Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session D25: Focus Session: Particle Dynamics and Organization; Polymer Tethers and Interfacial Segregation |
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Sponsoring Units: DPOLY Chair: Francis Starr; Wesleyan University Room: Baltimore Convention Center 322 |
Monday, March 13, 2006 2:30PM - 3:06PM |
D25.00001: Multiscale Simulation Studies of the Self-Association of Poly(ethylene oxide)-Tethered Fullerenes Invited Speaker: I will discuss our multiscale molecular simulation studies of the aggregation of PEO-tethered C-60 fullerenes in water. Our simulations reveal that adjustment of the attachment pattern and molecular weight of the PEO ligands provides exquisite control of the morphology of the self-associating nanostructures formed through a balance of strong fullerene-fullerene attraction, moderately attractive fullerene-PEO interactions and repulsive steric interactions between the PEO ligands. I will also discuss results of our investigations of the influence of external fields (electrical and shear) on the morphology of the self-assembled fullerene nanostructures in bulk aqueous solution as well as results of simulation studies of the self-association of PEO-tethered fullerenes at air-water interfaces. [Preview Abstract] |
Monday, March 13, 2006 3:06PM - 3:18PM |
D25.00002: Polymer Models of Interphase Chromosomes Joshua Martin, Jan\'{e} Kondev, Debra Bressen, James Haber Experiments during interphase, the growth phase of the cell cycle in eukaryotic cells, have shown that parts of chromosomes are tethered to the nuclear periphery[1]. Using a simple polymer model of interphase chromosomes that includes tethering, we compute the probability distribution for the distance between two marked points on the chromosome. These calculations are inspired by recent experiments with two or more fluorescent markers placed along the chromosome[2]. We demonstrate how experiments of this kind, in conjunction with simpe polymer models, can be used to systematically dissect the spatial organization of interphase chromosomes in the nucleus of living cells. This comparison of theory with experiments has lead to the conclusion that the structure of chromosome III in yeast is consistent with a 10nm-fiber model of chromatin. \newline [1]Wallace F. Marshall. Current Biology, 12, 2002. \newline [2] Kerstin Bystricky, Patrick Heun, Lutz Gehlen, J\"{o}rg Langowski and Susan M. Gasser. PNAS, 101(47) 2004 [Preview Abstract] |
Monday, March 13, 2006 3:18PM - 3:30PM |
D25.00003: Dynamics of Adsorption-Desorption of Linear Polymer Chains to Spherical Nanoparticles: A Monte Carlo Investigation Peter J. Dionne, Catalin R. Picu, Rahmi Ozisik Dynamics of attachment/detachment processes of chains to/from spherical fillers in a polymer nanocomposite is investigated by means of numerical simulations using a chemistry-specific model for the polymer. The effects of chain length, chain-to-filler distance, filler radius, and polymer-particle interaction energy on the attachment/detachment processes are studied. It is found that the time a chain is in contact with a filler scales with the number of attached beads as expected from Rouse behavior. A deviation from Rouse behavior is observed at long attachment times where a plateau value in the number of attached beads is observed. This deviation was found to depend on the relative size of the chain and adsorption volume but was not related to entanglement effects. Changing the polymer-particle interaction energy from repulsive to attractive slows down the detachment process. An average characteristic detachment time was calculated as a function of polymer-particle interaction energy that follows an Arrhenius equation, where the activation energy is proportional to the polymer-particle interaction energy. [Preview Abstract] |
Monday, March 13, 2006 3:30PM - 3:42PM |
D25.00004: Manipulating assembly of nanoparticles by polymer tethers Zhenli Zhang, Mark Horsch, Christopher Iacovella, Sharon Glotzer A major challenge in nanoscience and nanotechnology is the ability to control and guide the self-assembly of nano building blocks into target structures in a predictable way. In this talk, we use molecular simulation to show how polymer tethers can be used to manipulate the assembly of nanoparticles into various one-dimensional, two-dimensional, and three-dimensional structures. We present results on the self-assembly of polymer-tethered nanospheres, nanorods, and more exotic shapes, and present temperature versus concentration phase diagrams for the nanosphere and nanorod systems. For polymer-tethered nanorods we predict tetragonally perforated lamellar and honeycomb phases, which have been observed experimentally but have not been predicted by any previous theory. We also predict a new phase---a racemic mixture of hexagonally ordered chiral cylinders that self-assemble from these achiral building blocks. For the system of polymer-tethered nanospheres we predict that in contrast to flexible amphiphiles, the nanospheres are locally ordered and there is an increase in the local ordering with an increase in concentration or relative nanoparticle diameter. [1] Zhang, Mark A. Horsch, Monica H. Lamm, and Sharon C. Glotzer, \textit{Nano Lett.}, 3(10), 1341-1346, 2003. [2] Mark A. Horsch, Zhenli Zhang and Sharon C. Glotzer, \textit{Phys. Rev. Lett.}, 95(5), 056106, 2005. [3] Christopher R. Iacovella, Mark A. Horsch, Zhenli Zhang and Sharon C. Glotzer, \textit{Langmuir}, 21(21), 9488, 2005. [Preview Abstract] |
