Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W45: Structure and Phase Behavior of Charged and Ion Containing Polymers |
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Sponsoring Units: DPOLY Chair: Anupriya Agrawal, Clemson University Room: 216AB |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W45.00001: A molecular simulation study on salt response of polyelectrolyte complexes Hanne Antila, Paul Van Tassel, Maria Sammalkorpi In aqueous solutions, oppositely charged polymers, polyelectrolytes (PEs) form complexes which are known to be sensitive to added salt with responses ranging from shrinking to full destabilization of the complex. As a specific application of PE complexes, the complex formation of DNA with polycations has been demonstrated to be an effective means of transfecting genetic material in gene therapy. We use all-atom molecular dynamics and coarse-grained Monte Carlo simulations to investigate the effect of excess salt on DNA-polycation complex stability. The detailed all-atom simulations demonstrate the mechanism of polycation and ion species specific salt-driven dissociation [1] involving charge reversal. More generally, other possible mechanisms of salt driven dissociation exist as well. The coarse grained approach, which describes the PE complex as oppositely charged, rigid rods and ions as hard spheres, provides a more complete understanding of PE interactions in salt, and suggests possible mechanisms leading to repulsion between the oppositely charged polyelectrolytes. [1] H. S. Antila, M. Sammalkorpi, J. Phys. Chem. B, 2014. [Preview Abstract] |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W45.00002: Coarse-grained Molecular Simulation Studies of Complexation of Sulfobetaine-Lysine Copolymer and DNA for Gene Delivery Ahmadreza F. Ghobadi, Arthi Jayaraman Gene delivery involves successful transfection of therapeutic DNA by a vector into target cells and protein expression of that genetic material. Viral vectors are effective at gene delivery but elicit harmful immunogenic responses, thus motivating ongoing research on non-viral transfection agents. Cationic polymers are a promising class of non-viral vectors due to their low immugenic responses and low toxicity, and their ability to bind to the polyanionic DNA backbone to form a polycation-DNA complex (polyplex) that is then internalized in the target cell. While past studies have shown many polycations with differing DNA transfection efficacies, there is a need for general design guidelines that can relate the molecular features of the polycation to its DNA transfection efficiency. Using atomistic and coarse-grained molecular dynamics simulations we connect polycation design to polycation-DNA binding and experimentally observed transfection efficiency. Specifically in this presentation we will discuss our recent work looking into the effect of incorporating zwitterions into lysine based polycations on the resulting polyplex structure, shape, surface charge density and stability of DNA-polycation complexes. [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W45.00003: Experiments of salt concentration effects on translocation dynamics of polyelectrolytes passing through alpha-hemolysin pore Byoung-jin Jeon, Murugappan Muthukumar We have investigated physical mechanisms of electric field driven single file translocation of polyelectrolytes through an alpha-hemolysin pore by measuring the translocation time under different voltages, salt concentrations, and pH. Our experiments reveal an intricate coupling among various driving forces in dictating the polyelectrolyte translocation. For example, we find that the salt concentrations in the donor and the recipient compartments influence the polymer translocation dynamics differently, depending on pH. From a series of systematic experiments, we demonstrate that the salt concentration in the donor compartment influences the polymer charge and the free energy barrier for entrance and that the salt concentration in the receiver compartment influences the electrostatic interaction between the polymer and pore. We provide a physical model for the free energy landscape of the translocation process and offer an explanation of the origin of the salt concentration effects on the polymer translocation dynamics for different pH conditions. This study offers an opportunity to understand how different driving forces get coupled in dictating the polyelectrolyte dynamics under nonequilibrium conditions. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W45.00004: Salt Effects on the Structure and Stability of Ionizable Polydots - SANS Study Naresh Osti, Sidath Wijesinghe, Manjula Senanayake, Anuradhi Wickramasinghe, Thusitha Etampawala, Dvora Perahia Confinement of rigid luminescent polymers into nano-dimension forms polydots, long lived nanoparticles, even though the polymer chains are far from their thermodynamically equilibrium conformations. These polydots bare the potential to be tunable by changing the conformation of the polymer, making them promising for new bio-imaging markers and drug delivery vehicles. Here, we investigate ionizable polydots formed by di-alkoxy poly para-polyphenyleneethynylene (PPEs). Incorporating an ionic group opens the way to tether bio-active molecules to these markers as well as tuning their conformation and hence their luminescence. Our small angle neutron scattering (SANS) have shown that these ultra-stable polydots respond to changes in their electrostatic environment where exposure to NaOH modifies both the structure and stability. