Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V24: Charged and Ion-Containing Polymers: Properties |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Ralph Colby, Penn State University Room: Baltimore Convention Center 321 |
Thursday, March 16, 2006 11:15AM - 11:27AM |
V24.00001: Morphology Diagrams for Polyelectrolytic Diblock Copolymers Rajeev Kumar, Murugappan Muthukumar We have calculated morphology diagrams for polyelectrolytic diblock copolymers in melts and highly concentrated solutions. Using the random phase approximation and self-consistent field theory, stability limits of the standard morphologies (lamellae, cylinders and spheres) have been considered both in weak and strong segregation limits. Effects of Coulomb interaction strength, degree of ionization, Debye screening length, block length, chain length, and the chi parameter on the periods of these morphologies will be discussed. Also, the crossover behavior in the whole range of segregation will be presented. Charging a polymer block with electrical charges leads to many unexpected behaviors, which will be discussed in the context of previous theories and experiments. [Preview Abstract] |
Thursday, March 16, 2006 11:27AM - 11:39AM |
V24.00002: Synthesis, Solution Phase Behavior, and Properties of Ionic/Nonionic Block Copolymers Mehul Vora, Frank Bates The study of amphiphilic block copolymers in aqueous solutions has shown rich phase behavior and interesting solution properties. The aim of the current work is to develop an amphiphilic diblock copolymer system containing an ionic block in order to better understand how ionicity affects the phase behavior and solution properties. Relatively monodisperse PEP-$b$-PMAA (poly(ethylene propylene)-$b$-methacrylic acid) copolymer was prepared from anionically synthesized poly(isoprene-$b$-\textit{tert}-butyl methacrylate). The rheological behavior of aqueous solutions of PEP-$b$-PMAA in the presence of different counterions was studied. The choice of counterion has a strong influence on the final solution properties. Cryo-TEM and SAXS experiments are used to determine the morphology of the copolymers in these solutions, while rheological experiments revealed the role of diblock composition, counterion type and concentration, and overall polymer loading on the viscometric properties. [Preview Abstract] |
Thursday, March 16, 2006 11:39AM - 11:51AM |
V24.00003: Morphological Origin of Thermomechanical Behavior in Semicrystalline Ethylene/Methacrylic Acid Ionomers Katsuyuki Wakabayashi, Richard A. Register Two peculiar and intriguing phenomena in ethylene/methacrylic acid (E/MAA) ionomers are an initial sharp increase in stiffness with neutralization and an inverse dependence of Young’s modulus on crystallinity. We have identified how the polyethylene crystallites, amorphous polymer segments, and ionic aggregates combine to produce these unusual effects. At temperatures just below the melting point of the primary crystallites, the ionomers can be satisfactorily described as two-phase composites of crystallites and ionically-crosslinked rubber, but at room temperature, the modulus is much greater. We trace this effect to a synergy between the ionic aggregates and secondary crystallites, which together form percolated rigid pathways through the amorphous phase at room temperature, generating a far higher modulus than one would anticipate from the modest crystallinity and ion content. When the secondary crystallites melt and/or the segments in the regions of restricted mobility surrounding the aggregates devitrify, these paths break down and the simple two-phase composite description is recovered. [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:03PM |
