08:00 to 08:50 Registration 08:50 to 09:00 Welcome - Uwe Thiele/Peter Olmsted 09:00 to 09:30 T Squires (University of California, Santa Barbara)Dynamics of grainy liquid crystalline monolayers: visible and hidden grain boundaries and chiral rheology Co-authors: Kyuhan Kim (UCSB ChE), SiYoung Choi (UCSB ChE), Joe Zasadzinski (Minnesota CEMS) While the equilibrium properties of fluid interfaces have been manipulated and studied for centuries, their dynamic, rheological properties (e.g. viscosity and elasticity) have proven more elusive. Despite the dominant role that even molecularly-thin interfaces can play in multiphase flows, the viscosity of the bulk fluids on either side of the interface can easily overwhelm any attempt at measuring surface rheology. I will describe a technique we have developed to measure the interfacial rheology -- the viscous and elastic properties -- of fluid-fluid interfaces, typically laden with some surface-active species (molecular surfactants, copolymers, colloids, etc.). A novel feature is our ability to visualize the interface during the measurement, enabling us to directly relate the measured response to the microstructure of the interface. In particular, we study model lung surfactant monolayers that consist of liquid-condensed phases of the phospholipid DPPC and, in some cases, cholesterol. We directly visualize the deformation of liquid-crystalline domains under both linear and nonlinear deformations. Despite the simplicity of the system -- a single-component, 2 nm-thick molecular monolayer -- we find an extraordinarily rich rheological response, including a soft, glassy response, elastic strain energy that is stored over a shockingly long time, two-dimensional yielding behavior, aging, rejuvenation, and anisotropically chiral rheology, exhibiting either ductile plasticity or brittle fracture, depending on the sense of the shear. We relate these rheological responses to observed boundaries between individual DPPC crystals, as well as hidden boundaries where tail group tilt orientations change rapidly. 09:30 to 10:00 M Buzza (University of Hull)Two-Dimensional Colloidal Alloys Co-authors: Adam Law (Max-Planck-Institut fuer Intelligente Systeme), Melodie Auriol (Ecole Nationale Superieure de Chimie de Rennes), Dean Smith (University of Hull), Tommy Horozov (University of Hull) We study the self-assembly of mixed monolayers of hydrophobic and hydrophilic colloidal particles adsorbed at oil/water interfaces both experimentally and theoretically. Experimentally, we find that by tuning the interactions, composition and packing geometry of the mixed monolayer, a rich variety of two-dimensional super-lattice [1] and cluster [2] structures are formed which are stabilised by strong electrostatic interactions mediated through the oil phase. The 2D structures obtained are in excellent agreement with zero temperature lattice sum calculations [1-3], indicating that the self-assembly process can be effectively controlled for the creation of novel 2D structures. [1] A.D. Law, D.M.A. Buzza, T.S. Horozov, Phys. Rev. Lett., 106, 128302 (2011) [2] A.D. Law, M. Auriol, D. Smith, T.S. Horozov, D.M.A. Buzza, Phys. Rev. Lett., 110, 138301 (2013) [3] A.D. Law, T.S. Horozov, D.M.A. Buzza, Soft Matter, 7, 8923 (2011) 10:00 to 10:30 Soundbites from Attendees Emanuela Del Gado: Crowding and ordering in the adsorption of nanoparticles at air-water interfaces Lorenzo Botto: Rod-like particles at fluid interfaces: adsorption, in-plane interactions, and Êmicromechanics of particle chains Daniel Rings: SPH for complex fluids: A path to hydrodynamics with moving boundaries and inhomogeneities Wieland Marth: Signaling networks and cell motility - a computational approach using a phase field description Alice Thompson: Can consecutive droplet deposition yield liquid films of uniform depth? Adriano Tiribocchi: A minimal model for a crawling cell John Joseph Williamson: Domain registration transition in lipid bilayer phase separation Wieland Marth: Signaling networks and cell motility Lailai Zhu: Deformability-induced cell sorting in micro-fluidic devices 10:30 to 11:00 Morning Coffee 11:00 to 11:30 R Hawkins (University of Sheffield)Active gel flow in finite domains with applications to cell motility in confinement Co-authors: Carl Whitfield (University of Sheffield), Raphael Voituriez (UPMC/CNRS, Paris), Davide Marenduzzo (University of Edinburgh) Motility of cells in confinement is relevant to cell migration in tissues. Motility is powered by the cell cytoskeleton, which consists of biopolymer filaments and active cross linkers (molecular motors), fueled by biochemical energy. Modelling the cell cytoskeleton as a finite domain of active polar gel, we calculate internal flow fields. These velocity fields are dependent on the boundary conditions. In addition, coupling these internal flows to external media gives rise to mechanisms for motion of the active droplet. The internal dynamics also affect the shape of the active domain. I will present results of analytical calculations and numerical simulations of velocity fields with different boundary conditions. As well as showing results I will discuss some future challenges that are currently unsolved. 11:30 to 12:00 E Lushi (Imperial College London)Active suspensions in domains with static or moving boundaries I will briefly describe a novel fast computational method that enables us to trace the coupled dynamics of thousands on micro-swimmers that interact directly as well as via the collectively generated fluid flows. I will illustrate with results involving such an active'' micro-swimmer suspension inside a drop where the spontaneous organization that emerges depends not only on confinement and steric effects, but also on the presence of hydrodynamics. Lastly, I will discuss the case when the active suspension is inside a domain with moving boundaries, such as a peristaltic pump, and where the transport of passive tracers gets effected by the swimmers' collective motion. 