Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J14: Focus Session: Anisotropic Building Blocks: Synthesis and Assembly |
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Sponsoring Units: FIAP DMP Chair: Sharon Glotzer, University of Michigan Room: LACC 403B |
Tuesday, March 22, 2005 11:15AM - 11:51AM |
J14.00001: Self-assembly on curved surfaces: a tool to generate novel Nano-Materials Invited Speaker: It is known that thiolated molecules spontaneously form poly-crystalline self-assembled monolayers (SAMs) on flat gold surfaces. Scanning tunneling microscopy (STM) studies have shown that, in SAMs composed of more than one type of molecule (mixed-SAMs), domains of random shape and size phase-separate. Here we will show that, when mixed SAMs are formed on gold nano-crystals with a radius of curvature $<$ 20 nm, they spontaneously phase-separate into highly ordered domains of unprecedented size. In the case of binary mixture of thiolated ligands on gold particles, domains, only 0.5 nm wide, of alternating composition encircling or spiraling around the metallic core spontaneously assemble. This new family of nano-structured nano-materials[1] shows properties that are determined by this unique morphology, such as solubility. Also, due to the ordered alternation of hydrophobic and hydrophilic regions, surfaces coated with these particles show the ability of suppressing protein nonspecific adsorption. Recent results show that these particles can be forced to assemble into chains, rings and triangles. [1] Jackson A. M., Myerson J. W., Stellacci F. Nature Materials, 3, 330, 2004 [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:27PM |
J14.00002: Biphasic nanoparticles made by electrified jetting Invited Speaker: Nano-colloids have recently attracted intense attention due to unique properties that are distinctly different from bulk solid-state materials; including unique magnetic, electronic, optical, chemical, and biological characteristics. The vision that these nano-objects could essentially act as functional components in novel device generations, which ``magically'' assemble following a master blueprint void any human manipulation, has resulted in a new ``gold rush'' in materials science. These concepts have results in the synthesis of a multitude of nano-objects, such as nano-wires, nano-rods, nano-disks, or nano-prisms.$^{ }$ Recently, nano-particles with anisotropic materials distributions (biphasic nano-particles) moved in the focus of research. Our approach differs fundamentally from the above-mentioned methods in that it takes advantage of electrified polymer jets to create anisotropic materials distributions in nano-objects. jetting is a process to generate liquid jets by use of electrostatic forces. It is well-known that high electrical potentials (typically several thousand volts) applied between the jetting liquids that are fed through a capillary and a collecting substrate will induce jetting of a charged liquid. The differences in the final morphologies from similar processes are mainly determined by the properties of the jetting liquids and the process parameters. transmission electron microscopy, scanning electron microscopy, and scanning laser confocal microscopy, we demonstrate the applicability of the process to control size, shape, and materials distribution at the nanoscale. The resulting anisotropic nanoparticles may have potential applications for targeted drug delivery or as electro-rehological fluids.$\backslash $ a) F. M. Van der Kooij, K. Kassapidou and H. N. W. Lekkerkerker, \textbf{Liquid crystal phase transitions in suspensions of polydisperse plate-like particles,} \textit{Nature }\textbf{406}, 868 (2000); b) C. A. Mirkin, R. L. Letsinger, R. C. Mucic and J. J. Storhoff, \textbf{A DNA-based method for rationally assembling nano-particles into macroscopic materials}'' \textit{Nature }382, 607 (1996); c) N. B. Bowden, M. Weck, I. S. Choi and G. M. Whitesides, \textbf{Molecule-mimetic chemistry and mesoscale self-assembly}, \textit{Accounts of Chemical Research }\textbf{34}, 231 (2001). [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J14.00003: Guiding Rules for Self-Assembly of Patchy Particles Sharon Glotzer, Ting Chen, Zhenli Zhang The functionalization and patterning of nanoparticle and colloidal building blocks with organic and biomolecular ligands provides new possibilities for directing their self-assembly into complex structures for novel materials and devices. We seek to develop an intuitive and general framework for predicting the assembly of building blocks functionalized at specific locations with patches of attractively-interacting molecules. We present the results of molecular simulations of the self-assembly of spherical