Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F43: Blends and Block Copolymers |
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Sponsoring Units: DPOLY Chair: Ron Jones, National Institute of Standards and Technology Room: 214C |
Tuesday, March 3, 2015 8:00AM - 8:36AM |
F43.00001: BREAK |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F43.00002: Controlling Phase Separation of Interpenetrating Polymer Networks by Addition of Block Copolymers Brian Rohde, Ramanan Krishnamoorti, Megan Robertson Interpenetrating polymer networks (IPNs) offer a unique way to produce mechanically superior thermoset blends relative to the neat components. In this study, IPNs were prepared consisting of polydicyclopentadiene (polyDCPD), contributing high fracture toughness, and an epoxy resin (the diglycidyl ether of bisphenol A cured with nadic methyl anhydride), contributing high tensile strength and modulus. In the absence of compatibilization, the simultaneous curing of the networks leads to a macroscopically phase separated blend that exhibits poor mechanical behavior. To control phase separation and drive the system towards more mechanically robust nanostructured IPNs, block copolymers were designed to compatibilize this system, where one block possesses affinity to polyDCPD (polynorbornene in this study) and the other block possesses affinity to DGEBA (poly($\epsilon$-caprolactone) in this study). The influence of the block copolymer composition on the degree of phase separation and interfacial adhesion in the IPN was studied using a combination of small-angle scattering and imaging techniques. The resultant mechanical properties were explored and structure-property relationships were developed in this blend system. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:00AM |
F43.00003: Melt-Miscibility in Block Copolymers Containing Polyethylene and Substituted Polynorbornene Blocks William Mulhearn, Richard Register Block copolymers containing a crystallizable block, such as polyethylene (PE), and a high-T$_{\mathrm{g}}$ amorphous block are potentially interesting materials since the rigid glassy block can mitigate the poor yield strength of the PE crystals. However, chemical incompatibility between blocks, quantified by the Flory interaction parameter $\chi $ or the interaction energy density $X$, drives microphase separation at low temperatures or high chain lengths. To prepare a high molecular weight PE-containing block copolymer that is easy to process (i.e. with a disordered low-viscosity melt) it is necessary to select amorphous blocks that have low mixing energies with PE. The only suitable polymers currently known are chemically similar to PE and therefore have similarly low glass transition temperatures. We investigate a series of both low- and high-T$_{\mathrm{g}}$ polymers based on substituted norbornene monomers, polymerized via ring-opening metathesis polymerization (ROMP). Several ROMP polymers of this type exhibit high T$_{\mathrm{g}}$ and low interaction energy against PE. For example, hydrogenated poly(cyclohexyl norbornene) has T$_{\mathrm{g}} \quad =$ 88 $^{\mathrm{o}}$C and has interaction energy density $X_{\mathrm{hPCyN-PE}} \quad \approx $ 0.8 MPa, comparable to the interaction energy density between PE and hydrogenated polyisoprene. The miscibility of an amorphous block can be further tuned by statistical copolymerization of norbornene units with aromatic side-groups (high Hildebrand solubility parameter) and norbornene units with aliphatic side-groups (low Hildebrand solubility parameter). [Preview Abstract] |
Tuesday, March 3, 2015 9:00AM - 9:12AM |
F43.00004: Fluctuation Effects in AB/A/B Diblock Copolymer-Homopolymer Ternary Mixtures near the Lamellar-Disorder Transition Timothy Gillard, Robert Hickey, Brian Habersberger, Timothy Lodge, Frank Bates Fluctuations profoundly influence the phase behavior of block polymer-based soft materials. In ternary blends of an AB diblock copolymer with A- and B-type homopolymers, fluctuations destroy a mean-field predicted higher-order multicritical Lifshitz point and lead to the formation of the technologically important polymeric bicontinuous microemulsion phase (B$\mu$E). Here we report a fascinating change in character of the lamellar-to-disorder phase transition as the composition of homopolymer in the ternary blend is increased from zero (neat diblock) to the onset of the B$\mu$E channel. As the B$\mu$E channel is approached, the transition exhibits increasingly second-order character with the development of large-scale fluctuating smectic correlations in the disordered state near the transition. This change in character of the transition is documented with a combination of scattering, optical transmission, rheology, and TEM experiments in model blends of poly(cyclohexylethylene-$b$-ethylene) with the constituent homopolymers. [Preview Abstract] |
