Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session V19: Focus Session: Polymer-Nanoparticle Interactions II |
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Sponsoring Units: DPOLY Chair: Chris Ellison, University of Texas at Austin Room: B118-B119 |
Thursday, March 18, 2010 8:00AM - 8:36AM |
V19.00001: The Effects of Thin Films and Confinement on Nanopattering Invited Speaker: There is an extensive body of literature on the effects of thin film confinement on the glass transition and dynamics of polymeric materials. Most of this literature focuses on identifying the fundamental ways in which the properties of a polymer are altered when it is confined in a film whose thickness approaches the natural dimensions of the macromolecule. In this presentation we look at the practical example of nanoimprint lithography (NIL) where the polymer thin film is squeezed into the nanoscale cavity of an imprint mold. We correlate incoherent neutron scattering measurements on thin polystyrene (PS) films with the resistance of the material to flow or create patterns during imprint process. As the PS film thickness drops strongly below 50 nm, the neutron scattering reveals a strong suppression of the mean-square atomic displacements (MSD) on the PS chains. Attempts to NIL pattern PS films of similar thickness at temperatures moderately above the glass transition temperature of the bulk material show a resistance to flow or create patterns that depends on the magnitude MSD suppression. Only when the thin films are heated to a high enough temperature for the dynamics in the MSD to sufficiently recover can patterns be realized. This resistance to flow is also encountered after imprinting, when the patterns are heated to temperatures slightly above their bulk Tg. The decay of the pattern back into underlying residual layer is hindered when residual layer thickness is also below approximately 50 nm. These measurements collectively suggest that viscous flow is hindered in thin polymer films. The possible origins of this response are discussed in detail. [Preview Abstract] |
Thursday, March 18, 2010 8:36AM - 8:48AM |
V19.00002: A SAXS study of the impregnation of pH-responsive polymeric microgels with metal nanoparticles S.H. Anastasiadis, E. Pavlopoulou, M. Vamvakaki, K.E. Christodoulakis, G. Portale, W. Bras We follow the synthesis of metal nanoparticles within poly(2- (diethylamino)ethyl methacrylate), PDEA, microgels by SAXS. Colloidal Pt nanocrystals are formed within the microgels by the incorporation of the appropriate metal precursor, i.e., $H_ {2}PtCl_{6}$, followed by metal reduction. We report the structural study of these systems by SAXS during the three steps of the metal nanoparticle synthesis: the original dispersions in water, the metal-loaded polymer matrices and the metal-nanoparticle-containing microgels after reduction. The scattering profiles of the pure microgel dispersions exhibit two contributions; a Porod-like wavevector q contribution arising from the water/microgel interface and a power law fractal contribution due to the microgel network. Both the Porod and the power-law scattering are still evident after metal incorporation, while the shoulder appearing at higher q's can be attributed to the formation of domains of higher scattering intensity due to the aggregation of the ion- neutralized hydrophobic polymer within the microgels. After metal reduction, Pt nanoparticles are formed with sizes of around 1.5 nm in diameter. Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU. [Preview Abstract] |
Thursday, March 18, 2010 8:48AM - 9:00AM |
