styfloat

Contact:

Dr. O. KampsCenter for Nonlinear ScienceUniversity of MünsterCorrensstraße 2

48149 MünsterTel.: +49 251 83 33515

Fax: +49 251 83 33513

okamp@uni-muenster.de

Picture on title page: ©kichigin19/Taiga (Fotolia)

L O C AT I O N

The workshop takes place at the "Schloss" of the University of Münster

Schlossplatz 2

48149 Münster

©WWU - Peter Grewer

N O N L I N E A R D Y N A M I C S O F S T R U C T U R E F O R M AT I O N ATI N T E R FA C E S

Interfaces and surfaces are very important and often dynamic elements ofmany processes in nature and industry. Therefore they are subject of intensetheoretical, computational and experimental research in all natural sciencesand their understanding is of central interest in many branches of contem-porary engineering. Examples are on the one hand, soft adaptive polymersurfaces which change their properties triggered by the environment or softand hard surfaces or layers with evolving ordered patterns or disordered tex-tures in the nanometer range. On the other hand, surfaces and interfacesare of paramount importance for the mesoscale behaviour of biological andbiomimetic systems, e.g., dynamic structures at and in biological cell mem-branes such as lipid rafts and self-organised protein patterns.

The scope of the workshop is to foster the exchange of recent results andideas related to the dynamics of and at interfaces and surfaces that are in-vestigated in a variety of (interdisciplinary) fields in the natural sciences andapplied mathematics. As in many cases the resulting structures result fromspontaneous self-organisation, a specific aim is to identify universal featuresrelated to the nonlinear character of the underlying processes, to place the in-dividual systems and phenomena into the wider context of the understandingof out-of-equilibrium phenomena. Ample opportunities for exchange (includ-ing discussions after each talk and a poster session) shall allow early-stage anddistinguished scientists to discuss challenges and open problems across fieldsand to identify ways to coordinate future efforts.

M Ü N S T E R A N I A N T O RT U R I A L S

The Münsteranian Torturials are a series of tutorials designed to close the gapbetween scientific education and active research. The first part of the seriesintroduces to the technique of continuation using examples related to dropsand decomposition. This method is an invaluable tool to find branches ofstable and unstable solutions of systems described by nonlinear ordinary orpartial differential equations and is extremely helpful for exploring complexphenomena like structure formation at interfaces. The tutorials are based onthe software auto. For further information vist

www.uni-muenster.de/cenos/muensteraniantorturials

P R O G R A M

monday 02 .03 .2015

12.30 Registration and Lunch

14.10 Opening U. Thiele14.30 Non-equilibrium conformations and phase morpholo-

gies in polymer blendsU. Steiner

15.00 Active motion of microswimmers: role of interfaces H. Stark

15.30 Coffee

16:00 Structure formation in 2D systems: from surfaces tomembranes

A. Heuer

16.30 Control and selection of spatio-temporal patterns in dy-namic self-assembly systems

S. Gurevich

17.00 Variational models for phase transitions C. Zeppieri

17:30 End

tuesday 03 .03 .2015

9:00 Drops on lubricant-infused textured slippery sur-faces

H. J. Butt

9:45 On ripples and rafts: Curvature inducednanoscale structures in lipid membranes

F. Schmid

10:30 Coffee

11:00 Cluster formation on surfaces: Nucleation andmorphology

P. Maass

11:30 Entropic electrokinetics. Dynamics of chargedtracers and electrolytes under strong confinement

I. Pagonabarraga

12:00 Soft wetting: Liquid drops on (visco)elastic solids J. Snoeijer

12:30 Lunch

14:00 Postersession and Coffee

15:30 Domains in Asymmetric Membranes: Structureand Dynamics

D. Andelman

16:15 Controlled pattern formation of molecular sys-tems on surfaces

H.Fuchs

17:00 End

19:00 Conference Dinner

wednesday 04 .03 .2015

9.00 Non-equilibrium phenomena at nanoscopicand macroscopic interfaces: from molecularswitching to dynamic self-assembly

B. Grzybowski

9.45 Do crystallization seeds seed crystallization?Some time

H. Löwen

10.30 Coffee

11.00 Complex dynamics in multiscale systems S. Kalliadasis11.30 Breath figures: Anomalous scaling due to

droplet growth and coagulationJ. Vollmer

12.00 Spiral actin-polymerization waves can generateamoeboidal cell crawling

K. Kruse

12.30 Lunch

14.00 Pinning and gas oversaturation imply stablesingle surface nanobubbles: An exact calcula-tion

D. Lohse

14.45 Nonlinear effects in layer growth and conduc-tivity of Layer-by-Layer films

M. Schönhoff

15:15 Coffee

15:45 Protein-induced lipid segregation in biologicalmembranes

V. Gerke

16:15 Optimization of polarity establishment throughcoupling of multiple feedback loops

R. Wedlich-Söldner

16:45 End

thursday 04 .09 .2014

9:00 Continuum modeling of deposition, erosion and re-deposition

C. Diddens

9:30 Membranes and vesicles with bilayer asymmetry:Molecular simulations and engulfment of nanopar-ticles

R. Lipowsky

10:15 Coffee

10:45 Modeling the dynamics of solid-state dewetting P. Pierre-Louis11:30 Shaping evaporative ring deposits T. Witten

12:15 Closing and Lunch

A B S T R A C T S

U. Steiner Adolphe Merkle Institute, Universität Freiburg

Non-equilibrium conformations and phase morphologies inpolymer blends

Structure and properties in polymer melts are mostly considered close to ther-modynamic equilibrium. Because of their entangled nature, however, densemacromolecular systems may not always reach equilibrium in practical set-tings. My conference contribution will discuss two scenarios, where the prop-erties of macromolecular melts are determined by the interplay of thermody-namic and kinetic processes.

The first topic concerns polymer films, in which chain conformations arearrested during spin-coating. Under conditions that are typical for thin filmpreparation, the arrest of chain reptation during processing result in rheolog-ical properties of the film that differ substantially from the equilibrium melt.The post-deposition thermal equilibration of these films is typically very slow,and in some instances impractical.

The second topic investigates the structure formation in blends containingconjugated polymers. Films of these blends are important for optoelectronicapplications, e..g. polymer-based solar cells. Here we demonstrate that struc-ture formation is dominated by the crystallisation of one of the conjugatedcomponents, resulting in a hierarchical morphology. It is likely that the inter-play of crystallisation and phase separation in these blends determine theirelectronic properties.

H. Stark Institut für Theoretische Physik, TU Berlin

Active motion of microswimmers: role of interfaces

Active motion of microswimmers has attracted much interest recently. Beingnon-equilibrium systems, microswimmers give rise to novel appealing physicssuch as emergent collective behavior but they are also important in the biologi-cal world. The talk discusses at a few examples the role of interfaces for activemotion. It explains how an emulsion droplet becomes active via structureformation at the fluid-fluid interface initiated by Marangoni flow [1] and it

shows examples of non-trivial collective patterns, which microswimmers cre-ate at interfaces of thin films [2]. We also shortly illustrate how hydrodynamicflow fields determine the collective dynamics of microswimmers in a quasi-2Dgeometry [3] and how, in conjunction with noise, they influence the swimmer-surface interaction [4].

[1] M. Schmitt and H. Stark, Europhys. Lett. 101, 44008 (2013).[2] A. Pototsky, U. Thiele, and H. Stark, Phys. Rev. E 90, 030401(R) 2014.[3] A. Zöttl and H. Stark, Phys. Rev. Lett. 112, 118101 (2014)[4] K. Schaar, A. Zöttl, and H. Stark, submitted to Phys. Rev. Lett.