and cone-shaped particles decorated with sticky patches. ~We relate the geometry of polyhedral terminal structures formed from small numbers of particles, to geometrical details of the building blocks and the anisotropy of the patch patterns. ~We compare the structures obtained in our simulations with colloidal polyhedra formed by droplet evaporation. [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J14.00004: Self-assembly of particles with anisotropic interactions Wolfgang Losert, Justin Stambaugh We investigate the self-assembly of hard core particles with additional dipolar and higher order (in particular octopolar) interactions using a model system of vertically vibrated magnetic spheres. Self-assembly in such a driven dissipative system is similar to transitions to self-assembly seen in equilibrium polymerization. We show the crucial role of the anisotropy of interaction on the pattern of self-assembly in our experimental model system. In particular, we observe clusters, chains, and branched networks. We show that energy minimization in a simple point charge model can be used to predict the preferred self-assembly pattern. We also show that such a model containing a few carefully placed representative charges can successfully recreate self-assembly patterns in several related physical systems, including biological macromolecular self-assembly of e.g. tubulin. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J14.00005: Molecular Dynamics Simulation of Colloidal Nanoparticle Forces Kristen Fichthorn, Yong Qin An improved understanding of the forces between colloidal nanoparticles could lead to new strategies for achieving their selective assembly for a variety of different applications. We employ molecular dynamics simulations to study the interplay between solvation and van der Waals forces for model colloidal nanoparticles. We consider the influence of nanoparticle size, shape, and surface roughness, as well as solvent type (Lennard-Jones vs. n-decane) and solvent-solid interaction (“solvophobic” vs. “solvophilic”). We find that solvation forces can be comparable to van der Waals attraction and, thus, they can play an important role in determining the stability of colloidal suspensions. Surface roughness causes nanoparticles to rotate so they approach one another via paths of minimum free energy. This rotation causes crystalline (icosahedral) nanoparticles to approach one another via alternating face-face and vertex-vertex conformations, suggesting that solvation forces can control nanoparticle alignment during assembly. Finally, our simulations of solvophobic nanoparticles in n- decane yield insight into how the drying transition is influenced by the relative sizes of the solvent molecules and nanoparticles. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J14.00006: Error-Free DNA Directed Self-Assembly of Nanoparticle Clusters Nicholas Licata, Alexei Tkachenko We study DNA directed self-assembly of colloids into structures with controllable geometries. By introducing a soft-core repulsive potential between colloids, we can overcome excluded volume effects. A toy model is constructed to demonstrate these ideas, and its phase behaviour is studied numerically. We explain the route by which our proposal can be implemented experimentally. [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:27PM |
J14.00007: Nano hybrid shish-kebab: towards periodically functionalize carbon nanotubes Christopher Li, Lingyu Li, Wenwen Cai, Stephen Kodjie, Kishore Tenneti Both chemical and non-covalent wrapping methods have been used to functionalize carbon nanotubes (CNT). Periodical functionalization of CNT remains a challenging task and few works have been dedicated to this research field. We report a novel method of functionalizing CNT surface using controlled polymer crystallization. CNTs were periodically decorated with polymer lamellar crystals, resulting in ``nano hybrid shish-kebabs'' structure. The periodicity of the polymer lamellae varies from 20 - 70 nm. Both polyethylene and Nylon 6,6 have been successfully decorated on multi-walled as well as single-walled CNTs. This method opens a gateway to functionalizing CNTs in an ordered and controlled manner, an attractive research field that is yet to be explored. It also directly leads to the synthesis of the ``ideal'' polymer/CNT nanocomposites with controllable tube-to-tube distance. [Preview Abstract] |
Tuesday, March 22, 2005 1:27PM - 1:39PM |
