Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J18: Physics of Copolymers |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Svetlana Sukhishvili, Stevens Institute of Technology Room: B117 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J18.00001: On the Phase behavior of polystyrene-$b$-poly(methyl methacrylate) diblock copolymer Junhan Cho, Hyungju Ahn, Du Yeol Ryu, Youngmin Kim The phase behavior of polystyrene-$b$-poly(methyl methacrylate) (PS-$b$-PMMA) copolymers of various molecular weights has been studied by using small-angle X-ray scattering (SAXS) and depolarized light scattering (DLS). The empirical Flory \textit{$\chi $}, determined from scattering intensity profiles for a fully disordered PS-$b$-PMMA copolymer, was shown to behave differently depending on temperature range. \textit{$\chi $} was described mostly by enthalpic contribution at higher temperatures, but a dominant entropic contribution appeared in \textit{$\chi $ }at lower temperatures. The order-disorder transition (ODT) temperatures for the series of copolymers with the controlled molecular weights were directly measured through SAXS and DLS. The resultant ODTs were then compared with a compressible random-phase approximation theory to determine cross interactions between block components. It was found that effective \textit{$\chi $} from theory is also mostly described by enthalpic contribution, which yields a moderate change in ODT upon the increase of copolymer molecular weight. In addition, we discussed the pressure response of the copolymer using \textit{$\chi $} from theory. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J18.00002: Disorder-to-order transition of diblock copolymers induced by alkyne/azide click chemistry Xinyu Wei, Wei Chen, Xiangji Chen, Todd Emrick, Thomas Russell Alkyne/azide click chemistry is shown as a novel approach to induce the disorder-to-order transition (DOT) of diblock copolymers. A series of poly(ethylene oxide)-b-poly(n-butyl methacrylate-r-propargyl methacrylate) (PEO-b-P(nBMA-r-PgMA)) diblock copolymers were prepared and it is shown that the neat diblock copolymers are in the phase mixed state over the temperature range invetigated. Microphase separation was observed when the diblock copolymers were mixed with rhodamine B azide and annealed at elevated temperature. The azide molecule reacted with the terminal alkyne groups in P(nBMA-r-PgMA) block and attached to polymer backbone, resulting in a significant increase in the nonfavorable interaction between the two blocks. The DOT of these blends was observed both in the bulk and in thin films. The evolution of the morphology during the transition is determined by the mole ratio between alkyne and azide groups, annealing time and temperature, and interfacial energy. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J18.00003: Thermodynamic Characteristics of Poly(cyclohexylethylene-$b$-ethylene-\textit{co-}ethylethylene) Block Copolymers Ameara Mansour, Leah Johnson, Timothy Lodge, Frank Bates A series of poly(cyclohexylethylene-$b$-ethylene-\textit{co-}ethylethylene) (C-E/E$_{E})$ diblock copolymers containing approximately 50{\%} by volume glassy C blocks and varying fraction ($x)$ of E$_{E}$ repeat units, 0.07 $\le \quad x \quad \le $ 0.90, was synthesized by anionic polymerization and catalytic hydrogenation. The effects of ethyl branch content on the melt state segment-segment (\textit{$\chi $}) interaction parameter and soft (E/E$_{E})$ block crystallinity will be presented. The percent crystallinity ranged from approximately 30{\%} at $x$ = 0.07 to 0{\%} at about $x \ge $ 0.30, while the melting temperature changed from 101 \r{ }C at $x$ = 0.07 to 44 \r{ }C at $x =$ 0.28. Dynamic mechanical spectroscopy was employed to determine the order-disorder transition (ODT) temperatures, from which \textit{$\chi $} was calculated assuming the mean-field prediction (\textit{$\chi $N}$_{n})_{ODT}$ = 10.5. Previously published results for the temperature dependent binary interaction parameters for C-E ($x$ = 0.07), C-E$_{E}$ ($x$ = 0.90), and E-E$_{E}$ ($x$ = 0.07 and $x $= 0.90) fail to account for the quantitative $x$ dependence of $\chi $, based on a simple binary interaction model. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:03PM |
J18.00004: Decay of a Metastable Cylinder Phase via Nucleation of the Stable Lamellar Phase in a Diblock Copolymer Melt Russell Spencer, Robert Wickham We simulate the time-dependent Landau-Brazovskii equation in three dimensions and study the kinetics of a lamellar phase nucleating from a metastable cylinder phase in a diblock copolymer melt. The underlying microstructure leads to a complicated droplet interface structure, an orientation-dependent interfacial velocity, and non-spherical nuclei. In part, our motivation is to compare with an earlier nucleation theory by Wickham, Shi and Wang (2003), which uses approximations not present in our simulations. Our numerically computed droplet shape compares well with the theory, as do our critical volume and free-energy near coexistence. Farther from coexistence, the droplet shape is more spherical, and the critical volume is larger than theory predicts. We go beyond the static theory to find the orientation-dependent interface velocity and droplet growth rates, the fastest of which is in the direction normal to the lamellae. [Preview Abstract] |
