Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session K24: Polymer Nanomaterials II |
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Sponsoring Units: DPOLY Chair: Azar Alizadeh, General Electric Room: Baltimore Convention Center 321 |
Tuesday, March 14, 2006 2:30PM - 3:06PM |
K24.00001: BREAK
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Tuesday, March 14, 2006 3:06PM - 3:18PM |
K24.00002: Cracks and Topological Defects in Nematic Nanotube Gels A.G. Yodh, M.F. Islam, A.M. Alsayed, Z. Dogic, M. Nobili, J. Zhang, Fangfu Ye, T.C. Lubensky We have created [1] and studied [2] lyotropic nematic gels composed of aligned single wall carbon nanotubes (SWNTs) in a crosslinked N-isopropyl acrylamide (NIPA) polymer matrix. These composites are created by dispersing surfactant stabilized SWNTs at low concentration in a solution of NIPA monomer that is then polymerized and crosslinked to form a gel, and then inducing a temperature-dependent volume-compression transition of the NIPA gel. Quantitative measurements of SWNT order parameter reveal a concentration-dependent crossover from isotropic to nematic phases. Due to the coupling of nematic order and elasticity of the polymer matrix, we also observe: (i) undulations and then cusping of the gel sidewalls, (ii) a nematic director that evolves as the gel sidewalls deform, (iii) networks of surface cracks that are orthogonal to the nematic director, and (iv) fissures at the sidewall cusps and associated topological defects that would not form in liquid nematics. This work is supported by grants from NSF (MRSEC DMR 05-20020 and DMR-0505048) and NASA NAG8-2172. References: 1. Islam, Alsayed, Dogic, Zhang, Lubensky, Yodh, PRL \textbf{92}, 088303 (2004). 2. Islam, Nobili, Ye, Lubensky, Yodh, PRL \textbf{95}, 148301 (2005). [Preview Abstract] |
Tuesday, March 14, 2006 3:18PM - 3:30PM |
K24.00003: Composite Polymer Nanofibers with Carbon Nanotubes and Titanium Dioxide Particles with Photocatalytic Activity Shahar Kedem, Yaron Paz, Yachin Cohen Composite nanofibers containing Multi Walled Carbon Nanotubes (MWCNT) and nanometric TiO$_{2}$ particles dispersed in poly(acrylonitrile) (PAN) were prepared by the electrospinning (ES) technique. The fabricated nanofibers, the diameters of which were in the 20-200 nm range, contained well-oriented nanotubes and spherical TiO$_{2}$ nanoparticles in close proximity. The carbon nanotubes stabilize the polymer nanofibers against photodegradation by UV radiation, as compared with nanofibers composed only of PAN and TiO$_{2}$. Preliminary results on the photocatalytic activity of these nanofibers in decomposition of organic molecules will be reported. [Preview Abstract] |
Tuesday, March 14, 2006 3:30PM - 3:42PM |
K24.00004: The Impact of Sample Preparation on Polymer Carbon Nanotube Nanocomposites. Chang-Uk Lee, Mark Dadmun The dispersion of multi-walled carbon nanotubes (MWNTs) in a polymer matrix is a critical parameter that impacts the ability of that MWNT to improve the properties of the polymer matrix. In this study, the impact of the sample preparation process on the dispersion and properties of the resultant nanocomposite is discussed. Additionally, the impact of intermolecular interactions between the MWNT and polymer matrix on the mechanical properties of the polymer nanocomposites was investigated. Polymer nanocomposites composed of 1 wt{\%} MWNT and poly(styrene-co-4-vinyl phenol) (PS-co-VPh) random copolymers were prepared by three different methods, including melt-mixing and solution casting. The MWNT are either oxidized to incorporate oxygenated defects or utilized as received. DMA results suggest that solution casting allows the formation of more intermolecular hydrogen bonding between MWNT and polymers than melt mixing. DMA data also suggests that more intermolecular hydrogen bonding results in improved mechanical properties of the resultant polymer nanocomposites. [Preview Abstract] |
Tuesday, March 14, 2006 3:42PM - 3:54PM |
K24.00005: NMR Characterization of the Interface in Polyurethane/Carbon Nanotube Composites Peter Mirau, Daniel Powers, Jennifer Garber, Hilmar Koerner, Richard Vaia Solid-state proton NMR has been used to investigate the structure and dynamics of shape recovery polymers and composites with carbon nanotubes (CNT’s). The thermoplastic polyurethane (Morthane) has both soft and hard segments. The soft segments are mobile at ambient temperature and give rise to a 2 kHz-wide proton signal. The protons signals shift and broaden with the introduction of CNT’s. The proton spin- lattice and spin-spin relaxation times are relatively insensitive to the presence of CNT, demonstrating that the broadening is a consequence of proximity of the CNT’s rather than a change in the molecular dynamics. The structures of the films in the stretched and relaxed states are probed using proton spin diffusion experiments. The results show the hard segments form 12 nm-sized domains and that the spin diffusion curves are very sensitive to the onset of soft-segment crystallinity as the samples are stretched. The effect of CNT’s on the domain sizes and spacings are also measured in stretched and relaxed films. [Preview Abstract] |
