Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session V30: Flow of Immiscible Polymer Blends |
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Sponsoring Units: DPOLY Chair: Gary Leal, University of California-Santa Barbara Room: LACC 505 |
Thursday, March 24, 2005 11:15AM - 11:51AM |
V30.00001: Slip at Polymer-Polymer Interfaces Invited Speaker: A number of studies have shown that blends of immiscible polymers have anomalously low viscosity at high shear rates (Utracki, 1983). In some blends the viscosity is even lower than either of the components. Slip at the interface between the two polymers has been proposed to explain these results. Interfacial slip has also been identified as the mechanism behind the ability of fluoroelastomer process aids to reduce melt fracture (Migler, 2001). We have found that the apparent shear viscosity of multilayer samples decreases with increasing number of layers. From this viscosity decrease we have calculated slip velocities (Zhao, 2002). The theory of Furukawa (1989) and de Gennes (1992) predicts fewer chain entanglements near the interface of an immiscible polymer pair. Goveas and Fredrickson (1998) have extended the theory to calculate slip velocities. These are greater than we measure and independent of shear stress. We find that slip velocity increases with shear stress. The adhesion between coextruded layers also depends on interfacial entanglements (Cole, 2003) and thus should be related to slip. We find that adhesion decreases with increasing shear stress, but is quickly recovered with annealing for times longer than the reptation time. Reactive coupling between chains in the interface can greatly reduce interfacial slip and increase adhesion. Surprisingly, reaction rates are also accelerated greatly by flow. The addition of premade block copolymer was only effective at reducing slip after static annealing. P.J. Cole, R.F. Cook, and C.W. Macosko, Macromolecules 2003, 36, 2808-2815. R. Zhao and C.W. Macosko, J. Rheol. 2002, 46, 145-167. [Preview Abstract] |
Thursday, March 24, 2005 11:51AM - 12:27PM |
V30.00002: Stretching and colliding surfactant-coated drops Invited Speaker: Equilibrium and kinetic properties of interfacial tension govern the structure, dynamics, stability and performance of immiscible fluids, such as polymer blends, detergents and reaction and separation media. These properties also play a substantial role in microcapillary devices. Using extension flow to stretch drops, we develop a microfluidic approach to probe equilibrium and kinetic surfactant adsorption. We also monitor drop population dynamics in simple shear (over a wide range of capillary number) and identify surfactant properties and mechanisms that regulate the coalescence of drops in emulsions. [Preview Abstract] |
Thursday, March 24, 2005 12:27PM - 12:39PM |
V30.00003: Theoretical Studies of Flow-Induced Coalescence L. Gary Leal, Fabio Baldessari Recent experimental studies of coalescence involving two equal size drops in a flow, both with and without a copolymer surfactant, have provided detailed data on the conditions for coalescence. This data presents a number of puzzles that are not explained by existing theoretical models of coalescence. In this presentation, we summarize our recent theoretical attempts to understand this data, via a combination of a small capillary number asymptotic theory for film drainage, exact boundary integral calculations of the two drop collision and coalescence process, and thin-film stability theory. [Preview Abstract] |
Thursday, March 24, 2005 12:39PM - 12:51PM |
V30.00004: Rheology and flow-induced structure in a polystyrene-polyisoprene biocontinuous microemulsion Kristin Brinker, Wesley Burghardt Polymer bicontinuous microemulsions are blends of immiscible polymers compatibilized with diblock copolymer in such a way as to produce an equilibrium interconnected morphology. Previous experiments on a microemulsion of poly(ethyl ethylene) (PEE) and poly(dimethyl siloxane) (PDMS) have revealed a fascinating array of rheological and flow-induced structural phenomena. We have prepared a new microemulsion sample from low molecular weight polystyrene (PS) and polyisoprene (PI) and their corresponding block copolymer. Despite the fact that the constituent homopolymers are strictly Newtonian, the microemulsion exhibits substantial viscoelasticity associated with flow-induced deformation of the supramolecular organization. The linear viscoelastic properties of the PS-PI microemulsion closely resemble those previously found in the PEE- PDMS system. Under even fairly weakly nonlinear flow conditions, the PS-PI microemulsion exhibits a flow-induced phase transition. In situ small-angle x-ray scattering is used to probe both the flow-induced deformation of the equilibrium microemulsion structure as well as the onset and development of a flow-induced bulk phase separation. The higher suscepibility of the PS-PI system to phase separation may be related to a higher viscosity contrast between its constituents and those in the previously studied PEE-PDMS system. [Preview Abstract] |