A. Heuer Institut für Physikalische Chemie, WWU Münster

Structure formation in 2D systems: from surfaces to membranes

Structure formation in 2D can be important for applications and its analysisis attractive due to the ability to visualize the structural and kinetic effects. Inthis talk two different types of systems are discussed. (1) Multi-componentmembranes can form so called liquid ordered and liquid disordered regimes(sometimes called raft formation) with different structural and dynamical equi-librium properties. We present results of computer simulations, using atom-istic and coarse grained force fields and discuss how to identify the key prereq-uisites for raft formation. (2) In contrast, when studying the structure forma-tion of molecules after vacuum deposition on a substrate, the final structuremay result from strongly non-equilibrium kinetic effects. Here, we discussthe structure formation of chain molecules on surfaces as well as of organicmolecules on prepatterned surfaces. The results are compared with recent ex-periments. Non-trivial flux dependencies are observed in simulations and ex-periments which reflect a complex interplay of kinetic trapping and approach-ing equilibrium.

S. Gurevich Institut für Theoretische Physik, WWU Münster

Control and selection of spatio-temporal patterns in dynamicself-assembly systems

Self-organization or dynamic self-assembly is a mechanism responsible for theformation of complex structures through multiple interactions among the mi-croscopic components of the system. In the first part of the talk the formationof regular stripe patterns during the transfer of surfactant monolayers from

water surfaces onto moving solid substrates is discussed by means of a gen-eralized Cahn-Hilliard model. A combination of numerical simulations andcontinuation methods is employed to investigate stationary and time-periodicsolutions of the model . The second part of the talk deals with the influenceof a periodic spatial forcing on the pattern formation in Langmuir-Blodgetttransfer experiments. We show that the occurring locking effects enable a con-trol mechanism for the pattern formation process. In the one-dimensional casethe parameter range in which patterns are created can be increased and theproperties of occurring structures can be adjusted in a broader range. Alterna-tively, in two dimensions, one-dimensional stripe patterns can be destabilized,giving rise to a multitude of complex two-dimensional structures, includingoblique and lattice patterns. In addition, a different control mechanism bymeans of a modulated transfer velocity is discussed. Our theoretical resultspredict that this method can also be used as an effective tool to control thepattern formation process.

C. Zeppieri Applied Mathematics, WWU Münster

Variational models for phase transitions

Singular-perturbation models involving a penalization of the first-order deriva-tives have provided a new insight into the role played by surface energies inthe study of phase transition problems. Motivated by the study of phase tran-sitions for higher-order materials, in this talk we discuss the behaviour ofnon-convex functionals singularly perturbed by a second-order gradient term.From the stand point of global minimization, we show that the limit as theperturbation vanishes gives rise to a sharp interface.

H. J. Butt MPI for Polymer Research, Mainz

Drops on lubricant-infused textured slippery surfaces

Droplets on lubricant-infused textured surfaces "slip" when tilting the surfaceeven by few degrees. Still, the underlying mechanism of how the lubricantchanges the static and dynamic properties of the drop and the role of the solidsubstrate are unclear. We monitored the shape of the wetting ridge of lubri-cant surrounding a drop by laser scanning confocal microscopy. We quantifythe contact angles at the liquid and solid three-phase contact lines and imagewe how a drop advances and recedes. The ârealâ contact angle of the drop/lu-

bricant interface with the solid substrate exceeds 150◦ although macroscopiccontour images suggest contact angles of < 90◦. Moving drops recede via de-pinning from protrusions at a defined receding contact angle. The advancingside remains pinned at a protrusion until the drop/lubricant interface gradu-ally bends downwards and touches the top face of the next protrusion. Thus,the effective advancing contact angle is 180◦. Cloaking of the drop by the lu-bricant cannot be predicted by the surface tension of pure liquids, as dramaticchanges can be induced even by slight miscibility.

F. Schmid Johannes Gutenberg-Universität Mainz

On ripples and rafts: Curvature induced nanoscale structuresin lipid membranes

Biomembranes are ubiquitous in all living matter. They are essential for com-partmentalization and controlling processes that are central for life such astransport or signalling. The basic frame of a biomembrane is a bilayer ofself-assembled lipids, in which proteins are incorporated that perform variousbiological functions. Whereas research has long focussed on the membraneproteins, the role of the lipid bilayer for controlling and organizing the pro-teins is more and more acknowledged. This implies that important biologicalprocesses are driven or at least strongly influenced by physical processes.

For physicist’s, membranes have many fascinating aspects: First, they arebeautiful examples of self-assembled mesoscale structures, second, they arereal-life examples of two-dimensional fluctuating manifolds in space, andthird, they have a rich phase behavior, and all of these aspects contribute to thebiological function of membranes. The talk will start with a short introductionto membranes and lipid bilayers, and then focus on our own work in this area.

I will present a generic coarse-grained simulation model for lipids which re-produces many important properties of lipid bilayers [1], and briefly discussthe interaction of these bilayers with simple cylindrical inclusions [2,3]. Theseinteractions can be analyzed at a quantitative level within an elastic theory thatdescribes the membranes by two coupled elastic (monolayer) sheets [2]. Thistheory has been extended to multiphase systems that can undergo in-planephase separation between two phases with different spontaneous monolayercurvature [4,5]. The interplay of monolayer elasticity and phase separationleads to nanoscale ordering. Thus the theory rationalizes in a unified man-ner the observation of a variety of nanoscale structures in lipid membranes:Rippled states in one-component membranes, lipid rafts in multicomponent

membranes. Both are observed in our generic simulations, with propertiesthat are compatible with experimental observations [1,4,6].

[1] O. Lenz, F. Schmid, Phys. Rev. Lett. 98, 058104 (2007).[2] B. West, F.L.H. Brown, F. Schmid, Biophysical Journal 96, 101 (2009).[3] J. Neder, P. Nielaba, B. West, F. Schmid, New J. Physics 14, 125017 (2014).[4] S. Meinhardt, R.L.C. Vink, F. Schmid, PNAS 119, 4476 (2013).[5] F. Schmid, S. Dolezel, O. Lenz, S. Meinhardt, J. Physics: Conference Series487, 012004 (2014).[6] L. Toppozini, S. Meinhardt, C.L. Armstrong, Z. Yamani, N. Kuvcerka, F.Schmid, M. Rheinstaedter, Phys. Rev. Lett. 113, 228101 (2014).

P. Maas Department of Physics, University of Osnabrück

Cluster formation on surfaces: Nucleation and morphology

Understanding and control of cluster growth on solid surfaces is a subjectof intensive research to develop nanomaterials with new physical properties.Of particular interest is the self-organized structure formation by depositionof atoms and molecules on surfaces, where the interplay of diffusion, nucle-ation, aggregation, segregation and superlattice ordering yields a rich vari-ety of growth phenomena. The resulting structures are often frozen-in non-equilibrium structures with properties distinctly different from the equilib-rium bulk phases. In the talk I will address three interrelated problems [1]:second layer nucleation, growth of binary alloy nanoclusters with perpendicu-lar magnetic anisotropy, and morphologies of fullerene clusters on insulatingsubstrates.

[1] M. Einax, W. Dieterich, and P. Maass, Colloquium: Cluster Growth on Sur-faces: Densities, Size Distributions, and Morphologies. Rev. Mod. Phys. 85,921 (2013).

I. Pagonabarraga Universitat de Barcelona

Entropic electrokinetics. Dynamics of charged tracers and elec-trolytes under strong confinement

I will analyze the dynamics of electrolytes under confinement. I will describecomputational and theoretical methods that allow us to understand how theheterogeneous spatial confinement ( found in a wide variety of situations such

as porous media, or membrane ion channels ) can modify qualitatively thednamics and transport in charged fluids. Understand the physical mecha-nisms controlling electrolyte dynamcs in such conditions will shade light ontheir relevance in a wide variety of situations, ranging from nano- and micro-fluidic devices to biological systems. I will show that when particles are sus-pended in an electrolyte confined between corrugated charged surfaces, elec-trokinetic flows lead to a new set of phenomena such as particle separation,mixing for low-Reynolds micro- and nano-metric devices and negative mobil-ity.

