Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session W43: Morphology and Transport in Charged Polymers, Block Copolymers, Membranes, and Films |
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Sponsoring Units: DPOLY Chair: LaShanda Korley, Case Western Reserve University Room: A306/307 |
Thursday, March 24, 2011 11:15AM - 11:27AM |
W43.00001: Characterization of a Model Polyelectrolyte Membrane Using a Semi-crystalline Block Copolymer Keith Beers, Xin Wang, Nitash Balsara The microstructured block copolymer sulfonated polystyrene-block-polyethylene is studied as model system for use as a proton exchange membrane in a fuel cell. Self-assembly of this system creates proton conducting hydrophilic channels in the form of sulfonated polystyrene domains, while the polyethylene domains create a hydrophobic matrix to provide mechanical stability. This system serves as a powerful model system since the effects of domain size, morphology and crystallinity on water uptake and proton conductivity can be investigated. Similar systems have shown the ability of small hydrophilic channels to prevent drying at high temperatures in humid air, but have focused on amorphous hydrophobic blocks. The morphology, water uptake, and proton conductivity of this semi-crystalline model system will be discussed. [Preview Abstract] |
Thursday, March 24, 2011 11:27AM - 11:39AM |
W43.00002: Structure-Property Relationships in Sulfonated Pentablock Copolymers Jae-Hong Choi, Carl Willis, Karen I. Winey Membranes of pentablock copolymers consisting of poly(\textit{tert}-butyl styrene) (TBS), hydrogenated polyisoprene (HI), and partially sulfonated poly(styrene-\textit{ran}-styrene sulfonate) (SS) were studied using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The TBS-HI-SS-HI-TBS pentablock copolymer in solution forms spherical micelles with a core of SS and a corona of solvated HI and TBS. The spherical micelles in solution compact as the solvent evaporates and some of SS cores merge to form interconnected SS microdomains without substantially changing their shape. The number of connections increases with the volume fraction of the SS block, which increases with sulfonation level. The structure does not have long-range order, because strong ionic interactions prevent extensive rearrangement. The morphologies of the sulfonated pentablock copolymers will be correlated with their transport properties. [Preview Abstract] |
Thursday, March 24, 2011 11:39AM - 11:51AM |
W43.00003: Interfacial Stability of Solid Block Copolymer Electrolytes for Rechargeable Lithium Metal Batteries Greg Stone, Scott Mullin, Nitash Balsara Solid electrolytes that can resist dendrite growth from the lithium surface and adhere to the electrode surface are needed for the development of rechargeable batteries with lithium metal anodes. We show that self-assembled block copolymer electrolytes are inherently more stable against lithium metal anodes than homogeneous homopolymers. This is due to an unusual combination of solid-like properties in the bulk to resist dendrite growth, arising from a randomly oriented granular structure, and the liquid-like properties of perpendicularly oriented lamellae that are formed at the lithium-electrolyte interface providing adhesion to the electrode. [Preview Abstract] |
Thursday, March 24, 2011 11:51AM - 12:03PM |
W43.00004: Local dielectric constant and its effects on the microphase separation in charged-neutral diblock copolymer melts Rajeev Kumar, Scott Sides, Bobby Sumpter Using block copolymers as mesoscale templates has potential applications for improved photovoltaic devices and fuel-cells. Charged species in these polyelectrolytic copolymers play a vital role in determining the details of the nanoscale morphologies formed when these systems phase segregate. We have carried out a quantitative analysis of the local dielectric constant for charged-neutral diblock copolymer melts using field-theoretic simulations based on the self-consistent field theory (SCFT). Quantitative expression for the local dielectric constant in terms of the local electric field will be presented along with its effects on the microphase separation in these systems. Using large-scale SCFT simulations, we will explore the effects of different experimental parameters on the morphology diagram. These parameters include the chain length, temperature, degree of ionization and length fraction of the charged block. Also, the effect of added salt on the disorder-order transition temperature and the domain spacings of the ordered morphologies along with the distribution of small ions (counterions and co-ions) will be presented. [Preview Abstract] |