J14.00008: Shape Separation of Gold Nanorods using Centrifugation Vivek Sharma, Kyoung weon Park, Mohan Srinivasarao We describe the shape separation of colloidal gold nanorods using centrifugation. Nanoparticle synthesis is characterized by a polydispersity in the shape and size of particles. Since the shape and size determine the properties and applications of nanoparticles, the separation of nanorods from a mixture of different shapes is necessary. We describe the hydrodynamics of nanorods and nanospheres undergoing centrifugation, elucidating how this can be efficiently exploited for the shape and size separation. For nanoparticles in dilute concentration, the relative sedimentation velocity of rods and spheres is obtained by describing Brownian motion of the particles in presence of external forces, accounting for shape dependent drag, as well as hydrodynamic interaction. The hydrodynamic arguments illustrate the effect of shape and size on both relative sedimentation velocities and concentration profiles. The arguments advanced here, with described caveats, are quite general and applicable to shape and size separation in organic, inorganic and biological systems. In present study, we report the efficient separation of gold nanorods from mixture of shapes obtained from synthesis by the seed mediated method. [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 1:51PM |
J14.00009: DNA Templating of Au Nanowires David Wood, Andrew Cleland, Gary Braun, Eran Levy, August Estabrook, Stephanie Wilkinson, Norbert Reich, Katsuhiko Inagaki We have developed a process for fabricating nanoscale wires using DNA templates. The templates were subsequently decorated with gold nanoparticles to make metallic wires. We have successfully deposited linear, straight sections of random ($\lambda$-phage) and regular-repeat sequences of DNA, of various lengths, on oxidized silicon substrates. We have also successfully deposited thiolated DNA on gold electrodes, allowing the DNA to electrically bridge gaps between electrode pairs. Electrode gaps ranged from 50 nm to 300 nm, fabricated using electron beam lithography. We decorated the DNA with gold nanoparticles with diameters in the range of 1-13 nm, and have used the nanoparticles as nucleation sites for the growth of continuous gold wires. We have performed AFM characterization of all surfaces and structures. In addition, we have performed current-voltage measurements on the undecorated DNA, the nanoparticle-decorated DNA, and the gold nanowires. [Preview Abstract] |
Tuesday, March 22, 2005 1:51PM - 2:03PM |
J14.00010: Manipulation and Assembly of Semiconductor Nanowires with Holographic Optical Traps Ritesh Agarwal, Kosta Ladavac, Guihua Yu, Charles Lieber, David Grier Semiconductor nanowires are versatile building blocks for the assembly of functional electronic and photonic devices. Yet to realize their potential will require assembly into increasingly complex architectures with placement at specific locations in a parallel process. Here we describe progress towards the use of the holographic optical tweezer (HOT) technique for manipulating nanowires in solution. The HOT technique can create hundreds of individually controlled optical traps with the ability to manipulate objects in three dimensions. Our results show that individual nanowires can be aligned along a line of optical traps. Single traps cannot manipulate individual nanowires suggesting that the mechanism of trapping may be different than previously observed for dielectric microspheres. Our results also show that individual nanowires can be rotated in circles using an optical vortex, and that it is possible to fuse nanowire junctions and deposit nanowires irreversibly on substrates. Efforts towards creating nanowire arrays and other complex structures will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 2:03PM - 2:15PM |
J14.00011: Guiding 3-D Self Assembly of Nanostructures by DNA Hybridization Phillip Rogers, Carl Bauer, Stephen Vanderet, Daniel Hansen, Antoine Calvez, Jackson Crews, Alistair Wood, Khodadad Dinyari, Brad Roberts, James Lau, David Pine, Eric Michel, Peter Schwartz The directed three dimensional self-assembly of microstructures and nanostructures through the selective hybridization of DNA is the focus of great interest toward the fabrication of new materials. Single stranded DNA is covalently attached to polystyrene latex microspheres and functions as a ``smart Velcro'' by only bonding to another strand of DNA of complementary sequence. The attached DNA increases the charge stabilization of the microspheres and allows controllable aggregation of microspheres by hybridization of complementary DNA sequences. The process is perfectly selective and reversible by heating, with a characteristic ``aggregate dissociation temperature'' that is dependent on salt concentration, and the evolution of aggregate dissociation with temperature is observed with optical microscopy. [Preview Abstract] |
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