Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U32: Charged Polymers and Ionic Liquids |
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Sponsoring Units: DPOLY Chair: Mu Ping Nieh, University of Connecticut Room: 340 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U32.00001: An Optimized Solvation Theory for Charged Macromolecules Immersed in Aqueous Electrolyte Solutions Zaven Ovanesyan, Bharat Medasani, Marcelo Marucho In this talk, we introduce an accurate solvation model based on integral equation theory to study highly interacting charged systems. This approach is able to account for strong ion screening effects on charged macromolecules where conventional approaches may be inappropriate. A detailed knowledge of the structural arrangement of ions and solvent molecules in the vicinity of macromolecules is of crucial importance to get a microscopic understanding of these polyelectrolyte systems. We present the results obtained for ion-sphere density profiles, integrated charge and mean-electrostatic potential. These calculations are generated at low computational cost without losing important structural features of these strongly interacting charged systems. The results predict charge inversion and are in good agreement with Monte Carlo simulations. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U32.00002: Effect of Ion Content on Conductivity and Morphology of Single-Ion Conducting Ionomers Jing-Han Helen Wang, Ralph H. Colby Ionomers based on short poly(ethylene oxide) side chains and sodium sulfonated styrene are synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization, to systematically study the effect of ion content and counterion species on ionic conductivity. Glass transition temperature increases gradually as ions are incorporated at low ion content then sharply as the ion content reaches 1:4 ions to ether oxygen (EO) ratio. Dielectric relaxation spectroscopy is used to measure the conductivity, dielectric constant and segmental relaxations in these ionomers. The ionomer with 1:80 ions to EO ratio shows highest room temperature conductivity that results from the best combination of number density of simultaneously conducting ions and their mobility, assessed by an electrode polarization model. The micro-phase separation that is anticipated in the ionomers with higher ion contents is probed by x-ray scattering. Sodium counterions are mostly trapped in ionic aggregates while larger counterions, such as tetramethylammonium, exhibit higher conductivity and conducting ion concentration. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U32.00003: Charge regulation and local dielectric function in planar polyelectrolyte brushes Rajeev Kumar, Bobby Sumpter, S. Michael Kilbey II Understanding the effect of inhomogeneity on the charge regulation and dielectric properties, and how it depends on the conformational characteristics of the macromolecules is a long-standing problem. In order to address this problem, we have developed a field-theory (J. Chem. Phys. 136, 234901 (2012)) to study charge regulation and local dielectric function in planar polyelectrolyte brushes. The theory is used to study a polyacid brush in equilibrium with a bulk solution containing monovalent salt ions, solvent molecules, and pH controlling acid. In particular, we focus on the effects of the concentration of added salt and pH of the bulk in determining the local charge and dielectric function. Our theoretical investigations reveal that the dipole moment of the ion-pairs formed as a result of counterion adsorption on the chain backbones play a key role in affecting the local dielectric function. Furthermore, an increase in the bulk salt concentration is shown to increase the local charge inside the brush region. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U32.00004: Resolving the Difference in Electric Potential within a Charged Macromolecule Shuangjiang Luo, Jingfa Yang, Jiang Zhao The difference of the electric potential between the middle and end of polystyrene sulfonate (PSS-) chain is discovered experimentally. Using a pH-responsive fluorophore attached to these two locations on the PSS- chain, the local pH value was determined by single molecule fluorescence technique: photon counting histogram (PCH). By the observation of a very high accumulation of proton (2-3 orders of magnitude in concentration) at the vicinity of the PSS- as the result of the electrostatic attraction between the charged chain and protons, the electric potential of the PSS- chain is determined. A higher extent of counterion adsorption is discovered at the middle of the PSS- chain than the chain end. The entropy effect of the counterion adsorption is also discovered - upon the dilution of protons, previously adsorbed counterions are detached from the chain. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U32.00005: Effects of the dielectric inhomogeneity in polyelectrolyte solution Issei Nakamura, Zhen-Gang Wang We study the effects of dielectric inhomogeneity on the statistical properties of polyelectrolyte in solution, developing a new lattice Monte Carlo method based on the bond fluctuation model with a local algorithm for computing the electrostatic interactions. Our theory accounts for the difference in the dielectric properties between the polymer backbone and the solvent. Taking the coil-globule transition of a single polyelectrolyte in solvent as an example, we show that the chain conformation and the degree of counterion condensation are substantially affected by the electrostatic response of the polymer backbone. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U32.00006: Polyelectrolyte solutions in solvents of extremely high dielectric constant Thomas Seery, Sergey Fillipov, Jiri Panek, Peter Cernoch, Petr Stepanek The physics of polyelectrolyte solutions are of great importance in understanding various processes in nature but they pose a challenge due to their complex behavior. For strong electrolytes discussed here the fraction of the condensed counterions depends on the charge density of polyion, i.e., 1-1/z$\lambda $ where z is the valence of the counterions, and $\lambda $ is the reduced coupling constant defined by .$\lambda =l_{B} /a$Here $a$ is the distance between ions on the polyion and $l_{B}$ is the Bjerrum length $l_{B} =\frac{e^{2}}{4\pi \varepsilon_{0} \varepsilon kT}$ where $e$ is the elementary charge, $\varepsilon $ the dielectric constant of the solvent, $k$~the Boltzmann constant and $T$ absolute temperature. The Bjerrum length is the distance between charged species (counterions, co-ions or charged monomers) when the electrostatic energy between them is equal to the thermal energy k$T$. We exploit the strong temperature dependence of dielectric constant of N-methylformamide to vary the Bjerrum length in a solution of polyelectrolytes (sodium polystyrene sulfonate) and to thus investigate the dynamic properties of salt-free solutions over a broad temperature range, from $+$54 to --58$^{o}$C. Fast and slow diffusion processes are observed. The ratio of diffusion coefficients, $D_{s}$/$D_{f}$ , increases and the ratio of amplitudes $A_{s}$/$A_{f}$ decreases, both by a factor of about two in this temperature range corresponding to the expected temperature variation of the Bjerrum length. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U32.00007: Highly-correlated charges in polyelectrolyte gels Charles Sing, Johannes Zwanikken, Monica Olvera de la Cruz Polyelectrolyte gels are ubiquitous in polymer physics due to their attractive combination of structural and chemical features that permit the realization of ``environmentally responsive'' systems. The conventional conceptual picture of the volume response of these systems is based on a competition between osmotic and elastic effects. We elaborate on this fundamental understanding by including ion correlations through the use of liquid-state integral equation theory. This allows for a statistical mechanical representation of the state of the system that not only surpasses traditional Poisson-Boltzmann theories but also renders structural features in a highly accurate fashion. In particular, the local ion structure is elucidated, allowing for detailed articulation of charge inversion and condensation effects in the context of gel swelling. The inclusion of correlations has a number of ramifications that become apparent, with enhanced gel collapse and excluded volume competitions that give rise to novel and ion-dependent reentrant swelling effects. We expect this rigorous theory to prove instructive in understanding any number of gelated structures, such as chromosomes or designed synthetic materials for drug delivery. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U32.00008: Ionic Association States in Polyester Copolymer Ionomers Hanqing Masser, Shichen Dou, Ralph Colby, Paul Painter, James Runt A series of random copolyester ionomers were previously synthesized from poly(ethylene oxide) (PEO600) and poly(tetramethylene oxide) (PTMO650) oligomers, separated by the lithium or sodium salt of a sulfonated phthalate. PEO exhibits better solvating ability, while PTMO based ionomers have somewhat lower T$_{\mathrm{g}}$. By changing the ratio of PEO/PTMO, the polymer's ability to solvate ions at the same ion content was varied, in order to explore the trade-off between ion solvation and lower T$_{\mathrm{g}}$. Ionomers with different PEO/PTMO ratios were investigated by FTIR spectroscopy. The results show a systematic change in the ion association states and ion aggregation geometries with PEO/PTMO ratio and temperature. Ionomers with sodium cations have more ion pairs compared to the Lithium ionomers at the same PEO/PTMO ratio, which correspond to the higher dielectric constants in the sodium ionomers. These findings agree with previous X-ray scattering and dielectric relaxation spectroscopy results that the system microphase separates into PEO-rich and a PTMO-rich microphases and the majority of the cations reside in the PEO-rich microphase. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U32.00009: Controlling self-assembly and transport properties of ionomer thin films Miguel Modestino, Rachel Segalman Electrochemically active materials, such as ionomer composites, allow for both ionic and electrical conduction. Commonly, these materials involve inorganic electrocatalytic particles surrounded by ionomer thin films. This work presents insights in the effects of confinement and wetting interactions in the self-assembly and transport properties of perflourosulfonic acid ionomers thin films. Using in situ grazing-incidence X-ray scattering (GISAXS), we demonstrate that interfacial interactions and thin-film confinement can significantly affect phase separation, domain orientation and dynamics of ionomer films during water uptake. Thin-films casted on hydrophobic substrates result in parallel orientation of ionomer domains, while films prepared on SiO$_{2}$ surfaces result in isotropic orientation of these domains. These morphological characteristics, translate directly into effects on their macroscopic swelling behavior, where parallel orientation of ionomer domains limits the maximum water uptake of films. Furthermore, confinement to thickness below 10 nm hinders microphase separation of the material and results in high levels water uptake. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U32.00010: Effect of Morphology on Ion Transport in Polymerized Ionic Liquid Block Copolymers Jae-Hong Choi, Yuesheng Ye, Yossef Elabd, Karen Winey We investigate the impact of morphology on ion transport in single-ion conductor polymerized ionic liquid (PIL) diblock copolymers. The morphology for two types of PIL block copolymers with different degrees of miscibility between blocks was studied using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). For poly(methyl methacrylate-b-1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium-bis(trifluoromethylsulfonyl)imide) (MMA-b-MEBIm-TFSI) PIL diblock copolymers, the partial miscibility between the MEBIm-TFSI and MMA blocks resulted in a weakly microphase-separated morphology without long-range order. In poly(styrene-b-1-[(2-acryloyloxy)ethyl]-3-butylimidazolium-TFSI) (S-b-AEBIm-TFSI) PIL block copolymers, a variety of self-assembled nanostructures including hexagonally packed cylinders, lamellae, and coexisting lamellae and network morphologies were observed by varying PIL composition. A comparison of ionic conductivity between PMMA- and PS-based PIL block copolymers suggests that strong microphase separation with well-defined structures can improve ionic conductivity. The local ion concentration and connectivity of the conducting microdomains also play an important role in ion conduction in these PIL block copolymers. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U32.00011: Diffusion of polyelectrolyte chains within layer-by-layer films: a combined FRAP and neutron reflectometry study Viktar Selin, Li Xu, John F. Ankner, Svetlana A. Sukhishvili We report a comparative study of the diffusion of polyelectrolyte chains of various types and various molecular weights within polyelectrolyte layer-by-layer (LbL) films. To that end, we used a combination of fluorescence recovery after photobleaching (FRAP) and neutron reflectometry (NR) to probe chain diffusion in directions parallel and perpendicular to the substrate, respectively. LbL films were assembled using poly(methacrylic acid) (PMAA) as a polyanion and poly-2-(dimethylamino)ethyl methacrylate (PDMA) or quaternized PDMA (QPDMA) as a polycation. Fluorescently labeled and/or deuterated PMAA chains were incorporated within films as marker layers in FRAP and NR experiments, respectively. We found that in solutions of 0.2-0.6 M NaCl, chain diffusion was enhanced, with significantly faster chain motion in the direction parallel to the substrate. We will also discuss the effects of pH, salt concentration and polyelectrolyte type and molecular weight on mobility of polyelectrolyte chains within LbL films. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U32.00012: Origins of Symmetry in Polymer Ionic Liquid Phase Diagrams Jane Lipson, Ronald White Recent experimental work [Lee et al. \textit{Macromolecules} \textbf{45}, 3627 (2012)] reveals rather symmetric looking coexistence curves for poly(ethylene oxide) in [EMIM][BF$_{4}$]. This is in marked contrast to solutions involving non-ionic solvents, which show a characteristic and strong asymmetry, correlated with the molecular weight disparity between the two components. Using our simple theoretical approach we show that the special character of this systems derives from two thermodynamically-based properties. First, we find that the ionic solvent has a considerably stronger cohesive energy densities than non-ionic counterparts. In addition, we propose that aggregation in the ionic liquid has a significant impact on the entropy of mixing, typically a strong driving force for miscibility in polymer solutions. In this talk we explain how each of these features serves to drive the critical composition to the middle of the phase diagram. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U32.00013: Ordered and Disordered Polymerized Ionic Liquid Block Copolymers: Morphology and Ionic Conductivity Sharon Wang, Yuesheng Ye, Yossef Elabd, Karen Winey We systematically studied the influence of temperature and relative humidity on morphology and ionic conductivity in polymerized ionic liquid block copolymers (PIL BCP). Poly(methyl methacrylate-$b$-1-[2-(methacryloyloxy)ethyl]-3-butylimidazolium-X$^{\mathrm{-}})$ block copolymers (X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$, Br$^{\mathrm{-}})$ were characterized by SAXS, dynamical mechanical analysis, and electrochemical impedance spectroscopy. At 25 $^{\mathrm{^{\circ}}}$C, weak microphase separation was observed for the PIL BCP with $\phi _{\mathrm{PIL}} \quad =$ 0.38 and X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$. Upon increasing the relative humidity to 90{\%}, this polymer exhibited an order-disorder transition (ODT). The ODT was further studied in the PIL BCPs with X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$ and 0.11 \textless $\phi _{\mathrm{PIL}}$ \textless 0.38 over a range of temperatures and {\%}RH. In contrast, the PIL BCP with $\phi_{\mathrm{PIL}} \quad =$ 0.38 and X$^{\mathrm{-}} \quad =$ Br$^{\mathrm{-}}$ formed strongly microphase separated lamellae at all investigated T and {\%}RH. At elevated temperature and 90 {\%}RH, ionic conductivities of 30 and 6 mS/cm were observed for $\phi _{\mathrm{PIL}} \quad =$ 0.38 and X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$ and Br$^{\mathrm{-}}$, respectively, surpassing the conductivities of the corresponding PIL homopolymer. By selecting the counterion and relative humidity, we significantly impact the morphology and ionic conductivity of these PIL block copolymers. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U32.00014: Morphology, Modulus, and Ionic Conductivity of a Triblock Terpolymer/Ionic Liquid Electrolyte Membrane Lucas D. McIntosh, Timothy P. Lodge A key challenge in designing solid polymer electrolytes is increasing bulk mechanical properties such as stiffness, without sacrificing ionic conductivity. Previous work has focused on diblock copolymers, where one block is a stiff, glassy insulator and the other is a flexible ion conductor. Disadvantages of these systems include difficulty in achieving network morphologies, which minimize dead-ends for ion transport, and the necessity to operate below both the \textit{T}$_{g}$ of the glassy block and the order-disorder temperature. We have investigated the triblock terpolymer poly[isoprene-\textit{b}-(styrene-\textit{co}-norbornenylethyl styrene)-\textit{b}-ethylene oxide] because it self-assembles into a triply-continuous network structure. SAXS and TEM revealed the bulk morphology of INSO to be disordered but strongly correlated after solvent casting from dichloromethane. This apparent disordered network structure was retained after chemical crosslinking and addition of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide. Impedance spectroscopy confirmed the expected conductivity for ions confined to continuous PEO channels. The mechanical response before and after crosslinking showed an increase in the material modulus. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U32.00015: Decoupling of charge transport from structural dynamics in protic ionic liquids Joshua Sangoro, Alexei Sokolov, Friedrich Kremer, Marian Paluch Broadband dielectric spectroscopy, differential scanning calorimetry and rheology are employed to investigate charge transport and dynamics in protic and aprotic ionic liquids. While the structural $\alpha$-relaxation rates and the characteristic charge diffusion rates coincide for aprotic ionic liquids, the latter is found to be more than 100 times for the protic ionic liquids studied. Moreover, the analysis of protic ionic liquids revealed a decoupling of temperature dependence of ionic transport from that of structural relaxation with the degree of decoupling increasing with fragility of the liquid. The potential technological impact of these results will be discussed. [Preview Abstract] |
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