Tuesday, March 3, 2015 9:12AM - 9:24AM |
F43.00005: How to Place Block Copolymer Molecules at the Interface of a Binary Blend Zhong-Ren Chen, Yuci Xu, Shuo Zhong Block copolymers have been used to reduce the domain size of immiscible polymer blends and thus improve the mechanical and other properties. The effectiveness of this method, however, depends on the percentage of these polymeric surfactants residing at the interface of the blend. In fact, theoretical as well as experimental work indicate that a large percentage of block copolymers form micelles in the bulk of one or both of the component polymers. These micelles may serve as weak spots initiating crack propagation. Previous work have been focused on the design of molecular architecture and synthesis of new block copolymers to address this problem. In this presentation, a simple mixing strategy is applied to make each block copolymer molecule stay at the interface. As one example, when this strategy is used to mix natural rubber (NR) with butadiene rubber (BR), a small amount of low molecular weight block copolymer (LIR) improves both processing characteristics such as melt viscosity and mechanical properties of cured samples, such as crack resistance. AFM micrographs show the much smaller domain size; and an original real-time monitoring system reveals the lowest crack growth rate. Using a model A/B/A-B binary blend, we have witnessed by microscopy that all block copolymer molecules form micelles at the first mixing step, and all of these micelles are disappeared and all block copolymer molecules stay at the interface after the second mixing step. [Preview Abstract] |
Tuesday, March 3, 2015 9:24AM - 9:36AM |
F43.00006: Pressure dependence of various phase transitions for the miscible block copolymer blends Du Yeol Ryu, Yonghoon Lee, Hoyeon Lee, Yeongsik Kim The phase behaviors of block copolymer (BCP) blends composed of the weakly interacting (with no specific interaction) polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA) and deuterated polystyrene-b-poly-(n-hexyl methacrylate) (dPS-b-PnHMA) were investigated by Small-Angle Neutron Scattering (SANS) and Depolarized Light Scattering (DPLS) measurements. The various composition-dependent phase behaviors were generated due to a miscible phase between the PnBMA and PnHMA blocks in the BCP blends. To elucidate the origin and difference in baroplasticity of weakly interacting BCP blends, the pressure dependence of transition temperatures was evaluated using enthalpic and volumetric changes at phase transitions. We also demonstrate that the entropic compressibility for the miscible BCP blends is a baroplastic indicator, which was characterized by the negative volume change on mixing (Vmix) at transitions. [Preview Abstract] |
Tuesday, March 3, 2015 9:36AM - 9:48AM |
F43.00007: Crystallization of a bimodally distributed copolymer system and a blend containing propylene-ethylene moieties Onyenkachi Wamuo, Ying Wu, Shaw Hsu, Charles(Chuck) Paul, Andrea Eodice The competitive crystallization behavior of a multicomponent system is fundamentally interesting and has significant practical implications. The relative molecular weight and molecular architecture of the polymers involved needs to be considered carefully in the characterization of the entire crystallization process; nucleation and the crystal growth phase. We have considered two types of propylene-ethylene copolymers with virtually the same chemical composition but different block sequences. A comparison is being made between a bimodally distributed copolymer and a random copolymer. The unique feature of the bimodal system is the presence of a two-step crystallization process, where the longer sequences nucleated first and additional shorter segments are transported onto the crystal growth front. This system is compared to a copolymer of virtually identical random copolymer that is nucleated differently. Calorimetric, diffraction and spectroscopic measurements have been employed in order to understand the dynamics and mechanism of crystallization and the size and perfection of the crystals formed. The relative efficiency of crystallization by controlling the polymer configuration can then be compared to the traditional approach using a nucleation agent to affect the crystallization behavior. This new approach not only provides extremely fast crystallization but also overcomes practical considerations such as dispersion of the nucleation agents. [Preview Abstract] |