Thursday, March 24, 2011 12:03PM - 12:15PM |
W43.00005: Magnetically aligned ion-transport polymer membranes Pawel Majewski, Manesh Gopinadhan, Chinedum Osuji We present the use of magnetic fields to direct the self assembly and impose long-range order in amphiphilic block-copolymers which can be utilized as solid electrolytes for ion-transport membranes or nanomaterials synthesis templates. Our approach allows us to produce highly aligned hexagonally packed cylindrical or lamellar polymer microdomains over macroscopic areas. We systematically explore the influence of several parameters; the strength of magnetic field used for alignment, lithium ion content and temperature on the conductivity of such membranes. A surprising order of magnitude increase in conductivity is found in films aligned in the conduction direction relative to the non-aligned case. The conductivity of field aligned samples shows a non-monotonic dependence on temperature, with a distinct decrease on heating in the proximity of the order-disorder transition of the system before increasing again at elevated temperatures in homogenous melt state. The data suggest that domain-confined ion transport in hexagonally packed cylindrical systems differs greatly in anisotropy compared to lamellar systems. [Preview Abstract] |
Thursday, March 24, 2011 12:15PM - 12:27PM |
W43.00006: The effect of salt-doping on the lamellar phase of AB diblock copolymers Issei Nakamura, Zhen-Gang Wang We study the effect of adding salts on the lamellar phase of AB diblock copolymers by means of the self-consistent field theory. We consider a model in which the A and B blocks have different dielectric constants. We include the Born energy to account for the preference of salt ions to be solvated by higher dielectric polymer. We first show that the effective $\chi$ parameter can be increased upon addition of salt, depending on the size of salt particles, with an accompanied increase in the domain spacing of the lamellar phase. The salt ions tend to be localized in the microphase where the higher dielectric components are dominant. The effect of the incompressibility on the distribution of salt ions is also studied. Moreover, we include a binding interaction between one of the blocks and one of the salt ions (e.g., cations), and study the effects of such strong binding on the distribution of the counterions (anions). [Preview Abstract] |
Thursday, March 24, 2011 12:27PM - 12:39PM |
W43.00007: Impact of morphology on conductivity of lamellar block copolymer electrolytes for battery applications Venkat Ganesan, Victor Pryamitsyn We use bond fluctuation model based Monte Carlo simulations to study the correlations between structure and the conductivity of the lamella phase of block copolymer electrolytes. We investigate the effects of degree of segregation, polymer molecular weights and the alignment of the lamellae upon the conductivity of the block copolymer lamella. Our results indicate different influences of the preceding factors upon the conductivities parallel and perpendicular to the lamellae. These results are rationalized in terms of the distributions of the ions and the overall inhomogeneous dynamics of the polymer molecules. [Preview Abstract] |
Thursday, March 24, 2011 12:39PM - 12:51PM |
W43.00008: Dynamics of water in sulfonated poly(phenylene) membranes Naresh Osti, Thusitha Etampawala, Umesh Shrestha, Dvora Perahia, Christopher Cornelius The dynamics of water in networks formed by highly rigid ionic polymers, sulfonated poly(phenylene) as observed by quasi elastic neutron scattering (QENS) is presented. These rigid ionic polymers have potential as effective ion exchange membranes with impact on a large number of applications from water purification to clean energy, where its rigidity distinguishes it from other ionic polymers. Its transport characteristics are affected by its rigidness as well as by direct interactions with the solvent. Our QENS studies as a function of sulfonation levels, temperature and solvent content have shown that on the time scale of the measurement, the polymers are rigid. While macroscopically all samples swell, and transport water, the water molecules appear locally rather confined. Water however remind non-frozen to subzero temperatures. The results will be discussed in view of theoretical models including continues diffusion and hopping of solvent molecules. [Preview Abstract] |