Tuesday, March 16, 2010 12:03PM - 12:15PM |
J18.00005: Kinetics of Transition between HEX and Gyroid Phases in a Diblock Copolymer Solution in a Selective Solvent Julian Spring, Yongsheng Liu, Rama Bansil, Milos Steinhart Synchrotron based time-resolved small angle x-ray scattering (SAXS), was used to study the kinetics of the formation of a gyroid phase in solutions of a poly (styrene - isoprene) diblock copolymer in dimethyl phthalate, a selective solvent for the polystyrene block. From temperature ramp measurements on a 75{\%} (w/v) sample, a hexagonally-packed-cylinders (HEX) phase was identified below 110 C, a gyroid between 110 C and 150 C, above which the sample formed disordered spherical micelles. The kinetics of the transitions from HEX to gyroid, gyroid to disorder and disorder to gyroid was examined using temperature jump experiments over the temperature range of 5 165C. We found that the HEX to gyroid phase transition is irreversible, while gyroid to disorder is reversible. Detailed analysis of the time evolution of the Bragg peaks to follow the kinetics of the transition between these phases will be presented [Preview Abstract] |
Tuesday, March 16, 2010 12:15PM - 12:27PM |
J18.00006: Shear induced order in SEP diblock copolymer micelles: multiple BCC slip systems Maria A. Torija, SooHyung Choi, Frank S. Bates, Timothy P. Lodge Poly(styrene-$b$-ethylene-\textit{alt}-propylene) (SEP) diblock copolymers are solvated by squalane leading to glassy poly(styrene) domains dispersed in a viscoelastic medium. For diblocks containing less than about 50{\%} by weight poly(styrene) and at SEP concentrations greater than 6 w. {\%} these mixtures self-assemble into glassy spherical microdomains that order on a body centered cubic (BCC) lattice. We have investigated how polycrystalline configurations respond to large amplitude oscillatory shear as a function of shear rate, strain amplitude and block copolymer composition. Structure was characterized by small-angle X-ray scattering measurements while simultaneously deforming the mixtures with an \textit{in-situ} rheometer. All three slip systems associated with plastic deformation in BCC metals$\{110\}<\bar {1}11>,\{211\}<\bar {1}11>,\{321\}<\bar {1}11>$, were identified with the x-ray beam oriented perpendicular to the shear plane. Higher shear rates and larger strain amplitudes produced more slip within the $\{211\}<\bar {1}11>$ system. These results represent one of the most comprehensive assessments of BCC structure in solvated copolymers and will be discussed within the context of the associated linear viscoelastic behavior. [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J18.00007: Secondary Structure-Induced Micro- and Macro-Phase Separation in Polypeptide Diblock, Triblock and Star-Block Copolymers Antoni Sanchez-Ferrer, Raffaele Mezzenga Self-organized polypeptide block copolymers are of great interest due to their potential uses as materials for nano-devices and bio-engineering. In order to explore the effect of block copolymer topologies on their structures, a series of di-, tri- and tetra-block copolymers has been synthesized. A coil-like soft block based on poly(propylene oxide) chemistry was chosen due to its low glass transition temperature, amorphous nature and immiscibility with biological systems. On the other hand, rod-like block polypeptide based on poly($L$-glutamic acid \textit{$\gamma $}-benzyl ester) was selected and grown from the coil soft macroinitiator by ring opening polymerization. Because of the mono-, bi-, or tri-functionality of the coiled blocks, linear di-block, tri-block and star-like tetra-block copolymers could be successfully synthesized. The resulting materials show micro-phase separated liquid-crystalline morphologies, in which the architecture or connectivity of the blocks, the molecular weight of the coil segment, the volume fraction and the secondary structure of the polypeptide blocks all contribute to their micro-phase separated features. These materials can be seen as model reference systems towards the design of biocompatible scaffolds and artificial muscles. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J18.00008: Self-assembly of crystalline bioinspired block copolymers Adrianne M. Rosales, Hannah K. Murnen, Ronald N. Zuckermann, Rachel A. Segalman Polypeptoids are sequence-specific bioinspired polymers based on N-substituted glycines which hold promise for investigating the effects of monomer sequence on polymer physics. Sequence control allows for a degree of tunability in the physical and thermal properties not available in classical polymer systems. Melting transitions of crystalline peptoid homopolymers can be tuned via the introduction of defects (as a side chain substitution), with the resulting melting point depending on defect type, amount, and distribution. The sequence specificity of the polypeptoids enables complete control over the position of the defect, and it is demonstrated that both the melting transitions and heats of melting depend on the location of the defects for several peptoid homopolymers with exactly two defects each. In addition to thermal properties, chain conformation can be controlled by introducing monomers with chiral side chains in a three fold periodic fashion. Bioinspired rod-coil block copolymers were synthesized using this sequence motif as a handle on the rigidity of the rod-like block, which make these systems an ideal platform for studying the effects of conformational asymmetry on self-assembly. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J18.00009: Thermoreversible Transition between Nanophase- and Macrophase-Separation from Block Supramacromolecules via Hydrogen Bonding in an Ionic Liquid Atsushi Noro, Hajime Yamagishi, Yushu Matsushita We investigate thermoreversible transition between nanophase- and macrophase-separation from block supramacromolecules in an ionic liquid induced by association-dissociation of two macromolecules with hydrogen bonding end-linkers, where supramacromolecules are termed as supramolecular assembly of macromolecules via non-covalent bonding. A thermally stable ionic liquid with negligible vapor pressure, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, was used as a solvent to attain the molecular mobility of the system under better control. Two macromolecular building blocks were prepared: one is a poly(trimethoxystyrene) with a small end-linker of poly(hydroxystyrene) ($M_{n}$ = 53k) and the other is a poly(butyl acrylate) with a small end-linker of poly(vinylpyridine) ($M_{n}$ = 54k), both of which dissolve in the ionic liquid. Phenol should be hydrogen-bonded with pyridine. Nanophase-separated structure was observed in the ionic liquid solution of the blend by small-angle X-ray scattering at 30 $^{\circ}$C, because of the formation of block supramacromolecules. But there are no scattering peaks above 90 $^{\circ}$C in X-ray profiles: The sample is causing macrophase separation. It has also been found that the formation of supramacromolecules is thermoreversible due to hydrogen bonding. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J18.00010: Ionic Conductivity of Nanostructured Block Copolymer and Ionic Liquid Membranes Megan L. Hoarfrost, Justin M. Virgili, Rachel A. Segalman Block copolymer and ionic liquid mixtures are of interest for creating ionically conductive, thermally stable, and nanostructured membranes. For mixtures of poly(styrene-b-2-vinylpyridine) (S2VP) and the ionic liquid bis(trifluoromethanesulfonyl)imide ([Im][TFSI]), nanostructured ion-conducting domains are formed due to [Im][TFSI] selectively residing in the P2VP domains of the block copolymer. The dependence of ionic conductivity on temperature, ionic liquid loading, and volume fraction of PS in the neat block copolymer was investigated for membranes with the matrix phase being P2VP/[Im][TFSI]. It was determined that the temperature dependence of conductivity follows the Vogel-Tamman-Fulcher equation, with the activation energy determined by the ratio of [Im][TFSI] to 2VP monomers. The overall weight fraction of [Im][TFSI] in the mixtures, however, is the dominating factor determining conductivity, regardless of PS volume fraction. The insight gained from this work will be important for further investigation into the effect on the ion transport properties of ionic liquids when confined to minority nanostructured domains. [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J18.00011: How Universal Are Correlations in Disordered Diblock Copolymers: A Comparison of Three Simulation Models Jian Qin, David Morse, Marcus Mueller The Random Phase Approximation (RPA) predicts that the structure function $S(q)$ of symmetric homogeneous diblock copolymer melts is a universal function of $\chi N$ and a dimensionless wavenumber $qR$ alone, where the Flory-Huggins $\chi$ parameter is model-specific $N$-independent function of more microscopic parameters. More sophisticated coarse-grained theories suggest that $S(q)$ is a function of $\chi N$, $qR$, and the invariant degree of polymerization $\bar{N}$, but that the dominant corrections to the RPA decrease as $\bar{N}^{-1/2}$ with increasing chain length. We have directly tested this extended ``corresponding states'' hypothesis by comparing simulation results for several chain lengths from three different simulation models (a continuum bead-spring model, an FCC lattice model studied by Matsen and coworkers, and the bond-fluctuation model), by comparing results of different models at equal values of $\bar{N}$. We have devised a method to test universality while allowing for unknown dependences of the effective $\chi$ parameter upon the microscopic parameters of each model. The data for both the