Tuesday, March 3, 2015 9:48AM - 10:00AM |
F43.00008: Understanding How the Presence of Uniform Electric Fields Can Shift the Miscibility of Polystyrene / Poly(vinyl methyl ether) Blends Annika Kriisa, Connie B. Roth Techniques which can externally control and manipulate the phase behavior of polymeric systems, without altering chemistry on a molecular level, have great practical benefits. One such possible mechanism is the use of electric fields, shown to cause interfacial instabilities, orientation of morphologies, and phase transitions in polymer blends and block copolymers. We have recently demonstrated that the presence of uniform electric fields can also strongly enhance the miscibility of polystyrene (PS) / poly(vinyl methyl ether) (PVME) blends [J. Chem. Phys. 2014, 141, 134908]. Using fluorescence to measure the phase separation temperature $T_{\mathrm{s}}$ of PS/PVME blends with and without electric fields, we show that $T_{\mathrm{s}}$ can be reproducibly and reversibly increased by 13.5 $+$/- 1.4 K for electric fields of 17 kV/mm for this lower critical solution temperature (LCST) blend. This increase in blend miscibility with electric fields represents some of the largest absolute shifts in Ts ever recorded, well outside of experimental error. The best theoretical prediction for the expected shift in $T_{\mathrm{s}}$ with electric field for this system is still two orders of magnitude smaller than that observed experimentally. We discuss the limitations of this theoretical prediction and consider possible factors affecting miscibility that may need to be also included. [Preview Abstract] |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F43.00009: Magnetic Field Alignment of PS-P4VP: a Non-Liquid Crystalline Coil-Coil Block Copolymer Yekaterina Rokhlenko, Kai Zhang, Steven Larson, Padma Gopalan, Corey O'Hern, Chinedum Osuji Magnetic fields provide the ability to control alignment of self-assembled soft materials such as block copolymers. Most prior work in this area has relied on the presence of ordered assemblies of anisotropic liquid crystalline species to ensure sufficient magnetic anisotropy to drive alignment. Recent experiments with poly(styrene-b-4-vinylpyridine), a non-liquid crystalline BCP, however, show field-induced alignment of a lamellar microstructure during cooling across the order-disorder transition. Using \textit{in situ} x-ray scattering, we examine the roles of field strength and cooling rate on the alignment response of this low MW coil-coil BCP. Alignment is first observed at field strengths as low as 1 Tesla and improves markedly with both increasing field strength and slower cooling. We present a geometric argument to illustrate the origin of a finite, non-trivial magnetic susceptibility anisotropy for highly stretched surface-tethered polymer chains and corroborate this using coarse-grained molecular dynamics simulations. We rationalize the magnetic field response of the system in terms of the mobility afforded by the absence of entanglements, the intrinsic anisotropy resulting from the stretched polymer chains and sterically constrained conjugated rings, and the large grain size in these low molecular weight materials. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F43.00010: Phase Behavior of Binary Blend Consisting of Asymmetric Polystyrene-block-poly(2-vinylpyridine) Copolymer and Asymmetric Deuterated Polystyrene-block-poly(4-hydroxystyrene) Copolymer Having Hydrogen Bonding Jongheon Kwak, Sung Hyun Han, Hong Chul Moon, Victor Pryamitsyn, Venkat Ganesan, Jin Kon Kim We investigated the phase behavior of a binary blend of asymmetric polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) and deuterated polystyrene-block-polyhydroxystyrene copolymer (dPS-b-PHS) blends. The blend showed highly asymmetric lamellar microdomains. To explain the unexpected results, we study, via small angle X-ray scattering (SAXS) and neutron reflectivity (NR), the exact location of shorter dPS