Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Q19: The Physics of Polymer Nanocomposites: Rheology and Mechanical Properties |
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Sponsoring Units: DPOLY Chair: Francis Starr, Wesleyan University Room: 320 |
Wednesday, March 18, 2009 11:15AM - 11:27AM |
Q19.00001: Influence of Nanoparticles on the Amplitude of Molecular Motions and the Fragility a Model Glass-Forming Polymer Melt. Jack Douglas, Francis Starr We investigate the impact of the addition of nanoparticles on both the fast and slow dynamics of a coarse-grained polymer fluid by molecular dynamics. The fast dynamics is characterized by the Debye-Waller factor (the average mean square particle displacement at a characteristic time in the caged particle motion regime) and the slow structural relaxation is characterized by the coherent intermediate scattering function. Our study explores how both the polymer-particle and nanoparticle volume fraction change the amplitude of the high frequency molecular motions (relative to the pure melt reference condition) and the strength of the temperature dependence of the structural relaxation time (defining the fragility of glass formation, as well as the glass transition temperature). Substantial variations of the Debye-Waller factor are observed and we test the effectiveness of the Buchenau relation linking the Debye-Waller factor to the long time structural relaxation time. We also consider how the presence of nanoparticles in the polymer melt influence the fragility of glass formation, where a range of criteria are utilized to define fragility. Appreciable changes of fragility are observed, these changes being dependent on the nanoparticle concentration and particle-polymer interaction. [Preview Abstract] |
Wednesday, March 18, 2009 11:27AM - 11:39AM |
Q19.00002: Macroscopic dynamics of polystyrene grafted silica nanoparticles in a homopolymer matrix Joseph Moll, Pinar Akcora, Sanat Kumar, Ralph Colby Silica nanoparticles grafted with polymers, dispersed in a homopolymer matrix, and annealed over time adopt a broad range of dispersion states which depend on grafting density, annealing time, weight percent silica, and the molecular weights of the polymers.~ We tuned these variables to give desired dispersion states, from uniformly dispersed particles to agglomerated clusters.~ Rheology was used to critically determine how the dispersion state affects the mechanical reinforcement of the composite.~ We have run both steady shear and small amplitude oscillatory shear experiments on nanocomposites comprising a range of dispersion states. By mapping the observed reinforcement on a morphology diagram, we observe the location of a maximum in reinforcement. [Preview Abstract] |
Wednesday, March 18, 2009 11:39AM - 11:51AM |
Q19.00003: Structure, ion transport and rheology of nanoparticle organic hybrids Haibo Qi, Lynden Archer We report a new class of liquid nanoparticle organic hybrid materials (NOHMs), produced by tethering an organic oligomer corona to the surface of inorganic nanoparticles, and investigate their use as electrolytes. This talk focuses on the structure factor and transport properties of these materials. Specifically, because the suspending solvent is covalently tethered to the NOHMs cores, the structure factor is predicted to vanish in the limit of small q. This behavior arises fundamentally from the presence of a new entropic attraction force produced by the tethered solvent, which constrains separation of the nanoparticle cores. Additionally, we show that NOHMs based on lithium conducting corona provide high ionic conductivities and lithium transfer numbers when doped with lithium salts. The enhanced conductivity is investigated in detail by studying how the core particles affect the melting transition, rheology, and activation energy for ion transport in the corona. [Preview Abstract] |
Wednesday, March 18, 2009 11:51AM - 12:03PM |
Q19.00004: Effect of filler surface properties on stress relaxation behavior of carbon nanofiber/polyurethane nanocomposites I. Sedat Gunes, Guillermo Jimenez, Sadhan Jana The effect of carbon nanofiber (CNF) surface properties on tensile stress relaxation behavior of CNF/polyurethane (PU) nanocomposites was analyzed. PU was synthesized from methylene diisocyanate, polypropylene glycol (PPG diol), and butanediol. CNF, oxidized CNF (ox-CNF), and PPG diol grafted CNF (ol-CNF) were selected as fillers. ol-CNF was obtained by grafting PPG diol onto ox-CNF by reacting it with the carboxyl groups present on ox-CNF surface. The atomic ratios of oxygen to carbon present on the filler surfaces were 0.13 and 0.18 on ox-CNF and on ol-CNF as compared to 0.015 on CNF, mostly due to the presence oxygen containing polar groups on the surfaces of the former. The composites were prepared by in-situ polymerization and melt mixing in a chaotic mixer. The stress relaxation behavior of composites was determined at room temperature after inducing a tensile strain of 100{\%}. The presence of fillers augmented the rate of stress relaxation in composites which was highest in the presence of CNF. The results suggested that relatively weak polymer-filler interactions in composites of CNF promoted higher stress relaxation. [Preview Abstract] |
