Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y18: Polymer Blends |
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Sponsoring Units: DPOLY Chair: Valeriy Ginzburg, Dow Chemical Room: Colorado Convention Center 103 |
Friday, March 9, 2007 11:15AM - 11:27AM |
Y18.00001: Thermodynamic Properties of A/B/A-C Polymer Blends from SANS and USANS Nisita Wanakule, Megan Robertson, David Lohse, Nitash Balsara We have studied the thermodynamic properties of blends of two homopolymers and a block copolymer (A/B/A-C blends) by small angle neutron scattering (SANS) and mean field theories. The binary A-C interactions demonstrate an upper solution critical temperature, B-C interactions show a lower solution critical temperature, and A-B interactions exhibit entropic behavior. We have demonstrated that as little as 1\% of the A-C block copolymer is adequate for stabilization of 50/50 A/B mixtures. It is however, difficult to quantify the structure of blends with very low copolymer concentrations alone because the periodic length scales obtained are in the 100s of nanometers. We are thus embarking on ultra-low angle SANS (USANS) experiments to elucidate the properties of these systems. A comparison of SANS and USANS data obtained from these blends will be presented at the meeting. [Preview Abstract] |
Friday, March 9, 2007 11:27AM - 11:39AM |
Y18.00002: Kinetic Studies of Pressure-Quenched A/B/A-C Polymer Blends Alisyn Nedoma, Megan Robertson, David Lohse, Nitash Balsara The pressure-dependence of the thermodynamics of multicomponent A/B/A-C polymer blends was studied using small angle neutron scattering (SANS) and mean field theories. At atmospheric pressure, the A/C and A/B Flory-Huggins chi parameters are positive and decrease with increasing temperature while the B/C chi parameter is negative at room temperature and it increases with increasing temperature. Under ambient conditions a microphase separated state exists for low temperatures, a disordered micelle phase for intermediate temperatures, and a macrophase separated state for high temperatures. Surprisingly, we find that at elevated pressures the system is homogeneous over a wide range of temperatures and pressures. Starting from the homogeneous phase, we will perform time-resolved SANS experiments after a reverse pressure quench on our A/B/A-C blend to study the kinetics of macrophase and microphase separation. The results of these experiments will be presented at the meeting. [Preview Abstract] |
Friday, March 9, 2007 11:39AM - 11:51AM |
Y18.00003: Effects of deuterium labeling at PS/PMMA interfaces studied with resonant soft x-ray reflectivity H. Ade, C. Wang, S. E. Harton, B. Watts, T. Araki The interfacial widths of PS/PMMA and deuterated-PS/PMMA bilayer interfaces were analyzed using resonant soft x-ray reflectivity (RSoXR). The PS and dPS utilized had the same molecular weight and poly-dispersity. Identical sample preparation and film thicknesses were used, respectively. The PS/PMMA bilayer width was consistently smaller than the dPS/PMMA width for a number of different thickness combinations. This is unexpected, based on previously reported bulk Flory-Huggins parameters for PS/PMMA and dPS/PMMA, respectively. Based on these bulk values, self consistent field theory asserts that the width of a PS/PMMA interface would be greater than that of a dPS/PMMA interface. In contrast, Harton \textit{et al. }[1] have recently reported the strong preferential segregation of dPS to a dPS:PS/PMMA interface. The RSoXR results are qualitatively consistent with the results of Harton \textit{et al} and confirm that the thermodynamic properties of PS/PMMA interfaces are substantially different from the properties in the bulk. [1] S. E. Harton\textit{ et al.}, Macromolecules \textbf{39}, 1639 (2006). [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:03PM |
Y18.00004: Ion solvation and its effects on polymer blend miscibility Zhen-Gang Wang We study the solvation of small ions in a binary blend of two homopolymers having different dielectric constants. The preferential solvation of ions by the high dielectric constant component results in decreased miscibility of the two polymers. We first consider the solvation of a single ion in the mixture and its effect on the local composition change using the Flory-Huggins-de Gennes free energy for the polymer blend. This single-ion information is then used to construct a bulk free energy valid for small ion concentrations, from which the shift in the spinodal and coexistence curve is calculated. [Preview Abstract] |
Friday, March 9, 2007 12:03PM - 12:15PM |
Y18.00005: Thermoreversible bond formation in multi-component polymer blends Richard Elliott, Glenn Fredrickson We investigate theoretically thermoreversible bond formation and phase transitions in a system composed of end-linking, difunctional linear polymers. The two chemically distinct polymer species are allowed to bond heterogeneously so that only linear chains with alternating block sequences form. Interactions between dissimilar segments are described with Flory-Huggins contact potential, whereas the amount of reversible bonding is controlled with a single parameter of binding affinity. We use a mean-field approach to describe the onset of meso-scale ordering as a function of the binding affinity. [Preview Abstract] |
Friday, March 9, 2007 12:15PM - 12:27PM |
