Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L42: Dillon Medal Symposium |
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Sponsoring Units: DPOLY Chair: Spiros Anastasiadis, IESL- FORTH Room: A302/303 |
Tuesday, March 22, 2011 2:30PM - 3:06PM |
L42.00001: John H. Dillon Medal Talk: Protein Fibrils, Polymer Physics: Encounter at the Nanoscale Invited Speaker: Aggregation of proteins is central to many aspects of daily life, ranging from blood coagulation, to eye cataract formation disease, food processing, or neurodegenerative infections. In particular, the physical mechanisms responsible for amyloidosis, the irreversible fibril formation of various proteins implicated in protein misfolding disorders such as Alzheimer, Creutzfeldt-Jakob or Huntington's diseases, have not yet been fully elucidated. In this talk I will discuss how polymer physics and colloidal science concepts can be used to reveal very useful information on the formation, structure and properties of amyloid protein fibrils. I will discuss their physical properties at various length scales, from their collective liquid crystalline behavior in solution to their structural features at the single molecule length scale and show how polymer science notions can shed a new light on these interesting systems. 1) ``Understanding amyloid aggregation by statistical analysis of atomic force microscopy images'' J. Adamcik, J.-M. Jung, J. Flakowski, P. De Los Rios, G. Dietler and R. Mezzenga, Nature nanotechnology, 5, 423 (2010) [Preview Abstract] |
Tuesday, March 22, 2011 3:06PM - 3:18PM |
L42.00002: Interdiffusion in bilayers of PCBM fullerene and poly(3-hexyl thiophene) P3HT Edward J. Kramer, Neal D. Treat, Michael A. Brady, Michael F. Toney, Michael L. Chabinyc, Craig J. Hawker Bulk heterojunction (BHJ) photovoltaic materials, typified by blends of PCBM and P3HT, are often regarded as immiscible in the absence of casting solvent. We use dynamic secondary ion mass spectrometry and grazing incidence wide angle X-ray scattering to probe the interdiffusion of bilayers of P3HT and deuterated dPCBM. We find that the as cast P3HT film is semicrystalline, while the dPCBM film is amorphous, and that there is complete interdiffusion between dPCBM and P3HT after annealing for 300 s at T = 150$^{\circ}$C, a typical treatment to improve device efficiency. This interdiffusion occurs without disrupting the ordered lamellar stacking in the P3HT crystallites, showing that PCBM is miscible with amorphous P3HT at this temperature (the size and/or perfection of the P3HT crystallites actually increases during the annealing). At T $<$ 150$^{\circ}$C rapid diffusion of dPCBM into P3HT still occurs but the dPCBM concentration reaches an apparent solubility limit after long anneals, a limit that decreases with decreasing temperature. This result suggests that dPCBM will phase separate from amorphous P3HT in the BHJ on cooling from 150$^{\circ}$C to room temperature. [Preview Abstract] |
Tuesday, March 22, 2011 3:18PM - 3:30PM |
L42.00003: Geroges Hadziioannou |
Tuesday, March 22, 2011 3:30PM - 3:42PM |
L42.00004: Coarse grained polystyrene simulations: Static and dynamic properties Kurt Kremer By combining input from short simulation runs of rather small systems with all atomistic details together with properly adapted coarse grained models we are able quantitatively predict static and especially dynamical properties of both pure polymer melts of long entangled chains but also of systems with low molecular weight additives. Comparisons to rather different experiments such as diffusion constant measurements, NMR relaxation experiments and dielectric spectroscopy show a remarkable quantitative agreement without any adjustable parameter. The model is also able to distinguish different tacticities and to study the consequences for static and dynamic properties. Reintroduction of chemical details into the coarse grained trajectories allows the study of long time trajectories in all atomistic detail providing the opportunity for rather different means of data analysis. [Preview Abstract] |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L42.00005: Effects of Side Chains on the Self-Assembly and Photovoltaic Properties of Conjugated Polymer Semiconductors Samson Jenekhe Conjugated polymer semiconductors are of growing interest in electronics and optoelectronics. Although it is now well established that the electronic band structure, charge transport, and electronic properties of conjugated polymers can be varied over a wide range through manipulation of the molecular backbone structure, little is known about the effects of alkyl side chains on the solid state morphology and properties of these materials. We have investigated homologous series of conjugated homopolymers, block copolymers, and random copolymers with controlled variation of their alkyl sides towards understanding the effects the size and typology of the side chains on self-assembly, morphology, and photovoltaic properties. We found that diblock copoly(3-alkylthiophenes) exhibit highly crystalline and phase-separated nanostructures in blend films with fullerene derivatives, resulting in superior photovoltaic properties compared to the corresponding homopolymers. The solid state morphology and photovoltaic efficiency of a series of donor-acceptor copolymer semiconductors that have the same optical band gap but different alkyl side chains were found to vary dramatically. Self-assembled block copolymer nanowires with widths of 10-30 nm and aspect ratios of up to 900 have been found to be promising building blocks for constructing efficient bulk heterojunction solar cells. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L42.00006: Nacre-Mimetic Composites via Single-Step Self-Assemblies of Polymer-Coated Colloids Olli Ikkala We demonstrate a scalable single-step self-assembly of polymer-modified plate-like colloidal platelets for nacre-mimetic materials, which overcomes the problem of sequential deposition to prepare hard and soft nacre-mimetic assemblies, which is inherently slow and not scalable. The materials have low density and show good mechanical properties, i.e., modulus of 45 GPa and strength 250 MPa, i.e. partly surpassing those of nacre (Walther et al, Nano Letters 2010, Angew Chem 2010). We expect that the concepts open a route for biomimetic materials from the lab to technology. [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L42.00007: On the Crystallinity and Chain Conformation in PEO / Layered Silicate Nanocomposites Spiros H. Anastasiadis, K. Chrissopoulou, S. Bollas, K. Andrikopoulos, S. Fotiadou, D. Christofilos, G.A. Voyiatzis The structure of nanohybrid materials as well as the chain conformation under confinement is investigated in hydrophilic polymer / layered silicate nanocomposites. A series of PEO / sodium montmorilonite hybrids was synthesized utilizing melt intercalation with compositions covering the whole range from pure polymer to pure clay. Intercalated nanocomposites with mono- and bi-layers of PEO chains are obtained in all cases. The intercalated chains as well as the ones adsorbed on the outer surface of the clay particles remain purely amorphous; nevertheless, their conformations exhibit different characteristics from those of the amorphous bulk material with the intercalated PEO chains adopting preferably gauche conformations. It is only for compositions where a large amount of excess polymer exists outside the completely full galleries that the polymer crystallinity is recovered. Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU. [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:30PM |
L42.00008: Formation and application of functional coatings on synthetic fibers Kiran Goli, Ali Ozcam, Kristen Roskov, Richard Spontak, Orlando Rojas, Jan Genzer We present two simple methods for modifying synthetic fibers made of polypropylene (PP) and poly(ethylene terephthalate) (PET). Specifically, we alter the inert PP fiber mats by physisorbing denatured proteins, and cross-linking the protein layers using glutaraldehyde. The amino- and hydroxyl-functionalities present in the protein coatings serve as attachment points for polymerization initiators. In addition, PET fibers are modified chemically by amidation with 3-aminopropyltriethoxysilane (APTES), followed by hydrolysis, which yields silanol groups that permit surface attachment of the initiator molecules. ``Grafting from'' polymerization from such modified PP and PET surfaces is employed following the atom transfer radical polymerization protocol to form functional and responsive polymer coatings. These include arrays of poly(2-hydroxyethyl methacrylate) (PHEMA) as well as chemically-modified PHEMA layers. Selected applications of these functional fibers will be outlined briefly, including, capture of metals or other contaminants from waters, prevention of protein adsorption, and attachment of metallic nanoparticles. [Preview Abstract] |
Tuesday, March 22, 2011 4:30PM - 4:42PM |
L42.00009: Peptide assembly for nanoscale control of materials Darrin Pochan Self-assembly of molecules is an attractive materials construction strategy due to its simplicity in application. By considering peptidic, charged synthetic molecules in the bottom-up materials self-assembly design process, one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, and electrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, to define hierarchical material structure and consequent properties. Design strategies for materials self-assembly based on small (less than 24 amino acids) beta-hairpin peptides will be discussed. Self-assembly of the peptides is predicated on an intramolecular folding event caused by desired solution properties. Importantly, kinetics of self-assembly can be tuned in order to control gelation time. The final gel behaves as a shear thinning, but immediately rehealing, solid that is potentially useful for cell injection therapies. The morphological, and viscoelastic properties of these peptide hydrogels will be discussed. In addition, slight changes in peptide primary sequence can have drastic effects on the self-assembled morphology. Additional sequences will be discussed that do not form hydrogels but rather form nanoscale templates for inorganic material assembly. [Preview Abstract] |
