Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L50: Self and Directed Assembly I: Mostly Nanoparticles/Rods and Colloids |
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Sponsoring Units: GSOFT Chair: Alberto Olson-Reichhardt, Georgia Institute of Technology Room: 218 |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L50.00001: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L50.00002: Switchable End-Linking of Gold Nanorods Induced by a Computationally Designed, Metal-Binding Peptide Robert C. Ferrier, Matthew Eibling, Christopher MacDermaid, Christopher Lanci, Jeffery G. Saven, Russell J. Composto Gold nanorods (AuNRs) possess unique optical properties that depend on the local orientation and separation of the individual rods. Previously, our group has explored the `permanent' end-linking of AuNRs with alkane dithiols. The present work investigates the switchable end-linking of AuNRs via a computationally designed peptide. AuNRs are end-functionalized with a peptide designed \textit{in silico} to bind a specific metal-ion. AuNRs end-to-end assemble when this metal-ion is present in solution above a particular concentration. The effect of metal-ion concentration on AuNR assembly is probed via UV/Visible spectroscopy and electron microscopy. A chelating agent is added to disassemble the AuNRs, returning the AuNRs to their original, unlinked, state. AuNRs can then be assembled again by adding more metal-ions, thereby allowing the solution optical properties to be switched between two states. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L50.00003: Electrical anisotropy in coatings of aligned silver nanowires Ye Xu, Gabriel Galderon-Ortiz, Annemarie Exarhos, Ahmed Alsayed, Karen Winey, Jay Kikkawa, Arjun Yodh Conductive and transparent coatings consisting of silver nanowires (AgNWs) have been suggested as a promising candidate to replace traditional ITO coatings for emerging flexible electronics applications. The electrical properties of such AgNW coatings depend strongly on the structure of nanowire networks formed by various processing methods. In this work, we study how the alignment of nanowires affects the electrical anisotropy in AgNW coatings. Specifically, we introduce a robust method to prepare coatings of well-aligned AgNWs on glass substrates; the method utilizes the rapid flow of AgNW suspensions through a confined geometry. The angle-dependent sheet resistance of the coatings was measured, and large anisotropy in surface conductivity was found to characterize the aligned AgNW networks. We also explore the degree of alignment and surface coverage of AgNWs in the networks, thereby establishing connections between microscopy network structures and macroscopic electrical anisotropy. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L50.00004: Molecular simulations of PEGylated lipids at interfaces: size selective dispersion of nanoscale objects Maria Sammalkorpi, Sampsa Vierros, Paul R. Van Tassel, Jukka M\"a\"att\"a Phospholipids and phospholipid derivatives offer efficient, noncovalent functionalization and dispersion of hydrophobic objects, e.g. therapeutic molecules and nanoparticles including carbon nanotubes (CNTs). However, the relation of lipid aggregates in bulk solution and in the presence of the object, and the resulting dispersion remain important questions. We employ here molecular dynamics simulations to explore PEGylated lipid aggregates at interfaces and the resulting dispersion efficiency. By varying lipid and substrate curvature, and the PEG chain length, we find 1) lipid-CNT and PEGylated lipid-CNT aggregation behavior consistent with recent experiments, 2) the assembled morphology to vary from micellar-like to tubular coating (phospholipids) and micellar to monolayer-like (PEGylated lipids) with the transition depending on lipid curvature and for PEGylated lipids also on the PEG chain length and CNT diameter, 3) aggregation morphology dependent CNT dispersion ability, and 4) good agreement between simulation and scaling theories of a brush-type PEG [1,2]. Finally, we discuss the implications to size-selective separation of hydrophobic particles and experimental observations. \\[4pt] [1] J. Chem. Eng. \& Data 59 (10), 3080-3089 (2014).\\[0pt] [2] Soft Matter 9, 2136-2144 (2013). [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L50.00005: Designing entropy-driven binary ordered superlattices from polyhedral nanoparticles Mihir Khadilkar, Fernando Escobedo While ordered multicomponent structures of nanoparticles are certainly desirable in view of multiple potential applications, their self-assembly often requires highly tuned enthalpic interactions between the different constituents. We present simulation results\footnote{Mihir R. Khadilkar, Fernando A. Escobedo, \textbf{Phys. Rev. Lett. 113}, 165504 (2014)} on binary mixtures of hard polyhedral nanoparticles that form ordered superlattices without any enthalpic interaction, with the help of shape anisotropy alone. We also identify a rule that maximizes packing compatibility and hence promotes the formation of ordered superlattices based on the order-disorder transition pressures of the pure components. Results show formation of plastic solid solutions in the case of binary mixtures involving nanoparticle shapes from the truncated cube family, whose pure-components also form plastic crystals. Preliminary results for 2D systems will also be presented. [Preview Abstract] |
(Author Not Attending)
