Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S43: Focus Session: Dynamics of Glassy Polymers Under Confinement I |
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Sponsoring Units: DPOLY Chair: Rob Riggleman, University of Pennsylvania Room: 214C |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S43.00001: Structural Recovery for a Single Polystyrene Ultrathin Film Using Flash DSC Yung P. Koh, Siyang Gao, Sindee L. Simon The kinetic features of the glass transition under~nanoconfinement of ultrathin films are studied using nanocalorimetry, with a particular focus on the cooling rate dependence of the glass transition temperature (Tg) and on the time-dependent structural recovery behavior of a 20 nm-thick polystyrene film. Measurements are performed using a commercial rapid-scanning chip calorimeter, the Mettler Toledo Flash differential scanning calorimeter (DSC). The~Tg depression of the 20 nm-thick film is found to be a function of cooling rate, decreasing with increasing cooling rate; at high enough cooling rates (e.g., 1000 K/s),~Tg is the same as the bulk within the error of the measurements.~ Structural recovery is performed as a function of aging time and temperature, and the evolution of the fictive temperature is followed. The advantages of the Flash DSC include sufficient sensitivity to measure enthalpy recovery for a single 20 nm-thick film, as well as extension of the measurements to aging~temperatures as high as 15 K above nominal Tg and to aging times as short as 0.01 s.~The aging behavior will be compared to that for bulk-like single thin films measured by Flash DSC, as well as to the results for stacked ultrathin films measured using conventional DSC. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S43.00002: Dynamics of Poly(2-vinylpyridine)/Silica Nanocomposites from Brillouin and Raman Light Scattering Shiwang Cheng, Alexander Kisliuk, Vladimir Novikov, Adam P. Holt, Alexei P. Sokolov Recent studies show an interfacial layer exists between polymer matrix and nanoparticle surface in polymer nanocomposites (PNCs)[1],which could potentially explain the drastic mechanical enhancement in such materials [2]. Dynamics of this interfacial layer were captured by various techniques, where the typical dynamic range was limited to be below 1 GHz. However, the fast dynamics (above 1 GHz) of the interfacial layer is also important to the application of PNCs under severe conditions. Unfortunately, little work has been done to explore the structure and the dynamics of this layer at high frequencies. In this study, we demonstrated that Brillouin Light Scattering (BLS) can be used to estimate the thickness of the interfacial layer and its mechanical properties. By combining BLS and Raman Scattering, we probed the dynamics in the range from 1 GHz to 5 THz of the Poly(2-vinylpyridine)/Silica nanocomposites with loadings from 5{\%} wt to 52{\%} wt. The various features observed can also be explained in the spirit of the existence of an interfacial layer between the polymer matrix and nanoparticles. [1] Holt, A. P., et al; \textit{Macromolecules }\textbf{2014,} \textit{47}, 1837-1843. [2] Papon, A. et al; \textit{Soft Matter }\textbf{2012,} \textit{8}, 4090-4096. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S43.00003: Improving Dielectric Breakdown Strength: Physically Aging Amorphous Polymers and Nanocomposites Richard A. Vaia, Christopher A. Grabowski, Hilmar Koerner Processing conditions play a significant role in maximizing the available energy storage density of polymer dielectrics. Trapped solvents and voids act as defect sites that prematurely trigger breakdown and reduce dielectric strength. To address these issues, solvent-cast films are conventionally annealed above the glass transition and under vacuum; however these procedures can yield materials far from thermodynamic equilibrium with substantial free-volume. Here in, we demonstrate improvement in dielectric performance via controlled post-deposition annealing based on their structural relaxation characteristics. Using enthalpy relaxation studies, we quantify how local chain packing evolves in the glass during controlled cooling or physical aging; and how this impacts dielectric breakdown, complex permittivity, and energy storage density for polystyrene, poly(methyl methacrylate), and their related blended and single-component nanocomposites. These process-performance correlations, and their dependence on nanocomposite topography, provide a basis for the rational design of dielectrics for high performance capacitors. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S43.00004: Temperature Step Dewetting Method for Determination of T$_{\mathrm{g}}$ Dependence on Thickness for Linear and Star Branched Polystyrene Astrid Torres Arellano, Gregory McKenna The current liquid dewetting study is an extension of work previously presented by Bodiguel and Fretigny [Phys. Rev. Lett., \textbf{97}, (2006)] and Wang and McKenna [J. Polym. Sci., Part B: Polym. Phys., \textbf{51}, (2013)]. The liquid dewetting method consists of floating a thin polymer film on a liquid (glycerol) substrate. The film shrinks in a homothetic way while the thickness increases. The current goal is to obtain the glass transition temperature T$_{\mathrm{g}}$ as a function of thickness h for low and high molecular weight linear polystyrene (PS), long branched 3 arm star PS, and short and long branched 8 arm star PS. In the normal dewetting method and in pseudo-thermodynamic methods a new sample is required to obtain the T$_{\mathrm{g}}$ vs. h for each individual thickness. The temperature step dewetting technique can be used to obtain the T$_{\mathrm{g}}$ vs h dependence using one single thin polymer film with initial known thickness h$_{\mathrm{o}}$. Thereby, obtaining rapidly the same information that would have required multiple individual tests. The T$_{\mathrm{g}}$ reductions are compared to previously presented liquid dewetting results, as well as those for supported and freely standing polystyrene thin films. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S43.00005: Influence of the Free Interface on the Glass Transition Temperature of Irreversibly Adsorbed Polystyrene Thin Films Mary Burroughs, Rodney Priestley Polymers confined to the nanometer length scale have been shown to exhibit deviations in the glass transition temperature (T$_{g})$ from that of the bulk. Confinement effects on T$_{g}$ have largely been attributed to the combined influences of the free surface and substrate interface. Recent work with polymer thin films has investigated a phenomenon at the substrate interface in which polymer chains physically adsorb to the substrate when annealed at sufficient temperature. This process, dubbed ``irreversible adsorption'' has been connected with changes in T$_{g}$ under confinement. We seek to investigate how the competition between enhanced mobility at the free surface and arrested mobility due to irreversible adsorption at the substrate influences the glass transition temperature in polymer thin films. Here we use fluorescence, a technique capable of probing local dynamics, to study the T$_{g\, }$of a model system consisting of polystyrene (PS) irreversibly adsorbed on silica. Incorporating fluorescently-labeled PS in a series of single and multi-layer films, we selectively measure the T$_{g}$ of adsorbed layers, with and without a free surface, as a function of annealing time. We then further anneal the bilayer films and measure changes in the T$_{g}$ of the irreversibly adsorbed layers to investigate chain interpenetration and its implications for the influence of irreversible adsorption on the T$_{g}$ distribution throughout the film. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S43.00006: Modeling Mobility in Glassy Thin Films Jeffrey DeFelice, Jane Lipson, Nicholas Tito, Scott Milner In this talk we explore the role of mobility in glassy systems and examine the effect of coupling sample mobility to system equilibration. Using our Limited Mobility (LM) model, we implement a new kinetic constraint such that the presence of mobility is required to facilitate local density equilibration. The LM model was developed to study dynamic heterogeneity in systems that exhibit kinetic arrest, i.e. a glass transition. It has been applied to investigate the behavior of sample mobility at and near this transition in bulk, buried slab, and supported film systems. Here we aim to probe the competition between kinetic and thermodynamic driving forces in the vicinity of the glass transition by coupling mobility with density equilibration. In thin films, the depth to which enhanced mobility from the free surface extends into the film diminishes upon cooling below the glass transition. We find that the new requirement that density equilibration be facilitated by mobility leads to ``frustrated'' behavior. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:48AM |
