Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y30: Solid Amorphous Polymers |
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Sponsoring Units: DPOLY Chair: Greg McKenna, Texas Tech Room: LACC 505 |
Friday, March 25, 2005 11:15AM - 11:27AM |
Y30.00001: Effective Medium Theory of the Translation-Rotation Paradox for Probe Diffusion in Glass Grigori Medvedev, James Caruthers Whereas classic Stokes-Einstein and Debye (SED) theories state that the ratio of translational and rotational diffusion coefficients for a particle in a viscous fluid is a constant, studies of the probe diffusion in supercooled liquids have shown that these diffusion coefficients have essentially different temperature dependencies. The dynamic heterogeneity of the medium near glass transition has been postulated to be the source of the apparent violation of the SED prediction in the numerical simulation by Ediger and co-workers; however these authors did not deal with the rotational diffusion explicitly, estimating it as a simple average over all spatial locations. We expand the Zwanzig theory of diffusion in a dynamically disordered medium to include both translational and rotational diffusion. Our main result is that there exists a range of fractions of ``fast'' domains in which the translational diffusion is already above its percolation threshold, and thus enhanced, whereas the rotational diffusion is still below its percolation threshold, and thus controlled by the ``slow'' domains. [Preview Abstract] |
Friday, March 25, 2005 11:27AM - 11:39AM |
Y30.00002: A Comparison of Techniques for Analyzing Dielectric Relaxation Spectra Containing DC Conductivity Chad Snyder Because of its versatility and broad frequency range, dielectric relaxation spectroscopy (DRS) continues to find new applications in materials science. The one limitation of the technique is that DC conductivity ($\sigma _{DC}$) can overwhelm the dielectric loss spectra ($\varepsilon ^{\prime \prime}(\omega )$), making meaningful analysis difficult. As a result of this difficulty, a number of methods have been developed over the years to estimate $\sigma _{DC}$ and thereby "remove" it from $\varepsilon ^{\prime \prime }(\omega )$. A comparison is made of the benefits and limitations of several of these methods, including graphical methods based on complex plane analysis, curve fitting, and numerical Kramers-Kronig methods. [Preview Abstract] |
Friday, March 25, 2005 11:39AM - 11:51AM |
Y30.00003: Evolution of entanglements in crazing of glassy polymers Robert S. Hoy, Mark O. Robbins Highly entangled polymer glasses often fail via crazing [1]. The polymer expands by a large factor $\lambda$ from an initial dense state to a craze network of fibrils and voids. The value of $\lambda$ is found to correlate with the chemical distance between entanglements in both experiments [1] and simulations [2], indicating that the entanglements act like chemical bonds in limiting the expansion. We have applied the primitive path analysis method developed by Everaers et. al. [3] to follow the real space structure of entanglements in model polymer glasses during crazing. A wide range of initial states corresponding to melts with different Kuhn lengths and entanglement lengths was studied. In each case the primitive paths deform affinely and the number of entanglements remains constant during craze formation. Straining the craze past $\lambda$ leads to a gradual reduction in the number of entanglements, and ultimately to craze fracture.\newline 1. E. Kramer and L. L. Berger, Adv. Polym. Sci. {\bf 91/92}, 1 (1990).\newline 2. J. Rottler and M. O. Robbins, Phys. Rev. E {\bf 68}, 011801 (2003).\newline 3. R. Everaers, {\it et al.}, Science {\bf 203}, 823 (2004). [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:03PM |
Y30.00004: Heat Capacity of Poly(vinylmethylether) in the Presence and Absence of Water M. Pyda, K. Van Durme, B. Wunderlich, B. Van Mele Heat capacity, $C_{p}$, of poly(vinylmethylether), PVME, without and with water has been measured from 5-375 K, using adiabatic and differential scanning calorimetry. The PVME has a glass transition at 248 K. At lower temperatures, $C_{p}$ of the solid is linked to group and skeletal vibrations. The skeletal vibrations are described by a Tarasov equation with three characteristic temperatures. The experimental $C_{p}$ agrees to better than $\pm $3{\%}. The $C_{p}$ of the liquid is 72.36 + 0.136~$T$ [J/(K mol)] and compares well with results estimated from constituent groups of other polymers using the ATHAS Data Bank. The calculated solid and liquid $C_{p}$ was used as baseline for the analysis of amorphous PVME with different thermal history, to follow the crystallization, melting, mixing, and demixing within the PVME-water system. Also, knowing $C_{p}$ of the solid and liquid, the enthalpy, entropy, and Gibbs function of glassy and liquid PVME was calculated.. [Preview Abstract] |
Friday, March 25, 2005 12:03PM - 12:15PM |
Y30.00005: Dynamics of phenylene rings in engineering thermoplastics. A quasielastic neutron scattering study Arantxa Arbe, Silvia Arrese-Igor, Iban Quintana, Angel Alegria, Juan Colmenero, Bernhard Frick By using quasielastic neutron scattering we have contributed to the long-standing question of the molecular motions behind the secondary relaxations in engineering thermoplastics. The phenylene Hydrogen motions in polyethersulfone and bisphenol-A polysulfone, polycarbonate and phenoxy have been studied by combining time of flight and backscattering techniques in the time range from about 0.1 ps to 1ns. After vibrations and fast processes below 2 ps, the Hydrogen motions reveal relatively fast oscillations and 180$^{\circ}$ flips of the rings in all cases. Polycarbonate phenylene groups additionally show rotations of about 90$^{\circ}$. Relationships among the microscopically observed motions and the secondary relaxations as followed by mechanical and/or dielectric spectroscopy are established. [Preview Abstract] |
Friday, March 25, 2005 12:15PM - 12:27PM |
