Collective behavior of soft and active matter under confinement
- Arash Nikoubashman (Johannes Gutenberg University Mainz, Germany)
- Athanassios Panagiotopoulos (Princeton University, USA)
- Sara Jabbari-Farouji (Johannes Gutenberg-Universität Mainz, Germany)
General Workshop Information
- Registration deadline: 31st of August
- Abstract submission deadline for contributed talks: 1st of June
- Location: Schloss Waldthausen, Budenheim, Germany
- Registration fee: free of charge
Scientific Workshop Program
Soft materials under confinement are ubiquitous in nature and technology , ranging from the crowded and fluctuating interior of biological cells [2, 3] to thin films of synthetic block copolymers . Confinement can either be imposed externally through a specific geometry or an external field . 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 . 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 .
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 , and that self-propelled colloidal rods form transiently jammed clusters at planar channel walls . Microswimmers individually interact with surfaces through their self-generated hydrodynamic and chemical fields . 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 .
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 .
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?
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