S43.00007: Perturbation of Glassy Dynamics in Thin Polymer Films due to Interfaces Invited Speaker: Connie B. Roth Many confinement studies have focused on free-standing polymer films, having been historically billed as the simplest system, containing only two symmetric air-polymer interfaces with no substrate interactions. However, free-standing films have instead exhibited some of the most complex molecular weight (MW)-dependent average film glass transition temperature Tg(h) behavior with decreasing film thickness. We have previously demonstrated that high MW free-standing polystyrene (PS) films can exhibit two distinct transitions in thermal expansion on cooling, with qualitatively different MW dependences suggesting that two separate mechanisms are acting simultaneously to propagate enhanced mobility from the free surface deeper into the material. To investigate the nature of these transitions, we present physical aging measurements below and in-between these two transitions. How the presence of a free surface alters the Tg in confined systems is complicated by the ill-defined magnitude of the perturbation in local mobility. Thus, we have recently begun investigating polymer-polymer interfaces where the magnitude of the Tg perturbation at the interface can be readily determined. Such studies provide a more well-defined system for investigating the length scales over which such perturbations are propagated, which we believe are associated with the glass transition. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S43.00008: A Comparison of Particle Embedment and Nanoindentation: Probing the Surface Properties of Polymeric Materials Meiyu Zhai, Heedong Yoon, Gregory McKenna In this work, we report the results from a comparison of viscoelastic surface properties of polymer obtained from two different techniques: the spontaneous particle embedment technique and nanoindentation technique. The surface compliance for polystyrene(PS) and poly(isobutyl methacrylate) (PiBMA) were determined using multi curve fitting method to extract the viscoelastic response from the experimental results. The surface layer rheological properties obtained from particle embedment experiment and indentation are compared both with each other and with the bulk properties. For both materials we observed surface softening when the test temperature is below the macroscopic glass transition temperature. This is followed by a crossover to a surface stiffening region when the test temperature is higher than the macroscopic glass temperature. \textbf{KEYWORDS:} nanoindentation, particle embedment, multi curve fitting method, viscoelastic properties [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S43.00009: Investigating the effect of chain architecture on the dynamics of thin entangled polymer films Ethan Glor, Zahra Fakhraai Recent work in polymer physics shows that the structural relaxation time near a free surface of a thin polystyrene film is significantly different from that of the bulk polymer. This can have a large influence on their properties. For instance, studies have shown that polystyrene thin films exhibit a decreased glass transition temperature as the thickness decreases below 60 nm. A wide range of experimental techniques show that the dynamics at the free surface of polystyrene have a weaker temperature dependence than that of the bulk. Here we use cooling rate dependent T$_{g}$ measurements (CR-Tg) to show that the dynamics in thin, entangled polystyrene films are directly influenced by the free surface. These studies also show that the deviations from bulk dynamics begin at a particular temperature (T*), providing an explanation for why some studies observe no interfacial effects in ultra-thin polymer films. A puzzling aspect of this work is that computational studies and studies on molecular glasses, which also exhibit enhanced surface dynamics, do not observe T*. We use CR-Tg to study thin films of various polymers to determine 1. If T* is a phenomenon common to all polymer glasses, and 2. If the value of T* is dependent on the chemistry or T$_{g}$ of the polymer. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S43.00010: Dynamic glass transition measurements on nm-thin films of low molecular mass substances using AC chip-nanocalorimetry Mathias Ahrenberg, Christoph Schick, Heiko Huth We are using AC chip nano-calorimetry for the in-situ investigation of the dynamic glass transition of vapor-deposited thin films of toluene$^{3}$ and indomethacin of thicknesses between several hundred nm down to ten nm. With these experiments on low molecular mass substances we complement our data on similar thin polymer films$^{3}$. Firstly, the deposition-related thermodynamic state (stable glass) of each film is erased by transforming them into ordinary glasses. Secondly, upon reheating the thin ordinary glass films a direct comparison of the subsequently measured frequency-dependent dynamic glass transition temperatures becomes possible. The frequency of temperature modulation can be varied from 1 Hz up to about 1000 Hz. Film thicknesses for indomethacin are measured ex-situ with an atomic force microscope directly on the membrane of the chip-sensors. Similar to the thin polymer films no thickness dependence of the dynamic glass transition temperature (main relaxation) is seen. The results are in agreement with the explanation given by Cangialosi et al.