Statistical Physics and Mechanics of Forms and Shapes

27 May 2015, 15:00 → 30 May 2015, 18:00 Europe/Stockholm

Mariehamn, Åland

Marcelo A. Dias (Aalto University), Mikko Alava (Aalto University), Petia Vlahovska (School of Engineering, Brown University), Ralf Eichhorn (Nordita)

Venue

Mariehamn, Åland

The venue is Hotel Arkipelag (Mariehamn, the capital of the province of Åland, Finland). The venue is easily reachable by ferry from Stockholm, Turku (Finland), and Helsinki. Moreover there are flights from Sweden and Finland.

Scope

Over the past few decades, experiments in mechanics of soft and thin materials have stimulated new approaches to technological applications as well as brought to light many fundamental questions in our understanding of morphology in biological matter and non-linear material response to external stimuli. Manifestations of patterns such as wrinkles, folds, and singular creases, are ubiquitous mechanical instabilities found in nature and they happen at many different length-scales, from cell membranes to leaves and flowers. The ways materials respond to external forcing, deformation, failure, etc, are intrinsically geometric effects that get transmitted across length scales, from the geometric microstructure to the bulk. While standard treatments of thin-body mechanics typically neglect geometric non-linearities by assuming that the deformed shape deviates only slightly from a known reference shape, this assumption is often violated in real world problems, where materials are often found to be soft and capable to undergo large deformations. The goal of this meeting is to target cutting edge questions on the mechanics of shape formation and response of intrinsically 2-dimensional soft-matter with focus on the question how microstructure architectures may result into macroscopic phenomena that are effectively non-linear and anisotropic responses to external forces and strains. In this workshop we will bring together experts that have helped to advance the frontiers in the field of soft and biological matter

Format

The workshop will be over 2.5 full days (Thursday to Saturday noon) The program will start it on the ferry from Stockholm Wednesday afternoon, with arrival late Wednesday evening in Mariehamn.

Program

The program is now available from the web page.

[Timetable - available from start of the program]

There is no workshop fee. Travel on the ferry from Stockholm to Mariehamn, including dinner on the ferry, is free for all participants, as are coffee and lunches at the workshop. We also plan for a workshop dinner on Thursday.

The participants should aim for arriving to Stockholm so as to reach the ferry terminal by 16.00 on Wednesday, and plan for an arrival to back to Stockholm around 18.30 on Saturday (alternative possibilities exist eg. for travel via Finland).

Invited speakers (confirmed)

Martine Ben Amar (Ecole Normale Supérieure, France) Mark Bowick (Syracuse University, USA) Markus Deserno (Carnegie Mellon University, USA) Haim Diamant (Tel Aviv University, Israel) Gerhard Gompper (Institute of Complex Systems and Institute for Advanced Simulation, Germany) Francois Graner (Matière et Systèmes Complexes, France)

André H. Gröschel (Aalto University, Finland) Michael A Lomholt (University of Southern Denmark) Klaus Mecke (Universität Erlangen-Nürnberg, Germany) Chaouqi Misbah (Université Grenoble I and CNRS) Christian Santangelo (University of Massachusetts Amherst, USA) Rastko Sknepnek (University of Dundee, UK) Tuomas Tallinen (University of Jyväskylä, Finland)

Application

If you want to apply for participation in the workshop, please fill in the application form. You will be informed by the organizers shortly after the application deadline whether your application has been approved. Due to space restrictions, the total number of participants is strictly limited (40 slots are foreseen, invited speakers are of course automatically approved, but need to register anyway.)

Application deadline: 31 March 2015 - shifted for late arrivals to 10 April 2015

There is no registration fee.

Travel Reimbursement

PhD students and young Postdoc fellows are eligible for travel grants to participate in the program. If you are interested in such a grant, please mark the corresponding field in the application form, briefly summarize your interest in the program in the comments field, and indicate an estimation of your expected travel expenses. Since only a limited number of grants is available, decision concerning the grants will be made on a case-by-case basis and you will be notified shortly after the application deadline.

Accommodation

From the registration page you may book a room at one of the two hotels we have reserved for the participants. The accommodation is paid on spot. N.b (May 5th) your requests have been honoured; PhD students will share rooms at Park.

