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Workshops

Collective behavior of soft and active matter under confinement

September 24, 2018 to September 26, 2018
Location : CECAM-DE-SMSM (Mainz, Germany)

Organisers

  • Arash Nikoubashman (Johannes Gutenberg University Mainz, Germany)
  • Athanassios Panagiotopoulos (Princeton University, USA)
  • Sara Jabbari-Farouji (Johannes Gutenberg-Universität Mainz, Germany)

Supports

   CECAM

Description

General Workshop Information  

  • Abstract submission deadline for contributed talks: 1st of June
  • Location: Schloss Waldthausen, Budenheim, Germany
  • We have reached maximum capacity for the number of participants and unfortunately can’t accept new applications anymore.

Scientific Workshop Program

Soft materials under confinement are ubiquitous in nature and technology [1], ranging from the crowded and fluctuating interior of biological cells [2, 3] to thin films of synthetic block copolymers [4]. Confinement can either be imposed externally through a specific geometry or an external field [5]. Alternatively, confinement can emerge spontaneously through the collective self-organization of the constituents into ordered assemblies, e.g. the lipid bilayer formation [6, 7]. One crucial aspect of confined systems is the shape of the enclosing geometry, which can be, for example, planar, cylindrical or spherical. Further, the confining interface can be rigid, flexible, porous or semipermeable.

Confined systems are characterized by a high surface area to volume ratio, which can lead to strong deviations from the bulk behavior, even at regions far away from the confining interface. Confinement decreases substantially the available degrees of freedom, and can lead to a wealth of intriguing phenomena. For example, in thin block copolymer films, the orientation of the domains can be controlled through the film thickness and the substrate properties [8]. Spherical enclosure can also frustrate nematic order in systems of short stiff rods and semiflexible polymers, leading to bipolar and quadrupolar “tennis ball” structures on the confining surface [3, 9-12]. Additionally, confinement often gives rise to a dramatic slowing down of collective dynamics [13].

Confinement also significantly influences the individual dynamics and collective behavior of active particle suspensions [14-18]. For example, it was found that pusher types of swimmers (like spermatozoa) strongly migrate toward solid surfaces [19], and that self-propelled colloidal rods form transiently jammed clusters at planar channel walls [20]. Microswimmers individually interact with surfaces through their self-generated hydrodynamic and chemical fields [21]. Additionally, surfaces modify the interactions between microswimmers. The combination of self-propulsion and confinement leads to new patterns of dynamics [22, 23] that are not observed in their passive counterparts. For instance, phoretic microswimmers speed up in confining channels [24].

In view of this rich phenomenology, the field is in need of rules, mechanisms, and models relating the phase behavior, dynamics, and other aspects of physics involved to the confinement properties. However, the theoretical description and simulation of these complex systems involves a number of challenges: for instance, the confining interface introduces additional interactions and parameters, which need to be related to experimental systems. Further, many computational techniques for dealing with long-ranged interactions (e.g. hydrodynamics and electrostatics) need to be adapted to work efficiently in confined geometries [25].

This workshop will bring together scientists from physics, chemistry and engineering to discuss the fundamental properties and specific applications of soft materials under confinement. Due to the complexity of the systems and phenomena, different studies have focused on different aspects of confinement (see “state of the art”). This topical breadth implies also that many different numerical methods and approaches have been employed. Therefore, key goals of this workshop are to give an overview of the recent developments in this field, to identify common concepts and challenges, and to discuss and develop suitable solution strategies. In particular, the proposed workshop will focus on the following questions:

- When does confinement matter and what are the relevant length scales? How do the (intrinsic) finite size effects manifest themselves and affect the collective behavior?

- How can long-ranged interactions (e.g. hydrodynamic interactions and electrostatics) be treated efficiently in computer simulations, and how do these effects influence the properties of active and passive particles?

- How do the rigidity and fluctuations of the confinement influence the static and dynamic behavior of the confined system?

- What are good experimental probes of confinement effects on the static and dynamic behavior?

- What new dynamical ordered states result from the interplay between activity, topological constraints, and deformability of active particles? Can we classify them?

- What are the effects of active or dynamic confinement boundaries on self-organization?