Thursday, March 24, 2011 12:51PM - 1:03PM |
W43.00009: Morphology and Transport Properties of Phosphonium-containing Styrenic Ionomers with Random Charge Placement Rick Beyer, Kristoffer Stokes, Joshua Orlicki, Yuesheng Ye, Yossef Elabd Alkaline fuel cell (AFC) technology is currently of interest for portable power supplies due in part to the use of less expensive non-noble metals (nickel, iron, cobalt) as the catalyst material. Wide-spread use of the AFC has been prevented by the use of aqueous KOH as the liquid electrolyte, easily poisoned by CO$_{2}$. Development of an semipermeable polymeric alkali anion exchange membrane (AEM) would significantly improve the usefulness of AFCs. We have synthesized a series of random copolymers of styrene and p-vinylbenzyl-trimethylphosphonium chloride, via RAFT polymerization. Detailed $^{1}$H-NMR analysis of the polymerization conditions allowed us to refine our approach and generate materials with random monomer addition. $^{1}$H-NMR was also used to quantify ion contents, which range from 15 mol{\%} to 100 mol{\%}. In this presentation, we will review the synthesis and characterization of these novel cationomers, and then report on their anion transport characteristics and morphological behavior as characterized via SAXS and TEM. [Preview Abstract] |
Thursday, March 24, 2011 1:03PM - 1:15PM |
W43.00010: Morphology of precise acid copolymers neutralized with monovalent cations Michelle Seitz, Kathleen Opper, Kenneth Wagener, Karen Winey Poly(ethylene-co-acrylic acid) copolymers with precisely spaced acid groups along the strictly linear chain backbone form the basis of a new family of ionomers with unprecedented molecular uniformity. These copolymers were neutralized with monovalent cations (Li, Na, and Cs) and their morphologies were studied using X-ray scattering. In order to more fully understand the ionic aggregation in these systems, both the low and high angle features are considered. At low angle a sharp ionomer peak arises from interaggregate interference and shifts with acid spacing. At high angle, the amorphous halo from the average backbone separation is observed. For materials with an acid group on every 9th carbon, additional high angle scattering is observed which may be related to either the internal aggregate structure or isolated ion pairs. [Preview Abstract] |
Thursday, March 24, 2011 1:15PM - 1:27PM |
W43.00011: Cubic Ordering of Aggregates in Precise Phosphonic Acid Copolymers Francisco Buitrago, Kathleen Opper, Kenneth Wagener, Karen Winey Polyethylene-acid copolymers were synthesized by acyclic diene metathesis (ADMET) chemistry. The result is a series of strictly linear, high molecular weight polyethylenes with pendent acid groups separated by a precisely controlled number of methylene units. Previous studies have been focused on acrylic acid copolymers and ionomers. Here, we focus on phosphonic acid pendent groups in single and geminal architectures. The morphology of these materials has been studied by X-ray scattering at 25 and 150\r{ }C, along with transmission electron microscopy. For a geminal acid copolymer with low acid content, the precise molecular structure produces thermally persistent acid aggregates on a cubic lattice. This is the first report of cubic aggregate packing in polyethylene-acid copolymers. [Preview Abstract] |
Thursday, March 24, 2011 1:27PM - 1:39PM |
