Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L44: Surfaces, Interfaces, and Polymer Thin Films II |
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Sponsoring Units: DPOLY Chair: Russell Thompson, University of Waterloo Room: A309 |
Tuesday, March 22, 2011 2:30PM - 3:06PM |
L44.00001: Dillon Medal Break |
Tuesday, March 22, 2011 3:06PM - 3:18PM |
L44.00002: Confinement and elastic modulus in polymer nanofibers Eyal Zussman, Michael Burman, Arkadii Arinstein Size-dependant behavior is considered in electrospun polymer nanofibers. Experimental results unambiguously show that the abrupt increase in the elastic modulus of polymer nanofibers, below a cross-over diameter, relative to the bulk could not be attributed to surface energy effect. Polyamide (\textit{Nylon-6.6}) nanofibers were tested by using either bending or tensile deformation modes (the surface energy affects the effective modulus only in the case of bending, and has no effect in the case of tensile deformation). It turns out that the obtained experimental data cannot be explained by the influence of surface energy upon the elastic modulus either qualitatively or quantitatively. This fact supports the explanation which is based on the geometrical confinement of the supermolecular structures of nano-objects. [Preview Abstract] |
Tuesday, March 22, 2011 3:18PM - 3:30PM |
L44.00003: Size-dependent behavior of electrospun polymer nanofibers under small deformation Arkadii Arinstein, Eyal Zussman A model describing a mechanism resulting in size-dependent behavior of electrospun polymer nanofibers under small deformation is proposed. According this model, the polymer matrix of the nanofibers consists of correlated groups of chains/subchains, partially orientated along the fiber. These supermolecular structures which were formed during electrospinning are confined by the fiber boundary. Thus, when the fiber elongates under external force the relative rotations of these correlated regions are hindered. As a result the elastic modulus depends on the diameter of the deformed fiber. In case of small fiber diameters this restriction is dominant while this effect decreases with increase of fiber diameter, and tends to zero for large fiber diameters according to square-law which was verified by experimental observations. [Preview Abstract] |
Tuesday, March 22, 2011 3:30PM - 3:42PM |
L44.00004: ABSTRACT WITHDRAWN |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L44.00005: Ionic conduction at liquid-liquid interfaces Francisco Solis, Monica Olvera de la Cruz In coexisting liquid phases with different dielectric constants, ionic species do not have, in general, uniform concentrations. Salt ions accumulate predominately in the liquid with higher dielectric constant. Furthermore, excess accumulation and depletion of ions appears at the interface between the liquids, In this presentation we explore the effects of these non-uniform ionic distributions in the AC conductivity of the liquid mixture. We describe in detail the frequency dependence of of the conductivity for each of the ionic components. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L44.00006: Vapor-Phase Free Radical Polymerization in the Presence of Ionic Liquids Malancha Gupta Ionic liquids (ILs) have recently attracted significant interest as an environmentally-friendly alternative to traditional volatile organic solvents because ILs are non-volatile, non-flammable, and can be easily recycled. ILs can be exploited in many ways to improve the selectivity and kinetics of chemical reactions, including polymer synthesis. Ionic liquids have negligible vapor pressure and are therefore stable under vacuum. A few studies have investigated ILs as substrates in inorganic vacuum deposition processes, but to our knowledge ILs have not been used in vapor phase polymerization systems. We have recently introduced ionic liquids into the initiated chemical vapor deposition (iCVD) process for the first time. The iCVD polymerization process occurs via a free-radical mechanism, and the deposited polymeric films are compositionally analogous to solution-phase polymers. Despite the wide range of polymers that have been synthesized using iCVD, it has proven difficult to polymerize monomers with low surface concentrations such as styrene and low propagation rates such as methyl methacrylate and it is difficult to produce block copolymers. In this talk, we will show