Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A8: Colloidal Self-Assembly I |
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Sponsoring Units: DFD Chair: Hans Wyss, Harvard University Room: Morial Convention Center RO6 |
Monday, March 10, 2008 8:00AM - 8:12AM |
A8.00001: Directed Self-Assembly of Spherical Particles Natalie Arkus, Guangnan Meng, Vinothan Manoharan, Michael Brenner \par We examine the kinetics and energetics of self-assembly in systems containing a small number of spherical colloidal nanoparticles using a combination of theory, simulation, and experiment. We then explore how the addition of spherically symmetric binding specificity can be used to direct the self-assembly of a given structure. \par Using graph theoretic, numerical, and algebraic geometric techniques, we denumerate all possible packings for a system of $n$ particles. We map out the energy landscape of these packings, which is determined not only by the value of the potential energy at these minima, but also by the vibrational normal modes of the structures. Experiments for a 6 particle system show that the likelihood of a given packing follows this expected equilibrium distribution. \par To explore the kinetics of packing formation, we simulate the self-assembly of these systems in the irreversible binding limit. For the 6 particle system, this reveals that the kinetics required to form one of the packings is highly unlikely, resulting in the other packing forming with 100\% probability. With the addition of binding specificity however, we can cause the unlikely packing to form with 100\% probability. We show how the addition of binding specificity effects the energetic landscape of these systems, and that it alone is sufficient to direct self-assembly. [Preview Abstract] |
Monday, March 10, 2008 8:12AM - 8:24AM |
A8.00002: Controlling assembly of micro- and nano-particle systems with DNA. Dmytro Nykypanchuk, Mathew Maye, Daniel van der Lelie, Oleg Gang Addressable biological interactions provide attractive platform for rational self-assembly, however the strength of such interactions are often difficult to control. Here we present an approach where DNA molecules are used to balance attractive and repulsive interactions during particles assembly while preserving the interaction addressability. We show, that by changing the composition and structure of DNA shall of micro- (2 um) or nanoparticles (10 nm), assembly kinetics, aggregate sizes, and the systems melting properties can be tuned. At constant environmental conditions, this strategy allows for rational control of interaction energy landscape for nano- and micro-systems in a wide dynamic range. [Preview Abstract] |
Monday, March 10, 2008 8:24AM - 8:36AM |
A8.00003: Evaporation-Driven Assembly of Microspheres with Polymer in Emulsion Droplets Keng-hui Lin, Liang-jie Lai, Chih-Chung Chang, Hui Chen We study the packing of colloidal microspheres mixed with polymer in oil-in-water emulsion droplets through evaporation. The addition of polymer produce non-unique configurations of final clusters when the number of particles $N$ inside the droplet is larger than 4. The cluster configurations are classified into three categories based on the symmetry. Stablized colloidal clusters of spherical packings are observed. Observation on packing process shed light to the mechanisms which cause different and non-unique structures. The osmotic pressure and interparticle interaction due to polymer play important roles in packing. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 8:48AM |
A8.00004: Entropy-driven self-assembly of dimers Issei Nakamura, An-Chang Shi Supramolecular self-assembly is an important phenomenon with applications ranging from chemical synthesis to biological systems. Although the driving force of assembly is the weak non-covalent intermolecular interaction such as hydrogen bonding and dispersion force, the self-assembly is a result from balancing the enthalpic and entropic contributions. In general, the disassembled/disordered phase is expected as temperature is raised because of the entropic gain from the components of the aggregate. However, it has been observed that the self-assembled/ordered phase can be promoted with increasing temperature. This implies that the self-assembly is driven by entropy. In order to provide a better understanding of this entropy-driven transition, we have studied a statistical mechanical model for the aggregation of macromolecular dimers immersed in solvents. The model demonstrates that solvent molecules absorbed on the surface of the solute are released with increasing temperature, leading to an increase of the total entropy of the system. Consequently, the cooperative stability of the dimeric state is induced. The thermodynamic features of this transition are analyzed. [Preview Abstract] |
Monday, March 10, 2008 8:48AM - 9:00AM |
A8.00005: Hydrodynamic interactions effects on the dipole-induced self-assembly of $\beta$-peptides and Brownian-induced polymer pore translocation Juan Hernandez-Ortiz, Michael Graham, Juan de Pablo A novel method that scales linearly with the number of particles is used to study Brownian-systems considering fluctuating hydrodynamic interactions. The method is demostrated in the concept of two applications: the dipole-induced self-assembly of $\beta$-peptides and the Brownian-motion-induced translocation of a polymer thought a rectangular pore. The method includes the long-range interactions by the Green's function formalism. It allows the consideration of peptides at intermediate concentrations and the inclusion of the non-periodic domain of the translocation. The hydrodynamics interactions affect the dynamics of the peptides agglomeration and the mean-squared-displacement indicates significant changes in the long-time diffusion coefficient. The polymer translocation is study using a transition path sampling based methodology. In particular it is used to calculate the translocation rate constant. Even for a single bead there are differences once hydrodynamics are included. These differences are due to the changes of mobility near walls and the change in polymer chain diffusion coefficient. [Preview Abstract] |
