Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session V24: Phase Transitions in Polymeric Systems II |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Kristopher Lavery, National Institute of Standards and Technology Room: Colorado Convention Center 201 |
Thursday, March 8, 2007 11:15AM - 11:51AM |
V24.00001: Phase Transition of Long Chain Normal Alkanes in Confined Geometry Invited Speaker: Encapsulated normal ($n-)$ alkanes can provide well-defined model systems for studying the complex crystallization behaviors of polymers. The size controllable microcapsules with different surface morphology (SEM) have been prepared in the present work, which provide ideal confined geometry for the crystallization research of long chain $n$-alkanes. Crystallization and phase transition behaviors of long chain $n$-alkanes (from C18 to C21) in microcapsules were studied with the combination of differential scanning calorimetry (DSC), X-ray diffraction (XRD) as well as Fourier transform infrared spectroscopy (FTIR). As evident from the DSC measurement, a surface freezing monolayer, which is formed in the microcapsules before the bulk crystallization, induces a novel metastable rotator phase (RII) on the cooling process of microencapsulated $n-$nonadecane. We argue that the existence of the surface freezing monolayer provides the ideal nucleation sites, and consequently decreases the nucleating potential barrier of RII phase and turns the transient RII phase to a ``long-lived'' metastable phase. [Preview Abstract] |
Thursday, March 8, 2007 11:51AM - 12:03PM |
V24.00002: Supercritical Fluid-Assisted Electrospinning of Polymers Mark McHugh, Manuel Marquez, Zhihao Shen, Jun Liu, Sanho Lee In this talk we describe the application of near-critical and supercritical CO$_{2}$ as an electrospinning processing aid to create fibers with novel morphology readily varied by adjusting the operating pressure and temperature. We demonstrate the application of CO$_{2}$ to electrospin poly(vinyl pyrrolidone) (PVP) from PVP-dichloromethane (DCM) solutions. The formation of PVP fibers is directly related to the DCM-CO$_{2}$ phase behavior since the electrospinning operating pressures are well below those needed to dissolve neat PVP in CO$_{2}$. In addition, when spinning into a CO$_{2}$-rich bath, an open-cell fiber morphology is created with features that correlate with the operating pressure. We emphasize in the talk that extreme pressures are not needed to tailor a specific morphology when using CO$_{2}$. The effective removal of the solvent from the polymer solution depends on the partitioning of the liquid solvent between the PVP-rich phase and the CO$_{2}$-rich phase so the thermodynamics of polymer-SCF solvent phase behavior plays a significant role in this process. [Preview Abstract] |
Thursday, March 8, 2007 12:03PM - 12:15PM |
V24.00003: Origin of the Difference in Order-Disorder Transition \mbox{Temperature} Between Polystyrene-block-Poly(2-vinylpyridine) and Polystyrene-block-Poly(4-vinylpyridine) Copolymers Jin Kon Kim, Dong Hyun Lee, Sung Hyun Han, Weibin Zha, Chang Dae Han, Jin Ho Kang, Cheol Park The order-disorder transition temperatures (T$_{ODT}$) of polystyrene-block-poly(2-vinylpyridine) (S2VP diblock) and polystyrene-block-poly(4-vinylpyridine) (S4VP diblock) copolymers were determined using oscillatory shear rheometry and small-angle X-ray scattering (SAXS). It has been found that for comparable molecular weight and block composition, the T$_{ODT}$ of S4VP diblock copolymer is exceedingly high compared with that of S2VP diblock copolymer. This observation is attributable to the stronger polarizability of P4VP in S4VP diblock copolymer compared with the polarizability of P2VP in S2VP diblock copolymer. With the SAXS profiles obtained in the disordered state of low-molecular-weight S2VP and S4VP diblock copolymers, we determined, with the aid of the Leibler theory, the temperature-dependent segmental interaction parameter ($\alpha$) for PS/P2VP and PS/P4VP pairs. The values of $\alpha$ for PS/P2VP pair were found to be much smaller than those for PS/P4VP pair. [Preview Abstract] |
Thursday, March 8, 2007 12:15PM - 12:27PM |
V24.00004: Stucture and dynamics of a microphase separating block copolymer melt. Amish Patel, Nitash Balsara, Suresh Narayanan, Alec Sandy, Simon Mochrie A block copolymer melt is quenched from the disordered state to a temperature ($T_{q})$ below the order-to-disorder transition ($T_{ODT})$. The structure and dynamics of the melt is studied as a function of quench time using Small-Angle X-ray Scattering (SAXS) and X-ray Photon Correlation Spectroscopy (XPCS) respectively. For $T_{q}$ well below $T_{ODT}$, we observe that the broad SAXS peak corresponding to the disordered state transforms into a sharp peak indicating the formation of the ordered state. The ordering process is accompanied by an increase in the XPCS relaxation time. On the