that our novel ILiCVD system can address some of these shortcomings. We will explain the effects of deposition time, temperature, and monomer solubility on the morphology of the polymer and the molecular weight of the polymer chains. [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L44.00007: Molecular orientation and photo-degradation of PTCDA films on TiO$_{2}$(110) Orhan Kizilkaya, Eizi Morikawa, Phillip Sprunger The molecular orientation and photo-degradation process of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) films on TiO$_{2}$(110) were investigated by near edge X-ray absorption spectroscopy (NEXAFS). As the incidence angle of p-polarized synchrotron light with respect to the substrate surface normal increases, the intensity of the $\sigma $* resonances diminishes and the $\pi $* resonances is greatly enhanced. This finding indicates that the molecular orientation of the PTCDA film is flat on the TiO$_{2}$(110) surface. NEXAFS results of pristine and photo-degraded PTCDA films exposed to synchrotron white light at the VLSPGM beamline of CAMD revealed the photo-degradation mechanism. We found that the intensity of $\sigma $* states diminishes and the intensity of $\pi $* states of increases upon the PTCDA film exposed to white light for 30 minutes. [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:30PM |
L44.00008: Functionalization dependence of the electron beam sensitivity of bridged calix[6]arenes Gregory Spencer, Daniel Ralls, Anup Bandyopadhyay, Michael Blanda Calixarenes have long been studied as a class of high resolution, negative electron beam resists. Previous work has shown the sensitivity can be improved by adding functional groups to the monomer's molecular rim to allow for a more efficient cross-linking mechanism. However, all previous studies dealt with either unfunctionalized resists or monomers that were fully functionalized. In this study, the number of attached functional groups was deliberately varied to directly observe its effect on sensitivity. A bridged calix[6]arene monomer was used as the basic structure. The number of these attached allyl groups ranged from 0 to 8 in steps of 2 per separate synthesis. The bridging units were xylenyl groups which produced both a cone conformer and a 1-2-3-alternate conformer. Resists were formed using all nine different calix[6]arenes and each was subjected to testing. Contrast curves for the cone and alternate conformers were measured by AFM. Resist sensitivities were found as a function of the number of attached groups. The sensitivity was found to be a strong function of the number of attached groups. These results will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 4:30PM - 4:42PM |
L44.00009: Surface Segregation of Small Macrocyclic Shih-Fan Wang, Xiaopeng Li, Renfeng Hu, Bulent Akgun, Rebecca Agapov, Chrys Wesdemiotis, David T. Wu, Mark D. Foster Surface segregation of the thin film blends containing 20wt{\%} 2k macrocyclic polystyrene were studied using surface MALDI-ToF mass spectrometry (MS), time of flight secondary ion mass spectrometry (ToF-SIMS), and neutron reflectometry (NR). To provide contrast between the species for these techniques, the linear polymer in the blend was deuterated. MALDI-ToF MS results show that the 2k macrocyclic chains are depleted from the surface after a film of an isotopic macrocylic/linear blend (h-CPS2K/ d-LPS2K) is annealed at 125$^{\circ}$C for 12hrs. The surface concentration of CPS is less than 1wt{\%}, while the surface concentration of the hydrogenous component in an analogous h-LPS2K/ d-LPS2K film is 20wt{\%} after annealing. The isotopic effect is not significant for the 2k blends and the architecture effect determines the surface segregation. ToF-SIMS and NR results corroborate this view. [Preview Abstract] |
Tuesday, March 22, 2011 4:42PM - 4:54PM |
