Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V19: Focus Session: Hierarchically Ordered Systems |
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Sponsoring Units: DPOLY Chair: Albertu Striolo, University of Oklahoma Room: 320 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V19.00001: Semi-crystalline PMMA Stereocomplex Fibers Matija Crne, Shin-Woong Kang, Jung Ok Park, Satyendra Kumar, Mohan Srinivasarao A mixture of isotactic and syndiotactic PMMA polymers forms a supramolecular helical structure, called ``stereocomplex'' PMMA, which is held together by non-covalent bonding. The helices can pack together, resulting in a semi-crystalline material with a melting point of 172$^{o}$C. Furthermore, the solutions exhibit gelation behavior in appropriate solvents. We have utilized these properties to make oriented stereocomplex PMMA fibers by three different methods -- wet spinning, gel spinning and electrospinning. These fibers are highly oriented and crystalline. They are resistant to high temperatures up to 160$^{\circ}$C. They are also resistant to the PMMA polymerization conditions. We have examined the fibers using X-ray diffraction and Raman spectroscopy. The results agree with the recently proposed triple helical structure where two isotactic PMMA chains wrap around each other in a double helix and then the syndiotactic chain wraps around this double helix. The resulting structure is a triple helix with a 1:2 molar ratio of isotactic : syndiotactic PMMA. [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V19.00002: Hierarchically Organized Peptide Core-Silica Shell Hybrids Aysegul Altunbas, Nikhil Sharma, Darrin J. Pochan A biomimetic approach was applied for the fabrication of a 3D hybrid network that displays hierarchical organization of an inorganic layer around an organic self-assembled peptide fibril template. The 20 amino acid peptide used in this study consisted of alternating hydrophilic (lysine) and hydrophobic (valine) residues flanking a four amino acid turn sequence in the center. After intramolecular folding into a beta-hairpin conformation on addition of a desired solution stimulus, this peptide self-assembles into a 3D network of entangled fibrils rich in beta-sheet with a high density of lysine groups exposed on the fibril-surfaces. The lysine-rich surface chemistry was utilized to create a silica shell around the fibrils. The mineralization process of the fibrils was initiated under physiological conditions by adding the silica precursor, tetramethyl orthosilicate, to the pre-assembled hydrogel, which results in a porous silica network that retains the mesoscale structure of the peptide fibril network. Structural characterization via Transmission Electron Microscopy, cryogenic-Scanning Electron Microscopy, Small Angle Neutron and X-ray Scattering and mechanical characterization via oscillatory rheology will be presented. [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V19.00003: Hierarchically Structured Regioregular Conjugated Polymer via Evaporative Self-Assembly Myunghwan Byun, Robyn Laskowski, Feng Qiu, Malika Jeffries-EL, Zhiqun Lin Regioregular conjugated polymers, poly (3-hexylthiophene) (P3HT) toluene solution was confined in a sphere-on-flat geometry. The geometrically constrained P3HT solution led to the formation an axially symmetric liquid capillary bridge, from which the consecutive ``stick-slip'' motion of the contact line of the solution due to the solvent evaporation was effectively regulated. As a result, hierarchical ``snake-skin'' like structures of high regularity were yielded, namely, the microscopic structures were composed of P3HT nanofibers. This facile, \textit{one-step} technique based on evaporative self-assembly opens up a new avenue for organizing semicrystalline conjugated polymers into two-dimensional patterns in a cost-effective and nondestructive manner [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 9:12AM |
V19.00004: Combining Small Molecule with Block Copolymer: a Facile Approach to Direct Hierarchical Assembly of Nanoparticles Invited Speaker: Precise control over the spatial organization of nanoscopic building blocks over multiple length scales is a bottleneck in the ``bottom-up'' approach to generate technologically important materials. We demonstrate a new paradigm to control the hierarchical assembly of nanoparticles through the synergistic co-assembly of block copolymers (BCP), small molecules and readily available nanoparticles. Organizations of nanoparticles into one, two and three-dimensional arrays with controlled inter-particle separation and ordering were achieved without any chemical modification of either the nanoparticles or BCPs. The ordering and distribution of small molecules between different BCP blocks are temperature dependent, leading to responsive materials where the spatial distribution of the nanoparticles can be varied, changing the local environment and the areal density of the nanoparticles. The approach described is versatile; compatible with existing fabrication processes and enables a nondisruptive approach for the generation of functional devices. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V19.00005: Hierarchical volume gratings by combining holographic-patterning and block copolymer self-assembly Michael Birnkrant, Russell Marron, Christopher Li, Lalgudi Natarajan, Vincent Tondiglia, Timothy Bunning A novel hierarchical photonic crystal (HPC) was fabricated by combining top-down and bottom-up nanomanufacturing techniques. The hierarchical structure was fabricated from a volume of material by combining holographic patterning (HP) and block copolymer (BCP) self assembly. The structure of the HPC was investigated as a function of the BCP architecture, BCP concentration and crystallization temperature. Upon heating the photonic crystal a red shift in the reflected wavelength occurs; but, an initial decrease in diffraction efficiency (DE) followed by an increase in DE indicates a non-monotonic change in the structure of the HPC. Upon cooling the reverse occurs reflecting the dynamic change in the hierarchical structure. Transmission electron microscopy, in-situ FTIR and optical spectroscopy were used to correlate the optical property change with BCP/HPC morphology. This approach could open a gateway to fabricating multifunctional hierarchical nanostructures. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V19.00006: Heteroarm Star Block Copolyampholytes as Templates for Hierarchically-Ordered Polyelectrolyte-Surfactant Complexes Matthew Hammond, Chaoxu Li, Constantinos Tsitsilianis, Raffaele Mezzenga We report on the hierarchical ordering observed in dry, solid samples of polyelectrolyte surfactant complexes based upon a novel heteroarm star block terpolymer bearing short polystyrene (PS) arms and an equal number of longer poly(2-vinylpyridine)- \emph{block}-poly(acrylic acid) (P2VP-\emph{b}-PAA) arms. The ampholytic nature of the star block copolymer allowed for complexation to be carried out on either the P2VP blocks (with negatively charged surfactants) or on the PAA blocks (with positively charged surfactants), depending only on the pH at which the complexation reaction was carried out. X-ray scattering and transmission electron microscopy data reveal that the various complexes display self-organization on the length scale of the polyelectrolyte-surfactant complex (ca. 3 - 4 nm) and on that of the overall copolymer (ca. 20 - 40 nm), with the specific repeat distances and self-organized morphologies being dramatically affected by the choice of block to be complexed. This study clearly illustrates how topological design possibilities in hierarchical self-assembly of block copolymer-based supramolecular complexes can be greatly enhanced by increasing the level of complexity of the macromolecular templates used. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V19.00007: Assembly of Organic/Nanoparticle Hybrid Systems Stephen Z.D. Cheng, Yingfeng Tu, Chun Ye, Wenbin Zhang, Xinfei Yu, Ryan M. Van Horn, Chien-Lung Wang The structure, dispersion, and chemical functionality of particles in a material are critical to the material's properties. We are working to build the scientific and technological foundations of using particles such as C60 and POSS to develop new, highly functional, self-assembled materials. These efforts have involved developing new synthetic techniques to efficiently and precisely manipulate particles to control their dispersion and structure within the organic material. First, C60-polymer and POSS-polymer molecules have been synthesized. These materials are capable of crystallizing in solution, enabling the formation of highly conducting or insulating sheets on the basal surfaces of the crystals. Additionally, these molecules may form micelles in solution. Next, POSS-C60-porphyrin molecules were synthesized and were found to self-assemble into discotic columnar structures where the intimately arranged porphyrin core harvests photons and the C60 enhances charge transport, making these materials ideal for organic photovoltaic applications. Finally, C60-POSS conjugate molecules have been synthesized that crystallize into a bilayer structure with alternating conducting and insulating layers. From these investigations, we will develop how best to chemically incorporate particles into materials from a fundamental level for significant technological advancements. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V19.00008: Quantification of the Molecular Topology for Hierarchical Macromolecules Gregory Beaucage Hierarchical structures are often produced from ramified macromolecules such as comb, star, hyperbranched and dendritic polymers. We have recently derived a method for the description of complex molecular and nanostructural topologies based on a statistical analysis [1,2]. The method has been applied to a wide range of hierarchical materials from long chain branched polyolefins, hyperbranched polymers [3], star polymers, H-branched polymers to cyclics, biopolymers [4], and branched nanostructured aggregates. This method, when applied to neutron scattering data, yields the mole fraction of a structure involved in branching, the number of branch sites, the average branch length, and the number if inner chain segments. Further, quantitative measures of the convolution or tortuosity of the structure and the connectivity of the branching network can be made, opening a new window for our understanding of complex molecular topologies. This understanding has recently been applied to biological chain molecules to understand protein and RNA folding [4] for example as well as to aggregated, nanostructured, carbon soot. \\[0pt] [1] Beaucage, G, \textit{Phys. Rev. E} \textbf{2004}, 70, 031401. [2] Kulkarni, AS {\&} Beaucage, G, \textit{J. Polym. Sci. Part B: Polym. Phys.} \textbf{2006}, 44, 1395. [3] Kulkarni, AS {\&} Beaucage, G, \textit{Macromol. Rapid Comm.} \textbf{2007}, 28, 1312.?4) Beaucage, G, \textit{Biophysical J.