Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W29: Electrostatic Manipulation of Fluids and Soft Matter II: Self-AssemblyFocus
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Sponsoring Units: DSOFT DPOLY DBIO DFD Chair: Jonathan Singer, Rutgers University, New Brunswick Room: 501 |
Friday, March 6, 2020 8:00AM - 8:12AM |
W29.00001: Precision measurement of tribocharging in acoustically levitated sub-millimeter grains Adam Kline, Melody Lim, Heinrich M. Jaeger Contact electrification of dielectric grains forms the basis for a myriad of physical phenomena. However, even the basic aspects of collisional charging between grains are still unclear. In this talk, we present a new experimental method [1], extending a prior approach [2] based on acoustic levitation, which allows us to controllably and repeatedly collide two sub-millimeter grains head-on and measure the evolution of their electric charges. This is the first collisional tribocharging experiment to provide complete electric isolation of the grain-grain system from its surroundings. We use this method to measure collisional charging rates between pairs of grains for three different material combinations: polyethylene-polyethylene, polystyrene-polystyrene, and polystyrene-sulfonated polystyrene. The ability to directly and noninvasively collide particles of different constituent materials, chemical functionality, size, and shape opens the door to detailed studies of collisional charging in granular materials. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W29.00002: Tuning friction and slip at solid-nanoparticle suspension interfaces by electric fields. Caitlin M Seed, Biplav Acharya, Donald W Brenner, Alex I Smirnov, Jacqueline Krim Pathways to achieve climate stabilization consistently require a diverse mix of technologies, with energy efficiency being the largest contributor, ranging from 35-40% in virtually all proposed scenarios. Reductions in frictional energy losses and improved lubrication methodologies are key to such energy savings. Nanoparticles in aqueous suspensions hold particular promise for such purposes. We report an experimental Quartz Crystal Microbalance (QCM) study of tuning interfacial friction and slip lengths for aqueous suspensions of ceramic (Al2O3, TiO2 and SiO2) nanoparticles on planar platinum surfaces by external electric fields. Attraction and retraction of particles perpendicular to the surface by means of an externally applied fields resulted in increased and decreased interfacial friction levels and slip lengths. The variation was observed to be non-monotonic, with a profile attributed to the physical properties of interstitial water layers present between the nanoparticles and the platinum substrate. The results are compared and contrasted with macroscale friction measurements performed on the same materials. |
Friday, March 6, 2020 8:24AM - 9:00AM |
W29.00003: Particle assembly using confined electro-hydrodynamics: Driven versus active assembly Invited Speaker: Jon Otto Fossum We give examples of driven colloidal shell assembly on drop interfaces by application of DC-electrohydrodynamics and dielectrophoresis, using standard leaky dielectric carrier fluids for non-polarisable and/or polarizable colloids. We summarize how this can be used to fabricate static or dynamic colloidal shells with patchy structure and functionality. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W29.00004: Electrostatic patterns from peeling tape Mary Reiter, Matthew VanDusen-Gross, Troy Shinbrot It has been known since the 17th century that as mercury rolls from glass, “barometric light” is emitted[1]. Similarly, as tape is pulled from surfaces, light is emitted that can even extend to produce enough x-rays to image bones within a finger[2]. It has been proposed that the light is generated by discharges that follow triboelectric charging by the tape. In this talk, we discuss new and surprising aspects of triboelectric charging associated with tape peeling including entirely different charge patterns on formerly adjoining surfaces. We describe these unique patterns as well as implications for the charging and adhesion of surfaces and particles in nature and industry. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W29.00005: Sublattice Melting in Binary Superionic Colloidal Crystals Yange Lin, Monica Olvera De La Cruz In superionic compounds one component pre-melts providing high ionic conductivity to solid state electrolytes. Here, we fifind sublattice melting in colloidal crystals of oppositely charged particles that are highly asymmetric in size and charge in salt solutions. The small particles in ionic compounds melt when the temperature increases forming a superionic phase. These delocalized small particles in a crystal of large oppositely charged particles, in contrast to superionic phases in atomic systems, form crystals with non-electroneutral stoichiometric ratios. This generates structures with multiple domains of ionic crystals in percolated superionic phases with adjustable stoichiometries. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W29.00006: Band-collision gel electrophoresis (BCGE) for visualizing molecular and colloidal interactions Dimitri Bikos, Thomas Mason Electrophoretic mobility shift assays (EMSAs) are widely used to study binding interactions between different molecular species loaded into a single well within an electrophoresis gel. However, shift assays can explore only a subset of reaction possibilities that would otherwise be accessible if separate bands of reagent species were instead collisionally reacted. We fabricate a gel with two or more wells within a single lane and load these wells with different reagent species. By applying an electric field, we produce collisional reactions between propagating pulse-like bands of these species and record the images optically. We observe cases where bands pass through one another undisturbed, while in other cases, we observe complexing and precipitation, indicating strong attractive interactions. This band-collision gel electrophoresis (BCGE) approach is generalizable to a variety of reaction types, such as acid-base, ligand exchange, and redox, as well as to colloidal species in passivated large-pore gels. |
Friday, March 6, 2020 9:36AM - 9:48AM |
W29.00007: Controlling surfactant self-assembly in dodecane via applied potential Maisa Vuorte, Aapo Lokka, Maria Sammalkorpi The response of colloidal assemblies in apolar solvents to applied electrostatic potential plays a key role in both electrostatic stabilization and manipulation of the resulting nanoemulsion, drug delivery, and synthesis platforms. Here, we present a molecular modelling study of the aggregation of dioctyl sodium sulfosuccinate (AOT) surfactant in apolar dodecane solvent under applied potential. We probe the sensitivity of the self-assembling, reverse micellar surfactant structures and their dynamics to the magnitude of the applied potential and presence of moisture in the system. While the anionic AOT surfactant readily forms reverse micellar aggregates even in the absence of trace water, presence of moisture greatly increases the size of the formed aggregates and their dynamics. The applied potential controls the AOT sodium counterion mobility but the charge transfer via the counterions is also influenced strongly by the degree of hydration of the AOT head groups. We discuss the significance of the findings against literature and experimental data. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W29.00008: Dumbbell model for the simulation of polyelectrolytes in combination of flow and electric fields Angelo Setaro, Patrick Underhill The combination of Poiseuille flow and electric fields has been used to drive the transverse migration of charged polyelectrolytes in channels, resulting in non-uniform concentration profiles. Manipulation of these profiles can be used to drive separations of charged polyelectrolytes such as double stranded DNA. Interestingly, the amount of migration is not monotonic in electric field strength. Rather the migration peaks at intermediate electric fields before decreasing. To date, the mechanism for this non-monotonic trend has been poorly understood as prior models have been unable to reproduce this behavior. To gain insight to the underlying phenomena, we used a combination of theoretical calculations and Brownian Dynamics simulations in order to understand the mechanism of migration and why it results in a non-monotonic trend. It was found that at high electric field strengths, the migratory flux of polymers was able to impact the conformational distribution, altering the electrophoretic mobility and, in turn, limiting the migration. Further, when comparing to experimental migration data, our model captures the position of the maximal migration with near quantitative accuracy. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W29.00009: Electrostatically Stabilized Microphase Separation in Polyelectrolyte Blends: Analogy to Nuclear "Pasta" Phases Artem Rumyantsev, Juan De Pablo We develop the weak segregation theory of microphase separation in stoichiometric blends of oppositely and weakly charged polyelectrolytes, which would be immiscible in the absence of charged units. Short-range repulsions between polycation and polyanion monomers induce the formation of oppositely charged domains, whose size is controlled by their excess Coulomb energy. The diagram of blend morphologies is constructed in the framework of a Leibler’s mean-field approach and, to account for fluctuations, within a Brazovskii-Fredrickson-Helfand approximation. Phase behavior of the polyelectrolyte blends is fully analogous to that of neutral diblock copolymers. In asymmetric blends, increasing incompatibility between polyelectrolytes triggers the usual cascade of first order phase transitions, disordered blend → bcc → hex → lam. We also discuss that microphase separation in polyelectrolyte blends (and hence neutral diblock copolymers) and the formation of nuclear “pasta” phases arising within neutron stars are governed by similar physical principles, despite the six orders of magnitude difference in the periods of these structures (nanometers vs femtometers, respectively). |