Y18.00006: Modeling of Crystallization and Phase Separation in Binary Blends Driven by Photopolymerization Pankaj Rathi, Thein Kyu Polymerization of a reactive component in a binary blend raises the molecular weight of the reactive species which drives phase transformation involving phase-separation, mesophase ordering in liquid crystals or crystallization. We demonstrate a novel phenomenon of photo-polymerization induced crystallization in a blend of a crystalline component and reacting monomer. Blending a crystalline substance with a solvent or monomer lowers melting temperature of the crystalline component. When photopolymerization is carried out at an isotropic phase temperature above the melting point of the blend, the depressed melting point curve of the crystalline component shifts above the reaction temperature and triggers crystallization. To predict this phenomenon, a theoretical model has been developed. Phase diagrams are calculated from the free energy description of a blend containing crystalline constituent. Snapshots indicating the movement of melting point curve and the upper critical solution temperature with polymerization reaction are demonstrated. Pattern formation dynamics are calculated to demonstrate the crystal growth driven by photopolymerization. [Preview Abstract] |
Friday, March 9, 2007 12:27PM - 12:39PM |
Y18.00007: Shear-induced Crystallization of and Polypropylene/Poly(Ethylene-co-Octene) Blends Xia Dong, Kun Meng, Chenggui Zhang, Tongchen Sun, Charles C. Han, Jianhua Dong Isothermal crystallization under shear in a blend of isotactic polypropylene (iPP) and poly (ethylene-co-octene) (PEOc) was investigated by in-situ optical microscopy and shear hot stage under various thermal and shear histories. Shish-kebab crystal structures were observed under shear in phase separated iPP/PEOc blends. Very long cylindrites can form under shear, with length scale much longer than the dimension of the liquid-liquid phase separated domains under the applied shear conditions. The cylindrites appear to grow through crystallizable domains, as well as through non-crystallizable ones. All evidences points to the exacted that the nuclei (`shish') came from the orientation of the entangle network chains instead of pull out chain bundles. The shear rate and the shear time have different effects on the formation of the cylindrites after liquid-liquid phase separation. [Preview Abstract] |
Friday, March 9, 2007 12:39PM - 12:51PM |
Y18.00008: Nanoparticles as Blend Compatibilizers: Layered Silicates and Fullerenes Jitendra Sharma, Romesh Patel, Liang Xu, Ramanan Krishnamoorti Blending of polymers is an excellent way to achieve designer materials that combine specific properties of individual polymers to obtain end product with improved properties. However, processing of such materials many times is confounded by the undesirable large scale phase separation. Recent research has focused on utilizing micron-sized additives like carbon black(1) and glass beads(2) etc., to reduce the interfacial energy and promote mixing. Despite industry-scale success of the method, features like high particle loadings and the subsequent increase in the density of the material is undesirable. Replacement of micron-sized particles with nanoparticles (NPs) and the resultant increase in the interfacial surface to volume ratio potentially helps resolve this issue. We present results from our investigation of the role of two different classes of NPs namely, layered silicates and fullerenes (covering a range of three dimensional architecture and aspect ratio), on the compatibilization of two immiscible polymers of PS and PMMA as probed by AFM. \begin{enumerate} \item C. Calberg et al., \textit{Appl. Phys. } \textbf{1999}, $32$, 1517. \item H. Tanaka et al., \textit{Phys Rev Lett.} \textbf{1994}, $72$, 2581. \end{enumerate} [Preview Abstract] |
Friday, March 9, 2007 12:51PM - 1:03PM |
Y18.00009: Compatibilization of Polymer Blends via Reactive Processing with Telechelic Copolymers Earl Ashcraft, Mark Dadmun Blends of polystyrene and polyisoprene are reactively compatibilized using telechelic polystyrene and polyisoprene additives. A blend of PS/PI and telechelic polymers is melt mixed at 180\r{ }C, resulting in the in-situ formation of multi-block copolymers during mixing by the reaction of telechelics at the interface, which compatibilize the phase-separated homopolymer blend. The conversion of telechelic polymer into copolymer is quantified using GPC with fluorescence detection. In this project, the effect of using high and low reactivity end-groups is examined. The effect of the telechelic molecular weight on copolymer formation and blend properties is also examined. The results show that the anhydride/amine pair yields approximately 30{\%} - 50{\%} conversion after 10 minutes of mixing, with no further conversion after this time period. The epoxy/COOH pair shows much slower conversion. The stability of the blend morphology is quantified by determining the coarsening constant of the phase-separated blend from SEM. Preliminary DMA data suggests that the multi-block copolymers improve the interfacial adhesion of the blend, supporting the GPC and SEM results. [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:15PM |