J. Snoeijer University of Twente & TU Eindhoven

Soft wetting: Liquid drops on (visco)elastic solids

The wetting of a liquid on a solid usually assumes the substrate to be per-fectly rigid. However, this is no longer appropriate when the substrate is verysoft: capillary forces can induce substantial elastic deformations, as has beendemonstrated e.g. for drops on elastomers. In this talk we discuss the fun-damentals of elasto-capillary interactions. For static situations we show howsoft solids are deformed under the influence of a droplet or bubble. We thenturn to droplet dynamics. Remarkably, the contact line motion is primarilygoverned by the viscoelastic properties of the solid while the liquid hydrody-namics plays a negligible role. Experimental results are successfully comparedto a theory based on the substrate rheology, which also explains stick-slip mo-tion of the contact line.

D. Andelman Tel Aviv University

Domains in Asymmetric Membranes: Structure and Dynamics

In recent years the notion of ‘raftsâ in biological membranes became popu-lar, and the current understanding is that these are most probably small anddynamical domains composed of lipids, cholesterol and protein mixtures. Af-ter a short introduction of domains in biological membranes, I will discussa model addressing the formation of lateral domains in membranes, whichare composed of two coupled and spatially modulated leaflets. We obtain thephase diagrams when the two monolayers have the same preferred modula-tion wavelength. Due to this inter-leaflet coupling, a spatial modulation in

one of the leaflets induces a similar periodic structure in the second one. Wehave also performed numerical simulations for the case when the two leafletshave different modulation wavelengths. Complex patterns may arise from thefrustration between the two incommensurate but annealed structures. The dy-namics of domain formation is also investigated via the membrane structurefactor.

H. Fuchs Physikalisches Institut & CeNTech, WWU Münster

Controlled pattern formation of molecular systems on surfacessystems

The interplay of intermolecular and molecule-substrate interactions can beused to determine the large scale self-assembled pattern formation of moleculeson surfaces. By adjusting these competing interactions separately, kinetic con-trol of the patterns is achieved and, in addition, subsequent chemical reactioncan be either promoted or inhibited e.g. in the case of non-templated substratesystems. Two-dimensional long range orientational order and disorder can beintroduced by appropriately modifying the molecular structure, with keepingthe nature of the surfaces unmodified. More complex super-structures can begenerated by making use of thermodynamic and subsequent kinetic control,which may result in large scale A/B-type molecular layers without using anykind of lithographic pre-structuring. The latter technique can be used to gen-erate phase separation with kinetic control making use of differing materialsdeposited on a given substrate, and by varying, e.g. the pitch or the templatestructures, the evaporation speed, and the deposition temperature. Examplesfor the differing strategies will be given.

B. A. Grzybowski Northwestern University

Non-equilibrium phenomena at nanoscopic and macroscopicinterfaces: from molecular switching to dynamic self-assembly

Materials operating and organizing away from thermodynamic equilibriumare interesting because they can perform life-like functions such as sensing,adaptability to external conditions, taxis, or potentially even self-replication.The design of such non-equilibrium materials and systems often depends onour ability to engineer interfaces that are responsive to external changes/stim-

uli. In my talk I will illustrate how this can be done both at the nano- and themacroscales. In the former case, I will focus on interfaces comprising switch-able molecules whose conformational changes can drive self-assembly anddisassembly processes. In the latter case, I will discuss systems in which theinterfaces between liquids help set up concentration gradients that effectivelymove macroscopic objects allowing these objects to dynamically assemble oreven form primitive swarms.

H. Löwen Heinrich-Heine-Universität Düsseldorf

Do crystallization seeds seed crystallization? Some time

Crystallization is a prime example of a disorder-order transition. Becausein many applications container walls and impurities are present, frequentlycrystallization is heterogeneously seeded. However, rarely these seeds are per-fectly compatible with the thermodynamically-favored crystal structure andthus induce elastic distortions, which impede further crystal growth. We quan-titatively investigated this process on an individual-particle level by experi-ments, simulations and theory using a colloidal model system which allowsus to quantitatively control the induced distortions. The crystallite is found todetach from the seed upon exceeding a critical size. The detached and relaxedcrystallite continues to grow in bulk except close to the seed which now pre-vents crystallization. Hence crystallization seeds seed crystallization only forsome time and then act as impurity.

S. Kalliadasis Imperial College London

Complex dynamics in multiscale systems

Understanding the evolution of complex multiscale systems is crucial froma fundamental but also the applications’ point of view. For instance, manyengineering systems are complex and multiscale and understanding their dy-namics has the potential to predict a specific system’s behavior, engineer itsdesign and build-in response to arrive at a highly optimal and robust system.We combine elements from nonlinear science, statistical physics, critical phe-nomena and information theory to develop a number of novel and genericmethodologies that enable us to undertake the rigorous and systematic studyof the emergence of complex behavior in multiscale systems. The method-

ologies are exemplified with paradigmatic prototypes from different classesof complex systems such as interface dynamics in disordered media, convec-tively unstable open flows and stochastic multiscale processes.

J. Vollmer MPI for Dynamics and Self-Organization, Göttingen

Breath figures: Anomalous scaling due to droplet growth andcoagulation

Droplet patterns condensing on solid substrates (breath figures) tend to evolveinto a self-similar regime, characterized by a bimodal droplet size distribution.The distributions comprise a bell-shaped peak of monodisperse large droplets,and a broad range of smaller droplets following a scaling law characterizedby a non-trivial polydispersity exponent. Blackman and Brochard (Phys. Rev.Lett., 2000) predicted that this exponent takes the universal value 1 + (5d −

3)/4D, where D and d are the dimension of the droplets and the substrate,repectively.

Here, we present experimental and numerical data strongly indicating that– in contrast to this assertion – the polydispersity exponent is not universal.Rather it depends on microscopic details of the growth process. For instance,for three-dimensional droplets (D = 3) growing on a one-dimensional fiber(d = 1) the exponent depends explicitly on the thickness of the fiber and ondetails of the droplet interaction leading to merging. Moreover, in the fullrange of data we find values for the polydispersity exponent that are system-atically smaller than the prediction. Possible causes of this discrepancy arepointed out.

K. Kruse Theoretische Biologische Physik, Universität des Saarlandes

Spiral actin-polymerization waves can generate amoeboidal cellcrawling

Amoeboidal cell crawling on solid substrates is characterized by protrusionsthat seemingly appear randomly along the cell periphery and drive the cellforward. For many cell types it is known that the protrusions result frompolymerization of the actin cytoskeleton. However, little is known about howthe formation of protrusions is triggered and whether the appearance of sub-sequent protrusions is coordinated. Recently, the spontaneous formation of

actin polymerization waves was observed. These waves have been proposedto orchestrate the cytoskeletal dynamics during cell crawling. Here, we studythe impact of cytoskeletal polymerization waves on cell migration using aphase-field approach. In addition to directionally moving cells, we find statesreminiscent of amoeboidal cell crawling. In this framework, new protrusionsare seen to emerge from a nucleation process generating spiral actin waves inthe cell interior. Nucleation of new spirals does not require noise, but occursin a state that is apparently displaying spatio-temporal chaos. Finally, we com-pare our results to the motion of some biological cells.

D. Lohse University of Twente

Pinning and gas oversaturation imply stable single surfacenanobubbles: An exact calculation

Surface nanobubbles are experimentally known to survive for days at hy-drophobic surfaces immersed in gas-oversaturated water. This is differentfrom bulk nanobubbles, which are pressed out by the Laplace pressure againstany gas oversaturation and dissolve in sub-milliseconds, as derived by Epsteinand Plesset [J. Chem. Phys. 18, 1505 (1950)]. Pinning of the contact line hasbeen speculated to be the reason for the stability of the surface nanobubbles.Building on an exact result by Popov [Phys. Rev. E 71, 036313 (2005)] on coffeestain evaporation, here we confirm this speculation by an exact calculation forsingle surface nanobubbles. It is based only on (i) the diffusion equation, (ii)Laplace pressure, and (iii) Henryâs equation, i.e., fluid dynamical equationswhich are all known to be valid down to the nanometer scale. The crucial pa-rameter is the gas oversaturation ζ of the liquid. At the stable equilibrium, theinflux into the surface nanobubble due to this gas-oversaturation is balancedby the outflux due to the Laplace pressure. The theory predicts how the con-tact angle of the pinned bubble depends on ζ and the surface nanobubble’sfootprint lateral extension L. It also predicts an upper lateral extension thresh-old for stable surface nanobubbles to exist.

