Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J07: Electrostatic Manipulation of Fluids and Soft Matter IFocus Live
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Sponsoring Units: DSOFT DPOLY DBIO DFD Chair: Jonathan Singer, Rutgers University, New Brunswick Room: 07 |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J07.00001: Influence of controlled ionic conductivity on melt electrospinning of polyethylene Neelam Sheoran, Brenton David Boland, Samuel Thornton, Russell E Gorga, Jason R Bochinski, Laura Clarke The ionic conductivity of thermoplastic melts was increased by incorporating commercial additives which altered the characteristic size scales in the electrospinning process, resulting in an order of magnitude decrease in fiber diameter and formation of some fibers as small as 200-300 nm. By utilizing an unconfined geometry (a fluid-covered flat plate), where the melt spontaneously forms and organizes many fiber-generating cone-jets, changes in the wetting properties under the applied electric field can be observed. These changes can be described by simple models and confirm results from independent fluid property measurements. We discuss results from two commercial formulations of linear low-density polyethylene as a function of additive concentration and correlate changes in fluid properties with the time to first fluid perturbation, the number of jets, the capillary length (due to the electric force), the cone and jet sizes and the resulting fiber diameter. The development of high strength mesoscale thermoplastic nanofibers could have significant importance for filtration and biological applications. |
Tuesday, March 16, 2021 3:12PM - 3:48PM Live |
J07.00002: Using Multiplexed Electrosprays To Manipulate Fluids and (soft) Materials Invited Speaker: Sandro Gomez The cone-jet electrospray has revolutionized the field of mass spectrometry but, despite the unique ability of this device to produce quasi-monodispersed particles in a phenomenal size range down to the nanoscale, it has not been applied to other fields, except for small scale proof-of-concept demonstrations. The primary reason for the lack of widespread use is the low flow rate at which the spray is dispersed. Using fluid mechanics and electrostatics, we a) developed criteria for compact multiplexing to increase flow rate drastically, b) microfabricated systems with high packing densities (1.1 104 sources/cm2), reducing the cost per electrospray source, and c) demonstrated successful operation of these devices in the synthesis of (soft) materials (e.g., polymer nanoparticles of controlled shape for drug delivery and battery materials) and in microchip cooling. I will review design criteria and applications. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J07.00003: Finite Element Method Modeling of Self-Limiting Electrospray Deposition Catherine Nachtigal, Dylan Kovacevich, Lin Lei, Jonathan Singer Electrospray deposition (ESD) is a manufacturing tool that involves passing a solution through a charged capillary, allowing the solution to disperse into a spray. Some materials undergo self-limiting electrospray deposition (SLED) when sprayed, in which the charge of the spray builds up on the spray target, resulting in the deflection of further spray onto unsprayed portions, creating an even coating. To model the SLED process, COMSOL was used to create a model of the spray needle, target, and electric field, creating a particle trace representing the spray. This was used in combination with a MATLAB interpolation to calculate the surface charge based on the droplets deposited and the charge decay, and a MATLAB wrapper which ran the simulation with the interpolation over several iterations to simulate the film deposition over time. These patterns were compared to experimental polystyrene sprays to determine its charge decay constant, allowing the proper charge decay constant to be found and used to model the spray on various target geometries and conductivity patterns. This study can allow for the calculation of various spray materials’ charge decay constants and spray patterns on various geometries. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J07.00004: Self-limiting electrospray deposition to create bioactive coating Sarah Park, Lin Lei, Emran Lallow, Catherine Nachtigal, Hao Lin, Jonathan Singer Electrospray deposition (ESD) is a well-established technique for thin film creation from the spray of highly charged droplets loaded with the material to be deposited. Recently, we have characterized self-limiting electrospray deposition (SLED). In SLED, manipulation of electrostatic repulsion, hydrodynamic forces and evaporation kinetics can conformally cover 3D architectures with microcoatings. The coatings are hierarchical, possessing nanoshell or nanoparticle microstructure. Initial demonstrations of SLED used single glassy polymers as the solutes and simple cm-scale geometries as substrates. Here, I will discuss opportunities to create bioactive conformal coatings on medically-relevant architectures with blending, self-assembly, and complex geometries. We explore coating transdermal microneedles with blends of DNA vaccines and rapid-dissolving matrixes as a high-efficiency, scalable alternative to dip or inkjet coating. We demonstrate that we can deposit up to 70wt% viable coatings of DNA in a sugar matrix that quickly dissolve upon insertion into the skin and show expression of GFP(pEGFP-N1). This method is compatible with rapid continuous manufacturing and provides a shelf-stable, low-training vaccination for the current and future pandemic crises. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J07.00005: The Influence of Charge Injection on Melting Gels Delivered via Electrospray Deposition Michael Grzenda, Arielle Marie Marie Gamboa, Lin Lei, James Mercado, Alfusainey Samateh, Lisa Klein, Andrei Jitianu, Jonathan Singer Melting gels are a class of hybrid organic-inorganic gels that are solid below their glass transition temperatures but show thermoplastic behavior when heated. While this phase change is reversible, heating the gel past its consolidation temperature produces a highly crosslinked glassy organic/inorganic material. This crosslinking is highly dependent on charge interactions, raising the question of how these materials will interact with a processing technique, like electrospray deposition (ESD), which is dependent on charge delivery. Previous results showed that both film thickness and chemistry were influenced by spray polarity and substrate temperature. Here, these explorations were furthered by controlling the rate at which charge was delivered to the substrate and by isolating the viscosity of the arriving material from temperature through the use of modifiers in the spray solution. Results were further compared to samples produced by spin coating to compare to systems without charge injection. Optical images, film thickness measurements, nanoindentation, and FTIR were used to characterize the sprayed melting gel with the goal of developing a robust processing space for producing highly cross linked, hydrophobic, dielectric coatings. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J07.00006: Stability limit of droplets in combined fields Justin Beroz, A. John Hart, John W M Bush The condition for stability of a droplet subject to an external field arises in many practical and theoretical circumstances. Here we present the experimental results for a droplet’s stability limit under combined electrostatic and gravitational fields – a nonlinear system in which the droplet takes various non-elementary shapes at different combined field strengths. The system is characterized in terms of three dimensionless groups prescribing the drop geometry and the relative magnitudes of electrostatic, gravitational and capillary pressures. The stability limit is well represented by a plane in the coordinate system spanning these dimensionless groups, a result valid across several orders of magnitude of experimental data. We rationalize this result on the basis of the scaling for the energy differentials of the unstable mode. Our methodology may be more broadly applied in deducing the stability limits of systems subject to combined fields. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J07.00007: The transition from induced charge electroosmotic flow to electrothermal flow in a constriction microchannel Amirreza Malekanfard, Zhijian Liu, Xiangchun Xuan Electric field is the method of choice in microfluidic particle-handling devices because of the precise transport and placement of particles via fluid electroosmosis and particle electrophoresis. Insulator-based dielectrophoretic microdevices have been increasingly used for particle manipulation purposes, where insulating structures are exploited to create electric field gradietns for the dielectrophoretic focusing, trapping and separation etc. However, the presence of the insulating strucutres, especially those with sharp edges, may influence the linear electroosmotic fluid low by two nonlinear electrokinetic phenomena: induced charge electroosmotic flow and electrothermal flow. We present a combined experimental and numerical study of the transition from the induced charge electroosmotic flow in a low-conductivity fluid to the electrothermal flow in a high-conductivity fluid. A parametric study is also conducted to understand these two nonlinear electrokinetic phenomena competing with one another in the transition fluid conductivities. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J07.00008: Using Electrohydrodynamic Deposition for In-Space Manufacture of Perovskite Solar Cells Samuel Erickson, William Delmas, Albert DiBenedetto, Lyndsey McMillon-Brown, Timothy Peshek, Sayantani Ghosh We have developed a thin film preparation technique utilizing electrohydrodynamic deposition (EHD) for in situ fabrication of photovoltaic (PV) devices during space missions. EHD entails drawing bi-solvent perovskite precursor solution to a substrate via an applied electric field. The difference in vapor pressure between the solvents drives surface coverage in a phenomenon known as Marangoni flow. Aside from deposition technique, the chemical composition of the absorbing and charge transport layers are among the many choices to address when making a PV device. To best direct our research, metrics such as power conversion efficiency and long-term stability were extracted and analyzed through extensive data mining. Key discoveries include the choice of methylammonium/formamidinium (MA/FA) in the active layer, followed by tin oxide as the preferred electron transport layer. This talk will focus on the EHD process, the data analytics, and our results in thin film fabrication. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J07.00009: Electrohydrodynamic Thermal Oscillators for Waste Heat Harvesting Applications Tianxing Ma, Darrel Dsouza, Kyrsten McKenzie Ryerson, Matthew G Signorelli, Jonathan Singer, Mingjiang Zhong, Michael Loewenberg, Chinedum Osuji There is a great need for a high efficiency, scalable thermal oscillator for applications such as pyroelectric waste heat harvesting. This work attempts to design and test the efficiency of a novel liquid-based thermal oscillator, which utilizes periodic electrohydrodynamic (EHD) capillary bridging and debridging between two coaxial droplets in a parallel plate capacitor under an electric field. In preliminary testing of liquids, five modes of liquid motion were observed and found to be dependent on liquid properties, as well as the applied voltage and gap width of the capacitor. Through droplet profile extraction from test videos of the thermal oscillator, electrical, surface, and gravitational energies were calculated using finite element method simulations in COMSOL. Each liquid behavior exhibited unique energy configurations, and optimal behavior was found when bridge free energy was lowered, but surface energy was raised compared to the debridged (droplet) state. Finally, thermal tests were conducted by placing a pyroelectric material in contact with the liquid droplet EHD switches. This resulted in efficient thermal cycling and power produced through the Olsen cycle, demonstrating the device's ability to effectively generate temperature oscillations. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J07.00010: Dynamic Modulation of Dielectrophoretic Force Using Resonant Feedback Punnag Padhy, Mohammad Asif Zaman, Michael Anthony Jensen, Lambertus Hesselink Dielectrophoresis is the backbone of micromanipulation in lab-on-a-chip platforms. In such systems, once the electrodes are defined by fabrication the spatial profile of the dielectrophoretic force is fixed. Modification of the force profile entails refabrication of entire systems with the redesigned electrodes. To overcome this problem, we propose to connect the trap electrodes in series with an external resistor and an inductor to form a resonant RLC circuit. As a dielectrophoretically trapped droplet moves, it modifies the capacitance between the electrodes by inducing additional charges on them, which in turn shift the circuit resonance and the voltage across the electrodes to exert an additional feed-back force on the droplet. We show that by tuning the A.C. supply frequency and the circuit resistance the detuning and linewidth of the resonant circuit can be modulated to dynamically control the spatial profile of the dielectrophoretic force through the feed-back effect. The additional handles introduced by the resonant circuit allow to extend the trap range while ensuring that the trapped sample is not exposed to high electric fields at the stable trapping position, an extremely important criterion for the trapping of sensitive biochemical specimen. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J07.00011: Interfacial and bulk assembly of ellipsoidal microparticles under the influences of external electric fields Samuel Trevenen, Peter J Beltramo This talk will present recent work using Mirau Interferometry to accurately map the interfacial deformation around polymer microellipsoids pinned to an air-water interface under various external fields. We first explore how these particles align in bulk solution under different solution and electric field conditions to inform a set of design parameters when working at the interface. Measurements of particle dynamics in bulk were performed in order evaluate the torque on an ellipsoid due to a uniform AC electric field. At two-dimensional water-air interfaces, phase-shift Mirau interferometry is used to monitor the change in contact line undulations surrounding an ellipsoid at an air-water interface due to an electric field. By measuring the location of the three-phase contact line, we can determine the contact angle of pinned particles as a function of aspect ratio, hydrophilicity, solution conditions, and electric field characteristics. In doing so, an improved understanding of the forces acting on a particle at the interface as well as how applied electric fields can manipulate the pinning and ultimate assembly of such particles is achieved. |
Tuesday, March 16, 2021 5:36PM - 5:48PM Live |
J07.00012: Interfacial Tension Hysteresis in Oxidizing Eutectic Gallium-Indium Keith Hillaire, Minyung Song, Abolfazl Kiani, Sahar Rashid-Nadimi, Michael Dickey, Karen Daniels Eutectic gallium-indium (EGaIn), a room-temperature liquid metal alloy, has the largest interfacial tension of any liquid at room temperature. Under an applied voltage in an electrolytic bath, the interfacial tension of EGaIn is decreased by orders of magnitude. We observe that the interfacial tension depends not only on the applied voltage and the concentration of the bath’s electrolyte, but also exhibits history-dependence when the applied voltage is swept. We examine the interfacial tension’s dependence on voltage, voltage sweep rate and direction, and on time, and present a model of the droplet’s surface free energy as dependent on charge density and molecular composition of the interface to describe the voltage history dependence of the interfacial tension. |
Tuesday, March 16, 2021 5:48PM - 6:00PM Live |
J07.00013: Electrospray Deposition of Polyimide with Passive Material Focusing Bryce Kingsley, Emma Pawliczak, Thomas Hurley, Paul Chiarot Electrospray deposition (ESD) is a novel printing technology that uses a strong electric field to atomize a liquid suspension into a plume of electrically charged micro-droplets. Solvent evaporation within the plume leaves behind dry solute that is directed onto a substrate to build thin films with micro- and nano-scale structure. Silicon substrates were targeted using ESD to print films of polyimide, an important material in electronics manufacturing. Using electrostatic lensing, the material was passively focused to constrain the deposit area and increase the rate of film growth. Various processing conditions were investigated, including polyimide concentration, flow rate, spray time, and solution electrical conductivity. For low rates of polyimide delivery, the film thickness increased linearly for spray times up to 60 mins. During printing, the film roughness would increase and decrease cyclically, indicating a charge-induced pin-holing mechanism in the evolving film. The rate of film growth was suppressed at high rates of polyimide delivery due to the accumulation of electric charge on the substrate during printing. |
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