Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E54: Thermocapillary and Solvocapillary Methods for the Manipulation of Soft MatterFocus
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Sponsoring Units: GSOFT Chair: Jonathan Singer, Vivek Sharma, Rutgers University, University of Illinois at Chicago Room: LACC 514 |
Tuesday, March 6, 2018 8:00AM - 8:12AM |
E54.00001: Tears of Wine Prerana Rathore, Chenxian Xu, Vivek Sharma ‘Tears of wine’ refer to the rows of wine-drops that spontaneously emerge within a glass of strong wine. Evaporation-driven Marangoni flows near the meniscus of water-alcohol mixtures drive liquid upward forming a thin liquid film, and a rim forms near the moving contact line. Eventually the rim undergoes an instability, thus forming drops, that roll back into the bulk reservoir as the so-called tears of wine. Most studies in literature argue the evaporation of more volatile, lower surface tension component (alcohol) results in a concentration-dependent surface tension gradient that drives the climbing flow within the thin film. Though it is well-known that evaporative cooling can create temperature gradients that could provide additional contribution to the climbing flows, the role of thermocapillary flows is less well-understood. Furthermore, the patterns, flows and instabilities that occur near the rim, and determine the size and periodicity of tears, are not well-studied. Using experiments and theory, we visualize and analyze the formation and growth of tears of wine. The sliding drops, released from the rim towards the bulk reservoir, show oscillations and a cascade of fascinating flows that are analyzed for the first time. |
Tuesday, March 6, 2018 8:12AM - 8:24AM |
E54.00002: Droplet migration and interactions from coupled mass transport Harishankar Manikantan, Nan Shi, Arash Nowbahar, Todd Squires Mass transport of solutes often results in non-uniform concentration profiles. Nevertheless, the presence of such solute gradients and subsequent fluid flows and colloidal migration/interactions in many circumstances have not been fully appreciated. Here, we present studies on internal flows of neighboring droplets, where local solute gradients arise from coupled mass transport between droplets. First, we show that such local solute gradients can induce interfacial Marangoni flow that drives bulk fluid motion. Observed flow profiles inside droplets depend on the direction of interfacial mass transport and suggest interesting interactions between neighboring droplets. In addition, we combine experiments and COMSOL simulation to identify two distinct mechanisms that drive flows in neighboring droplets with coupled mass transport. Further investigations reveal that the transition between these two mechanisms is related to the separating distance between droplets. Finally, we design droplet pairs with a source-sink configuration in their chemical compositions. Visualization of internal flows indicates distinct droplet-droplet interactions as the separating distance varies. |
Tuesday, March 6, 2018 8:24AM - 8:36AM |
E54.00003: Interfacial Marangoni flows during non-solvent induced phase separation of a ternary polymer solution Douglas Tree, Kris Delaney, Glenn Fredrickson Non-solvent induced phase separation (NIPS) processes are widely used by industry and by Nature as a means of controlling the microstructure of polymer materials. While the general principles of the NIPS process are well-known, a detailed quantitative description has proven difficult, in part due to a lack of robust theories and quantitative models. We recently addressed this need by developing a multi-fluid model of the NIPS process that combines continuum fluid mechanics with a field-theoretic description of polymer thermodynamics. Using our model, we show that non-solvent transport during the initiation of NIPS can lead to strong interfacial Marangoni flows. We will discuss the conditions necessary to achieve these flows, as well as the implications they have on the evolution of the microstructure of materials such as polymer membranes. |
Tuesday, March 6, 2018 8:36AM - 8:48AM |