Wednesday, March 18, 2009 12:03PM - 12:15PM |
Q19.00005: Synthesis of metal-molecule-metal structures for single-molecule transport and spectroscopy measurements Alex Neuhausen, David Goldhaber-Gordon, Chris Chidsey Robust, repeatable metal-molecule contacts are an elusive yet important hurdle in the development of molecular electronic devices. This project explores the chemical synthesis of metal-molecule-metal structures for single-molecule spectroscopy and transport measurements. Conjugated thiol-azide molecules are self-assembled on gold nanoparticles, which are then linked with dialkyne bridge molecules using Sharpless ``click'' reactions. [Preview Abstract] |
Wednesday, March 18, 2009 12:15PM - 12:27PM |
Q19.00006: Impact of Nanofillers on the Durability of Polymeric Coatings and Composites Li-Piin Sung, Stephanie Watson, Aaron Forster, Sheng Lin-Gibson Metal oxide nanoparticles have been incorporated into polymer systems to improve durability performance properties, for example Ultra Violet (UV) degradation and scratch resistance. In this paper, we present recent research results on (1) the effect of particle dispersion and photorectivity of TiO$_{2}$ on the UV degradation of polymeric coatings exposed to high intensity UV radiations at two different humidity conditions; (2) the impact of nano-SiO$_{2}$ concentration on surface mechanical properties (surface morphology and scratch behavior) of polymeric coatings and composites. The physical and chemical degradation of the coatings were monitored in periodic intervals using a combination of laser confocal scanning confocal microscopy (LSCM) and attenuated total reflectance{\-}Fourier transform infrared spectroscopy. An instrumented nanoindentation and LSCM are utilized to measure surface modulus, perform scratch testing, and map scratch damage patterns. A strong impact on the durability performance in both studies was observed in the presence of nanofillers. Particularly in the scratch resistance study, the addition of nanofillers reduces surface roughness and increase scratch resistance of the nanofiller-polymer composites. [Preview Abstract] |
Wednesday, March 18, 2009 12:27PM - 12:39PM |
Q19.00007: The ``Music" of Silica-Poly(methyl methacrylate) Core-Shell Spheres: Eigenvibrations and Mechanical Properties at the Nanoscale Tim Still, Rebecca Sainidou, Goetz Hellmann, George Fytas We report on the measurement of elastic vibrational modes (eigenvibrations) in silica--poly(methyl meth\-acrylate) ($\mathrm{SiO}_2$--PMMA) core-shell spheres and corresponding spherical hollow capsules (PMMA) with different particle size (dia\-meter: 232~nm--405~nm) and shell thickness (25~nm--112~nm) using Brillouin light scattering, supported by numerical calculations.~[T.\ Still et al., Nano Lett.\ \textbf{8}, 3194 (2008)] These localized modes allow to access the mechanical moduli of core and shell material. We observe reduced mechanical strength of the porous silica core and for the core-shell spheres a striking increase of the moduli in both the $\mathrm{SiO}_2$ core and the PMMA shell. The peculiar behavior of the vibrational modes in the hollow capsules is attributed to antagonistic dependence on overall size and layer thickness. The present investigation of the acoustical properties of the individual core-shell particles can lead to the use of such nanoscale engineered particles in more eloborate systems to control hypersonic phonons. [Preview Abstract] |
Wednesday, March 18, 2009 12:39PM - 12:51PM |
Q19.00008: A Microscopic Model for the Reinforcement and the Non Linear Behaviour of Filled Elastomers and Thermoplastic Elastomers (Payne and Mullins Effects) Didier Long, Samy Merabia, Paul Sotta We present a model regarding reinforcement properties of nano- structured polymers. Then, we show how it can be solved numerically by Dissipative Particles Dynamics. The model is based on the presence of glassy layers around the fillers. Strong reinforcement is obtained when these layers overlap. Key is the life-times distribution of these glassy bridges. The latter depend on polymer-filler interaction, the thermo- mechanical history, on the temperature, on the distance between fillers, and on the local stress in the material. Under applied strain, we show how the dynamics of yield and rebirth of glassy bridges account for the non-linear Payne and Mullins effects, which are a large drop of the elastic modulus at intermediate deformations, and a progressive recovery of the initial modulus when the samples are subsequently put at rest, respectively. These mechanisms account also for dissipative properties of filled elastomers. Our model opens the way for predicting mechanical behavior of nano-filled elastomers according to the filler structures and dispersion, polymer- filler interactions and temperature, in order to prepare systems with taylored properties. [Preview Abstract] |