Thursday, March 24, 2005 12:51PM - 1:03PM |
V30.00005: An Experimental Investigation of the Effects of Copolymer Surfactants on Coalescence Yosang Yoon, Adam Hsu, L. Gary Leal We report on experimental studies of the effects of copolymer surfactants on the coalescence of two equal size drops in flows generated in a 4-roll mill. In this work, the drop is polybutadiene (PBd) and the suspending fluid is polydimethylsiloxane (PDMS). A copolymer is formed at the interface via the introduction of small quantities of end-functionalized PBd and PDMS that form an ionic complex. We consider the effects of the viscosity ratio of the bulk fluids, the mean surface concentration of copolymer, the molecular weight of the copolymer, the strength of the flow (measured via the capillary number), and the collision trajectory on the conditions for coalescence. [Preview Abstract] |
Thursday, March 24, 2005 1:03PM - 1:15PM |
V30.00006: Local control of periodic pattern formation in driven binary immiscible fluid Olga Kuksenok, David Jasnow, Anna C. Balazs Via a coarse-grained model, we simulate the dynamics of a binary, immiscible blend that is driven through a three dimensional microchannel. At the inlet of the channel, we assume a checkerboard arrangement of the components. We find that local perturbations in the temperature at the center of this checkerboard pattern can be exploited to create periodic, oscillatory patterns along the length of the channel. We derive scaling arguments that allow us to estimate the period of the oscillatory structures. We also analyze the stability of these patterns and the mechanism for the wavelength selection within the system. We find that relatively small changes in the local perturbations at the inlet of the channel can lead to dramatic changes in the morphology along the channel's length and can be used to design well-controlled periodic structures. [Preview Abstract] |
Thursday, March 24, 2005 1:15PM - 1:27PM |
V30.00007: Effect of Shear Flow on Morphology Development near Critical Point of Phase Diagram in Polymer Blend Toshiaki Ougizawa, Machiko Naito The effects of simple shear flow on the phase behavior and morphology near critical point of phase diagram were investigated by a rotational parallel-plates apparatus for a blend of poly(methyl methacrylate) (PMMA)/poly(styrene-\textit{co}-acrylonitrile)(SAN29, 29wt{\%}AN) which has a Lower Critical Solution Temperature-type phase diagram. In the two phase region near critical point, for the parallel direction to the shear flow, the highly elongated morphology was observed by a transmission electron microscope. However, for the perpendicular direction, very fine co-continuous morphology which has size less than 100nm was observed in spite of shear flow field. It was considered that this morphology was formed by elongating modulated structure which was formed by the conventional spinodal decomposition (SD). The coarsening behavior from this fine morphology after shear cessation took place competing with usual SD. However, SD was superior and finally the shear memory for morphology disappeared. [Preview Abstract] |
Thursday, March 24, 2005 1:27PM - 1:39PM |
V30.00008: Multi-scale simulation of dynamical properties of polymer blend interfaces Bharadwaj Narayanan, Victor Pryamitsyn, Venkat Ganesan We present the results of a multiscale simulation approach which combines Brownian dynamics simulations with polymer self- consistent field theory and continuum mechanics to study two effects: (i) The dynamical properties of polymer blend interfaces and the influence of block copolymer compatiblizers; (ii) The effect of externally applied simple shear flow on the phase behavior of polymer blends. In the first context, our numerical results agree quite well with the predictions from scaling approaches and phenomenological theories. Moreover, these results also provide a microscopic explanation of the negatively deviating viscosities of polymer blends. We also present results elucidating the "slip suppressing" influence of block compatiblizers. In the second context, we explore the effects of visoelastic asymmetry and the composition dependence of polymer mobilities as driving forces for shear induced mixing and de-mixing phenomena seen in polymer blends. Our results suggest a rich variety of behavior arising from the interplay between viscoelasticity and thermodynamics and is in qualitative agreement with other theories and experimental observations. [Preview Abstract] |
