Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W43: Focus Session: Dynamics of Glassy Polymers Under Confinement III |
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Sponsoring Units: DPOLY Chair: David Simmons, University of Akron Room: 214C |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W43.00001: Molecular-weight Dependent Tg Depression of Silica-supported Poly(alpha-methyl styrene) Films Ophelia Tsui, Kun Geng The glass transition temperature ($T_g$) of poly($\alpha$-methyl styrene) (P$\alpha$MS) films supported by silica is studied as a function of film thicknesses from ~17 to ~168 nm at three molecular weights of 1.3, 20 and 420 kg/mol. For the 20 and 420 kg/mol films, the glass transition temperature decreases with decreasing film thickness, consistent with previous results. But for the 1.3 kg/mol films, it becomes independent of the film thickness. We tentatively suggest the $T_g$ depression to be caused by free volume excess at the polymer-air interface and that its influence diminishes at low enough molecular weights because of a chain stiffness effect. [Preview Abstract] |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W43.00002: Influence of the chemical structure on the slip boundary condition of liquids Mischa Klos, Sebastian Backes, Juan Manuel Castillo Sanchez, Martin Horsch, Hans Hasse, Karin Jacobs On small scales, especially in microfluidic devices, the role of the solid/liquid interface gets more important for the flow dynamics. Our experiments probe slippage via the dewetting of thin polymer films on hydrophobic substrates [1]. As hydrophobic coatings we use amorphous polymers (AF1600, AF2400) and different types of highly ordered self-assembled silane monolayers on top of silicon substrates. On silane surfaces, polystyrene (PS) of low molecular weight exhibit slip lengths up to micrometers [2]. On AF1600, no significant slip is observed. Scattering studies reveal an ordering of the PS side chains at the solid/liquid interface depending on the structure of the substrate [3]. Recent simulations were able to characterize these SAMs [4]. However, the situation changes if PMMA or polyvinylpyridine (PVP) are used: Dewetting experiments show that slip is less pronounced in PVP and in PMMA films. Obviously, the structure of the side groups plays a significant role. X-ray reflectometry supplements this hypothesis and give further insight to the slippage mechanism at the solid/liquid interface. [1] O. B\"aumchen, et.al., J Phys Condens Matter 24 (2012) [2] R. Fetzer, et.al, Europhys Lett 75 (2006) [3] P. Gutfreund, et.al., Phys Rev E 87 (2013) [4] J.M. Castillo Sanchez, et. al. submitted [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W43.00003: New paradigm for stabilization of liquid polymer films on solids Tad Koga, Naisheng Jiang, Jiaxun Wang, Xiaoyu Di, Justin Cheung, Maya Endoh We report that wetting/dewetting behavior of liquid polymer films on solids can be controlled by nanoscale architectures of polymer chains irreversibly adsorbed on the impenetrable surfaces. Monodisperse polystyrene (PS) ultrathin films (20 nm in thickness) with different molecular weights on silicon (Si) substrates with a natural amorphous Si dioxide layer were used as models. The PS thin films were annealed at high temperatures at T\textgreater Tg (Tg is the bulk glass transition temperature) for several days, and the surface structures were studied by using optical and atomic force microscopes. At the same time, the annealed PS films were further leached with a good solvent and the residue films (i.e., irreversibly adsorbed layers) were characterized by x-ray reflectivity. The experimental data reveals a strong correlation between the conformations of the adsorbed polymer chains and the stability of the liquid films on top. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W43.00004: Approach to universal self-similar attractor for the levelling of thin liquid films Elie Raphael, Michael Benzaquen, Paul Fowler, Laetitia Jubin, Thomas Salez, Kari Dalnoki-Veress We compare the capillary levelling of a random surface perturbation on a thin polystyrene film with a theoretical study on the two-dimensional capillary-driven thin film equation. Using atomic force microscopy, we follow the time evolution of samples prepared with different initial perturbations of the free surface. In particular, we show that the surface profiles present long term self-similarity, and furthermore, that they converge to a universal self-similar attractor that only depends on the volume of the perturbation, consistent with the theory. Finally, we look at the convergence time for the different samples and find very good agreement with the analytical predictions. