Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H14: Colloids III: Formation and Control |
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Sponsoring Units: DFD Chair: Itai Cohen, Cornell University Room: 315 |
Tuesday, March 17, 2009 8:00AM - 8:12AM |
H14.00001: Connecting structure and rheology in sheared colloidal suspensions Jonathan McCoy, Itai Cohen We investigate the shear properties of colloidal suspensions confined between parallel plates. When the distance between the plates is very small, i.e. approaching the size of the colloidal particles, a number of dramatic phase behaviors are observed under shear, including buckling, banding, jamming, and crystallization. This strongly confined regime is difficult to access using standard rheological techniques. Our experiment explores connections between microstructural behaviors and macroscopic flow by combining confocal microscopy and force measurement techniques in a custom-built thin-film shear cell. Here, we will focus on the interplay between confinement, slip, and order. [Preview Abstract] |
Tuesday, March 17, 2009 8:12AM - 8:24AM |
H14.00002: Modulation of attractive colloidal interactions by lipid and protein membrane functionalization Yupeng Kong, Raghuveer Parthasarathy The broad technological and scientific importance of colloidal materials has spurred a large body of research into the functionalization of micron-scale particles. Progress towards self-assembled microparticle superstructures remains slow, however, and fundamental mysteries such as the attractions observed between like-charged particles near a confining wall remain unresolved. These difficulties arise in large part due to the lack of experimental systems with tunable, attractive interparticle interactions. Biomembranes are appealing candidates for colloidal functionalization, enabling access to electrostatic and chemical properties that influence inter-particle relations. We describe here the first measurements of the pair interaction energy for membrane-functionalized colloids, using a newly developed optical line trapping technique. Two classes of particles, derivatized with lipid-only and lipid-plus-protein membranes, each show attractive interactions. The two particle types exhibit different relations between the depth and spatial range of the interactions, however. Control of lipid composition allows the first reported decomposition of like-charge interactions into charge-dependent and -independent terms, leading to a striking insight into the long-standing paradox of like-charge attraction: the charge-dependent term in the interaction is purely repulsive, while the attraction is independent of particle charge. [Preview Abstract] |
Tuesday, March 17, 2009 8:24AM - 8:36AM |
H14.00003: Self-protected interactions in DNA-functionalized colloids: Nano Contact Glue Mirjam Leunissen, Remi Dreyfus, Roujie Sha, Nadrian Seeman, David Pine, Paul Chaikin The ability of single-stranded DNA to form a variety of sequence-dependent secondary structures, such as hairpins, is frequently used in DNA nanotechnology, but has so far not been explored for the directed assembly of (nano)colloidal structures. We will show how mono- and bimolecular hybridization events in the DNA coatings of individual micrometer-sized beads can give rise to unusual, quench-rate dependent aggregation behavior, and how it can give additional control over the colloidal self-assembly process. For example, it provides us with `self-protected' interactions that are activated by temperature or prolonged proximity and that facilitate the formation of finite-sized structures. A simple quantitative model describes the underlying competition between intra- and interparticle hybridization events, based on the known thermodynamic parameters of the DNA sticky ends. [Preview Abstract] |
Tuesday, March 17, 2009 8:36AM - 8:48AM |
H14.00004: A simple quantitative model for the reversible association of DNA coated colloids Remi Dreyfus, Mirjam Leunissen, Roujie Shah, Alexei Tkachenko, Nadrian Seeman, David Pine, Paul Chaikin We investigate the reversible association of micrometer-sized colloids coated with complementary single-stranded DNA `sticky ends' as a function of the temperature and the sticky end coverage. We find that even a qualitative description of the dissociation transition curves requires the inclusion of an entropic cost. We develop a simple general model for this cost in terms of the configurational entropy loss due to binding and confinement of the tethered DNA between neighboring particles. With this easy-to-use model, we demonstrate for different kinds of DNA constructs quantitative control over the dissociation temperature and the sharpness of the dissociation curve, both essential properties for complex self-assembly processes. [Preview Abstract] |
