Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H42: Polymer Assembly II |
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Sponsoring Units: DPOLY Chair: Boualem Hammouda, NIST Room: 345 |
Tuesday, March 15, 2016 2:30PM - 2:42PM |
H42.00001: Phase Behavior and Micellar Packing of Impurity-Free Pluronic Block Copolymers in Water Chang Yeol Ryu, Hanjin Park We have investigated the impacts of the non-micellizable polymeric impurities on the micellar packing and solution phase behavior of Pluronic block copolymers in water. In particular, small angle x-ray scattering, rheology and dynamic light scattering techniques have been employed to elucidate how the low MW impurities affect the micellar packing and solution phase diagram in water, when ordered cubic structures of spherical micelles are formed. A silica slurry method has been developed using the competitive adsorption of the PEO-PPO-PEO triblock copolymers over the low MW polymeric impurities for a large scale purification of Pluronics and it purity of Pluronics has been assessed by interaction chromatography. Based on the comparative studies on micellar packing between As-Received (AR) and Purified (Pure) Pluronic F108 solutions, we found experimental evidence to support the hypothesis that the inter-micellar distance of Pluronic cubic structures in aqueous solution is governed by the effective polymer concentration in terms of PEO-PPO-PEO triblock copolymers. Removal of the impurities in AR F108 offers an important clue on window into the onset of BCC ordering via hydrodynamic contact between micelles in solution. [Preview Abstract] |
Tuesday, March 15, 2016 2:42PM - 2:54PM |
H42.00002: Controlled Solution Self-Assembly of a Midblock-Sulfonated Pentablock Copolymer Kenneth Mineart, Michael Gradzielski, Richard Spontak The solution self-assembly of midblock-sulfonated block ionomers (SBIs) has been shown to translate to their bulk, solution-cast morphology, which can further impact their function in applications such as desalination, fuel cell, and photovoltaic membranes. Previous studies have identified that increasing the degree of sulfonation (DOS) in SBIs dispersed in a nonpolar solvent results in the growth of micellar aggregates due to increased interfacial energy. However, these works have not attempted to control the assembly at a given DOS by tuning the solvent environment. The current study probes the tunability of SBI aggregation behavior using a nonpolar/polar solvent mixture varying in composition. A combination of light scattering (SLS and DLS) and small angle X-ray scattering (SAXS) independently confirm that SBI micelles grow larger, both in core and corona, as the solvent environment becomes more nonpolar. The increases in both core and corona size will be explained using polymer thermodynamics and further supported through presentation of small angle neutron scattering (SANS) data. In addition, these results will be compared with SBI self-assembly in a single solvent, which is expected to distribute between the micelle cores and bulk solvent environment. [Preview Abstract] |
Tuesday, March 15, 2016 2:54PM - 3:06PM |
H42.00003: Self-Assembly of Soft Colloids with Multi-scale Phase-Separated Structures Chris Sosa, Robert K. Prud'homme, Rodney D. Priestley The ability of polymers and block co-polymers to self-assemble into highly-ordered structures in bulk two-dimensional films under specific environmental conditions has allowed in recent years for the fabrication of nano-porous membranes, nano-structured surfaces, and sacrificial templates for the preparation of inorganic nanomaterials with well-defined geometries. Extending these fairly specific fabrication techniques to the creation of similar three-dimensional colloidal structures in bulk solutions, however, has proven quite challenging despite the significant need for heterogeneously-structured colloidal materials in medicine and industry. Here we present a strategy for controlling the structural heterogeneity of soft polymer particles along multiple length scales by inducing the rapid phase-separation of polymer mixtures through a continuous nanoprecipitation process. [Preview Abstract] |
Tuesday, March 15, 2016 3:06PM - 3:18PM |