W43.00012: The Effect of Sulfonation and Neutralization on the Dynamics of Zn Neutralized Sulfonated Polystyrene Ionomers Alicia Castagna, Wenqin Wang, Karen I. Winey, James Runt The effect of sulfonation and neutralization levels on structure and dynamics of Zn neutralized sulfonated polystyrene (SPS) ionomers were investigated using scanning transmission electron microscopy (STEM), X-ray scattering, and dielectric relaxation spectroscopy. STEM and X-ray scattering revealed the presence of spherical aggregates 2 nm in diameter. Successful fitting of the scattering data to the Kinning-Thomas modified hard sphere model revealed that aggregate size is independent of degree of sulfonation and neutralization level, and that aggregate composition becomes increasingly ionic with increasing neutralization. Two segmental relaxations were identified in dielectric loss spectra corresponding to cooperative motion of chain segments in the unrestricted matrix and motions of chain segments restricted by aggregates. A Maxwell-Wagner-Sillars interfacial polarization process was revealed, with relaxation times that were in good agreement with predictions from a simple model of dispersed ionic spheres. [Preview Abstract] |
Thursday, March 24, 2011 1:39PM - 1:51PM |
W43.00013: Proton Transport in Nanostructured Block Copolymer/Ionic Liquid Membranes Megan Hoarfrost, Madhu Tyagi, Jeffrey Reimer, Rachel Segalman Nanostructured block copolymer/ionic liquid mixtures are of interest for creating membranes having high proton conductivity coupled with high thermal stability. In these mixtures, it is anticipated that nanoconfinement to block copolymer domains will affect ionic liquid proton transport properties. Using pulsed-field gradient NMR and quasi-elastic neutron scattering, this relationship has been investigated for mixtures of poly(styrene-b- 2-vinylpyridine) (S2VP) with ionic liquids composed of imidazole and bis(trifluoromethane)sulfonimide (HTFSI), where the ionic liquids selectively reside in the P2VP domains of the block copolymer. Proton mobility is highest in the neat ionic liquids when there is an excess of imidazole compared to HTFSI due to proton hopping between hydrogen-bonded imidazoles. As predicted, the amount of proton hopping can be tuned by nanoconfinement, as evidenced by the finding that a lamellar mixture of an imidazole- excess ionic liquid with S2VP has greater proton mobility than a corresponding disordered mixture of the ionic liquid with P2VP homopolymer. [Preview Abstract] |
Thursday, March 24, 2011 1:51PM - 2:03PM |
W43.00014: Simultaneous Electronic and Ionic Charge Transport in Poly(3-hexylthiophene)-b-Poly(ethylene oxide) Shrayesh Patel, Anna Javier, Nitash Balsara Block copolymers can self-assemble to distinct channels, which allows for simultaneous transport of electronic and ionic charge carriers. A potential polymer system is Poly(3-hexylthiophene)-b-Poly(ethylene oxide) (P3HT-b-PEO). P3HT serves as the electronic conducting channel while the PEO serves as the ionic conducting channel. Both conductive blocks are doped to induce simultaneous electronic and ionic conduction. The PEO phase is doped with LiTFSI while the P3HT is doped with F$_{4}$TCNQ, which generates hole carriers. In addition, we take into account the case where no electronic dopant is added to P3HT phase. The charge transport properties of the material are analyzed via ac impedance spectroscopy and dc polarization techniques. These experiments provide decoupled electronic and ionic transport in P3HT-b-PEO. [Preview Abstract] |
Thursday, March 24, 2011 2:03PM - 2:15PM |
W43.00015: Confinement Effects on Watery Domains in Hydrated Block Copolymer Electrolyte Membranes Moon Jeong Park, Sung Yeon Kim, Joomi Yeo The morphology of a series of diblock copolymers comprising randomly sulfonated polystyrene (PSS) and polymethylbutylene (PMB) blocks equilibrated with humid air was determined by in- situ small angle neutron scattering (SANS). In-situ SANS data were collected over a wide angular range permitting the determination of the superstructure of the hydrophilic PSS-rich and hydrophobic PMB-rich domains and the substructure within the hydrophilic PSS-rich domains. When the characteristic length of the superstructure is larger than 10 nm, the hydrophilic PSS domains are heterogeneous with periodically arranged watery domains. The scattering signature of the watery domains is very similar to the well-established ``ionomer peak.'' This peak vanishes when the neutron scattering length density of the water (H2O/D2O mixture) is matched to that of the PSS block. The spacing between watery domains depends only on sulfonation level of the PSS block. When the characteristic length of the superstructure is less than 10 nm, the watery substructure disappears and homogeneous hydrated PSS-rich domains are obtained. [Preview Abstract] |
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