Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session Z24: Polymer Melts & Solutions: Rheology & Dynamics |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Yonathan Thio, Georgia Tech Room: Baltimore Convention Center 321 |
Friday, March 17, 2006 11:15AM - 11:27AM |
Z24.00001: Predicting the Positions and Breadths of the Glass Transitions in Polymer-Diluent Mixtures J.E.G. Lipson, S.T. Milner When a plasticizer is added to a polymer the effect is to lower and broaden the glass transition of the polymer. Less frequently studied is the opposite range of the concentration scale, which presumably raises and broadens the diluent glass transition. In fact, although the default assumption is that this miscible combination will exhibit only one transition, we expect two transitions on theoretical grounds, one for the polymer and one for the diluent. Both should be visible at intermediate compositions unless the pure component glass temperatures are rather close. The development of our theory has been stimulated by the appearance of recent experimental data on polystyrene dibutylphthalate; the results presented in the talk will focus on its application to a series of polystyrene-diluent mixtures. Finally, the ability of our approach to predict both the transition temperatures and breadths, as well as the conditions under which two transitions may be observed, will be discussed. [Preview Abstract] |
Friday, March 17, 2006 11:27AM - 11:39AM |
Z24.00002: A Novel Technique to Measure Enthalpy Recovery for Polymer Glasses Subsequent to Temperature and Plasticizer Concentration Jumps. Lameck Banda, Mataz Alcoutlabi, Gregory McKenna We report results of the enthalpy recovery of polymer glasses subsequent to temperature jumps and carbon dioxide pressure jumps in the isothermal mode. The results were performed on a novel system that was built in our laboratory. The system is a Setaram C80 calvet calorimeter that we modified to include pressure capabilities. The system also offers the advantage of large bore chambers that facilitate the use of large samples. Additionally, experiments of enthalpy recovery subsequent to plasticizer concentration histories in the isothermal mode are feasible. Enthalpy recovery results show qualitative similarities with volumetric measurements reported in our previous work. Particularly, the three signatures of structural recovery; intrinsic isopiestics, asymmetry and the memory effect are observed. Further, consistent with the volumetric observations, enthalpy recovery results also show that equilibration times for the polymer glass are longer when the glass transition is traversed through a plasticizer jump than when traversed through a temperature jump. [Preview Abstract] |
Friday, March 17, 2006 11:39AM - 11:51AM |
Z24.00003: Glass Transition Temperature of Polyetherimide: Relationship between Thin Films and Nanoporous Materials Rahmi Ozisik, Tong Liu, Richard W. Siegel The glass transition temperature (T$_{g}$) of nanoporous polyetherimide (PEI) was investigated using differential scanning calorimetry. Nanosized pores were created by spin coating a solution of PEI and polycaprolactone-diol (PCLD) in their common solvent dichloromethane. The nanoporous structure was created by fast phase separation during spin coating and subsequent removal of PCLD with acetone. Atomic force microscopy, scanning electron microscopy and statistical methods were used to characterize the pore structure. The glass transition temperatures of both the thin PEI films and nanoporous PEI samples were lower than that of bulk PEI. The T$_{g}$ of nanoporous PEI was found to depend strongly on pore volume fraction. A Monte Carlo simulation was performed to investigate the relationship between thin films and nanoporous systems. The distribution of nearest neighbor distances (\textit{h}) were obtained from the Monte Carlo simulation, which was biased to create the pore size distribution obtained from experiments. Various moments of \textit{h} was calculated and used to compare the findings to thin film data. [Preview Abstract] |
Friday, March 17, 2006 11:51AM - 12:03PM |