E54.00004: Mesoscale Simulation of Nanoparticle Deposition in Evaporating Colloidal Droplet Xin Yong, Mingfei Zhao The research on nanoparticle deposition induced by evaporation of colloidal droplet expands rapidly in the past years due to its importance in many applications, including materials printing and thin-film processing. Revealing the detailed particle dynamics during evaporation can produce understanding of the much-needed processing-structure relationships in the drying process. We apply a 3D lattice Boltzmann-Brownian dynamics model to simulate evaporating sessile droplets with particles dispersed in the bulk and adsorbed at the interface. A new LBM fluid model is developed to model liquid-vapor phase change heat transfer of a single-component fluid with a contact line pinning scheme that allows us to explore evaporation on solid substrates with different wetting properties, namely constant contact radius and constant contact angle regimes. We observe the process of nanoparticle self-assembly during the evaporation of droplets and quantitatively analyze the deposit structure. We further elucidate the particle dynamics in the presence of Marangoni convection induced by inhomogeneous evaporation, which provide critical insight into evaporation-driven depositions under experimentally relevant conditions. |
Tuesday, March 6, 2018 8:48AM - 9:00AM |
E54.00005: Metrology of Thin Films by Focused Laser Spike Dewetting Tianxing Ma, Jonathan Singer Focused laser spike (FLaSk) dewetting utilizes thermocapillary shear forces generated by laser-induced extreme thermal gradients to move molten materials down thermal gradients. Past work, which has explored the patterning potential of this technique, demonstrated that evolution of the driven dewetting patterns formed by FLaSk is highly sensitive to not only the parameters of the laser, but also to specific parameters of the dewetted material. The most significant effects tie to the melt viscosity. This talk will discuss the use of FLaSk as a tool to probe factors that affect the viscosity of the melt, including surface modification, crystallization, and phase separation. The key advantage to this approach is that a single FLaSk “experiment,” consisting of a point-exposure with a controlled set of parameters, can occur on a sub-mm or even sub-micron region independently from other FLaSk experiments. Therefore, a mm-patch of material can contain hundreds to millions of experimental conditions. By using a calibrated heating substrate, the thermal conditions of the different exposure profiles can be well characterized. Further, optical analysis techniques can lead to high-throughput evaluation of the results. |
Tuesday, March 6, 2018 9:00AM - 9:36AM |
E54.00006: MicroAngelo Technique: 3D Sculpting of Nanofilms by Spatiotemporal Modulation of Thermocapillary Forces Invited Speaker: Sandra Troian With just a crude hammer and chisel at the age of 17, Michelangelo sculpted one of the most beautiful 3D marble reliefs ever known - the Madonna of the Steps. Its complex topography, with less than millimeter thickness variations, lends an awe inspiring quality to this masterpiece. Though not an aesthetic parallel, the photolithographic fabrication of today's integrated circuits also relies on complex topographic sculpting of nanofilms wherein light passed through a photomask engraves a pattern into photosensitive layers revealed after chemical treatment. Deep UV can yield feature sizes well below 100 nm, a true marvel as well. Here we present the theoretical foundations and experimental validation of a sculpting technique for contactless, one step patterning of nanofilms called MicroAngelo.This technique relies on spatiotemporal modulation of thermocapillary forces by projection of thermal distributions onto the gas/liquid or liquid/solid interface. Liquid is thereby drawn out-of-plane into desired 3D shapes by enormous surface forces that orient parallel to the moving boundary. The liquid film can track and replicate a moving patterned target until the final shape solidifies in-situ. Theoretical analysis will focus on predictions obtained from linear and weakly non-linear analysis, Lyapunov analysis, parametric resonance, nonlinear evolution, proximity corrections and resolution limits. Experimental analysis will focus on decades of effort by researchers worldwide in identifying the primary physical mechanism and subsequent successful fabrication of complex microlens arrays, linear waveguides, ring resonator shapes, and non-array intricate patterns. We believe these findings evidence the enormous potential inherent in this and alternative 3D microscale lithographic techniques based on film sculpting by powerful surface forces. |
Tuesday, March 6, 2018 9:36AM - 9:48AM |