Monday, March 10, 2008 9:00AM - 9:12AM |
A8.00006: Self-assembly of complex shaped colloidal particles Adeline Perro, Vinothan N. Manoharan We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 75{\%} purity) using a combination of emulsion polymerization and inorganic surface chemistry. The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched sphere doublets with a small strongly scattering inorganic core between the two spheres, allowing us to track the center of mass of each doublet. We have generalized the preparation procedure to create even more complex geometries, including hybrid tetrahedra and octahedra. We present some preliminary studies on the self-assembly of these systems based on various optical experiments, including confocal microscopy, light scattering, and digital holographic microscopy. [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:24AM |
A8.00007: Progress on systems of DNA modified colloidal particles for self-replication Paul Chaikin, Mirjam Leunissen, Remi Dreyfus, Roujie Sha, Nadrian Seeman, David Grier, David Pine Our goal is to create new materials that can self-replicate and self-assemble. For this, we modify the interactions between micrometer-sized colloids by coating them with single-stranded DNA `sticky ends', which specifically recognize complementary sequences on other colloids. We find that the aggregation-dissociation behavior is fully reversible for at least tens of temperature cycles. Using magnetic beads or optical tweezers, we form a chain-like `seed' structure, which acts as a template to assemble copies of itself from a soup of singlets. To determine what are the preferred binding sites, we studied the interactions between the singlets and their complementary particles in the seed. Important in our replication scheme is that each particle has two different types of sticky ends: one for `longitudinal' bonding along the chain and another for `transverse' bonding between seed and daughter chains. Contrary to the transverse linkers, the longitudinal linkers form AT/TA bonds, which can be crosslinked with an intercalator and UV irradiation. In this way, we permanently fix the seed and its copies. [Preview Abstract] |
Monday, March 10, 2008 9:24AM - 9:36AM |
A8.00008: Binary Colloidal Assembly by Dielectrophoresis Peter Hoffman, Yingxi Elaine Zhu Dielectrophoresis (DEP)-driven colloidal assembly has been recently explored as a new route to manipulate colloids and rapidly form nanostructured materials. In this talk, we demonstrate that colloidal particles of varied sizes can be assembled with controllable packing configurations in the presence of AC-electrical fields. We investigate binary latex particles of varied size ratios from 0.25 to 0.8 and directly monitor the dynamic assembly process with final structural characterization by using high-speed confocal microscopy. We observe rich phase behaviors of binary colloidal assembly with a strong dependence of applied AC-field frequency and medium conductivity. The obtained structural phase diagram can be well predicted by the DEP mobility and the Peclet number. We also present a mechanism that underlies the colloidal charge polarization due to charge segregation and entrainment within the double layer at several distinct frequencies, which cannot be explained by the classical Maxwell-Wagner theory. We recently also employ the same mechanism to form binary colloidal crystals. [Preview Abstract] |
Monday, March 10, 2008 9:36AM - 9:48AM |
A8.00009: Unusual aggregation behavior of colloids coated with palindromic DNA Mirjam Leunissen, Remi Dreyfus, David Pine, Paul Chaikin Coating particles with single-stranded DNA `sticky ends' gives excellent control over the specificity, strength and range of their interactions. Usually, a pair of complementary `Watson-Crick' sequences is used to obtain thermoreversible binding of different colloids. However, for certain purposes one could also use self-complementary `palindrome' sequences. Using light microscopy, we studied the aggregation behavior of micrometer-sized palindrome-coated colloids. Unlike Watson-Crick sticky ends, we found that it is of great importance whether the palindrome sticky end is attached to a flexible single strand or a rigid double-stranded `rod'. While the latter system displayed normal dissociation at elevated temperature, the former system showed enhanced aggregation with increasing temperature and no aggregation during fast temperature quenches. We explain these unusual observations by a competition between intra- and interparticle bonds. This provides us with an additional level of control over the interparticle bonding, besides the sequence of the sticky ends, the salt concentration and the DNA density on the beads. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:00AM |