Z24.00004: Dynamics of Polyethylene, Studied by Monte-Carlo Simulations E. von Meerwall, H. Lin, W.L. Mattice To compare with our diffusion (D) measurements in polyethylene (PE) melts and blends we have performed Monte-Carlo simulations on the second-nearest-neighbor diamond lattice, exploring static and dynamic properties of PE from C40 to C324 (molecular weights M from 584 to 4538) at 180 deg. C. The bridging method is based on beads combining neighboring moieties and now incorporates two-bead moves; it permits detailed reconstruction of the PE chain at any stage. It uses the short-range rotational isomeric state model and long-range intra- and interchain Lennard-Jones potentials as discretized. Reliable results depend on extended prior equilibration. In static properties, chain statistics is non-Gaussian for all but the longest chains, evidenced by an anomalous non-Rouse scaling of Rg with M; at low M chain-end effects become important. But the autocorrelation functions of the end-to-end vectors still adhere to Rouse and reptation theories for chains longer than C82. Above C100 the relaxation times scale with M in keeping with reptation theory. Center-of-mass D, converted from Monte-Carlo steps to time units according to D measured at a single M, is in excellent agreement with experiment at all M. D of five n-alkanes in M=33k PE extrapolated to trace concentration conforms to the pure Rouse 1/M prediction in the absence of chain-end free-volume enhancements, in good agreement with current experiment. [Preview Abstract] |
Friday, March 17, 2006 12:03PM - 12:15PM |
Z24.00005: Molecular dynamics studies of slow relaxation phenomena in glassy polymeric systems. Sanat Kumar, Sergei Shenogin, Arun Yethiraj, Jack F. Douglas Molecular dynamics simulations were used to study long-time structural relaxations in glass-forming polymeric systems. The model system was composed of identical hard spherical beads linked into the chains by the bonds. The minimum length of each bond was limited to 1.05 of the bead diameter to prohibit crystallization at higher densities and create completely amorphous structures. The packing volume fraction ranges from 0.45 to 0.62, with glass transition at volume fraction around 0.565. It was shown that for glassy structures the distribution of mean-squared displacements deviates from Fickian form, showing the presence of ``mobile'' particles with caged (hop-like) mechanism of mobility. As the result, dynamic heterogeneity emerges in glassy structures with two distinct distributions of ``mobile'' and ``immobile'' particles relative to the Brownian motion. Structural relaxation, shear viscosity and their relationship to particle mobility was studied for systems with different densities. These results provide the evidence that the excessive mobility of ``hopping'' particles is the reason of breakdown of Stokes-Einstein relationship in glassy systems. [Preview Abstract] |
Friday, March 17, 2006 12:15PM - 12:27PM |
Z24.00006: On the determination of primitive paths in entangled polymer melts and networks Michael Lang, Michael Rubinstein The primitive path of a polymer chain in a melt or a network can be understood as the center line for the minima of a constraining potential, which describes the essence of the entanglement interactions of neighboring chains with a given polymer. Thus, the conformation of the primitive path plays a key role for the determination of tube parameters or the shape of the tube potential. In recent years, different methods and models for the determination of the primitive paths in entangled polymer melts and networks have been proposed leading to different results for the primitive path. In this contribution, the differences of these models as well as their assumptions on systems, calculations, or simulations will be compared and discussed in order to determine the optimal method for finding a primitive path. [Preview Abstract] |
Friday, March 17, 2006 12:27PM - 12:39PM |
