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 Z14: Electrostatic Self-Assembly |
Hide Abstracts |
Sponsoring Units: DSOFT DPOLY DFD Chair: Saurabh Nath, Massachusetts Institute of Technology Room: Room 206 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z14.00001: Numerical investigation of colloid-transport in nonpolar solvents for electronic paper displays Wei Liu, Mohammad K Ahmadi, Alex Henzen, Jan Groenewold, Hans M Wyss Electrophoresis (EP) is the movement of charged particles relative to a stationary liquid, induced by an applied electric field. Electroosmosis (EO), on the other hand, is the movement of a liquid relative to a stationary charged surface caused by an external electric field. In nonpolar systems, charges are generated in the form of charged inverse micelles (CIMs). The addition of surfactants helps disperse particles in nonpolar systems and makes it possible for Electrophoresis (EP) and Electroosmosis (EO) to take place. A detailed 2D model is proposed to numerically study the combination of EP and EO in nonpolar solvents, in which the Navier-Stokes equation, Nernst-Planck equation, and Poisson equation are coupled together to solve the fluid and particle motion, and the electroosmotic boundary condition is utilized to investigate the influence of the zeta potential. The comparable results between experiments and simulations imply that the particle motion is dominated by both EP and EO. Based on the gained insight, the idea of increasing the zeta potential of the substrate is proposed, which we show can significantly improve the speed at which colloidal particles migrate across the fluid cell. This work may benefit the fundamental understanding of EP and EO in nonpolar systems and help develop improved, fast-switching electrokinetic displays. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z14.00002: Electrostatic Interactions of Colloidal Particles Straddling a Fluid-Fluid Interface. Subramaniam Chembai Ganesh, Charles Maldarelli, Jeffrey F Morris, Joel Koplik Colloidal particles can irreversibility adsorb and exhibit finite contact angles at a fluid-fluid interface (Binks 2002). Such particle laden interfaces are often encountered in applications involving multiphase systems such as foams, drops and bubbles where the particles are added as stabilizing agents or can be present naturally as impurities (Binks 2017). These particles can modify the rheology of the fluid interface and can introduce additional physics (such as aggregation, interfacial undulations etc.) especially under the presence of interparticle interactions. The presence of an applied electric field or charges on the particle surface can lead to the well-established electrostatic interactions that are often studied in the asymptotic limit of dilute surface concentrations of particles (Danov and Kralchevsky 2006). Here we present a more detailed look at the electrostatic interactions between two spherical particles for arbitrary finite separations under the presence of an electric field. We investigate in detail the effect of the contact angles and the dielectric properties of the particles along with that of the fluid media. These results can prove beneficial in improving the current models (Laal-Dehghani and Christopher 2019) for simulating particle laden interfaces. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z14.00003: Brownian dynamics modeling of colloidal assembly on curved interfaces subject to isotropic and anisotropic electrostatic interactions Nasir Amiri, Xin Yong Understanding and manipulating the assembly dynamics of colloidal particles confined at a fluid interface is important for many chemical and biological processes. Brownian motion, interface curvature, and interparticle forces are among the most important factors affecting particle dynamics and assembly structures on the interface. In this research, a new Brownian dynamics algorithm is exploited to simulate microparticle dynamics on curved surfaces of arbitrary geometries that cannot be parametrized analytically. The particle motion is modeled on the discretized triangular mesh using a velocity-folding scheme. We explore the particle behaviors on surfaces with uniform and non-uniform curvatures, including sphere, oblate, prolate, and geometrically controlled sessile droplets. We systematically investigate the effects of relative particle size, particle concentration, and interparticle interactions on the dynamics and associated assembly structures. Inspired by experiments, we particularly focus on the assembly dynamics of charged colloids subject to isotropic electrodipping attraction or anisotropic in-plane dipolar attractions due to inhomogeneous surface charge. These cases are also compared with the systems of uncharged particles interacting through capillary multipoles. