Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D43: Focus Session: Self Assembled Block Copolymers and Soft Nanoparticles in Solution I |
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Sponsoring Units: DPOLY Chair: Sangwoo Lee, Rensselaer Polytechnic Institute Room: 214C |
Monday, March 2, 2015 2:30PM - 2:42PM |
D43.00001: Exotic nanoparticles with block copolymer design and solution construction with kinetic contro Darrin Pochan Kinetic pathways and temporal stabilities of different micelles and nanoscale aggregates have been used to construct exotic nanoparticles in solution. Due to low chain exchange dynamics between block copolymeric micelles and solvent, global thermodynamic equilibrium is extremely difficult, if not impossible, to achieve in block copolymer assembly. However, by taking advantage of this slow kinetic behavior of polymeric micelles in solution, one can purposely produce multicompartment nanoparticles and mulitgeometry nanoparticles by forcing different block copolymers to reside in the same nanoscale structure through kinetic processing. While kinetically trapped in common nanostructures, local phase separation can occur producing compartments. This compartmentalization can be used within common micelle geometries to make complex spheres and cylinders or can be used to make new nanostructures such as multigeometry aggregates (e.g. hybrid cylinder-sphere aggregates, disk-cylinder nanoparticles). Furthermore, new interparticle nanomaterials can be created with hierarchical solution construction methods. [Preview Abstract] |
Monday, March 2, 2015 2:42PM - 2:54PM |
D43.00002: Corona contraction and polyelectrolyte complexation of polybasic micelles in buffered aqueous solution Jennifer Laaser, Yaming Jiang, Theresa Reineke, Timothy Lodge We investigate the pH- and ionic strength-induced contraction of polycationic micelles with a polystyrene core and poly(dimethylaminoethyl methacrylate) corona in buffered aqueous solutions, and report on complexation of these micelles with poly(styrene sulfonate) under varying ionic strength conditions. We find that in monoprotic buffers, the micelle corona behaves as a salted osmotic brush, as has been observed for other block polyelectrolyte micelle systems in unbuffered solutions. In polyprotic buffers, however, we find that concentration of the charged buffer species in the micelle corona shifts the buffer dissociation equilibrium farther toward multivalent species than in the bulk, resulting in an anomalously high degree of corona contraction. In our complexation experiments, we observe multimodal size distributions that evolve on timescales of days to weeks at physiologically relevant ionic strengths, which may have implications for the design of gene- and drug-delivery vehicles using these types of interpolyelectrolyte complexes. [Preview Abstract] |
Monday, March 2, 2015 2:54PM - 3:06PM |
D43.00003: Predicting the Solution Morphology of a Sulfonated Block Copolymer in Binary Solvent Mixtures Philip Griffin, Grace Salmon, Jamie Ford, Karen Winey The physicochemical properties of solvent-casted block copolymer films are highly dependent on the microscopic morphology of the solutions from which they are cast. In order to achieve macroscopically homogenous polymer solutions, binary or higher-degree solvent mixtures are often required, which introduces additional complexity in understanding the molecular level interactions that control block copolymer self-assembly in solution. Using small angle x-ray scattering, we have explored the solution morphology in ternary blends of a sulfonated pentablock copolymer in select binary solvent mixtures over a range of solvent compositions and polymer concentrations. We have found that the solution morphologies in these ternary blends depend strongly on the composition of the solvent mixture. Furthermore, we demonstrate that the solvent-composition-dependent morphologies can be accurately predicted by quantifying the polymer/solvent interactions using Hansen solubility parameters. These studies are an important step toward developing a complete and predictive understanding of the solution morphology of complex polymer/solvent mixtures. [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:18PM |
D43.00004: Structure of block copolymer micelles in the presence of co-solvents Megan Robertson, Shu Wang, Kim Mai Le, Rachele Piemonte, Louis Madsen Amphiphilic block copolymer micelles in water are under broad exploration for drug delivery applications due to their high loading capacity and targeted drug delivery. We aim to understand the kinetic and thermodynamic processes that underlie the self-assembly of diblock copolymer micelle systems. The present work focuses on diblock copolymers containing poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic polymer), which spontaneously self-assemble into spherical micelles in water. Addition of a common good solvent (a co-solvent) for both of the constituting blocks, such as tetrahydrofuran (THF), reduces the interfacial tension at the core-corona interface. We are currently investigating the effect of this phenomenon on the micelle structural properties, using scattering experiments and nuclear magnetic resonance. We have characterized the hydrodynamic radius, core radius, corona thickness, aggregation number, degree of swelling of the micelle core with the co-solvent, and unimer (free chain) concentration, as a function of the co-solvent concentration. Fundamental knowledge from these studies will inform design of drug delivery systems by allowing us to tailor micelle properties for optimal cargo loading. [Preview Abstract] |