Z24.00007: Properties of Well-Defined Elastomeric Poly(alkylnorbornene)s and Their Hydrogenated Derivatives Richard Register, John Hatjopoulos, John Bishop Narrow-distribution homopolymers of various 5-n-alkylnorbornenes were synthesized by living ring-opening metathesis polymerization (ROMP), and subsequently hydrogenated to yield materials with the good thermooxidative stability of polyolefins. The unsubstituted hydrogenated polynorbornene is highly crystalline, with Tm = 140-150C, but all the substituted norbornenes (before and after hydrogenation) are amorphous. Hydrogenation reduces the glass transition temperature (Tg) modestly; polymers with butyl or longer substituents have Tg below ambient due to internal plasticization by the alkyl sidechains (Tg = -40C for hydrogenated polydecylnorbornene). The fractional decrease in Tg with increasing sidechain length is in good quantitative agreement with that for polyolefins, polymethacrylates, and poly(alkylstyrene)s, when the sidechain length is normalized by the number of backbone carbons per mer. The rubbery plateau moduli for these hydrogenated products are typical for elastomers, and tunable through the length of the alkyl sidechain; lengthening the sidechain from butyl to decyl increases the entanglement molecular weight by nearly a factor of three. These materials show promise as the midblocks in ROMP thermoplastic elastomers with crystalline endblocks. [work supported by NSF Polymers Program, DMR-0505940] [Preview Abstract] |
Friday, March 17, 2006 12:39PM - 12:51PM |
Z24.00008: The viscoelastic properties of ultrathin polymer films as measured with a novel nanobubble inflation technique Paul OConnell, Gregory McKenna Using a novel microbubble inflation technique developed within our laboratory, we are able to measure the absolute biaxial compliance of polymer films as thin as 13 nm. Experiments performed on both poly(vinyl acetate) (PVAc) and polystyrene (PS) films show that large reductions in the glass transition temperature at the nano-scale are non-universal, viz., the PVAc shows no reduction even for the thinnest films while the PS shows a significant reduction at a thickness below approximately 80nm. More surprisingly, the rubbery plateau region for both materials shows dramatic stiffening as the thickness is reduced (by up to 300 times), perhaps due to surface pinning of the entanglement network. The compliance increases as approximately the square of film thickness until the bulk values are achieved at a thickness of the order of 300nm. [Preview Abstract] |
Friday, March 17, 2006 12:51PM - 1:03PM |
Z24.00009: Viscoelastic Properties of Metathesis Synthesized Linear and Cyclic Macromolecules Jian Wang, Gregory McKenna, Irina Gorodetskaya, Robert Grubbs A novel method of synthesis$^{1}$ now permits the creation of closed, uncatenated rings in relatively large amounts ($>$ 1g). The metathesis synthesis route results in samples with relatively low polydispersities of $<$2. Here we report on a series of experiments on poly(octenamer) and polyethylene rings made by hydrogenating the poly(octenamer). The samples are being characterized for molecular weight, radius of gyration and intrinsic viscosity to assure their ring-like nature. Then, using conventional methods of rheometry, we are obtaining the dynamic moduli and zero shear rate (zero frequency) viscosities of the materials and comparing them to their linear analogues. Results for polymers having molecular weights between 1x10$^{5}$ and 5x10$^{5}$ g/mol, which is between 80 and 400 entanglements per chain assuming the linear entanglement molecular weight, will be discussed. Finally, in spite of the relatively low polydispersity of these samples, additional work is ongoing to fractionate them in order to obtain narrow fractions (M$_{w}$/M$_{n}<$1.1) in order that the plateau modulus and the steady state rubbery plateau modulus can be obtained. Initial work suggests that G$_{N}^{0}$ for the rings and for the linear chains is similar. $^{1}$ Bielawki, C. W.; Benitez, D; Grubbs, R. H.; \textit{Science} \textbf{2002}, 297, 2041. [Preview Abstract] |
Friday, March 17, 2006 1:03PM - 1:15PM |
Z24.00010: Observation of high viscous stress of oriented polyolefin under uniaxial tensile Qiang Fu, Bing Na, Hao Zou, Ke Wang, Qin Zhang, Charles C. Han In this work, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples, including high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP), has been determined. The viscous stress in the oriented samples takes up to 50 -70{\%} of the total stress, which is unusually high, compared with their isotropic counterparts. More over, the enhanced modulus of oriented polyolefin was found not mainly caused by the existence of shish-kebab structure, but mainly come from the contribution of viscous stress. The result is new and provides deep understanding of the origin of high modulus for oriented polymers. [Preview Abstract] |
Friday, March 17, 2006 1:15PM - 1:27PM |