H42.00004: Solution assembly behaviors of 3-hexylthiophene polymer based rod-coil graft copolymer Youngkwon Kim, Jin-Sung Kim, Hyeong Jun Kim, Bumjoon Kim Solution assembly of conjugated polymer based block copolymers (BCPs) is an attractive approach for achieving conducting nanowires (NWs) with nanometer-scale cross-sectional dimensions. In particular, conjugated block offers one-dimensional self-growth of crystalline NWs, and secondary block gives rise to stable dispersion of NWs and additional tuning parameter for the structures of NWs. Herein, we developed a series of poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP) rod-coil copolymers with systematically controlled crystallinity by modifying both grafting density and molecular weight (Mn) of coil block, and their solution assembly behaviors were carefully examined. As increasing the volume fraction and grafting density of the secondary blocks, melting temperatures, crystallization temperatures, and the crystallinity were gradually decreased by hindering rod-rod interaction between P3HT backbones, resulting in the formation of short NWs. Furthermore, the length of NMs was relatively shorter for the densely grafted copolymer despite same volume fraction of secondary block. These results suggested that controlling Mn and the number of branched coil block was critical to regulate the crystalline properties and new approach for determining the NWs growth. [Preview Abstract] |
Tuesday, March 15, 2016 3:18PM - 3:30PM |
H42.00005: Tuning nanoscale viscoelasticity of polyelectrolyte complexes with multiple types of cross-links Tianzhu Ma, Biao Han, Daeyeon Lee, Lin Han Mechanical properties of hydrogels are manifestation of cross-link type and density, fixed charges and water-polymer interactions. In this study, we revealed how different types of cross-links regulate the nanoscale viscoelasticity of polyelectrolyte networks. Ionically cross-linked PAH/PAA layer-by-layer complexes were modified to include covalent cross-links using EDC. AFM-nanoindentation and force relaxation were performed at various ionic strength (0.01-1M) and pH (1.5-5.5). As-assembled networks, held only by ionic cross-links, underwent \textgreater 95{\%} relaxation, dominated by cross-link breaking and re-formation. Addition of covalent cross-links increased the instantaneous modulus by 1.6-fold and attenuated relaxation to $\approx $80{\%} of net neutral states (pH$\ge $3.5), as covalent cross-links provide additional elastic components. The network remained stabilized when all ionic cross-links were dissociated at pH$\le $1.5, whereby further attenuation to 31{\%} in relaxation could be due to viscoelastic polymer conformational changes and fluid flow-induced poroelasticity. Taken together, this study demonstrates the potential of using multiple cross-linking types to tune the viscoelastic mechanisms in polyelectrolyte complexes. [Preview Abstract] |
Tuesday, March 15, 2016 3:30PM - 3:42PM |
H42.00006: Coarse-grained Simulation of Complexation between Small Interfering RNA and Polycations Zonghui Wei, Yong Ren, John-Michael Williford, Hai-Quan Mao, Erik Luijten Nanoparticles formed through self-assembly of polycations and nucleic acids are promising systems for gene delivery. A full understanding of the behavior of these particles in physiological context requires detailed knowledge of their physical properties. All-atom molecular dynamics simulations can provide insight into the interaction of polymeric carriers with genomic material, but only at limited time and length scales. To overcome these limitations and explore the full complexation process, a reliable coarse-grained model is needed. Here, we systematically develop such a model for a system comprised of small interfering RNA (siRNA) and polyethyleneimine-based carriers, and evaluate the quality of the coarse-grained model through comparison with all-atom simulations. We show that our coarse-grained model provides a reliable description of detailed binding pictures, charge characteristics, and water dynamics, while accelerating the simulations by two orders of magnitude. This makes it possible to quantitatively investigate nanoparticle formation involving multiple siRNA molecules and cationic copolymers. [Preview Abstract] |
Tuesday, March 15, 2016 3:42PM - 3:54PM |
