Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C38: Assembly of Soft Nanoparticles and Colloids in SolutionFocus
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Sponsoring Units: DPOLY GSOFT Chair: Du Yeol Ryu, Yonsei University Room: 341 |
Monday, March 14, 2016 2:30PM - 2:42PM |
C38.00001: Self-assembly of Iron Oxide Nanoparticles on Liquid Surfaces by Using Miscible Solvent Pairs Jiayang Hu, Datong Zhang, Kathleen M. Kennedy, Irving P. Herman Nanoparticle (NP) self-assembly on liquid-air interfaces by using immiscible solvent pairs is a fast and effective way to prepare two-dimensional (2D) close-packed superlattices. However, this technique is limited by the number of available solvent pairs that are immiscible with each other while being different in the dispersity of NPs. Here, we report forming 2D superlattices using toluene/dimethyl sulfoxide miscible solvent pairs. In-situ small angle X-ray scattering patterns from NP layers sitting on the meniscus agree with patterns expected from 2D tilted closed packed superlattices. Real time optical microscopy shows that after drop casting, most of NPs coagulate immediately and sink to the bottom over several days, but leave a continuous ML on the surface, without forming 3D clusters that are usually seen in the immiscible techniques generated by the “coffee ring” effect. TEM images show that NPs nucleate simultaneously on different parts on the liquid surface until they touch, therefore covering the whole surface. [Preview Abstract] |
Monday, March 14, 2016 2:42PM - 2:54PM |
C38.00002: The effects of surfactant dynamics on deposition patterns in evaporating colloidal drops Narina Jung, Haewon Seo, Pilwon Kim, Chun Sang Yoo Evaporation of a colloidal droplet typically leaves ring-like deposit patterns on a substrate, now well-known as the coffee ring effect. We investigate the effect of surfactant dynamics on the deposition process in a drying droplet. A coarse grained model has been developed to simulate cases with Marangoni stresses, adsorption kinetics, and intermolecular interaction of surfactant particles and to examine the related deposit formation of colloidal particles. By using the two-dimensional lattice for the lateral cross-section of a droplet, we are able to capture the full dynamics of recirculating flows with surfactant and colloidal particles during drying. The roles of surfactant on droplet and colloidal particle dynamics are investigated by systematically varying parameters, such as the maximum area fraction and the initial concentration of surfactant. We further highlight important factors to generate Marangoni eddies. [Preview Abstract] |
Monday, March 14, 2016 2:54PM - 3:06PM |
C38.00003: Non-equilibrium colloidal assembly pathways via synergistic dipolar, depletion, and hydrodynamic interactions Anna Coughlan, Michael Bevan The ability to assemble nano- and micro- colloidal particles into ordered materials and controllable devices provides the basis for emerging technologies. However, current capabilities for manipulating colloidal assembly are limited by the degree of order, time to generate/reconfigure structures, and scalability to large areas. These limitations are due to problems with designing, controlling, and optimizing the thermodynamics and kinetics of colloidal assembly. Our approach is to provide viable non-equilibrium pathways for rapid assembly of defect free colloidal crystals using combinations of magnetic field and depletion mediated assembly. Results include video microscopy experiments and Stokesian Dynamic computer simulations of superparamagnetic colloidal particles experiencing depletion attraction in time varying magnetic fields. Findings show multi-body hydrodynamic interactions and magnetic dipole relaxation mechanisms are essential to capture assembly and annealing of attractive colloidal crystals. With the ability to measure, model and tune colloidal interactions and dynamics, we demonstrate the use of time varying fields to manipulate non-equilibrium pathways for the assembly, disassembly, and repair of colloidal microstructures. [Preview Abstract] |
Monday, March 14, 2016 3:06PM - 3:18PM |
C38.00004: Criterion for noise-induced synchronization: application to colloidal alignment Jonah Eaton, Thomas A Witten, Brian Moths \def\S{synchroniz} \def\H{\Delta H} \def\D{dynamical system} \def\M{<\log|d\psi/d\phi|>} Asymmetric, self-assembled colloidal clusters can rotate stably as they descend under gravity. One may \S{}e a dispersion of copies of such a cluster using a force that randomly switches between two different directions[1]. This is an instance of ``noise-induced \S{}ation," demonstrated broadly in \D{}s that have a stable, periodic motion[2]. When such a system is perturbed by a prescribed transient force, it acquires a phase angle $\psi$ that depends on its initial phase $\phi$. For our colloidal dispersion the probability distribution of phases $\psi$ long after a switch in forcing is in general not uniform; thus the entropy $H$ of the ensemble has decreased. The phase map $\psi(\phi)$ provides strong constraints on the change $\H$ resulting from a switch: we show that the quantity $\M$ is an upper bound on $<\H>$. Thus whenever $\M~<0$, $H$ must decrease indefinitely on average. Our simulations show that this average is a good guide to the actual \S{}ation behavior. This bound and other properties of $\H$ apply broadly to any \D{} with a well-defined $\psi(\phi)$. [1] B. Moths, T. Witten. Phys Rev Lett, {\bf 110} 028301 (2013). [2] H. Nakao et al. Phys Rev E, {\bf 72} 026220 (2005). [Preview Abstract] |