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W45.00005: Ionic Effect on Conformational Structure of Weak Polyelectrolyte in Dilute Solution: from Monovalent, Multivalent to Macro ions Chen Qu The electrostatic environment near a charged polymer chain is critical to the structure and function of the polymer in aqueous media. In this work, we compare the effect of small monovalent and divalent ions and multivalent inorganic macroions on the conformational structure of weak polyelectrolyte, poly(2-vinyl pyridine) (P2VP), in dilute aqueous solutions by single molecule spectroscopy. Divalent counterions at low concentration range show the similar effect as monovalent ones to cause the shift of the critical pH for the coil-to-globule conformational transition of P2VP to the higher pH range. In contrast, divalent counterions at high concentration range and inorganic nanocluster anions cause the shift the critical transition pH to the opposite lower pH range. The measurement of local pH near a single P2VP chain indicates that adding counterions can effectively increase the protonation degree on the P2VP chain. Yet the electric potential of the P2PV is found to decrease upon addition of divalent ions and anionic macroions, suggesting enhanced counterion condensation by multivalent ions. It is also found that inorganic nanocluster macroion of 1 nm in diameter can form dense complexes with P2VP, whose dimension becomes independent of solution pH. [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W45.00006: Phase Behavior of Charged Nanoparticle-Polyelectrolyte Solution Gunja Pandav, Venkat Ganesan Interactions between charged nanoparticles suspended in a polyelectrolyte solution are studied using single chain in mean field simulations. We consider a model in which the particles and polymers carry a fixed charge in presence of counterions and salt. The effect of particle charge, particle volume fraction, particle size, and polymer density on the phase behavior of the system is examined. In addition, we discuss the effective interactions between nanoparticles arising due to multibody effects and compare it with two-body potentials calculated using a mean-field approach. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W45.00007: Effects of mixing ratio, salt concentration and temporal trend on the formation of polyelectrolyte complex Yanpu Zhang, Erol Yildirim, Hanne Antila, Maria Sammalkorpi, Jodie Lutkenhaus Polyelectrolytes complexes (PEC) form by mixing polycation/polyanion solutions together. Promising applications of PECs range from industrial flocculants, coatings, and membranes to advanced materials for solar cells, injectable hydrogels, and chemical sensors. One challenge for PEC processing and application is that their physical properties are often time-dependent. In this work, we report on the influence of polycation/polyanion mixing ratio, salt concentration, and time on the formation of PECs made from poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate sodium salt) (PSS). Physical such as turbidity, hydrodynamic size, and zeta potential are investigated as a function of time. We find various critical values that can be used to predict whether a PEC will remain stable in suspension or whether it will gradually aggregate and precipitate. We discuss these findings in relation to the stepwise aggregation model that depicts primary PEC particles gradually form larger aggregates. Finally, we perform detailed molecular dynamics simulations to examine the structure and effective charge distribution of the PECs with their temporal stability at varying mixing ratios and salt concentrations to support the experimental findings. [Preview Abstract] |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W45.00008: Molecular Connectivity and Correlation Effects in Polymeric Complex Coacervates Mithun Radhakrishna, Charles Sing Complex Coacervation is a liquid-liquid phase separation induced by oppositely charges species and is a complicated process influenced by many factors like the solution pH, temperature, salt concentration, charge size and valency of the salt. Because of this inherent tunability complex coacervates have garnered a significant amount of attention as materials for under water adhesives, drug delivery platforms and self assembled structures. Most theoretical studies to address the complex coacervate materials to date have relied on the use of Poisson-Boltzmann theory (or extensions thereof). While these thermodynamic studies capture