Thursday, March 24, 2005 1:39PM - 1:51PM |
V30.00009: Low Temperature Processing of Core-Shell Baroplastics Juan A. Gonzalez Leon, Sang-Woog Ryu, Sheldon A. Hewlett, Jeffrey A. Borowitz, Anne M. Mayes Baroplastics are nanophase materials that exhibit the ability to flow and be molded under pressure at reduced temperatures. Core-shell nanoparticle baroplastics comprised of one soft component, such as poly(butyl acrylate), and one glassy component, such as polystyrene, were synthesized by miniemulsion polymerization and processed at temperature as low as 25$^{\circ}$C by compression molding and extrusion. The resulting specimens are clear and well-defined solid objects with a diverse range of mechanical properties depending on composition, ranging from tough, rigid materials to rubbery materials comparable to commercial thermoplastic elastomers. SANS and DSC measurements on the core-shell materials before and after processing reveal pressure induced partial mixing of the hard and soft components, while TEM studies show that the core-shell morphology is substantially retained, even after 20 reprocessing cycles. Mechanical properties of the processed samples were measured to elucidate the effects of processing pressure and temperature and to isolate the role of the pressure-induced miscibility. [Preview Abstract] |
Thursday, March 24, 2005 1:51PM - 2:03PM |
V30.00010: Surfactant effects on drop breakup and tip streaming Charles Eggleton, Kathleen Stebe Whenever one fluid is to be dispersed in another, the interface between the fluids are stretched and deformed. The dispersing fluid breaks into smaller droplets under the effects of viscous stresses exerted by the continuous fluid. For immiscible fluids with surfactant-free interfaces, there is generally good agreement between observed and predicted deformations and breakup modes. Surfactants are commonly added to reduce the surface tension, and hence the work required to create new interface. In a flowing system, surfactants distribute themselves non-uniformly on drop interfaces, thereby creating complex interfacial boundary conditions that depend on the amount of surfactant adsorbed, the mass transfer dynamics of that surfactant and the equation of state relating the surface tension to the local surfactant concentration. Droplet deformation is simulated as a function of these physicochemical parameters resulting in a wide variety of responses. Surfactants can cause a drop to break under flow conditions where they would otherwise be stable and cause the tip streaming mode of drop breakup. Compared to the insoluble case, as surfactant mass transfer rates are increased the drop is first destabilized, breaking up at lower rates of strain; then stabilized breaking up at higher rate of strain in a different mode. [Preview Abstract] |
Thursday, March 24, 2005 2:03PM - 2:15PM |
V30.00011: Effect of the Shear Rate on the Morphology Development for Compatibilized PA6/SAN25 Blends Toshiaki Ougizawa, Naoyuki Kitayama The effect of shear rate on the morphology development for uncompatibilized and compatibilized PA6/SAN25 blends has been studied. Two kinds of anhydride-grafted SAN25 (MAH) with different functionality were used as compatibilizers and the content of MAH was varied from 1 to 5wt {\%}. At the composition of 50/50, the blend morphology sensitively evolves with the shear rate applied, and the transition from SAN25 phase to PA6 phase continuity via a phase inversion is observed. Adding MAH causes the shear rate where the phase inversion occurs to shift to a higher shear rate. At the compositions of 75/25 and 25/75, the dispersed particle size decreases with the increase in the shear rate applied; whereas, it grows with the further increase in the shear rate after it reaches the minimum regardless of the compatibilization. This means that once finely disperse particles aggregate and form larger dispersions under a certain shear condition. This fact contradicts to the widely believed conventional compatibilization concept, and it is speculated that the excessive energy may mechanically destroy the interfacial layer formed with reactive compatibilizers and two component polymers [Preview Abstract] |
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