M. Schönhoff WWU Münster

Nonlinear effects in layer growth and conductivity of Layer-by-Layer films

For the fabrication of nanostructures, self-organized bottom-up approachesbased on deposition and/or erosion processes are promising alternatives totypical nanolithography methods. Since the corresponding surface evolutioncan reach from stochastically rough, spatio-temporally chaotic up to well-ordered patterns, the understanding of the underlying physical mechanismsleading to this variety of morphologies constitutes a major theoretical chal-lenge. In particular, the method of constructing nonlinear continuum equa-tions for the spatio-temporal evolution of the surface morphology by combin-ing symmetry requirements, small gradient expansions and models for vari-ous roughening and smoothing mechanisms seems to be a viable approachto obtain deeper insight into surface structuring. After presenting a rathergeneral introduction into the subject, we discuss two specific topics: the sur-face evolution due to (1) deposition of low-energetic particles and (2) erosionof target material caused by low-energetic impinging particles including rede-position. In both cases, we review the potential physical mechanisms beingresponsible for the competition of roughening and smoothing processes onthe surfaces, present corresponding evolution equations for the surface mor-phologies in form of generalized Kuramoto-Sivashinsky equations, analyzethe pattern forming properties of these equations and compare them with rep-resentative experiments.

Polyelectrolyte multilayers (PEM) are formed by the Layer-by-Layer method,involving the alternating adsorption of polycations and polyanions to a chargedinterface, resulting in defined ultrathin layers in the nanometer range. Themethod is rather robust concerning the materials involved, as long as the ad-sorbant is charged and of nanometer dimensions.

In most cases the growth law, e.g. thickness in dependence on number oflayers, is linear. However, in the case of biopolymers nonlinearity, i.e. anexponential growth, has commonly been observed and was attributed to aninterdiffusion of the polyelectrolytes (PE). Recently, we had shown that evenPEM from two weak synthetic polyelectrolytes can exhibit nonlinear growth,and we identified pH-dependent growth regimes with exponential or lineargrowth, respectively [1]. Here, we investigate further PE combinations in orderto elucidate their growth laws, in particular in dependence on the pH duringpreparation. We study (i) poly(diallyldimethyl-ammonium) and poly(acrylicacid) (PDADMA/PAA) as a system containing one weak as well as one strong

PE component and (ii) poly(L-lysine) and hyaluronic acid (PLL/HA) as a typ-ical biopolymer system, respectively. Quartz crystal microbalance (QCM-D)is used to investigate the build-up process in-situ. Raw data are analyzed byKelvin-Voigt viscoelastic modeling, delivering film parameters such as thick-ness, viscosity and shear modulus. As a result, PDADMA/PAA multilayersshow a pH-dependent growth behavior: Regimes of differently pronouncedexponential growth as well as regimes of linear growth are observed. Asa mechanism for nonlinear growth we can again postulate interdiffusion ofchains, which is strongly dependent on the charge density of the chain andthus on the pH value during preparation. PLL/HA films show exponentialgrowth at all pH values. However, the parameters describing the growth lawdepend on the pH environment during film formation. Chain interdiffusioncausing nonlinearity thus occurs for rather different charge densities at allpH values, but to a different extent. Furthermore, PEM are, due to their in-herently low thickness, interesting candidates for applications as electrolytes.With this motivation we are studying fundamental charge transport propertiesby impedance spectroscopy, where nonlinearities occur in dependence on therelative humidity: Earlier results showed a strong exponential dependence asa general law. As charge carriers, protons were identified [2]. Here, we presentconductivity data for LbL films doped with gold nanoparticles [3]. With in-creasing relative humidity, a decrease of the conductivity is seen, opposedto the conductivity of PEM without nanoparticles. In this case, the conduc-tivity is explained by electronic charge transport via the gold particles as thedominating conduction mechanism, involving electron tunneling processes be-tween particles. Furthermore, the conductivity can be reversibly tuned by hu-midity via control of interparticle tunneling probabilities.

[1] Bieker, P.; Schönhoff, M. Macromolecules 2010, 43(11), 5052-5059.[2] Akgöl, Y.; Cramer, C.; Hofmann, C.; Karatas, Y.; Wiemhöfer H.D. ; Schön-hoff, M. Macromolecules 2010, 43(17), 7282-7287.[3] Ostendorf, A.; Cramer, C.; Decher, G.; Schönhoff, M. J. Phys. Chem. C,submitted.

V. Gerke Institute of Medical Biochemistry, WWU Münster

Protein-induced lipid segregation in biological membranes

Cellular membranes are a patchwork of domains showing local concentrationsof proteins and lipids that are quite different from the average of the entiremembrane. The dynamic formation of spatially restricted membrane domainsis linked to a diverse number of cellular events that range from the transduc-tion of signals received at the cell surface to the regulation of cell shape andintracellular membrane transport. It is driven by intrinsic properties of mem-brane lipids and integral as well as membrane-associated proteins. We analyzefundamental mechanisms underlying membrane microdomain formation us-ing cellular systems as well as artificial biological membranes. One focus ison lipid segregation induced by peripheral membrane binding proteins suchas the annexins, a family of Ca2+-regulated proteins that interact with acidicphospholipids. Lipid segregation is studied in giant liposomes and in lipidbilayers formed on solid supports and knowledge obtained in these artificialsystems is transferred to the dynamic organization of membranes in livingcells.

Wedlich-Söldner Institute of Cell Dynamics and Imaging, WWU Münster

Optimization of polarity establishment through coupling ofmultiple feedback loops

Establishment of cell polarity - or symmetry breaking - relies on local accu-mulation of polarity regulators. While simple positive feedback is in prin-ciple sufficient to drive symmetry breaking, living cells simultaneously em-ploy several feedback mechanisms to localize polarity factors. The reason forthis apparent redundancy is not well understood. By integrating mathemati-cal modeling with quantitative experimental validations we show that in theyeast Saccharomyces cerevisiae only a combination of active transport andreaction-diffusion systems is able to robustly concentrate polarity regulatorsat a single site during bud initiation. Our results demonstrate how cells op-timize symmetry-breaking through coupling of multiple feedback loops withdistinct pros and cons.

C. Diddens TU Eindhoven

Continuum modeling of deposition, erosion and redeposition

For the fabrication of nanostructures, self-organized bottom-up approachesbased on deposition and/or erosion processes are promising alternatives totypical nanolithography methods. Since the corresponding surface evolutioncan reach from stochastically rough, spatio-temporally chaotic up to well-ordered patterns, the understanding of the underlying physical mechanismsleading to this variety of morphologies constitutes a major theoretical chal-lenge. In particular, the method of constructing nonlinear continuum equa-tions for the spatio-temporal evolution of the surface morphology by combin-ing symmetry requirements, small gradient expansions and models for vari-ous roughening and smoothing mechanisms seems to be a viable approachto obtain deeper insight into surface structuring. After presenting a rathergeneral introduction into the subject, we discuss two specific topics: the sur-face evolution due to (1) deposition of low-energetic particles and (2) erosionof target material caused by low-energetic impinging particles including rede-position. In both cases, we review the potential physical mechanisms beingresponsible for the competition of roughening and smoothing processes onthe surfaces, present corresponding evolution equations for the surface mor-phologies in form of generalized Kuramoto-Sivashinsky equations, analyzethe pattern forming properties of these equations and compare them with rep-resentative experiments.