H42.00007: Mesoscale Lattices Assembled from Charge-Tunable Block Copolymer Blends in Selective Solvents Seyoung Kim, Jewon Choi, Soo-Hyung Choi, Kookheon Char Recent studies revealed that block copolymer (BCP) microdomains are capable of being organized into unusual symmetries such as the Frank-Casper phases. These unique structures result from a compromise between domain geometry and space-filling constraint; in other words, the deformability of soft matter. Our mesoscale micellar lattices co-assembled from the blends of oppositely charged BCPs demonstrate the nature of deformable soft materials in a distinctive way. The micellar structures and interactions of BCPs in selective solvents can be finely tuned by controlling the charge density such that the spherical micelles further assemble into hexagonal arrays. The micellar lattices show unconventional symmetry and sub-10 nm clean facet formation compared to hard-sphere counterparts reported so far. We attribute these novel phenomena to multi-compartment intrastructure of the micelles assembled and their strong interactions, since the crystalline symmetry disappears with a subtle control of solvency, mixing ratio of BCP blends, and micellar interactions. Analysis on the nucleation condition reveals that such deviation in the micellar lattices arises from the soft nature of BCP assemblies which can be readily deformed upon swelling. [Preview Abstract] |
Tuesday, March 15, 2016 3:54PM - 4:06PM |
H42.00008: The Sheet Trapped in a Plumber's Nightmare Christopher O'Bryan, Tapomoy Bhattacharjee, W. Gregory Sawyer, Thomas Angelini Block co-polymer systems offer exquisite control in the molecular-level design of self-assembled structures. The application of block copolymer phases has been generally limited to their use as bulk stabilizing agents in mass produced commodity chemicals and plastics. Recently, we have found the complex phase structures of self-assembled styrene ethylene/propylene diblock and styrene ethylene/butylene triblock co-polymers useful in 3D printing of other soft materials; the co-polymer structure yields around a writing nozzle as it moves through space while leaving material (polymers or colloids) trapped in the form of programmed structures. However, the relationship between the structural phase of the co-polymer self-assembly and its ability to support printed soft matter materials is not understood. In this study, we explore how different block co-polymer assemblies interact with and support soft matter materials once localized yielding has occurred. [Preview Abstract] |
Tuesday, March 15, 2016 4:06PM - 4:18PM |
H42.00009: Structural transformation of peptide amphiphile self-assembly induced by headgroup charge and size regulation Changrui Gao, Michael Bedzyk, Monica Olvera, Sumit Kewalramani, Liam Palmer The ability to control the nano and the meso-scale architecture of molecular assemblies is one of the major challenges in nanoscience. Significantly, structural transformations of amphiphilic aggregates induced by variations in environmental conditions have attracted attention due to their biotechnological relevance. Here, we study the assembly in aqueous solution for a modular series of peptide amphiphiles with 3, 2 or 1 lysine groups conjugated to a C$_{\mathrm{16}}$ carbon tail (C$_{\mathrm{16}}$K$_{\mathrm{3}}$, C$_{\mathrm{16}}$K$_{\mathrm{2,\thinspace }}$and C$_{\mathrm{16}}$K$_{\mathrm{1}})$. This system design allow us to probe how the equilibrium structure of the self-assembly can be tuned by controlling the coupling between steric (via choice of headgroup: K3, K2, or K1) and electrostatic (via solution pH) interactions. Solution small- and wide-angle X-ray scattering (SAXS/WAXS) and transmission electron microscopy (TEM) studies reveal that depending on pH and number of lysines in the lipid headgroup, amphiphiles can assemble into a range of structures: spherical micelles, bilayer ribbons and vesicles. We also perform detailed phase space mapping of pH-and headgroup size dependency of the structures of assembly over 0.1-100 nm length scales via SAXS/WAXS. The experimental results in conjunction with molecular dynamics (MD) simulations deduce quantitative relations between pH-dependent molecular charges, steric constraints and self-assembly morphologies, which is significant for developing experimental routes to obtain assembly structures with specific nano- and meso-scale features through controlled external stimuli. [Preview Abstract] |
Tuesday, March 15, 2016 4:18PM - 4:30PM |
