Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V17: Field-Driven Colloidal AssemblyFocus
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Sponsoring Units: GSOFT Chair: Josh Socolar, Duke University Room: 276 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V17.00001: Light-Driven Control of DNA-Mediated Colloidal Assembly Emily W. Gehrels, Anatoly Rinberg, Andrew M. Bergman, Vinothan N. Manoharan Despite the success in programming the equilibrium structures of systems of DNA-coated colloids, little work has been done to program the self-assembly kinetics of these systems. Here we present a new approach towards dynamic control of systems of DNA-coated colloids that involves light-modulated interactions between particle pairs. To achieve this control, we introduce different dyes into different particle species. These dyes cause the particles to locally heat upon illumination with the appropriate wavelength, thereby affecting only the DNA binding between particles of the targeted color. With this new control we rapidly and reversibly switch chosen pairs of particle species between binding and unbinding, and we demonstrate how this modulation can be used to understand the behavior of driven, out-of-equilibrium systems. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V17.00002: Colloidal assembly by capacitive deionization Rodrigo Guerra, Paul Chaikin Compared to the fine spatial and temporal control that can be exerted on the temperature, mechanical stress, and electric and magnetic fields in a colloid, our control over salt concentration stands out as relatively primitive. Like these other parameters, ionic strength is a crucial state variable for many colloidal dispersions, and salt gradients cause stresses, flows, and instabilities that are difficult to explore using conventional techniques. Here we demonstrate a simple approach to control the salt concentration in a colloid using the supercapacitance of mesoporous electrodes. First, we show that these electrodes can push charged particles apart by pulling nearly all the ions out of the surrounding fluid, enabling electrostatic screening lengths several microns long in fluids with large dielectric constants. We also show how these electrodes can controllably pull particles together by modulating the salt concentration in a dispersion of oppositely charged particles. [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V17.00003: Soft Interactions and Structure Formation of Colloidal Microgels with a Cross-linker Gradient Niels Boon, Sofi Nöjd, Peter Holmqvist, Jérôme Crassous, Peter Schurtenberger Microgels are colloidal particles with a backbone composed of a cross-linked polymer. They offer high control (in situ) over shape, size, charge, and soft interactions by stimuli such as temperature and pH. This can be used to explore novel routes towards complex-structure formation, which may be aided by external forces such as shear or electric fields. We study soft interactions between PNIPAM microgels, which are among the most commonly used microgels. Due to a heterogeneous distribution of cross-linker, these particles do not exactly behave like bulk gels. Our ab initio calculations confirm the presence of an heterogeneously swollen core that co-exists with a relatively large soft corona with dangling polymer ends. Also, we find a density profile that is in close agreement with measured form factors. This suggests that at low to moderate densities the microgels interact by means of interpenetrating dangling ends, while the cross-linked core deforms only at high packing fractions. We propose a model for understanding how soft interactions define high-density packings of these particles. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V17.00004: Self-assembled colloidal alloys of clusters and spheres: Diamond, Pyrochlore and Unnatural Crystals Etienne Ducrot, Gi-Ra Yi, David Pine The assembly of percolating low volume fraction ordered structures at the colloidal scale is a challenging problem with applications in photonics and in the emerging field of metamaterials. DNA coated particles have been proposed and successfully applied as a versatile tool for programming the self assembly of micrometer size particles. Nevertheless highly though out percolating structures such as diamond and pyrochlore lattices failed self-assembly. Here we present a new design principle that uses the combination of DNA coatings and elementary preassembled components to build colloidal alloys with self assembled lattices never build before. Mixed with complementary spheres, preassembled parts of the desired structure arrange particles around them, imposing a local symmetry otherwise inaccessible using only short-range interactions and spherical particles. Guided by Brownian dynamics simulations, we apply this strategy to the self assembly of spheres with colloidal tetrahedral clusters leading to a family of colloidal superstructures, among which percolating diamond and pyrochlore as well as cubic and tetragonal colloidal crystals with no known atomic equivalent. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V17.00005: Diamond Lattice Colloidal Crystals from Binary DNA-grafted Microspheres John Crocker, Yifan Wang, Ian Jenkins, James McGinley, Talid Sinno Future optical materials promise to do for photonics what semiconductors did for electronics, but the challenge has long been in creating the structure they require—a regular, three-dimensional array of transparent microspheres arranged like the atoms in a diamond crystal. Here we demonstrate a simple approach for spontaneously growing double-diamond (or B32) crystals from a binary suspension of sub-micron polymer microspheres with synthetic DNA grafted to their surfaces. While diamond symmetry crystals have previously been grown from much smaller nanoparticles, none of those methods appear workable for the larger particles needed for photonic applications, whose size must be comparable to the wavelength of visible light. Intriguingly, matched simulations fail to nucleate or grow B32 crystals from suspension; nor have they been predicted on the basis of theoretical arguments. We conjecture that the B32 crystals may form via transformation from a precursor with a different lattice structure in the bulk or on its surface. The feasibility of converting our self-assembled crystals into diamond-symmetry photonic templates will be discussed. This finding suggests that still other unexpected microstructures may be accessible using this approach. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V17.00006: Towards Ordering Bare and Polymer-Grafted Nanoparticles in Dip Coating Process Chongfeng Zhang, Pinar Akcora The unusual phenomenon of anisotropic assembly of microspheres during evaporation of polymer droplets is being investigated in our group. Dynamics of contact-line movement under varying evaporation conditions and the growth of clusters with time on surfaces differing in hydrophilicity will be presented in this talk. We observed that distinctive stripes were formed when the internal shear flows arising from the phase separation of particles from polymer chains were balanced with the Marangoni flows. Contrary to formation of lines of particles with a stick-slip mechanism, our microspheres and nanoparticles assemble parallel to the withdraw direction in dip coating. By varying the polymer concentration and chain length, we were able to show that width and periodicity of lines can be tuned. Further, with the PAA-grafted silica nanoparticles, the effect of strong attraction between free and grafted chains on the assembly process was examined. The mechanism of ordering colloids and nanoparticles with physical bridging of polymers or hydrogen bonding between different polymers has important implications in controlling the organization of functional particles using dip coating process. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 4:18PM |
V17.00007: Sonocrystallization---application of radiation forces from acoustic standing waves for configurable assembly Invited Speaker: Charles Shields Acoustic radiation forces offer a promising approach to rapidly arrange particles across a broad range of scales, yet it remains largely unexplored compared to classical methods like centrifugation, electrophoresis, and magnetophoresis. Acoustic forces offer numerous advantages, including scalability, programmability, and the ability to manipulate particles of variable composition (i.e., without narrowly defined electromagnetic or other properties). While some groups have shown the ability to concentrate particles with ultrasonic radiation, the capabilities and limitations for precise particle assembly and morphological control remain poorly understood. Here, I will discuss our recent efforts to explore the flexibility and limitations of acoustophoresis to rapidly arrange microparticles into organized and programmable structures. In order to execute these studies, we employ a simple ``sonocrystallization chamber'' that creates multidimensional bulk acoustic standing waves to propel particles toward the pressure nodes or antinodes, depending on their contrast factor. We can thus create thousands of size-limited assemblies within minutes. We pair these experiments with simulations and theory to model the migration kinetics and assembly patterns of different particles types. I will further discuss how we have extended these results to understand the lower particle size limit for assembly in systems such as gold nanoparticles with diameters \textless 200 nm. Finally, I will show how we incorporated a simple light-based crosslinking approach for stabilizing the assembly in the small particle limit (i.e., beyond the acoustic focusing limit), which might enable use in a variety of plasmonic and photonic applications. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V17.00008: Driving morphological changes in magnetic nanoparticle structures through the application of acoustic waves and magnetic fields Ann Huang, Morteza Miansari, James Friend The growing interest in acoustic manipulation of particles in micro to nanofluidics using surface acoustic waves (SAW), together with the many applications of magnetic nanoparticles---whether individual or in arrays---underpins our discovery of how these forces can be used to rapidly, easily, and irreversibly form 1D chains and 2D films. These films and chains are currently difficult to produce yet offer many advantages over individual nanoparticles in suspension. Making use of the scale of the structures formed, $10^{-9}$ to $10^{-5}$~m, and by taking a balance of the relevant external and interparticle forces, the underlying mechanisms responsible for the phenomena become apparent. For 1D chains, the magnetic field alone is sufficient, though applying an acoustic field drives a topology change from loosely connected chains to loops of $\sim 10$--100 particles. Adding the acoustic field drives a transition from these looped structures to dense 2D arrays via interparticle Bjerknes forces. Inter-particle drainage of the surrounding fluid leaves these structures intact after removal of the externally applied forces. Clear morphology transitions are present and depend on the relative amplitude of the incident Brownian, Bjerknes, and magnetic forces. [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V17.00009: Acoustic Effects in Classical Nucleation Theory James Baird, Ching-Hua Su The effect of sound wave oscillations on the rate of nucleation of a second phase from a parent phase can be calculated by expanding the free energy of formation of a nucleus of the second phase in powers of the acoustic pressure. Since the period of sound wave oscillation is much shorter than the time scale for nucleation, the acoustic effect can be calculated as a time average of the free energy of formation of the nucleus. The leading non-zero term in the time average is proportional to the square of the acoustic pressure. The Young-Laplace equation for the surface tension of the nucleus can be used to link the time average of the square of the pressure in the parent phase to its time average in the nucleus of the second phase. Due to the surface tension, the pressure in the nuclear phase is higher than the pressure in the parent phase. The effect is to lower the free energy of formation of the nucleus and increase the rate of nucleation. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V17.00010: Forming Nanoparticle Monolayers at Liquid-Air Interfaces by Using Miscible Liquids Jiayang Hu, Datong Zhang, Kathleen M. Kennedy, Irving P. Herman The usual standard way to form monolayers (MLs) of nanoparticles (NPs) is to drop-cast a NP dispersion in one solvent onto a second immiscible solvent; after the upper solvent evaporates the NP MLs can be transferred to a solid substrate by liftoff. We show that this previously-universal solvent immiscibility is not necessarily a barrier in forming NP MLs at liquid surfaces, and large-scale, continuous, close-packed, hexagonally ordered NP MLs can self-assemble at liquid-air interfaces when some miscible solvent pairs are used instead. We demonstrate this by drop-casting an iron oxide NP dispersion in toluene on a dimethyl sulfoxide (DMSO) liquid substrate. The NPs are energetically stable at the DMSO surface and remain there even with solvent mixing. Excess NPs coagulate and precipitate in the DMSO, and this self-limits NPs at the surface to approximately 1 ML. The ML domains at the surface nucleate independently, which is in contrast to ML growth at the receding edge of the drying drop, as is common in immiscible solvent pair system. We also show that MLs can be formed by using other miscible solvent pairs such as benzene/DMSO and fluorobenzene/DMSO, and a wider range of NPs. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V17.00011: Ribbons of superparamagnetic colloids in magnetic field Alexis Darras, Jorge Fiscina, Maryam Pakpour, Nicolas Vandewalle, Geoffroy Lumay While the aggregation process of superparamagnetic colloids in strong magnetic field is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a long time. In this talk, we present experimental observations of this equilibrium state with a two-dimensional system and we compare our data with the predictions of a pre-existing model. Above a critical aggregation size, a deviation between the model and the experimental data is observed. This deviation is explained by the formation of ribbon-shaped aggregates, due to lateral aggregation of chains. Interestingly, when the magnetic field is removed, particles then freely diffuse from their positions in the agglomerate. It is worthwhile to notice that all the particles initially have the same coordinate on the axis perpendicular to the initial chain. This configuration then enables the observer to study the one dimensional diffusion process, while actually seeing the underlying Brownian motion of the microscopic particles. By studying the evolution of the particles distribution, a measurement of the diffusion coefficient is performed. With a calibration using a fluid of known viscosity, this process allows measurement of local viscosities through the Stokes-Einstein relation. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V17.00012: Chaotic routes to colloidal molecules Hamed Abdi, Rasam Soheilian, Randall Erb, Craig Maloney We present computer simulation and experiments on dilute suspensions of superparamagnetic particles subject to rotating magnetic fields. ~We focus on short chains of particles and their decay routes to stable structures. ~At sufficiently high rates, the typical behavior of a small set of particles, initially aligned in a chain along the axis of the field is to go through a period of chaotic motion and, after some time to decay into one of a number of possible periodic orbits with a compact spatial structure. Transition between these periodic orbits is also possible and will depend on both rotation rate and finite temperature.~We show the entry into and transitions between periodic orbits is an activated process with no memory and report on associated rate constants for the transitions. [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V17.00013: Phase separation in two-dimensional colloidal suspension using rotating magnetic fields An Pham, Yuan Zhuang, Paige Detwiler, Ashutosh Chilkoti, Joshua E. S. Socolar, Patrick Charbonneau, Benjamin B. Yellen We study phase separation in a quasi two-dimensional system of magnetically susceptible colloids in a high-frequency rotating magnetic field. By tuning the interparticle interactions and particle area fractions in-situ, we construct an experimental phase diagram that matches with simulatios. Our theoretical model is based on the pairwise interaction energy between magnetic point dipoles, which are simulated with advanced Monte Carlo simulation methods. The best fit between experiments and simulations allows us to calibrate the magnetic susceptibility of the beads. We also show that the simulations match the experimental dynamics of the domain coarsening process. Based on the calibrated experimental apparatus, we change the cone angle of the rotating field and study the change in the kinetic pathways of phase separation. For low tilt angles~(in plane fields), the system separates into a bicontinuous morphology, whereas at tilt angles near the magic angle, the system aggregate by Ostwald ripening. [Preview Abstract] |
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