Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z34: Polymeric Glasses |
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Sponsoring Units: DPOLY Chair: Yunlong Guo, Princeton University Room: 342 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z34.00001: Nanostructured glassy polymer films deposited via matrix assisted pulsed laser evaporation Kimberly Shepard, Rodney Priestley It has recently been illustrated that nanostructured glassy polymer films can be formed via Matrix Assisted Pulsed Laser Evaporation (MAPLE). During the MAPLE process, a pulsed laser beam strikes a target, which is made of a frozen dilute polymer solution held under high vacuum. The interaction between laser light and target causes phase explosion and subsequent formation of a plume, containing clusters of polymer and solvent. The solvent is pumped off as the plume travels away from the target. The plume is collected on a temperature-controlled substrate, where a polymer film forms at a controlled, slow growth rate. The glassy films formed by MAPLE can exhibit an unusual combination of material properties. For instance, a significant reduction in density may be accompanied with a simultaneous increase in thermal/kinetic stability. These interesting material properties are a result of the films' nanostructured morphology, i.e., they exhibit a nanoglobular morphology. Here, we present further evidence connecting the global film properties to those of the nanoscale building blocks, i.e., the nanoglobules. In addition, we explore the impact of concentration (a key processing parameter) on the morphology of the films. Finally, we demonstrate the generality of nanostructured film formation via MAPLE for a series of poly(n-methacrylate)s. [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z34.00002: Acid Diffusion in a Reacting Polymer Glass Abhijit Patil, Ginusha Perera, Yogendra Pandey, Manolis Doxastakis, Gila Stein The acid-catalyzed deprotection of glassy polymer films is an important process in photolithography. It is well-established that acid diffusion controls the deprotection kinetics, but simple Fickian transport models cannot capture experimental data. We examined the acid-catalyzed deprotection of a glassy poly(4-hydroxystyrene-co-tertbutylacrylate) resin using infrared absorbance spectroscopy and stochastic simulations. Experimental data were interpreted with a model that explicitly accounts for acid transport, where heterogeneities at local length scales are introduced through a non-exponential distribution of waiting times between successive hopping events. Subdiffusive behavior predicts key attributes of the observed deprotection rates, such as fast reaction at short times, slow reaction at long times, and a non-linear dependence on acid loading. These studies suggest that macroscopic deprotection rates are controlled by a strongly non-Fickian acid transport in the glassy polymer resin. [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z34.00003: Effect of Hydrogenation on the Glass Transition Temperatures of Novel Ring-Opened Polynorbornenes Adam Burns, Sheng Li, Richard Register Ring-opening metathesis polymerization (ROMP) of norbornene-type monomers has been demonstrated as a facile way to produce block copolymers incorporating semicrystalline, glassy, and rubbery blocks. Of particular interest are block copolymers, made by ROMP, with thermoplastic elastomeric properties. For this application we seek blocks with glass transition temperatures (T$_{\mathrm{g}})$ in excess of 100 $^{\mathrm{o}}$C. To this end, novel substituted norbornene-type monomers with large, rigid substituents have been investigated. A key consequence of the ROMP mechanism is that unsaturation in the monomer is preserved in the polymer. Unsaturation in the polymer backbone is susceptible to degradation; therefore, hydrogenation is required to enhance the long-term stability of these polymers. Hydrogenation can also have a significant impact on the thermal behavior. To investigate this, we have synthesized ROMP polymers of 5-phenyl-2-norbornene and 5-cyclohexyl-2-norbornene. Hydrogenation yielded derivatives with saturated backbones. This series of polymers provides a systematic study on the influence of hydrogenation on the T$_{\mathrm{g}}$ of glassy ROMP polymers. We find that saturation of the side group increases the T$_{\mathrm{g}}$ by 14 $^{\mathrm{o}}$C, irrespective of backbone saturation. Conversely, saturation of the backbone reduces T$_{\mathrm{g}}$ by 17 $^{\mathrm{o}}$C for both aromatic and cycloaliphatic side groups. When compared to analogous studies on other ROMP polymers, it becomes clear that these trends are difficult to predict, highlighting the importance of experimental measurements. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z34.00004: Observing density-dependent formation of a fragile glass in surface-bound molecular chains L.I. Clarke, M.P. Roman, D.R. Stevens, M.C. Scott, J.R. Bochinski Dynamics within a monolayer collection of surface-bound substituted-alkyl chains are studied with narrow-band dielectric spectroscopy. A transition from independent (intra-molecular) motion to complex, glassy (inter-molecular) motion is observed as the surface density increases. At high density, both the glassy mode [1,2] and the sub-T$_{g}$ relaxation [3] have a direct analogy to the equivalent relaxations in polyethylene. Thus, this experimental approach enables observation of the formation of a fragile glass as an explicit function of density. Addition of a strong terminal dipole shows the transition occurring at lower density, dipole-mediated interacting dynamics in the low density regime, and increased dominance of the sub-T$_{g}$ local mode. We will discuss results from monolayers and an analogous siloxane-based substrate where alkyl chain-chain distance can be similarly controlled. [1] M. C. Scott et al. \textit{ACS Nano} \textbf{2}, 2392 (2008). [2] M. Beiner and H. Huth, \textit{Nat. Mater.} \textbf{2}, 595 (2003). [3] Q. Zhang et al., \textit{J. Phys. Chem. B} \textbf{110}, 4924 (2006). [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z34.00005: States of Water in Non-Equilibrium Glassy Polymers Eric Davis, Yossef Elabd For many applications (e.g., packaging, medical devices) a deeper fundamental understanding of the molecular nature of water in glassy polymer coatings is of significant interest. In this study, the sorption and diffusion of water in two glassy polymers, poly(methyl methacrylate) (PMMA) and poly(styrene) (PS), were measured with both quartz crystal microbalance (QSM) and time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian diffusion was observed in both PMMA and PS using both experimental techniques due to the non-equilibrium state of the polymers. The specific states of water were observed with FTIR-ATR spectroscopy, where dimers exist in PMMA below a critical concentration and larger clusters were observed above this concentration. Contrastingly, water only exists in PS as larger clusters over the entire sorption isotherm. A correlation between the states of water and the diffusive activation energy of water was observed. Additionally, the pseudo-equilibrium water sorption isotherms in PMMA and PS were accurately predicted with the non-equilibrium statistical associating fluid theory (NE-SAFT). We predict that the combination of time-resolved FTIR-ATR spectroscopy and NE-SAFT can be used on other water-glassy polymer systems to provide a molecular understanding of non-equilibrium sorption and diffusion. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z34.00006: Role of quantum effects in the glass transition Vladimir Novikov, Alexei Sokolov It is shown that quantum effects lead to a significant decrease of the glass transition temperature $T_{g}$ with respect to the melting temperature $T_{m}$, so that the ratio $T_{g}$/$T_{m}$ can be much smaller than the typical value of 2/3 in materials where $T_{g}$ is near or below $\sim$ 60 K. Furthermore, it is demonstrated that the viscosity or structural relaxation time in such low temperature glass-formers should exhibit highly unusual temperature dependence, namely a decrease of the apparent activation energy upon approaching $T_{g}$ (instead of traditional increase). [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z34.00007: Potential energy landscape contribution to the dynamic heat capacity John McCoy, Jonathan Brown The dynamic heat capacity of a simple polymeric, model glass former was computed using molecular dynamics simulations by sinusoidally driving the temperature and recording the resultant energy. The underlying potential energy landscape of the system was probed by taking a time series of particle positions and quenching them. The resulting dynamic heat capacity demonstrates that the long time relaxation is the direct result of dynamics resulting from the potential energy landscape. [Preview Abstract] |
Friday, March 22, 2013 12:39PM - 12:51PM |
Z34.00008: Coarse grained dynamics in the glass phase Anton Smessaert, J\"org Rottler Atomic scale dynamics in glasses is dominated by extended periods of localized vibration, where the crowded surroundings of a particle act as a cage. Collective motion is necessary to escape the cage, and the succession of particle jumps or hops leads to diffusion. Each jump is an elementary relaxation event since the local structure is stable until a jump occurs. The link between local dynamics and structural properties has become of increasing interest in recent years. Aging of the mechanical response has been tied to a power-law distribution of persistence times in the cages, and concentration of hops into dynamical heterogeneities (DH) was observed in granular media and simulations of supercooled liquids in 2D. These studies were limited to small systems or hop detection in subsets, because of the post processing requirements. We present results based on a new algorithm that allows us to detect the hops of all particles during a molecular dynamics simulation. This complete coarse-grained ``map'' of the dynamics allows us to directly investigate temporal and spatial correlations between relaxation events. Furthermore, we can readily identify DH using a cluster algorithm and we explore the impact of aging and deformation on the size and shape of DH. [Preview Abstract] |