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z14.00004: Nucleation around a charged particle in a polar environment Roni Kroll, Yoav Tsori Condensation of drops from a vapor phase is crucial to understanding many research fields, particularly environmental science. Droplets are formed by nucleation, where the vapor is supersaturated, but the creation of a new phase is delayed by an energy barrier. In recent years, ion-induced nucleation has been studied extensively. The Thomson model showed that nucleation around a charged particle in a nonpolar environment reduces the energy barrier due to electrostatic interactions. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z14.00005: Phase separation of water-in-oil nanoscale emulsion using non-Laplacian electrostatic field Simon Rufer, Sreedath Panat, Vishnu Jayaprakash, Kripa K Varanasi Oil-water separation of crude oil containing emulsified water droplets is a complex and intensive process in the oil and gas industry. Small micro- and nano-metric droplet sizes render gravity-based separation impractical. Conventional electro-coalescers using immersed electrodes for oil-water separation must limit their applied electric field to avoid electrical shorting, making them ineffective for coalescing nanoscale droplets. Environmentally toxic demulsifying chemicals are thus used to further promote coalescence, but the process effluent reaches water bodies including the ocean and fresh water. In this talk, we demonstrate a significantly more effective electro-coalescence method based on corona discharge that drastically enhances the rate of phase separation of nanoscale emulsions and eliminates the use of toxic demulsifiers. By introducing a space charge emitter electrode with an air gap separating the electrode and the emulsion, we can avoid droplet-mediated electrical shorting and apply ~8 times stronger electric field, resulting in much faster phase separation of nanoscale water in oil emulsions for water cuts between 2% and 20%. We visualize the droplet chaining and coalescence events and demonstrate that the rate of oil-water separation via electrocoalesence scales with the square of the applied electric field. Last, we design a practical embodiment of a corona-demulsifier which enables rapid, continuous oil-water separation of nanoscale emulsions. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z14.00006: Electrophoresis of ferroelectric nematic liquid crystal droplets Mojtaba Rajabi, Oleg D Lavrentovich Electrophoresis is the dynamics of colloidal inclusions in a fluid, driven by a uniform electric field. The effect has been studied in isotropic and nematic environments and has found many applications in particle separation, microfluidics, electrophoretic displays, etc. Here, we report on the electrophoresis of ferroelectric nematic (NF) liquid crystal droplets confined between two plates with a uniform alignment of the director and surrounded by an isotropic fluid. When a direct current (dc) field is applied, NF droplets propel along the field. The mechanism of motion is attributed to the electric polarization reorientation in response to the field. An alternating current (ac) field with a frequency results in a biased oscillatory motion of the droplet, which yields a net displacement over several cycles. The direction of the net displacement is set by the polarity of surface anchoring imposed through the bounding plates. The work is supported by NSF grant ECCS-2122399. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z14.00007: Electrophoretic NMR Measurements of POSS-based Multivalent Electrolytes David Halat, Saheli Chakraborty, Julia Im, Darby Hickson, Jeffrey A Reimer, Nitash P Balsara An outstanding goal in the development of next-generation Li-ion battery electrolytes is fine-tuned control over ion and solvent motion, in particular, chemistries that enable faster cation mobility relative to that of the anion, yielding greater cationic transference numbers. Polymer electrolytes are a promising approach, as anionic species can be coupled to the polymer backbone, but for full characterization, techniques that can pinpoint changes in ionic diffusivities and velocities are required. In this work, we perform pulsed-field-gradient (PFG) NMR and electrophoretic NMR (eNMR) measurements on a novel polyhedral oligomeric silsesquioxane (POSS)-based polyanionic electrolyte dissolved in a carbonate-based solvent. PFG measurements clearly indicate slower anion self-diffusion as compared to the cation, seeming to imply large transference numbers. However, electrophoretic NMR data, which comprise the electric-field-induced velocities of the cation, anion, and solvent, reveal a more complex picture in which the cation velocity is negative in the laboratory frame. We interpret this result as a demonstration of strong clustering between the cations and the polyanions, such that Li+ cations migrate the “wrong way” under application of an electric field. Thus the resulting transference number determined by electrophoretic NMR in these multivalent electrolytes is consistently negative, in contrast to the naïve expectation from the self-diffusion results. This work highlights the importance of quantifying cation, anion and solvent motion under an electric field with electrophoretic NMR, and extends the approach to multivalent systems. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z14.00008: Anomalous Diffusion of Lithium-Anion Clusters in Ionic Liquids using MD simulations and Deep Learning analysis YeongKyu Lee To understand the lithium ion transport dissolved in the ionic liquids, we conducted molecular dynamics (MD) simulations consist of [PYR14][TFSI] with added [Li][TFSI] salt. It is well known that the transport of lithium ions involves local shell exchanges of TFSI- in the medium. We found shell exchanges of TFSI- undergo power law which is a scale free, or non-Poissonian. We analyzed the non-Poissonian processes of lithium ions transport as two-state (soft and hard) model. We analytically calculated transition probability of two-state model, and this well explains the lifetime autocorrelation functions of Li-TFSI shells. To closely find the fractions of the two states, we utilized the graph neutral network and calculated the diffusion coefficients of each and total states. We can see that soft state mostly contribute to the transport of the lithium ions. Hence, it is necessary to incorporate the idea of increasing the fractions of the soft state to get better lithium ion transport properties under ionic liquids medium. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z14.00009: Capacitance and Phase Behavior of Diluted Ionic Liquid Supercapacitors Samuel L Varner, Zhen-Gang Wang Room-temperature ionic liquids (RTILs) are synthetic electrolytes that have a large electrochemical stability window, making them attractive candidates for electric double-layer capacitor (EDLC) applications. Due to their high viscosities and low ionic conductivities, RTILs are often diluted with organic solvent for practical use. We study the effects of dilution on the performance of RTIL EDLCs using a simple mean-field model. We find that dilution diminishes the unfavorable hysteresis that results from a spontaneous surface charge separation (SSCS). As a result, the RTIL concentration can be used to modulate the proximity to the SSCS transition, and maximize capacitance. The interplay between the concentration and the correlation strength gives rise to complex zero-potential phase behavior, including a tricritical point and a λ-line, very similar to the Blume–Capel dilute Ising model. Additionally, electrodes that are solvophilic aid in the prevention of SSCS by drawing solvent molecules to the electrode and displacing ions. Solvophilic electrodes give rise to a phase transition at finite potential where the surface charge rapidly increases with a small increase in potential, leading to a substantial increase in capacitance and energy storage. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z14.00010: AC-electrokinetic manipulation of organic-inorganic polymeric coacervates Ali Hatami, Yingxi Elaine Zhu, JAMUNA K VAISHNAV Complex Coacervates are aqueous liquid-liquid phase separating materials formed between charged macromolecules, including polyelectrolytes, proteins, and charged nanocolloids. Coacervates have been applied for storage and recovery of biomasses in biomimetic aqueous environment in food and pharmaceutical industry and recently explored to remove trace organic molecules and industrial contaminates for water treatment. To enable large scale industrial application, we have recently explored rich ac-electrokinetics to manipulate and assemble complex coacervates in aqueous media using coacervates formed between polyelectrolytes and charged macroions such as polyoxometalates (POMs) and quantum dots (QDs). When applied ac-electric field exceed a critical value, we observe the droplet-like coacervate formation and chain-like coacervate assembly in response to dielectrophoresis (DEP) in non-uniformed ac-fields across two coplanar microelectrodes. The critical ac-field strength for POM-based coacervate formation varies considerably from that for QD-based coacervate formation, clearly indicating the effect of nanocolloidal surface charge density on ac-electrokinetic characteristics. More intriguingly, as fine tuning ac-frequency, we observe the in-situ droplet-in-droplet dual complex coacervate formation in aqueous media. The combination of DEP-induced complex coacervate formation and assembly is further integrated with ac-electrospinning to enable the nanomanufacturing of functional coacervate fibers and membranes for practical biomedical and environmental applications. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z14.00011: Impact of Ionic Surfactants on the Electrokinetic Control of Viscous Fingering: An Experimental Approach Benedicta Nwani, Ian Gates, Anne M Benneker The displacement of a more viscous fluid by a less viscous one in a porous medium results in viscous fingering (VF), an interfacial instability where viscous and capillary forces compete. VF control is an ongoing challenge, as in some applications this instability is desirable (mixing in porous media) while in others it is detrimental (e.g. enhanced oil recovery). Control methods are divided in passive and active approaches, where in active approaches VF is controlled in-operando, while passive methods involve system alterations prior to displacement. A promising active control method is the electrokinetic method, in which an applied field induces electrokinetic thinning or thickening of the fluid, resulting in a controlled displacement. In this work we experimentally investigate the synergetic effect of an externally applied electric field and ionic surfactants on the (de)-stabilization of the interface between a more viscous perfect dielectric fluid and an immiscible, less viscous, conducting surfactant solution. We use surfactant concentrations around the critical micelle concentration for the displacement and apply the electric field in both the same and opposite direction to pressure driven flow to investigate both stabilization and destabilization situations. Our results show that in applications where instabilities are required, viscous forces should dominate capillary forces, which is achieved through a combination of an anionic surfactant and a negatively applied electric field. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z14.00012: The Coupling of Charge Regulation and Geometry in Soft Ionizable Molecular Assemblies Joseph McCourt, Sumit Kewalramani, Leticia Lopez-Flores, Michael J Bedzyk, Monica Olvera De La Cruz The size, shape, and charge of soft assembled nano-structures, like those in biology, respond in an interconnected manner to solution ionic conditions. Customarily, the charge regulation of ionizable groups is described through a pKa (ion dissociation constant), deduced from Henderson-Hasselbalch or Hill model fits to titration data. However, such models do not account for the size and shape of assemblies and lack a physical explanation for apparent pKa shifts. This leaves a gap in the intuitive understanding of the charge regulation process. To tackle this problem, we combined X-ray scattering, molecular dynamics simulations and Poisson-Boltzmann theory to predict the degree of ionization in charged assemblies. We analyzed the self-assembly and charge regulation of the peptide amphiphile C16K2: a two ionizable amino acid [Lysine (K)] head group coupled to a 16-carbon length tail. Experiments and simulations revealed assembly shape and size transitions as a function of pH and salt concentration. An electrostatic model then allowed extraction of the shape and size-dependent degree of ionization. Overall, our study elucidates key principles in analyzing the coupling of electrostatics and nano-scale details of soft nano-structures which play a crucial role in biological systems. |
Friday, March 10, 2023 1:54PM - 2:06PM Author not Attending |
Z14.00013: Flow around a circular cylinder controlled by asymmetric plasma actuation Zihao Zhu The flow field over a circular cylinder with a pair of dielectric-barrier-discharge (DBD) plasma actuators under steady and unsteady actuation in quiescent air is simulated by solving the Navier-Stokes equations. During the duty cycle actuation, duty cycle ratio determines the fraction of time when the left actuator is turned on during a duty cycle period T=1/f, where f is the duty cycle frequency. When the left actuator is turned on, the right actuator is turned off and vice versa. Under this actuation, vortices are generated alternately from each side of the cylinder. The present study focuses on the detailed flow structure including the wall jets, the evolution of vortices, and the resultant momentum of the flow induced by the DBD actuators in order to gain more insight into flow control mechanisms under different types of actuation. Simulations are performed for f ranging from 5Hz to 100Hz and duty cycle ratio from 0.3 to 0.7. For low duty cycle frequencies, a pair of discrete vortices are generated in each actuation cycle. They interact and move downstream in response to the on-off signals of the actuators. As the frequency increases, the distance between vortices from successive duty cycles decreases so that the vortices are packed together as a vortex train along a narrow path line. As the frequency further increases, the vortices in the train lose their individual characteristics and the vortex trains become two jets, one on each side of the cylinder. |
Friday, March 10, 2023 2:06PM - 2:18PM |
Z14.00014: Nanomaterials patterning in an extrusion-based 3D printing process Samuel Hales, Jared Anklam, Yong Lin Kong The ability to control and pattern nanomaterials can create hybrid devices with advanced functional integration. Here we explore various strategies to integrate a broad range of forces into an extrusion-based 3D printing process. We show the ability to modulate nanomaterials pattern and create a freeform architecture where the material properties can be locally programmed. Ultimately, we seek to leverage the manufacturing capability to create novel biomedical devices that can address unmet clinical needs. |
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