H42.00010: Multibody Interactions, Phase Behavior and Clustering in Nanoparticle-Polyelectrolyte Mixtures Venkatraghavan Ganesan, Gunja Pandav, Victor Pryamitsyn, Jeffrey Errington We present the results of a computational study of the interactions, phase-behavior and aggregation characteristics of charged nanoparticles (CNPs) suspended in solution of oppositely charged polyelectrolytes (PEs). We used an extension of the mean-field polymer self-consistent field theory (SCFT) model to explicitly characterize the multibody interactions in such systems. For dilute-moderate particle volume fractions, the magnitudes of three and higher multibody interactions were seen to be weak relative to the contributions from pair interactions. We embedded the pair-interaction potentials within a thermodynamic perturbation theory approach to identify the phase behavior of such systems. The results of such a framework suggested that the gas and FCC crystal phases were thermodynamically stable, whereas the fluid-like phase was metastable in such systems. To complement the parameters studied, we used a recently developed simulation approach to study the aggregation and cluster morphologies in CNP-PE mixtures. For low particle charges, such systems mainly exhibited clusters arising from direct contact aggregation between CNPs. However, for higher particle and PE charges and low PE concentrations, large regions of PE-bridged clusters were seen to form. [Preview Abstract] |
Tuesday, March 15, 2016 4:30PM - 4:42PM |
H42.00011: Early Stage Kinetics in Polyelectrolyte Complexation Studied in a Stopped-Flow Configuration Xiaoqing Liu, Marie Haddou, Joanna Giermanska, Christophe Schatz, Jean-Paul Chapel Polyelectrolyte complexes (PECs) are the association complexes formed between oppositely charged macromolecules. A large body of work has been devoted to the preparation and morphology characterizations of PECs. Much less attention was paid on formation kinetics of PECs, which often occurs under non-equilibrium conditions. Stopped-flow technique combined with light scattering was used to investigate the early stage complexation kinetics in the poly(acrylic acid) and poly(diallyldimethylammonium chloride) system. It was found that initial complexes form within a few ms. Depending on the PEs molar charge ratio z, initial complexes followed different evolution pathways. For z \textgreater 0.7, a large complex aggregation ascribed to the onset of coacervation was identified by an increase of the scattered intensity while an unexpected decay was observed for z \textless 0.7 where small PECs are formed. The appearance of characteristic bell-shaped curves in the presence of different ionic strengths (I) highlighted the strong influence of the interaction intensity on the complexation/reorganization kinetics. The results revealed distinct assembly and ageing mechanisms as a function of z, I and molecular weights. [Preview Abstract] |
Tuesday, March 15, 2016 4:42PM - 4:54PM |
H42.00012: Supramolecular Assemblies of Poly(propyleneimine) Dendrimers Driven by Simple Monovalent Counterions Seyed Ali Eghtesadi, Fadi Haso, Marjan Alsadat Kashfipour, Dr. Robert Lillard, Dr. Tianbo Liu Polyelectrolytes (PE) are fascinating class of polymers carrying dissociative ionic groups which give them unique properties in solutions and at charged surfaces. The properties of these polymers in solution are mainly depending on the fraction of dissociated ionic groups, the quality of solvent and salt concentration. Describing the solution properties of polyelectrolytes have always been an obstacle for polymer scientists due to their different behavior as a result of their dual character of being highly charged electrolytes and at macromolecular size. The question we tried to address was what happens to solution behavior of charged polyelectrolytes when they reach to the nano-scale size which can neither be considered as point charges nor colloids. Second generation of poly(propyleneimine) dendrimer in different solvent qualities, salt concentrations, pH and temperatures were studied using techniques such as LLS, TEM, AFM and zeta-potential, and dominant controlling factors over their self-assembly into hollow spherical ``Blackberry'' like nanoparticles was investigated. [Preview Abstract] |
Tuesday, March 15, 2016 4:54PM - 5:06PM |