Friday, March 22, 2013 12:51PM - 1:03PM |
Z34.00009: Dynamic Deformation of Thermosetting Polymers---All Atomistic Simulations Mesfin Tsige, Natalia Shenogina, Sharmila Mukhopadhyay, Soumya Patnaik We are using all-atom molecular dynamics simulations to investigate the interconnection between structural and mechanical properties of highly cross-linked polymer networks. In this study we focused on the widely used resin-hardener system composed of DGEBA epoxy oligomers and aromatic amine hardener DETDA. Accurate cross-linked models were developed using the effective cross-linking procedure that enables to generate thermoset structures with realistic structural characteristics. These models were used to examine the elastic properties of thermosetting networks with various degrees of curing and length of resin strands both in glassy and rubbery states. In our recent study we employed static deformation approach to estimate potential energy contribution to the mechanical response. In the present work we are using dynamic deformation approach which takes into account both potential energy and thermal motions in the structure. Uniaxial, volumetric and shear dynamic deformation modes were used to obtain Young's, bulk, shear moduli and Poisson's ratio directly. We also calculated elastic constants using formulae of linear elasticity and analyzed the results obtained by direct deformation and interconversion methods. The elastic properties determined from these two approaches are in good agreement with each other and also with experimental data. [Preview Abstract] |
Friday, March 22, 2013 1:03PM - 1:15PM |
Z34.00010: How melt stretching affect the brittle-ductile transition temperature of polymer glasses Shiwang Cheng, Shi-Qing Wang Upon increasing temperature a brittle polymer glass can turn ductile. PMMA is a good example. For a while this brittle-ductile transition (BDT) was thought to be determined by the emergence of a secondary relaxation....$^{\mathrm{1-3}}$ On the other hand, it has been known for a long time...$^{\mathrm{4-6}}$ that predeformation in the melt state (e.g., melt stretching) can also make brittle glasses behave in a ductile manner. This transformation has recently received a satisfactory explanation based on a picture of structural hybrid for polymer glasses....$^{\mathrm{7}}$ It appears that BDT is dictated by the relative mechanical characteristics of the primary structure (due to the van der Waals bonds) and the chain network. The present work, based on conventional Instron tensile extension tests and DMA tests, shows that melt stretching does not alter the secondary relaxation behavior of PMMA and PC yet can turn them the brittle PMMA ductile and the ductile PC brittle. Moreover, sufficient melt stretching makes the brittle PS ductile although it does not produce any secondary relaxation process. .1. Monnerie, L.; Laupretre, F.; Halary, J. L. \textit{Adv. Polym. Sci }\textbf{2005,} 187, 35-213. 2. Monnerie, L.; Halary, J. L.; Kausch, H. \textit{Adv. Polym. Sci }\textbf{2005,} 187, 215-364. 3. Wu, S. \textit{J. Appl. Polym. Sci. }\textbf{1992,} 46, (4), 619-624. 4. Vincent, P. I. \textit{Polymer }\textbf{1960,} 1, (0), 425-444. 5. Harris, J. S.; Ward, I. M. \textit{J. Mater. Sci. }\textbf{1970,} 5, (7), 573-579. 6. Ender, D. H.; Andrews, R. D. \textit{J. Appl. Phys. }\textbf{1965,} 36, (10), 3057-3062. 7. Zartman, G. D.; Cheng, S.; Li, X.; Lin, F.; Becker, M. L.; Wang, S.-Q. \textit{Macromolecules }\textbf{2012,} 45, (16), 6719-6732. [Preview Abstract] |
Friday, March 22, 2013 1:15PM - 1:27PM |
Z34.00011: Influence of entanglements on glass transition temperature of polystyrene Toshiaki Ougizawa, Yoshinori Kinugasa Chain entanglement is essential behavior of polymeric molecules and it seems to affect many physical properties such as not only viscosity of melt state but also glass transition temperature (Tg). But we have not attained the quantitative estimation because the entanglement density is considered as an intrinsic value of the polymer at melt state depending on the chemical structure. Freeze-drying method is known as one of the few ways to make different entanglement density sample from dilute solution. In this study, the influence of entanglements on Tg of polystyrene obtained by the freeze-dried method was estimated quantitatively. The freeze-dried samples showed Tg depression with decreasing the concentration of precursor solution due to the lower entanglement density and their depressed Tg would be saturated when the almost no intermolecular entanglement was formed. The molecular weight dependence of the maximum value of Tg depression was discussed. [Preview Abstract] |
