Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A28: Polymer Blends |
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Sponsoring Units: DPOLY Chair: Kalman Migler, National Institute of Standards and Technology Room: Baltimore Convention Center 325 |
Monday, March 13, 2006 8:00AM - 8:12AM |
A28.00001: Component Terminal Dynamics in PEO / PMMA Blends Timothy Lodge, Ilan Zeroni, Sahban Ozair As our understanding of the linear viscoelasticity of linear homopolymers improves, miscible blends of linear homopolymers constitute model systems at the next level of complexity. PEO / PMMA miscible blends are remarkable in that the disparity between the component glass transitions and monomeric friction factors is immense. We are exploring this system further by obtaining component terminal dynamics for linear PEO/PMMA miscible blends of various compositions using two different methods: forced Rayleigh scattering, providing tracer diffusivity of a labeled component, and tracer rheology, examining the relaxation of a few long chains in lower molecular weight blend matrices of varying composition. Results obtained by the two methods agree well. Furthermore, results show that the mobility of PMMA is strongly affected by the presence of PEO, its monomeric friction factor dropping precipitously upon addition of small amounts of PEO. The mobility of PEO, on the other hand, is not as greatly affected by the presence of PMMA, although still much more than indicated by published measurements on PEO segmental dynamics. These results will be discussed in the context of current models. [Preview Abstract] |
Monday, March 13, 2006 8:12AM - 8:24AM |
A28.00002: A molecular dynamics simulation study of the segmental relaxations in model polymer blends Dmitry Bedrov Molecular dynamics simulations of model miscible polymer blends consisting of chemically realistic 1,4-polybutadiene (CR-PBD) (slow component) and PBD chains with reduced dihedral barriers (LB-PBD) (fast component) have been performed in order to study the influence of blending on segmental relaxation processes. We find that blending with a slow (high glass transition temperature, or T$_{g})$ component significantly increases the separation between the $\alpha $- and $\beta $-relaxations of the fast (low T$_{g})$ component, which may be unresolvable or nearly unresolvable in the pure melt. Detailed analysis of the dielectric response of the blend allows us to conclude that the high-frequency loss observed in numerous dielectric spectroscopy studies of miscible polymer blends that is apparently uninfluenced by blending can be due to the intrinsic $\beta $-relaxation of the fast component and not due to concentration fluctuations and/or structural heterogeneities within the blend. In other words, instead of assuming that some fraction of the fast component is not affected upon blending due to presence of the pure melt-like local environments. We further investigate the segmental relaxations by examining torsional autocorrelation functions, dipole moment autocorrelation function, and dielectric response for each component and for the blend as a function of temperature and concentration. [Preview Abstract] |
Monday, March 13, 2006 8:24AM - 8:36AM |
A28.00003: Dielectric Spectroscopy of Miscible Polymer Blends Wenjuan Liu, Ralph H. Colby, Jane E. G. Lipson Segmental dynamics are studied in two miscible polymer blends; both involve polystyrene, which has sufficiently small polarizability to be ignored in dielectric spectroscopy. One blend is with poly (vinyl methyl ether) where the low-T$_{g}$ component is seen in dielectric response and the other blend is with tetra-methyl BPA- polycarbonate where the high-T$_{g}$ component dominates the dielectric response. Both blends have reasonably disparate glass transitions, and both are weakly interacting. The glass transition temperature (T$_{g})$, linear viscoelasticity and dielectric spectroscopy of the pure components and blends, respectively, are measured by differential scanning calorimetry, Rheometric Scientific ARES$^{TM}$ Rheometer and Novocontrol Broadband Dielectric Spectrometer in the frequency range of 10$^{-2}\sim $10$^{6}$ Hz. We compare the experimental results with a prediction for the relaxation spectrum obtained using a simple lattice model, wherein we generate a distribution of environments around a given segment in the blend which leads to a prediction for that component's dielectric relaxation spectrum. We show that it is possible to model the dielectric relaxation spectrum by considering concentration fluctuations at the scale of the Kuhn length (the shortest Rouse mode), which we take to be both composition and temperature independent. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A28.00004: Assessment of the Flory diluent theory to evaluate its applicability in the determination of the amorphous-amorphous interaction energy Rushikesh Matkar, Thein Kyu In the derivation of the Flory diluent theory, Flory has removed two of three assumptions inherent in Prigogine's model to determine the solubility of solids using regular solution theory, but the third assumption that solvent is completely immiscible in the crystal. An analytical expression for the calculation of the liquidus line is a consequence of the third assumption. Various researchers have also applied this theory to determine $\chi _{FH}$ representing the amorphous-amorphous interaction energy. We contest this methodology in light of the reported discrepancies in the determination of $\chi _{FH}$ in comparison with other test methods. We have removed the third assumption and established the thermodynamics of binary crystalline mixtures by the incorporation of crystal-solvent interaction effects. We identify the source of the discrepancies in this framework and recommend that all literature regarding the present topic should be treated with circumspect. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A28.00005: Designing Balanced Surfactants for Organizing Immiscible Polymers Megan Ruegg, Benedict Reynolds, Nitash Balsara, Min Lin, David Lohse The phase behavior of A/B/A-C polymer blends with attractive and repulsive interactions was analyzed with scattering experiments and mean field theories. Transitions between lamellar phases, microemulsions, homogeneous phases and macrophase separated states are easily accessed in A/B/A-C blends simply by adjusting the temperature. The domain spacing was predicted utilizing the Random Phase Approximation (RPA) and Self-Consistent Field Theory (SCFT) in the homogeneous and organized states, respectively, with no adjustable parameters. The only inputs into the calculations were the binary Flory-Huggins interaction parameters (chi) and statistical segment lengths. The domain spacing determined from theory was often within 5 percent of the experimental values. Furthermore, in this particular A/B/A-C system, in which the chi parameter between the immiscble A and B homopolymers is 2.0-2.6 in our accessible temperature range, a blend was found to form an organized phase with only 3 percent of the diblock copolymer in the blend. This is the lowest amount of polymeric surfactant to form an organized phase to our knowledge. The transition temperature from single-phase systems to a macrophase separated state determined from theory was in good agreement with experimental values. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A28.00006: The Effect of Copolymer Composition on the Dynamics of Random Copolymers in a Homopolymer Matrix. Sudesh Kamath, Mark Dadmun Copolymers can be used as interfacial modifiers in phase separated polymer blends and selective surface segregation. Important parameters in both processes include the amount of copolymer that migrates to the surface and the rate of this segregation, both of which are altered by changing the copolymer composition. The dynamics of random copolymers in a homopolymer matrix are studied using Neutron Reflectivity (NR), Quasi-Elastic Neutron Scattering (QENS) and Lattice Monte Carlo simulations. We have carried out NR and QENS measurements on blends containing 10{\%} Poly(S-ran-MMA) random copolymers with 3 different copolymer compositions dispersed in a PMMA matrix. We have also carried out lattice Monte-Carlo simulations on blends of A-B random copolymers containing 33{\%}, 50{\%} and 66{\%} A in a matrix of a homopolymer melt containing only A monomers using the bond-fluctuation model for polymer melts. Our results indicate that the copolymer composition has a significant impact on the dynamics of the copolymer. Our simulation results also indicate that copolymer composition has a significant impact on the conformation of the copolymer in the homopolymer melt, which in turn has an impact on the system dynamics. [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A28.00007: Dynamics of Ternary Mixtures with Photosensitive Chemical Reactions: Designing Three Dimensional Hierarchically Ordered Composites Olga Kuksenok, Rui D.M. Travasso, Anna C. Balazs Using coarse-grained computer modeling, we show that photo-induced chemical reactions can be exploited to create long-range order in binary and ternary mixtures. In the binary case, a photosensitive AB blend is illuminated by a spatially uniform light and therefore undergoes both a reversible chemical reaction and phase separation. The late-time morphology resembles the lamellar morphology of diblock copolymers, with lamellae oriented isotropically within the sample. Rastering a secondary, higher intensity light over the sample locally increases the reaction rate and introduces long-range ordering along the rastering direction (i.e., effectively ``combing'' the lamellar domains). We also illustrate an application of our combing technique as a replicative process, which transfers an image on the substrate through the sample. In the ternary case, we add a non-reactive component C, which is immiscible with both A and B. We show that C migrates to regions that are illuminated by the secondary, higher intensity light. Using a stationary secondary light source allows us to effectively write a three-dimensional pattern of C onto the AB sample. Rastering over the ternary system with an additional light source leads to hierarchically ordered patterns of A, B and C. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A28.00008: Shear-Induced Crystallization and Rheology Behavior of Isotactic Polypropylene and Poly (ethylene-co-octene) Blend Xia Dong, Kun Meng, Charles C. Han, Yongyan Pang, Dujin Wang Shear-induced crystallization of isotactic polypropylene (iPP) and poly (ethylene-co-octene) (PEOc) blend was studied by means of in-situ optical microscopy with a shear hot stage. Shear promoted the orientation of the polymer chains in shear direction, which results in cylindrite crystals. The cylindrites were observed when the shear rate is necessarily higher than 10s$^{-1 }$after liquid-liquid phase separation (LLPS) at 170${^\circ}$ for 420min. The cylindrites appear and grow across the phase regions and have some defects after decomposition. The cylindrites growth rates remain unchanged with shear at any given temperature, while the nucleation density increases dramatically after LLPS when shear rate is more than 10s$^{-1}$. The Blends viscosity and modulus depending on shear frequency was increased with the PEOc contents. [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A28.00009: Eutectic Modeling of Blend Crystallization from the Homogeneous Melt Sudhakar Balijepalli, Jerold Schultz The morphology and kinetics of binary polymer blends crystallizing from the homogeneous melt is similar to that of eutectic crystallization in small-molecule or metal systems. While analyses of the small molecule case exist, extension to the polymer blend case requires accounting for (a) large deviation from equilibrium and (b) growth velocity dependence on temperature and composition. Such analytical modeling has been performed, assuming low Peclet numbers. The model and results are presented here and compared with the crystallization of a blend of high and low molecular weight fractions of poly(ethylene oxide). The analysis shows a sharply peaked relationship between growth arm periodicity and velocity of growth. An assumption that the operating condition is the maximum growth velocity appears to hold. A satisfactory correlation between analysis and experiment is found. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A28.00010: Interplay Between Two Phase Transitions: Crystallization and Liquid-Liquid Phase Separation in a Polyolefin Blend Charles C. Han, Xiaohua Zhang The correlation between liquid-liquid phase separation (LLPS) and crystallization at several compositions in statistical copolymer blends of poly (ethylene-co-hexene) (PEH) and poly (ethylene-co-butene) (PEB) has been examined by optical microscopy (OM), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The overwhelming change in the crystallization kinetics due to the density fluctuation caused by the spontaneous spinodal LLPS is observed. This coupling mechanism suggests a new mechanism in the nucleation-crystallization process. All evidences are pointing to a cross-over mechanism from the spinodal fluctuations (of liquid-liquid phase separation) to the nucleation and than crystallization. The detailed experimental evidences and a suggested physical model will be presented. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A28.00011: Rheological modeling relating mesoscopic morphology for polymer blends Yuanze Xu, Wei Yu, Charles C. Han The key issue to model polyblends rheologically is to solve the problem of dynamic coupling between interfacial morphology and viscoelastic flow. This work will outline our approaches. The framework of irreversible thermodynamics was employed and the conformation of both polymer chains are introduced. By comparing with the ellipsoidal model, the constitutive equation of dilute immiscible viscoelastic blends is established. To construct the model of concentrated blends, the hydrodynamic interaction of drops was treated. The theoretical predictions were proved by measured rheological material functions and the drop dynamics in a four-roll mill rheometer. Even greater challenge exists in the formulation of multi-scale rheological model of immiscible blends with complex morphology evolution, including drop break-up and collapse. Experiments show how the interfacial processes are interfered by non-linear viscoelasticity of polymers. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A28.00012: Design of Co-Continuous Nanostructured Polymer Blends by Solid-State Shear Pulverization. Ying Tao, Jungki Kim, John M. Torkelson Achievement of co-continuous nanostructured polymer blends is of interest as such materials may have enhanced properties (e.g., toughness, stress at break, and creep resistance) in comparison to conventional blends with a micron-scale dispersed phase in a matrix phase. Leibler and co-workers (Nature Materials 1, 54 (2002)) recently produced co-continuous nanostructured blends via reactive melt blending in which irregular graft copolymers were made in situ. Here we demonstrate that achievement of such blends is possible in the solid state by use of solid-state shear pulverization (SSSP). During SSSP, polymers are mixed by exposure to high shear and compressive forces in the absence of melt processing. The morphology of the blended SSSP output is obtained by forming a consolidated sample using a cold platen press and then analyzing by scanning electron microscopy. In the case of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends, the PMMA phase can be etched with acetic acid, revealing the presence of a 3-D, nanostructured ($\sim $ 100 nm length-scale), irregular morphology. Studies are underway to determine whether such a blend nanostructure can be maintained during subsequent, limited melt processing into a final product via addition of block copolymers or gradient copolymers to the blend during SSSP. Studies are also underway with other blend systems. [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A28.00013: Polymer blends containing Linear Telechelic Supramolecular Polymers Mitchell Anthamatten, Michelle Wrue We are studying a new class of polymer blends: linear polymers blended with end-to-end associating supramolecular polymers (unimers). Since the degree of unimer association depends on concentration and temperature, we expect unusual phase behavior that differs greatly from traditional blends of two linear polymers. Low molecular weight polybutadiene unimers that bear strong hydrogen-bonding, ureidopyrimidinone end groups were synthesized. These polymers were systematically blended with monodisperse polystyrene polymers, and the resulting blends were studied using a combination of optical microscopy and light scattering techniques. Results are compared to predictions made using a simple lattice association model. Inputs include the lengths of the unimers and polymers, the free energy of forming supramolecular bonds, and a Flory-Huggins interaction parameter. [Preview Abstract] |
Monday, March 13, 2006 10:36AM - 10:48AM |
A28.00014: Rheology of blends of dense star-like polystyrene soft nanospheres Ajay Kulkarni, R.M. Kannan Highly branched polymeric materials exhibit significantly different rheological behavior compared to linear polymers, suggesting that controlled branch density can have technological benefits. We have synthesized a dense star polystyrene molecule, (PS$_{nano})$ with 50 arms, M$_{a}$= 5,000 g/mol. Using rheo-optics and triple-detection GPC, we have shown that these materials act as soft nanospheres, with a size of $\sim $ 8 nm. We are studying the effect of the nanospheres on the blending behavior of miscible polystyrene/ poly (vinyl methyl ether) (PS/PVME) blends with the help of dynamic stress-optical measurements. In PS$_{nano}$/PVME blends, at higher PS$_{nano }$wt. fractions,$_{ }$the interparticle distance between PS$_{nano}$ is smaller than radius of gyration of PVME. Therefore we expect to see the conformational changes in PVME chains induced by PS$_{nano }$and compare it with linear PS (L-PS)/PVME blends. However the rheo-optics data suggests that the relaxation dynamics of PVME is not significantly altered by PS$_{nano }$whereas for L-PS/PVME blends the relaxation dynamics of PVME is slowed down by L-PS. DSC results show a single transition suggesting miscibility. Our results suggest that, the segments of PS near the periphery of PS$_{nano }$may be miscible, but the segments at the core would be immiscible, resulting in a molecularly dispersed blend, rather than a segmentaly miscible L-PS/PVME blend. [Preview Abstract] |
Monday, March 13, 2006 10:48AM - 11:00AM |
A28.00015: Reactive extrusion: A computational approach. Manoranjan Prusty, Patrick Anderson, Han Goossens, Han Meijer Reactive extrusion is attractive for various reasons. One of them is the flexibility of extruders for processing of polymers, but also the choice of the scale of the operation that can be adjusted to the needs for research and development or commercial production. We model reactive extrusion using a diffuse interface modeling (DIM) approach. The problem is studied by dividing it into four small/sub problems. First, the structure growth in case of homo-polymer blends was studied with the effect of hydrodynamics. The logarithmic structure factor was found to scale as 1/3 with time for higher capillary numbers and 2/3 for lower capillary numbers. Second, the growth of structure for the block copolymer was studied for the symmetric blocks, for which only micro phase separation was observed. Then, the structure growth for the mixture of block copolymers and homo-polymers was studied and both micro and macro phase separation can be observed. The final step including the reaction kinetics of the formation of block copolymers from the homo-polymer is studied. Results are mainly presented showing morphology development and growth rates as a function of time. [Preview Abstract] |
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