H42.00013: Self-Assembly of Polyoxometalate and Polyelectrolyte Macroions into Mechanically Strong Supramolecular Hydrogels Benxin Jing, Y. Elaine Zhu Polyoxometalate (POM) macroions are the nanoclusters of transition metal oxide with size 1-10 nm and well-defined structure at the atom level. Because of their stoichiometric surface groups and high solubility in polar solvents to form thermodynamically stable solution, POMs are studied as excellent model macroions at nanoscale. In this work, we explore the electrostatic controlled self-assembly of anionic POMs and cationic or zwitterionic polyelectrolytes (PEs) in aqueous solution. Specifically we examine the complex formation of zwitterionic poly (3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide) (PSBMA) and cationic poly(diallyldimethylammonium chloride) (PDADMAC) with tungstate based POMs of varied valence. The phase diagram of POM/polyelectrolyte complexes is determined with varied POM/PE charge ratios. It is interesting to observe the coacervation of POMs with PSBMA. With cationic PDADMAC, hybrid POM-PDADMAC hydrogels can be formed. Nevertheless, POM-PDADMAC complexes exhibit much enhanced mechanical properties in comparison to polymer hydrogel. The viscoelastic properties of hybrid macroion complexes strongly depend on PDADMAC concentration, POM-to-PDADMAC molar ratio, the size and valence of POMs. At the intermediate range of POM-to-PDADMAC concentration ratio, shear thickening and strain hardening are observed with soft supramolecular hydrogels, which is resulted from the non-Gaussian stretching of polymer chains. [Preview Abstract] |
Tuesday, March 15, 2016 5:06PM - 5:18PM |
H42.00014: Polyelectrolyte Complex Hydrogels: Self-assembly and the Influence of Charged and Neutral Blocks Samanvaya Srivastava, David Goldfeld, Adam Levi, Jun Mao, Wei Chen, Matthew Tirrell Polyelectrolyte complexes (PEC) form when oppositely charged polyelectrolyte chains spontaneously associate and phase separate in aqueous mediums. Bulk phase separation of the PECs can be evaded by combining one or both of the polyelectrolytes with a neutral polymer, thus engineering pathways for self-assembled PEC micelles and hydrogels. The PEC domains in these assemblies can encapsulate therapeutics as well as genetic materials and thus have tremendous potential in drug delivery and tissue engineering applications. We will present insights on the equilibrium structure and self-assembly kinetics of PEC hydrogels with large-scale ordering of the nanoscale PEC domains through detailed structure characterization and rheology studies of self-assembled materials comprising of functionalized polyallyl glycidyl ethers (PAGE) connected to either single poly(ethylene glycol) (PEG) chain to form diblock copolymers or as functionalized end-groups on a triblock copolymer with a PEG midblock. The effect of key parameters such as polymer concentration, polymer block lengths, salt, ionic strength, and degree of charge mismatch on the equilibrium materials properties will be discussed, with a special emphasis on the structure-defining role of the charged blocks and the structure-directing role of neutral blocks. Additionally, interesting similarities, and differences between structures and dynamics of hydrogels comprising diblock and corresponding triblock polyelectrolytes, respectively, will be discussed. [Preview Abstract] |
Tuesday, March 15, 2016 5:18PM - 5:30PM |
H42.00015: Thermo-reversible morphology and conductivity of a conjugated polymer network embedded in polymeric self-assembly. Youngkyu Han, Jan-Michael Y. Carrillo, Zhe Zhang, Yunchao Li, Kunlun Hong, Bobby G. Sumpter, Michael Ohl, Mariappan Parans Paranthaman, Gregory S. Smith, Changwoo Do Self-assembly of block copolymers provides opportunities to create nano hybrid materials, utilizing self-assembled micro-domains with a variety of morphology and periodic architectures as templates for functional nano-fillers. Here we report new progress towards the fabrication of a thermally responsive conducting polymer self-assembly made from a water-soluble poly(thiophene) derivative with short PEO side chains and Pluronic L62 solution in water. The structural and electrical properties of conjugated polymer-embedded nanostructures were investigated by combining SANS, SAXS, CGMD simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporating them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellar-to-lamellar phase transition defines the embedded conjugated polymer network. The conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. [Preview Abstract] |
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