Sponsored by:

The event receives support from Nordita and the Aalto Science Institute (AScI).

agenda Preliminary workshop program

Wednesday 27 May

15:30 Meeting at the ferry terminal

1 Effective Field Theory approach towards fluid surface mediated interactions

Speaker: Markus Deserno (Carnegie Mellon University, USA)

2 Tension control of domain nucleation in lipid bilayers

When lipid molecules in a bilayer freeze they tend to lower the area that they occupy in the membrane. Thus during the nucleation process of a solid domain of lipids the nucleating domain will have to pull against the local tension in the bilayer, an effect that will lower the rate at which these domains nucleate. In this talk I will present a model of domain nucleation and growth, which explains how the dynamics of the tension via this effect can determine the distribution of nucleation points observed in experiments on supported lipid bilayers. The friction between the bilayer and the support plays an important role in this model, by slowing down the relaxation of locally increased tension.

Speaker: Michael A Lomholt (MEMPHYS - Center for Biomembrane Physics, University of Southern Denmark)

18:00 Short break

3 Deformation and fracture of graphene sheets

Speaker: Stefano Zapperi (University of Milano)

19:00 Dinner

Thursday 28 May

4 Statistical physics of cellular materials: Mechanics of forms and shapes of bubble and cell assemblies

Liquid foams are made of gas bubbles surrounded by water. They are model systems to understand the physics of complex cellular materials (made of cells tiling the space), which behave simultaneously as solids and liquids. We have established statistical tools to link the discrete description of each bubble shape (and shape evolution) with a continuous description which encompasses the shape information useful at the global level. This enabled us to suggest and validate a mechanical model able to predict efficiently, despite two strong non-linearities, how a foam flows in general geometries. Such multi-scale descriptive approach applies to a large class of disordered systems, including aggregates of living cells or developing tissues in the fruit fly.

Speaker: Francois Graner (Univ. Denis Diderot - Paris 7)

5 Volume fluctuations during active cell deformations

Speaker: Caterina La Porta (University of Milano)

11:00 Coffee break

6 The mechanics of invagination and folding

We address the mechanical folding induced by differential growth in soft layered solids via an elementary model that consists of a soft growing neo-Hookean elastic layer adhered to a deep elastic substrate. The model displays a transition from supercritical smooth folding to subcritical cusped folding as the layer/substrate modulus ratio is varied from above unity toward zero. We demonstrate the diverse patterns of cusped folds that can be generated in three dimensions when the layer and substrate are of comparable softness, providing understanding for some of the compressive folding patterns found in soft tissues.

Speaker: Tuomas Tallinen (University of Jyväskylä)

7 Optimal wrapping of liquids with ultrathin sheets

Speaker: Joseph Paulsen (University of Massachusetts)

12:15 Lunch

8 Structural hierarchy as a means to efficient, robust materials

Speaker: Daniel Rayneau-Kirkhope (Aalto University)

9 Wrinkles and folds in a fluid-supported elastic sheet

A thin elastic sheet, floating on top of a fluid, buckles under uniaxial confinement via periodic wrinkles. Upon further confinement the periodic pattern localizes into a deep fold. For a sheet whose length $L$ is much larger than the wrinkle wavelength $\lambda$, the localization transition occurs at an arbitrarily small confinement equal to $\lambda^2/L$. Exact profiles are obtained for wrinkled finite sheets and for folded infinite ones. We show that the integrability of this system is related to a new type of "phason-like" symmetry. For a folded finite sheet we derive the weakly localized profile formed above the wrinkle-to-fold transition and obtain the detailed features of the transition.