Monday, March 13, 2006 3:42PM - 3:54PM |
D25.00005: Phase behavior and clustering of nanoparticles with approximate polymer interactions Andrew Rahedi, Francis Starr In nanoparticle polymer composite (NPC) materials, the clustering or dispersion of the nanoparticles strongly influences the material properties. The purpose of this study is to better understand the factors that influence nanoparticle clustering as a step towards developing more efficient simulation approaches. To understand the clustering of nanoparticles in an NPC, we simulate both pure nanoparticles and nanoparticles with approximate polymer interactions and compare our results with simulations that include explicit polymer interactions. We find that pure nanoparticles without polymeric interactions undergo ordinary phase separation. Thus the previously observed lack of nanoparticle phase separation in an NPC is due to interactions with the polymer matrix; this interaction includes short-range attractions due to monomer interactions and long-range repulsions due to the excluded volume of the chains. We approximate this interaction by including a Yukawa potential as a weak long-ranged repulsion acting between nanoparticles. Since the simulation of an NPC is computationally expensive due to the polymer-polymer interactions, this approach improves the efficiency of our simulations and enables us to study the thermodynamic properties over a much broader range of conditions. [Preview Abstract] |
Monday, March 13, 2006 3:54PM - 4:06PM |
D25.00006: Stable Bicontinuous Polymer Blend Films by Jamming Nanoparticles at the Interface Russell J. Composto, Hyun-joong Chung, Kohji Ohno, Takeshi Fukuda Polymer blends containing nanoparticles (NP) are attractive functional material for optoelectronic devices, chemical sensors, and nanoreactors. Because structure governs performances of these devices, a self-regulating, stable structure is highly desirable for many applications. Adding surface-modified silica NP to dPMMA:SAN (50:50) films (550 nm), we demonstrate that directed interfacial segregation of NP stabilize either three dimensional (3D) interpenetrating or 2D discrete structures at high and low volume fractions of NP, respectively. A simple interfacial energy argument provides a general guideline for predicting whether the NP are directed into one phase or to the interface between phases. If NP partition into one phase, the structural evolution slows down, but phase coarsening continues resulting in a roughened film [Europhys. Lett. (2004) \textbf{68}, 219]. However, if NP are driven to the interface between phases, phase coarsening ceases when NP jamming occurs at the interface. The final morphology and domain size can be predicted from the volume fraction of NP, film thickness, and NP size [Nano Lett. (2005) \textbf{5}, 1878]. These studies show that wetting and domain coarsening in polymer blend films can be controlled by the judicial addition of surface modified NP. [Preview Abstract] |
Monday, March 13, 2006 4:06PM - 4:18PM |
D25.00007: Directed self-assembly of nanoscale building blocks through coded bonding potentials Jason J. Benkoski, Ronald L. Jones, Jack F. Douglas, Alamgir Karim Herein we investigate the competition among the forces that drive the assembly of nanoscale building blocks, the results of which lay the groundwork for complex, hierarchichal topologies like those seen in Nature. We observed the self assembly of various nanoscale building blocks at the interface between water and a photocrosslinkable oil (dodecanediol dimethacrylate, DMA). While both liquids have a low viscosity at room temperature, DMA can be flash cured with UV light in the presence of a photoinitiator to produce a solid in less than 1 s. Such crosslinking allows one to obtain a ``snapshot'' of the self-assembly process for particles that segregate to the oil/water interface. Among the particles investigated were 400 nm PMMA latex spheres, 10 nm quantum dots, multi-walled carbon nanotubes, and colloidosomes. Micrographs of each experiment were then captured using either an atomic force microscope (AFM) or light optical microscope (LOM). The agglomerates formed by this process were typically either globular or fractal-like in appearance. By comparing with theory and simulation, we argue that the geometry of the aggregates is coded directly in the particles through the symmetry of the bonding potentials. [Preview Abstract] |
Monday, March 13, 2006 4:18PM - 4:30PM |
