brownian dynamics.

room 1.40, Pasteura 5 at 09:30

Jonasz Słomka (ETH Zuerich)

Encounter rates involving elongated marine microorganisms

Marine microorganisms control the global biogeochemistry of the oceans through interactions between individual cells and between cells and particles of organic matter. Prominent examples include marine snow formation by elongated phytoplankton following a phytoplankton bloom or bacterial degradation of marine snow responsible for carbon export from the upper ocean in the biological pump. A variety of physical mechanisms can drive these interactions, including diffusion, active swimming, gravitational settling and turbulent mixing, and the concept of encounter rates provide a unifying framework to describe them. However, the corresponding collision kernels, which map the physical mechanisms to the frequency of encounters, have been traditionally computed for spherical particles. Here, we first describe the impact of elongation on marine snow formation. We derive the collision kernels between identical and dissimilar rods settling in a quiescent fluid and show that marine snow formation by elongated phytoplakton can proceed efficiently even under quiescent conditions and that the resulting coagulation dynamics can lead to periodic bursts in the concentration of marine snow particles [1, 2]. Later, we describe the impact of elongation and fluid shear on the encounters between non-motile and motile bacteria and sinking particles of organic matter [3]. There, we find that the shape-shear coupling has a considerable effect on the encounter rate and encounter location through the mechanisms of hydrodynamic focusing and screening. Overall, our results demonstrate that elongation and fluid shear must be taken into account to accurately predict encounter rates at the microscale, which govern the large carbon flux in the ocean’s biological pump.

References
[1] Słomka J & Stocker R. PNAS (accepted), 2020.
[2] Słomka J & Stocker R. in preparation, 2020.
[3] Słomka J et al. arXiv :1908.08376.

room 1.40, Pasteura 5 at 09:30

Michał Jagielski [I], Stanisław Żukowski [II] (FUW)

Snow Crystals (part I) & Relationship between geometries and growth laws in Laplacian growth model (part II)

Part I:
Snow Crystals
Abstract: Snow crystal formation is one of those phenomena that are easy to observebut their intrinsic complexity makes creating comprehensive model thatreproduces crystal growth in all regimes surprisingly difficult. In thistalk I will showcase some of the effects important in snow crystalformation and their influence on final crystal geometry.
Part II
Relationship between geometries and growth laws in Laplacian growth model
Abstract: Laplacian growth describes processes as formation of electric breakdown, blood vessel or river networks, growth of bacterial colonies and many others. The presentation will show how the final patterns in such systems depends on growth laws.

room 1.40, Pasteura 5 at 09:30

Krzysztof Mizerski (IGF PAN)

Large-scale hydromagnetic dynamo mechanisms from renormalized MHD equations

It is well known that a field of random waves in a fluid of non-zero resistivity is capable of exciting a large-scale magnetic field through creation of an electromotive force (EMF) which leads to exponential growth of magnetic energy until the growing Lorentz force reacts back upon the wave field, leading to a saturated state. For highly conducting plasma it is generally found that kinematic fast-dynamos with finite growth rate in the limit of vanishing resistivity, have a pathological structure, non-differentiable wherever they are non-zero; the applicability of fast-dynamo theory to natural physical systems is then questionable.
Here we relax the standard simplifying assumptions of stationarity and homogeneity of the background turbulence and introduce new fast-dynamo mechanisms, fully dynamic, that is incorporating the back reaction of the Lorentz force on the flow (hitherto scarcely considered), for which the growing magnetic field remains smooth during the whole dynamo process. This results from a random superposition of waves, perturbed by the magnetic field. Particularly effective are the interactions of ‘beating’ waves (close-frequency waves) and nonlinear effects in the mean electromotive force leading to very fast amplification of the mean magnetic field. The renormalization approach is udertaken to obtain final mean-field equations and saturation of the large-scale field.
The theory has the potential to be applied to the dynamo generation of magnetic fields in the ionised gas of the early universe, both before and during the process of galaxy formation. In such a plasma, the resistivity is extremely low, giving characteristic diffusion times many orders of magnitude greater than the age of the entire universe and hence negligible. Nevertheless the large-scale galactic magnetic fields and fields of galaxy clusters are observed, thus non-resistive dynamo mechanisms are strongly desirable in this context.

room 1.40, Pasteura 5 at 09:30

Paweł Żuk (IPPT PAN)

Strong long-range repulsion between oppositely charged surfaces

Two oppositely charged surfaces separated by a dielectric medium attract each other. In contrast, using the Surface Force Apparatus, we observe a strong repulsion between two plates of a capacitor that is filled with an aqueous electrolyte upon application of an alternating potential difference between the plates. This long-range force is observed on the distances two orders of magnitude larger than Debye length, the typical length scale for the extension of electrostatic effects. It increases with the ratio of diffusion coefficients of the ions in the medium and reaches steady state after a few minutes, which is much larger than the millisecond time scale of diffusion across the narrow gap. The repulsive force is an order of magnitude stronger than the electrostatic attraction observed in the same setup in air. We find that it results from the increase in osmotic pressure as a consequence of the field-induced excess of cations and anions due to lateral transport from adjacent reservoirs. Oppositely to what is observed with DC fields the ion concentration is elevated across the whole narrow gap instead of in the double layer region only. The unexpected distribution of ions in the thin electrolyte film under AC voltage points to the new design principles for fine control of local ionic concentration.

room 1.40, Pasteura 5 at 09:30

Paweł Sznajder (IPPT PAN)

Velocity fluctuations and plasma-like screening in sedimenting suspension

In this short talk I will present the problem of diverging expressions for velocity fluctuations in a stationary state of uniform sedimenting suspension. Those divergencies, as suggested by Koch and Shaqfeh, can be eliminated by plasma like screening conditions for correlation functions. Unfortunately BBGKY hierarchy for that system derived by Cichocki and Sadlej can not have solutions which obey those conditions.

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