Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y31: Phase Behavior of Copolymers |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Chris Ellison, University of Texas at Austin Room: 339 |
Friday, March 22, 2013 8:00AM - 8:12AM |
Y31.00001: Phase Behavior of All-Hydrocarbon ``Diblock-Random'' Copolymers Bryan Beckingham, Richard Register ``Block-random'' copolymers (A$_{x}$B$_{1-x})$-(A$_{y}$B$_{1-y})$, where each of the two blocks is a random copolymer of monomers A and B, present a convenient and useful variation on the typical block copolymer architecture, as the interblock interactions and physical properties can be tuned continuously through the random block's composition. The ability to tune the effective interaction parameter between the blocks continuously, allows for the order-disorder transition temperature (T$_{ODT})$ to be tuned independently of molecular weight using only two monomers. This flexibility makes block-random copolymers a versatile platform for the exploration of polymer phase behavior and structure-property relationships. Here, we present the phase behavior of hydrogenated derivatives of various lamellae-forming diblock-random copolymers where one block is a styrene/isoprene (S$r$I) random copolymer. Using small-angle x-ray scattering, we investigate a series of isoprene hydrogenated hI-S$r$hI with varying styrene content, determine order-disorder transition temperatures and compare the observed phase behavior to that of more typical S-hI block copolymers via mean-field theory. Additionally, diblock-random copolymers, 50 wt. {\%} styrene in the S$r$I block, are synthesized with polyisoprene, polybutadiene or polystyrene blocks and we examine the phase behavior of both their hydrogenated derivatives, prepared with catalysts which either leave the S units intact or saturate them to vinylcyclohexane. [Preview Abstract] |
Friday, March 22, 2013 8:12AM - 8:24AM |
Y31.00002: Self-consistent field theory for directed self-assembly in non-cylindrical confinement Tatsuhiro Iwama, Nabil Laachi, Bongkeun Kim, Kris Delaney, Glenn Fredrickson We use self-consistent field theory to study the directed self-assembly (DSA) of diblock copolymers under non-cylindrical pore confinement such as oval, rectangular or the like. Our goal is to understand whether block copolymers can rectify non-cylindrical holes with reduced critical dimension in both minor direction and major direction of the non-cylindrical prepatterns. We explore a wide range of prepattern shapes, polymer characteristics to optimize DSA non-cylindrical holes. We also discover defects of DSA morphologies in the non-cylindrical prepattterns. [Preview Abstract] |
Friday, March 22, 2013 8:24AM - 8:36AM |
Y31.00003: Phase behavior of binary blends of asymmetric diblock copolymers: Bulk and thin films Adetunji Onikoyi, Edward Kramer Experimental and theoretical investigations of the phase behavior of binary blends of block copolymers in bulk state have been published, yet there is little work on the effects of confinement of such blends to thin films. We investigate the phase behavior of blends of two poly(styrene-b-2vinylpyridine) diblock copolymers; one sphere forming (BCP1, with f$_{\mathrm{P2VP}} =$ 0.12, N$=$538) and the other cylinder forming (BCP2, with f$_{\mathrm{P2VP}}=$0.25, N$=$355). SAXS, TEM and SFM are used to characterize the microstructures formed as a function of temperature, blend compositions and film thickness. Results show that increased surface-induced free energy penalties in thin films lead to a significant change in phase behavior when compared to similar samples in bulk. Order disorder temperatures (ODT), mixing regimes and overall microstructure are strongly affected by the dominant contributions of the surface to the overall free energy of the system. Furthermore, for a regime (with BCP1 blend composition $\sim$ 0.4-0.6) of expected mixed phases of 2D hexagonal spheres and parallel cylinders in thin films, we are able to selectively stabilize 2D hexagonal sphere phases rather than the cylindrical phase by appropriate choice of confinement size and geometry. [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y31.00004: Identifying the ODT in simulations of diblock copolymers using thermodynamic integration with a flexible simulation cell Pavani Medapuram, Jens Glaser, David Morse The order-disorder transition (ODT) has been precisely identified in several simulation models by using a thermodynamic integration procedure introduced by Mueller and Daoulas (\textit{J. Chem. Phys.}, 128, 024903, 2008). We have applied the method to constant pressure simulations with a flexible tetragonal simulation unit cell to avoid incommensurability effects. The transition is found to be surprisingly weakly first order, even for very short chains, in agreement with recent experiment results on short, strongly-incompatible diblocks. Precise values for the value of $\chi$ N at the transition are obtained by combining this free energy method with a fit of the disordered state scattering data to the renormalized one-loop theory, which is found to give an excellent fit for several different models over a wide range of molecular weights. Results from different chain lengths and models are compared to test the degree of universality of the ODT, and to test the accuracy of the Fredrickson-Helfand theory predictions for the ODT. [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y31.00005: Identifying the ODT in simulations of diblock copolymers using metadynamics Jens Glaser, David Morse We propose a novel approach based on the structure factor as an order parameter and metadynamics as a free-energy technique to precisely locate the order-disorder transition in melts of symmetric diblock copolymers, which is flucutation-induced first-order. We are able to directly measure the height of the free energy barrier separating the