Y30.00006: Chemical Vapor Deposition of Polybenzoxazole Precursors Mitchell Anthamatten, Xichong Chen Polybenzoxazoles are well known for their outstanding thermal and mechanical properties. We will describe a new solventless, chemical vapor deposition approach to fabricating films of high strength polybenzoxazoles. Advantages of such an approach are: 1) control of film thickness, 2) conformal coating onto substrates, and 3) potential improvement of in-plane mechanical properties. Our process involves the vacuum evaporation of two monomers: a hydroxyl-functionalized diamine (DHB) and a dianhydride (PMDA). The resulting films appear uniform and contain poly(amic acid) linkages. FTIR experiments show that the poly(amic acid) converts to a polyimide material upon curing at 150 to 200 degrees C. At higher temperatures there is evidence that benzoxazole linkages form, though, interestingly, we also observe a concomitant decrease in the film's mass. Our current studies aim at understanding these high-temperature processes and how they impact the polymer's crystallinity and mechanical properties. [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 12:39PM |
Y30.00007: Depletion Effect on Self-Organization of atactic Polymer Chain Segments in Microcells Zhaoqu Wang, Kaiyi Liu, Bo Che, Gi Xue Glass transitions for atactic polystyrene and poly(methyl methacrylate) prepared in nano-cells by microemulsion polymerization in the presence of non-solvents were measured by DSC experiments. An increase in $T_{g }$was observed for these polymers. The first DSC scan for the virgin polymers indicated $T_{g}$ at 112 $^{o}$C and 138 $^{o}$C for$ a$-PS and $a$-PMMA, respectively. While the re-precipitated samples show $T_{g}$ at 105 $^{o}$C and 125 $^{o}$C, respectively. Solid-state NMR relaxation and wide angle X-ray diffraction experiments indicated that the virgin polymer powders were in compact and partially self-organized states. The re-precipitated $a$-PS and $a$-PMMA did not show any self-organization under the same experimental conditions, although there are no changes in molecular weight or tacticity of the polymer chains. A depletion-interaction phenomenon was understood to provide entropic force for the self-organization of polymer chains inside the walls of the microemulsion cells during polymerization. [Preview Abstract] |
Friday, March 25, 2005 12:39PM - 12:51PM |
Y30.00008: Structure Effect on the Crosslinking Behavior of Bismaleimides Jung Park, Sung Jang The molecular structure effect on the cure characteristics of some bismaleimides (BMIs) was investigated. Four different types of BMI resins were synthesized via addition reaction of diglycidyl ether of bisphenol A with N-(3-carboxy phenyl) maleimide or N-(4-carboxy phenyl) maleimide. The change in the chemical structure was confirmed by FTIR and NMR. Kinetic parameters were determined from dynamic and isothermal differential scanning calorimetry (DSC). The maximum conversion as a function of temperature was compared with the viscosity change during cure. Both DSC and chemorheology studies show that the overall curing rate is faster for meta substituted BMIs than para substituted ones. At a fixed heating rate in the chemorheology study, viscosity started to increase at higher temperature for meta substituted BMIs, compared with para substituted BMIs. The asymptotic final viscosities were higher for shorter chains due to their resultant higher crosslinking densities. The substituent position showed much greater effect on the cure kinetics than the chain length within the experimental range of this study. The activation energies of the cure reactions were obtained from both DSC and viscosity measurements. [Preview Abstract] |
Friday, March 25, 2005 12:51PM - 1:03PM |
Y30.00009: Frontal photopolymerization and applications in complex fabrication Joao Cabral, Steven D. Hudson, Christopher Harrison, Jack Douglas The exposure of a photopolymerizable liquid to light may leads to a propagating wavefront of network formation that invades the unpolymerized material from the illuminated surface. We theoretically describe this light-driven frontal photo-polymerization (FPP) process, which is the basis of many commercially important fabrication methods, in terms an order parameter phi(x,t) characterizing the extent of monomer-to-polymer conversion, the temporally and spatially evolving optical attenuation T(x,t) of the medium, and the height h(t) of the resulting solidified material. The non-trivial aspects of this frontal polymerization process derive from the coupling of miu(x,t) and the growing non-uniform network h(x,t) and we consider limiting situations in which the optical attenuation increases (`photodarkening') or decreases (`photobleaching') in time. Since FPP fabrication of complex three-dimensional structures containing components having different material characteristics would greatly extend the practical utility of this method, we explore the influence of nanoparticle (silica, titania, and multi-wall carbon nanotube) additives on FPP front propagation. We also characterize the influence of temperature on the kinetics of FPP since this factor can often be controlled in practice. Our results are utilized in the fabrication of complex structures and in particular, of microfluidic masters and devices. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:15PM |
Y30.00010: Chain Length Dependence of the Thermodynamic Properties of Linear and Cyclic Alkanes and Polymers Sindee Simon, Dinghai Huang, Gregory McKenna The specific heat capacity was measured with step-scan DSC for linear alkanes from pentane to nonadecane, for several cyclic alkanes, for linear and cyclic polyethylenes, and for a linear and a cyclic polystyrene. For the linear alkanes, the specific heat capacity in the equilibrium liquid state decreases as chain length increases; above a carbon number N of 10 (decane) the specific heat asymptotes to a constant value. For the cyclic alkanes, the heat capacity in the equilibrium liquid state is lower than that of the corresponding linear chains and increases with increasing chain length. At high enough molecular weights, the heat capacities of cyclic and linear molecules are expected to be equal, and this is found to be the case for the polyethylenes and polystyrenes studied. The thermal expansion coefficients and the specific volumes of the linear and cyclic alkanes are also calculated from literature data and compared with the trends in the specific heats. [Preview Abstract] |
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