$^{3}$. 1. M. Ahrenberg et al., \textit{The Journal of Chemical Physics}, 2013, \textbf{138}, 024501-024511. 2. H. Huth et al., \textit{Eur. Phys. J. Special Topics}, 2007, \textbf{141}, 153-160. 3. S. Napolitano and D. Cangialosi, \textit{Macromolecules}, 2013, \textbf{46}, 8051-8053. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S43.00011: Why do some diluents alter the magnitude of nanoconfinement effects on the glass transition? Jayachandra Hari Mangalara, Nicholas Weiner, Michael Marvin, David Simmons Polymers subject to nanoconfinement can exhibit large alterations in their glass transition and associated dynamic and mechanical properties. Several studies have indicated that introduction of small-molecule additives can attenuate the magnitude of nanoconfinement affects, offering a potential method of tuning the properties of nanostructured polymers in applications from microelectronics to structural nanocomposites. However, the relationship between additive molecular properties and their effects on nanoconfined glass formation remains poorly understood. A number of studies have implicated changes in the fragility of glass formation in mediating these effects; however, this remains a matter of considerable debate. Here, we report on two sets of simulations of nanoconfined polymer films: one in which we introduce several oligomeric additives with effects ranging from suppression to enhancement of bulk Tg and fragility; one in which we reduce the polymer's bulk fragility via a simple, additive-free, structural modification. Results provide new insight into the impact of additives on nanoconfined glass formation as well as into the role of fragility in determining nanoconfinement effects. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S43.00012: Tuning the Tg-Confinement Effect by Controlling the Amount of Residual Surfactant Present in Emulsion Polymerized Polystyrene Thin Films Lawrence Chen, John Torkelson The nanoconfinement effect of polystyrene (PS) ultra-thin films supported on silica has been well studied over the past two decades. In order to systematically study the influence surfactants have on the Tg-confinement effect in thin films, PS was synthesized using conventional emulsion polymerization (E-PS) using sodium dodecyl sulfate (SDS) as the surfactant. After rigorous purification, the amount of SDS remaining in the bulk E-PS sample was quantified by using a modified Epton's Method to be 0.023 wt{\%}. This technique not only allows us to quantitate the amount of surfactant present in bulk polymer but also allows for the fine-tuning of surfactants present in the polymer. We find that a minute amount of surfactant is capable of significantly suppressing the Tg-confinement effect as well as narrowing the Tg breadth in sufficiently thin E-PS films; the magnitude of the Tg-confinement effect is strongly dependent on the amount of SDS present in bulk E-PS. Finally, using XPS depth profiling we demonstrate that the anionic surfactant preferentially resides at the free surface layer of the film thus eliminating the free surface effect. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S43.00013: Homogeneous nucleation of polymers under confinement and its relation to the liquid-to-glass ``transition'' Yasuhito Suzuki, Hatice Duran, Martin Steinhart, Hans-J\"urgen Butt, George Floudas The crystallization and local dynamics of model semi-crystalline polymers confined to self-ordered nanoporous alumina (AAO) were studied as a function of pore size, molecular weight and cooling/heating rate by differential scanning calorimetry, wide-angle X-ray diffraction and dielectric spectroscopy. In contrast to the bulk, polymers located inside nanoporous alumina crystallize via distinct nucleation mechanisms. Under confinement, the usual heterogeneous nucleation of bulk polymers is suppressed. Instead, within the smaller pores polymer crystallization is initiated via homogeneous nucleation. We provide the phase diagram of crystallizable polymers under confinement. We find that homogeneous nucleation is strongly coupled to the local viscosity and hence to the liquid-to-glass ``transition.'' Dielectric spectroscopy revealed that confinement affects both the distribution of relaxation times (much broader under confinement) and the rate of segmental motion (faster dynamics under confinement). [Preview Abstract] |
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