R. Lipowsky MPI of Colloids and Interfaces, Potsdam

Membranes and vesicles with bilayer asymmetry: Molecularsimulations and engulfment of nanoparticles

Biomimetic and biological membranes consist of molecular bilayers with twoleaflets which are typically exposed to different aqueous environments andmay differ in their molecular density or composition. Because of these asym-metries, the membranes prefer to curve in a certain manner as quantitativelydescribed by their spontaneous curvature. The talk will focus on two recentstudies of this curvature. First, using molecular dynamics simulations, wehave shown that the adsorption of relatively small solute particles with a sizebelow 1 nm can generate large spontaneous curvatures up to about 1/(24nm)[1]. Second, the spontaneous curvature turns out to have a rather strong effect

on the engulfment of nanoparticles by membranes and vesicles, as predictedfrom curvature-elastic membrane models [2].

[1] B. Rozycki and R. Lipowsky, J. Chem. Phys. (in press)[2] J. Agudo-Canalejo and R. Lipowsky, (under review)

O. Pierre-Louis Université Claude Bernard Lyon

Modeling the dynamics of solid-state dewetting

At scales smaller than the micron, surface diffusion can be an efficient way totransport atoms, leading to shape changes in solid-state films, particles, andother nano-structures. As a consequence, energy-minimizing shape changessimilar to the wetting and dewetting of liquids appears in nanoscale solids.We will discuss the similarities and the differences between solid-state andliquid-state wetting, with a focus on the modeling of the dewetting of solidfilms.

T. A. Witten The University of Chicago

Shaping evaporative ring deposits

This talk reviews the “coffee ring" phenomenon that has been shown to bea powerful means of shaping the deposition of colloidal solutes. We focuson two aspects that show special conceptual novelty. The first is depositionfrom a receding drop with fixed contact angle, recently demonstrated in ex-periments. Here evaporation and retraction of the contact line lead to inwardflow. This creates a singular mound of solute at the center of the drop. Thesecond shows how late deposition onto a drop has a controllable power-lawform. The power laws previously established for circular drops are general-ized to a wide range of drop shapes. Situations where the normal behaviorbreaks down are explored.

P O S T E R S

H. H. Boltz TU Dortmund

Sedimentation of Soft Elastic Capsules in Axisymmetric Vis-cous Flow

We introduce an iterative solution scheme to find the stationary shape and thevelocity of a deformable axisymmetric elastic capsule driven through a viscousfluid by an external force, such as gravity. We use this approach to systemati-cally study the sedimentation of soft elastic capsules with Hookean stretchingand bending energies. We find three types of possible axisymmetric stationaryshapes for sedimenting capsules with spherical rest shape: a pseudosphericalstate, a pear-shaped state, and a pair of two buckled shapes. The capsulecan undergo shape transformations as a function of the elastic properties char-acterized by the Föppl-von-Karman number and gravity as characterized bythe Bond number. The transition between a spherical and pear shapes is adiscontinuous transition with a hysteretic saddle node bifurcation for smallFöppl-von-Karman number or large Bond number. The corresponding transi-tion line terminates in a critical point. We also obtain the force-velocity relationof sedimenting capsules. Interestingly, up to three capsule shapes with differ-ent velocities can occur for the same gravitational driving force. Finally, westudy the correponding shapes for capsules pushed by a point force.

O. Buller Institut für Physikalische Chemie, WWU Münster

Single-island formation on prepatterned surfaces: a simulationapproach

Interesting structures are observed in vapor deposition experiments with or-ganic semiconducting molecules on surfaces which are prepatterned with goldon a silicon oxide substrate. The gold is forming a regular grid. The interac-tion of the deposited molecules is much higher with the gold rather than withthe substrate. In dependence on the experimental parameters flux, substratetemperature, and lattice size different structures are observed, reaching from

the absence of molecular clusters to the limit of multi-island formation persquare.

We use a simple discrete stochastic model to reproduce the observed struc-tures and the scaling of the formations with substrate temperature, flux andlattice size. Among others we check to which degree the experimentally rel-evant scenario of just a single cluster per square can be understood from atheoretical perspective.

A. Chervanyov Institut für Theoretische Physik, WWU Münster

Theory of Polymer Adsorption Onto Selected Chemically Pat-terned Surfaces

We theoretically studied the reversible adsorption of polymers onto selectedrigid and soft chemically non-uniform adsorbing surfaces with the objectiveto identify the main factors that affect the effective affinity of these surfaces. Inthe course of our study, we developed two independent theoretical methods,the self-consistent perturbation expansion and the transfer operator formal-ism, which made it possible to thoroughly investigate the density structureof polymers adsorbed onto chemically non-uniform substrates. As successivestages of our research, we applied the above theoretical methods to the studyof the polymer adsorption onto selected substrates, as follows: (i) periodicallypatterned rigid surface; (ii) randomly patterned rigid surface; (iii) surface thatbears an array of periodically distributed adsorption centers with/without de-fects; (iv) ripple, random and dimple morphologies of the binary mixed brush.By comparing the results obtained for the above listed systems we derive thequalitative trends that are common for the polymer adsorption onto the in-vestigated chemically non-uniform substrates. On the basis of the presentedanalysis, we identify the main factors that influence the polymer adsorptiononto the patterned substrates and ways of effective reducing/enhancing thepolymer adsorption by manipulating these competitive factors.

S. Eickelmann MPI of Colloids and Interfaces, Potsdam

Real-Time Imaging of Planar Film Evaporation, Deposition andPrecipitation in a Spin-Cast Configuration

Spin casting is a commonly used technique to deposit thin films of uniformthickness on planar substrates. Typically the deposited thin film is preparedfrom a mixture of a volatile solvent and a non-volatile solute (which formsthe deposited film). In this case the spin cast process is an interplay betweenhydrodynamic flow and solvent evaporation. However, aside from transientinitial processes (solvent deposition and planarization), the main process i.e.,the thinning of the planarized liquid film, the solute enrichment and the solutedeposition is dominated by evaporation. It can be shown that it is indepen-dent from the starting conditions. It is equivalent to the homogenous dryingof a planar film commencing at a "transition height" htr [1], which reflects thehydrodynamic spin cast contribution (rotation speed, viscosity) to the process.With this approach the film thinning, the spatio-temporal evolution of the so-lute and the resulting solute deposit can be modeled/accessed quantitatively.

We have built a set-up for the in-situ imaging of the liquid film thinning andthe solute deposition during the spin coating process with a time resolution ofmilliseconds, a spatial lateral resolution of microns, and a (vertical) thicknessresolution of nanometers [2]. We present experimental imaging data from avariety of solute/solvent systems under different spin cast conditions and com-pare/analyse them with the quantitative theoretical predictions [1]. Thus wegain new insights into the drying and de-wetting behaviour of thinning liquidfilms as well as into the nucleation and growth of aggregates/precipitates ofthe solute after exceeding its supersaturation limit in the course of the solventevaporation.

[1] S. Karpitschka, CM. Weber, H. Riegler, Chemical Engineering Science,http://dx.doi.org/10.1016/j.ces.2015.01.028

[2] R. Köhler, P. Lazar, H. Riegler, Appl. Phys. Lett. 89, 241906 (2006)

A. Eremin Otto-von-Guericke-Universität, Magdeburg

Relaxation dynamics in nonpolar colloidal suspensions of ani-sometric pigment particles

Colloidal suspensions of anisometric particles have become an attractive fieldof study for their ability to form structured phases (such as nematics and smec-tics) and their complex behaviour in electric fields. Long-range interparticleinteractions in nonpolar suspensions, resulting from weakly screened electro-static forces, may strongly affect the particle dynamics. Here, we study thedynamic behaviour of a colloidal suspension formed by dichroic solid rod-shaped pigments in a non-polar solvent (dodecane). The primary particlesize is about 250x40 nm. This suspension displays an unusual electro-opticalbehaviour showing a strong optical response in an electric field. Nematic orglass-like behaviour was found at a volume fraction as low as 0.12. At interme-diate fractions (10 – 12 wt%), the suspension is disordered, forming a globallyisotropic structure. Our study was focused on two types of behaviour: a) diffu-sion in diluted suspensions and b) relaxation dynamics of the phase separatedpatterns into the field-free state. The diffusive behaviour is observed for vari-ous concentrations by small angle- dynamic light scattering. Both translationaland rotational modes can be distinguished via VH- and VV-scattering, wherethe diffusion coefficients are found to increase with an increase of concentra-tion in a power law-like fashion, which is not yet fully understood. Reversibleparticle aggregation in an electric field gives rise to a rich variety of phases(in a field-frequency domain) showing patterns with different morphologiessuch as static and dynamic islands, labyrinths, etc. Relaxation of the patternsinto the homogeneous field-free state was studied using video-aided Fourier-Transform microscopy. We observed, that various patterns show different re-laxation dynamics, which often differs from the diffusion. Analysis of thedispersion relations for different modes indicates that long-range inter- parti-cle interactions may be responsible for this unusual dynamic behaviour.

