Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D16: Electrostatic Generation of Sprays and FilamentsFocus
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Sponsoring Units: DSOFT DPOLY DFD Chair: Jonathan Singer, Rutgers University Room: Room 208 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D16.00001: Bead Encapsulation and Ejection from Droplet for Solid-Phase Synthesis Punnag Padhy, Mohammad A Zaman, Michael A Jensen, Yao-Te Cheng, Ludwig Galambos, Ronald W Davis, Lambertus Hesselink Solid-phase synthesis techniques are at the heart of synthesis of polymeric molecules like oligonucleotides (DNA and RNA), oligopeptides, oligosaccharides as well as the generation of combinatorial libraries for drug and vaccine development. Droplet microfluidic implementation of solid-phase synthesis has emerged as an important unmet technological challenge that can automate, massively parallelize, enhance throughput, and reduce reagent consumption of these otherwise traditionally expensive, labor, time and cost intensive processes. This can in turn facilitate the synthesis of longer DNA strands. However, this has remained challenging from a physical sample handling standpoint due to the inability to move individual beads across the droplet-medium interfaces. Here, we show the electric field assisted encapsulation and ejection of individual hydrophobic beads from aqueous microdroplets and describe its operation as a voltage dependent change in the electrofluidic potential energy of the system. We discuss the interfacial tension, contact angle, viscosity, bead, and droplet size dependence of the above process. As a proof-of-concept implementation of solid-phase synthesis, we demonstrate the enzymatic coupling of a fluorescently labelled nucleotide to a functionalized bead using the above process. |
Monday, March 6, 2023 3:12PM - 3:24PM Author not Attending |
D16.00002: Inverse Solution for High Fidelity Shaping of Slender Liquid Films by Electrohydrodynamic Patterning Yi Hua Chang, Sandra M Troian Electrohydrodynamic patterning describes a technique whereby a slender liquid film is deformed into complex shapes by application of a strong transverse electric field pattern and then solidified in-situ. Most studies have focused on the forward problem in which the evolution equation for the liquid interface, which is subject to an applied field pattern, is propagated in time. Since the governing equation is 4th order and highly nonlinear, field patterns based on an intuitive approach typically fail to yield high fidelity shapes required for stringent micro-optical applications. In this study, we tackle the inverse problem and identify the optimal field patterns required to achieve specific shapes in a given time interval by posing the problem as a PDE-constrained optimization problem. We illustrate this methodology, which can efficiently handle both static and time-dependent field distributions, by deforming a flat film into a lens or waveguide. This ttalk shall conclude with discussion of optimal parameter sets and limitations of this approach. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D16.00003: Studying the Influence of Temperature on the Emission of Ions from a Nanoscale, Electrified Meniscus Brandon Pugnet, Jackson Moore, Nicholas Drachman, Derek Stein Motivated by the goal of sequencing single protein molecules, we have built a custom mass spectrometer featuring a nanocapillary ion source that emits single amino acid ions directly into high vacuum from the charged meniscus. In this talk we describe a study of the ion emission process. The mass spectrum obtained from aqueous solutions of arginine in positive ion mode shows a broad distribution of peaks corresponding to arginine clustered with different numbers of water molecules, as well as various hydronium-water clusters. An apparatus housed inside the mass spectrometer then applied heat to the ion source capillary to raise the temperature at the meniscus. Radiative cooling along the heated capillary limited the maximum temperature at the tip to about 55°C. The heated ion source changed the mass spectra in significant and interesting ways: The number of ion-solvent mass peaks decreased, as the highest mass ion clusters disappeared as well as the lightest ones corresponding to hydronium-water clusters. The emission rate of the remaining arginine-water clusters was relatively unchanged. Interestingly, this culminated in a lower overall emission current at higher temperature. A similar study of positive ion emission from aqueous sodium iodide solutions showed a decrease in the abundance of high mass ion clusters. We discuss how the ion emission mechanism may change with temperature in view of these findings. |