Y18.00010: The Effect of Copolymer Composition on the Dynamics of Random Copolymers of Styrene and Methylmethacrylate in a PMMA Matrix: A Neutron Reflectivity Study Sudesh Kamath, Mark Dadmun, William Hamilton, Michael Arlen The effect of copolymer composition on their dynamics in a homopolymer matrix have been studied using specular neutron reflectivity (NR). Four random copolymers containing 50, 54, 67 and 80 $\%$ MMA were studied at 10 $\%$ wt loading in d-PMMA. The mutual and tracer diffusion coefficients, the effective friction coefficients, and the relaxation times for these copolymers were determined. The results demonstrate that copolymer composition has a significant impact on their dynamics. Analysis of the friction factor using the Lodge-Mcleish model indicates that the local composition around a copolymer is richer in Styrene than the model predictions. We attribute this to the fact that the model uses only chain-connectivity to calculate the self-concentration and ignores contributions due to thermodynamic interactions between the two blend components. Our data indicate that the local environment around a copolymer is richer in styrene. This is in agreement with our simulation results and indicates that the styrene monomers in the copolymer aggregate together to minimize contact with the PMMA matrix. [Preview Abstract] |
Friday, March 9, 2007 1:15PM - 1:27PM |
Y18.00011: Nucleation in Polymer Blends Edward Feng The existing theories for nucleation in polymer blends fail to capture the results of recent experiments by Balsara and coworkers. Part of the explanation for this disagreement is the thermodynamic nature of these theories which does not account for kinetic effects. In order to study effect of dynamics on nucleation, we consider a kinetic Ising model in which the total magnetization is constant, the simplest realistic model for liquid-liquid phase separation. [Preview Abstract] |
Friday, March 9, 2007 1:27PM - 1:39PM |
Y18.00012: Poly(ethylene oxide) Dynamics in Blends with Poly(vinyl acetate) Junshu Zhao, Mark Ediger $^{2}$H NMR relaxation measurements were performed to study the segmental dynamics of perdeuteropoly(ethylene oxide) (d$_{4}$PEO) in miscible blends with poly(vinyl acetate) (PVAc). For two compositions (2{\%} and 50{\%} d$_{4}$PEO), spin-lattice relaxation times were measured in a temperature range well above T$_{g}$. Over the temperature range studied, the segmental dynamics of the PEO component in 2{\%} PEO/PVAc blend is almost the same as that in 3{\%} PEO/PMMA blend reported by Lutz et al. (\textit{Macromolecules 2003, 36, 1724-1730}), even though the T$_{g}$ of PVAc is 100K lower than that of PMMA. In the 2{\%} d$_{4}$PEO blend, the segmental dynamics of PEO is 9 orders of magnitude faster than PVAc segmental dynamics at the blend T$_{g}$. For the two compositions studied, segmental dynamics of the PEO component can be well described by L-M model with a self-concentration of 0.3. By comparing the segmental correlation times of the PEO component with viscoelastic shift factors reported by Urakawa et al. (\textit{J. Non-Crystalline Solids 352, 2006 5042-5049}), it is found that the temperature dependence of the segmental dynamics of the PEO component is weaker than the temperature dependence of the PEO terminal dynamics. [Preview Abstract] |
Friday, March 9, 2007 1:39PM - 1:51PM |
Y18.00013: Viscosity of ``Nanoparticle''/Polymer Mixtures John G. Curro, Amalie L. Frischknecht Recently it has been observed by Tuteja et al. (Macromolecules 38, 8000 (2005)) that when single crosslinked polystyrene macromolecules (nanoparticles) are added to sufficiently high molecular weight linear polystyrene melts, the viscosity of the mixture decreases in apparent contradiction to Einstein's law of viscosity of dilute suspensions. We propose that this unexpected behavior can be understood by considering the system as a miscible polymer blend rather than a suspension. An approximate formulation for the blend viscosity is developed based on an additive mixing rule using the Rouse and reptation models for the linear melt at low and high molecular weights respectively. This theory predicts that upon addition of crosslinked macromolecules, the mixture viscosity increases (decreases) for low (high) molecular weights of the linear chain component in qualitative agreement with experiment. Moreover, the effect of the molecular weight of the crosslinked macromolecules on the mixture viscosity was in accordance with the data of Tuteja and coworkers. [Preview Abstract] |
Friday, March 9, 2007 1:51PM - 2:03PM |
Y18.00014: T$_{g}$ in Polymer/Oligomer Athermal Blends Wei Zheng, Sindee Simon The glass transition behavior of poly($\alpha $-methyl styrene), its tridecamer, and athermal blends with its hexamer is investigated using differential scanning calorimetry. The blends are prepared to exhibit approximately the same T$_{g}$ as the tridecamer but with varying molecular weight distributions. The glass transition of the blends is found to become broader than that of the pure materials. However, the absolute heat capacity of the blends maintains unchanged from its components indicating that the blends are athermal mixtures. The broadening of the Tg is evaluated in the context of recent models describing this behavior. In addition, we examine the ability of the TNM model to describe the rate dependence of T$_{g}$ and aging effects. [Preview Abstract] |
Friday, March 9, 2007 2:03PM - 2:15PM |
Y18.00015: Surface-induced structure formation of polymer dispersed liquid crystals on chemically gradient substrate Jun Wang, Jianfeng Xia, Suck Won Hong, Feng Qiu, Zhiqun Lin We investigate that the domains of polymer dispersed liquid crystals (PDLC) thin film can be directed into ordered structures by a chemically gradient substrate. A unique phase separation kinetics was observed. The pattern on the substrate was successfully transferred to the PDLC film, resulting in alternating LC rich phase and polymer rich phase as confirmed by confocal Raman measurements. This simple yet novel approach enables the organization of micrometer size LC domains in thin polymer matrix without photo irradiation. [Preview Abstract] |
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