Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A30: Self-Assembly of Particles, Droplets, and Amphiphilic Molecules |
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Sponsoring Units: DFD Chair: Zhengdong Cheng, Texas A&M University Room: Colorado Convention Center 304 |
Monday, March 5, 2007 8:00AM - 8:12AM |
A30.00001: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 8:12AM - 8:24AM |
A30.00002: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 8:24AM - 8:36AM |
A30.00003: Solution Phase Behavior of Gold Nanoparticles in Colloidal Solution Hao Yan, Amitabha Chakrabarti, Christopher Sorensen Gold nanoparticles in colloidal solution can aggregate to form gold nanocrystal superlattices. To explore and understand the solution phase behavior of nanoparticles, the gold nanoparticles ligated with dodecanthiol in a mixture of 4-tert-butyltoluene and butanone were studied by UV-vis spectroscopy, static light scattering and dynamic light scattering. The results showed that there is a reversible dissolution-aggregation process. The phase diagram was obtained by measuring the size of the nanoparticles with dynamic light scattering and the scattered light intensity. The UV-vis spectroscopy also proved the existence of a phase transition. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 8:48AM |
A30.00004: Self Assembly of Colloidal Particles at Small N Guangnan Meng, Zhengdong Cheng, Michael Brenner, Vinothan Manoharan We confine the dilute colloidal suspension inside emulsion droplets and study the structures of the aggregated clusters at small particle number ($N\approx10$) in order to understand the governing rules of equilibrium self-assembly. The aggregation process is controlled by the short-range weak depletion attraction between particles, and the structural and dynamic properties of self-assembled colloidal clusters are monitored via optical microscopy. We compare the experimental results with the theory and simulations, which probe how the number of local minima increases with number of particles. Our system may be a good model system for understanding generic features of glass and gel transitions. [Preview Abstract] |
Monday, March 5, 2007 8:48AM - 9:00AM |
A30.00005: Self-Organization of Bouncing Oil Drops: Two-Dimensional Lattices and Spinning Clusters Suzanne Lieber, Melissa Hendershott, Apichart Pattanaporkratana, Joseph Maclennan Multiple oil drops bouncing on the surface of a vertically vibrating bath of the same oil exhibit self-organization behavior in two dimensions. S.~Proti\`ere et al. [J.~Phys.: Condens.\ Matter \textbf{17}, S3529 (2005)] recently reported that such drops arrange themselves in triangular lattices, with a lattice spacing dependent on the driving frequency of the bath. We describe here the morphology and dynamic behavior of stable assemblies of large bouncing oil drops, for which we find that not only the spacing but the lattice structure itself changes with frequency, with variants of both square and hexagonal structures being observed. Large ``rafts'' of drops form soft triangular lattices with faceted boundaries. Small clusters of drops are unstable to coherent, collective spinning under certain driving conditions, manifesting spontaneous rotational symmetry breaking. [Preview Abstract] |
Monday, March 5, 2007 9:00AM - 9:12AM |
A30.00006: Self-assembly of helical tubules using a single-tailed surfactant. Hee-Young Lee, Srinivasa Raghavan Hollow micro or nanotubules are an unusual type of self-assembled structure that can be formed in aqueous solution. Such structures could be useful in a variety of applications such as in controlled drug delivery and in electroactive composites. However, these structures are typically formed only by some unusual lipids (i.e., two-tailed amphiphiles) or certain peptides. Here we present a very simple and economical process to make stable tubules by using a single-tailed diacetylenic surfactant in conjunction with an alcohol. The formation of tubules as a function of solution composition and temperature are systematically investigated in this study. The tubules are visualized by optical microscopy, while their detailed structure is seen under TEM. We find that the tubules have helical markings, which is remarkable considering that the precursor molecules are achiral. Our results provide further evidence that molecular chirality is not essential to forming tubules; presumably, tubules can form from achiral molecules by a chiral symmetry-breaking process. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:24AM |