E54.00007: Programming surface energy driven Marangoni convection to pattern polymer films Christopher Ellison, Chae Bin Kim, Talha Arshad, Roger Bonnecaze The Marangoni effect describes how fluid flows in response to gradients in surface energy. We recently developed a method for photochemically preprograming spatial surface energy patterns in glassy polystyrene (PS) thin films. UV irradiation through a mask selectively dehydrogenates the PS, thus increasing surface energy in the UV exposed regions compared to the unexposed regions. After heating the film to the liquid state, transport of polymer occurs from regions of low surface energy to regions of high surface energy. This method can be harnessed to rapidly manufacture polymer films possessing prescribed three-dimensional topographies reflective of the original light exposure pattern without solvent washes or etching procedures. To better understand this phenomenon, a theoretical model will be presented that reveals the physics of this process, its limits and ways to apply it efficiently for various target metrics. |
Tuesday, March 6, 2018 9:48AM - 10:00AM |
E54.00008: Unconventional micro and nanopatterning method by precisely temperature-controllable mold Jong Uk Kim, Kwang Su Kim, Pil J. Yoo, Tae-il Kim Unconventional lithographic techniques are often used for fabrication as an alternative to photolithography because they are faster, cost-effective and simpler to use. However, these techniques such as nanoimprint lithography are limited in scalability and utility because of the collapse of pre-printed structures during step-and-repeat processes. Here, we propose a new class of temperature-controllable polymeric molds that are coated with a metal such that any site-specific patterning can be accomplished in a programmable manner via precisely controlled joule-heating system. This technique allows site-selective dewetting, sub-100 nm patterning, step-and-repeat processing and hierarchical structure generation. The programmable feature can be utilized for the structural coloring and shaping of objects. Large-area programmable patterning, semiconductor device manufacturing, and the fabrication of iridescent security devices would benefit from the unique features of the proposed strategy. |
Tuesday, March 6, 2018 10:00AM - 10:12AM |
E54.00009: Theory and Simulation of Capillary Forces on a Nanoparticle at a Liquid-Vapor Interface Yanfei Tang, Shengfeng Cheng The Young-Laplace equation of a liquid-vapor interface serves as the basis of the continuum theory of capillarity. We use molecular dynamics simulations to investigate a nanoparticle straddling a liquid-vapor interface and explore if the Young-Laplace equation can be used to describe capillary action at nanoscale. In equilibrium, the interface is flat and intersects with the nanoparticle surface. When the nanoparticle is out of equilibrium location but still straddles the interface, a capillary rise or fall will occur, inducing a restoring force that drives the nanoparticle back to its equilibrium location. Our simulation results fit well to the continuum theory of capillarity. The force on the nanoparticle is approximately linear with displacement from its equilibrium location and the associated spring constant depends logarithmically on the lateral span of the interface. Our results clarify the physical foundation of a method of modeling soft matter solutions in which the interface is replaced by a potential well for particles straddling the interface or solutes dispersed in the liquid phase. With this method, the solvent is eliminated and larger systems can be modeled. |
Tuesday, March 6, 2018 10:12AM - 10:24AM |
E54.00010: Templating Electrohydrodynamic Instabilities with Thermocapillary Multidewetting Arielle Marie Gamboa, Tianxing Ma, Lin Lei, Valeria Saro-Cortes, Jonathan Singer Thermocapillary dewetting of liquids and molten films has recently emerged as a viable alternative to conventional microprocessing methods. Its dependence on fundamental thermal gradients allows it to be applied to various combinations of materials, including metals and polymers, with sufficiently different melting points. Here, we investigate the application of focused laser spike (FLaSk) multidewetting to direct electrospray deposition. Electrospray deposition utilizes narrow dispersion microdroplet sprays generated by high voltage to deposit micro/nanocoatings. Due to the charged nature of these sprays, they are sensitive to the ability of the spray target to dissipate and redistribute charge on arrival. By the independent greyscale pattering of insulators and conductors through FLaSk, it is possible to create complex masks to template paths to ground for electrospray deposition. These templates can act as both stencils and lenses to trigger and enhance electrohydrodynamic instabilities. The net result is both a fundamental platform for the study of these phenomena and, by crosslinking of the templated fluids, a means of patterning desired structures. |