Monday, March 14, 2016 3:18PM - 3:30PM |
C38.00005: Characterization of hyperuniformity in colloidal suspensions through small angle static light scattering. Coline Bretz, Tim Still, Denis Bartolo, Jean Baudry, Arjun Yodh, Remi Dreyfus Hyperuniform materials have attracted increasing interest over the past decade due to their potential exciting photonic properties. Our work aims at exploring novel ways of assembling hyperuniform materials from colloidal suspensions. Three-dimensional systems of micrometer-sized colloids are considered and characterized by studying their structure factor using static small angle light scattering (SLS). A SLS set-up has been constructed for this purpose. Using an index-matched suspension of colloidal particles, we are able to record the structure factors of suspensions of micrometer-sized colloids in a three-dimensional cell. We will show how our apparatus allows us to follow the spatial organization of the colloids and characterize their hyperuniformity. [Preview Abstract] |
Monday, March 14, 2016 3:30PM - 3:42PM |
C38.00006: Nanoparticle interactions in electrolyte solutions: A classical density functional theory and molecular dynamics study K. Michael Salerno, Amalie L. Frischknecht, Mark Stevens We know that multivalent ions can dramatically alter the interactions between macroions, and we are interested in the fundamentals of nanoparticle interactions. We performed molecular dynamics (MD) simulations at the primitive model level and classical fluids density functional theory (DFT) calculations of negatively charged interacting nanoparticles, 2 - 7 nm in diameter, in solution with 1:1, 1:2, or 1:3 salt. We found qualitative agreement between the MD simulations and DFT calculations for the ion density profiles around the nanoparticles and for the interaction free energy between two nanoparticles. As expected, the nanoparticle interaction free energies depend strongly on the cation valence, with pure repulsion for a 1:1 salt, changing to attraction for multivalent cations due to formation of charge ordered structures. Attractive free energy depths can reach 10 kT for 7 nm diameter nanoparticles, indicating that kinetic arrest and aggregation may occur. The interaction free energies depend non-monotonically on the nanoparticle charge due to layering of the counterions around the nanoparticles for large nanoparticle charges. [Preview Abstract] |
Monday, March 14, 2016 3:42PM - 4:18PM |
C38.00007: Self-Assembly of DNA-coated colloids Invited Speaker: David Pine DNA-coated particles have emerged as a powerful tool for programming the self-assembly of colloids and nanoparticles. The power of this approach lies in the highly specific molecular recognition properties of DNA and in the thermal reversibility of the interactions between DNA strands attached to different particles. These two properties taken together can, in principle, direct the bottom-up self-assembly of different materials into almost any desired structure. Here we discuss the self-assembly of single and multi-component crystals of DNA-coated colloids. [Preview Abstract] |
Monday, March 14, 2016 4:18PM - 4:30PM |
C38.00008: Hierarchical assembly of anisotropic particles in AC electric fields. Isaac Torres Diaz, Bradley Rupp, Xiaoqing Hua, Yuguang Yang, Michael A. Bevan Hierarchical microstructures composed of colloids are of great interest for technological applications and advanced materials such as metamaterials and microfluidic devices. The dynamics of spherical colloidal particles has been analyzed previously for several systems, and has led to the control of the formation of perfect crystals using AC electric fields. However, spherical particles do not have a dependence on its orientation as anisotropic particles. Recently, researchers reported experiments showing the capabilities of anisotropic particles to assemble in different configurations, yet a detailed understanding of the mechanism and control is lacking. This work shows both theoretical and experimental results of the control of a colloidal system composed of anisotropic colloidal particles with a tri-axial ellipsoidal shape subjected to a non-uniform electric field close to a planar wall. We show that particles pack into different structures and orientations as a function of the applied electric field amplitude and frequency by taking into account dipole-field, dipole-dipole, and colloidal interactions. This analysis provides a theoretical framework for the equilibrium and non-equilibrium structures that can be formed via field mediated interaction, which are validated by experimental microscopy results, and can ultimately be used to engineer the hierarchical assembly of anisotropic particles. [Preview Abstract] |
Monday, March 14, 2016 4:30PM - 4:42PM |
C38.00009: Quantitative Characterization of Surface Self-Assembly Imaging Using Shapelets Nasser Mohieddin Abukhdeir, Robert Suderman, Daniel J. Lizotte Microscopy and imaging of surface self-assembly phenomena have advanced significantly over the past decade. In order to determine structure/property relationships robust automated analysis of the resulting images is required, but has not advanced at an equally rapid pace. Recently, quantitative characterization techniques have been developed and applied, such as using bond-orientational order (BOO) theory. BOO-based methods have significant limitations in that they do not provide pixel-level resolution and are not robust in the presence of measurement noise. In this work, a fundamentally different method for automated quantitative characterization of surface self-assembly imaging is presented which uses a family of localized functions called ``shapelets''. The method is presented and applied to quantitative characterization of stripe and hexagonal patterns which are frequently observed in surface self-assembly. The shapelet-based method is shown to be general, highly accurate, and robust in the presence of measurement noise. It is able to efficiently determine local pattern characteristics such as pattern strength and orientation for the determination of structure/property relationships. [Preview Abstract] |