D25.00008: Selective trapping nanoparticles on an adaptive, topographic surface Shu Yang, Ying Zhang, Shuhui Qin, John A. Taylor, Joanna Aizenberg Control of interfacial properties, such as wettability, adhesion, and friction, is of great importance for both fundamental science and practical applications. One of the major challenges is how to spatially control the molecular recognition in different regions of surface and interface. Here, we report selective trapping and repelling of particles at different locations of a topographic substrate. It is achieved by tuning surface from highly hydrophobic to superhydrophilic within a narrow temperature window ($=sim$10$^{\circ}$C). A thin layer ($\sim$ 10 nm) of thermoresponsive polymer brushes from poly(N-isopropylacrylamide) (PNIPA) were ``grafted from'' the tips or everywhere on the micropost arrays (1 micron in diameter, 10 micron tall and 1 micron pitch), using surface- initiated atom transfer radical polymerization (ATRP). PNIPA has a lower critical solution temperature (LCST) of 32$^{\circ}$C in water and becomes increasingly hydrophobic when heated from room temperature to 40$^{\circ}$C. Above 40$^{\circ}$C, the surface is highly hydrophobic (contact angle of 120-135 degree) on the microposts, which repels the hydrophilic silica particles. At room temperature, the surface becomes superhydrophilic (contact angle $<$ 10 degrees). The silica particles are found selectively trapped either on the tips, the bottom, or homogeneously along the microposts, depending on the particle size (900 nm vs. 90 nm), type of brushes (single vs. binary brushes), and the grafting location of PNIPA. [Preview Abstract] |
Monday, March 13, 2006 4:30PM - 4:42PM |
D25.00009: Wetting of polymer thin films with nanoparticles Igal Szleifer We theoretically study the ability of nanoparticles to induce wetting of polymer thin films on flat solid surfaces. Our studies show that there is an entropically driven attraction between the nanoparticles and the surface. The strength and range of the attraction depends upon the polymer melt molecular weight and the nanoparticles size. When the nanoparticles are mixed with the polymer melt and the film is put in contact with the surface, a very large number of nanoparticles adsorb on the surface, lowering the surface tension and enabling the wetting of the surface by the polymer melt. If the surface is modified with a grafted polymer layer of the same type as the polymer melt, nanoparticle adsorption on the surface is reduced for intermediate tethered polymers surface coverage. For high grafted surface coverage we predict a large adsorption of nanoparticle on the tip of the brush. As a result we find that nanoparticle induces wetting of polymer thin films on bare surfaces and on surfaces with grafted polymers at high surface coverage. These are the two regimes where experiments have shown that polymer thin films do not wet the surfaces. The predictions of the theory will be put in the context of available experimental observations. [Preview Abstract] |
Monday, March 13, 2006 4:42PM - 4:54PM |
D25.00010: The Effects of Supercritical CO$_{2}$ and Nanoparticles on Metallization of Polymer Thin Films B. Kugler, F. Shaikh, J. Rosengard, R. Holzer, J. Jerome, T. Koga, M. Rafailovich, J. Sokolov Thin films of Poly (methyl methacrylate), Polystyrene (PS), and Ethylene Vinyl Acetate (EVA) were metallized by vapor deposition of chromium (Cr). The surface morphology was analyzed using atomic force microscopy and correlated to the interfacial width between the polymer and metallized layers. The results showed that in all cases exposure of the substrates to supercritical CO$_{2}$ resulted in doubling the interfacial width between the metal and polymer. This was in turn manifested by a reduction of the RMS roughness and surface contact angles. Metallization of films containing nanoparticles was also performed. The results showed that the addition of POSS-PMMA particles dramatically reduced the RMS roughness for PMMA and EVA while increasing it for PS. Addition of Au nanoparticles decreased the roughness for EVA and PS. X-ray reflectivity indicated that the Au nanoparticles segregated to the surface thereby providing a wetting layer for the Cr. A model to explain these effects based or preferential surface segregation of nanoparticles for films exposed to supercritical fluids will be represented. [Preview Abstract] |
Monday, March 13, 2006 4:54PM - 5:06PM |
D25.00011: Optimal Confinement for Internal Polymer Binding Nam-Kyung Lee, Cameron Abrams, Albert Johner Internal binding between specific groups dilute along a polymer chain plays a paramount role in many technological and biological systems. Against common intuition, we show that the interplay between excluded volume correlations and hydrodynamic interactions can produce an optimal confinement where the binding is fastest. Similarly there is an optimal osmotic pressure for the binding rate of a chain immersed in a solution of (non-binding) spectator chains. When internal binding leads to higher order vertices as in self-assembly, confinement can set the same kinetic rate for the formation of several low order vertices. [Preview Abstract] |
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