Friday, March 22, 2013 1:27PM - 1:39PM |
Z34.00012: Translation-rotation decoupling and nonexponentiality in room temperature ionic liquids Philip Griffin, Alexander Agapov, Alexei Sokolov It is generally accepted that room temperature ionic liquids (RTILs) have many characteristics in common with prototypical molecular glass formers. In order to understand the glassy dynamics of RTILs, we have measured the temperature dependence of structural relaxation time and self diffusion in three imidazolium based RTILs. We demonstrate that self diffusion decouples from structural relaxation in these systems as the temperature is decreased toward Tg, but the degree of decoupling is shown to be exceptionally small. In addition to the weak decoupling, we demonstrate that the temperature dependence of structural relaxation time in all three liquids can be well described by a single Vogel-Fulcher-Tammann (VFT) function over 13 decades in time. Furthermore, the stretching of the structural relaxation is shown to be temperature independent over the same range of timescales, i.e. time-temperature superposition is valid for these ionic liquids in the entire temperature range. These properties are at odds with the usual behavior of most ``fragile'' glass forming liquids. We suggest that these differences may result from strong and directional intermolecular interactions characteristic to RTILs. [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 1:51PM |
Z34.00013: Statistical Properties of Fluctuating Local Phases and Fluctuating Local Relaxation Rates in Glass-forming Liquids Gcina Mavimbela, Horacio E. Castillo, Azita Parsaeian Using our recently developed method [1], we determine fluctuating local phases, and their time derivatives, the ``local relaxation rates'', in simulation data of glass forming systems. We determine probability distribution functions (PDFs)and power spectra of the time derivatives at different temperatures. Some of the temperatures are such that the systems are aging for the duration of the simulations and for some of the temperatures, the systems reach equilibrium during the duration of the simulations. We study how the power spectra change with temperature. For the aging systems, we study how the PDFs vary with time.\\[4pt] [1] G.~A.~Mavimbela, H.~E. Castillo and A.~Parsaeian, arxiv:1210.1249. [Preview Abstract] |
Friday, March 22, 2013 1:51PM - 2:03PM |
Z34.00014: The Defect Diffusion Model of Glass-Forming Liquids John Fontanella, John Bendler, Mary Wintersgill, Michael Shlesinger The defect diffusion model (DDM) provides an explanation of many properties of glass-forming liquids. For example, it has been used to interpret dielectric relaxation (alpha and beta relaxations and the boson peak), viscosity, ionic conductivity, (including the effects of temperature and pressure) positron annihilation lifetime spectroscopy data, the physical basis of fragility, scaling, the ratio of the apparent isochoric activation energy to the isobaric activation enthalpy and its relationship to monomer volume, and correlation lengths. In the model, the glass transition, Tg, occurs because of rigidity percolation. In addition the transition at T$_{\mathrm{B}}$ (or T$_{\mathrm{LL}})$ is associated with mobility percolation. In the simplest form of the DDM, a supercooled liquid contains mobile single defects (MSDs) and immobile, clustered single defects (ICSDs). Consequently, dynamic heterogeneity is a natural feature of the model. If the glass transition did not intervene, all MSDs would disappear at a critical temperature Tc. In the present talk, the model will be used to comment on the change of heat capacity, thermal expansion coefficient and compressibility at Tg. [Preview Abstract] |
Friday, March 22, 2013 2:03PM - 2:15PM |
Z34.00015: Phase behaviour of a 2D system exhibiting inverse melting Ahmad Almudallal, Sergey Buldyrev, Ivan Saika-Voivod We calculate the phase diagram for a square-shoulder square-well potential in two dimensions using Monte Carlo simulation techniques. This potential has been previously used as a model for understanding the connection between the anomalous properties of liquid water and a hypothesized metastable liquid-liquid critical point. In our phase diagram, we find that melting lines appear to be first order, and that one of them exhibits a maximum temperature as well as a maximum pressure, indicating inverse melting (crystallization upon heating) over a small range in pressure. We apply Hamiltonian Gibbs-Duhem integration to find potential parameters that maximize the pressure range over which inverse melting occurs. [Preview Abstract] |
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