V19.00003: Assembly of Conjugated Polymers- Gold Nanoparticles Naresh Osti, Thusitha Etampawala, Dilru Ratnaweera, Uwe Bunz, Vincent Rotello, Dvora Perahia The formation of hydrophilic modified \textit{disubstituted} \textit{para-polyphenyleneethylene} (PPE) nanoparticles (NP) complexes in aqueous media and their assemblies have been investigated. Both PPEs and gold NPs are electro-optically active. Controlling their association would allow formation of electro-optical tunable responsive materials. Small Angle Neutron Scattering (SANS) in conjunction with Atomic Force Microscopy (AFM) has been used to characterize the structures of the complexes formed. SANS studies have shown that spherical core shell NP-P complexes are formed in dilute solutions, with the gold NPs surrounded by almost fully stretched out PPE chains. With increasing the concentration of the NP-PPE complex in solution chains which consist of the basic core-shell aggregated are observed. These NP-PPE complexes were allowed to assemble at a solid surface. While the basic building block, observed by AFM, remains spherical, they assemble in different ways from random 2-d arrays to cable like structures, depending on the interaction of the NP with the PPEs and the nature of the PPE side chains. [Preview Abstract] |
Thursday, March 18, 2010 9:00AM - 9:12AM |
V19.00004: A Systematic Study of Noncovalent Interactions Between Polymers and Carbon Nanotubes via Molecular Dynamics Simulations Melissa Pasquinelli, Syamal Tallury Molecular dynamics simulations were used to study the noncovalent interactions between a zig-zag single-walled carbon nanotube (SWCNT) and polymer chains with varying degrees of saturation, aromaticity, and aliphaticity. The simulations indicate that polymers with both flexible and rigid backbones tend to wrap around the SWCNT, although in different conformations. Flexible backbones wrap in random conformations, which are dependent upon the aliphatic lengths along the backbone and the presence of chemical groups like carbonyls. Polymers with unsaturation along the backbones tend to have more distinct wrapping conformations, as did polyamides with large alkane portions in the monomer unit such as nylon-12. Polymers with bulky and aromatic side groups such as polymethylmethacrylate (PMMA) and polystyrene (PS) prefer intrachain interactions rather than wrap the SWCNT, although PS showed some pi-pi interactions with the SWCNT. Other trends and the correlation of the physical chemical features to the properties of nanocomposites will be discussed. [Preview Abstract] |
Thursday, March 18, 2010 9:12AM - 9:24AM |
V19.00005: Tunable Dispersion of Carbon Nanotubes in Water using pH-Responsive Polymers Krishna Etika, Michael Cox, Jaime Grunlan In an effort to control the level of carbon nanotube exfoliation in water, pH-responsive polymers (i.e, weak polyelectrolytes) have been used as stabilizers in water. This noncovalent functionalization of single-walled carbon nanotubes (SWNTs) results in suspensions whose dispersion state can be altered by simply changing pH. In this study poly(acrylic acid), poly(methacrylic acid), poly(allylamine) and polyethleneimine were used to stabilize aqueous SWNT suspensions. The results indicate that SWNTs stabilized with these polymers show a pH tailorable exfoliation and bundling in water, as evidenced by cryo-TEM images and shifts in suspension viscosity. Composite films prepared by drying these aqueous suspensions suggest that nanotube microstructure in the liquid state is largely preserved in solid composites, with more bundled/networked structures showing higher electrical conductivity. A stabilization mechanism based upon the results obtained is proposed to explain the exfoliation and aggregation behavior of SWNTs. This method of controlling the microstructure of SWNTs in liquid state with pH could have a significant impact on the ability to tailor the microstructure and properties of composites. [Preview Abstract] |
Thursday, March 18, 2010 9:24AM - 9:36AM |
V19.00006: The conformation of Pluronic{\textregistered} block copolymers adsorbed on carbon nanotubes and their interaction with water studied by small-angle neutron scattering Yachin Cohen, Meirav Granite, Wim Pyckhout-Hintzen, Aurel Radulescu Amphiphilic block copolymers are particularly useful in dispersing single-walled carbon nanotubes (SWCNT) in water. Small-angle neutron scattering measurements conducted at different D$_{2}$O/H$_{2}$O content of the dispersing medium provide quantitative information on the adsorption density and conformation of the polymer interacting with the nanotube surface. Data is presented on Pluronic{\textregistered} F108 - (EO)$_{132}$(PO)$_{50}$(EO)$_{132}$ and F127 (EO)$_{100}$(PO)$_{65}$(EO)$_{100}$, where EO-ethylene oxide and PO-propylene