L. Frastia Zilina

Thin film model for the formation of periodic deposits duringthe dewetting of suspensions

Experiments involving evaporating films or menisci of colloidal suspensionsor polymer solutions often show the deposition of regular patterns at the re-ceding contact line, e.g. concentric rings of deposited polymers or nanoparti-cles [1], formation of fingers perpendicular to dewetting front [2, 3] or morecomplex patterns when more sophisticated experimental setups are used [4].A recent review of experiments and models of patterned deposition is in [5].

We use a thin film model in lubrication approximation that extends a litera-ture model for an evaporating pure liquid [6, 7] for the case of an evaporatingsuspension. We show that using a viscosity that diverges at a critical soluteconcentration suffices to trigger a self-organised periodic pinning-depinningprocess that results in the deposition of regular line or ring patterns. Themodel is used to perform numerical simulations of the deposition process oc-curring at a receding contact line. In particular, we explore the parameterrange where ring patterns are deposited and analyse the underlying mech-anism. Characteristic measures of the ring profiles are determined and wediscuss their dependencies on the characteristic evaporation rate and initialmean concentration and other parameters of our model. We performed lim-ited investigation of the onset of formation of periodic deposits. Finally, werelate our findings to the experimental results.

The model is a simplified version of a related gradient dynamical systemconsidered in [8], as we do not consider here a free energy contribution of par-ticle interactions. The influence of nanoparticles concentration is here only viathe viscosity increase. Our evaporation term is also compatible with gradientdynamics. For a recent discussion of related gradient dynamics models see[9].

[1] S.W. Hong, J. Xia, and Z. Lin, Adv. Mater. 19, 1413 (2007)[2] M. Maillard, L. Motte, and M.-P. Pileni, Adv. Mater. 13(3), 200 (2001)[3] J. Xu, J. Xia, and Z. Lin, Angew. Chem. Int. Ed. 46, 1860 (2007)[4] H. Yabu and M. Shimomura, Adv. Funct. Mater. 15(4), 575 (2005)[5] U. Thiele, Advances in Colloid and Interface Science 206, 399-413 (2014)[6] A.V. Lyushnin, A.A. Golovin and L.M. Pismen, Phys. Rev. E 65, (2002)[7] U. Thiele et al, J. Phys.: Condens. Matter 21, 264016 (2009)[8] U. Thiele, Eur. Phys. J. Special Topics 197, 213â220 (2011)[9] M. Wilczek et al, Math. Model. Nat. Phenom., at press (2015)

A. Gupta Department of Physics, Univ. Rome "Tor Vergata" and INFN

Non-Newtonian effects on Droplet-deformation and breakupin confined geometries: a Lattice Boltzmann study

An important point for designing, developing and exploiting micro- and nanoflu-idic devices is to achieve a precise control over the process of formation ofdroplets, and characterization or, preferably, understanding of the scaling lawsthat describe the volume of droplets formed in the devices as a function of thematerials and flow parameters. The confinement that naturally accompaniesflows in small devices has significant qualitative and quantitative effects onthe drop dynamics and break-up. Moreover, relevant constituents have com-monly a viscoelastic -rather than Newtonian- nature. Setups where one isusually focusing the attention consists of confined shear flows. In this pa-per we will present results based on numerical simulations with the "latticeBoltzmann models" to highlight the non trivial role played by confinementand non-Newtonian effects. First we will investigate the dynamics and break-up processes of Newtonian droplets in strongly confined shear flows. Wewill characterize the conditions for the existence of break-up mechanisms andstudy the critical range of Capillary numbers at which the system transits froma squeezing mechanism into a shear-dominated droplet break-up, at changingthe degree of confinement. As an upgrade of complexity, we will introducenon-Newtonian bulk properties and investigate the droplet break-up in con-fined geometries for Newtonian droplets in a non-Newtonian fluid matrix andthe reverse case. In a real experiment all the various processes (flow param-eters, viscoelastic effects, wall-induced flow modifications) occur at the sametime and it is next to impossible to separately quantify their relative impor-tance. The opportunity of the study here proposed, based mainly on quanti-tative numerical methods, is to allow for a systematic analysis of each of theabove effects separately.

J. Imbrock Institut für Angewandte Physik, WWU Münster

Visualizing of ferroelectric domain dynamics in random quadraticmedia using Cerenkov second-harmonic microscopy

Cerenkov-type second-harmonic microscopy has recently attracted much at-tention because of its ability to resolute the ferroelectric domain walls evenin disordered crystals. As reported in [1], ferroelectric domain structures arefrom a few hundred of nanometers to several microns thick and they canbe resolved and visualized in both two and three dimensions. In general,Cerenkov-type second-harmonic emission is one of the most interesting non-collinear parametric patterns in far-field because of its spatial properties andspectral dependencies [2]. Much efforts have been devoted to investigate thephysical origin of this phenomena and its relation to the Fourier spectrum ofthe domain structures [3]. However, it has been proved that the sharp mod-ulation of the quadratic nonlinearity constitutes a sufficient condition for theemission of Cerenkov second harmonic in bulk materials [4]. So its high sen-sitivity to the ferroelectric domain walls offers an excellent tool to monitorthe ferroelectric domain growth and switching, even in bulk and in three di-mensions. Such a dynamic was until now a challenge to be visualized in realtime.

Here, the ferroelectric domains in a strontium barium niobate crystal (SBN)are microscopically investigated during their switching and growth. In prepa-ration, the SBN crystal is heated over the Curie temperature and cooled downwithout applying an electrical field to have a similar status to an as-grownsample. Applying an electrical field at room temperature will lead to pole thesample imperfectly because of the so called aging effect. It also leads to a dif-ferent domain size distribution because of growth and motion of the domainwalls[5]. At the end of the poling process, the electric field is switched in orderto allow the domains to switch and grow further. The switching cycle is com-bined with the switching current, which is in turn recorded to determine thepoling status on the hysteresis curve. That provides the ability to restore thesame domain status, meaning the average domain size. In this contributionwe will show both the temporal and spatial dynamics of ferroelectric domainsin SBN.

[1] Y. Sheng, A. Best, H.-J. Butt, W. Krolikowski, A. Arie, and K. Koynov, Opt.Express 18, 16539–16545 (2010).

[2]M. Ayoub, P. Roedig, J. Imbrock, and C. Denz, Opt. Lett. 36, 4371–4373

(2011).

[3] M. Ayoub, P. Roedig, K. Koynov, J. Imbrock, and C. Denz, Opt. Express 21,8220–8230 (2013).[4] Y. Sheng, V. Roppo, K. Kalinowski, and W. Krolikowski, Opt. Lett. 37,3864–3866 (2012).[5] M. Ayoub, J. Imbrock, and C. Denz, Opt. Express 19, 11340–11354 (2011).

T. Kajiya MPI for Polymer Research, Mainz

Receding Contact Line on a Soft Gel Surface in a Dip-CoatingGeometry

We investigated the behavior of a liquid contact line receding on a soft gelsurface (SBS-paraffin). To realize a well-defined geometry with an accuratecontrol of velocity, a dip-coating setup was implemented. As the elastic mod-ulus of the gel is small, a significant deformation takes place near the contactline, which in turn influences the wetting behaviour. Depending on the trans-lation velocity, the contact line exhibits different regimes of motions. Contin-uous motions are observed at high and low velocities, meanwhile two typesof stick-slip motions, periodic and erratic, appear at intermediate velocities.We conjecture that the observed transitions could be explained in terms ofthe competition between different frequencies, i.e., the frequency of the strainfield variation induced by the contact line motion and the cross over frequencyrelated to the material relaxation.

