Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S53: Assembly of Particles on Fluid InterfacesInvited
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Sponsoring Units: GSOFT DFD Chair: Emilie Dressaire, New York University Room: 287 |
Thursday, March 16, 2017 11:15AM - 11:51AM |
S53.00001: Curvature Capillary Repulsion Invited Speaker: Kathleen Stebe In prior work, we have studied capillary curvature attraction: a microparticle on a curved fluid interface interacts with the curvature field in a manner akin to a charged quadrupole in an applied external electrostatic field. Particles rotate to a preferred orientation, and migrate to minimize the excess area that they make in the interface. On curved interfaces formed around a micropost, particles migrate along principal axes to sites of high curvature, typically until they make contact with the micropost. Here we report capillary curvature repulsion, in which particles migrate to equilibrium sites far from contact with the micropost. Using theory and experiment, we explore the dependence of these interactions to particle and post geometry. Since fluid interfaces can be actively controlled, this work provides guidance on the formation of reconfigurable structures. We report preliminary work on active control of colloid assembly in this context. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:27PM |
S53.00002: Feedback Controlled Colloidal Assembly at Fluid Interfaces Invited Speaker: Michael Bevan The autonomous and reversible assembly of colloidal nano- and micro- scale components into ordered configurations is often suggested as a scalable process capable of manufacturing meta-materials with exotic electromagnetic properties. As a result, there is strong interest in understanding how thermal motion, particle interactions, patterned surfaces, and external fields can be optimally coupled to robustly control the assembly of colloidal components into hierarchically structured functional meta-materials. We approach this problem by directly relating equilibrium and dynamic colloidal microstructures to kT-scale energy landscapes mediated by colloidal forces, physically and chemically patterned surfaces, multiphase fluid interfaces, and electromagnetic fields. 3D colloidal trajectories are measured in real-space and real-time with nanometer resolution using an integrated suite of evanescent wave, video, and confocal microscopy methods. Equilibrium structures are connected to energy landscapes via statistical mechanical models. The dynamic evolution of initially disordered colloidal fluid configurations into colloidal crystals in the presence of tunable interactions (electromagnetic field mediated interactions, particle-interface interactions) is modeled using a novel approach based on fitting the Fokker-Planck equation to experimental microscopy and computer simulated assembly trajectories. This approach is based on the use of reaction coordinates that capture important microstructural features of crystallization processes and quantify both statistical mechanical (free energy) and fluid mechanical (hydrodynamic) contributions. Ultimately, we demonstrate real-time control of assembly, disassembly, and repair of colloidal crystals using both open loop and closed loop control to produce perfectly ordered colloidal microstructures. This approach is demonstrated for close packed colloidal crystals of spherical particles at fluid-solid interfaces and is being extended to anisotropic particles and multiphase fluid interfaces. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 1:03PM |
S53.00003: Electro-coalescence of particle-coated droplets Invited Speaker: Anderson Ho Cheung Shum Droplets in air or in an immiscible liquid phase are used widely in applications ranging from personal hygiene products to drug delivery. The stability of the droplets are highly linked to their utility, and thus have been systematically studied. To enhance the stability of the droplets, particles are often added to the droplets. In this talk, I will discuss how the particle layer at droplet interfaces responds to electrical charging of the droplets. The electrical forces can distort the droplet shape, which is opposed by the layer of particles adsorbed. A balance of the electrical and interfacial effects provides a quantitative indicator of the droplet instability. The coalescence of droplets in both air and liquid induced by electrically charging, which we call ``electro-coalescence'', will be introduced, with its potential application in devising a digital millifluidic platform. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:39PM |
S53.00004: How contact-line pinning affects the dynamics of colloidal particles at fluid interfaces Invited Speaker: Vinothan N. Manoharan Using digital holographic microscopy, a fast 3D imaging technique, we measure the motion of colloidal particles near a liquid interface. We find that micrometer-sized polymer particles take a surprisingly long time -- weeks or even months -- to relax to equilibrium. This behavior can be understood in terms of a dynamic wetting mechanism involving thermally-activated hopping of the contact line over surface defects. I will present results that probe the nature of the pinning sites and how they can affect the pathway to equilibrium. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 2:15PM |
S53.00005: Mathematical modelling for improved control of magnetic particle interfacial assembly Invited Speaker: Ian Griffiths Recently, microfluidic technologies have facilitated the self-assembly of a variety of particle clusters with enhanced control, at interfaces formed between immiscible liquid phases. In this talk we consider a microfluidic set-up composed of two immiscible fluids. Magnetic particles are inserted into one of the fluids and an applied magnetic field pulls the particles towards the second fluid. The magnetic field is chosen so that individual particles collect at the interface and only aggregates experience a sufficient force to overcome the interfacial tension between the two fluids to be pulled through into the second fluid. We present a mathematical model that captures the aggregation behaviour of the particles both during the approach to the interface and at the interface itself. We uncover the existence of different regimes of behaviour depending on the operating parameters: `cascading', when individual particles aggregate to form dimers that subsequently aggregate to form 4-mers, 8-mers and so on; and `hoovering' in which an aggregate is pulled through the fluid and collects individual particles on its way. The results of the model allows for tuning of the magnetic field and interfacial tension to facilitate a route for the formation of aggregates of a desired size. [Preview Abstract] |
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