Wednesday, March 18, 2009 12:51PM - 1:03PM |
Q19.00009: Molecular Simulation of Highly Crosslinked Epoxy Resin and POSS-Epoxy Nanocomposites Po-Han Lin, Rajesh Khare Generation of atomistic model structures of crosslinked epoxy at realistic density is a challenging task. In this work, we present an efficient approach for generating such model structures of highly crosslinked matrices. The approach utilizes simulated annealing optimization technique for carrying out one-step polymerization of the reaction mixture in the simulation box. The structures so generated are relaxed using a combination of molecular mechanics and molecular dynamics (MD) simulations. The developed technique is computationally efficient and has been used for creating atomistic model structures of both crosslinked epoxy and a nanocomposite formed by the incorporation of the polyhedral oligomeric silsesquioxane (POSS) molecules in the crosslinked epoxy matrix. MD simulations are used to determine the volume-temperature behavior of these structures. The density and the glass transition temperature of the simulated structures are compared with the literature experimental data. Furthermore, the molecular packing behavior of the POSS-epoxy nanocomposite is compared with the molecular packing in the crosslinked epoxy matrix. [Preview Abstract] |
Wednesday, March 18, 2009 1:03PM - 1:15PM |
Q19.00010: Reducing Strain in Electrophoretically Deposited Nanocrystal Films by Post-Deposition Incorporation of Polymers Theodore Kramer, Steffen Jockusch, Michael Steigerwald, Nicholas Turro, Irving Herman We have made dense nanoparticle-polymer films and investigated their mechanical properties using nano-indentation and other methods. Electrophoretically deposited (EPD) films of cadmium selenide nanocrystals were infiltrated with network-forming monomers and subsequently exposed to UV radiation in the presence of photoinitiators to facilitate polymerization of the monomer. This hybrid material exhibits the desirable photoluminecent properties of CdSe nanocrystals but does not fracture, as do thick electrphoretically grown nanoparticle films. This may be the result of effectively reducing strain in the films via void filling. The mechanical properties of these films differ from those of EPD films without the introduction of polymer, as seen by nanoindentation studies. These films offer the benefit of high particle density, as well as large film thickness ($>$ 2 micron), and may have useful applications in the area of flexible photovoltaic devices. [Preview Abstract] |
Wednesday, March 18, 2009 1:15PM - 1:27PM |
Q19.00011: Mechanics of nanoscale composite films from stress-electrical measurements: A nanoscale foam Chieu Nguyen, Vivek Maheshwari, Ravi Saraf Nanometer thin ($>$ 100nm) composite films consisting of polymers and organic-inorganic materials such as nanoparticles, quantum dots, nanotubes and dyes are widely researched for applications in designing a bio-mimetic cell membrane, solar cells, electronic and optical sensors, ion separation membranes and coatings. Being nanoscale in dimensions the mechanical properties of the film is critically governed by its morphology at nanoscale and the mutual interaction between the constituents of the film. The assembly process and the components of the film are detrimental in defining its morphology. A vast array of film morphologies is possible due to the multitude of combinations in processing and the components available to make the film. The study of mechanical properties of the film is hence important due their application in multitude of fields and correlating it to the nanoscale morphology and properties of its constituents. Here we present the stress-electrical measurements on a nanoscale ($\sim $100nm) nanocomposite film prepared using the well known spin assisted ionic self-assembly process. The film is a stack of nanoparticle layers, spaced by dielectric layer. Each dielectric layer consists of a stack of alternating anionic and cationic polyelectrolyte layers. The separation between the nanoparticle layers can be controlled with nanometer scale precession by modulating the number of polyelectrolyte layers in each dielectric layer. [Preview Abstract] |
Wednesday, March 18, 2009 1:27PM - 1:39PM |
