Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B21: Focus Session: Soft Nanoparticles, Block Copolymer Micelles and Polymersomes I |
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Sponsoring Units: DPOLY Chair: Thomas Epps III, University of Delaware Room: 406 |
Monday, March 3, 2014 11:15AM - 11:51AM |
B21.00001: Responsive Hydrogels and Ion Gels by Self-Assembly of ABA and ABC Triblock Polymers Invited Speaker: Timothy Lodge Gels -- polymeric networks swollen with a substantial amount of solvent -- represent a fascinating class of soft materials, with wide-ranging applications in fields as diverse as biomedicine, pharmaceutics, personal care products, foods, sensors, actuators, flexible electronics, oil recovery, and adhesives. Physical gels are held together by non-covalent interactions, which may be as specific as hydrogen bonds, or as general as solvophobic association of insoluble blocks. Among the attractive features of physical gels are reversibility, stimuli-responsiveness, and tunability of macroscopic properties. In this talk two classes of physical gels will be highlighted. In one, the ability of ABC block terpolymers to form novel structures will be demonstrated, where blocks A and C are mutually immiscible and solvophobic, while B is solvophilic. In particular, the formation of gels by sequential association (first A, then C) leads to a remarkably sharp gelation transition, at a relatively low polymer concentration, compared to analogous gels formed from ABA systems. In the second class, gels formed by self-assembly of a variety of ABA systems in ionic liquids will be described, and in particular how gelation can be controlled through factors such as block chemistry, temperature, choice of ionic liquid, and application of light. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B21.00002: Translocation of a vesicle through a single pore Hamidreza Shojaei, Murugappan Muthukumar When a single vesicle is squeezed through a pore, it suffers from an elastic barrier arising from bending and stretching elasticity of the vesicle. We will discuss the free energy landscape for the translocation of a vesicle through a uniform cylindrical pore in terms of the initial radius of the vesicle, the diameter and length of the pore, and the elastic properties of the vesicle. With the quasi-equilibrium assumption and the Fokker-Planck formalism, we will present theoretical results for the translocation kinetics for the vesicle across a pore. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B21.00003: Towards Deflated Polymersomes Changqian Yu, Steve Granick The mechanical properties of polymersomes made from block copolymers present interesting and useful differences from the conventional vesicles made from lipids. Their limited water permeability and high bending modulus promote spectacular shape transformation upon external stimuli. Here we describe a vivid example of dynamic evolution of polymersomes from spherical towards the deflated state, driven by extreme osmotic shock. [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B21.00004: Complex Morphology of Oppositely Charged Block Copolymer Micelles Misook Lee, Kyung Jee Min, Sheng Li, Kookheon Char The morphology of charged block copolymer micelle (BCM) complexes, consisting of polystyrene-\textit{block}-poly(acrylic acid) (PS-$b$-PAA) and polystyrene-\textit{block}-poly(4-vinyl pyridine) (PS-$b$-P4VP) micelles, was controlled by pH of aqueous solvent as well as solvent quality. To determine the effective pH range for the inter-corona combination of PAA and P4VP blocks in aqueous media, we studied the dissociation behavior of both coronas using Fourier Transform Infrared Spectroscopy. Lower pH region (4.0 \textless pH \textless 5.0) in aqueous medium offers stronger interactions between oppositely charged corona blocks, resulting in the formation of crystal-like complexes. Furthermore, the crystal habit of the micelle complex was found to be tunable by adjusting the relative size of the block copolymers and/or the pH of the aqueous medium. In the higher pH region (pH \textgreater 5.5), they first self-assembled into hierarchical bumpy spheres induced by the simple adsorption of small PS-$b$-PAA BCMs on the surfaces of PS-$b$-P4VP large compound micelles since the degree of ionization of P4VP blocks is relatively low. The final micelle morphology is highly dependent on the solvent quality. At low dimethylformamide (DMF) content, the internal structure of the BCM complex resembled spherical micelle. As the concentration of DMF increased, the internal PS-$b$-P4VP block copolymer structure transitioned from micelle-like to that resembled the morphology of the block copolymer in the bulk. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B21.00005: Stereoregularity Drives Precipitation in Polyelectrolyte Complex Formation Matthew Tirrell, Sarah Perry, Lorraine Leon, Matthew Kade, Dimitris Priftis, Katie Black, Kyle Hoffman, Jonathan Whitmer, Jian Qin, Juan de Pablo This study investigates the effect of stereoregularity on the formation of polypeptide-based complex formation and assembly into micelles, hydrogels and ordered phases. We demonstrate that fluid complex coacervate formation (rather than solid complex precipitation) between oppositely charged polypeptides requires at least one racemic partner in order to disrupt backbone hydrogen bonding networks and prevent the hydrophobic collapse of the polymers into compact, fibrillar secondary structures. Computer simulations bear this out and enable visualization of the molecular structure of the complexes. The ability to choose between conditions of fluid phase formation and solid phase formation is a useful tool in developing new self-assembled materials based on polyelectrolyte complex formation. [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B21.00006: Rapid and Quasi-reversible Poly(vinyl acetate-b-vinyl alcohol) Spherical Micelle Fusion Induced by Poly(ethylene oxide) in Water Mahesh Mahanthappa, Milton Repollet-Pedrosa Methods for triggering morphology changes in aqueous dispersions of amphiphilic block copolymers (ABCs) are crucial for their development as responsive fluids with properties that may be manipulated ``on demand.'' Numerous groups have reported methods for switching the morphologies of ABCs by the incorporation of thermal and photochemical switches, the addition of salts, and changes in pH. We report a new ABC system in which a dispersion of spherical micelles may be rapidly and quasi-reversibly transformed into a solution of worm-like micelles, upon the addition of a water-soluble homopolymer. More specifically, we demonstrate that the addition of varying amounts of poly(ethylene oxide) homopolymer to a dilute dispersion of poly(vinyl acetate-block-vinyl alcohol) spherical micelles results in either (1) their immediate precipitation, or (2) their rapid fusion into worm-like micelles. Dilution of the latter solution of worm-like micelles with pure water induces their reversion into spherical micelles. By evaluating the effects of PEO molecular weight and solution concentration on the micellar interconversion process, we propose two possible mechanisms for this unexpected morphological transformation. [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B21.00007: Comparing Fluid and Elastic Block Copolymer Shells Damith Rozairo, Andrew B. Croll Emulsions can be stabilized with the addition of an amphiphilic diblock copolymer, resulting in droplets surrounded and protected by a polymer monolayer. Such droplets show considerable promise as advanced cargo carriers in pharmaceuticals or cosmetics due to their strength and responsiveness. Diblock copolymer interfaces remain mostly fluid and may not be able to attain the mechanical performance desired by industry. To strengthen block copolymer emulsion droplets we have developed a novel method for creating thin elastic shells using polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS). Characterization of the fluid filled elastic shells is difficult with traditional means which lead us to develop a new and general method of mechanical measurement. Specifically, we use laser scanning confocal microscopy to achieve a high resolution measure of the deformation of soft spheres under the influence of gravity. To prove the resilience of the technique we examine both a polystyrene-b-poly(ethylene oxide) (PS-PEO) stabilized emulsion and the PS-PAA-PS emulsion. The mechanical measurement allows the physics of the polymer at the interface to be examined, which will ultimately lead to the rational development of these technologies. [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B21.00008: Polyoxometalate (POM) Macroion Decorated Polymersomes Benxin Jing, Erin Connor, Y. Elaine Zhu Polymersomes as one of the common self-assembled forms of amphiphilic block copolymers have been widely developed for applications from drug delivery to mirco/nanoreactors. The tunability of their materials properties, such as mechanical strength and permeability often relies on the chemistry of the selected polymer in a liquid medium. We have recently employed the emergent polyoxometalate (POM) nanoclusters as macroions to control their interaction and assembly with different polymersomes. For both neutral and cationic polymersomes decorated with highly charged anionic POM nanoclusters, the dispersion stability and mechanic strength can be significantly enhanced. AFM and TEM characterization further confirms the encapsulation of POM macroions into polymersomes to form inorganic-organic hybrid complexes, which lead to new potential applications in anticancer and antibacterial medicines and catalysts. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B21.00009: Tartaric Acid-Assisted Self-Assembly of Hybrid Block Copolymer Composites Li Yao, Ying Lin, James Watkins Enantiopure tartaric acid was used as an additive to increase the segregation strength of poly(ethylene oxide-block-tert-butyl acrylate) (PEO-b-PtBA) copolymers through strong, selective interactions with one of the polymer chain segments. Addition of tartaric acid to PEO-b-PtBA exhibiting cylindrical morphologies resulted in the formation of helical superstructures as observed by transmission electron microscopy. It was also found that this small acid additive can also enable phase-selective ultra-high loading of nanoparticles (NPs) into target domains of the block copolymer composites. The loading of tartaric acid can increase enthalpically favorable interactions between the nanoparticle ligands and the host domain and mitigate entropic penalties associated with NP incorporation into the target domain. A metal content of over 40 weight percent by mass of the resulting well ordered composites was achieved as measured by thermal gravimetric analysis in PEO-b-PtBA/tartaric acid/4-hydroxythiophenol functionalized Au NP hybrid system. [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B21.00010: Self-assembled Structures of a Multifunctional, Structured Block Copolymer in Solution; A SANS Study Thusitha Etampawala, Manjula Senanayake, Naresh Osti, Lilin He, William Heller, Dvora Perahia The self-assembly of multi block copolymer in solutions is controlled by a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interactions of the individual blocks with the solvent. We investigated the association of ABCBA penta-block copolymers, in solution using Small angle neutron scattering (SANS). The ABCBA penta-block comprises of centered randomly sulfonated polystyrene block to which rubbery polyisoprene is connected, terminated by blocks of polystyrene decorated with tertiary butyl group, kindly provided by Kraton LLC. The SANS studies have shown that the penta-block forms ellipsoidal core-shell structures with the sulfonated polystyrene in the core and Gaussian decaying chains of swollen polyisoprene and tertiary butyl polystyrene in the corona. The size of the micelle, the thickness of the corona and the aggregation number increased with increasing the solution concentration and temperature, while the solvent fraction in the core decreased. The dilute solutions promptly responded to thermal fluctuations. However, the temperature effects disappeared with increasing the solution concentration. [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B21.00011: Multigeometry Nanoparticle Engineering via Kinetic Control through Multistep assembly Yingchao Chen, Xiaojun Wang, Ke Zhang, Fuwu Zhang, Jimmy Mays, Karen Wooley, Darrin Pochan Organization of block copolymers into complicated multicompartment (MCM) and multigeometry (MGM) nanostructures is of increasing interest. Multistep, co-assembly methods resulting in kinetic control processing was used to produce complex nanoparticles that are not obtained via other assembly methods. Vesicle-cylinder, separate vesicle and cylinder, disk-cylinder, and mixed vesicle nanoparticles were constructed by binary blends of distinct diblock copolymers. Initially, the vesicle former polyacrylic acid-polyisoprene and cylinder former polyacrylic acid-polystyrene which share the same hydrophilic domain but immiscible hydrophobic domain were blended in THF. Secondly, dimaine molecules are added to associate with the common hydrophilic PAA. Importantly, and lastly, by tuning the kinetic addition rate of selective, miscible solvent water, the unlike hydrophobic blocks are kinetically trapped into one particle and eventually nanophase separate to form multiple compartments and multigeometries. The effective bottom-up multistep assembly strategies can be applied in other binary/ternary blends, in which new vesicle-sphere, disk-disk and cylinder-cylinder MCM/MGM nanoparticles were programed. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B21.00012: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 2:03PM - 2:15PM |
B21.00013: On the Effect of TiO2 Nanoparticles on the Crystallization of PEO Jesus Eduardo Saldana, Alin Cristian Chipara, Alejandro Castillo, James Hinthorne, Elamin Ibrahim, Mircea Chipara Nanocomposite consisting of various amounts of TiO2 nanoparticles dispersed within polyethylene oxide (PEO) have been prepared by melt mixing. The thermal properties of these nanocomposites have been investigated by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). TGA data revealed a weak increase of the thermal stability of the PEO matrix upon the loading with nanoparticles. The crystalline structure of PEO and TiO2 has been confirmed by Wide Angle X-Ray Scattering and electron microscopy. Isothermal and non isothermal DSC was used to investigate the melting/crystallization process. Additional information regarding the nanofiller has been obtained via Raman and FTIR spectroscopy. The shift of the melting and crystallization temperature due to the loading with TiO2 nanoparticles is analyzed. [Preview Abstract] |
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