Monday, March 2, 2015 3:18PM - 3:30PM |
D43.00005: Solvents effect on the structure of pentablock ionic polymers: A SANS study Manjula Senenayake, Thusitha Etampawala, Sidath Wijesinghe, Naresh Osti, Lilin He, Dvora Perahia Solution structure of ionic co-polymers is critical to their processing. The difference of the interactions between blocks with the solvent results in a rich phase diagram. Here, solutions of ABCBA symmetric ionic pentablock copolymer consisting of t-butyl polystyrene end blocks, hydrogenated isoprene inner blocks and randomly and selectively sulfoanted polystyrene as middle block, was studied by small angle neutron scattering (SANS). Specifically the impact of adding 1-propanol, a polar solvent to a cyclohexane-heptane solution was investigated. This polar solvent is associating ionizable block and it's expected to modify the packing of the polymer. Our results shows upon addition of 1-propanol, the spherical micelles transfer into worm like object. This transformation requires the break up of the ionic clusters formed by this polymer. These changes are in line with rheology measurements of Dr. Robert Weiss who has shown that propanol unlocks ionic clusters in polystyrene sulfonate. [Preview Abstract] |
Monday, March 2, 2015 3:30PM - 3:42PM |
D43.00006: Reversible, All-Aqueous Assembly of Hydrogen-Bonded Polymersomes Yuhao Wang, Svetlana Sukhishvili We report on sub-micron-sized polymersomes formed through single-step, all-aqueous assembly of hydrogen-bonded amphiphilic polymers. The hollow morphology of these assemblies was revealed by transmission electron microscopy (TEM), cryogenic scanning electron microscopy (cryo-SEM) and confocal laser scanning microscopy (CLSM). Stable in acidic media, these polymersomes could be dissolved by exposure to basic pH values. Importantly, the diameter of assembled hollow structures could be controlled in a wide range from 30 nm to 1 $\mu $m by the molecular weight of hydrogen-bonding polymers. We will discuss key quantitative aspects of these assemblies, including kinetics of hollow structure formation, time evolution of polymersome size, and the role of polymer molecular weight on membrane thickness and bending rigidity. We believe that our approach demonstrates an efficient and versatile way to rationally design nanocontainers for drug delivery, catalysis and personal care applications. [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 4:18PM |
D43.00007: Aqueous Self-Assembly of Non-Ionic Bottlebrush Block Copolymer Surfactants with Tunable Molecular Shapes Invited Speaker: Javid Rzayev Polymer amphiphiles provide a robust and versatile platform for the fabrication of nanostructured soft matter. In this research, we explore a new class of polymer surfactants based on comb-like bottlebrush architecture as highly tunable molecular building blocks for aqueous self-assembly. Excluded volume interactions between densely grafted polymer side chains in the bottlebrush architecture are alleviated by backbone stretching, which leads to the formation of shape-persistent cylindrical macromolecules whose molecular dimensions can be precisely tailored during chemical synthesis. Amphiphilic bottlebrush block copolymers containing hydrophobic polylactide (PLA) and hydrophilic poly(oligoethylene oxide methacrylate) (PEO) side chains of various lengths were synthesized by a combination of controlled radical and ring-opening polymerizations. In dilute aqueous solutions, bottlebrush surfactants rapidly assembled into spherical, cylindrical and bilayer aggregates, as visualized by cryogenic transmission electron microscopy (cryo-TEM). Depending on the compositional side chain asymmetry, the formation of spherical micelles with different sizes and dispersities was observed. The molecular shape-dependent assembly was analyzed with help of a packing parameter ($p)$ computed from the molecular composition data akin to small molecule surfactants, with most uniform spherical aggregates observed for bottlebrush amphiphiles with $p$ close to 0.3. The formation of highly uniform micelles and the presence of a rich morphological diagram with relatively narrow compositional windows were attributed to the lack of conformational freedom in bottlebrush surfactants. Similarly, the unusual formation of cylindrical micelles with long aspect ratios for such high molecular weight amphiphiles was attributed to their inability to stabilize morphological defects, such as Y-junctions, with large deviations from mean curvature. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:30PM |
