Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P18: Bulk Block Copolymers II |
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Sponsoring Units: DPOLY Chair: Bradley Olsen, California Institute of Technology Room: 319 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P18.00001: Directed Self-Assembly of Cadmium Selenide Nanocrystals in Conjugated Rod-Coil Block Copolymers B. L. McCulloch, J. Urban, R. A. Segalman Semiconducting polymer/nanocrystal composites are attractive for many applications; however their performance relies crucially on nanoscale morphology. We demonstrate that a conjugated rod-coil diblock copolymer can be used both to absorb light and template the location of CdSe nanocrystals. A combination of the liquid crystallinity of the conjugated rod block and the interactions of the nanocrystal ligand coat with the block copolymer control self-assembly. For example, incorporation of the nanocrystal in the rod nanodomain disrupts liquid crystallinity. In the case of a poly(alkoxy-phenylene vinylene-b-2-vinyl pyridine) (PPV-b-P2VP) block copolymer and CdSe nanocrystals, self-assembly leads to a bulk lamellar structure on the 10nm length scale. Small angle X-ray scattering confirms the addition of nanocrystals swells the domain size. We demonstrate via transmission electron microscopy the nanocrystals reside preferentially in the P2VP domain, presumably due to the strong nanocrystal surface interactions with polar P2VP and exclusion effects of the crystalline PPV phase. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P18.00002: ABSTRACT WITHDRAWN |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P18.00003: Nano-porous Poly(3-hexylthiophene) films: A novel route to prepare bulk heterojunction photovoltaic devices Tirtha Chatterjee, Kulandaivelu Sivanandan, Craig J. Hawker, Edward J. Kramer Conjugated polymers are excellent candidates for use in low-cost electronics and photovoltaics applications. Bulk heterojunction (BHJ) morphologies are promising device architecture as the close proximity of the electron donor and acceptor micro-domains (with domain size comparable with the exciton diffusion length) facilitates the charge transport process. In order to achieve a well ordered BHJ architecture, poly(3-hexylthiophene) (P3HT) based rod-coil copolymers are synthesized where coil blocks are grafted to the P3HT chain through a cleavable linker. The linker and the attached sacrificial coil block can easily be cleaved and removed by chemical treatment leaving a rough nano-porous P3HT film. Scanning force microscopy and grazing incidence small angle X-ray scattering convincingly show the nano-pore formation. Further, depth profiling using dynamic secondary ion mass spectroscopy indicates that nano-pores probably penetrate the entire depth of the film (device thickness). Subsequently refilling of the nano-pores by electron transporting component (fullerene derivatives) provides the required device morphology. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P18.00004: The Influence of Electric Fields on the Order-Disorder Transition Temperature of Block Copolymer Systems Heiko Schoberth, Kristin Schmidt, Kerstin Schindler, Alexander B\"oker We investigate the influence of electric fields on the phase behavior of diblock copolymers in concentrated solutions using synchrotron small-angle X-ray scattering (synchrotron SAXS). When heating the solutions through the order-disorder transition temperature {$T_{\mathrm{ODT}}$}, we find a significant decrease in {$T_{\mathrm{ODT}}$} with increasing electric-field strength. In addition we found a temperature regime in which it is possible to switch between the mixed and phase separated state at constant temperature upon application of a moderate electric field. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P18.00005: Phase Behavior of Polystyrene-block-Poly(n-alkyl-ran-n'alkyl methacrylate) Copolymers Hong Chul Moon, Junhan cho, Jin Kon Kim The phase behavior of polystyrene-block-poly(n-butyl-ran-n- hexyl) methacrylate copolymers and polystyrene-block-poly(n- octyl-ran-methyl) methacrylate copolymers were investigated by using small angle X-ray scattering, birefringence and rheometry. When the total molecular weight and the composition of the random copolymers were judiciously controlled, the closed-loop phase behavior with both a lower disorder-to-order transition and an upper order-to-disorder transition was observed. These block copolymers exhibited excellent baroplasticity. The observed phase behavior was explained by a compressible mean field approach. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P18.00006: Gas Pressure Effect on Phase Behavior of Deuterated Polystyrene-block-poly(n-pentyl methacrylate) Hye Jeong Kim, Jin Kon Kim, Du Yeol Ryu The pressure effect of various gases on the phase transitions of deuterated polystyrene-block-poly(n-pentyl methacrylate) copolymer was investigated by small angle neutron scattering (SANS) and birefringence. With increasing helium gas pressure, the size of closed-loop consisting of both the lower disordered- to-ordered transition and the upper ordered-to-disordered transition was decreased, which is similar to the hydrostatic pressure effect. On the other hand, when nitrogen gas was used, the size of the closed-loop became larger with increasing pressure. These interesting results are explained by the binding energy calculation. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P18.00007: Pressure Jump Studies of Block Copolymer Phase Transition in Selective Solvent Yongsheng Liu, Rama Bansil, Milos Steinhart Synchrotron based time-resolved small angle x-ray scattering (SAXS) was used to study the kinetics of the order-disorder transition (ODT) in a 30{\%} (w/v) solution of a diblock copolymer of poly(styrene -- isoprene) (SI 18-12) in diethylphthalate (DEP), a selective solvent for the PS block using pressure jump methods. The results show that the ODT temperature increases at about 20C/kbar with pressure. Time resolved pressure jump SAXS experiments were done to study the kinetics of disorder to BCC phase transition and the reverse transition. Pressure jump from 100 bar to 800 bar at 108 C from disordered state displayed a BCC structure at 30 seconds. Results of experiments with solvent viscosity increased by adding low molecular weight polystyrene will also be presented. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P18.00008: Self-assembled Oniontype Multiferroic Nanostructures Shenqiang Ren, Robert M. Briber, Manfred Wuttig Spontaneously self-assembled oniontype multiferroic nanostructures based on block copolymers as templating materials are reported. Diblock copolymer containing two different magnetoelectric precursors separately segregated to the two microdomains have been shown to form well-ordered templated lamellar structures. Onion-type multilamellar ordered multiferroic (PZT/CoFe$_{2}$O$_{4})$ nanostructures have been induced by room temperature solvent annealing in a magnetic field oriented perpendicular to the plane of the film. The evolution of the onion-like microstructure has been characterized by AFM, MFM, and TEM. The structure retains lamellar periodicity observed at zero field. The onion structure is superparamagnetic above and antiferromagnetic below the blocking temperature. This templating process opens a route for nanometer-scale patterning of magnetic toroids by means of self-assembly on length scales that are difficult to obtain by standard lithography techniques. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P18.00009: Periodic Polymers for PhoXonics Edwin Thomas Exploiting the size and shape dependence of material properties and accessing multi-functionality holds great promise for the development of materials that will contribute to novel future technologies. Polymers can act as hosts for metallic and dielectric nanoparticles as well as organic molecules, resulting in nanocomposites with combinations of properties not available by other means. \textit{Periodic} structural assemblies are of particular interest, due to their interesting interactions with waves: especially light and mechanical waves. Progress in this exciting area requires excellent control of structure formation. A top-down, bottom-up approach, involving interference lithography and self assembly is demonstrating good success in fabricating the requisite structures and desired properties for photonics and phononics. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P18.00010: Hydration and phase separation of polyethylene glycol in copolymers of tyrosine derived carbonates. N. Sanjeeva Murthy, Wenjie Wang, Joachim Kohn Effect of PEG fraction and its block size on the temperature-induced phase transitions and the hydration-induced phase separation were investigated in a copolymer of desaminotyrosyl tyrosine ethyl ester (DTE) and PEG using simultaneous SAXS/WAXS/DSC. The PEG segments crystallized when the block size was at least 2000 Daltons and present at $\sim $ 40 wt{\%}, and raised the T$_{g}$ of the polymer by $\sim $ 15 $^{\circ}$C. The PEG blocks in dry polymers with up to 50 wt{\%} PEG, even when crystalline, were found to be uniformly distributed with no evidence of phase separation at 10 nm length scales. The non-iodinated PEG-rich sample with 30 mole{\%} PEG$_{2k}$ showed the lower critical solution temperature (LCST) behavior with PEG blocks forming a separate phase above -21 $^{\circ}$C. In the iodinated version of this polymer, the PEG$_{2k}$ blocks were phase separated in the solid phase. In all samples, whether PEG was crystalline or not, hydration induced PEG to separate into 15 nm hydrated domains. Phase behavior was dependent on whether poly(DTE) or the PEG was the major (matrix) phase. Changes in the mobility of the chains brought about by water-mediated hydrogen-bonding, and modulated by heat, appear to be the common underlying explanation for the range of observed phase behavior. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P18.00011: Robustness of Pluronic Block Copolymer Nanostructure to Structural Changes in Dispersed Nanoparticles Theresa A. LaFollette, Lynn M. Walker Thermoreversible block copolymers [(PEO)n-(PPO)m-(PEO)n; trade name Pluronic] self assemble into ordered micelle gels. Nanoparticles (3-10nm) are templated in the interstitial spaces of Pluronic micelle gels to form nanocomposite systems. Globular hydrophilic proteins have served as model monodisperse nanoparticles in this work. We have shown that these proteins are templated in the interstitial sites of the cubic packed micelle gels at room temperature. By raising the temperature, the proteins are denatured to study the robustness of the micelle gel to structural changes due to the unfolded protein. Nanoscale structure is determined from small angle neutron