other hand, for $T_{q}$ close to $T_{ODT}$, the static structure factor remains unchanged and the melt remains disordered. However, even though the structure remains unchanged, the XPCS relaxation time increases and then reaches a plateau. Finally, we have shown that microphase separation can be stimulated in the above case of $T_{q}$ close to $T_{ODT}$. In order to do so, the melt is first taken to a temperature, $T'< T_{q}$, where microphase separation would eventually occur. After holding the melt at $T'$ for a short period of time, it is taken to $T_{q}$. At this time the melt is still disordered. However, in contrast to a direct quench to $T_{q}$, this procedure eventually results to the formation of a micrphase-separated state. [Preview Abstract] |
Thursday, March 8, 2007 12:27PM - 12:39PM |
V24.00005: Pressure Dependence of Block Copolymer Phase Transition in Selective Solvent. Yongsheng Liu, Rama Bansil, Milos Steinhart Synchrotron based small angle x-ray scattering (SAXS) was used to study the pressure dependence of the order-disorder transition (ODT) in a 30{\%} (w/v) solution of a diblock copolymer of poly(styrene -- isoprene) (SI 18-12, Polymer Source) in diethylphthalate (DEP), a selective solvent for the PS block. This diblock copolymer solution undergoes an order-disorder transition from the face-centered-cubic (FCC) phase to the disordered phase upon increasing the temperature. We will describe the design of the pressure instrument, sample cell and details of the experimental set up. The pressure applied to the sample is up to 0.35 GPa (3.5 kbar). The preliminary results show that the ODT temperature increases at about 20C/kbar with pressure. The spacing of the FCC lattice increases with pressure. [Preview Abstract] |
Thursday, March 8, 2007 12:39PM - 12:51PM |
V24.00006: Nanoporous Materials Formed in Condensed Carbon Dioxide William Edmonds, Timothy Lodge, Marc Hillmyer We propose a strategy utilizing condensed carbon dioxide as a selective--solvent for creating nanoporous materials from block copolymer templates. Cylinder--forming polystyrene--$b$--polylactide ($f_{PLA}$ = 0.37) monoliths were annealed in carbon dioxide at constant temperature and various solvent densities. The swollen structures were then quenched at low temperature isochorically. Small-angle X-ray scattering measurements indicated the domain spacing increased with increasing CO$_{2}$ density. This result is consistent with the formation of cylindrical pores within the intact polylactide domains, a conclusion confirmed by scanning electron micrographs of the processed monoliths. This controlled, non-destructive technique allows for creating tunable pore structures from a single block copolymer. [Preview Abstract] |
Thursday, March 8, 2007 12:51PM - 1:03PM |
V24.00007: Morphological transformation and mesostructure formation in diblock copolymer blends Kishore Tenneti, Xiaofang Chen, Christopher Li, Lixia Rong, Benjamin Hsiao We report the phase structures of a diblock copolymer (BCP) (PS- b-P4VP) blended with bent-core mesogen (BE3-10). High blending concentrations (1:1) resulted in phase separation. However, smaller concentrations resulted in the formation of complexes between the BE3-10 and the BCP. At moderate blending ratio of 1:5, the BCP morphology transformed from a lamellar to hexagonal cylindrical structure and the BE3-10 formed Sm layers that are oriented perpendicular to the BCP interface. At a blending ratio of 1:10, the sample showed remarkable enhancement in the lamellar ordering. In all the blends, the d- spacing was smaller than the original BCP. It is proposed that Sm layer formation and the corresponding chain stretching are responsible for this behavior. [Preview Abstract] |
Thursday, March 8, 2007 1:03PM - 1:15PM |
V24.00008: Salt Complexation in Cleavable Polystyrene-b-poly (ethylene oxide) Thin Films Ling Yang, Mingfu Zhang, Serkan Yurt, Matthew Misner, E. Bryan Coughlin, D. Venkataraman, Thomas Russell, Benjamin Ocko, Xuefa Li Salt complexation in a newly developed cylinder forming Polystyrene-b-polyethylene (PS-b-PEO) with a cleavable linker between two blocks was investigated. Highly oriented, close-packed arrays of nanoscopic cylindrical domains with a high degree of long-range lateral order was obtained in the copolymer thin films during solvent annealing and solvent evaporation at relatively low humidity or extremely dry condition. The orientation and lateral ordering of cylindrical microdomains were found to strongly depend on salt concentration. With the addition of certain amount of salt, we observed that the copolymer microdomains remained ordered at high degree of swelling by in-situ grazing incidence small angle X-ray scattering. With the ability to rapidly cleave the PEO block through the designed cleavable linker under mild condition, highly ordered porous structures are readily generated. [Preview Abstract] |
Thursday, March 8, 2007 1:15PM - 1:27PM |