the phase behavior of complex coacervates in a qualitative sense, most of these theories neglect some of the important factors such as the effect of polyion-driven connectivity correlations and excluded volume interactions between the ions in the solution. In the current work we study the effect of these factors on the phase behavior of complex coacervates through molecular simulations coupled to thermodynamic models for phase separation. We demonstrate that these neglected molecular features (connectivity, finite polymer and ion size) profoundly impact the thermodynamics, and by articulating them in theoretical or simulation models, we can start to understand how to design coacervate materials at a molecular level. [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W45.00009: Molecular Dynamics Simulations of Ultracentrifuged Polyelectrolyte Complexes Diddo Diddens, Albert Johner, J\"{o}rg Baschnagel Polyelectrolyte complexes (PECs) are formed by the aggregation of positively and negatively charged polymer species, which precipitate rapidly from solution in case of equimolar mixing. As the fast complexation kinetics prevents the formation of an optimized pairing between positive and negative charges, the microstructure of these aggregates is ill-defined, resulting in a material that is difficult to process further. Recently, Schlenoff~{\it et al.}~[1] have demonstrated that the precipitates can be reshaped via ultracentrifugation in concentrated sodium chloride solutions, yielding a compacted, gel-like material, whose rheological properties make them interesting candidates for bioimplants. However, despite the success of this novel route to post-process PECs, the underlying molecular mechanisms are not yet fully resolved. We study the complex structure before, during and after centrifugation in a non-equilibrium Molecular Dynamics simulation of a fully atomistic simulation model. In a second step, we investigate the effect of these structural changes on the dynamics inside the PECs, and discuss these findings in context with the experimental observations. \\[4pt] [1]~Porcel and Schlenoff, {\it Biomacromolecules}, {\bf 2009}, 10, 2968 [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W45.00010: Tuning the phase diagram of polyelectrolyte blends with a pinch of salt Jos Zwanikken, Monica Olvera de la Cruz Developments in 'smart' materials and devices for energy storage rely on the versatile properties of charged polymers. The charged properties of the polymer backbone and those of the accompanying ions have a large influence on larger scale (self-assembled) structure and miscibility. With statistical thermodynamic methods, we investigate local ionic structure and the influence of charge correlations on the phase diagram of polyelectrolyte blends. In particular, we study the effects of added salt on the coexistence lines, and explore the possibilities of multiple phase coexistence between phases with a different polymer fraction or charge concentration. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W45.00011: Image method for Coulomb energy for many-body system of charged dielectric spheres Jian Qin, Juan de Pablo, Karl Freed Ion polarization is important for understanding ion solvation and the stability of ion clusters in polymeric materials which typically exhibit a low and spatially inhomogeneous dielectric permittivity. The simplest approach for modeling ion polarization involves treating the ions as charged spheres with an internal dielectric permittivity differing from that of the medium. The surface polarization contribution to the electrostatic energy for a system of such dielectric spheres can be evaluated perturbatively. We derived closed-form expressions for this energy as a function of the positions of an arbitrary number of polarized surfaces. Our approach is a generalization of the image method for conducting spheres. Using this approach, we calculated the polarization corrections to the cohesion energy for ion clusters and for densely packed ionic crystals. The method can be readily adapted for investigating ion polarization effects in both Monte Carlo and molecular dynamics simulations. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W45.00012: Phase behavior and multi-body effects in polyelectrolyte - nanoparticles mixtures Victor Pryamitsyn, Venkat Ganesan, Jeffrey Errington Recently we have developed a SCFT approach which allowed us to compute the effective interactions between charged nanoparticles (CNP) and in a polyelectrolyte (PE) solution. We have adapted such an approach to study the hierarchy of the two-, three- and multi-body interactions between CNP's. We have found that for the strong PE's and absent polarization interactions, the CNP-CNP interactions are essentially pairwise. This result allowed us to use the thermodynamic perturbation theory and the MC simulations to access the phase diagram of PE/CNP mixtures. Such analysis indicates that CNP-PE mixtures exhibit only gas and crystal phases, and that the fluid phase is metastable. The