Tuesday, March 17, 2009 8:48AM - 9:00AM |
H14.00005: Observation of condensed phases of quasi-planar core-softened colloids Primoz Ziherl, Natan Osterman, Dusan Babic, Igor Poberaj, Jure Dobnikar We experimentally study the condensed phases of repelling core-softened spheres in two dimensions. The dipolar pair repulsion between superparamagnetic spheres trapped in a thin cell is induced by a transverse magnetic field and softened by suitably adjusting the cell thickness. We scan a broad density range and we materialize a large part of the theoretically predicted phases in systems of core-softened particles, including expanded and close-packed hexagonal, square, chain-like, stripe/labyrinthine, and honeycomb phase. Further insight into their structure is provided by Monte Carlo simulations. [Preview Abstract] |
Tuesday, March 17, 2009 9:00AM - 9:12AM |
H14.00006: In situ real time measurement of temperature responsive nanoparticles. Denis Pristinski, Thomas Q. Chastek, Vivek Prabhu, Kalman Migler In this work, we combine dynamic light scattering (DLS) and diffusing wave spectroscopy (DWS) to evaluate the size of temperature responsive nanoparticles over a broad range of concentrations. A fiber optic probe DLS instrument was previously demonstrated to measure nanoparticle solutions at a relatively high concentration. The incorporation of back-scattering DWS further extends the technique application to highly turbid conditions. The combined setup was designed to have a simplified and compact optical arrangement employing singlemode fiber based components. Data analysis for both methods was carried out using integrated open source cross-platform software. Measurements were conducted to monitor the progress of poly(N-isopropyl acrylamide) nanoparticle syntheses, including a multi-step seeded polymerization, commonly used to prepare core-shell particles. These particles have received a lot of attention due to their potential for use as targeted drug delivery systems. It was found that DLS and DWS were in good quantitative agreement, and able to accurately characterize the samples. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:24AM |
H14.00007: Enhanced particle transport in an oscillating sinusoidal optical potential. Weiqiang Mu, Lan Luan, Gang Wang, Gabriel Spalding, John Ketterson We have studied the delivery of a colloidal particle in the presence of an oscillating, spatially periodic, optical potential. The average particle velocity relative to the fluid velocity in this potential depends greatly on the oscillation amplitude and frequency. The results of both our simulations and experiments show that for some combinations of these parameters, the average particle velocity can be enhanced due to the synchronization of the particle movement with the oscillating potential. [Preview Abstract] |
Tuesday, March 17, 2009 9:24AM - 9:36AM |
H14.00008: Charge inversion in monovalent ionic solutions Alex Travesset, Alberto Martin-Molina, Carles Calero, Jordi Faraudo, Manuel Quesada-Perez, Roque Hidalgo-Alvarez We present measurements of the mobility of colloids as a function of the concentration of the monovalent salt Tetraphenyl Arsonium Chloride (TACl). The experiments show a decrease of the mobility with increasing salt concentration that flips sign (charge inversion) at mM salt concentrations. A modified version of the O'Brien and White theory taking into account the hydrophobic nature of the phenyl groups describes the experimental data without fitting parameters. Saturation effects in the mobility as well as possible generalizations are also discussed. [Preview Abstract] |
Tuesday, March 17, 2009 9:36AM - 9:48AM |
H14.00009: Position Control of Particles embedded in Microbeads and Fibers Produced by Electrohydrodynamics. Unyong Jeong, Eun Min Jo, Sungwon Lee, Kyu Tae Kim Electrohydrodynamics is a good approach to produce uniform-sized colloids and fibers in a continuous process. The dimension can be controlled from tens of nanometers to a few micrometers. The structure of the colloids and nanofibers from electrohydrodynamics has been diversified according to the uses. Especially, core-shell structure and hybridization with functional nanomaterials are fascinating due to their possible uses in drug-delivery systems, multifunctional scaffolds, organic/inorganic hybrids with new functions, and highly sensitive gas- or bio-sensors. This talk will present the structural variations by tuning the position of small particles in the colloids and fibers produced from electrohydrodynamics and demonstrate their possible applications. [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:00AM |