Q19.00012: Local dielectric permittivity profiles of sapphire/polypropylene interfaces Liping Yu, V. Ranjan, M. Buongiorno Nardelli, J. Bernholc Recently, the need for high-power-density capacitors has stimulated research to develop composite dielectric materials with high-k nanoparticles embedded in a polymer matrix. In these materials, surfaces and interfaces may play an important role in determining the overall dielectric properties. We present first-principles investigations of the dielectric permittivity profiles across slabs and interfaces of sapphire($\alpha$-Al$_2$O$_3$)/isotactic-polypropylene(iPP). Our results indicate that the permittivity profile at interface strongly depends on the nanoscale averaging procedure. We propose an averaging model that ensures near-locality of the dielectric function. We find that: (i) the dielectric permittivity approaches the corresponding bulk value just a few atomic layers away from the interface or surface; (ii) the dielectric constant is enhanced at the surfaces of the isolated $\alpha$-Al$_2$O$_3$ slabs, while no enhancement is observed at the iPP slab surfaces; and (iii) the dielectric transition at the $\alpha$Al$_2$O$_3$/iPP is mainly confined in the $\alpha$Al$_2$O$_3$ side. [Preview Abstract] |
Wednesday, March 18, 2009 1:39PM - 1:51PM |
Q19.00013: Flow induced orientation behavior of concentrated dispersions of multi-wall carbon nanotube suspensions under shear flow: Effect of aspect ratio and concentration Saswati Pujari, Wesley Burghardt, Sameer Rahatekar, Jeffrey Gilman, Krzysztof Koziol, Alan Windle We report studies of average orientation state of concentrated dispersions of multi-walled carbon nanotube (MWNTs) in steady shear flow. Uncured epoxy was used as a viscous, Newtonian suspending medium, and samples were prepared from 'aligned' MWNTs using methods previously reported (Rahatekar et al., J Rheol 40:599, 2006). Flow induced structural measurements were made in the vorticity (1-3) plane of simple shear flow using in- situ wide angle x-ray scattering techniques in a rotating disc shear cell. Azimuthally-dependent diffraction from the internal layered structure of the MWNTs was used to characterize aligment. Steady state anisotropy of MWNT dispersions decrease with increasing the length of the MWNTs. Surprisingly, the anisotropy is seen to increase with increasing concentration. For one of the samples, more detailed orientation dynamics are studied in steady shear and transient shear flow both in the 1-2 (flow gradient) and 1-3 (vorticity) planes of shear flow, and through comparison of wide-angle and small-angle scattering signatures of flow-induced nanotube alignment. [Preview Abstract] |
Wednesday, March 18, 2009 1:51PM - 2:03PM |
Q19.00014: Polymorphism in electrospun poly(vinylidene fluoride)/nanoclay composite nanofibers Lei Yu, Peggy Cebe We investigated the morphology and polymorphism behavior of electrospun (ES) composite nanofibers of poly(vinylidene fluoride) (PVDF) with two nanoclays: Lucentite$^{TM}$ STN and SWN. Lucentite$^{TM}$ STN and SWN synthetic nanoclays are based on hectrite structure, but only STN contains an organic modifier between the hectrite layers. The PVDF was dissolved, and nanoclay was dispersed, in N,N-dimethylformamide/acetone and then electrospun into nanofibers with diameters ranging from 100$\sim $1000 nm. The nanoclay content ranged from 0.2{\%} to 10{\%}. The addition of STN can greatly decrease the number of beads and makes the diameter of the ES nanofibers more uniform due to an increase of solution conductivity. From wide angle X-ray scattering and Fourier transform infrared spectroscopy, we found both STN and SWN can induce more beta phase PVDF crystals and TTT conformers, while reducing the alpha phase crystal content in ES PVDF/nanoclay composite nanofibers. STN can completely eliminate the alpha phase crystals, even at low STN content. The ionic organic modifier makes STN much more effective than SWN in promoting beta phase PVDF crystals. [Preview Abstract] |
Wednesday, March 18, 2009 2:03PM - 2:15PM |
Q19.00015: Polymer/inorganic nanocomposites with prescribed morphologies E. Manias, M.J. Heidecker, J. Zhang, G. Polizos Despite the proliferation of polymer/inorganic nanocomposites in academic research and the commercialization of tens of products based on such materials, their true potential still remains largely untapped. One of the major hurdles in this endeavor is to capitalize on the novel properties afforded by a true--'nano'morphology, {\it i.e.}, beyond simple nanoparticulate dispersions and towards prescribed filler/phase arrangements and tailored filler--polymer interfaces. We comparatively present nanocomposites with prescribed {\it nano}morphologies, which can be made in large, industrial-scale, quantities (e.g. composites with spatially arranged fillers: such as shear--aligned fillers in blown PE films and filler-induced compatibilization of PC/PET blends). We discuss the fundamental mechanisms of achieving the prescribed {\it nano}morphologies and the related novel functionalities. In particular, we emphasize on extraordinary properties achieved by simultaneous control of the composite morphology and of the polymer--filler interface, such as an impressive toughening effectin PC/PET nanocomposites, and PE nanocomposites with a predetermined tensile strength by tailoring the polymer--filer interfacial adhesion. [Preview Abstract] |
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