} \textbf{2008}, 95, 503. [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V19.00009: Nanoparticle Assemblies via Self-Assembling Peptide Molecules Nikhil Sharma, Matthew Lamm, Joel Schneider, Kristi Kiick, Darrin Pochan The bottom up approach towards nano-scale patterning presents the possibility of creating hierarchical architectures through simple self-assembly strategies. Herein, we elucidate the self-assembly of different types of peptide molecules into unique nano-scale morphologies and demonstrate their application in the construction of linear arrays of inorganic nanoparticles. A 20 amino acid peptide, consisting of alternating hydrophilic (lysine) and hydrophobic (valine) residues flanking a central diproline turn sequence (VKVKVKVKVPPTKVKVKVKV-NH$_{2})$ was employed as a nano-scale template for the organization of 2nm gold particles. This peptide self assembles into a laminated morphology in solution and has a periodic nanostructure consisting of alternating hydrophobic and hydrophilic layers with a lateral periodicity of 2.5 nm. Negatively charged gold nanoparticles are templated into the positively charged lysine layer through electrostatic interaction and are aligned within the template to form laterally spaced (2D) linear arrays. Also, a long chain alanine-rich polypeptide was used to create 1D nanoparticle assemblies. This peptide assembles into fibrils with monodisperse widths and presents its charged functional groups periodically along the length of the fibril. These functional groups bind nanoparticles that results in their spatially modulated linear arrangement. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V19.00010: Robust Three Dimensional Liquid Films through Nanoparticle Assembly Tzu-chia Tseng, Erin McGarrity, Phillip Duxbury, Amalie Frischknecht, Michael Mackay We create three-dimensional thin liquid films that cover rough surfaces, typically thought to be un-wettable, by employing a nanoparticle self-assembly technique. In this technique, the nanoparticles assemble at the liquid-substrate interface during annealing and they stabilize the liquid-air interface by screening its interactions with the substrate. This results in robust liquid films capable of wetting surface protrusions that are greater than their thicknesses. In this work, blends of polystyrene and CdSe nanoparticles were spincoated onto silicon substrates containing sparsely distributed SiO2 particles (circa 110 nm) and thermally annealed. Film profiles of different thicknesses (40-180 nm) were characterized using atomic force microscopy (AFM). Calculations based on a continuum theory were performed and found to be in agreement with the AFM profile data. Cross-sectional transmission electron microscopy (TEM) was performed to provide validation of the film profile contours and the 3D-assembly of the nanoparticles. This method could be used, for example, to enlarge the interfacial area for exciton dissociation in organic photovoltaic cells. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V19.00011: The path and motion of an electrospinning jet observed with videography and stereography Kaiyi Liu, Camden Ertley, Darrell Reneker An electrospinning jet illuminated with both a steady intense light and a short flash was stereoscopically recorded through a pair of prisms in a video, producing images of both traces of moving glints reflected from the surface of a jet and the instantaneous positions of the path of the jet. The relationship between the visual observation and the jet path described in the Reneker-Yarin model$^{1,2}$ was explained by analyzing the stereographic images. Computer modeling was used to elucidate the relationship between the onset of the bending instability and the bifurcation of a glint trace. The velocities and positions, in 3-dimensional space, of segments of a jet were calculated from the stererographic images. The distributions of velocities and positions of segments along the vertical direction were analyzed. A novel and facile method was used to observe the handedness of the coiled path of an electrospinning jet. 1. D.H. Reneker, A.L. Yarin, Polymer, Vol. 49, (2008) pp 2387-2425. 2. D.H. Reneker, A.L. Yarin, E. Zussman, H. Xu, Advances in Applied Mechanics, Vol. 41 (2006) pp 43-195. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V19.00012: Electrospinning Semicrystalline Block Copolymer Assemblies into Microfibers Kristen Roskov, Ian Manners, Richard Spontak Cylindrical micelles consisting of a diblock copolymer composed of poly(ferrocenyldimethylsilane) (PFDMS)-$b-$poly(2-vinylpyridine) (P2VP) develop in dimethylformamide (DMF), a P2VP-selective solvent, with lengths exceeding one micron. These self-assembled micelles are then incorporated into P2VP homopolymer solution and electrospun. Addition of the cylindrical micelles is found to improve the ability of P2VP to be electrospun and dramatically decrease the bead density that appears in the electrospun microfiber mat. Scanning and transmission electron microscopies are used to investigate both the surface and internal morphology of these fibers, along with the robustness of the micelles. The combination of self-assembled structures within a polymer matrix can lead to fascinating response behavior dependent on temperature; if the sample is heated and the melting point of PFS is surpassed, the micelles will melt and then form classical morphologies. In the case of self-assembled, conductive cylinders of PFS block copolymers, heating the sample destroys conductive pathways. The PFS-$b$-P2VP self-assembled cylinders have also been incorporated into other DMF-selective polymers to verify that the micelles remain intact upon electrospinning. [Preview Abstract] |
Thursday, March 19, 2009 10:48AM - 11:00AM |
V19.00013: Electrospinning of native cellulose from nonvolatile solvent system Shanshan Xu, Aihua He, Charles C. Han Electrospinning of cellulose in a highly efficient RTIL of 1-allyl-3-methylimidazolium chloride (AMIMCl) was investigated. It was found that the introduction of co-solvent dimethyl sulfoxide (DMSO) contributed to a continuous jet. The problems lying in nonvolatility and the high ionic strength of the RTIL were successfully resolved using a rotating copper-wire drum as a collector and solidifying the jet under high relative humidity. The water vapor played an important role in leading to ``skin formation'' which helped to stabilize the fibrous morphology, and finally smooth ultra-thin regenerated cellulose fibers were obtained [Preview Abstract] |
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