Tuesday, March 22, 2011 4:42PM - 4:54PM |
L42.00010: Food Materials - a natural playground for soft matter physics Adam Burbidge Traditional food science has its origins in chemistry, and has therefore tended to focus on trying to link molecular formulation and functional performance. Nevertheless, foods are almost always complex hierarchically structured materials of biological origin, far from thermodynamic equilibrium. These kinds of systems provide a challenge of relating structure to function, which is a natural playground for many ideas and concepts of soft matter physics. In this talk I will briefly outline the incredibly rich structural complexity of food products and highlight some areas which are appear to be amenable to physically based reasoning. Despite some notable contributions, food materials physics is a field very much in it's infancy, and I will highlight some outstanding (in both senses of the word) problems! [Preview Abstract] |
Tuesday, March 22, 2011 4:54PM - 5:06PM |
L42.00011: Assembly of conjugated-polymer-based nanostructures driven by solution-state crystallization Ryan Hayward, Felicia Bokel, Eunji Lee, Brent Hammer, P.K. Sudeep, Emily Pentzer, Todd Emrick Conjugated polymers such as regioregular poly(3-alkyl thiophenes), are well known to crystallize into extended one-dimensional nanowires or fibrils. This behavior is not only important for the efficiency of charge transport in device layers, but can also provide a driving force to assemble different optoelectronic components into well- defined nanostructures. We have investigated the assembly of two systems that rely on solution-state crystallization of poly(3-hexyl thiophene) (P3HT). In the first case, co- crystallization of freely dissolved and particle-bound P3HT provides hybrid fibrils of polymers flanked with n-type inorganic nanoparticles. In the second case, crystallization of P3HT-poly(3-triethylene glycol thiophene) diblock copolymers yields fibrils that can form supramolecular helical assemblies in the presence of salt. We seek to elucidate the mechanisms of self-assembly and the optoelectronic properties of the resulting nanostructures. [Preview Abstract] |
Tuesday, March 22, 2011 5:06PM - 5:18PM |
L42.00012: Temperature responsive hydrogel nanofibers and nanoparticles Janne Ruokolainen Poly(N-isopropylacrylamide) (PNIPAM) is one of the most extensively investigated synthetic temperature-responsive polymers. In this work temperature-responsive PNIPAM based triblock copolymer hydrogels, their self-assembly and phase behavior in bulk, are described. Additionally, recent results from responsive hydrogel nanofibers and hydrogel nanoparticles are shown. It is known that block copolymers form well-organized nano structures in bulk or thin films when annealed thermally or in solvent vapours. However, in the case of nanofibers or nanoparticles, the annealing leads in most cases to aggregation and particle sintering. This work utilizes aerosol-based gas phase method where the preparation and annealing of hydrogel nanoparticles with well-organized, hierarchical inner structures are performed without any particle coagulation or sintering. In the method, the block copolymers assemble within aerosol nanoparticles to form, for instance, lamellar onion-like or gyroid inner structures. [Preview Abstract] |
Tuesday, March 22, 2011 5:18PM - 5:30PM |
L42.00013: Orientation and Order in High-Efficiency Polymer Solar Cell Active Layers M.R. Hammond, R.J. Kline, L.J. Richter, C.L. Soles, D.M. DeLongchamp, T. Xu, L. Yu, M.F. Toney Using a combination of scattering and spectroscopy techniques, we have characterized molecular orientation and order in bulk heterojunction (BHJ) organic photovoltaic cells based upon thieno[3,4-\emph{b}]thiophene-\emph{alt}-benzodithiophene copolymers (PTB) and fullerene derivatives. The various techniques probe complimentary aspects of the full distribution of (e.g.) polymer chain orientations, so analysis of the data in tandem allows us to evaluate the relative likelihood of several model distributions. Specifically, X-ray diffraction data yielded a full orientation distribution for the polymer pi-stacking direction within well-ordered regions, with the nominal result of a strong preference for pi-stacking in the vertical direction. This structural characteristic may enhance vertical charge mobility and thus be one factor leading to the outstanding performance of PTB based devices. However, the most plausible model distribution would suggest that those ordered (diffracting) regions of the PTB BHJ films comprise only a small percentage of the total polymer volume within the film. [Preview Abstract] |
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