L44.00010: Structure Formation and Transition Mechanism in Two-Dimensional Molecular Chiral Phases Ye-liang Wang, Bing Yang, Nan Jiang, Huan-yao Cun, Shi-xuan Du, Yue Wang, Karl-Heinz Enrst, Hong-jun Gao The self-assemble behavior of prochiral species, QA16C molecules, on a Au(111) surface and the induced chirality by 2D confinement on solid surfaces as well as its chiral transferring process will be presented in this presentation. Initial stages of a chiral phase transition in the monolayer of QA16C molecules on the Au(111) surface were investigated by scanning tunneling microscopy (STM) at submolecular resolution. The prochiral molecules form a homochiral lamella phase at low coverages upon adsorption. A transition to a racemate lattice is observed with increasing coverage. Enantiomers of a homochiral lamella line become specifically substituted by opposite enantiomers such that a heterochiral structure evolves. To explain this phenomenon, we propose a ``chiral replacement'' model: enantiomers replace QA molecules in enantiopure phase, leading to racemic one. Our findings are significant for the understanding and control of chiral phase transitions in related molecular systems like liquid crystals. [Preview Abstract] |
Tuesday, March 22, 2011 4:54PM - 5:06PM |
L44.00011: Formation and Collapse of Biodegradable Polymer Monolayers at the Air-Water Interface Hae-Woong Park, Kimberly Ohn, You-Yeon Won Poly(lactide-\textit{ran}-glycolide) (PLGA) is widely used as an excipient in formulations of aerosol drugs. It has recently been reported that the surface pressure-area isotherm of PLGA at the air-water interface shows a plateau at intermediate compression levels and a sharp rise in pressure upon further compression. In order to investigate the molecular origin of this behavior, we have conducted an extensive set of surface pressure and AFM imaging measurements with PLGA materials having a range of different molecular weights. The results suggest that (1) the plateau occurs due to the formation (and collapse) of a continuous water-free monolayer of the polymer under continuous compression, and (2) the monolayer becomes significantly resistant to compression at high compression because at that condition the collapsed domains become large enough to become glassy. We will also demonstrate that this property of PLGA allows the polymer to be used as an anchoring block to form a smooth biodegradable monolayer of block copolymers at the air-water interface. [Preview Abstract] |
Tuesday, March 22, 2011 5:06PM - 5:18PM |
L44.00012: 8CB-Langmuir Layer at air/water interface: Line Tension vs. Dipolar Repulsion Pritam Mandal, Andrew Bernoff, Adin Mann, James Alexander, Elizabeth Mann Langmuir \={ }lms of 8CB, a smectic liquid crystal at room temperature, exhibits coexistence of phases with di{\textregistered}erent thicknesses. With decompression of a 8CB-liquid-monolayer gaseous holes appear in liquid monolayer. Molecular interactions controlling the phase separation include short-range van der Waals attraction and long range dipolar repulsion. At small distances where attraction dominates gaseous domains return to energy-minimizing circular shapes. But with size of the holes increasing beyond a critical value, dipolar repulsion becomes strong enough to deform the domains; forming even labyrinth patterns. We use Brewster angle microscopy to study the \={ }lm. Our objective is to obtain a critical diameter of the domains beyond which they are non-circular. Experimental value will be compared with that from theory. [Preview Abstract] |
Tuesday, March 22, 2011 5:18PM - 5:30PM |
L44.00013: Origins of the Failure of Classical Nucleation Theory for Nanocellular Polymer Foams Russell Thompson, Yeongyoon Kim The behavior of nanocellular polymer foams, in which nanometer-sized bubbles of fluid are dispersed in a polymer matrix, is dominated by its internal surfaces. In particular, nucleation of a nanocellular foam can involve fundamentally different physics from microcellular or regular foams due to properties of the surfaces. Nucleation rates for nano-bubbles in polymer have been calculated using both classical nucleation theory and self-consistent field theory. An identical model is used for both calculations showing that classical nucleation theory predictions are off by many orders of magnitude. The cause of the failure of classical nucleation theory can be traced primarily to its representation of a bubble surface as an infinite planar interface. For nanoscopic bubbles, the curvature of the bubble surface is comparable to the size of the polymer molecules. Polymers on the outside of a curved bubble surface can explore more conformations than can polymers next to a flat interface. This results in a lower free energy for the curved interface system with respect to a flat interface system, which gives a significantly smaller barrier energy to nucleation and thus a much higher nucleation rate. [Preview Abstract] |
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