Tuesday, March 14, 2006 3:54PM - 4:06PM |
K24.00006: Single-wall carbon nanotube aerogels M. B. Bryning, M. F. Islam, L. A. Hough, A. G. Yodh Aerogels of single-wall carbon nanotubes (SWNTs) were created by freeze drying and critical point drying of aqueous SWNT gels. The resulting aerogels maintain the strongly-connected three-dimensional SWNT network of the original gel and have density less than 0.1 g/cm3. While these pure SWNT aerogels are self-supporting, reinforcement with small amounts of added polyvinylalcohol (PVA) produces much stronger structures that are easy to handle. Electrical conductivity of order 1 S/cm is observed in the self-supporting aerogels, and similar conductivity can be achieved in PVA-reinforced aerogels through additional processing. The aerogels can be backfilled with polymers such as epoxy to create composite materials that retain the high conductivity of the network. Other potential applications for these structures, such as sensors, actuators, and thermoelectric devices, are currently being explored. This work is supported by grants from NSF (MRSEC DMR05-20020 and DMR-0505048) and NASA NAG8-2172. [Preview Abstract] |
Tuesday, March 14, 2006 4:06PM - 4:18PM |
K24.00007: Polymer crystallization-driven, periodical patterning on carbon nanotubes Lingyu Li, Christopher Li We report herein a unique means to periodically pattern polymers on carbon nanotubes (CNTs) using controlled polymer crystallization method. CNTs were periodically decorated with polymer lamellar crystals, resulting in nano hybrid shish-kebab (NHSK) structures. The periodicity of adjacent kebabs varies from 20 - 150 nm. The kebabs are approximately 5 nm thick (along CNT direction) with a lateral size of $\sim $ 20 nm to micrometers, which can be readily controlled by varying crystallization conditions. Both polyethylene and Nylon 66 were successfully decorated on single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT), as well as vapor grown carbon nanofibers (CNF). The formation mechanism was attributed to ``size dependent soft epitaxy''. NHSK structure was discussed with an emphasis on the periodicity of adjacent kebabs. The influence of experimental parameters on the periodicity was investigated in details Since NHSK formation conditions depend upon CNT structures, it further provides a unique opportunity for CNT separation. The reported method opens a gateway to periodically patterning polymers and different functional groups on individual CNTs in an ordered and controlled manner, an attractive research field that is yet to be explored. [Preview Abstract] |
Tuesday, March 14, 2006 4:18PM - 4:30PM |
K24.00008: Alignment and Alignment Modulation of Single Wall Carbon Nanotubes Using Lyotropic Chromonic Liquid Crystals M. F. Islam, I. I. Smalyukh, O. D. Lavrentovich, A. G. Yodh We report alignment and local alignment modulation of single wall carbon nanotubes (SWNTs) dispersed in a nematic solvent of lyotropic chromonic liquid crystals (LCLCs). Polarized optical absorption suggests that when SWNTs are coated with surfactant molecules, e.g., sodium dodecyl benzene sulfonate (NaDDBS), the SWNTs align along the nematic director of the LCLCs, possibly due to elastic interaction between the anisotropic SWNTs and the nematic field of the LCLCs. In contrast, if the SWNTs are not coated with surfactant, then SWNTs align normal to the LCLC nematic director, possibly due to $\pi-\pi$ interactions between the aromatic groups of the LCLCs and the graphitic surface of SWNTs. We describe these observations and show that SWNTs can easily be realigned via realignment of nematic LCLCs using a magnetic field of only a few KGauss. This work is supported by grants from NSF (MRSEC DMR 05-20020 and DMR-0505048) and NASA NAG8-2172. [Preview Abstract] |
Tuesday, March 14, 2006 4:30PM - 4:42PM |
K24.00009: Theoretical investigation of the atomic and electronic structure of amino acids on Si(100) surfaces Xuan Luo, Gefei Qian, Celeste Sagui, Christopher Roland There are currently considerable efforts underway to combine silicon-based device technology with myriad of organic molecules, thereby fabricating new structures that take advantage of the tunable electronic and optical properties of organic molecules. A key aspect of this integration process is binding of the organics to the silicon surfaces. As part of this effort, we have been investigating the binding of several amino acids -- the building blocks for proteins -- on the Si (100) surface with state-of-the art density functional theory methods. Specifically, the binding between the buckled Si(100) and the NH2, CH2, COOH, C=0 and NC entities at various surface sites have been investigated. We report and discuss on the resulting structures and their electronic properties. [Preview Abstract] |