disordered and the ordered phase. We quantify finite size effects on the free energy minima and barrier. [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y31.00006: Rod-Coil Block Copolymer Simulation With SCFT Lee Trask, Eric Cochran Theoretical and experimental investigations of rod-coil block copolymer systems have made leaps forward recently. Fully 3D computer simulations of rod-coil diblock copolymer systems using self-consistent field theory (SCFT) have become feasible due to advances in theory and computer resources, while a number of experimental papers have illustrated a wide array of phases. These simulations include the use of all spatial and orientational degrees of freedom along with a Maier-Saupe interaction to describe the rod-rod alignment interactions. However, these 3D simulations have not been compared to experimental data. Simulations of moderately segregated poly(alkoxyphenylenevinylene-\textsl{b}-isoprene) (PPV-\textsl{b}-PI) are performed for a range of characteristic parameters linked to these systems. For different Flory-Huggins parameters, compositions, Maier-Saupe parameters, and geometric asymmetries, phase diagrams are constructed and compared with the phase diagrams previously reported in the literature. Along with phase space information, the domain space scaling relationship of the lamellar phase as a function of molecular weight is compared. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y31.00007: Self-consistent Field Theory Simulations of the Phase Behavior of Tapered Diblock Copolymers Jonathan Brown, Lisa Hall Phase diagrams of tapered and inverse-tapered diblock copolymers were computed by self-consistent field theory. These copolymers consist of three ``blocks'': a pure A block, a linear gradient ``block'' that is either A to B (tapered) or B to A (inverse-tapered), and a pure B block. This composition was approximated using a multi-block model in which the tapered region consisted of alternating A and B blocks of appropriate size to approximate the gradient. Phase diagrams were produced for varying sizes of the tapered region, showing a shift of the ordered phases to higher $\chi N$ for larger tapered regions (and higher still for inverse-tapered systems), while preserving non-lamellar phases in some cases. [Preview Abstract] |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y31.00008: Theory of Chiral Block Copolymer Melts: Mesoscopic Helicity from Inter-Segment Twist Gregory Grason, Wei Zhao, Thomas Russell We study the effects of chirality at the segment scale on the thermodynamics of block copolymer melts using self consistent field theory. In linear diblock melts where segments of one block prefer a twisted, or cholesteric, texture, we show that melt assembly is critically sensitive to the ratio of random coil size to the preferred pitch of cholesteric twist. For weakly-chiral melts (large pitch), mesophases remain achiral, while below a critical value of pitch, two mesocopically chiral phases are stable: an undulated lamellar phase; and a phase of hexagonally-ordered helices. We show that the non-linear sensitivity of meso-scale chiral order to preferred pitch derives specifically from the geometric and thermodynamic coupling of the helical mesodomain shape to the twisted packing of chiral segments within the core, giving rise to a second-order cylinder-to-helix transition. [Preview Abstract] |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y31.00009: Self-assembly of peptoid block copolymers with tunable conformational asymmetry Adrianne Rosales, Ronald Zuckermann, Rachel Segalman Functional polymers such as conjugated or biological molecules have been shown to have a variety of chain conformations that affect their self-assembly. Polypeptoids are sequence-specific biomimetic polymers for which the statistical segment length can be tuned by the introduction of monomers with bulky, chiral side chains, allowing one to change the polymer conformation independent of chemical structure or molecular weight. Furthermore, sequence specificity enables the precise placement of those chiral monomers along the polymer chain. This work presents a systematic study of block copolymer self-assembly using chiral polypeptoids or their racemic analogs and poly(n-butyl acrylate). For the chiral block copolymers, SAXS measurements reveal that the change in conformational asymmetry increases the morphological domain spacing and decreases the corresponding interfacial area per chain, indicating that the chiral peptoid chains can pack more closely within the domain compared to the racemic peptoid chains. The effect on domain spacing is also probed by changing the position of the chiral monomers with respect to the block copolymer junction. These results lend insight to the design of block copolymers with secondary structure. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y31.00010: Phase coexistence calculations via a unit-cell Gibbs ensemble formalism for melts of reversibly bonded block copolymers Zoltan Mester, Nathaniel Lynd, Glenn Fredrickson Melts of block copolymer blends can exhibit coexistence between compositionally and morphologically distinct phases. We derived a unit-cell approach for a field theoretic Gibbs ensemble formalism to rapidly map out such coexistence regions. We also developed a canonical ensemble model for the reversible reaction of supramolecular polymers and integrated it into the Gibbs ensemble scheme. This creates a faster method for generating phase diagrams in complex supramolecular systems than the usual grand canonical ensemble method and allows us to specify the system in experimentally accessible volume fractions rather than chemical potentials. The integrated approach is used to calculate phase diagrams for AB diblock copolymers reversibly reacting with B homopolymers to form a new diblocks we term ``ABB.'' For our case, we use