A8.00010: Functionalized Au nanoparticles in solution Gary S. Grest, J. Matthew D. Lane The properties of functionalized Au nanoparticles in decane and water were studied by large-scale explicit atom, molecular dynamics simulations. Gold nanoparticles functionalized with S-(CH$_2$)$_9$-X alkanethiols chains (X = COOH or CH$_3$) were studied at the liquid-vapor interface and in the bulk. The structure of the functional groups on the nanoparticle was found to depend strongly on the end group and solvent. At the interface methyl terminated nanoparticles repel the water and move toward the vapor while in decane, the decane molecules engulf the nanoparticle. In the bulk, results for the nanoparticle/nanoparticle pair correlation function and nanoparticle diffusion will be presented as a function of nanoparticle concentration. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04- 94AL85000. [Preview Abstract] |
Monday, March 10, 2008 10:00AM - 10:12AM |
A8.00011: DNA-Grafted Janus Particles Ching Hsueh, Keng-hui Lin, Wen-Tau Juan Recently there have been advances in generating Janus microspheres whose two hemispheres have different chemical compositions [1-4]. The new types of particles open up possibilities for assembly of complex structures. Here we attach DNA molecules onto one side of Janus microspheres. The new type of colloidal particles resembles surfactant molecules and may give us interesting new structures.\\ \textbf{Reference:} [1] Y. Lu, H. Xiong, X. Jiang, Y.Xia, M. Prentiss and G. M.Whitesides, J. Am. Chem. Soc. \textbf{125}, 12724 (2003) [2] O.Cayre, V. N.Paunov and O. D. Velev, J. Mater. Chem. \textbf{13}, 2445 (2003) [3] R. F. Shepherd, J. C. Conrad, S. K. Rhodes, D. R. Link, M. Marquez, D. A. Weitz and J. A. Lewis, Langmuir \textbf{22}, 8618 (2006) [4] L. Hong, S. Jiang and S. Granick, Langmuir \textbf{22}, 9495 (2006) [Preview Abstract] |
Monday, March 10, 2008 10:12AM - 10:24AM |
A8.00012: The importance of repulsion in the aggregation-dissociation behavior of DNA coated colloids Remi Dreyfus, Mirjam Leunissen, Roujie Sha, Nadrian Seeman, David Grier, David Pine, Paul Chaikin Coating particles with DNA gives excellent control over the specificity, strength and range of their interactions. In our experiments, a pair of complementary `Watson-Crick' sequences is used to obtain thermoreversible binding of different colloids. Colloids coated with such complementary `sticky' DNA aggregate when they are mixed together, the aggregates dissolve again when they are heated. We investigate the melting behavior of colloids coated with both sticky and non-sticky DNA. By changing the ratio between the sticky and non-sticky DNA, the obtained melting curves have very different melting temperatures, but almost the same sharpness. We show that the sharpness does not change because a high number of bonds bridges the particles, and that the strong shift in melting temperature is due to a repulsive interaction induced by the confinement of the non-sticky DNA when the particles come close together. [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 10:36AM |
A8.00013: Self Assembly of Colloidal Particles at Small $N$ Guangnan Meng, Natalie Arkus, Ryan McGorty, Michael Brenner, Vinothan Manoharan We confine a small number ($N\approx10$) of micron-sized colloidal particles within micro-wells, and we use this finite system to study the process of self-assembly. The reversible aggregation of colloidal particles is controlled by a short-range depletion attraction, which is induced by poly($N$-isopropylacrylamide) nano particles. We use digital holographic microscopy to monitor the structural and kinetic properties of self-assembled colloidal clusters, and we use micro-wells to collect ensemble statistics. We compare our experimental results with theory and simulations, which probe how energetics and kinetics affect the packing structures. [Preview Abstract] |
Monday, March 10, 2008 10:36AM - 10:48AM |
A8.00014: 2D crystals of Janus amphiphilic colloidal spheres Shan Jiang, Stephen Anthony, Angelo Cacciuto, Erik Luijten, Steve Granick Colloidal spheres with one side hydrophilic and the other side hydrophobic assemble into 2D crystals with hexagonal translational order complemented by a high degree of orientational organization. Factors that determine the crystal structure are investigated, especially the dependence on ionic strength and on Janus balance. Depending on these variables, patches of the orientational order can be altered: from doublets to extended lines containing dozens of particles. Janus particles with different geometry (Janus balance) self-assemble into different cluster structures. Collective motion is evident from time-resolved optical microscopy. [Preview Abstract] |
Monday, March 10, 2008 10:48AM - 11:00AM |
A8.00015: Harnessing Elastic Instability for the self-assembly of complex patterns Elisabetta Matsumoto, Ying Zhang, Anna Peter, Pei-Chun Lin, Randall Kamien, Shu Yang Directed pattern formation through the self-assembly of complex polymer systems promises to be a powerful approach in the pursuit of novel, transformative technologies. Current approaches to create desired motifs at the nanoscale utilize flow, shear, fields, and other externally imposed, top-down forces. Nature, on the other hand, provides us with a plethora of examples of intrinsic, bottom-up effects: from the phyllotactic growth of plants to animal stripes to fingerprints, instabilities, packing constraints, and simple geometries can drive the formation of delicate, detailed, and beautiful patterns. By harnessing the elastic instability in flexible poly(dimethylsiloxane) (PDMS) membranes with a square lattice of circular pores exposed to a solvent, we distort the pores into a pattern featuring long-range orientational order. Within linear elasticity theory, we find the groundstate configuration of a lattice of interacting deformation elements, or ``dislocation dipoles'' to be in complete agreement with the observed pattern. Our theory allows us a means to design the patterns formed by such elastic frustration. [Preview Abstract] |
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