Monday, March 6, 2023 3:36PM - 3:48PM Author not Attending |
D16.00004: Electrohydrodynamic Simulations of Self-Similar Cuspidal Formations Relevant to Liquid Metal Ion Sources Cheolmin Im, Sandra M Troian Liquid metal ion sources, used in applications ranging from metal deposition or ion doping to space propulsion, rely on spontaneous emission in liquids subject to strong electric fields. The liquid source, placed in close proximity to a counter electrode with a circular aperture, is typically either a small droplet at the tip of a capillary tube or a thin film made to coat the rounded tip and length of a solid needle. While the latter geometry affords certain advantages, it introduces significant complexity in the spatiotemporal response of the film prior to emission, behavior which can only be explored by high fidelity electrohydrodynamic simulations. In this talk, we present results based on finite element modeling of electrified films coating a solid needle which reveal formation of liquid conformations not previously reported. The accelerating cuspidal shapes, pressure and velocity field values at the apical tip evolve by a self-similar process terminating in blowup, which can be characterized by various exponents. We discuss parameter ranges and factors controlling film response by presenting a novel “phase diagram” delineating those configurations so far observed. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D16.00005: Explosive Emulsification Induced by an Electric Field Zachary Fink, Xuefei Wu, Thomas P Russell We explore the behavior of explosive emulsification of a droplet of an aqueous dispersion of carboxy-functionalized nanoparticles (NPs) immersed in a toluene solution of triamine-modified polystyrene (PS-triNH2), a cationic surfactant under a dc electric field. The E-field biases the movement of the charged NPs and the stability of the NPs surfactants (NPSs) at the interface. For a positively charged interface, the NPs are depleted from the interface, due to the electric potential gradient, while, regardless of the field direction, the adsorption rate of the PS-triNH2 to the interface is increased due to electric field-induced flows. As a result, the NPSs formed at a negatively charged interface have a higher binding energy by anchoring the NPs to the ligands, spontaneous emulsification is suppressed, leading to an oversaturation of the interface and an interfacial tension much lower than the equilibrium value. Dipolar interactions between the NPSs are absent when the field is removed, triggering an explosive emulsification, where tens of thousands microdroplets (d ~4 μm) are ejected from the interface with velocities of up to 5 mm/s. The propulsion of the droplets occurring during this explosive event is sufficient to move a droplet (d=1.8 mm) at a velocity of 8 mm/s. The interface, oversaturated with NPSs, represents a unique energy storage system. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D16.00006: Controlling morphology in electrosprayed methylcellulose nanowires via nanoparticle addition Xin Yong, Jonathan M Blisko, Michael J Grzenda, Rachel M Vladimirsky, Christopher E Shuck, Jonathan P Singer Electrospray deposition (ESD) has shown great promise for manufacturing micro- and nanostructured coatings at scale on versatile substrates with complex geometries. ESD exhibits a broad spectrum of morphologies depending upon the properties of spray fluids. Among them are nanowire forests or foams obtained via the in-air gelation of electrospray droplets formed from methylcellulose (MC) solutions. In this study, we explored MC ESD loaded with nanoparticles of various shapes and uncovered the effects of particle fillers on morphology evolution using coarse-grained simulations and physical experiments. Utilizing electrostatic dissipative particle dynamics, we modeled the electrohydrodynamic deformation of particle-laden MC droplets undergoing in-flight evaporation. The simulations quantitively predict the suppression of droplet deformation as the size or concentration of spherical nanoparticles increases. While small particles can be readily encapsulated into the nanowire body, large particles can arrest nanowire formation. The model was extended to nanoparticles with complex topologies, showing MC nanowires emerging from particle edges and vertices due to curvature-enhanced electric stress. In all cases, strong agreements were found between simulation and experimental results. These results demonstrate the efficacy of the coarse-grained model in predicting morphological evolution and lay the groundwork for employing MC nanowires for developing nanostructured composites. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D16.00007: Characteristics of Dry and Semi-dry Electrospray-printed Polymeric Films Bryce J Kingsley, Paul Chiarot In electrospray printing, high electric potentials are used to atomize a print material solution into a spray of charged droplets. The droplets follow electric field lines from the emitter to the target surfaces to create thin, conformal films. The extent of in-flight solvent evaporation determines the microstructure and function of the film. Dry, particulate films are formed when the solvent completely evaporates, while for incomplete evaporation, residual solvent is delivered with the print material to create a dense film. We report on the microstructural differences of these two print regimes defined as dry and semi-dry electrospray printing. Here, the print solution consisted of polyimide dispersed in dimethylformamide. The degree of solvent evaporation was controlled via the print solution flow rate and the flow rate of co-flowing air introduced during printing. Low solution flow rates or high co-flowing air resulted in dry films of polyimide, while semi-dry films were printed at high solution flow rates and no co-flowing air. The films were evaluated for their dielectric strength, optical characteristics, and corrosion resistance. Compared to the dry printed films, the semi-dry films had high optical transparency and superior dielectric strength, with breakdown field strengths of nearly 400 V/µm. Both print regimes showed excellent corrosion resistance when used to protect thin (30 µm) metal wires bonded to metallic pads. However, the semi-dry printed films performed better at low print times. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D16.00008: Effects of Solvent Conductivity on the Self-Limiting Electrospray Deposition (SLED) of Polymer Films Robert A Green-Warren, Noah M McAllister, Maxim A Arkhipov, Jonathan P Singer Self-Limiting Electrospray Deposition (SLED) is a derivative of the classic electrospray process for depositing both homogenous and composite films. The unique advantages of SLED are the abilities to deposit monodisperse and conformal coatings onto complex surfaces of both conducting and insulating surfaces. The resulting microstructure of the deposited film depends on numerous input parameters including the polymer characteristics, solution concentration, applied voltage, separation distance, and solvent conductivity. In this work, the effects of solvent conductivity on SLED polystyrene films are evaluated. The addition of ammonium salts and mixtures of various solvents such as acetonitrile are studied. Finally, the effects of solvent conductivity on the hierarchical microstructure of the deposited films are evaluated via scanning electron microscopy and compared. Preliminary results indicate that an increase in solvent conductivity results in a decrease in size of PS particles deposited via SLED resulting in a more uniform film. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D16.00009: Same-Polarity Biasing to Tune Thickness of Self-Limiting Electrospray Deposition Coatings Ayman Rouf, Jonathan P Singer, Michael Grzenda A characteristic of self-limiting electrospray deposition (SLED), an electrostatically driven method of spraying objects, is that over time substrates develop a charged film on their surface which repels oncoming spray towards uncoated portions of the substrate. This phenomenon leads to uniform coatings of self-limited thickness on the substrate. However, if the substrate were to have a repelling electric field on it from the beginning of the spray, it would repel oncoming spray as if a charged film had developed on the substrate, effectively acting as if the substrate had already been sprayed for some time. We sprayed silicon wafer samples held at varying levels of applied voltage with SLED polystyrene coatings and used microscopic reflectometry to measure the resulting densified thicknesses. Compared to a sample sprayed for the same duration with no applied voltage, all the samples with applied voltage had a lower thickness deposited on them. In addition, we identified that the resulting thicknesses on the samples decrease as the amount of applied voltage increases linearly up to the point where virtually no coating is deposited on a sample. In this way, it should be possible to dial in a desired self-limited thickness for a given target coating thickness. |
Monday, March 6, 2023 4:48PM - 5:24PM |