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L50.00006: Computer simulation study on the self-assembly structure of soft Janus particles Zhao-Yan Sun, Zhan-Wei Li Soft and deformable Janus particles have received more attention due to their unique properties and enormous potential applications in recent years. Here we present a mesoscale model for soft Janus particles, which successfully reflects their physical nature by directly mapping onto experimentally measurable particle properties. By properly tuning Janus balance and the strength of attraction between attractive patches, soft Janus particles can reversibly self-assemble into a number of fascinating hierarchical superstructures in dilute solutions, such as micelles, wormlike strings, single helices, double helices, bilayers, tetragonal bilayers, complex supermicelles, and in bulk systems, such as the hexagonal columnar structure and the body-centered tetragonal structure. We also introduce a new concept in achieving template-free fabrication of diverse 2D ordered nanostructures by utilizing anisotropic characteristics of soft triblock Janus particles. Our work demonstrates that soft Janus particles with the deformable and non-centrosymmetric characteristics hide many surprises in the design and fabrication of hierarchically self-assembled superstructures. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L50.00007: Self-organization in periodically sheared granular materials Sam Wilken, Gary L Hunter, Paul M Chaikin Self-organization as a result of periodic shear is becoming a feature observed in an increasing number of systems. In our experiments, we enforce cyclic shear on a three dimensional system of non-Brownian particles to investigate the global packing behavior of the granular assembly. By starting with a dilated, loosely packed system and measuring the packing fraction after each shear cycle, we find the system compacts to reach a steady state with a well defined packing fraction. The shear amplitude determines the steady state packing fraction, where large amplitude shear produces a lower packing density and small amplitude shear produces a higher packing density. We also study the phase diagram of this system which exhibits caged motion and a transition to vorticity. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L50.00008: Bio-inspired Structural Colors from Deposition of Synthetic Melanin Nanoparticles by Evaporative Self-assembly Ming Xiao, Yiwen Li, Dimitri Deheyn, Xiujun Yue, Nathan Gianneschi, Matthew Shawkey, Ali Dhinojwala Melanin, a ubiquitous black or brown pigment in the animal kingdom, is a unique but poorly understood biomaterial. Many bird feathers contain melanosomes (melanin-containing organelles), which pack into ordered nanostructures, like multilayer or two-dimensional photonic crystal structures, to produce structural colors. To understand the optical properties of melanin and how melanosomes assemble into certain structures to produce colors, we prepared synthetic melanin (polydopamine) particles with variable sizes and aspect ratios. We have characterized the absorption and refractive index of the synthetic melanin particles. We have also shown that we can use an evaporative process to self-assemble melanin films with a wide range of colors. The colors obtained using this technique is modeled using a thin-film interference model and the optical properties of the synthetic melanin nanoparticles. Our results on self-assembly of synthetic melanin nanoparticles provide an explanation as why the use of melanosomes to produce colors is prevalent in the animal kingdom. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L50.00009: Mobility and diffusion of bound DNA-coated colloids Etienne Ducrot, Jeremy S. Yodh, Yu Wang, Yufeng Wang, Xiaolong Zheng, Marcus Weck, David J. Pine DNA coatings have been proposed as a versatile means for programming the self-assembly of micrometer and nanometer size particles. Progress in achieving this goal for particles larger than about 100 nm, where the DNA coatings are typically much thinner than the particle diameter, has been impeded because such DNA-coated colloids stick to each other like Velcro; they collide and bind but fail to anneal into their preprogrammed structure. Most notably, they generally fail to assemble into colloidal crystals but form random aggregates We have prepared micrometer-size colloids coated with single stranded DNA that are mobile even after they bind, so that the particles can rapidly rearrange. Here we report measurements of the mean square displacement $\Delta r^{2}$ of one ssDNA particle on a second ssDNA particle immobilized on a substrate, when the temperature is quenched to just below the melting temperature (near 40$^{\circ}$C). For shallow quenches of $\Delta$T 0.5$^{\circ}$C, the mean square displacement is proportional to time, $\Delta r^{2}$=At, indicating diffusive motion. For deeper quenches of $\Delta$T 1$^{\circ}$C, $\Delta r^{2}$=At$^{\alpha}$, where $\alpha$<1, indicating subdiffusive motion. This behavior is discussed in terms of a random distribution of traps. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L50.00010: High-yield production of stable colloidal clusters and their use in hierarchical DNA-directed assemblies James McGinley, Yifan Wang, Ian Jenkins, Talid Sinno, John Crocker Our goal is to produce and purify high yields of stable DNA-coated colloidal clusters by using crystal templates and reprogrammable DNA interactions. First, we incorporate ``impurity'' particles into a ``host'' colloidal crystal made up of DNA-coated polymer microspheres, and ensure that the only bonds that are preserved are those between the impurity particles' DNA strands and those of their nearest neighboring host particles. After dispersing the host crystal and making all DNA bonds permanent using a DNA-reactive enzyme, we are left with stable colloidal clusters, each comprised of a single impurity particle surrounded by a number of particles dictated by the host crystal structure. The clusters can be made with Icosahedral, Cuboctahedral, Tetrahedral, Cubic, and Octahedral symmetries, and can then be purified using density gradient fractionation. We will demonstrate that the scalable production of purified, well-oriented and stable DNA-coated colloidal clusters allows for the exploration of hierarchical assemblies with asymmetric building blocks and directional bonding. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L50.00011: Using Microfluidics to Measure the Equation of State for a 2D Colloidal Membrane Andrew Balchunas, Rafael Cabanas, Seth Fraden, Zvonimir Dogic In the presence of non-adsorbing polymer, monodisperse filamentous viruses assemble into colloidal membranes, which are 2D liquid-like one-rod-length-thick monolayers of aligned rods. Colloidal membranes are of particular interest because their properties are accounted for by the same theoretical models that are used to describe the biophysics of conventional lipid bilayers. However, bulk membrane formation only occurs over a very limited range of depletant concentrations and ionic strengths. In order to explore the properties of the colloidal membranes under a much wider range of molecular parameters, we have developed a microfluidic technique that allows for in-site exchange of the enveloping polymer suspension. This allows us to access the region of phase space where membranes are metastable. Using our technique we can measure how the colloidal membrane area depends on applied osmotic pressure, allowing us to determine its equation of state. We also characterize the dynamics of the constituent rods by using single molecule tracking techniques. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L50.00012: Assembly and interactions of achiral rafts in colloidal membranes Joia Miller, Prerna Sharma, Zvonimir Dogic Two-dimensional colloidal membranes composed of rods of different lengths display rich phase behavior. In particular, chirality of constituent rods stabilizes assembly of colloidal rafts, micron sized droplets enriched in one type of rod floating in the background membrane. Colloidal rafts interact via long-range repulsive interactions that are mediated by local rod twisting due to their rods' inherent chirality. We explore the behavior of an achiral bidisperse mixture of colloidal rods. Even in the achiral limit we observe assembly of stable or meta-stable finite-sized rafts. However, in contrast to the chiral limit, the long-range interactions between achiral rafts are attractive. These rafts are embedded in a host membrane that has nearly critical fluctuations in composition. We correlate the attractive domain interactions with these critical fluctuations. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L50.00013: Patchy particles using colloidal caps Christine Middleton, David Pine We present a method for making patchy particles functionalized with single stranded sticky end DNA only on their patches. This is done by adding ``spherical cap'' particles as patches to spherical colloids using the depletion interaction. The caps are then functionalized with single stranded DNA using copper-free click chemistry. Due to being attached only by depletion, the patches diffuse on the surface of the particle. The patchy particles can then interact with each other in a specific, directional way through the mobile, DNA functionalized patches. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L50.00014: Temperature controlled nanoparticle stability in concentrated polymer solutions So Youn Kim, Charles F. Zukoski Polyethylene glycol (PEG) in water is known to display a lower critical solution temperature (LCST) and a closed loop at high temperature. When silica nanoparticles are suspended in concentrated PEG solution, we observe temperature dependent phase separation even below the 60C which is much lower temperature than the LCST for the lowest PEG reported. Depending on the conditions, nanoparticles form clusters and show gelation and both can be reversible. Small angle x-ray scattering (SAXS) is used to characterize microstructure of nanoparticle dispersion and diffusing wave spectroscopy (DWS) and other light scattering techniques are employed to understand particle correlations in dense systems. Polymer dynamics near particle substrate is discussed with NMR Free Induction decay experiment. These combined experimental studies help to understand the detailed mechanism of nanoparticle gelation in polymer solutions. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L50.00015: A Directional Entropic Force Approach to Assemble Anisotropic Nanoparticles into Superlattices Byeongdu Lee We introduce a directional entropic force approach (DEFA) for controlling the assembly of anisotropic nanoparticles into crystalline lattices. The method relies on surfactant micelle-induced depletion interactions to assemble anisotropic gold nanoparticles into reconfigurable, non-close-packed (open) superlattices in solution. The anisotropic nanoparticles align along their flat facets to maximize entropy, and therefore minimize the free energy of the system, leading to assemblies with long-range order. Importantly, our experimental work complements recent theoretical work that proposes directional entropic forces between nanoparticle facets as a viable means for thermodynamically assembling nanoparticle superlattices. The experimental work herein uses depletants to create strong attractive forces that can drive assembly of reversible superlattices with tunable spacing in solution. These directional entropic forces are analogous to the directional bonding between atoms in molecules. The resulting crystalline superlattices are therefore shape-dependent. We show that the electrostatic and depletion interactions combine to determine the lattice spacing, and can be tuned independently with surfactant concentration and ionic strength to reconfigure the lattice constant. . [Preview Abstract] |
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