Tuesday, March 14, 2006 4:42PM - 4:54PM |
K24.00010: Dynamics of poly(ethylene oxide)/Li$^{+}$ complexes confined in 1nm slits Georgios Polizos, Vikram Kuppa, Andreas Sch\"{o}nhals, Evangelos Manias Poly(ethylene oxide) (PEO)/Li$^{+}$ complexes were nanoscopically confined in 1nm slit pores between inorganic solids of controlled Li$^{+}$ charge surface density ({\em cf.} varied cation exchange capacity Li$^{+}$ montmorillonites). The experimental systems were prepared by direct melt intercalation and investigated by dielectric relaxation spectroscopy over broad frequency and temperature ranges. Ionic conductivity/diffusion effects and the interfacial polarization relaxation process (due to the motion of the Li$^{+}$ ions in the slits) are systematically explored and analyzed. We present their dependences on frequency, temperature, Li$^{+}$ surface density, and PEO/Li$^{+}$ interactions. The above results are discussed in the context of previous Molecular Dynamics computer simulations, and mechanisms associated with the existence of water in the slit are thus identified. [Preview Abstract] |
Tuesday, March 14, 2006 4:54PM - 5:06PM |
K24.00011: Development of New Elastomers and Elastic Nanocomposites from Plant Oils Lin Zhu, Richard Wool Economic and environmental concerns lead to the development of new polymers from renewable resources. In this research, new elastomers were synthesized from plant oil based resins. Acrylated oleic methyl ester (AOME), synthesized from high oleic triglycerides, can readily undergo free radical polymerization and form a linear polymer. To achieve the elastic properties, different strategies have been developed to generate an elastic network and control the crosslink density. The elastomers are reinforced by nanoclays. The intercalated state has a network structure similar to thermoplastic elastomers in which the hard segments aggregate to give ordered crystalline domains. The selected organically modified clay and AOME matrix have similar solubility parameters, therefore intercalation of the monomer/polymer into the clay layers occurs and the nano-scale multilayered structure is stable. \textit{In situ} intercalation and solution intercalation were used to prepare the elastic nanocomposites. Dramatic improvement in mechanical properties was observed. Changes of tensile strength, strain, Young's modulus and fracture energy were related to the clay concentration. The fracture surface was studied to further understand clay effects on the mechanical properties. Self-Healing of the intercalated nanobeams, thermal stability, biocompatibility and biodegradability of this new elastomer were also explored. [Preview Abstract] |
Tuesday, March 14, 2006 5:06PM - 5:18PM |
K24.00012: Simulations of Polymer Nanocomposites Thomas Clancy Simulations of polymer nanocomposites were undertaken in order to determine the effect of molecular structure on macroscopic properties. Due to the large amount of interfacial area present in nanostructured materials, the effect of structural details at this interface is influential in the resulting material properties. These simulations focus on variation in molecular structural details at this interface and the effect on the resulting macroscopic properties of the nanocomposite. [Preview Abstract] |
Tuesday, March 14, 2006 5:18PM - 5:30PM |
K24.00013: Characterizing the structural properties of organic-inorganic hybrid semiconductors by first-principles calculations Chang-Youn Moon, Gustavo Dalpian, Yong Zhang, Su-Huai Wei, Xiaoying Huang, Jing Li Recently, a new type of hybrid materials A$_{II}$B$_{VI}$(en)$_ {0.5}$, consisting inorganic II-VI semiconductor slabs connected by organic molecule spacers have been synthesized.[1] These materials have the advantage of possessing both inorganic and organic constituents: good electric and optical properties of the inorganic part, and the easiness of assembly of the organic part.[1,2] In this work, using first principles method, we study the stability and structural properties of A$_{II}$B$_{VI}$(en) $_{0.5}$ (A=Zn or Cd, B=S, Se, or Te, and en=ethylenediamine) in the known $\alpha $ and $\beta $ phases. We found that the relative stability of the $\alpha $ and $\beta $ phases of the hybrids is closely related to the intrinsic stability of the two phases of the inorganic semiconductor constituent: wurtzite (WZ) and zincblende (ZB). An inorganic compound with WZ ground state will prefer to exist in the $\alpha $ phase, whereas a ZB compound will prefer to exist in the $\beta $ phase.The relative stability is also affected by the size of the inorganic constituents and the spacing and bond angle of the en molecules. The results are analyzed by considering the contribution from the organic and inorganic part separately. [1] X. Huang et al., J. Am. Chem. Soc. 122, 8789 (2000); 125, 7049 (2003). [2] B. Fluegel et al., Phys. Rev. B 70, 205308 (2004) [Preview Abstract] |
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