V24.00004: Influence of Chain Flexibility on the Self-Assembly of Nanoscale Ionic Aggregates in Ionomers. Nicholas Benetatos, Karen Winey Rigorously establishing the fundamental physics that govern the morphology of ionomers is essential to continuing the development of this versatile class of materials. To explore how chain flexibility impacts the nanoscale self assembly of ionic aggregates, we have investigated the morphology of Cu neutralized poly(styrene-\textit{ran}-methacrylic acid) (SMAA) and poly(3-methylstyrene-\textit{ran}-methacrylic acid) (3Me-SMAA) ionomers with small angle X-ray scattering (SAXS) and real space imaging via scanning transmission electron microscopy (STEM). The copolymer 3Me-SMAA is slightly less flexible on local length scales as evidenced by a shift in the position of the ``polymerization'' SAXS peak (q $\sim $ 6 nm$^{-1})$ to lower q compared to that of SMAA (q $\sim $ 7 nm$^{-1})$. A commensurate shift toward lower q in the position of the ionomer SAXS peak was observed for Cu-3Me-SMAA. Interpreting these SAXS data with a multi-functional model, including that of Yarusso and Cooper, suggests a homogeneous collection of spherical ionic aggregates with diameters of 1.0 nm and 1.2 nm in Cu-SMAA and Cu-3Me-SMAA, respectively. From STEM imaging, the ionic aggregates in both Cu-SMAA and Cu-3Me-SMAA are indeed spherical with a uniform, dense spatial distribution and average diameters of 1.2 \underline {+} 0.3 nm and 1.4 \underline {+} 0.3 nm, respectively, showing slightly larger size as local chain flexibility decreases. [Preview Abstract] |
Thursday, March 16, 2006 12:03PM - 12:15PM |
V24.00005: The Effect of Counterions on the Blend Miscibility of Polystyrene with Sulfonated Polystyrene Ionomers Nancy C. Zhou, Wesley R. Burghardt, Russell J. Composto, Karen I. Winey Our previous study probed the miscibility of polystyrene (PS) and sulfonated polystyrene (P(S-SS$x))$ of differing sulfonation levels ($x)$ and found a narrow window of miscibility. Specifically, the PS:P(S-SS$x)$ blend system becomes completely immiscible at unexpectedly low sulfonation level, x = 2.7 mol$\% $. Here we extend the study of blend miscibility of PS with P(S-SS$_{0.007} )$ to include materials neutralized with sodium, barium and zinc cations. These ionomer blends exhibit an upper critical solution temperature (UCST) behavior with an increase in critical temperature as compared to the blend with unneutralized P(S-SS$_{0.007} )$. Forward recoil spectrometry (FRES) results indicate that Zn$^{++}$ and Ba$^{++}$ neutralized ionomers are less miscible than Na$^+$ when fully neutralized, while the blend miscibility for Na$^+$ and Zn$^{++}$ neutralized ionomers behave similarly when partially neutralized. Rheological studies are underway to compliment the blend miscibility studies. These miscibility information gained from PS/P(S-SS$x)$ ionomers blends will serve as a foundation for future ionomer morphology studies. [Preview Abstract] |
Thursday, March 16, 2006 12:15PM - 12:27PM |
V24.00006: Viscosity of Aqueous Polyelectrolyte Solutions with Oppositely Charged Surfactant Matthew Eggert, Ralph Colby The viscosity of polyelectrolyte solutions with oppositely charged surfactants is measured for a series of anionic polyelectrolytes of variable hydrophobicity (alternating copolymers of sodium maleate with hydrocarbon comonomers) in the presence of cationic trimethyl ammonium bromides with various alkyl tail lengths. These results are compared with a simple model that modifies the scaling theory for unentangled semidilute polyelectrolyte solutions to account for the addition of oppositely charged surfactant. The surfactant lowers the viscosity of these solutions through two means. The polyelectrolyte binds to the surface of the surfactant micelle, reducing the effective chain length of the polymer. The binding also causes counterions of the polyelectrolyte and the surfactant to be released into solution, acting as a salt that screens the repulsion between charges of the polyelectrolyte, causing the chains to have smaller size. The fraction of effectively charged monomers ($i.e$., free counterions) on the polyelectrolyte is measured via an ion-selective electrode, meaning the simple model has no adjustable parameters. Additional electrodes are used to measure the amount of free surfactant in solution in order to estimate the amount of surfactant associated with each polyelectrolyte chain. [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 12:39PM |