Monday, March 14, 2016 4:42PM - 4:54PM |
C38.00010: Micro-evaporators: a powerful tool to control the growth of dense organized colloidal materials celine burel, Jacques Leng, bertrand donnio, remi dreyfus, jean-baptiste salmon Latex colloids have been concentrated inside a microfluidic channel, referred to as a microevaporator, in a controlled way up to the formation of millimeter-long colloidal materials. The solvent of this colloidal dispersion is transported by pervaporation through a thin PDMS membrane sealing the channel, inducing a flow from the reservoir containing the dispersion, up to the tip of the channel. Thus, as pervaporation occurs, colloids get concentrated at the tip of the channel up to the growth of a packed bed of colloids. The frontier between the dilute dispersion and the concentrated jammed or crystalline phase is clearly delimited by a concentration front. The position of the latter was recorded by using direct videomicroscopy. We investigated the dynamics of growth of such concentrated materials by measuring the position of the concentration front as a function of time. From these data we also estimated the volume fraction of the colloids within the concentrated material using mass conservation. We found that the estimated values are much smaller than the expected volume fractions for a dense colloidal assembly. We finally propose some explanations for such a discrepancy. [Preview Abstract] |
Monday, March 14, 2016 4:54PM - 5:06PM |
C38.00011: Prediction of Binary Nanoparticle Superlattices from Soft Potentials Nathan Horst, Alex Travesset Driven by the hypothesis that a sufficiently continuous short-ranged potential is able to account for shell flexibility and phonon modes and therefore provides a more realistic description of nanoparticle interactions than a hard sphere model, we compute the solid phase diagram of particles of different radii interacting with an inverse power law potential. We explore 24 candidate lattices where the p-exponent, determining the short-range properties of the potential, is varied between p=12 and p=6, and optimize the free energy with respect to additional internal parameters. The phase diagrams contain the phases found in ongoing self-assembly experiments, including DNA programmable self-assembly and nanoparticles with capping ligands assembled by evaporation from an organic solvent. The resulting phase diagrams can be mapped quantitatively to existing experiments as a function of only two parameters: nanoparticle radius ratio ($\gamma$) and softness asymmetry (SA). [Preview Abstract] |
Monday, March 14, 2016 5:06PM - 5:18PM |
C38.00012: Meniscus height controlled convective self-assembly Satyan Choudhary, Alfred Crosby Convective self-assembly techniques based on the ‘coffee-ring effect’ allow for the fabrication of materials with structural hierarchy and multi-functionality across a wide range of length scales. The coffee-ring effect describes deposition of non-volatiles at the edge of droplet due to capillary flow and pattern formations due to pinning and de-pinning of meniscus with the solvent evaporation. We demonstrate a novel convective self-assembly method which uses a piezo-actuated bending motion for driving the de-pinning step. In this method, a dilute solution of nanoparticles or polymers is trapped by capillary forces between a blade and substrate. As the blade oscillates with a fixed frequency and amplitude and the substrate translates at a fixed velocity, the height of the capillary meniscus oscillates. The meniscus height controls the contact angle of three phase contact line and at a critical angle de-pinning occurs. The combination of convective flux and continuously changing contact angle drives the assembly of the solute and subsequent de-pinning step, providing a direct means for producing linear assemblies. We demonstrate a new method for convective self-assembly at an accelerated rate when compared to other techniques, with control over deposit dimensions. [Preview Abstract] |
Monday, March 14, 2016 5:18PM - 5:30PM |
C38.00013: Strain-Temperature-Transformation (STT) Diagram for Soft Solids Shoubo Li, Wentao Xiong, Xiaorong Wang Soft materials comprise a variety of physical states that are easily deformed by shear stains or thermal fluctuations. They include suspensions, colloids, polymers, foams, gels, liquid crystals, and a number of biological materials. In this contribution, a generalized strain-temperature-transformation (STT) diagram for many soft materials is presented in which the physical states encountered are related to the strain and temperature changes. The boundary defined for the solid-to–liquid transformation in the STT diagram displays a surprising Z-shaped curve. We discuss this feature with respect to the physical nature of materials. [Preview Abstract] |
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