Speaker: Haim Diamant (Tel Aviv University)

10 Wrinkles and folds in a compressible finite sheet

Speaker: Oz Oshri (Tel Aviv University)

19:00 Conference dinner

Friday 29 May

11 Origami and metamaterials

Speaker: Christian Santangelo (University of Massachusetts)

12 Shape memory at the molecular level

Speaker: Vikram Reddy Ardham (TU Darmstadt)

10:45 Coffee break

13 Defects in Self-assembled Bilayers: Tomographic Characterisation and Influence on Folding Behaviour

Self-assembly describes the spontaneous arrangement of building blocks into complex architectures and patterns with internal symmetries and long-range order. Growth from the bottom-up often involves local packing disorder and defect formation. This presentation discusses the nucleation and evolution of topological defects in template-free self-assembled bilayer sheets growing to closed capsules with bilayer thickness. For that, block copolymers were self-assembled to 50 nm thick sheets and decorated on both sides with a cylinder morphology forming distinct pattern with disclinations of topological strength +1/2 in the origin. The number as well as the distance of disclinations has subtle influence on the local bending modulus of the sheets that affect roll-up mechanism and ultimately govern capsule shape through screening of areas with high-energy curvatures. Since closed capsules still carry cylinders on in- and outside of the membrane (50 nm), topological defects reorganise to four disclinations to satisfy Euler Characteristic. Electron tomography of the bilayers suggests communication between the four disclinations on either side of the membrane, but also across the membrane most likely connecting all eight defects. Topological defects on self-assembled closed shells supports the understanding of complex soft matter nanostructures and may open routes to precise functionalization for hierarchical self-assembly and advanced gating.

Speaker: Andre Gröschel (School of Science, Aalto University)

14 Deformation of a cell membrane in a low Reynold's number fluid

Speaker: Arghyadip Mukherjee (Indian Institute of Science & Liebniz Institut für Polymerforschung)

12:15 Lunch

15 Polyhedral Order in Soft Systems

The competition between order and shape in thin shell soft systems can lead to a wide variety of ground state shapes including sharp faceted polyhedra. The precise shapes and the type of polyhedron depend on the nature of the order, the topology of the shell and the material parameters of the system.

Speaker: Mark Bowick (Syracuse University)

16 Integral Geometry and Physics of Random Spatial Structures

A morphometric analysis of stochastic geometries is introduced by using tensorial valuations, i.e., tensor-valued Minkowski functionals. Tensorial physical properties such as elasticity, permeability and conductance of microstructured heterogeneous materials require quantitative measures for anisotropic characteristics of random spatial structure. Tensor-valued Minkowski functionals, defined in the framework of integral geometry, provide a concise set of descriptors. The talk provides an overview on the application on stochastic geometries used in physics. A robust computation of these measures is presented for microscopy images and polygonal shapes by linear-time algorithms. Their relevance for shape description, their versatility and their robustness is demonstrated by applying them to experimental datasets, specifically microscopy datasets. Applications are shown in two dimensions on Turing patterns and on sections of ice grains from Antarctic cores. In three dimensions Minkowski tensors have been used to quantify the anisotropy of fluids and granular matter, of confocal microscopy images of sheared biopolymers and of triply-periodic minimal surface models for amphiphilic self-assembly.

Speaker: Klaus Mecke (Universität Erlangen-Nürnberg)

17 Microstructure of random networks

Speaker: Axel Ekman (University of Jyväskylä, Finland)

Saturday 30 May

18 Flocks on a globe: Coupling between curvature and collective active motion

Speaker: Rastko Sknepnek (University of Dundee)

19 Collective phenomena in blood flow

Red blood cells (RBCs) dictate Blood flow properties, in healthy conditions. Intricate collective phenomena will be described. It will be shown that blood flow elements, if hematocrit is not too large, organize in ordered patterns with several impacts on rheology. Simulation results together with experimental observations will be reported. For example, spatial organization significantly lower the effective viscosity, and limits the increase of the viscosity with hematocrit in microcirculation, ensuring a proper regulation of oxygen transport even when hematocrit is sensibly beyond the normally admitted value. For example, athletics adopting blood doping as well as in some diseases (like primary and secondary polycythemia) an increase in hematocrit normally causes blood to become more viscous in macrocirculation. However, in microcirculation, depletion of RBCs close to the vessel walls, as well as spatial organization significantly moderate the increase of viscosity with hematocrit.