V24.00007: Simulations of Volume Phase Transitions in Polyelectrolyte Networks Upon Counterion Exchange De-Wei Yin, Juan J. de Pablo Polyelectrolyte networks are known to undergo discontinuous volume phase transitions, the onset of which may be caused by a number of factors. We have shown through molecular dynamics simulations that the interplay between the counterion excluded-volume entropy and the electrostatic energy---factors not explicitly considered in the classical Flory--Tanaka model---appears to have an important role in driving the phase transitions [Yin, Yan, and de Pablo, J. Chem. Phys. 123(17):174909, (2005)]. In our current work, we examine how the exchange of monovalent and divalent counterions induces discontinuous phase transitions in polyelectrolyte networks. It is revealed that divalent counterions condense preferentially over monovalent counterions onto the polyelectrolyte network backbone, thereby screening the charges on the backbone, and thus the different counterion species contribute differently to the osmotic pressure and hence to the free energy of the system. We present our findings as they relate to experiments performed near physiological conditions. [Preview Abstract] |
Thursday, March 16, 2006 12:39PM - 12:51PM |
V24.00008: Electrophoretically Assessing Polyelectrolyte Effective Charge Alexey Popov, David Hoagland Capillary electrophoresis revealed how polyelectrolyte effective charge density varies with backbone charge spacing and solvent dielectric constant. The study focused on ionenes, polyelectrolytes that possess regularly spaced quaternary ammonium groups in the backbone. Complete ionization of functional units and good solvency in water and mixtures of water with methanol or acetonitrile enabled measurements of ionene effective charge density as solvent dielectric constant continuously varied. Ionenes with aliphatic and oxyethylene spacers in the backbone were examined. As expected, effective charge density rose linearly with fixed charge density to a critical value, above which effective charge was nearly constant. Deviating from expectation, the onset of condensation did not occur at a critical fixed charge density predicted by Manning theory. Instead, condensation initiated at the constant critical Bjerrum length. The same onset condition was found for quaternized poly(vinyl pyridine). These results suggest a new type of condensation, one driven by ion-pairing. In support of the ion-pairing hypothesis, the onset of condensation correlates with counterion size. [Preview Abstract] |
Thursday, March 16, 2006 12:51PM - 1:03PM |
V24.00009: SAXS Determination of the Correlation Length of Semidilute Polyelectrolyte Solutions Shichen Dou, Ralph H. Colby In semidilute solutions, polyelectrolyte chains have a random walk conformation of correlation blobs. The size of those space filling correlation blobs can be measured using Small Angle X-ray Scattering from the wavevector at which there is a peak. In this study we randomly quaternized monodisperse poly(2-vinyl pyridine) (P2VP) and neutralized to make polyelectrolytes with either chloride or iodide counterions. We study a random copolymer for which 60{\%} of the charges are neutralized, at 25 $^{o}$C in three solvents: (1) Ethylene glycol (EG) is a good solvent for P2VP, with dielectric constant $\varepsilon $ = 37 making the Bjerrum length 15 {\AA} and dielectric spectroscopy measures the fraction of monomers bearing an effective charge $f$ = 0.17 for Cl$^{-}$ and $f$ = 0.07 for I$^{-}$ counterions. (2) Water is a poor solvent for P2VP, with $\varepsilon $ = 78 making the Bjerrum length 7.1 {\AA} and $f$ = 0.25 for I$^{-}$ counterions. (3) N-methyl formamide (NMF) is a good solvent for P2VP, with $\varepsilon $ = 182 making the Bjerrum length 3.1 {\AA} and $f$ = 0.60 for I$^{-}$ counterions (meaning that all counterions are free in NMF). We find that the correlation length of these polyelectrolyte solutions obeys the power law concentration dependence expected by scaling theory, and the correlation length decreases at a given concentration as the solvent is made more polar, because the polyelectrolyte chain has a larger effective charge. [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:15PM |
