Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A32: Surface Tension Effects I: Particles and Structure at the Interface |
Hide Abstracts |
Chair: Steve Wereley, Purdue University Room: 403 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A32.00001: An asymmetric Cheerio: Torque on objects floating on a liquid interface Michael Miller, Khoi Nguyen, Shreyas Mandre Objects suspended on a fluid interface by surface tension are subject to attractive and repulsive forces towards each other. When symmetry is broken, a capillary torque acts to rotate the objects into an equilibrium orientation. We employ optical refraction from the meniscus to obtain the shape of the liquid surface, and use the shape to calculate the torque. Through application of an analytical asymptotic analysis at a polygonal object's vertices, supported by empirical results, we gain an understanding of the rotational effects of sharp corners in a suspended object's contact line. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A32.00002: Designing spherical patchy particles for optimum surface activity at liquid-fluid interfaces Hossein Rezvantalab, Ali Hashemi, Shahab Shojaei-Zadeh Adsorption of spherical patchy particles to a flat liquid-fluid interface is investigated. Chemical heterogeneity in form of patches with different number and size can be introduced on the surface of a homogeneous particle to induce an amphiphilic character. Compared to homogeneous particles, amphiphilic particles show stronger adhesion to the interface and thus can be used as effective interface stabilizers. Using the concept of detachment energy for a particle at an interface, we analytically developed a criterion to design single-patch particles with maximum surface activity. The method is then extended to include particles with two symmetric patches. The energy landscapes reveal the existence of two local minima for such double-patch particles when the patches are oriented either parallel or normal to the interface. We evaluate the effectiveness of introducing the second patch on the particle as a function of its size and wettability. Addition of a second symmetric patch can enhance the surface activity, compared to a single -- patch particle, provided that the patch groups are relatively small, each with close affinity to the fluid phases. On the other hand, single-patch particles are more surface active for highly amphiphilic cases. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A32.00003: The Effect of Contact Angle on the Orientation, Stability and Assembly of Dense Floating Cubes Jonathan Rothstein, Michael Donnell, Robert Daniello In this talk, the effect of contact angle, density and size on the orientation, stability and assembly of floating cubes will be presented. All the cubes tested were denser than water. Floatation occurred as a result of capillary stresses induced by deformation of the air water interface. The cubes were observed to float in one of three primary orientations depending on contact angle: edge up, vertex up and face up. Measurements net force on the cubes showed that the maximum capillary forces were always experienced for the face up orientation. However, when floatation was possible in the vertex up orientation, it was found to be the most stable cube orientation because it had the lowest center of gravity. A series of theoretical predictions were performed for the cubes floating in each of the three primary orientations to calculate the net force on the cube. The theoretical predictions were found to match the experimental measurements well. The assembly of cubes floating face up and vertex up were also studied for assemblies of two, three and many cubes. Cubes floating face up were found to assemble face to face and form regular checkerboard arrays with no free interface between cubes. Cubes floating vertex up cubes were found to assemble in a variety of different arrangements including edge to edge, vertex to vertex, face to face and vertex to face with the most probably assembly being edge to edge. Large numbers of vertex up cubes were found to pack with a distribution of orientations and alignment. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A32.00004: Estimation of Forces between Objects in the Cheerios Effect Khoi Nguyen, Michael Miller, Shreyas Mandre We develop an analysis and method to estimate the attractive forces due to the capillary interactions between nearby interfacial objects, often dubbed as the Cheerios effect. The method involve mapping the 3-dimensional surface deformation surrounding a floating object and estimating the force directly from the gradient field. The surface deformation is obtained by correlating the image of a random dot background with its refraction from the liquid surface. The scaling of attractive force as a function of distance for objects of arbitrary shape is directly obtainable from a series of gradient fields. We specialize to the case of objects with sharp corners and observe that force scales exponentially with distance on the order of a capillary length. Furthermore, this optical method is potentially instrumental in studying colloidal self-assembly because it can be implemented in real time in a dynamically changing array of floating objects. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A32.00005: Inter-particle interactions and assembly of ellipsoidal Janus particles at liquid interfaces Hossein Rezvantalab, Stephen Rowe, Shahab Shojaei-Zadeh We study the capillary-induced interactions between ellipsoidal Janus particles adsorbed at flat liquid-fluid interfaces. In contrast to spherical particles, isolated Janus ellipsoids with a large aspect ratio or a small difference in the wettability of the two regions tend to tilt at their equilibrium orientation. The interface around such tilted particles deforms and their overlap results in capillary interactions between neighboring particles. These interactions are quantified through minimization of interfacial energy variation as a function of the separation distance between the particles. We show that Janus ellipsoids prefer to align side-by-side at the interface. We also evaluate the role of particle aspect ratio and the degree of amphiphilicity between its two regions on the inter-particle capillary forces and torques. For particles of equal surface area, the energy profiles are independent of the aspect ratio, while increasing the amphiphilicity results in an enhancement in the capillary force in-contact and the torque inducing the side-by-side configuration. This indicates that Janus ellipsoids exhibit stronger interactions compared to their homogeneous counterparts. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A32.00006: Induced phase transitions of nanoparticle-stabilized emulsions Stefan Frijters, Florian G{\"u}nther, Jens Harting Nanoparticles can stabilize fluid-fluid interfaces over long timescales and are nowadays commonly used, e.g. in emulsions. However, their fundamental properties are as of yet poorly understood. Nanoparticle-stabilized emulsions can exhibit different phases, such as Pickering emulsions or bijels, which can be characterized by their different topologies and rheology. We investigate the effect of various initial conditions on random mixtures of two fluids and nanoparticles - in particular, the final state these systems will reach. For this, we use the well-established 3D lattice Boltzmann method, extended to allow for the added nanoparticles. After the evolution of the emulsions has stopped, we induce transitions from one state to another by gradually changing the wettability of the nanoparticles over time. This changes the preferential local curvature of the interfaces, which strongly affects the global state. We observe strong hysteresis effects because of the energy barrier presented by the necessary massive reordering of the particles. Being able to change emulsion states \textit{in situ} has potential application possibilities in filtering technology, or creating particle scaffolds. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A32.00007: Particle shedding from coated magnetic microbubbles Chon U. Chan, Yu Gao, Chenjie Xu, Manish Arora, Claus-Dieter Ohl Nanoparticle-coated microbubbles have found applications for diagnostic imaging as well as drug delivery, yet the release of shell material due to ultrasonic excitation has not been studied in detail. We find that particles are ejected from the shell if the bubbles are driven resonantly with ultrasound. The bubble oscillation and the release of the particles are observed with high-speed photography while floating in microfluidic channels. The nanoparticles are shed when the bubble wall acceleration exceeds a threshold. When bubbles are excited into shape oscillations the particle shedding is observed at the velocity antinodes of the bubble surface. Particle release and transport is modelled with a force balance, considering inertia of the particle, the oscillatory fluid flow created by bubble oscillation, and the viscous force acting on the particle. We also demonstrate the ability to control the location of microbubbles in liquid using a diverging magnetic field and an optical feed-back loop. Then the magnetic microbubbles can be stabilized and translated in a three dimensional bubble trap. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A32.00008: Visualization and minimization of clustering of micro-pillars and walls due to liquid film evaporation Tae-Hong Kim, Jungchul Kim, Ho-Young Kim The spin drying, in which a rinsing liquid deposited on a wafer is rapidly dried by wafer spinning, is an essential step in the semiconductor manufacturing process. While the liquid evaporates, its meniscus straddles neighboring submicron-size patterns such as pillars and walls. Then the capillary effects that pull the patterns together may lead to direct contact of the patterns, which is often referred to as pattern leaning. This poses a problem becoming more and more serious as the pattern size shrinks and the aspect ratio of the patterns increases. While the clustering behavior of high-aspect-ratio micro- and nanopillars was investigated before, a technical strategy to prevent such clustering has been pursed in industrial practices without being supported by the recently established theory of elastocapillarity. Here we visualize the clustering behavior of polymer micropatterns with the evaporation of liquid film while varying the sizes and temperature of the micropatterns. We find a critical role of substrate temperature in preventing the leaning of the patterns via changing the evaporation rate and behavior of the liquid film. Also, we construct a regime map that guides us to find a process condition to avoid pattern leaning in semiconductor manufacturing. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700