Speaker: Chaouqi Misbah (Laboratoire Interdisciplinaire de Physique, Univ. J. Fourier and CNRS)

11:00 Coffee break

20 Blood Cells under Flow

The flow behavior of vesicles and blood cells is important in many applications in biology and medicine. For example, the flow properties of blood in micro-vessels is determined by the rheological properties of red blood cells (RBCs). Blood flow is therefore strongly affected by diseases such as malaria or diabetes, where RBC deformability is strongly reduced. Furthermore, microfluidic devices have been developed recently, which allow the manipulation of small amounts of suspensions of particles or cells. Of fundamental interest is here the relation between the flow behavior and the elasticity and deformability of the blood cells, their long-range hydrodynamic interactions in microchannels, and thermal membrane undulations [1]. We study these mechanisms by combination of particle-based mesoscale simulation techniques [2] for the fluid hydrodynamics with triangulated-surface models [3, 4, 5] for the membrane. The essential control parameters are the volume fraction of RBCs (tube hematocrit), the cell shape and deformability, the flow velocity, and the capillary radius. In narrow channels, single red blood cells in capillary flow show a transition from the biconcave disk shape at low flow velocities to a parachute shape at high flow velocities [4, 6]. For somewhat wider channels, other shapes such as slippers intervene between these states [6]. At higher volume fractions, hydrodynamic interactions are responsible for a strong deformation-mediated clustering tendency at low hematocrits, as well as several distinct flow phases at higher hematocrits [7]. For large vessels, blood behaves like a continuum fluid, which displays a strong shear-thinning behavior; our simulations show quantitatively how this behavior arises due to RBC deformability and cell-cell attraction [8]. Finally, the interaction of RBCs with other blood cells or drug carriers is shown to lead to the margination of these particles at intermediate hematocrits and not too large flow rates [9, 10]. The properties of sedimenting RBCs are also briefly discussed [11]. [1] D. A. Fedosov, H. Noguchi, and G. Gompper. Multiscale Modeling of Blood Flow: From Single Cells to Blood Rheology. Biomech. Model. Mechanobiol. 13, 239-258 (2014). [2] G. Gompper, T. Ihle, D. M. Kroll, and R. G. Winkler. Multi-Particle Collision Dynamics - a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids. Adv. Polymer Sci. 221, 1 (2009). [3] G. Gompper and D. M. Kroll. Triangulated-Surface Models of Fluctuating Membranes. In Statistical Mechanics of Membranes and Surfaces, 2nd edition, edited by D. R. Nelson and T. Piran and S. Weinberg (World Scientific, Singapore, 2004). [4] H. Noguchi and G. Gompper. Shape Transitions of Fluid Vesicles and Red Blood Cells in Capillary Flows. Proc. Natl. Acad. Sci. USA 102, 14159 (2005). [5] D. A. Fedosov, B. Caswell, and G. E. Karniadakis. A multiscale red blood cell model with accurate mechanics, rheology, and dynamics. Biophys. J. 98, 2215 (2010). [6] D. A. Fedosov, M. Peltomäki, and G. Gompper. Shapes and Deformation of Red Blood Cells in Microvessel Flows. Soft Matter 10, 4258-4267 (2014). [7] J. L. McWhirter, H. Noguchi, and G. Gompper. Flow-Induced Clustering and Alignment of Red Blood Cells in Microchannels. Proc. Natl. Acad. Sci. USA 106, 6039 (2009). [8] D. A. Fedosov, W. Pan, B. Caswell, G. Gompper, and G. E. Karniadakis. Predicting blood rheology in silico. Proc. Natl. Acad. Sci. USA 108, 11772 (2011). [9] D. A. Fedosov, J. Fornleitner, and G. Gompper. Margination of White Blood Cells in Microcapillary Flow. Phys. Rev. Lett. 108, 028104 (2012). [10] K. Müller, D. A. Fedosov, and G. Gompper, Margination of micro- and nano-particles in blood flow and its effect on the effciency of drug delivery. Sci. Rep. 4, 4871 (2014). [11] M. Peltomäki and G. Gompper, Sedimentation of Single Red Blood Cells. Soft Matter 9, 8346{8358 (2013).

Speaker: Gerhard Gompper (Institute of Complex Systems and Institute for Advanced Simulation, Germany)

21 Multi-blob coarse graining for ring polymer solutions

Speaker: Arturo Narros Gonzalez (Queen Mary University of London)