oxide, well below the critical micellization temperature of the polymer. A dense coating of the PPO blocks on the nanotube surface is determined with the PEO chains extended from the cylindrical core-shell structure. The data from the two Pluronic systems show minimal scattering at about 70{\%} D$_{2}$O in the dispersing water, which exhibit a $q ^{-1}$ power law of the scattering vector ($q )$. This indicates near matching of the polymer chains at a surprisingly high scattering length density. The model fit required considerations of tight association of water molecules around PEO chains and slight isotopic selectivity. [Preview Abstract] |
Thursday, March 18, 2010 9:36AM - 9:48AM |
V19.00007: Localized, plasmon-mediated heating from embedded nanoparticles in nanocomposites Somsubhra Maity, Lori Downen, Jason Bochinski, Laura Clarke Metallic nanoparticles exhibit a surface plasmon resonance which, when excited with visible light, results in a dramatic increase in the nanoparticle temperature. Previously such localized heating has been primarily employed in biomedical research and other experiments involving aqueous environments. In this work, we investigated use of the nanoparticles in solid phase to re-shape, bond, melt, and otherwise process nanofibrous mats of $\sim $200 nm diameter nanofibers doped with $\sim $80 nm spherical gold nanoparticles. Under low light intensities (100 mW/cm$^{2}$ @ 532 nm) and dilute nanoparticle loading ($\sim $0.15{\%} volume fraction), irradiation of a few minutes melted nanofibrous mats of poly (ethylene oxide) (T$_{m}$ = 65 degree C). Control samples without gold nanoparticles displayed no melting. Because the heat is generated from within the material and only at the nanoparticle locations, this technique enables true nanoprocessing -- the non-contact, controlled application of heat at specific nano-sized locations within a material to effect desired local changes. Funded by CMMI-0829379. [Preview Abstract] |
Thursday, March 18, 2010 9:48AM - 10:00AM |
V19.00008: The Morphology of Silver Layers on SU8 polymers prepared by Electroless Deposition Aniruddha Dutta, Biao Yuan, Helge Heinrich, Chris Grabill, Henry Williams, Stephen Kuebler, Aniket Bhattacharya Silver was deposited onto the functionalized surface of polymeric SU-8 where gold nanoparticles (Au-NPs) act as nucleation sites using electroless metallization chemistry. Here we report on the evolution of the nanoscale morphology of deposited Ag studied by Transmission Electron Microscopy (TEM). In TEM of sample cross sections correlations between the original gold and the silver nanoparticles were obtained while plan-view TEM results showed the distribution of nanoparticles on the surface. Scanning TEM with a high-angle annular dark field detector was used to obtain atomic number contrast. The morphology of the deposited Ag was controlled through the presence and absence of gum Arabic. The thickness and height fluctuations of the Ag layer were determined as a function of time and a statistical analysis of the growth process was conducted for the initial deposition periods. [Preview Abstract] |
Thursday, March 18, 2010 10:00AM - 10:12AM |
V19.00009: Semi Fluorinated Polymers Mediated Nanoparticle Assemblies Dilru Ratnaweera, Umesh Shrestha, Dennis W. Smith Jr., Dvora Perahia, Scott T. Iacono , Joseph Mabry Thin films of semifluorinated (SF) polymer-mediated nanoparticle (NP) assemblies have been investigated using neutron reflectometry. The inherent incompatibility between fluorinated (F) and protonated (H) domains within SF polymers coupled with modification of the surface of the NPs offer a means to control the interactions between the polymer and the NP and drive the structure and dynamics of the composite films. A random copolymer, Biphenyl Perfluorocyclobutane, has been used as the host for POSS (Polyhedral Oligomeric Silsesquioxanes) NPs whose surfaces were modified by either F or H side chains. Films of NPs, tethered to the polymer chains or blended, were spin cast from a mutual solvent, resulting in an initial homogenous distribution of the particles. With annealing as layering of the polymer takes place, the NPs have migrated to the F/H interfacial regions, with a distinct preference of the F-POSS to segregate into the F regions. Both tethers and blended NPs migrated to the film interfaces with the air interface enriched by the F one and the solid interface by the H one. The degree of enrichment of the interfaces was larger for the free NPs compared to tethered ones. [Preview Abstract] |
