Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session V2: Liquid Droplets: From Surface Topology to Active MotionInvited
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Sponsoring Units: DCMP GSOFT Chair: Paul Chakin, New York University Room: Ballroom II |
Thursday, March 17, 2016 2:30PM - 3:06PM |
V2.00001: Vapour-mediated sensing and active motion in two-component droplets Invited Speaker: Manu Prakash |
Thursday, March 17, 2016 3:06PM - 3:42PM |
V2.00002: Toroidal Nematics Invited Speaker: Alberto Fernandez-Nieves We will discuss how nematic liquid crystals organize inside toroidal droplets. When the director is parallel to the bounding surface, we find spontaneous reflection symmetry breaking, which we attribute to the role played by saddle-splay contributions to the Frank free energy. When the director is perpendicular to the bounding surface, we find that the structure is reminiscent of the escape radial configuration seen in cylinders, but with a central doubly-twisted organization, which we attribute to the geometry of the torus. We will end by presenting recent experiments with active nematics on the toroidal surface. In this case, topology and activity both affect the structure and dynamics of the material. [Preview Abstract] |
Thursday, March 17, 2016 3:42PM - 4:18PM |
V2.00003: Active Mesogenic Droplets: Impact of Liquid Crystallinity and Collective Behavior Invited Speaker: Christian Bahr Droplets of common mesogenic compounds show a self-propelled motion when immersed in aqueous solutions containing ionic surfactants at concentrations well above the critical micelle concentration. After introducing some general properties of this type of artificial microswimmer, we focus on two topics: the influence of liquid crystallinity on the swimming behavior and the collective behavior of ensembles of a larger number of droplets. The mesogenic properties are not essential for the basic mechanism of self-propulsion, nevertheless they considerably influence the swimming behavior of the droplets. For instance, the shape of the trajectories strongly depends on whether the droplets are in the nematic or isotropic state. The droplet swimmers are also ideally suited for the study of collective behavior: Microfluidics enables the generation of large numbers of identical swimmers and we can tune their buoyancy. We report on the collective behavior in three-dimensional environments. [Preview Abstract] |
Thursday, March 17, 2016 4:18PM - 4:54PM |
V2.00004: Dynamically Reconfigurable Complex Emulsions via Tunable Interfacial Tensions Invited Speaker: Timothy Swager This lecture will focus on the design of systems wherein a reconfiguration of the materials can be triggered chemically of mechanically. The utility of these methods is to generate transduction mechanisms by which chemical and biological sensors can be developed. Three different types of systems will be discussed. (1) Particles wherein a protease enzyme releases strain in the particle by breaking crosslinks. (2) Assemblies of polymers at air water interfaces and the demonstration of a luminescence strain response upon compression. (3) Dynamic colloids produced from immiscible fluorocarbon/hydrocarbon mixtures and ability to convert the core and shell layers of the particles as well as the conversion to Janus particles. The latter system’s morphology changes can be triggered chemically or optically. [Preview Abstract] |
Thursday, March 17, 2016 4:54PM - 5:30PM |
V2.00005: How faceted liquid droplets grow tails: from surface topology to active motion Invited Speaker: Eli Sloutskin Among all possible shapes of a volume $V$, a sphere has the smallest surface area $A$. Therefore, liquid droplets are spherical, minimizing their interfacial energy $\gamma A$ for a given interfacial tension $\gamma >0$. \newline This talk will demonstrate that liquid oil (alkane) droplets in water, stabilized by a common surfactant can be temperature-tuned to adopt icosahedral and other faceted shapes, above the bulk melting temperature of the oil. Although emulsions have been studied for centuries no faceted liquid droplets have ever been reported. The formation of an icosahedral shape is attributed to the interplay between $\gamma$ and the elastic properties of the interfacial monomolecular layer, which crystallizes here 10-15K above bulk melting, leaving the droplet's bulk liquid. The icosahedral symmetry is dictated by twelve five-fold topological defects, forming within the hexagonally-packed interfacial crystalline monolayer. Moreover, we demonstrate that upon further cooling this `interfacial freezing’ effect makes $\gamma$ transiently switch its sign, leading to a spontaneous splitting of droplets and an active growth of their surface area, reminiscent of the classical spontaneous emulsification, yet driven by completely different physics. \newline The observed phenomena allow deeper insights to be gained into the fundamentals of molecular elasticity and open new vitas for a wide range of novel nanotechnological applications, from self-assembly of complex shapes to new delivery strategies in bio-medicine. [Preview Abstract] |
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