Z24.00011: Probing the breakdown of chain entanglement in simple shear: The effect of molecular weight distribution Pouyan Boukany, Shi-Qing Wang Our latest particle-tracking velocimetric (PTV) observations indicate [1] that a shear rate gradient develops across the gap in cone-plate shear cell when a fairly polydisperse entangled polymer solution is subjected to a velocity-controlled shear. The co-existence of a continuous spectrum of shear rates in the different layers is inconsistent with any theoretical description of shear banding (where only two values of shear rate would coexist). Could the smooth shear rate gradient be an artifact of the cone-plate shear cell? The present study applies the PTV measurements for a linearly-displaced shear cell that is free of any stress gradient. By examining a highly monodisperse sample and comparing its behavior with that of the polydisperse sample, we aim to explore the origin of the shear rate gradient and find out whether shear banding occurs in the monodisperse sample instead of a gradient of shear rate. [1] Tapadia, P.; Wang, S. Q. \textit{Phys. Rev. Lett. }, in press (2005). [Preview Abstract] |
Friday, March 17, 2006 1:27PM - 1:39PM |
Z24.00012: Short-Range Helical Ordering of Isotactic Vinyl Polymers in the Liquid State John G. Curro, A. Habenschuss, Gustavo A. Carri Wide-angle x-ray scattering measurements on various vinyl polymer melts show that the main amorphous peak (at k$\sim $1.5 A$^{-1})$ in the structure factor initially broadens, and then forms a ``pre-peak'' that shifts to lower k as the size of the pendant group increases. To investigate this behavior we performed self-consistent PRISM calculations on isotactic polypropylene and polystyrene liquids. Good qualitative agreement was seen for the theoretical structure factors with scattering data. Analysis of the torsional angle distribution shows a significant amount of short-range helical content in the iPP and iPS melts. At 450$^{o}$K the average number of consecutive trans/gauche pairs along the chain backbone was significantly higher than for a random distribution of torsional angles. The theory indicates that the location of the pre-peak is a measure of the helix-helix correlation distance or helix ``thickness''. [Preview Abstract] |
Friday, March 17, 2006 1:39PM - 1:51PM |
Z24.00013: Concurrent Physical Aging and Polymer Degradation during Weathering of Coatings Stuart Croll, Dilhan Fernando A polyester-urethane coating system was subjected to ``accelerated'' weathering cycles under UV light, elevated temperature and moisture (in a Q-Sun 1000® chamber). Cross-link density values obtained from high temperature modulus data demonstrated chain scission with increased exposure. However, increasing Tg and tensile modulus with weathering require an additional explanation to chemical degradation. Physical aging was explored to explain the behavior. Regular and modulated DSC analysis of the coating clearly shows increasing enthalpy recovery with increased weathering of the coating. Enthalpy recovery rate in degraded polymer films was much larger than in films that had only undergone the thermal component of exposure. An effort was also made to characterize the concurrent physical-chemical aging effects by tracking the changes in the non-linearity of the molecular relaxation times and the distribution of molecular relaxation times of the weathered coating. Understanding the physical relaxation properties of polymers subjected to accelerated weathering may help in resolving differences between natural weathering and accelerated weathering cycles, and also may be used to refine models for lifetime prediction of coatings. [Preview Abstract] |
Friday, March 17, 2006 1:51PM - 2:03PM |
Z24.00014: Statics and Dynamics in model Dendrimer Melts Kostas Karatasos Molecular Dynamics simulations were employed in order to explore the static and dynamic response of model AB2 dendrimer melts of generations 3 to 6. This study was performed in a temperature range covering the states of enhanced mobility, as well as the states where a significant dynamic slow-down led to the freezing-in of the dendrimer motion. Particular emphasis was given to the investigation of the effects of the dendritic geometry and the dendrimer size to local polymer dynamics associated with the glass transition phenomena. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700