wavenumber $q^{*}$ at the maximum in $S(q)$ and for peak intensity $S(q^{*})$ are shown to be consistent with the existence of a universal function for $S(q)$ of the proposed form. [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J18.00012: Network Structures in Poly(isoprene-b-styrene-b-methyl methacrylate) [ISM] Triblock Copolymer-Homopolymer Blends Maeva S. Tureau, Thomas H. Epps, III The exploration of the styrene-rich network phase window in the poly(isoprene-b-styrene-b-methyl methacrylate) [ISM] system is achieved using neat triblock copolymers and via the blending of ISM triblock copolymers with poly(styrene) and poly(methyl methacrylate) homopolymers. Morphological characterization of the neat ISM triblocks and associated blends is accomplished primarily through small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The blended specimens exhibit phase transformations that show well-ordered structures and minimal macrophase separation with homopolymer volume fractions up to 26 vol{\%}. ISM triblock-homopolymer blending permitted the identification of phase boundaries between various morphologies including core-shell gyroid, alternating gyroid, and orthorhombic network structures. The phase behavior of the blended mixtures closely matches the phases identified in our neat ISM systems. Additionally, blends from different neat triblocks to the same final component volume fractions exhibit the same nanostructure. This approach provides a robust experimental framework for estimating the compositional window of ISM networks. [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 1:51PM |
J18.00013: \textit{Fddd} structure of SI diblock copolymer melts in PS-rich region Mikihito Takenaka, Myung Im Kim, Kuniaki Matsuda, Hirokazu Hasegawa We previously confirmed \textit{Fddd} structure exists as an equilibrium structure in polystyrene-block-polyisoprene (SI) diblock copolymer melts in polyisoprene (PI) rich region. The, we determined the stable region of \textit{Fddd} structure in the phase diagram of SI diblock copolymers. In this study, we investigated whether \textit{Fddd} structure is formed in polystyrene (PS) rich region by using small-angle X-ray scattering (SAXS) and transmission electron microscopy. We found the Fddd region in PS-rich region and the region exists as an equilibrium phase. As found in \textit{Fddd} structure in PI-rich region, the ratio of unit cell parameters (a:b:c) estimated from the peak positions of the scattering function agrees with the result of the theoretical calculation by Tyler et al., and the higher order reflections 022, and 004 overlaps with the reflection 111 at the first order peak. [Preview Abstract] |
Tuesday, March 16, 2010 1:51PM - 2:03PM |
J18.00014: Mechanism of Molecular Exchange in Copolymer Micelles Soo-Hyung Choi, Timothy Lodge, Frank Bates Compared to thermodynamic structure, much less has been known about the kinetics of block copolymer micelles which should underlay the attainment of thermodynamic equilibrium. In this presentation, molecular exchange between spherical micelles formed by isotopically labeled diblock copolymers was investigated using time-resolved small-angle neutron scattering. Two pairs of structurally matched poly(styrene-$b$-ethylene-\textit{alt}-propylene) (PS-PEP) were synthesized and dispersed in isotopic mixture of squalane, highly selective to PEP block. Each pair includes polymers with fully deuterated (dPS-PEP) and a normal (hPS-PEP) PS blocks. Temperature dependence of the micelle exchange rate $R(t)$ is consistent with melt dynamics for the core polymer. Furthermore, $R(t)$ is significantly sensitive to the core block length $N$ due to the thermodynamic penalty associated with ejecting a core block into the solvent. This hypersensitivity, combined with modest polydispersity in $N$, leads to an approximately logarithmic decay in $R(t)$. [Preview Abstract] |
Tuesday, March 16, 2010 2:03PM - 2:15PM |
J18.00015: Multicompartment micelles with block copolymer blending through kinetic control of solution assembly Darrin Pochan, Jiahua Zhu, Ke Zhang, Karen Wooley By manipulating the interaction of charged poly(acrylic acid) (PAA) hydrophilic corona blocks with organic multiamines, and controlling the kinetic pathway of block copolymer solution assembly, multicompartment micelles were formed. Specifically, block copolymers with the same hydrophilic block PAA chemistry but different hydrophobic block chemistry were blended together and forced to reside within the same micelle particle. The hydrophobic core blocks phase separate into distinct domains within the micelle. Unlike core blocks were used to construct different sizes of compartments and also different shapes such as sphere-cylinder hybrid micelles. The kinetic control required to construct such blended micelles will be discussed. The system has been investigated by means of cryogenic transmission electron microscopy (cryo-TEM) and small angle neutron scattering (SANS). [Preview Abstract] |
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