Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A21: Focus Session: Soft Nanoparticles, Block Copolymer Micelles, and Polymersomes I |
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Sponsoring Units: DPOLY Chair: Darrin Pochan, University of Delaware Room: 406 |
Monday, March 3, 2014 8:00AM - 8:36AM |
A21.00001: Solution Self-Assembly of Globular Protein-Polymer Conjugate Block Copolymers Invited Speaker: Bradley Olsen Controlling the nanostructured self-assembly of globular proteins and enzymes can significantly advance the applications of soft materials as catalysts, sensors, and medical materials. However, the incorporation of globular proteins as one block in the block copolymer introduces changes in chain shape, chain entropy, and specific interactions that significantly impact the thermodynamics of self-assembly. Here, we explore the self-assembly of model globular protein-polymer block copolymers in concentrated solutions to form nanostructured materials. A phase diagram as a function of concentration and temperature for a model material mCherry-poly(N-isopropylacrylamide) (PNIPAM) is asymmetric, showing hexagonal cylinders for coil fractions less than 0.5 and a lamellar ordering for coil fractions greater than 0.5, divided by a narrow region of hexagonally perforated lamellae. Order-order transitions as a function of temperature are driven by the thermoresponsive desolvation of PNIPAM. Surprisingly, the materials exhibit reentrant order-disorder transition behavior, such that the conjugate block copolymers are disordered at both low and high concentrations but well-ordered at intermediate concentrations. Changing the polymer chemistry to monomers with different types of hydrogen bonding results in significant changes in the self-assembly, including the observation of a cubic phase that shows the same scattering pattern as the gyroid phase observed in traditional block copolymers. The choice of polymer also has a strong impact on the order-disorder transition concentration, demonstrating that the polymer-protein interaction plays a significant role in governing self-assembly in solution. Consistent with this effect, the order-disorder transition concentration is minimized in symmetric conjugates. Changing the protein from mCherry to myoglobin results in a reduction in ordering, suggesting that the regularity of the protein shape is important. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A21.00002: Tethered Nanoparticle$-$Polymer Composites: Phase behavior and rheology Rahul Mangal, Lynden A. Archer Polymer nanocomposites with particle radius (a) approaching the radius of gyration (R$_{g})$ of entangled host polymer have been reported to exhibit an unusual negative reinforcement effect, which leads to an anomalous reduction in relative an anomalous reduction in relative viscosity at low particle loadings ($\varphi )$. This so-called Non-Einsteinian flow behavior is understood to be sensitive to the dispersion state of particles in host polymer. We studied suspensions of SiO$_{2}$ nanoparticles tethered with polethylene glycol (PEG) in polymethylmethacralate (PMMA) with molecular weights (Mw) from 17 KDa to 280 KDa. Due to strong enthalpic interactions between PEG and PMMA ($\chi =$ -0.65), nanoparticles are expected to be well-dispersed, independent of Mw of PMMA. Using small angle x-ray scattering measurements we show that the phase stability of suspensions depends on Mw of the tethered PEG, host PMMA, and $\varphi $. Particles functionalized with low molecular weight PEG aggregate at low $\varphi $, but disperse at high $\varphi $. In contrast, nanoparticles functionalized with higher molecular weight PEG are well dispersed for host chain lengths (P) to tethered chain length (N), (P/N), is as high as 160. The stability boundary of these suspensions extends well beyond expectations for nanocomposites based on tethered PEG chains suspended in PEG. Through in-depth analysis of rheology and x-ray photon correlation spectra we explore the fundamental origins of non-Einsteinian flow behavior. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A21.00003: Effect of Protein Surface Potential on Globular Protein-Polymer Block Copolymer Self-Assembly Christopher Lam, Minkyu Kim, Carla Thomas, Dongsook Chang, Gabriel Sanoja, Chimdimma Okwara, Bradley Olsen The effects of protein surface potential on the self-assembly of protein-polymer block copolymers are investigated in globular proteins with a controlled shape through two approaches: (1) the self-assembly of the two structurally homologous proteins mCherry and EGFP conjugated to poly(N-isoprpopylacrylamide) (PNIPAM) and (2) bioconjugates containing mutants of mCherryS131C are prepared to specifically alter the electrostatic patchiness of the protein. Despite the large difference in amino acid sequence between mCherry and EGFP, identical phases are observed in concentrated solution at low temperatures and in bulk. At high temperatures above the thermoresponsive transition temperature, differences in micellar stability are observed at low concentrations, and different phases are observed between conjugates at high concentrations. Similarly, conjugates of four mCherryS131C variants with changes to their electrostatic surface patchiness showed minimal change in the concentrated solution phase behavior. Measurements of protein/polymer miscibility, protein second virial coefficients, and zeta potential indicate that coarse-grained interactions are able to largely capture the relevant physics for soluble, monomeric globular protein-polymer conjugate self-assembly. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A21.00004: Equilibrium Structure and Miscibility of Soft Nanoparticles in Polymer Melts Debapriya Banerjee, Kenneth Schweizer Crosslinked polymeric nanoparticles of tunable softness are modeled statistically using particle form factors obtained from scattering experiments. The model yields effective interactions between two fluctuating particles, and one fuzzy particle and a monomer. Using these effective interactions, microscopic PRISM integral equation theory is employed to study the structure and miscibility of soft nanogels in homopolymer melt. In the dilute particle limit, under chemistry-matched conditions, the monomer-particle pair correlations exhibit increasing polymer penetration in the nanogels with increasing surface fuzziness leading to improved dispersion of the particles, contrary to the depletion attraction induced between hard spheres by non-adsorbing polymers. However, beyond certain fuzziness, the polymers are excluded from the surface and the particles tend to ``self-bridge'' leading to aggregation. Miscibility of soft nanogels turns out to be a non-monotonic function of both particle softness and size. Increasing the matrix degree of polymerization tends to destabilize the system. In the non-dilute-particle limit, the many-body effects of the particles on the structure are studied and different qualitative trends are predicted depending on the particle softness. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A21.00005: Thiol-Functionalized Gold-Nanoscale Organic Hybrid Materials-Attractive to Soft glasses Akanksha Agrawal, Lynden Archer We report on the flow properties of self-suspended nanoparticles based on gold nanoparticles densely grafted with polyethylene glycol methyl ether thiol(PEG) chains. We studied the effect of temperature, olume fraction and polymer chain length on the transition from attractive glass to soft glassy flow behavior. Gold nanoparticles densely grafted with short PEG-thiol chains(MW 800,2kDa and 6kDa)are shown to form self-suspended systems over a range of polymer grafting densities and particle volume fractions,$\varphi $.Transmission electron and atomic force microscopy measurements reveal that the particles are uniformly dispersed. Oscillatory shear measurements performed on low $\varphi $ systems show a two-step yielding behavior reflecting bond breaking and cage breaking transitions at the nanoscale; both characteristics of soft glassy materials dominated by attractive forces. With increased temperature a transition to one-step yielding and subsequently back to two-step yielding is observed. At high $\varphi $ a single yielding transition and soft glassy flow behavior are observed. We employ SAXS, vibration spectroscopy, thermal analysis, and rheology to interrogate the configuration state of the tethered chains and particle-particle interactions in detail. [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A21.00006: A quick and simple route to form soft Janus colloids Chris Sosa, Rodney Priestley, Robert Prud'homme Janus colloids, i.e., particles with two chemically distinct compartments or ``faces,'' are of significant scientific interest as they could serve as the enabling material for self-organizing superstructures and functional nanodevices. The internally segregated structures present in Janus particles are not only beneficial for self-assembly applications, but are also attractive from a more fundamental scientific perspective for the insight they can provide on hybrid material interfaces. Here, we present a novel, one-step nano-precipitation process for the formation of soft Janus colloids composed of two compositionally distinct and surface-active polymer domains. In particular, this approach allows for the fabrication of Janus particles from both homopolymers and block co-polymers, generates phase-separated Janus structures on extremely fast timescales, and provides excellent scalability. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A21.00007: Phase behavior of star-shaped polystyrene-block-poly(methyl methacrylate) copolymer Sangshin Jang, Hong Chul Moon, Dusik Bae, Jongheon Kwak, Youngmin Lee, WonBo Lee, Jin Kon Kim Phase behavior of star-shaped 18-arm polystyrene-block-poly(methyl methacrylate) copolymers ((PS-b-PMMA)$_{18}$) with various volume fraction of PS block (f$_{PS}$) was investigated via transmission electron microscopy and small angle X-ray scattering. (PS-b-PMMA)$_{18}$ was synthesized by atom transfer radical polymerization from $\alpha$-cyclodextrin ($\alpha$-CD) having 18 functional groups for the initiation. We also prepared corresponding linear PS-b-PMMAs by cutting the ester groups connecting $\alpha$-CD and PS chains in (PS-b-PMMA)$_{18}$ through the hydrolysis. The microdomains of (PS-b-PMMA)$_{18}$ changed from body-centered cubic spheres, hexagonally packed cylinders, perforated lamellae, and lamellae with decreasing fPS from 0.7 to 0.2. Interestingly, (PS-b-PMMA)n with f$_{PS}$ of 0.23 showed highly asymmetric lamellar microdomains, while corresponding linear PS-b-PMMA with the same volume fraction exhibited spherical microdomains. Thus, the microdomains are highly affected by the molecular architecture of block copolymer. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A21.00008: Synthesis and characterization of A2B Miktoarm Star Copolymers Composed of Regioregular Poly(3-hexylthiophene) and Poly(methyl methacrylate) containing rigid core Jicheol Park, Hong Chul Moon, Jin Kon Kim The $\pi$-$\pi$ interaction between P3HT arms in Miktoarm star copolymer composed of P3HT and PMMA ((P3HT)2PMMA) was strong enough to arrange two P3HT backbone chains in (P3HT)$_2$PMMA to stack one by one along the nanofibril axis on thin film. This is because of very small $\pi$-$\pi$ stacking distance between P3HT backbones compared with the size of the core. Here, we report a facile synthesis of (P3HT)$_2$PMMA containing rigid core. First, we synthesized coupled P3HT having 1,3-diazidobenzylaldehyde at the center using click reaction between mono-ethynyl P3HT and 1,3-diazidobenzylaldehyde. The aldehyde at center in coupled P3HT was replaced by ethynyl group using Grignard reaction with ethynyl magnesiumbromide (P3HT-core-P3HT). Then, copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition click reaction between P3HT-core-P3HT and PMMA-N$_3$ was performed to synthesize (P3HT)$_2$PMMA. The optical property and self-assembly of (P3HT)$_2$PMMA was investigated. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A21.00009: Polyelectrolyte Microcapsules: Ion Distributions from a Poisson-Boltzmann Model Qiyun Tang, Alan R. Denton, Damith Rozairo, Andrew B. Croll Recent experiments have shown that polystyrene-polyacrylic-acid-polystyrene (PS-PAA-PS) triblock copolymers in a solvent mixture of water and toluene can self-assemble into spherical microcapsules. Suspended in water, the microcapsules have a toluene core surrounded by an elastomer triblock shell. The longer, hydrophilic PAA blocks remain near the outer surface of the shell, becoming charged through dissociation of OH functional groups in water, while the shorter, hydrophobic PS blocks form a networked (glass or gel) structure. Within a mean-field Poisson-Boltzmann theory, we model these polyelectrolyte microcapsules as spherical charged shells, assuming different dielectric constants inside and outside the capsule. By numerically solving the nonlinear Poisson-Boltzmann equation, we calculate the radial distribution of anions and cations and the osmotic pressure within the shell as a function of salt concentration. Our predictions, which can be tested by comparison with experiments, may guide the design of microcapsules for practical applications, such as drug delivery. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A21.00010: Synchrotron Radiation Investigation in Epoxy Resin Modified with Polysiloxane System Wenjun Gan, Weizhen Li, Jindian Ding, Xiaodan Gu, Cheng Wang Epoxy resins are one of the most important classes of thermosetting polymers. Epoxy resin modified with polysiloxane is expected that the siloxane moiety may exert its qualities of thermal stability, impact toughness and surface-modification properties. Our group tried to introduce polysiloxane into epoxy resin by blending diglycidyl-ether of bisphenol-A with epoxypropoxypropyl terminated polydimethyl-siloxane and polyetherimide-siloxane in different proportion. These polysiloxane modified epoxy resins have been investigated using a combination of small- and wide angle X-ray scatterings (SAXS and WAXS) and scanning transmission soft X-ray microscopy (STXM). Nano- to micro-scale domain size, distribution and chemical composition were observed with spatial and spectroscopic sensitivities offered by both hard and soft x-ray scattering/microscopy. In-situ SAXS experiments were performed to understand the mechanism of microphase separation and dynamics of nanostructure evolution. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A21.00011: Association of Multi-Chain Pentablock Ionomers in Solutions: A Molecular Dynamics Simulation Study Dipak Aryal, Dvora Perahia, Thusitha Etampawala, Gary Grest Ionic block copolymers in solutions are of interest due to their fascinating ability to self-assemble into a variety of ordered microscopic structures such as ionic domains and hydrocarbon domains. These polymers show unique properties such as chemical and mechanical stability that arise from incompatibility between individual blocks, proton conductivity, ion transportability, and hydrophilicity. Using molecular dynamics simulations we have studied the association of multi-chain pentablock copolymers (A-B-C-B-A) in a 1:1 mixture of cyclohexane and heptane (mutual solvent), and in water at 300K and 500K. The center block consists of randomly sulfonated polystyrene connected to a flexible poly (ethylene-r-propylene) bridge and end caped with poly (t-butyl styrene). We found that the pentablock in mutual solvent forms micelles in solutions with the sulfonated polystyrene in the core and chains of swollen flexible poly (ethylene-r-propylene) and poly (t-butyl styrene) in the corona. In water, the micelle remains quasi-spherical with the ionic groups located on the outer surface at both temperatures. These results are good agreement with those obtained from small angle neutron scattering (SANS). [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A21.00012: Structure and Conformation of Ionic Conjugated Polymers: Polydots Naresh Osti, Thusitha Etampawala, Sidath Wijesinghe, Dvora Perahia Conjugated polymers confining into nano dimension form long-lived highly luminescent tunable organic particles of having enormous potential for intracellular imaging and drug delivery. Even though the chains are not in their thermodynamically stable conformation, the poly-dots remain stable over long period of times. Incorporation of ionic groups into conjugated polymers introduces a configuration control factor that impacts their conformation and their applications as luminescent probes. The current work investigates the structure and stability of poly-dots of di-alkoxy para polyphenyleneethynylene (PPE) conjugated polymer substituted with carboxylate side chain. Our small angle neutron scattering (SANS) studies have shown that ionic PPE forms spherical poly-dots in water. Ionic Poly-dots remain stable up to a temperature of 800C compare to neutral conjugated polymer poly dots. These polymer dots were allowed to assemble at a solid surface and observed by AFM which showed the nano aggregates of different sizes that assembled in different ways depending on the concentration and molecular parameters of the ionic PPEs used. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A21.00013: Giant surfactants of poly(ethylene oxide)-$b$-polystyrene-(molecular nanoparticle): nanoparticle-driven self-assembly with sub-10-nm nanostructures in thin films Chih-Hao Hsu, Zhiwei Lin, Xue-Hui Dong, I-Fan Hsieh, Stephen Z.D. Cheng Giant surfactants are built upon precisely attaching shape- and volume-persistent molecular nanoparticles (MNP) to polymeric flexible tails. The unique class of self-assembling materials, giant surfactants, has been demonstrated to form self-assembled ordered nanostructures, and their self-assembly behaviors are remarkably sensitive to primary chemical structures. In this work, two sets of giant surfactants with functionalized MNP attached to diblock copolymer tails were studied in thin films. Carboxylic acid-functionalized [60]fullerene (AC$_{60})$ tethered with PEO-$b$-PS (PEO-PS-AC$_{60})$ represents an ABA' (hydrophilic-hydrophobic-hydrophilic) giant surfactant, and fluoro-functionalized polyhedral oligomeric silsesquioxane (FPOSS) tethered with PEO-$b$-PS (PEO-PS-FPOSS) represents an ABC (hydrophilic-hydrophobic-omniphobic) one. The dissimilar chemical natures of the MNPs result in different arrangement of MNPs in self-assembled structures, the dispersion of AC$_{60}$ in PEO domain and the single domain of FPOSS. Moreover, the chemically bonded MNPs could induce the originally disordered small molecular PEO-$b$-PS to form ordered cylindrical and lamellar structure, as evidenced by TEM and GISAXS, leading to sub-10-nm nanostructures of copolymer in the thin film state. [Preview Abstract] |
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