A30.00007: Aggregation Properties and Liquid Crystal Phase of a Dye Based on Naphthalenetetracarboxylic Acid Michelle Tomasik, Peter Collings R003 is a dye produced for thin film optical components by Optiva, Inc.$^1$ made from the sulfonation of the dibenzimidazole derivative of naphthalenetetracarboxylic acid. Its molecular structure is very different from the aggregating food dye previously investigated in our laboratory$^2$ and R003 forms a liquid crystal phase at significantly lower concentrations. We have performed polarizing microscopy, absorption spectroscopy, and x-ray diffraction experiments in order to determine the phase diagram and aggregate structure. In addition, we have included both translational and orientational entropy in the theoretical analysis of the aggregation process, and have used a more realistic lineshape in analyzing the absorption data. Our results indicate that the ``bond energy'' for molecules in an aggregate is even larger than for the previously studied dye and that the aggregate structure has a cross-sectional area equal to two or three molecular areas rather than one.\\ $^1$Lazarev, P., N. Ovchinnikova, M. Paukshto, SID Int. Symp. Digest of Tech. Papers, San Jose, California, June XXXII, 571 (2001).\\ $^2$V. R. Horowitz, L. A. Janowitz, A. L. Modic, P. A. Heiney, and P. J. Collings, Phys. Rev. E 72, 041710 (2005). [Preview Abstract] |
Monday, March 5, 2007 9:24AM - 9:36AM |
A30.00008: Effects of Multivalent Salts and Polyamines on Lyotropic Chromonic Liquid Crystals L. Tortora, H.S. Park, D. Finotello, O.D. Lavrentovich Multivalent salts and polyamines cause significant structural and phase changes in lyotropic chromonic liquid crystals (LCLCs) such as water solutions of sunset yellow (also known as Edicol), disodium chromoglycate, and blue 27. Using polarizing microscopy, rheoscopy, retardance mapping, and preliminary small-angle neutron scattering data, we demonstrate that multivalent additives cause significant shifts of phase boundaries in the temperature-concentration coordinates, formation of aggregate bundles, as well as induce phase separation of a homogeneous nematic phase into hexagonal columnar and isotropic phases. The multivalent phenomena are discussed within the framework of the strong coupling model of polyelectrolyte interactions and hydration effects. [Preview Abstract] |
Monday, March 5, 2007 9:36AM - 9:48AM |
A30.00009: Nanoparticle organization in surfactant mesophases Guruswamy Kumaraswamy, Kamendra Sharma Dispersing colloidal particles in surfactant liquid crystalline phases leads to the formation of materials with ordered microstructures. The influence of the liquid crystalline medium leads to organization of the colloidal particles, and the driving force for self-assembly scales with the size of the colloids. Micron-sized colloids organize into linear arrays in liquid crystals, while nanoparticles can be confined in surfactant liquid crystal structures. We investigate the dispersion of silica nanoparticles with sizes of 7, 11 and 23nm in hexagonal mesophases of aqueous solutions of nonionic surfactants. The surfactant mesophase is preserved after dispersion of these particles, and the particles organize to form lamellar structures. We will discuss the implications of our results for the synthesis of novel materials. [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:00AM |
A30.00010: Self-assembly of ionic detergents: a simulation study of sodium dodecyl sulfate micellization Maria Sammalkorpi, Mikko Karttunen, Mikko Haataja Detergents, amphiphilic molecules used to separate and dissolve molecular aggregates and also as cleaning agents, consist of a polar head group and one or more hydrophobic tails. Above a critical concentration, they self-aggregate in an aqueous solution to form micelles. While industrially extremely important, surprisingly little is known about molecular details of the self-assembly of detergents. Here we extend our previous work of modeling and model construction of charged soft-matter systems [1] by a description of an anionic detergent, sodium dodecyl sulfate (SDS) [2]. We present the results of large-scale Molecular Dynamics simulations of the formation dynamics and structure of SDS micelles. We demonstrate that temperature affects micelle morphologies through the packing and discuss the effect of SDS concentration on the micellization. \newline [1] M. Patra et al., Biophys. J. 84, 3636 (2003); A. A. Gurtovenko et al., J. Phys. Chem. B 109, 21126 (2005); A. A. Gurtovenko et al., Biophys. J. 86, 3461 (2004). \newline [2] The SDS parameters are available at www.softsimu.org. [Preview Abstract] |
Monday, March 5, 2007 10:00AM - 10:12AM |
A30.00011: Evidence for condensed lipid/cholesterol complexes in lipid membranes. Maria K. Ratajczak, Shelli L. Frey, Eva Chi, Canay Ege, Theodore L. Steck, Yvonne Lange, Jarek Majewski, Kristian Kjaer, Ka Yee C. Lee Certain binary mixtures of phospholipids and cholesterol exhibit phase diagrams with two immiscibility regions with a sharp cusp in between. The cusp has been suggested to represent the stoichiometry of phospholipid/cholesterol complexes, and cholesterol is thought to exist in two states: a bound, low activity state, and an unbound, high activity state. To better understand the interaction between phospholipids and cholesterol, we have studied the effect of a possible displacing agent, hexadecanol, on the behavior of the binary mixture. Our cholesterol desorption assays indicate that hexadecanol can displace cholesterol from its association with phospholipids, thereby activating it. Phospholipid/cholesterol/hexadecanol systems in which a fraction of cholesterol is replaced by the alcohol have phase diagrams that mimic those of binary systems with the same apparent molar stoichiometry. X-ray data show a broad Bragg peak in these binary systems, indicating that order in these complexes extend over only several molecular dimensions. [Preview Abstract] |