Thursday, March 18, 2010 10:12AM - 10:24AM |
V19.00010: Experimental Characterization and Modeling of the Non-linear Mechanical behavior of a Carbon Black Filled SBR Grigori Medvedev, Aparajita Bhattacharya, James Caruthers Filled elastomers exhibit a number of peculiar features generally referred to as Mullins effect that include (i) large stress-softening (i.e. lower stress required to pull the sample to the same strain in second pull as compared to the first one), (ii) a dramatic drop in stress at the loading reversal point during the first cycle and, (iii) complete recovery of the virgin sample-like behavior when strain in second pull exceeds the previous maximum strain. Developing a constitutive model to describe these effects has proven a major challenge. One important reason for this, rectified by the present report, has been a dearth of experimental data performed on a well-characterized system where the potentially relevant parameters (temperature, deformation rate as well as the particulate loading, dispersion, particle size, surface area, and structure of carbon black) are systematically varied. We argue that the ``damage'' picture, which has been the only explanation for Mullins effect advanced in the literature, is inconsistent with the experimentally observed behavior. [Preview Abstract] |
Thursday, March 18, 2010 10:24AM - 10:36AM |
V19.00011: Balancing Size Exclusion and Adsorption of Methacrylate Polymers in Nanoporous Silica Asem Abdulahad, Sekyung Lee, Taihyun Chang, Chang Ryu Liquid chromatography at the critical condition (LCCC) is a high performance liquid chromatography (HPLC) technique that lies between size exclusion chromatography (SEC) and adsorption-based interaction chromatography (IC) where the elution of polymers becomes independent of polymer molecular weight. At LCCC, the balance between the entropic exclusion and the enthalpic adsorption interactions between polymers and stationary phases results in the simultaneous elution of polymers regardless of molecular weight. Using C18-bonded silica chromatographic columns we demonstrate the LCCC elution of a series of methacrylate polymers and discuss how the alkyl side groups in methacrylate polymers affects the adsorption of polymer chains against the size exclusion in nanopores. [Preview Abstract] |
Thursday, March 18, 2010 10:36AM - 10:48AM |
V19.00012: Radiation Effects on Polypropylene Carbon Nanofibers John Hamilton, Thomas Mion, Alin C. Chipara, Elamin I. Ibrahim, Karen Lozano, Magdalena Chipara, Steven C. Tidrow, Mircea Chipara Dispersion of carbon nanostructures within polymeric matrices affects most physical and chemical properties of the polymeric matrix (increased Young modulus, improved thermal stability, faster crystallization rates, higher equilibrium degree of crystallinity, modified glass, melting, and crystallization temperatures, enhanced thermal and electrical conductivity). Such changes have been reported and explained by thorough spectroscopic investigations. Nevertheless, little is known about the radiation stability of such nanocomposites. The research is focused on spectroscopic investigations of radiation-induced modifications in isotactic polypropylene (iPP)-vapor grown nanofiber (VGCNF)composites. VGCNF were dispersed within iPP by extrusion at 180$^{\circ}$C. Composites containing various amounts of VGCNFs ranging from 0 to 20 {\%} wt. were prepared and subjected to gamma irradiation, at room temperature, at various integral doses (10 MGy, 20 MGy, and 30 MGy). Raman spectroscopy, ATR, and WAXS were used to assess the radiation-induced modifications in these nanocomposites. Acknowledgements: This research was supported by the Welch Foundation (Department of Chemistry at UTPA) and by US Army Research Office (AMSRD-ARL-RO-SI: 54498-MS-ISP). [Preview Abstract] |
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