V24.00010: Phase behavior of semidilute polyelectrolyte mixtures of F-actin and DNA John Butler, Olena V. Zribi, Gerard C. L. Wong, Ramin Golastanian We investigate the phase behavior of semidilute mixtures of polyelectrolyte DNA coils and F-actin rods. F-actin has a persistence length of $\sim $10 microns and a linear charge density of -1e/0.25nm. DNA has a persistence length of $\sim $50nm and a linear charge density of --1e/0.17nm. Confocal and polarized microscopy data show that actin-DNA phase separates into ribbon-like birefringent domains of nematic F-actin and a disordered mesh of DNA coils. Synchrotron Small Angle X-ray Scattering (SAXS) show that DNA compresses F-actin into an ultradense dense nematic phase. The spacing between nematic F-actin domains shows a power-law dependence on DNA concentration which is independent of the contour lenth of either DNA or F-actin. [Preview Abstract] |
Thursday, March 16, 2006 1:15PM - 1:27PM |
V24.00011: Counterion correlations in charged macromolecular systems Arben Jusufi, Yu Mei, Matthias Ballauff We perfomed Molecular Dynamics simulations of a charged macroion surrounded by counterions. Various scattering contributions result from correlations between counterions, macroion, and between both of them. Experimentally, these scattering contributions can be measured by anomalous small-angle X-ray scattering (ASAXS) experiments. As a result the cross-correlation between the rigid macroion and counterions yields always a meanfield expression for the counterion density distribution even if the counterions exhibit correlated fluctuations. In contrast, in star-like polyelectrolytes, representing a fluctuating macroion, meanfield approximations are valid only if the functionality is sufficiently high. A systematic investigation of the strength of correlated fluctuations and their effect in scattering intensities is demonstrated for these systems. Furthermore, we demonstrate a collapse transition for spherical polyelectroylte brushes (SPB) by adding trivalent counterions. The collapse of the SPB is observed by simulations and experiments. [Preview Abstract] |
Thursday, March 16, 2006 1:27PM - 1:39PM |
V24.00012: Chiral Symmetry Breaking and Elastic Response of Frustrated Polyelectrolyte Bundles Gregory Grason, Robijn Bruinsma We present a model for hexagonal aggregates of charged, cylindrical macromolecules (DNA, microtubules, F-actin, {\it etc.}) in the presence of multivalent counterions at low temperature. Using the Wigner crystal picture of the neutralizing charge condensed onto the rod-like macromolecules, we establish a one-to-one mapping between the statistical mechanics of the charged bundle system and those governing the $T=0$ properties of a two-dimensional, frustrated Josephson junction array. We find that the superconducting phase of the {\it quantum} system corresponds to the low-temperature phase of our {\it classical} bundle system, where the condensed counterions are ordered in three dimensions, while the insulating phase corresponds to the phase where one-dimensional phonon fluctuations destroy long-range order of the condensed charge. Remarkably, the mapping makes the prediction that the transition to the charge-ordered state should be accompanied by a spontaneous breaking of chiral symmetry (even in the absence of any molecular chirality). Finally, we exploit the well-studied critical properties of the electromagnetic response of the two-dimensional {\it quantum} system to deduce the elastic response of the {\it classical} charged-rod bundle system. [Preview Abstract] |
Thursday, March 16, 2006 1:39PM - 1:51PM |
V24.00013: Studies of Glassy Dynamics in Ionomer melts Monojoy Goswami, Sanat Kumar, Aniket Bhattacharya In this work we investigate one of the challenging problems, the dynamics of ionomer aggregates using Molecular Dynamics simulations. Experimental results show that the glass transition temperature (T$_{g})$, diffusion and relaxation mechanisms can be influenced dramatically by ion-incorporation or by changing temperature of the system e.g., increase in ion content raises the T$_{g}$. In this work we show the dynamical behavior of ionomer melts as it goes from liquid to glass/gel state. In the context of ionomers, we investigated the analogy between reversible gelation and the glass transition, and show that many of the beneficial properties of ionomers and difficulties in understanding them can be understood in this framework. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700