References

[1] S. Perkin, J. Klein: Soft matter under confinement, Soft Matter 9, 10438 (2013).
[2] L.R. Serbus, B.-J. Cha, W.E. Theurkauf, W.M. Saxton: Dynein and the actin cytoskeleton control kinesin-driven cytoplasmic streaming in Drosophila oocytes. Development 132, 3743 (2005).
[3] J. Alvarado, B. M. Mulder, G.H. Koenderink: Alignment of nematic and bundled semiflexible polymers in cell-sized confinement, Soft Matter 10, 2329 (2014).
[4] L. Tsarkova, G.J.A. Sevink, G. Krausch: Nanopattern evolution in block copolymer films: Experiment, simulations and challenges, Adv. Polym. Sci. 227, 33 (2010).
[5] H. Löwen: Colloidal soft matter under external control, J. Phys.: Condens. Matter 13, R415 (2001).
[6] S.J. Singer, G.L. Nicolson: The fluid mosaic model of the structure of cell membranes, Science 175, 4023 (1972).
[7] K. Jacobson, O.G. Mouritsen, R.G.W. Anderson: Lipid rafts: at a crossroad between cell biology and physics, Nat. Cell. Biol. 9, 7 (2007).
[8] A. Knoll, A. Horvat, K.S. Lyakhova, G. Krausch, G.J.A. Sevink, A.V. Zvelindovsky, R. Magerle: Phase behavior in thin films of cylinder-forming block copolymers, Phys. Rev. Lett. 89, 035501 (2002).
[9] D. R. Nelson: Towards a tetravalent chemistry of colloids, Nano Letters 2, 1125 (2002).
[10] T. Lopez-Leon, V. Koning, K.B.S. Devaiah, V. Vitelli, A. Fernandez-Nieves: Frustrated nematic order in spherical geometries, Nature Phys. 7, 391 (2011).
[11] I.C. Garlea, P. Mulder, J. Alvarado, O. Dammone, D.G.A.L. Aarts, M.P. Lettinga, G.H. Koenderink, B.M. Mulder: Finite particle size drives defect-mediated domain structures in strongly confined colloidal liquid crystals, Nature Commun. 7, 12112 (2016).
[12] A. Nikoubashman, D.A. Vega, K. Binder, A. Milchev: Semiflexible polymers in spherical confinement: bipolar orientational order versus tennis ball states, Phys. Rev. Lett. 118, 217803 (2017).
[13] T. Franosch, S. Lang, R. Schilling: Fluids in extreme confinement, Phys. Rev. Lett. 109, 240601 (2012).
[14] A. Sokolov, M.M. Apodaca, B.A. Grzybowski, I.S. Aranson: Swimming bacteria power microscopic gears, Proc. Natl. Acad. Sci. U.S.A. 107, 969-974 (2010).
[15] S.E. Spagnolie, E. Lauga: Hydrodynamics of self-propulsion near a boundary: predictions and accuracy of far-field approximations, J. Fluid Mech. 700, 105 (2012).
[16] Y. Fily, A. Baskaran, M.F. Hagan: Dynamics of self-propelled particles under strong confinement, Soft Matter 10, 5609 (2014).
[17] C. Bechinger, R. Di Leonardo, H. Löwen, C. Reichhardt, G. Volpe: Active particles in complex and crowded environments, Rev. Mod. Phys. 88, 045006 (2016).
[18] J. de Graaf, A.J.T.M. Mathijssen, M. Fabritius, H. Menke, C. Holm , T.N. Shendruk: Understanding the onset of oscillatory swimming in microchannels, Soft Matter 12, 4704 (2016).
[19] J. Elgeti, G. Gompper: Wall accumulation of self-propelled spheres, Europhys. Lett. 101, 48003 (2013).
[20] H.H. Wensink, H. Löwen: Aggregation of self-propelled colloids rods near confining walls, Phys. Rev. E 78, 031409 (2008).
[21] W.E. Uspal, M.N. Popescu, S. Dietrich, M. Tasinkevych: Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering, Soft Matter 11, 434 (2015).
[22] R.J. Hawkins, M. Piel, G. Faure-Andre, A.M. Lennon-Dumenil, J.F. Joanny, J. Prost and R. Voituriez: Pushing off the walls: a mechanism of cell motility in confinement, Phys. Rev. Lett. 102, 058103 (2009).
[23] F.G. Woodhouse and R.E. Goldstein: Spontaneous circulation of confined active suspensions, Phys. Rev. Lett. 109, 168105 (2012).
[24] C. Liu, C. Zhou, W. Wang, and H.P. Zhang: Bimetallic microswimmers speed up in confining channels, Phys. Rev. Lett. 117, 198001 (2016).
[25] J.P. Hernández-Ortiz, J.J. de Pablo, M.D. Graham: Fast computation of many-particle hydrodynamic and electrostatic interactions in a confined geometry, Phys. Rev. Lett. 98, 140602 (2007).