scattering (SANS). It was expected that any change in the nanoparticle size would cause a change in the packing of the Pluronic micelle gel. However in SANS experiments, the FCC and BCC Pluronic templates show no nanoscale structural differences between a room temperature sample and a sample that has been heated to denature the protein and then cooled back to room temperature. There is a change in the template at longer length scales as evidenced by a low q upturn in the scattered intensity. The robustness of the micelle gel at different length scales will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P18.00012: Phase behavior of block copolymer nanocomposites George Papakonstantopoulos Incorporating nanoparticles in block copolymers can allow the creation of a material with tailored properties. In addition, the control of the nanoparticle location in a nanometer scale, can lead to novel applications for these materials. Although, the phase behavior of block copolymers in the bulk is well established, the effects of nanoparticles on their phase behavior, especially under confinement, are not well understood. We carried out a systematic study to investigate the self-assembly of block copolymer-nanoparticle composites using a coarse grain model. These systems are studied in the bulk and under confinement. The dependence of the location and distribution of the nanoparticles within the block copolymer as a function of particle-polymer interaction, size and shape were examined. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P18.00013: Effect of Chain Architecture on Nanoparticle Miscibility in Block Copolymer Nanocomposites Jessica Listak, Hyung Ju Ryu, Ilhem F. Hakem, Rangou Sofia, Politakos Nikolaos, Misichronis Konstantinos, Apostolos Avgeropoulos, Michael R. Bockstaller This contribution will present a combined experimental and theoretical analysis of the effect of block copolymer chain architecture on the miscibility and morphology of enthalpically neutralized particle additives. The chain architecture is found to be a critical parameter in facilitating particle dispersion imposing both direct as well as indirect constraints on the particle distribution. Continuous block configurations (such as the bridged midblocks in triblock copolymers) are found to inhibit particle compatibilization. Interestingly, the particle miscibility is found to be strongly affected by the configuration of the block adjacent to particle-filled domains (indirect constraint). In particular, incompatibility is observed for high branching densities in the adjacent domains (such as miktoarm chain architectures). A mean-field model will be presented to rationalize this observation as a consequence of segmental crowding that counteracts changes in the layer dimensions induced by particle sequestration. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P18.00014: Rheological and Mechanical Properties of Crosslinked Block Copolymer Nanofiber and Polystyrene Blends. Sungwon Ma, Yonathan Thio The mechanical and rheological properties of blends of crosslinked and uncrosslinked poly(styrene)-\textbf{\textit{b}}-poly(isoprene) copolymer with commercially available polystyrene were studied. Cylindrical morphology of PS-\textbf{\textit{b}}-PI copolymer was employed for generating nanofiber morphology. Cold vulcanization process using sulfur monochloride (S$_{2}$Cl$_{2})$ was used to preserve the morphology. Blends of uncrosslinked PS-\textbf{\textit{b}}-PI copolymer with neat polystyrene were also prepared. Both blend samples were prepared by solvent casting method with the filler contents varying between 0.5 and 10 wt{\%}. The mechanical and rheological properties were characterized and the microstructures of the fiber and the systems were imaged. The dynamic moduli (G' and G'') of the crosslinked system increased with increasing the fiber content compared to the uncrosslinked system. The results were compared to the rheological model by fitting to Cross-Williamson. This blend study indicated critical volume concentration of nanofiber between 5 and 10 wt{\%} of nanofiber content. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P18.00015: Well Ordered Polymer Melts with Sub 5-Nanometer Domains upon Blending Surfactants with Selectively Associating Additives Vikram Daga, Vijay Tirumala, Curran Chandler, Alvin Romang, Eric Anderson, Eric Lin, James Watkins Applications employing block copolymers such as templating mesoporous inorganic structures and patterning would benefit from reduction in domain size formed in well-ordered block copolymer templates. The extent to which the domain size can be reduced is limited by the minimum required segregation strength, $\chi N$, where $N$ determines the size of block copolymer chains and the domain size. We have shown that disordered block copolymer surfactants with molar mass less than 15 kg/mol, can be made to undergo disorder-to-order transition by blending selectively associating homopolymers as well as small molecule additives with multi-point, non-ionic interactions. Blending with selectively associating additives result in an increase in segregation strength $\chi N$ through an increase in apparent $\chi$. The resulting domain sizes were found to be as low as 5 nm which is significantly lower than that seen for a typical block copolymer template. [Preview Abstract] |
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