Friday, March 6, 2020 10:12AM - 10:24AM |
W29.00010: Determination of diffusion constant of antimicrobial peptide nisin interacting with Langmuir monolayers of DPPC and DPPG molecules Imran Pasha, Bharat Kumar We present a method of determining the diffusion constant of peptides interacting with lipid films. The method involves studying the interactions of diffusing peptides with the lipid Langmuir monolayer at the air-water interface. Due to the interaction between peptides and lipid molecules in the monolayer at the air-water interface, the surface pressure of the monolayer changes as a function of time which can be measured from the surface manometry technique. A model based on the diffusion of particles under the influence of a constant force is developed to obtain an analytical expression for change in the surface pressure of Langmuir monolayer as a function of time. The expression was found to fit well with the experimental data. The average hydrodynamic radius and the translational diffusion constant of the nisin molecules are calculated from the fit parameters for the different subphase pH solutions. The diffusion constant was found to vary with the pH of the media. |
Friday, March 6, 2020 10:24AM - 10:36AM |
W29.00011: Capture and Translocation of a Rod-like dsDNA by a Nanopore:~A Lattice Boltzmann Simulation Study Le Qiao, Christian L. Holm, Kai Szuttor, Gary W. Slater Short dsDNA, viruses like the tobacco mosaic virus and filamentous bacteriophages can be considered as a rigid rods. We previously argued that the field-driven orientation of a rod-like object will impact its capture by a nanopore because both its translational diffusion coefficient D and electrophoretic mobility μ vary with orientation. We also introduced a critical orientational capture radius to describe this effect. In this talk, we investigate this problem further using a coarse-grained (CG) model of a charged double-stranded DNA where the hydrodynamic interactions are added by coupling the CG DNA with a lattice-Boltzmann fluid via a raspberry approach. The electrostatic interactions with the salt ions are modeled with the P3M algorithm. We also discuss the capture of modified DNAs, including partially charged and branched DNAs. In all cases, we examine how molecular orientation affect capture and entry into the pore. |
Friday, March 6, 2020 10:36AM - 10:48AM |
W29.00012: Nontrivial effects of dielectric mismatch on the conformational behavior of confined polyelectrolytes Trung Nguyen, Monica Olvera De La Cruz We investigate the conformational behavior of a highly charged polyelectrolyte confined in a spherical cavity where the media inside and outside the cavity have different dielectric constants. Depending on the charge density of the cavity surface and dielectric mismatch, the polyelectrolyte either collapses into amorphous conformations, or folds into a four-fold symmetry conformation. On the contrary to the common wisdom that polarization effects would be negligible for charged surfaces, we find that such effects influence the polyelectrolyte conformational behavior in a nontrivial manner. Our study provides insight into the effects of dielectric mismatch in packaging and delivery of polyelectrolytes across media with different relative permittivities. Moreover, the reversible transformation of the polyelectrolyte conformations in response to environmental permittivity suggests potential applications in biosensing and medical monitoring. |
Friday, March 6, 2020 10:48AM - 11:00AM |
W29.00013: Interaction of highly charged rigid polymer in monovalent salt Yaohua Li, Felipe Jimenez-Angeles, Monica Olvera De La Cruz Charged polymers such as DNA bear important biological functions and have useful applications as a nanomaterial. Experiments of these polyelectrolytes are often performed in aqueous salt solutions. Using an empirical ion potential that reproduces pair correlations from all atom molecular dynamics (MD) simulations, we study ion distributions and DNA-DNA interactions by coarse-grained MD simulations with explicit salt ions. We focus on high concentration regimes, and found that at concentrations greater than 2M, both the ion distribution profile and the potential of mean force between DNAs becomes non-monotonic and has attractive wells. These results are in good agreement with our liquid state theory predictions. Furthermore, the importance of detailed DNA structure will be discussed using all atom MD simulation of DNAs. Our study can help interpret experimental results and help control the phase behavior of charged polymer using salts. |
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