Tuesday, March 6, 2018 10:24AM - 10:36AM |
E54.00011: Laser-Induced Thermocapillary Reorientation of Liquid Crystal Elastomers Michael Nitzsche, Tianxing Ma, Yu Xia, Shu Yang, Jonathan Singer Recent investigation of thermocapillary and thermosolvocapillary forces induced by focused laser spike (FLaSk) annealing has revealed that the interfacial shear generated by highly localized thermal pulses can be employed as a means to align and anneal mesoscale order in soft matter. This work explores the use of FLaSk of a photoabsorbing dye to direct the nematic phases of an RM82-based liquid crystal elastomer, which can be crosslinked either simultaneously or by separate treatment. The director orientation in such nematic systems have a drastic effect on the mechanical properties of the crystal, as mechanical or thermal stress will induce large directional strains along these molecules with only minimal transverse strain, and the deliberate patterning of crosslinked elastomer phases has been used to program the expansion behavior of three-dimensional liquid crystalline soft actuators. Results suggest that both the thermal gradient magnitude and the writing rate effect the overall reorientation for overlapping scans. Compared to previous efforts to optically template these phases, the driving force for this method is decoupled from the polarization of the beam. This allows for patterning of complex paths and even 3D effects. |
Tuesday, March 6, 2018 10:36AM - 10:48AM |
E54.00012: Focused Laser Dewetting of Gold Nanofilms and Laser Induced Localized Physical Vapor Deposition Tianxing Ma, Arielle Marie Gamboa, Michael Nitzsche, Warren Rucker, Dunbar Birnie, Jonathan Singer Focused laser spike (FLaSk) excitation has been repeatedly proven as a technique for the patterning of micro-to-nanoscale features locally by thermocapillary dewetting of thin films. Here we investigate the effect of overlapping laser exposures in the dewetting of ~15 nm gold films on borosilicate or quartz glass substrates. Due to the low viscosity and oxidation potential and high surface tension and vapor pressure of the gold melt, the FLaSk initiates the capillary and thermocapillary dewetting with the non-equilibrium vaporization simultaneously. The parameters of overlapping laser scans control the amount and temperature of the material heated, and thus we can tune the deposited film condition as well as the size and spacing of the nanoparticles deposited on the writing substrates or a positioned superstrate through a laser-induced localized physical vapor deposition (LILPVD) process. Additionally, if the substrate also melts during FLaSk, the liquid-on-liquid dewetting can broaden the patterning conditions by resisting the motion of the gold. Taking advantage of the ability to transfer a variety of nanoparticle morphologies to a target substrate, we have employed LILPVD to screen precursor morphologies for the growth of CdSe microstructures for tandem photovoltaic cells. |
Tuesday, March 6, 2018 10:48AM - 11:00AM |
E54.00013: Laser Streaming: Turning a Laser Beam into a Liquid Jet Flow Shuai Yue, Yanan Wang, Qiuhui Zhang, Zhuan Zhu, Feng Lin, jiangdong deng, Geng Ku, Suchuan Dong, Md Kamrul Alam, Dong Liu, Zhiming Wang, Emmanuel Epie, Wei-Kan Chu, Jiming Bao Transforming a laser beam into a mass jet flow has been a challenge both scientifically and technologically. I will present our recent demonstration of the generation of a liquid jet by simply focusing a pulsed laser into water through a glass window. The jet originates from the laser focusing spot on the glass and moves in the same direction as the refracted beam. Microscopically, this transformation is made possible by an underlying plasmonic nanoparticle-decorated cavity which is self-fabricated on the glass by nanoparticle-assisted laser etching and exhibits size and shape uniquely tailored to the incident beam profile. Hydrophone signals indicate that the jet is driven via acoustic streaming by a long-lasting ultrasound that is resonantly generated by laser and the cavity through the photoacoustic effect. creating new research in optofluidics and opening up enormous light-controlled device applications. The principle of this light-driven flow via ultrasound, i.e. photoacoustic streaming by coupling photoacoustics to acoustic streaming, is general and can be applied to any liquids. This generality is verified by our latest generation of jet flow by a pre-fabricated gold implanted glass window. |
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