D43.00008: Phase Transfer of Polystyrene-$b$-poly(ethylene oxide) Polymersomes from a Hydrophobic Ionic Liquid to Water Soonyong So, Timothy Lodge The phase transfer of molecules and supramolecular assemblies from one phase to the other in a biphasic system is desirable for various applications such as catalysis, separation, and delivery. Herein, we describe the phase transfer of polystyrene-$b$-poly(ethylene oxide) (PS-PEO) polymersomes from a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), into water. The phase transfer behavior of PS-PEO polymersomes was studied systematically by varying the molecular weight of PS and the PEO volume fraction of the PS-PEO. We demonstrate a general boundary for the phase transfer in terms of a reduced tethering density for PEO, which is independent of the molecular weight of the hydrophobic PS. The tethering density can be increased by increasing the block length of PEO and the size of the polymersomes, and the increased tethering density induces the phase transfer. This phase transfer were also analyzed thermodynamically with the free energy difference of the polymersomes in [EMIM][TFSI] and water. Higher grafting density can reduce the interfacial tension between PS and water, and leads the polymersomes to transfer from [EMIM][TFSI] to water at room temperature. [Preview Abstract] |
Monday, March 2, 2015 4:30PM - 4:42PM |
D43.00009: Micellizationa and Gelation of Water Soluable Thermo-and Light-sensitive Block Copolymer Investigated by SANS Lilin He, Bin Hu, Bin Zhao Here we present an extensive small-angle neutron scattering (SANS) characterization of micellization and gelation of PEO-b-P(TEGEA-co-NBA) in deuterated water in a wide range of temperatures and concentrations before and after the removal of o-nitrobenzyl group by UV irradiation. Scattering data analysis indicated that unimers predominated in the solutions at low temperatures and concentrations. The polymer self-assembled into micelles with the P(TEGEA-co-NBA) block packed into the core and PEO forming the corona layer. A core-shell model was used to fit SANS data and obtain sizes and scattering length densities. Structural parameters such as the aggregation numbers, the radius of gyration of the chains in the shell region, the number of water molecules in the both regions were determined. The structural information combined with the rheological data were used to describe the phase behaviors of the diblock copolymer in aqueous solution. [Preview Abstract] |
Monday, March 2, 2015 4:42PM - 4:54PM |
D43.00010: Writing with vesicles Chi Hang Boyce Tsang, Yongfeng Zhou, Steve Granick Ultra-stretchable vesicles on micrometer scale are prepared in dimethyl sulfoxide (DMSO) via hydration with ABC star triblock copolymeric amphiphiles. We selected poly(ethylene glycol) as the hydrophilic block, and polystyrene and poly-azobenzene as hydrophobic blocks. The resultant vesicle deforms in response to blue light (488 nm) illumination and thus can be manipulated by a laser. A rich spectrum of morphology was demonstrated through control of laser scanning, polarization and incident power. Such deformation can also be reversed by UV light (405 nm) illumination. [Preview Abstract] |
Monday, March 2, 2015 4:54PM - 5:06PM |
D43.00011: ABSTRACT WITHDRAWN |
(Author Not Attending)
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D43.00012: Characterization of Block Copolymer Self-Assembly: From Solution to Nanoporous Membranes Yachin Cohen, Liat Oss-Ronen, Yeshayahu Talmon, Judith Schmidt, Aurel Radulescu, Volker Abetz Nanoporous membranes, exhibiting a dense assembly of pores with a narrow size distribution, are fabricated by self-assembly of block copolymers in solution. In particular, a scalable solution casting process reported recently, provides a ``one-step'' method to prepare such isoporous membranes by casting a block copolymer solution. We study the state of micellization in the initial casting solution and its transformation by addition of water, in order to elucidate the formation mechanism of the dense isoporous structure, using a combination of cryogenic-temperature electron microscopy and small-angle neutron scattering. Contrast variation is employed to matching each respective block. We show that the starting point for membrane formation is a micellar solution with the hydrophilic minor blocks within the micelle core. As water is introduced, this structure is preserved in a system which is far from equilibrium, as the hydrophobic majority blocks densify outside the more hydrophilic micelle cores. This non-equilibrium structure is the progenitor of the cylindrical pores, formed as water continues to enter the system. [Preview Abstract] |
Monday, March 2, 2015 5:18PM - 5:30PM |
D43.00013: 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] |
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