V24.00009: Modeling of self-assembly in diblock copolymer and particle mixtures using self-consistent field theory Seung Ha Kim, Eric Cochran We use self-consistent field theory (SCFT) to investigate the spatial preference of particle position in the self-assembly of lamellae-forming diblock copolymer and spherical nanoparticle mixtures. We calculate the free energy of the system, which is dependent on the interaction parameter between B segments and particles ($\chi _{BP})$, the effective particle volume fraction ($\phi _{eff})$, and the ratio of the particle diameter to block copolymer domain spacing (d$_{p}$/d$_{BCP})$. We show that both small and large particles segregate to the intermaterial dividing surface (IMDS), whereas only for intermediate values of d$_{p}$/d$_{BCP}$ particles are located at the center of the domain. These results are interpreted as a subtle consequence of the competition between enthalpic polymer-particle interactions and the chain packing frustration imposed by the particulate inclusion. These findings are useful for understanding the mechanism of spontaneous assembly in block copolymer nanocomposites, and will assist in the rational design of systems where control of the particle placement is crucial. [Preview Abstract] |
Thursday, March 8, 2007 1:27PM - 1:39PM |
V24.00010: Effect of solvent vapor type on evolution of thin film morphology of block copolymer-nanoparticle composites. Deepali Palta, David Bucknall In this study we report the effect that different solvent vapors have on the resultant phase morphology of thin films of poly(styrene-butadiene-styrene) triblock copolymer (SBS) and the effect this has on the ordering when mixed with nanoparticulate inclusions. When exposed to different saturated solvent vapors, the surface morphology of the film changes depending on both the solvent vapor type and the exposure time. When the SBS film spun cast from cyclohexanone is exposed for 48 hours to vapors of the same solvent, the as made film morphology of in-plane cylinders changes to cylinders that are perpendicular to the substrate. These cylinders possess an almost perfect degree of crystallographic ordering over lateral dimensions of several microns. By contrast solvent annealing in chloroform or toluene which are also both relatively good solvents for both the blocks, the degree of order observed in cyclohexanone is not observed. In this presentation we describe the evolution of the phase morphology of these films as a function of film thickness ($<$1000 nm), type of solvent vapor, exposure time to the saturated vapors and percentage content of 3 different types of 1-50 nm particles (gold, FePt, and C60). [Preview Abstract] |
Thursday, March 8, 2007 1:39PM - 1:51PM |
V24.00011: An SCFT Study of Nanostructuring in Epoxy Thermosets Folusho Oyerokun, Glenn Fredrickson, Ludwik Leibler Increasing fracture resistance of epoxy thermosets via self assembly of block copolymers has generated significant interest in the past decade. Nanostructuring occurs because of the selectivity of the epoxy precursors to the different blocks of the block copolymer, i.e. one block is miscible (before curing), while the other block remains immiscible. The size and geometry of the nanostructures formed depends on the copolymer composition, solvent concentration and selectivity. Understanding the conditions at which nanostructuring occurs is important for rational design of high impact thermoset materials. A self-consistent field based study of blends of polystyrene-b-polybutadiene-b-polymethylmethacrylate (SBM) triblock and the reactive solvent DGEBA has been performed. At low copolymer concentration, the theory predicts micelles of PS and PB in the PMMA/DGEBA matrix. Increasing the copolymer concentration above a threshold value leads to formation of core-shell cylindrical or ``sphere-on-sphere'' morphologies, depending on the length of PB midblock. The theoretical predictions are in reasonable agreement with experiments. [Preview Abstract] |
Thursday, March 8, 2007 1:51PM - 2:03PM |
V24.00012: Fluctuation effects and stability of the Fddd phase in diblock copolymer melts Bing Miao, Robert Wickham Tyler and Morse recently found that an Fddd network phase is stable over a narrow region in the diblock copolymer phase diagram, within mean-field theory. However, in the weak segregation regime, where the Fddd phase is stable, it is well-known that composition fluctuations significantly modify the results of mean-field theory, including the phase diagram. We investigate the effect of composition fluctuations on the stability of the Fddd phase self-consistently at the one-loop level within the framework of the theory of Fredrickson and Helfand. The stability of the Fddd phase relative to the neighbouring lamellar, cylindrical, and gyroid phases will be discussed. [Preview Abstract] |
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