12:00 to 12:30 E Keaveny (Imperial College London)Undulatory locomotion in structured media Many swimming microorganisms inhabit heterogeneous environments consisting of solid particles immersed in viscous fluid. Such environments require the organisms attempting to move through them to negotiate both hydrodynamic forces and geometric constraints. Here, we study this kind of locomotion by first observing the kinematics of the small nematode and model organism Caenorhabditis elegans in fluid-filled, micro-pillar arrays. We then compare its dynamics with those given by numerical simulations of a purely mechanical worm model that accounts only for the hydrodynamic and contact interactions with the obstacles. We demonstrate that these interactions allow simple undulators to achieve speeds as much as an order of magnitude greater than their free-swimming values. More generally, what appears as behaviour and sensing can sometimes be explained through simple mechanics. 12:30 to 15:00 Lunch 15:00 to 15:30 SA Karpitschka (Max-Planck-Institut für Kolloid- und Grenzflächenforschung)Sharp Border between Coalescence and Noncoalescence of Sessile Drops from Miscible Liquids Co-author: Hans Riegler (MPIKG) Recently it has been shown that sessile drops from different but completely miscible liquids do not always coalesce instantaneously upon contact. Quite un­ex­pec­ted it is observed that after contact, the drop bodies remain separated in a temporary state of non­coale­scence, connected only through a thin liquid bridge [1,2]. The connected drops move as a twin drop con­figuration over the surface. The surface energy difference between the liquids causes a Marangoni flow. This stabilizes the bridge and drives the drop motion [3]. Up to now studies regarding the (non)coalescence behavior of sessile drops from different liquids were performed only without a systematic variation of the con­tact angles. Therefore it is unknown: (I) at which con­tact angles the transition between temporary non­coalescence and immediate coalescence occurs, (II) whether this transition is sharp or gradual, and (III) whether the behavior is different f or static and dynamic contact angles, respectively. We present quan­titative experimental data on the contact angle de­pen­dence of the coalescence behavior of sessile drops from completely miscible liquids. We find quantitatively the same coalescence behavior for both static and dynamic contact angles. The border between the coalescence and the non­coalescence regime is sharp and given by a power law relation between contact angle and surface tension contrast. The power laws are explained within a fluid dynamic thin film approach by scaling arguments. The sharp transition is quantitatively reproduced by numerical simulations. [1] H. Riegler, P. Lazar, Langmuir 24, 6395 (2008). [2] S. Karpitschka, H. Riegler, Langmuir 26, 11823 (2010). [3] S. Karpitschka, H. Riegler, Phys. Rev. Lett. 109, 066103 (2012). 15:30 to 16:00 B Chakrabarti (Durham University)Shaping and sculpting of liquid drops using laser beams Co-authors: David Tapp (Durham University), Jonathan Taylor (University of Glasgow), Colin Bain (Durham University) Motivated by recent experiments on optical sculpting of liquid drops with ultralow interfacial tension I discuss modeling approaches that predict droplet shapes in single and multiple optical traps using simulations and theory. 16:00 to 16:30 Afternoon Tea 16:30 to 17:00 MH Koepf (Technion - Israel Institute of Technology)A continuum model of epithelial spreading Co-author: Leonid M. Pismen (Department of Chemical Engineering, Technion - Israel Institute of Technology, 32000 Haifa, Israel) We present a continuum model of unconstrained epithelial spreading. The tissue is described as a polarizable and chemo-mechanically interacting layer with neo-Hookean elasticity. Our model reproduces the spontaneous formation of finger-like protrusions commonly observed in experiment. Statistics of velocity orientation obtained from numerical simulation show strong alignment in the fingers opposed to an isotropic distribution in the bulk, as has been measured by Reffay et al. (Reffay et al., Biophysical Journal, 2011). The results faithfully reproduce faster relative advance of cells close to the leading edge of the tissue, as well as spatial velocity correlations and stress accumulation within the tissue, which proceeds in form of a "mechanical wave", traveling from the wound edge inwards (cf. Serra-Picamal et al., Nature Physics, 2012). M. H. Koepf, L. M. Pismen: Non-equilibrium patterns in polarizable active layers, Physica D 259 (2013) 48-54 M. H. Koepf, L. M. Pismen: A continuum model of epithelial spreading, Soft Matter 9 (2013) 3727-3734 17:00 to 17:30 M Plapp ([CNRS/École Polytechnique])Equilibrium and growth shapes of fiber-covered surfaces Co-authors: Thi-Hanh Nguyen (CNRS, Ecole Polytechnique), Vincent Fleury (CNRS, Ecole Polytechnique), Hervé Henry (CNRS, Ecole Polytechnique) Branched growth patterns are generally formed by an interplay between instabilities that favor branching and stabilizing effects that result from the microscopic structure of matter. We consider nematic surfaces (that is, surfaces that are covered by fibers which remain tangential to the surface) and investigate the consequences of an anisotropic bending rigidity (surfaces are easier to bend in the direction normal to the fibers than along it) on equilibrium and growth shapes. We formulate a continuum model that allows us to determine the organization of the fibers and the geometric shape of a simply connected domain which correspond to a minimum of the total (free) energy. The coupling with a simple diffusive growth mechanisms leads to growth shapes that could not have been obtained with a simple crystalline material. Possible connections with the growth of biological structures will be discussed. 18:00 to 18:30 Wine reception 19:00 to 20:00 Dinner