M. Kettner Physikalisches Institut, WWU Münster

Spin-resolved electron transmission through self-assembled lay-ers of chiral molecules and proteins on metal surfaces.

Electron spin polarization has been measured for photoelectrons emitted fromaluminum and gold substrates and transmitted through self-assembled lay-ers of various chiral organic molecules. Samples are irradiated by circularlyas well as linearly polarized 213nm laser radiation to excite photoelectronswithin the metal substrate. These photoelectrons are then transmitted throughthe chiral layer. During this transmission through the layer electrons interactspin dependently with the chiral molecules and get polarized. The degree ofpolarization depends on the thickness and quality of the layer while the spin-orbit coupling in the substrate and the type of bonding seem to play a minor

role. Spin polarization values of up to -60% in case of DNA and -17% in caseof polypeptides are measured by a Mott polarimeter.

J. Kierfeld TU Dortmund

The secondary buckling transition: wrinkling of buckled spher-ical capsules

When spherical shells, such as plastic balls or microcapsules, are deflated,they always go through the same sequence of shapes: For small volume reduc-tion, they remain spherical; then they undergo the classical buckling instabilitywhere an axisymmetric dimple appears; and, finally, they lose their axisymme-try by wrinkles developing in the vicinity of the dimple edge in a secondarybuckling transition. We theoretically explain this sequence of shapes. Thefirst axisymmetric buckling transition is described by numerical integrationof the complete set of shape equations and an approximate analytic modeldue to Pogorelov. In the buckled shape, both approaches exhibit a locallycompressive hoop stress in a region where experiments and simulations showthe development of polygonal wrinkles along the dimple edge. In a simplifiedmodel based on the stability equations of shallow shells, a critical value for thecompressive hoop stress is derived, for which the compressed circumferentialfibers will buckle out of their circular shape in order to release the compres-sion. By applying this wrinkling criterion to the solutions of the axisymmet-ric models, we can calculate the critical volume for the secondary bucklingtransition. Using the Pogorelov approach, we also obtain an analytical expres-sion for the critical volume at the secondary buckling transition: The criticalvolume difference scales linearly with the bending stiffness, whereas the crit-ical volume difference at the classical axisymmetric buckling transition scaleswith the square root of the bending stiffness. These results are confirmed byanother stability analysis in the framework of Donnel, Mushtari and Vlasov(DMV) shell theory, and they are in close agreement with existing numericaldata.

G. Kitavtsev MPI for Mathematics in the Sciences, Leipzig

Gradient flow perspective on thin-film bilayer flowsWe study gradient flow formulations of thin-film bilayer flows with triple-junctions between liquid/liquid/air phase. First we highlight the gradientstructure in the Stokes free-boundary flow and identify its solutions with thewell-known PDE with boundary conditions. Next we propose a similar gradi-ent formulation for the corresponding reduced thin-film model and formallyidentify solutions with those of a PDE problem. A robust numerical algo-rithm for the thin-film gradient flow structure is then provided. Using thisalgorithm we compare the sharp triple-junction model with precursor models.For time-dependent solutions the comparison of numerical solutions shows agood agreement for small and moderate times.

M. Köpf Département de Physique, École Normale Supérieure, Paris

Collective cell migration induced by mechanical stress and sub-strate adhesivenessStress normal to the boundary of an epithelial sheet can arise in constrainedand unconstrained cell layers through pushing and pulling of surroundingtissue and wettability of the substrate, respectively. A continuum model de-scribes the epithelium as a polarizable and chemo-mechanically interactinglayer under the influence of such stresses. This model links the experimentallyobserved formation of finger-like protrusions at the edge of unconstrainedspreading cell monolayers to substrate wettability [1]. Statistics of the velocityorientation shows a strong alignment in the fingers opposed to an isotropic dis-tribution in the bulk, in agreement with measurements by Reffay et al [2]. Themodel further exhibits a stress accumulation within the tissue that proceeds inform of a mechanical wave, starting at the wound edge [3]. Additionally, fourtypes of spreading and motility can identified, depending on the normal stressat the boundaries: Uniform deformation, non-uniform deformation, uniformgliding and peristaltic ("worm-like") progression. Analytical and numericalsolutions are presented along with bifurcation diagrams using normal stressand active force as control parameters [4].[1] Köpf, Pismen, Soft Matter 9 (2013) 3727-3734

[2] Reffay et al., Biophysical Journal 100 (2011) 2566-2575

[3] Serra-Picamal et al., Nature Physics 8 (2012) 628-634

[4] Köpf, Phys. Rev. E 91 (2015) 012712

O. Manor Technion IIT, Haifa

Dynamic Wetting at MHz Frequency Substrate Vibration

MHz Substrate vibrations may excite dynamic wetting of liquid films, a phe-nomenon usually referred to as Acoustic Spreading. Fully wetting and highlyviscous liquids, such as silicon oil, spread spontaneously along or oppositethe path of a propagating vibration in the substrate. Partially wetting and lowviscosity liquids, such as water on most surfaces, is observed to resist spread-ing under similar excitation conditions but may be persuaded to spread con-tinuously once vibrational, capillary, and viscous mechanisms are balancedappropriately.

Using theory and experiment we discuss the spreading of liquid films un-der the influence of MHz substrate vibration and show opposite contributionsfrom capillary, viscous, and vibrational mechanisms are weighed within onenon-dimensional number that governs the tendency of a liquid film to spreador avoid spreading. We thus elucidate the discrepancy, observed in earlierstudies, between the response of oil and water atop a lithium-niobate sub-strate to MHz frequency vibrational excitation, and highlight a parametricregion where partially wetting liquids may undergo Acoustic Spreading.

P. K. Roy Institute of Physical Chemistry , University of Münster

Molecular Dynamics Simulation of Two-Dimensional silica us-ing multi-body potentials.

The recent discovery of a new material called "Two-dimensional silica bi-layer";independently in the group of H.J.Freund [1] and D.Muler [2]; has created agreat excitement among the glass scientists. With the use of STM and SPMmethod it was revealed that the material is extremely thin and in spite of being3-dimensional in its stable form, it behaves like two-dimensional system dueto a very remarkable symmetry present between the two layer. Under differentreaction condition it was possible to produce the bi-layer in both crystallineand amorphous form, and sometimes both in the same layer. The structuraltransition and nature of the amorphous form is very similar to the predictionof Zacharisen’s 2D silica glass model 80 yrs earlier [3].

Earlier a "Soft-Core Yukawa" [4] type potential, was used to a two-dimensionalmodel of silica bilayer to describe this structure formation by energy mini-

mization method following the "Inherent Structure" methodology developedby Stillinger and Weber [5] for glass-forming systems. To study the variousangular distributions of the silica-bi layer , a multi body potential; such asStillinger-Weber type three body potential was used [6]. Necessary modifica-tions were made to generate and study the ring distribution pattern of thevitreous phase of the 2D silica model.

[1] Heyde M., Shaikhutdinov S., Freund H.-J., Chem. Phys. Lett. 550, 1 (2012).[2] Huang P. Y. et al, Nano Lett. 12, 1081 (2012).[3] Zachariasen W.H., J. Am. Chem. Soc. 54, 3841 (1932).[4] Mendez-Maldonado G.A., et al., J. Chem. Phys. 137, 054711 (2012).[5] Stillinger F., Weber T.A., Phys. Rev. A 25, No. 2, 978(1982).[6] Feuston B.P., Garofalini S.H., J. Chem. Phys. 89, 9(1988).