block in the mixture near the interface of the microdomains. [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F43.00011: Quenching Phase Separation by Vapor Deposition Polymerization Ran Tao, Mitchell Anthamatten Initiated chemical vapor deposition (iCVD) is a solventless, free radical technique predominately used to deposit homogeneous films of linear and crosslinked polymers directly from gas phase feeds. We report a template-free method to fabricate continuous-phase porous polymer films by simultaneous phase separation during iCVD. Phase separation during film growth is achieved by condensing an inert porogen, along with initiator, monomer, and crosslinker. When the vapor mixture transports to the cooled substrate, phase separation occurs along with polymerization and crosslinking, which quench the state of phase separation. The kinetics of spontaneously phase separation can be qualitatively understood on the basis of Cahn-Hilliard theory. A series of films were grown by varying monomer and porogen's degree of saturation. Deposited films~were studied by electron microscopy and spectroscopic techniques. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F43.00012: Understanding Segregation Processes in Blends of Bottlebrush-Linear Polymer Thin Films Indranil Mitra, Xianyu Li, Stacy L. Pesek, Boris Makarenko, Brad S. Lokitz, David Uhrig, John F. Ankner, Rafael Verduzco, Gila E. Stein Bottlebrush polymer thin films have potential to generate surface coatings for a variety of applications ranging from tailored surface wettability and adhesion, antifouling surface coatings and self-assembled photonics. In this study, we examined the phase behavior for athermal blends of bottlebrush polystyrene (PS) and linear deuterated polystyrene (dPS) in thin films. The bottlebrush loading was 10\% by volume, and the ratio of linear dPS chain length to bottlebrush PS side chain length was systematically varied in the range of $\alpha = 0.3-41$. The depth-dependent concentration of bottlebrush was measured using dynamic secondary ion mass spectroscopy. When $\alpha < 2$, the bottlebrushes are dispersed throughout the film thickness with a slight excess at the free surface and substrate interface. When $\alpha > 8$, the bottlebrushes are depleted from the interior of the film and segregated at the interfaces. This behavior is consistent with wetting and dewetting transitions at a melt/brush interface and entropic attraction of highly branched polymers to surfaces. This work demonstrates that brushlike surfaces and interfaces can be generated in a linear polymer film through spontaneous, entropy driven segregation of properly designed bottlebrush additives. [Preview Abstract] |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F43.00013: Using $\beta $-NMR to Measure Surface Segregation of Short Chains in Binary Blends of Polystyrene Iain McKenzie, David L. Cortie, Chad R. Daley, Pendar Mahmoudi, Nasser M. Abukhdeir, Mark W. Matsen, Robert F. Kiefl, C. D. Philip Levy, W. Andrew MacFarlane, Ryan M. L. McFadden, Gerald D. Morris, Matthew R. Pearson, James A. Forrest A problem of significant interest in the studies of polymers at interfaces is the segregation of short chain polymers to the interface in a system with both long and short chains. It is difficult to study the segregation as methods used to introduce contrast between short and long chains often have an effect larger than that due simply to the different chain lengths. We have shown that $\beta $-detected nuclear spin relaxation of $^{\mathrm{8}}$Li$^{\mathrm{+}}$ can distinguish the two chains sizes without the need for any label. This, combined with the depth profiling ability of the technique, means we can determine the relative concentration of short and long chains in a blend without the need to introduce another perturbing factor. We have performed experiments on a 50/50 blend of 627 kg/mol and 0.980 kg/mol polystyrene-d8 and at depths ranging from 2.5 to 79 nm from the free surface. The results show definite surface segregation of short chains to the free surface. We theoretically examine the segregation of short chains to the surface of the binary blend using self-consistent field theory (SCFT). The model used in the calculation assumes an incompressible melt consisting of the freely-jointed polymer chains with either $N_{\mathrm{s}}$ or $N_{\mathrm{l}}$ monomers. [Preview Abstract] |
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