Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X19: Charged and Ion-containing Polymers |
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Sponsoring Units: DPOLY Chair: Jodie Lutkenhaus, Yale University Room: 320 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X19.00001: Molecular Weight and Charge Density Asymmetry in Polyelectrolyte Complexation Debra Audus, Glenn Fredrickson, Dominik Duechs We investigate the phase diagram of oppositely charged polymers in a good solvent using a field-theoretic model. Mean-field solutions fail to predict the experimentally observed macroscopic phase separation into a solvent-rich phase and a dense liquid aggregate of polymers - a ``complex coacervate.'' We therefore study the model within a one-loop approximation, which accounts for Gaussian fluctuations in electrostatic and chemical potentials. Our particular focus is the effect of molecular weight, ionic strength, and charge asymmetry on the phase envelope. A set of dimensionless parameters is identified that dictate the size and shape of the two-phase region. Our results should be helpful in guiding experimental studies of coacervation. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X19.00002: PEG-based Sulfonated Ionomers Microphase Separate with Increasing Temperature Wenqin Wang, Gregory J. Tudryn, Ralph H. Colby, Karen I. Winey A series of Li, Na, and Cs-neutralized sulfonated polyester ionomers with well-defined PEG spacer lengths have been investigated by in situ X-ray scattering over a wide temperature range. At room temperature, no ``ionomer peak'' at q=1-5 nm$^{-1}$ was observed, due to the high dielectric constant of the polymer matrix. As the length of the PEG segment increases, the crystallization of PEG segments is evidenced by multiple crystalline reflection peaks. In addition, crystallization produces periodic low-angle peaks, indicating a layered structure. Scanning transmission electron microscopy will be employed to facilitate the understanding of the nanoscale structures. At high temperatures, the PEG-based ionomers exhibit a new X-ray scattering peak in the angular range of 2-3 nm$^{-1}$, reminiscent of conventional ionomers. The peak intensity increases with temperature while the angular position remains fixed. The appearance of an ``ionomer peak'' at high temperature is attributed to the microphase separation of ionic aggregates as the PEG dielectric constant decreases. A mechanism is proposed to explain the ionic association behavior as a function of temperature. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X19.00003: Hierarchial Structures in PDMS-based Ammonium Ionenes David Salas-de la Cruz, Sudipto Das, Garth Wilkes, Karen Winey Ionenes are polymers with a charged entity in the backbone. Polydimethylsiloxane (PDMS) based ionenes were synthesized from 6-bromohexanoyl chloride and 1,4-diazabicyclo[2.2.2]octane (DABCO). X-ray scattering patterns were recorded at the small, intermediate and wide angle regions for both un-stretched and stretched films. Stretching induces orientation without changing the spacing in the morphology. The hard charged segments, that include DABCO, align in pseudo-cylindrical aggregates in the direction of the stretch and the PDMS soft segments remain amorphous. The orientation relative to the stretching direction suggests that the hard charged segments self assemble into anisotropic aggregates. This self-assembly arises from the hydrogen bonding of the urethane groups and ion sharing between Br- and N+. The characteristic spacing between the pseudo-cylindrical aggregates increases with the molecular weight of the PDMS segments and the size of the hard segments. Ionic conductivity measurements reveal that the through-plane conductivity increases by an order of magnitude upon stretching. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X19.00004: Temperature and pH Responsive Chargeable Copolymers with Tunable LCSTs Kiattikhun Manokruang, Evangelos Manias A series of alternating copolymers, made of $\alpha $,$\omega $-polyethylene glycol oligomers (M$_{w}$ 400 or 900) alternating with 1,6-diamino-hexane-\textit{stat}-lysine, is presented. Specifically their aqueous phase behavior is outlined, exhibiting temperature-controlled solubility (LCST) and a pH-controlled transition (across the point where lysine is charged). The terpolymers are uncharged at low pH while they become charged (containing lysine anions) when the solution pH increases; the phase diagrams in the temperature and pH space are drawn, and the tunability of the critical points in water as it is controlled by the copolymer composition is discussed. These copolymers, due to their hydrophilic polyethylene-oxide comonomers, exhibit a genuine LCST, i.e., a bona fide first order thermodynamic transition, rather than the usual micellization related LCST of copolymers that contain hydrophobic blocks or grafts. This last point is demonstrated by comparisons against micelle-forming copolymers, consisting of hydrophobic and chargeable comonomers. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X19.00005: Ionic Conductivity of Poly(ethylene oxide)-Containing Block Copolymers at Order-Disorder and Order-Order Transitions Nisita Wanakule, Ashoutosh Panday, Scott Mullin, Nitash Balsara The order-disorder transition (ODT) and order-order transition (OOT) of block copolymers with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salts are measured with a combination of small-angle x-ray scattering (SAXS) and birefringence. The block copolymers comprise of polyethylene oxide (PEO), a polymer with a higher dielectric constant that dissolves LiTFSI, and polystyrene (PS), a polymer with a lower dielectric constant that does not dissolve LiTFSI. Ionic conductivity of the block copolymers are measured through the observed ODT and OOT. The effect of morphology on the ionic conductivity will be presented and compared with literature results. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X19.00006: Origin of Lateral Nanoscale Heterogeneities in Weak Polyelectrolyte Brushes You-Yeon Won, Kevin Witte, Jaehyun Hur In this talk, we will first discuss experimental evidence of lateral nanoscale heterogeneities in a single-component weak polyelectrolyte brush system under zero to low salt conditions. Using an amphiphilic diblock copolymer, poly(2-(dimethylamino)ethyl methacrylate-$b-n$-butyl acrylate) (PDMAEMA-PnBA), for Langmuir film compression and Langmuir-Blodgett deposition on a hydrophobic substrate followed by fluid AFM imaging, we show the existence of regions of different brush heights, indicative of the thermodynamic instability (and resultant local clustering) of the PDMAEMA chains in the low-salt limit. Using SCF and scaling theories, we will also show that the lateral heterogeneities occur due to the combined effects of (i) the osmotic instability regulated by charge equilibrium and (ii) the hydrophobicity of the chains. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X19.00007: \textit{In situ} Neutron Reflectivity study of alcohols into ultra-thin ionmer films Thusitha Etampawala, Dvora Perahia, Lilin He, Christopher Cornelius For many applications a polymeric membrane with selective well-controlled transport are desired. A new class of materials that consists of rigid hydrophobic polyphenylene decorated by sulfonic acid functionalized phenylene side chains has shown a potential as controlled transport membranes for energy applications. The nature of the diffusion depends on the polymer structure and the interaction of its different segments with the solvent. In addition, the interfacial layer plays a critical roll in the transport characteristics. The current work introduces an \textit{in situ }neutron reflectivity study of penetration of long-chain alcohols into ultrathin films. The time dependence of the penetration of deuterated n-hexanol into films of 20nm thick ultra-thin films was determined and compared with that of less hydrophobic solvents. The process consists of two stages, a relatively fast stage in which the film thickness increases linearly with time followed by a slow phase in which structural changes take place. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X19.00008: Dynamic behavior of polyelectrolyte multilayer investigated by thin film calorimetry. H. Huth, R. Mueller, A. Fery, C. Schick Polyelectrolyte multilayer can be easily assembled using spraying or dipping of the different polyelectrolytes [1]. The thickness of the produced layers (nanometer range) is well controlled by the preparation conditions. Only a few methods are available for dynamic investigations, as afm for mechanical properties [2]. AC-chip calorimetry is used as a very sensitive tool for calorimetric investigations of such thin films as demonstrated for thin polymeric films in a wide frequency range [3]. To investigate the dynamic behavior of polyelectrolytes the humidity is used as a new parameter in addition to temperature for calorimetry. First measurements with the modified calorimeter for the PSS/PDADMAC polyelectrolyte multilayer system are shown. Further extensions of the calorimeter for better understanding of the phase behavior are discussed. [1] Decher, G. and J.D. Hong, Phys. Chem. Chem. Phys., 1991. 95(11): 1430. [2] Mueller, R., et al. Macromolecules, 2005. 38(23): 9766. [3] Huth, H., Minakov, A. A., Schick, C., J. Polym. Sci. B Polym. Phys. 2006 44: 2996. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X19.00009: Counter-ion fluctuations in the presence of a spherical macromolecule Leandro Boonzaaier, Kristian K. Mueller-Nedebock, Frederik G. Scholtz The effective interactions of charged macromolecules (e.g. polyelectrolytes) are still not fully understood. The role of counter-ion fluctuations, in the presence of these macromolecules, seems to be crucial in understanding these effective interactions. We consider a single charged spherical macromolecule, enclosed in a finite volume, in the presence of point-like counter-ions in an electrically neutral solution. Writing the partition function as a functional integral and only keeping terms up to quadratic order, we calculate the free energy in this approximation exactly. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X19.00010: Counterion Condensation and Collapse of Sodium Polystyrene Sulfonate in Water: A Molecular Dynamics Study Jan-Michael Carrillo, Andrey Dobrynin Hydrophobic polyelectrolytes are known to form necklace-like structures of dense beads connected by strings of monomers. This structure appears as a result of optimization of electrostatic and short-range interactions. To elucidate the effect of counterion condensation on polyelectrolyte conformations we performed two sets of molecular dynamics simulations of sodium polystyrene sulfonate (NaPSS) chains with degree of polymerizations $N$=16, 32 and 64 and fraction of charged monomers $f$=0.25, 0.33, 0.5 and 1.0 in aqueous solutions; (1) water molecules were considered explicitly using TIP3P model and (2) water molecules were modeled as a dielectric continuum with dielectric constant 77.73. Our simulations showed that with increasing $f$ a polyelectrolyte chain adopts an elongated conformation. The transition between collapsed and elongated states does not show any features of abrupt transition due to the fact that only relatively short chains were considered. Furthermore, even for our longest chains ($N$=64) the necklace-like globule was not observed. Effect of the water-ion interactions on counterion condensation was analyzed by comparing the radial distribution function between the sulfonate groups and sodium counterions for chains with different $f$. It was found that in simulations with explicit water ionized groups are located at the globular surface. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X19.00011: ABSTRACT WITHDRAWN |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X19.00012: Computational titrations of linear and branched polyethyleneimine Jesse Ziebarth, Yongmei Wang Despite a great deal of interest in polyethyleneimine (PEI) for its potential use as a gene therapy vector, the protonation state of this polycation is currently not well understood. PEI is rare among polyelectrolytes as every third atom along the backbone of the polymer is a protonable nitrogen. The closeness of these potentially charged sites can lead to high electrostatic repulsion and a large shift in the effective pKa of the amine groups as the degree of protonation increases. Previous experimental and theoretical estimates of the degree of protonation of PEI under physiological conditions have ranged from 0.15 to 0.80. Here, we perform computational titrations on coarse-grained models of both branched and linear PEI under various conditions. Chain length, degree of branching, salt concentration, and the solvent dielectric constant are varied to determine how these factors influence the protonation of PEI. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X19.00013: Phase diagrams of effective charge and size of an isolated polyelectrolyte chain and gels Arindam Kundagrami, Murugappan Muthukumar We consider an isolated polyelectrolyte chain and charged gels under poor solvent conditions and calculate the phase diagrams for the effective charge and size of the respective systems as functions of physical parameters such as temperature and salt concentration. Phase boundaries and the critical point for the first order collapse transition - induced cooperatively by counterion adsorption and solvent quality - are calculated self-consistently in terms of both the effective charge and the size of the chain with arbitrary ionizability. [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X19.00014: Single chain contraction and re-expansion by counterions of polyelectrolytes Pengxiang Jia, Jiang Zhao We have studied the re-entrant transition of polyelectrolytes at single chain level. Diffusion rate of single chains of polystyrene sulfonate (PSSNa) has been investigated by fluorescence correlation spectroscopy under different counterion condition. Upon the addition of external salts, the hydrodynamic radius of PSSNa was found to decrease with the increase of salt concentration, i.e., the chain contracts due to electrostatic screening and ion bridging effect. When the salt concentration increased beyond a certain value, the chains were observed to increase their dimension for a few mono-, double- and triple-valent counterions. The experimental evidence shows the single chain behavior of re-entrant transition of polyelectrolytes. [Preview Abstract] |
Thursday, March 19, 2009 5:18PM - 5:30PM |
X19.00015: Conformation and Dielectrophoresis of Single Weak Polyelectrolyte under AC Electric Field Shengqin Wang, Yingxi Zhu The application of AC-electric fields, when integrated with current microarray and ``lab-on-chip'' platforms, has emerged as a useful tool to manipulate and assemble supramolecular aggregates, such as AC-field induced protein crystallization and DNA hybridization, yet the detailed mechanism remains unclear. To understand the AC-polarization mechanism of biomacromolecules, we examine the conformational and dielectrophoretic behavior of polyelectrolytes under AC-electric field using fluorescence correlation spectroscopy (FCS) at single molecular level. We focus on poly (vinyl pyridine) (PVP) as a model polyelectrolyte whose conformation can be tuned by adjusting the pH and ionic strength. We observe that in the non-uniform AC electric field, PVP in a coil conformation experiences the positive DEP force at applied frequency below 500 kHz; it is also intriguing to observe the elongation of PVP coils at a characteristic AC-frequency of $\sim $ 200 kHz. In sharp contrast, PVP in a globule conformation shows insensitive to imposed AC-fields. We also examine the conformational change in a uniform AC-field where the DEP force is absent; the result suggests a redistribution of counterions with an induced dipole of polyelectrolyte. The behavior is further investigated with varied medium conductivity and microelectrode geometry. [Preview Abstract] |
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