B. ten Hagen Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf

Gravitaxis of asymmetric self-propelled colloidal particles

Many motile microorganisms adjust their swimming motion relative to thegravitational field and thus counteract sedimentation to the ground. Thisgravitactic behavior is often the result of an inhomogeneous mass distribu-tion which aligns the microorganism similar to a buoy. However, it has beensuggested that gravitaxis can also result from a geometric fore-rear asymme-try, typical for many self-propelling organisms. Despite several attempts, noconclusive evidence for such an asymmetry-induced gravitactic motion exists.Here, we study the motion of asymmetric self-propelled colloidal particleswhich have a homogeneous mass density and a well-defined shape. In exper-iments and by theoretical modeling we demonstrate that a shape anisotropyalone is sufficient to induce gravitactic motion with either preferential upwardor downward swimming. In addition, trochoid-like trajectories transversal tothe direction of gravity are observed.

W. Tewes Institut für Theoretische Physik, WWU Münster

A theoretical investigation of patterned deposition of solutefrom thin films of evaporating solution

We aim at a theoretical description of patterned deposition of solute from anevaporating thin film of solution on a substrate. For this purpose we formu-late partial differential equations for thin solution layers which describe phaseseparation within the solution, dewetting and evaporation of the solvent.Thedeposition process is investigated for a contact line of the solution film whichrecedes due to pulling of the substrate (dip-coating) and/or evaporation. De-position patterns obtained from direct numerical simulations are stripes andpatterns of hexagonal type.

A. Thompson Imperial College London

Modelling post-deposition interactions in inkjet printed lines

Control of deposition and spreading of printed liquid drops is crucial for themanufacture of high-precision printed products. Theoretical analysis of post-deposition behaviour is currently centred on full 3-D numerical simulations.However, these simulations must overcome the inherent challenges of dropletimpact and molecular-scale contact line motion, and so resolving inter-dropinteraction is at present feasible for only a few printed drops.

Here we use a combination of experiments and simplified modelling tostudy the consecutive deposition of a line of up to 60 equally spaced, overlap-ping droplets onto a flat solid substrate. The motivating application is the useof ink-jet technology to print polymer organic light-emitting diode (p-OLED)displays, where a short, continuous, uniform line of polymer is required foreach pixel. Our experiments were performed at Cambridge Display Technol-ogy Limited, and a high-speed camera was used to record the ink side viewas individual drops are printed. Our results show that the ink never adoptsa uniform configuration, instead forming a sequence of rivulets and bulges,each much bigger than any individual printed droplet.

We show that the detailed drop-by-drop fluid morphology observed in ourexperiments can be quantitatively predicted by models invoking surprisinglyfew physical mechanisms: surface tension and contact line hysteresis alonepredict primary head formation; while secondary bulges require a competing

effect of fluid viscosity. The models we have developed can be fully describedby 1-D or 2-D equations, and require few dimensionless parameters.

The excellent agreement between our experimental and theoretical results,despite significant simplifying assumptions for both droplet impact and con-tact line motion, establishes our drop-by-drop modelling approach as a promis-ing theoretical tool that may be extended to gain insight into additional phys-ical effects such as evaporation, substrate topography and wettability varia-tions.

Q. Vagne UMR 168 "Physico-Chimie Curie", Institut Curie

Sensing the system’s size through clustering in non-equilibriummembranes. Application to membrane-bond enzymatic reac-tions

The formation of dynamical clusters of proteins is ubiquitous in cellular mem-branes and is in part regulated by the recycling of membrane components.We show, using stochastic simulations and analytic modelling, that the out-of-equilibrium cluster size distribution of membrane components undergoingcontinuous recycling is strongly influenced by lateral confinement (finite-sizeeffects). This result have strong implication for the clustering of plasma mem-brane proteins whose mobility is hindered by cytoskeletal “corrals” and forprotein clustering in Cellular organelles experiencing in and out fluxes of ma-terial. We propose that the confinement size could be sensed through the sizedistribution of lateral membrane heterogeneities, and may be regulated to im-prove the efficiency of membrane-bound reactions. To illustrate this, we studya chain of enzymatic reactions sensitive to membrane protein clustering. Thereaction efficiency is found to be a non-monotonic function of the system size,and can be optimal for sizes comparable to those of cellular organelles.

M. Wilczek Institut für Theoretische Physik, WWU Münster

Control Methods for Pattern Formation in Langmuir-BlodgettTransfer

The Langmuir-Blodgett transfer is an established method to cover substrateswith monomolecular layers of amphiphilic molecules. Pattern formation dur-ing this transfer enables the production of inhomogeneously coated substrates.

Possible patterns are stripes with different orientation as well as lattice struc-tures that consist of the monolayer in different phases and densities. Theproperties of the patterns can be influenced by experimental parameters likethe transfer velocity. The use of prestructured substrates enables a powerfuladditional control over the patterning process.

We theoretically study the occurring synchronization and pattern locking ef-fects by means of a generalized Cahn-Hilliard model. We show that a prestruc-tured substrate can both stabilize and destabilize patterns. In two dimensionsnovel pattern types arise from the competition between the intrinsic patternforming behavior of the system and the external forcing through the prestruc-ture. The range of patterns comprises oblique stripe patterns, different latticepatterns and irregular structures.

A different control mechanism can be achieved by the use of a modulatedtransfer velocity, again leading to locking effects. Our theoretical results sug-gest that this method can be as effective as the use of prestructured substrates.Thus, a control of the patterning process can be achieved without the need fora separate production step for the prestructure.

P. Yatsyshin Imperial College London

Fluids in nano-pores: equilibrium and dynamics. A densityfunctional theory study.

For fluids inside nano-pores, where the characteristic pore dimensions exceedthe ranges of molecular interactions by only one or two orders of magnitude,the parameters of the fluid-substrate potential and the pore geometry act asthermodynamic degrees of freedom, and so varying these parameters mayinduce structural transitions in the fluid. In applications, enhancing our un-derstanding of adsorption in small pores is essential in new and rapidly devel-oping branches of engineering and science, such as micro- and nanofluidics,biomimetics, colloidal science, design of surfaces with tuneable wetting prop-erties and lab-on-a-chip devices.

A satisfactory theoretical description of nano-confined fluids has to accountfor the inhomogeneities of the fluid structure and the non-local character ofmolecular interactions. Density functional theory (DFT) for fluids offers a clas-sical statistical mechanical framework, where the free energy of the fluid isapproximated as a functional of the spatially varying fluid number density.Minimizing the free energy functional yields the fluid density profile, includ-ing interfaces and surface tensions. Analysing the free energy surface in the

space of thermodynamic variables yields information about phase transitions,e.g. the formation of liquid drops, films, finger-like structures, etc. Using a dy-namic extension of equilibrium DFT, we can investigate the diffusion-drivenevolution of the three-phase contact line to gain insight into the dynamic be-haviour of the microscopic contact angle, which still remains in debate.

N O T E S

N O T E S

N O T E S

T H E C E N T E R F O R N O N L I N E A R S C I E N C E

The study of nonlinear, complex systems is one of the most exciting and fastestgrowing branches in science nowadays. Understanding the mechanisms gov-erning cooperative, emergent phenomena in complex systems is considered asone of the most important challenges in science, because it is a highly interdis-ciplinary field that has important applications in fields ranging from physics,mathematics, chemistry, engineering and computer science to life sciences, so-ciology and finances.

The Center for Nonlinear Science (CeNoS) was founded to foster researchand education in the field of nonlinear science and to strengthen the dialoguebetween different scientific disciplines at the University of Münster. For fur-ther information visit:

www.uni-muenster.de/cenos

T H E W O R K S H O P S E R I E S " W I N D O W S T O C O M P L E X I T Y "

27.11.2007 Windows to Complexity09.-10.02.2009 Turbulence: From Basics to Geodynamics19.06.2009 Nonlinear Dynamics in Finance and Economics10.-11.06.2010 Extreme Events26.-27.09.2011 The Human Dynamic System02.-03.05.2013 Self-organization on the Nano Scale09.10.2013 Nonlinear Dynamics of Speculative Bubbles in Financial

Markets05.-06.032014 Complexity Meets Energy02.-05.03.2015 Nonlinear Dynamics of Structure Formation at

Interfaces

to be continued . . .