H14.00010: Using colloids to model atomic thin film growth Rajesh Ganapathy, Mark Buckley, Itai Cohen We epitaxially grow colloidal thin films by sedimenting micron sized colloidal particles on a microfabricated substrate. The attractive interaction between the colloids, induced by a depletant polymer, leads to the nucleation of islands that grow and coalesce with one another. We use confocal microscopy and particle tracking to study the dynamics of the colloidal particles as they diffuse, aggregate and rearrange configurations during deposition. The saturation island density is estimated as a function of the deposition rate and depletant concentration. We find that our results are in excellent agreement with those obtained from atomic deposition experiments suggesting that our system can be used to model various phenomena that occur in atomic thin film growth. Furthermore, we quantify the Ehrlich-Schwoebel step edge barrier by using holographic optical tweezers to create artificial islands and study the dynamics of colloidal monomers placed on the edge of these islands. Owing to the short-range of the attractive interaction in our system, the origin of the step edge barrier in colloids is strikingly different from atoms. [Preview Abstract] |
Tuesday, March 17, 2009 10:00AM - 10:12AM |
H14.00011: Stochastic Rotational Dynamics Simulations of Nanocolloid Suspensions Jeremy B. Lechman, Matt K. Petersen, Steven J. Plimpton, P. Randall Schunk, Gary S. Grest, Pieter in't Veld The use of nanoparticle suspensions to potentially tailor the functionality of composite devices has broad applicability, but is limited in practice, in part, due to poor understanding of the phenomena at that scale. In order to address this we have implemented a mesoscale fluid technique called Stochastic Rotation Dynamics (SRD). Here, we discuss the use of this method to investigate the behavior of hard sphere like nanocolloids. In particular we will present a direct, ``one-to-one'' comparison of an SRD fluid with an explicit Lennard Jones solvent. For small colloids in this low viscosity fluid no ``telescoping of timescales'' is required for efficiency, which allows us to consider the accuracy of the base numerical scheme without complicating approximations. We present the diffusion and reduced viscosity as a function of volume fraction of colloids and compare to well known results. The efficiency of an SRD simulation relative to an explicit atom simulation is also discussed. [Preview Abstract] |
Tuesday, March 17, 2009 10:12AM - 10:24AM |
H14.00012: Light-induced structure transformation of colloidal nanocrystals by using generalized Ewald-Kornfeld formulation M.J. Zheng, K.L. Chan, K.W. Yu When metallic nanoparticles are brought close together and they are illuminated by laser light, there will be strongly enhanced forces between these particles [1]. If these particles are suspended in a liquid, the force can promote aggregation. As a result, the cluster size can exceed the wavelength of light and retardation effect must be considered. For this sake, we derived a generalized Ewald- Kornfeld summation [2] which is valid for fully retarded electromagnetic interaction. More importantly, we have extended the formula for a many-point basis in a unit cell. We used the formula to study the colloidal nanocrystal formation and transition driven by surface plasmon resonance enhanced forces. Our results are of fundamental importance to the relevant topics in soft matter physics and can be widely applied in the research of light-induced manipulation. \\[3pt] [1] A. S. Zelenina, R. Quidant, M. N. Vesperinas, Opt. Lett. \textbf{32}, 1156 (2007). \\[0pt] [2] C. K. Lo, K. W. Yu, Phys. Rev. E \textbf{64}, 031501 (2001). [Preview Abstract] |
Tuesday, March 17, 2009 10:24AM - 10:36AM |
H14.00013: Universal Nanocolloid Deposition Patterns: Harmonics of a Taylor Cone and Separation of DNA-Hybridized Nanocolloids Xinguang Cheng, Hsueh-Chia Chang With judiciously placed far-field electrodes, harmonics of the Laplace equation are selected near a conducting Taylor cone with discrete polar angles for the field maxima. Charged nanocolloids ejected along the discrete electric field lines of these mode maxima are observed to deposit a universal spectrum of rings on an intersecting plane, with particles of different size occupying different spectral lines due to different residue charge. After an affine transformation, nanocolloids ejected into a microslit and deposited onto one substrate exhibit the same universal line spectra. The size-selective deposition pattern is used to quantify DNA hybridization yield onto oligo-functionalized nanocolloids. [Preview Abstract] |
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