D16.00010: Structural Design of Electrospun Ceramic Nanofibers Invited Speaker: Gideon Grader Design of ceramic nanofibers with complex surface, inner structure and specific chemical and physical properties is required for materials with improved performance in diverse applications. Fiber architecture offers a built-in directionality within the material as well as reduction of mass transport limitation and accessibility to a large functional surface. Porous or hollow fiber structures provide additional inner surface, opening opportunities for impregnation, and creation new interfaces within the porous body. Electrospinning is an effective method to produce continuous nanofibers of diverse materials. Obtaining the desired morphology in such fibers is the main challenge addressed in this presentation. Typically, electrospun nanofibers are synthesized from solutions that contain solvents and polymers for rheological reasons. The desired ceramic phase is obtained after drying and polymer removal by thermal treatment. During this stage, fibers shrinkage, deformation, and phase and morphology changes occur. The presentation will focus on creation of nanofibers with diverse surface and inner structures from variety of materials. Formation of lamellar, hollow and belt architectures for specific applications will be discussed. Models leading to these morphologies are suggested, showing the interplay between process conditions and the nanofibers' complex surface and inner structure. The relation between synthesis conditions, morphology and performance will be discussed in diverse cases such as catalytic, thermoelectric and electrochemical systems. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D16.00011: Chitosan and Citric Acid Thin Films as Renewable Compatibilizing Pretreatments for Self-Limiting Electrospray Deposition Zainab A Abd Al-Jaleel, Weronika Wasniowska, Ayman Rouf, Jonathan P Singer Electrospray deposition (ESD) requires that the deposited charge be dissipated at a similar rate to its deposition. Here, we explore whether thin films of acetic/citric acid-doped chitosan deposited on insulating fused quartz substrates can stand in for a traditionally conductive surface. It is shown that, in humid environments, a layer of chitosan of 2 µm is sufficient to dissipate the charge deposited by electrospray in the self-limiting electrospray deposition regime, where charge is allowed to build up to form asymptotic thickness coatings. Sprays conducted in these conditions produce coatings of similar self-limiting thickness to those produced on a conductive surface. The same technique demonstrated potential for applicability to complex surfaces, such as those produced by AM or non-woven polypropylene fabric, and can be integrated into roll-to-roll continuous manufacturing. In this way, it is shown that dip coating of objects in chitosan is a surface-agnostic pretreatment for the application of conformal sprayed coatings to complex, insulating surfaces. |
Monday, March 6, 2023 5:36PM - 5:48PM Author not Attending |
D16.00012: Electrohydrodynamics of complex emulsions Majid Bahraminasr, Anand Yethiraj Electrohydrodynamics of droplets immersed in an immiscible carrier fluid were first |
Monday, March 6, 2023 5:48PM - 6:00PM |
D16.00013: Targeted functional methylcellulose-nanocomposite materials via self-limiting electrospray deposition Rachel Vladimirsky, Jonathan P Singer Electrospray deposition (ESD) uses strong electric fields to produce monodisperse droplets from solutions that are driven towards grounded targets. Self-limiting electrospray deposition (SLED) is a regime of ESD that achieves targeted coatings by spraying insulating polymers below their glass transition temperatures, with sprayed material trapping charge and repelling incoming spray. Methylcellulose (MC) has been demonstrated as SLED compatible and uniquely forms nanowire morphologies when sprayed. Here, it is hypothesized that these nanowires can be used to prevent electrical percolation in sprays of conductive particles and allow for highly controlled deposition. However, it was also observed that nanoparticle size and shape impact nanowire morphology, which complicates this interaction. For this study, we use 2D Ti3C2 MXene of two different sizes as well as spherical ITO in MC composite sprays. To quantify material spread, photolithography patterned chips, with gratings of varying widths and spacings were designed and sprayed with varying particle concentration, and the resulting feature sizes were measured by optical microscopy. Scanning electron microscopy shows these deposited materials are able to maintain unique low-density morphologies. Informed by these studies, MXene containing spray was used to functionalize interdigitated electrodes with features and spacings as low as 50 microns and a substantial increase in capacitance was measured. |
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