results of MC simulations suggest the suppression of the phase segregation by the formation of highly anisotropic clusters of CNP. The qualitative analysis of the three- and multi-body interaction in comparison with two-body interaction shows that such interaction may enhance the anisotropy of CNP clusters. We have also analyzed of weak PE's and the presence of polarization interaction. In such systems CNP's interactions remain qualitatively similar to the above systems, but the multi-body interactions appears to be significantly enhanced, which makes anisotropic clustering of PE's even more plausible. [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W45.00013: Ionic Liquids: Trends in Behavior and Miscibility with Polymers Michelle Chen, Ronald White, Jane Lipson Trends in polymer solution miscibility can be understood by analyzing the properties of each pure component. In this work, families of ionic liquids were characterized using the Locally Correlated Lattice (LCL) model that was previously used to study numerous polymers as well as their solutions and blends. Ionic liquids were divided into families that incorporated size variation into each of the components. The cationic species comprised members of the CnMIM (1-alkyl-3-methylimidazolium) family with n ranging from 2 to 10. The anionic component varied from BF$_{\mathrm{4}}$ to PF$_{\mathrm{6}}$ to NTf$_{\mathrm{2}}$ (bis(trifluoromethylsulfonyl)amide). Each liquid was characterized using the LCL equation of state and properties such as percent free volume and cohesive energy density were calculated. These properties were observed to be correlated with alkyl chain length and anion size within each family. Analyzing these trends points towards a fundamental understanding of ionic liquid miscibility with poly(ethylene oxide), members of the polymethacrylate family, and others. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W45.00014: Surface Tension and Lamellar Spacing in Polyelectrolyte Blends and Block Copolymers Charles Sing, Monica Olvera de la Cruz Heterogeneous polymer systems such as block copolymers (BCPs) are governed primarily by a competition between the surface tension between different chemical species and the entropic stretching of the polymer chains. Charged BCPs represent a class of materials that is currently of great interest to the polymer community due to the promise of charged BCPs as nanostructured membranes for batteries and fuel cells. The inclusion of charge presents a powerful way to tune the structure of BCPs, and we develop our understanding of how to do so by investigating the interfacial properties (surface tension and microstructure size) of polyelectrolyte blends and block copolymers. We use a new method that combines the features of liquid state (LS) theory and self consistent field theory (SCFT) into a multiscale LS-SCFT theory that provides beyond-mean-field predictions of polyelectrolyte systems. We find that charge size, charge correlations, and the fraction of charged monomers plays a crucial role in determining surface tension, and we therefore demonstrate how BCP structure changes upon inclusion of charges. Finally, we will show that these predictions provide the ideal basis for comparison to experiment and subsequent refinement of LS-SCFT theory. [Preview Abstract] |
Thursday, March 5, 2015 5:18PM - 5:30PM |
W45.00015: Molecular Origins of Thermal Transitions in Polyelectrolyte Assemblies Erol Yildirim, Yanpu Zhang, Hanne S. Antila, Jodie L. Lutkenhaus, Maria Sammalkorpi Polyelectrolyte (PE) multilayers and complexes formed from oppositely charged polymers can exhibit extraordinary superhydrophobicity, mechanical strength and responsiveness resulting in applications ranging functional membranes, optics, sensors and drug delivery. Depending on the assembly conditions, PE assemblies may undergo a thermal transition from glassy to soft behavior under heating. Our earlier work using thermal analysis measurements shows a distinct thermal transition for PE layer-by-layer (LbL) systems assembled with added salt but no analogous transition in films assembled without added salt or dry systems [1]. These findings raise interesting questions on the nature of the thermal transition; here, we explore its molecular origins through characterization of the PE aggregates by temperature-controlled all-atom molecular dynamics simulations. We show via molecular simulations the thermal transition results from the existence of an LCST (lower critical solution temperature) in the PE systems: the diffusion behavior, hydrogen bond formation, and bridging capacity of water molecules plasticizing the complex changes at the transition temperature. We quantify the behavior, map its chemistry specificity through comparison of strongly and weakly charged PE complexes, and connect the findings to our interrelated QCM-D experiments. \\[4pt] [1] A. Vidyasagar, C. Sung, R. Gamble and J. L. Lutkenhaus, ACS Nano\textbf{ 6}, 6174 (2012). [Preview Abstract] |
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