Monday, March 5, 2007 10:12AM - 10:24AM |
A30.00012: Concentration-curvature coupling in endocytosis, Sarah Nowak, Tom Chou The wrapping of symmetric particles by lipid bilayers depends on the membrane bending rigidity and the adhesion between the membrane and the particle. We consider the additional effects of a membrane composed of a binary lipid mixture. The different lipid components induce different spontaneous curvatures, which mediates the wrapping process through an induced phase separation near the particle-membrane contact region. We find that mixtures always enhance the wrapping. Asymptotic results are also found for the membrane shape in the limit of strong and weak spontaneous curvature-lipid concentration coupling. [Preview Abstract] |
Monday, March 5, 2007 10:24AM - 10:36AM |
A30.00013: Entropy-driven ordering in soft matter Yu-qiang Ma In this talk, we discuss the entropic effects on the structural organization on the basis of the following three examples of our recent works: 1) phase behavior in thin film of confined colloid-polymer mixtures, 2) the organization in inclusion-membrane complexes, and 3) lateral organization in supported membrane on a geometrically patterned substrate. The result will be helpful for understanding the physical mechanism of structural organization and controlling novel structures of soft materials under the guidence of entropy driven ordering. [Preview Abstract] |
Monday, March 5, 2007 10:36AM - 10:48AM |
A30.00014: Soft quasicrystals - Why are they stable? Ron Lifshitz, Haim Diamant In the last two years we have witnessed the exciting experimental discovery of soft matter with nontrivial quasiperiodic long-range order---a new form of matter termed a \emph{soft quasicrystal}. Two groups have independently discovered such order in soft matter: The first in a system of dendrimer liquid crystals [1]; and the second in a system of ABC star-shaped polymers [2]. These newly discovered soft quasicrystals not only provide exciting platforms for the fundamental study of both quasicrystals and of soft matter, but also hold the promise for new applications based on self-assembled nanomaterials with unique physical properties that take advantage of the quasiperiodicity, such as complete and isotropic photonic band-gap materials [3]. Here we provide a concise review of the emerging field of soft quasicrystals [4], and invoke an old theory [5] suggesting that the existence of two natural length-scales, along with 3-body interactions, may constitute the underlying source of their stability.\par\noindent [1] Zeng \emph{et al.}, Nature {\bfseries 428} (2004) 157.\par\noindent [2] Takano \emph{et al.}, J.\ Polym.\ Sci.\ Polym.\ Phys.{\bfseries 43} (2005) 2427.\par\noindent [3] Zoorob \emph{et al.}, Nature {\bfseries 404} (2000) 740.\par\noindent [4] Lifshitz \& Diamant, preprint (cond-mat/0611115).\par\noindent [5] Lifshitz \& Petrich, Phys.\ Rev.\ Lett.\ {\bfseries 79} (1997) 1261. [Preview Abstract] |
Monday, March 5, 2007 10:48AM - 11:00AM |
A30.00015: Directing self-assembly by tailoring pair potentials of soft shoulder systems Zach Smith, Paul Beale, Noel Clark, Matt Glaser Monodisperse spheres interacting via `hard core/soft shoulder' (HCSS) pair potentials (e.g., hard spheres with an additional repulsive step interaction) exhibit extremely rich phase behavior, including a diverse array of two- and three-dimensional liquid crystal phases and a wide variety of complex crystal structures [M. A. Glaser et al., cond-mat/0609570], including relatively open crystal structures such as the 2D honeycomb lattice [E. A. Jagla, J. Chem. Phys. 110, 451 (1999)]. The complex phase behavior of this class of systems derives from competition between an underlying `soft shoulder' clustering instability [W. Klein et al., Physica A 205, 738 (1994)] and excluded volume constraints. We show that it is possible to derive soft shoulder potentials to promote self-assembly of specific target structures using only geometrical information. We have applied this approach to the self-assembly of a stable 3D diamond lattice in systems of particles with isotropic pair interactions, demonstrating that anisotropic, directional bonding is not a necessary requirement for formation of the diamond lattice. This approach, which exploits soft shoulder clustering behavior, is a powerful tool for the directed design of a variety of unusual and complex self-assembled systems. Work supported by NSF MRSEC Grant DMR-0213918 and GAANN Fellowship P200A030179. [Preview Abstract] |
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