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W43.00005: Confinement Effects with Films of Nonlinear Polystyrene Mark Foster, Qiming He, Suresh Narayanan, David Wu The surface fluctuations of annealed melt films of 6k cyclic polystyrene (CPS), its linear analog, and a long-branched chain were measured using X-ray photon correlation spectroscopy (XPCS) for films of various thicknesses. The surface fluctuations of the 6k linear PS melt films 17 nm and thicker and the 6k cyclic melt films 28 nm and thicker can be described using a hydrodynamic continuum theory (HCT) that assumes the film is characterized only by the bulk viscosity. When a film of CPS is 24 nm or thinner, the behavior can no longer be captured using the HCT with bulk viscosity. The surface fluctuations behave as though the film has an effective viscosity higher than the bulk value. The thickness at which confinement effects are seen for the 6k CPS chains is larger than that for the linear analogs. Confinement effects for long-branched chains appear at even larger thicknesses relative to $R_{g}$. Acknowledgements: Use of the Advanced Photon Source at Argonne National Laboratory was supported by the DOE's Office of Science under Contract DE-AC02-06-CH11357. This work was supported by NSF Grants CBET-0730692 and CBET-0731319. [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W43.00006: The Dynamics of a Polymer Confined in Anodic Aluminum Oxide Nanopore Gi Xue, Ye Sa The dynamics of poly (n-butyl methacrylate) confined in porous templates are investigated using DSC and Fluorescence nonradiative energy transfer. Two glass transition temperatures are obtained at a slow cooling rate of which one bulk-like phase reflects core layer while the other at much higher temperature indicates interfacial layer in the confined polymer glass. Because of cylindrical geometry, the glass transition energy barrier of interfacial layer is elevated, and the thereof temperature threshold to form one or two glass transitions is determined through adjusting infiltrating temperatures. In addition, the glass transition behavior is speculated to be meditated by the counterbalance of the size and interfacial effects in the confined space. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W43.00007: The effect of surface chemistry on the glass transition of amorphous polycarbonate inside cylindrical nanopores Dariya Reid, Marcela Alves Freire, Jodie Lutkenhaus Nanoporous anodic aluminum oxide (AAO) templates are used to study the effect of confinement on the glass transition of amorphous polycarbonate (PC). In order to further study the effect of surface chemistry on physical behavior, the bare AAO surface is modified using alkyl- and fluoro-silanes of varying length. PC nanowires (200 nm in diameter) are prepared by melt-wetting the polymer into AAO templates under applied pressure. Using modulated differential scanning calorimetry (MDSC) and thermogravimetric analysis (TGA), it is found that the hydrophilic surface of bare AAO contributes to the degradation of the polymer. Modifying the AAO surface using silane chemistry prevents polymer degradation and introduces additional features in MDSC thermograms, which could be due to the interaction of the polymer with the nanopore surface. Using scanning electron microscopy (SEM), changes are observed in the tips of the PC nanowires as the AAO surface transitions from hydrophilic to hydrophobic. [Preview Abstract] |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W43.00008: Large-scale diffusion of entangled polymers along nanochannels Kay Saalwachter, Frank Lange, Martin Steinhart, Patrick Judeinstein Confinement-induced changes in polymer mobility are still under active discussion. For weakly interacting poly(butadiene) chains in 100 $\mu$m long, 20 and 60 nm wide channels in anodic Al2O3 [1], we here report on the study of the large-scale pore-averaged self diffusion on a $\mu$m scale by 1H pulsed-gradient NMR. We find weak indications of an acceleration due to surface-induced disentanglement [2]. Unlike previous reports on polymer diffusion into particle nanocomposites of similar confinement scale [3], or start-up diffusivities out of even thinner films [4,5], we find an MW and temperature independent reduction of diffusivity that is solely determined by the confinement size. We rationalize this trend by a simple volume-average model, which suggests a 20-fold surface-enhanced monomeric friction on the scale of the packing length, which can be compared to a factor of 300 that our model predicts for comparable thin-film data of poly(styrene) on silica [4].\\[4pt] [1] S. Ok et al.{\em Macromolecules} {\bf 43} (2010) 4429;\\[0pt] [2] D.~M. Sussman et al. {\em Macromolecules} {\bf 47} (2014) 6462;\\[0pt] [3] J. Choi et al. {\em ACS Macro Lett.} {\bf 2} (2013) 485;\\[0pt] [4] B. Frank et al. {\em Macromolecules} {\bf 29} (1996) 6531;\\[0pt] [5] X. Zheng, et al. {\em Phys. Rev. Lett.