a diblock that is sixty percent A monomer and a homopolymer that is the same length as the diblock. In the limits of infinite reaction favorability (large equilibrium constant), the system approaches cases of an ABB diblock-B homopolymer blend when the AB diblock is the limiting reactant and AB diblock-ABB diblock blend when the homopolymer is the limiting reactant. As reaction favorability is decreased, the phase boundaries shift towards higher homopolymer compositions so that sufficient reaction can take place to produce the ABB diblock that has a deciding role stabilizing the observed phases. [Preview Abstract] |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y31.00011: Phase behavior of multi-arm star-shaped polystyrene-\textit{block}-poly(methyl methacrylate) copolymer Sangshin Jang, Hong Chul Moon, Dusik Bae, Jonghen Kwak, Jin Kon Kim We synthesized star-shaped polystyrene-\textit{block}-poly(methyl methacrylate) copolymer (PS-$b$-PMMA) by utilizing $\alpha $-cyclodextrin ($\alpha $-CD) as a core of the star-shaped block copolymer. Eighteen hydroxyl groups on $\alpha $-CD were transformed to bromine by the reaction with $\alpha $-bromoisobutyryl bromide. We found that the number of bromine substituted arms per one $\alpha $-CD was higher than 16, which was determined by nuclear magnetic resonance and Matrix-assisted laser desorption/ionization. We could control molecular weight of block copolymers by changing polymerization times. The block copolymers were characterized by gel permeation chromatography and nuclear magnetic resonance. Phase behaviors of these star-shaped block copolymers were investigated by small angle X-ray scattering and transmission electron microscopy. [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y31.00012: Pressure Effect of Various Inert Gases on the Phase Behavior of Polystyrene-\textit{block}-Poly(n-pentyl methacrylate) Copolymer Hong Chul Moon, Hye Jeong Kim, Junhan Cho, Jin Kon Kim We investigated the pressure effect of three inert gases (nitrogen, helium and argon) on the phase behavior of polystyrene-\textit{block}-poly(n-pentylmethacrylate) copolymer (PS-$b$-PnPMA) showing closed-loop phase behavior and baroplasticity. Helium gas pressure enhanced the miscibility between PS and PnPMA blocks similar to the hydrostatic pressure. Very interestingly, however, with increasing nitrogen and argon gas pressure, the miscibility between the two blocks decreased even though these two are also considered as inert gases. To explain these unexpected results, we measured the amount of gas absorption into each block. The experimentally measured gas absorption results are consistent with the theoretical ones based on the Sanchez-Lacombe theory. The results in this study imply that well-known and widely employed inert gases such as nitrogen and argon could significantly affect the phase behavior of a weakly interacting block copolymer at high pressures. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y31.00013: Micellization behavior of A-$b$-(B-\textit{alt}-C)$_{\mathrm{n}}$ multiblock terpolymers in a selective solvent for one terminal A-block Yu-Chieh Hsu, Ching-I Huang, Weihua Li, Feng Qiu, An-Chang Shi We used self-consistent field theory to investigate the micellization behavior of A-$b$-(B-\textit{alt}-C)$_{\mathrm{n}}$ multiblock terpolymers in the presence of a solvent that is selective to the terminal A-block. In particular, we focused on the effects of $\chi_{\mathrm{BC}}$, and $f_{\mathrm{A}}$, on the formation of micelles from ABC triblock and A(BC)$_3$ multiblock terpolymers, respectively. We observed a general trend that a segmented packing of B- and C-layers along the axial direction of the micelles is favored than the coaxial packing with the increasing of $\chi _{\mathrm{BC}}$ or decreasing of $f_{\mathrm{A}}$. The separation of B and C blocks within a micelle leads to the formation of a variety of multicompartment micelle morphologies, such as core-shell-corona spherical micelles, hamburgers, and bump-surface micelles, in the ABC triblock copolymers. In the A(BC)$_3$ multiblock terpolymers, we discovered more fascinating micelles by implementing the SCFT simulation than by the DPD simulation. Besides the BC-segmented worm-like micelles, which have been found in the DPD simulation work, concentric multilayer spheres and vesicles can be formed by the solvent-induced effect when the solvophilic A-block is a majority component. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y31.00014: Micellar Packing in Aqueous Solutions of As-Received and Pure Pluronic Block Copolymers Chang Ryu, Han Jin Park Pluronic block copolymers (Pluronics) are produced on a commercial scale to enable wide range of novel applications from emulsification and colloidal stabilization as nonionic surfactants. While the Pluronic block copolymers offer the advantages of being readily available for such applications, it contains non-micellizable low molecular weight (MW) impurities that would interfere with the self-assembly and micellar packing of PEO-PPO-PEO triblock copolymers in aqueous solutions. The impacts of the low MW impurities will be discussed on the micellar packing of Pluronics F108 and F127 solutions, which form BCC and FCC. While as-received Pluronic samples typically contain about 20 wt.{\%} low MW impurities, we were able to reduce the impurity level to less than 2 wt.{\%} using our large scale purification technique. Comparative studies on small angle x-ray scattering (SAXS) experiments on as-received and purified Pluronics solutions revealed that the contents of triblock copolymers in solutions essentially governs the inter-micellar distance of Pluronic cubic structures. A universal relationship between triblock copolymer concentration and SAXS-based domain spacing has been finally discussed. [Preview Abstract] |
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