Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G21: Physics of Copolymers: Ordering and Application of Block Copolymers |
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Sponsoring Units: DPOLY Chair: Issei Nakamura, Changchun Institute of Applied Chemistry Room: 406 |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G21.00001: Complex Ordering of Soft Spheres in Block Polymer Melts Sangwoo Lee, Jingwen Zhang, Frank S. Bates Hard sphere systems, such as low-z metallic elements and colloids, generally form densely packed crystalline states with BCC, FCC and HCP symmetry. In contrast, a certain self-assembling soft materials including block polymers, surfactants, and dendrimers have the capacity to order into more open crystalline structures. Recently, we have identified five discrete sphere-packing symmetries in poly(styrene-$b$-isoprene-$b$-styrene-$b$-ethylene oxide) (SISO) tetrablock terpolymers: BCC, Frank-Kasper $\sigma $-phase, dodecagonal quasicrystal (DQC), Pm$\bar{3}$n(A15), and non-close-packed hexagonal (sHEX). Some of these packing symmetries have been documented in certain heavy metals and organic dendrimers, and interestingly Landau theory anticipated a similar set of non-close-packed symmetries more than three decades ago. This talk will draw analogies between the ordering of spheres in soft and hard materials. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G21.00002: Chirality Effect on Self-Assembly of Chiral Block Copolymers Hsiao-Fang Wang, Ming-Chia Li, Rong-Ming Ho Here, we report the mechanisms of chiral transfer at various length scales in the self-assembly of enantiomeric chiral block copolymers (BCPs*). We show the evolution of homochirality from molecular chirality into phase chirality in the self-assembly of the BCPs*. The chirality of the molecule in the BCP* is identified from circular dichroism spectra, while the handedness of the helical conformation in the BCP* is determined from a split-type Cotton effect in vibrational circular dichroism spectra. Microphase separation of the BCP* is exploited to form a helical (H*) phase, and the handedness of helical nanostructure in the BCP* is directly visualized from transmission electron microscopy tomography. Moreover, the phase transitions from the H* phase to both the hexagonal cylinder phase and gyroid phase are found after long-time thermal annealing. Those results suggest that the H* phase is a long-lived metastable phase. To demonstrate the universal behavior of the chirality effect on BCPs*, different block copolymers containing chiral segment are synthesized and examined, suggesting that the chirality effect indeed plays an important role in the formation of H* phase. [Preview Abstract] |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G21.00003: Control of Block Copolymer Morphology through End-functional Groups Gyuha Jo, Moon Jeong Park Recently, poly(ethylene oxide) (PEO)-containing polymer electrolytes have attracted significant attention to be applied for lithium batteries. As the realization of high mechanical strength from the polymer electrolyte becomes of critical importance in high-energy lithium batteries, much effort has been devoted to developing PEO-based block copolymers comprising mechanically robust polymer chains. Interest in this topic has been further stimulated by multiple observations of significant electrolytic conductivity enhancement imparted by microphase separation of block copolymers. In the present study, we report an intriguing methodology for modulating the morphology of poly(styrene-ethylene oxide) (PS-PEO) block copolymers with a single ionic group tethered at the chain end of PEO. Unique intra- and inter-chain interactions deduced from the end functional group afforded enriched nanostructures, i.e. disorder, lamellae, hexagonal cylinder, and gyroid, with significant differences in conductivities depending on lithium salt concentration. In particular, a gyorid morphology with a twofold-enhanced lithium ion transport efficiency was found for the end-functionalized PS-PEO block copolymer, attributed to the structural advantages of the gyroid having co-continuous ionic channels. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G21.00004: Increase in the Domain Spacing from ARB-Type Triblock Copolymer Sanghoon Woo, Hyunjung Jung, June Huh, Du Yeol Ryu, Soo-Hyung Choi, Joona Bang It has been reported that the self-assembly of block copolymers (BCP) with very high molecular weight (MW) can achieve the length scale above 100 nm, which can be utilized as photonic band-gap materials or photonic crystals. However, due to slow chain dynamics, it is hard to fabricate well-controlled nano-patterns from high MW BCPs via thermal annealing process. In this work, we designed a new type of BCP, namely ARB-type BCP, where the R represents the short middle block composed of A and B random copolymer. It was expected that the R block provide the effect of increased polydispersity via compositional distribution, leading to an increased domain size compared to the AB diBCP with same MW and polydispersity. We prepared various ARB-type BCPs and AB diBCPs having the similar polydispersity via living-radical polymerization, and their morphologies were characterized by TEM, SAXS, and GISAXS. Consequently, it was shown that the ARB-type triBCP exhibited $\sim$30\% increase in the domain spacing compared to the AB diBCPs with same MW and polydispersity. These results were also compared with theoretical viewpoint. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G21.00005: The Order-Disorder Transition in Short Diblock Copolymers: Relaxation Calorimetry Experiments Timothy Gillard, Daniel Phelan, Sangwoo Lee, Chris Leighton, Frank Bates Fluctuation-driven, weakly first-order phase transitions occur in a variety of physical systems, including the order-disorder transition (ODT) in block copolymers (BCPs), and certain phase transitions in liquid crystals, magnetic materials, and superconductors. BCPs provide an attractive model system for studying this fascinating class of transitions since BCPs exhibit universal phase behavior dependent on a small number of parameters that are easily tuned during synthesis. However, thermal measurements of the ODT in BCPs are rare since the magnitude of the latent enthalpy of the transition scales inversely with $N$, the degree of polymerization. Here we extend a thermal measurement technique common in the inorganic materials community, relaxation calorimety, to accurately measure the temperature dependence of the heat capacity near the ODT of poly(1,4-isoprene-$b$-DL-lactide) BCPs that form ordered structures at low $N$. The transition temperature (371 K), latent heat (0.3 J/g), and temperature hysteresis ($\sim$ 1 K) were found to agree with values obtained from differential scanning calorimetry, rheology, and scattering experiments, establishing relaxation calorimety as a valuable new tool for studying the ODT in BCPs. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G21.00006: Alignment pathways and the effect of a Nematic-Smectic A transition on the orientational order of an LC block copolymer under magnetic fields Manesh Gopinadhan, Youngwoo Choo, Pawel Majewski, Chinedum Osuji We explore the effect of magnetic fields on the thermodynamics and alignment kinetics of a liquid crystalline block copolymer (LCBCP) using in situ SAXS. We examine the effect of magnetic fields on the order-disorder transition temperature (T$_{ODT})$, alignment pathways and the effect of liquid crystal ordering on the orientational order of the system. The application of the field did not result in any discernable shift in the phase behavior of the system. This is consistent with our observation that alignment occurred by slow grain rotation rather than by selective melting of field-destabilized grains, which is further supported by time and temperature resolved measurements. Zero field cooling conducted after field-annealing in the nematic phase result in highly-aligned structures despite the initial weak alignment in the nematic window. The strong enhancement of the alignment is correlated with the emergence of a smectic mesophase and highlights the strong orientational coupling of the BCP interfaces to the orientation of the smectic layer normal, k, and not to the molecular director field of the mesogens, n. These results suggest that the presence of a smetic A mesophase and the nematic-smectic sequence can be leveraged in designing schemes for magnetic field directed self-assembly of block copolymers. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G21.00007: Self-Assembly of Pluronic Block Copolymers in Solutions: Simulation and Neutron Scattering Zhe Zhang, Kunlun Hong, Changwoo Do Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers in water solution display various phase behaviors such as micellar, lamellar, and hexagonal phases and have been of great interest to researchers for their wide range of applications including templates of various nanostructures in solar cell and transportation of nanoparticles in drug delivery. In this study, we combined density functional theory-based mesoscale simulation and small-angle neutron scattering (SANS) experiments to investigate equilibrium structures of L62/water systems at different concentrations. Various simulation parameters found in the literature have been revisited with the experimental findings. Scattering experiments were found to be an excellent. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G21.00008: Chain exchange in block copolymer micelles Jie Lu, Frank Bates, Timothy Lodge Block copolymer micelles are aggregates formed by self-assembly of amphiphilic copolymers dispersed in a selective solvent, driven by unfavorable interactions between the solvent and the core-forming block. Due to the relatively long chains being subject to additional thermodynamic and dynamic constraints (e.g., entanglements, crystallinity, vitrification), block copolymer micelles exhibit significantly slower equilibration kinetics than small molecule surfactants. As a result, details of the mechanism(s) of equilibration in block copolymer micelles remain unclear. This present works focuses on the chain exchange kinetics of poly(styrene-b-ethylenepropylene) block copolymers in squalane (C30H62) using time-resolved small angle neutron scattering (TR-SANS). A mixture of h-squalane and d-squalane is chosen so that it contrast matches a mixed 50/50 h/d polystyrene micelle core. When the temperature is appropriate and isotopically labeled chains undergo mixing, the mean core contrast with respect to the solvent decreases, and the scattering intensity is therefore reduced. This strategy allows direct probing of chain exchange rate from the time dependent scattering intensity I(q, t). [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G21.00009: A Theoretically Informed Model for the Rheology of Entangled Block Copolymer Nanocomposites Yongrui Su, Abelardo Ramirez-Hernandez, Brandon Peters, Juan J. de Pablo The addition of nanoparticles to block copolymer systems has been shown to have important effects on their equilibrium structure and properties. Less is known about the non-equilibrium behavior of block polymer nanocomposites. A new particle-based, theoretically informed coarse-grained model for multicomponent nanocomposites is proposed to examine the effects of nanoparticles on the rheology of entangled block copolymer melts. Entanglements are treated at the two-molecule level, through slip-springs that couple the dynamics of neighboring pairs of chains. The inclusion of slip-springs changes the polymer dynamics from unentangled to entangled. The nanoparticles are functionalized with short polymer chains that can entangle with the copolymers. We study the nonlinear rheology of the resulting nanocomposites under shear flow with a dissipative particle dynamics (DPD) thermostat. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G21.00010: Baroplastic Behavior in Block Copolymer Blends Yonghoon Lee, Hyungju Ahn, Hoyeon Lee, Eunhye Kim, Young Soo Han, Du Yeol Ryu The study of block copolymer (BCP) blends, composed of the weakly interacting polystyrene-$b$-poly(n-butyl methacrylate) (PS-$b$-PnBMA) and polystyrene-$b$-poly-(n-hexyl methacrylate) (PS-$b$-PnHMA) presented the various composition-dependent phase behaviors arising from a miscible phase between the PnBMA and PnHMA blocks in the BCP blends. As the blend composition varied from PS-$b$-PnBMA to PS-$b$-PnHMA, a lower disorder-to-order transition (LDOT) to a closed-loop phase transition and to an order-to-disorder transition (ODT) on heating were observed. The hydrostatic pressure effects on the various phase behaviors of the BCP blends were further investigated using small-angle neutron scattering (SANS), depolarized light scattering (DPLS) and transmission electron microscope (TEM). [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G21.00011: Diblock copolymer bridges: the break-up dynamics and enhanced stability of structured liquids Robert Peters, Kari Dalnoki-Veress Liquid bridges form when a liquid is stretched between two boundaries, creating a freestanding fiber. The break-up of simple Newtonian liquid bridges has been studied both theoretically and experimentally for a wide variety of different initial conditions since Plateau and Rayleigh considered the instability of a liquid jet. Though the break-up of liquid bridges composed of linear polymer melts and polymer solutions have been well studied, very little focus has been placed on the dynamics of diblock copolymer bridges. When annealed above the glass transition temperature and below the order-disorder transition temperature (ODT), diblock copolymers can organize into well-defined structures determined by the weight fraction of each polymer block. Conversely, as the temperature is increased above the ODT, the diblock will disorder and have properties more similar to a linear polymer melt. In this work, we monitor the evolution of diblock copolymer bridges to study the effect that diblock order has on dynamics and stability. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G21.00012: Phase Transitions of Polystyrene-b-Polydimethylsiloxane in Solvents of Varying Selectivity Ting-Ya Lo, Chia-Cheng Chao, Rong-Ming Ho, Prokopios Georgopanos, Apostolos Avgeropoulos, Edwin L. Thomas A simple method to create a variety of nanostructures via the self-assembly of a single composition silicon-containing block copolymer (BCP) is developed. By using selective solvents for the self-assembly of polystyrene-block-polydimethylsiloxane (PS-PDMS), the phase behavior of intrinsic BCP can be enriched due to the strong segregation of the PS-PDMS enabling the clear-cut phase transitions during solvent evaporation. The solution-state phase behaviors of the strong segregation BCP system are systematically studied using temperature-resolved SAXS. Meanwhile, owing to the high etching contrast of the silicon-containing block versus the PS block, various nanostructured SiOC can be fabricated by using one-step oxidation. Furthermore, the recovery of the intrinsic lamellar phase can be achieved by thermal annealing the metastable cylinder and gyroid phases through order$-$order transition (OOT). Time-resolved SAXS and electron tomography are carried out to reveal the variation of the structural evolution in reciprocal space and real space, respectively. This result offers new insights into the phase behaviors of the OOT of BCPs. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G21.00013: Controlled orientation and ordering of nanostructured thin films from degradable block copolymer. Rong-Ming Ho, Ming-Shiuan She, Ting-Ya Lo, Yi-Hsiu Wu The fabrication of nanostructured thin films from the self-assembly of degradable block copolymers (BCPs) has attracted extensive attention. To create useful BCP thin films for practical uses, controlling the orientation of self-assembled nanostructures is essential. Here, we present a new method for forming well-ordered and oriented nanostructured thin films on a functionalized SiO$_{\mathrm{2}}$ surface, using homopolymers with hydroxyl group at the chain end to functionalize SiO$_{\mathrm{2}}$ surface, to give neutral substrate for the BCPs. To demonstrate the feasibility of suggested approaches, a series of degradable BCPs, polystyrene-$b$-poly(L-lactide) (PS-PLLA) with hexagonally packed cylinder and double gyroid phases, are used as model systems for creating nanostructured thin films with controlled orientation and ordering of BCP nanostructures. Different methods such as thermal and solvent annealing are utilized to exploit the fabricated neutral substrate for creating expected nanostructured thin films. By taking advantage of degradable character of PLLA, nanoporous PS thin film can be fabricated by hydrolysis and used as a template for synthesis of various nanohybrids and nanoporous materials. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G21.00014: Investigation of the self-healing mechanism of poly (ethylene co-methacrylic acid) copolymers utilizing ultrasonic time dependent resonant spectroscopy Nicholas R. Bowers, Kenneth A. Pestka II, Stephen J. Kalista, Jr. The ultrasonic resonant spectra of four different poly (ethylene-co-methacrylic acid) copolymers (EMAA copolymers) have been obtained using the Time Dependent Resonant Spectroscopy (TDRS) method. The spectra of these EMAA copolymers, developed by DuPont (commercially known as: Nucrel 925, Nucrel 960, Surlyn 8920, and Surlyn 8940), were analyzed. Evolution of resonances and the associated energy dissipation within the samples were observed over a period of 10 $\sim$ 50 hours. Results quantifying the influence of chemical properties (including molecular weight and ionic content), age, and damage mechanism on the self-healing response will be presented. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G21.00015: The Effect of Long Range Order on Ionic Conductivity in a Solid Block Copolymer Electrolyte Mahati Chintapalli, Jacob Thelen, Alexander Teran, Nitash Balsara Poly(styrene)-block-poly(ethylene oxide) (SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is a promising material for battery electrolytes due to its high ionic conductivity and ability to suppress lithium dendrite growth. Ion conduction has been found to depend on many aspects of the electrolyte microstructure, including the morphology and degree of ordering. The effect of long range order on ionic conductivity was investigated in a lamellar SEO/LiTFSI mixture by in situ small angle x-ray scattering and ac impedance spectroscopy during polymer annealing. The observation that increasing long range order decreases ionic conductivity indicates that disorder, due to small grain size or defects, enhances the ionic conductivity of the electrolyte. [Preview Abstract] |
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