} {\bf 74} (1995) 407 [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W43.00009: Nanoscale pattern fidelity and transfer of hierarchically patterned thermoplastics films Ying Chen, Manish Kulkarni, Allan Marshall, Jack Douglas, Alamgir Karim We demonstrate a versatile and inexpensive method for controlling the surface relief structure of both flexible elastomeric and glassy polymer films over large areas through a two-step imprinting process. First, nanoscale patterns were formed by nanoimprinting polymer films with a pattern on a DVD disk, obtained originally by nanoimprinting from a lithographically etched master pattern on a silicon wafer; micron-scale patterns were then superimposed on the nanoimprinted films by exposing them to ultraviolet radiation in oxygen (UVO) through a TEM grid mask having variable micron-scale patterning. This simple two-stage imprinting method allows for facile fabrication of hierarchically structured elastomer and thermoplastic polymer films. Besides, the thermodynamic properties of dewetting phenomenon of polystyrene film under the confinement of hierarchically patterned PDMS is studied. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W43.00010: Elevated single polymer surface diffusion on a film near its glass transition temperature Mark Geoghegan, Matthew Mears, Christopher Clarkson, Zhenyu Zhang, John Torkelson Fluorescence correlation spectroscopy data are presented to show that the diffusion coefficient of poly(ethylene oxide) (PEO) adsorbed onto poly(alkyl methacrylate) (PAMA) and polystyrene films in aqueous solution increases close to (but below) the surface glass transition temperature of the film. This increase disappeared at higher temperatures as the film liquified, although the diffusion coefficient for the PEO on the polystyrene surface remained greater than the diffusion coefficients for PEO on the PAMA films at temperatures greater than those at which the peak in diffusion occurred. A similar increase was found in the surface tension of all films studied. Experiments on (immiscible) blends of two PAMA homopolymers were performed where two peaks in the diffusion coefficient were observed with increasing temperature. Two peaks were also observed in the surface tension from contact angle experiments, although at temperatures slightly greater than those at which the peak in diffusion was observed. It is concluded that the enhanced surface mobility of the films near the surface glass transition temperature induces conformational changes in the adsorbed PEO molecules resulting in elevated diffusion coefficients. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W43.00011: Local Glass Transition Temperature Gradients Near Polymer-Polymer Interfaces Roman Baglay, Connie Roth For decades the glass transition in confined systems has been studied with the hopes of uncovering the governing length scales that impact these dynamics. However, understanding length scales of local gradients in glass transition temperature ($T_{\mathrm{g}})$ near a free surface have been hampered by limitations of how to treat the enhanced mobility at the free surface theoretically. We have previously reported on the local $T_{\mathrm{g}}$ in multilayer structures made from high molecular weight polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA), a weakly immiscible system with a $\sim$ 7 nm interfacial width. Using ultrathin (10-15 nm) pyrene-labeled layers inserted into the multilayer structure at different positions (z) from the glassy-rubbery interface, we were able to map the local Tg(z) profile across this glassy-rubbery interface with temperature-dependent fluorescence intensity measurements. Our work revealed an asymmetric local mobility gradient propagating hundreds of nanometers away from the glassy-rubbery PS-PnBMA interface into the glassy PS and rubbery PnBMA sides before bulk Tgs were recovered far from the interface. Here we extend these measurements to investigate how the local $T_{\mathrm{g}}$(z) profile in PS varies when in contact with a variety of immiscible polymers whose Tgs vary between $+$90 K to --80 K relative to the $T_{\mathrm{g}}$ of PS, so-called hard vs soft confinement. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W43.00012: Free Surface and Interfacial Effects on Tg Confinement Behavior of Template Supported Nanotubes Anthony Tan Free surface and interfacial effects have a large impact upon the magnitude and direction of Tg-confinement behavior for nanoscale materials. In this work, we study the Tg behavior of supported polymers in anodic aluminum oxide templates. The effects of attractive and neutral or non-interacting polymer substrate interactions were investigated. Tailored wall thicknesses were achieved using template melt infiltration by varying the annealing temperature and the molecular weight of the polymers. Nanotube thickness can be related to the polymer conformation and the interactions between the polymer and the substrate. Substantial Tg reductions as a function of wall thickness were observed for supported polystyrene nanotubes and Tg increases for supported poly(methyl methacrylate) or poly(2-vinylpyridine) nanotubes. The Tg-confinement behavior of supported nanotubes is found to be similar to the behavior of supported thin films in the presence or absence of interfacial effects. [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W43.00013: Residual Stress Relaxation and Stiffness-Confinement Effects in Polymer Films: Characterization by Non-Contact Ellipsometry and Fluorescence Techniques Shadid Askar, John Torkelson The relaxation of residual stresses in spin-coated polymer films is characterized using two optical techniques: ellipsometry and fluorescence. Both techniques show that residual stresses relax over hours at several tens of degrees above the film glass transition temperature (\textit{Tg}). Ellipsometry shows that thickness can increase or decrease during residual stress relaxation depending on thermal history of the film. However, the presence or relaxation of stresses has no measurable effect on \textit{Tg} as measured by ellipsometry. We have adapted the well-known sensitivity of the pyrene dye fluorescence spectral shape to local environment polarity in order to characterize stress relaxation and to monitor stiffness-confinement effects. The spectral shape of the pyrene fluorescence spectrum shows similar stress relaxation regardless of whether relaxation is accompanied by increases or decreases in film thickness. Fluorescence also indicates that single-layer polystyrene films supported on silica stiffen with decreasing nanoscale thickness. For the first time, stiffness gradients as a function of distance from interfaces are demonstrated using pyrene label fluorescence in conjunction with multilayer films. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W43.00014: Can a reduction in mass transport occur at invariant segmental time? Simone Napolitano, Michele Sferrazza The glassy dynamics of polymer melts adsorbed onto solid substrates shows a peculiar confinement effect: a severe reduction in mass transport occurs without a corresponding increase in segmental relaxation time. This phenomenon provides a ``negative violation'' of the Stokes-Einstein (SE) relation, not observed in bulk melts or confined water. Explaining those findings in analogy to the large drop of thermal expansion reported in polymers under 1D confinement, we considered the presence of an interfacial dead layer where tracer diffusivity assumes negligible values. To verify this hypothesis, we performed an extensive investigation of the diffusion of styrene oligomers, acting as tracers, into matrices of high molecular weight polystyrene, irreversibly adsorbed onto aluminum oxide. We demonstrate that the reduced interfacial diffusion is due to larger residence times of the tracers inside the dead layer, t$_{DL}$. In particular, we show that t$_{DL}$ is directly proportional to the amount of irreversibly adsorbed monomers, a quantity limiting the available space for diffusion. We thus discuss of a dynamic dead layer evolving within the adsorbed layer, and of its role on the dynamics of glassy polymers under confinement and the ``negative violation'' the SE relation. [Preview Abstract] |
Thursday, March 5, 2015 5:18PM - 5:30PM |
W43.00015: Physical Properties of PC-PMMA Multilayers Arifur Rahman, Eric Baer, Alin Cristian Chipara, Robert Vajtai, Pullickel M. Ajayan, James Hinthorne, Ibrahim Elamin, Mircea Chipara Multilayers of polycarbonate (PC) and polymethylmethacrylate (PMMA) have been obtained by the layer multiplying coextrusion method. Each sample (1024 layers, of equal thickness, with individual thickness between 10 and 200 nm) has been investigated at room temperature by Wide Angle X-Ray Scattering (WAXS) using a Bruker Discovery 8 spectrometer (Cu K$\alpha $ radiation), Raman spectroscopy (Bruker Senterra confocal Raman spectrometer operating at 785 nm), FTIR spectroscopy (Tensor 27 Bruker), and UV-Vis spectroscopy. Further details about the glass transition temperature in these samples have been obtained by Dynamical Mechanical Analysis, DMA, (TA Instruments Q800) at various frequencies in the range 1 to 100 Hz. Isothermal Differential Scanning Calorimetry, DSC, (TA Instruments Q200) was used to investigate the effect of the thickness of the polymeric film on the crystallization processes. Non-isothermal DSC measurements aimed at the identification and location of the main phase transitions (glass, crystallization, and melting) occurring in these multilayers. The effects of confinement on the phase transitions occurring in these multilayers are discussed in detail. [Preview Abstract] |
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