Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F52: Architectural Design of Polymers I: Assembly, Adsorption and DynamicsFocus
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Sponsoring Units: DPOLY Chair: Joshua Sangoro, Univ of Tennessee, Knoxville Room: LACC 512 |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F52.00001: Morphology Study of Poly(3-dodecylthiophene)-based Block Copolymers Depending on Regioregularity Jin-Seong Kim, Junghun Han, Jonathan Coote, Youngkwon Kim, Gila Stein, Bumjoon Kim Phase separation of conjugated–amorphous block copolymers (BCPs) is mainly determined by interplay between Flory–Huggins interaction (χ), liquid crystalline (LC) interaction and crystallization. In particular, the strong LC interaction and crystallization can provide morphological richness, but often suppress the formation of ordered domains. Therefore, tuning the LC and crystalline behavior can be a key to form desirable nanostructures of conjugated–amorphous BCPs. Here, we studied morphologies of poly(3-dodecylthiophene)-block-poly(2-vinylpyridine) (P3DDT-b-P2VP) depending on regioregularity (RR), which determines the LC and crystalline behavior of conjugated polymer. Above the melting temperature, we observed a clear transition in domain spacing of ordered structures as the RR decreased from 94% to 85%. This could be attributed to a change in chain-packing configuration due to the reduction in LC interaction. Upon cooling, the BCPs with 94% of RR showed morphology deformation driven by strong crystallization whereas the melt morphologies of lower RR BCPs were almost not affected. We will discuss the details of other morphological features of RR-controlled P3DDT-b-P2VP polymers at different P2VP volume fractions. |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F52.00002: Tuning Segregation Strength with Sequence-Defined Polypeptoid Diblock Copolymers Anastasia Patterson, Adrianne Rosales, Rachel Segalman Block copolymers with tunable compatibility enable direct control over segregation strength, a key driving force for self-assembly. The miscibility between blocks of an AB copolymer is increased by incorporating B-like units into the A block, and while tapered profiles from semibatch methods have shown compatibilizing effects, fully sequence-defined polymers offer a unique opportunity to control both the composition and distribution of comonomers. We have synthesized polypeptoid–polystyrene diblock copolymers, where the polypeptoid block has styrene-like units precisely incorporated with ether comonomers via high-yielding solid-phase synthesis. First, as styrene-like groups are added to the polypeptoid, the order–disorder transitions (ODTs) are lowered by more than 30 °C. Following this, compatibilizing units are incorporated in different sequences, such as tapered from the block junction or distributed evenly. Within this set of materials with identical composition but different sequence, the ODTs vary by 15 °C. It is expected that sequence affects the effective interaction parameter, chi, which can be quantified using interfacial segregation. These studies demonstrate the ability for sequence control to tune the phase stability of self-assembling block copolymers. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F52.00003: Physical origin and the architectural pathway to the “inverted” phases of the micro-segregated diblock copolymers Victor Pryamitsyn, Monica Olvera De La Cruz Self-assembly of block copolymers has received significant attention for its potential modern lithography applications due to the ability to achieve morphologies with dimensions in the range of 10-20 nm. However, the morphology of “conventional” diblock copolymers are limited: lamellar morphologies are usually restricted to nearly symmetric widths of the domains, and hexagonal and BCC morphologies always form cylinders and spheres from the minority phase. Producing highly asymmetric lamellae or “inverted” hexagonal phases where the minority phase goes into the outside matrix and the majority phase forms inside cylinders remains an important technological challenge. Recently, such asymmetric and inverted phases were experimentally observed in ionic copolymers, copolymers with hydrogen bonds, and blends of such copolymers. We have developed a set of Self-Consistent theoretical models in conjunction with coarse-grained Monte-Carlo modelling which explain the appearance of the observed “inverted” phases. These models recognize the role of ionic interactions and hydrogen bonding in the formation of such phases and suggest optimal architectural strategies for designing copolymers forming the “inverted” microphases. |
Tuesday, March 6, 2018 11:51AM - 12:27PM |
F52.00004: Architectural effect of polymer nanoparticles on block copolymer ordering Invited Speaker: Joona Bang Much of the focus on block copolymer/nanoparticle (BCP/NP) nanocomposites has been on the passive dispersion of NPs inside the BCP matrix. However, recent studies have looked into the active role of NPs in controlling the orientation of BCP thin film microdomains by an entropy-induced segregation of the NPs to the substrate and/or free surface. Notwithstanding the recent progress in understanding such systems, these nanocomposite systems are not yet fully understood because of the complex mechanism that arises when these two moieties meet. In this work, we employed organic nanoparticles (ONPs) in the form of star polymers and single chain nanoparticles (SCNPs) are used as fillers in BCP/ONP nanocomposite thin films to induce perpendicular microdomains without any substrate treatment. The nonselective ONPs for both blocks of BCP neutralize the substrate and the free surface via an entropy-driven boundary surface segregation process, which differs markedly from the conventional neutralization process relying on surface chemistry. To examine the architectural effect of ONPs for surface segregation, neutral star polymers with ∼30, 21, and 6 arms and SCNPs are used as fillers in PS-b-PMMA thin films in an attempt to produce perpendicular microdomains. Consequently, it was observed that ∼30- and 21-arm star polymers and SCNPs, which may behave like hard particles having excluded volume interactions with host BCPs, effectively induced perpendicular microdomains, while soft particle-like 6-arm stars led to morphological compatibilization with BCPs. The versatility of this method is evidenced by its applicability to both cylinder and lamellae systems. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F52.00005: Linear Viscoelasticity of Lamellae-Forming Brush Block Copolymers Benjamin Yavitt, Huafeng Fei, H. Winter, James Watkins We report the linear viscoelastic behavior of symmetric volume fraction poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) brush block copolymers (BBCP) with side chain lengths below the entanglement molecular weights over a range of overall backbone degree of polymerizations. The BBCPs readily self-assemble into microphase separated lamellar morphologies upon thermal annealing. The increasing backbone length results in a direct increase of the lamellar spacing from 29 to 90 nm. BBCPs are thermorheologically simple and maintain liquid-like rheological response even up to large molecular weights (~500 kg/mol). Scaling relationships in the dynamic master curves show power law behavior analogous to un-entangled Gaussian chain dynamics across all measured backbone lengths. The sequence of relaxations from the side chains and backbone are correlated to the overall molecular weight. This study expands upon the understanding of the unique “liquid-like” response of microphase separated BBCPs and their potential processing advantages over conventional LBCP materials. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F52.00006: Evidence for Backbone Flexibility of Bottlebrush Polymers Driven by Low Chi Assembly Daniel Sunday, Alice Chang, Christopher Liman, Eliot Gann, Dean DeLongchamp, Christopher Soles, Mark Matsen, Robert Grubbs Bottlebrush polymers are an intriguing class of materials, with unique properties due to their ability to reach large molecular weights without becoming entangled. Bottlebrush block copolymers (BCPs) are the natural extension of the homopolymer brushes, and systems with lamellar morphology have both larger scaling exponents compared to linear BCPs and higher mobility, enabling fast assembly of lamellae with large pitches. In one example, PLA-b-PS-b-PEO bottlebrushes exhibited unusual scaling behavior where an increase in the PEO backbone length resulted in a decrease in the pitch for BCP lamellae. Using soft X-ray reflectivity and near edge absorption fine structure spectroscopy (NEXAFS) measurements we evaluate how each component is distributed throughout the lamellae to determine the origin of this scaling. The presence of the midblock, PS, at the top surface of lamellae oriented parallel to a substrate is confirmed by both techniques and demonstrates that even for densely grafted bottlebrushes the formation of loops, analogous to linear triblocks, is possible. Self-consistent theory calculations match the experimentally determined component distributions and calculated backbone concentrations also provide evidence of backbone flexibility. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F52.00007: Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush Alice Chang, Tzu-Pin Lin, Byeongdu Lee, Robert Grubbs Grafting density is an important structural parameter that impacts the physical properties of architecturally complex polymers. The physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ Nbbα) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the backbone and side chain conformations. A model is proposed in which the characteristic ratio (C∞), a proxy for the backbone stiffness, scales with Nbb as a function of the grafting density: C∞ ~ Nbbf(z). Understanding the scaling behavior provides valuable insight into conformational changes with grafting density, thereby introducing new opportunities for block polymer and materials design. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F52.00008: Polymerization-Induced Morphology Transitions in Diblock Copolymer/Monomer Blends Robert Hickey In situ polymerization within confined spaces to either fix or template desired structures has found uses in numerous applications, but the process typically destroys the original structure. Here, we present on the polymerization-induced nanostructural evolution of diblock copolymer/monomer blends containing a lamellar-forming diblock copolymer, poly(styrene)-block-poly(1,2butadiene) (PS-1,2PBD) and styrene as the monomer. At high PS-1,2PBD volume fractions (φPS-1,2PBD > 40%), we are able to access lamellar morphologies, and at decreased volume fractions (φPS-1,2PBD ≤ 40%), we achieve a disordered morphology. On polymerization of the styrene within the blends, we are able to induce either a lamellar-to-hexagonal or a disorder-to-hexagonal transition. Interestingly, the order-order and disorder-order transitions occur via an unexpected mechanism in which the polymerized styrene monomer grafts from the pendent vinyl groups on the 1,2PBD. The polymerization of styrene leads to an increase in the overall molecular weight and the PS volume fraction of the PS-1,2PBD copolymer, driving the phase transitions. The work presented here highlights how the in situ process of converting standard linear diblock copolymers to block polymer bottlebrushes drives interesting morphology transitions. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F52.00009: Effects of Copolymer Architecture on the Structure and Thermodynamics of Self-Assembly in Block Copolymer Solutions: a Coarse-Grained Molecular Dynamics Study Michiel Wessels, Arthi Jayaraman Controlling the self-assembly of block copolymers in solution allows us to engineer nanostructured materials for a variety of applications such as drug-delivery, environmental cleanup, rheological modifiers, etc. While extensive past work, experimental and computational, have been focused on self-assembly of linear block copolymers in solutions, much less is known for non-linear architectures such as bottle brushes. In this talk, we present our computational work investigating assembly for a range of polymer architectures (from linear to star to bottle brush) with varying amphiphilic copolymer sequences (diblock and triblock) and compositions (symmetric composition and solvophobic-rich). We motivate molecular dynamics simulations as an effective tool to systematically explore this large design space to elucidate how changing polymer architecture affects the clustering behavior (aggregation number, micelle size and morphology) as well as assembly thermodynamics (unimer to micelle transition) as a function of solvophobicity. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F52.00010: Study of Solution Assembly Behaviors of Regioregularity Controlled P3HT-P2VP Block Copolymers Youngkwon Kim, Jin-Seong Kim, Hyeong Jun Kim, Hyeonjung Park, Junghun Han, Bumjoon Kim In selective solvents, poly(3-hexylthiophene) (P3HT)-based block copolymers (BCPs) assembles into crystallized nanowire (NW) structures in contrast to micelluar (MC) structures from conventional coil-coil BCP. Herein, we demonstrate a transition of NW to MC structures of P3HT-based BCPs as changing of their regioregularity (RR) and thus their crystallinity. We synthesized a series of P3HT-b-P2VP copolymers, of which RR was systemically regulated from 95 to 55% and investigated their solution behavior in binary solvent mixtures. As expected, the well-defined NW structure was produced from the P3HT-b-P2VP with high RR of 95%. Between 80% and 65% of RR, intermediate morphologies between NWs and MCs were observed. When RR decreased, the widths and heights of such quasi-NWs measured by TEM and AFM, respectively, were gradually increased in reverse proportion to reduction of crystallinity analyzed by GIWAXS and DSC measurement. Under 65% of RR, crystallization of the P3HT moiety is sufficiently suppressed so that only MC structures were formed. Therefore, we demonstrate that nanostructures from amorphous MC to crystalline NW can be tailored by RR of the P3HT in solution assembly behaviors. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F52.00011: Structure-Induced Switching of Interpolymer Adhesion by Polymer Chains Adsorbed onto a Planar Solid Justin Cheung, Naisheng Jiang, Mani Sen, Maya Endoh, Tadanori Koga, Masafumi Fukuto, Guangcui Yuan, Sushil Satija, Jan-Michael Carrillo, Bobby Sumpter We report a link between microscopic chain architecture and macroscopic adhesive property of polymer chains adsorbed on solids. Polyethylene oxide (PEO) was used as a model and two different chain conformations of the polymer adsorbed on silicon substrates were prepared. The adsorbed nanolayers consisted of densely packed “flattened chains”, and “loosely adsorbed polymer chains” which cover the flattened chains. Using a custom-built adhesion testing device, we investigated the adhesion properties of bilayers consisting of PEO overlayers atop flattened or loosely adsorbed chains. Results revealed that the flattened chains do not show any adhesive strength even when chemically identical polymer on top is above the melting temperature, while the loosely adsorbed chains exhibit adhesion. Neutron reflectivity and molecular dynamics simulations indicated that loops, whose size is above the threshold for entanglement, formed in the loosely adsorbed chains, bridging free chains and substrate surface. These findings shed light on interfacial structure-property relationships and provide a novel approach for developing adhesive technologies through precise control of interfacial polymer architecture. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F52.00012: Controlling Reinforcement in Polymer Nanocomposites by Changing Rigidity of Adsorbed Chains Mohammed Hassan, Siyang Yang, Pinar Akcora The study of polymer interface in polymer nanocomposites (PNC) has seen considerable attention in the last decade. We investigate the interactions between polymer-adsorbed nanoparticles (NP) and the matrix polymer, and the effect of polymer rigidity on the mechanical properties. In this study, we compare three distinct high glass transition temperature (Tg) polymers, poly(carbonate), poly(methyl methacrylate), and poly(2-vinylpyridine), having different characteristic ratio (C∞), adsorbed on silica NPs and dispersed in the same matrix polymer, poly(ethylene oxide). Our rheology results show that the mechanical response of the PNC decreases with increasing the rigidity of the adsorbed polymer. The storage modulus of the least rigid polymer was found to be 10 times higher than that of the most rigid one at low frequencies. This unusual rheological result is attributed to the adsorbed polymer chains’ conformation on the substrate and the degree of entanglement with the matrix polymer. Rigid polymer tends to have flattened chains on the substrate which limits the interaction with the matrix polymer. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F52.00013: Dynamics of 3-Dimensional Giant Molecules, Clusters of Molecular Nanoparticles Gengxin Liu, Xueyan Feng, Kening Lang, Ruimeng Zhang, Dong Guo, Shuguang Yang, Stephen Cheng The extreme architecture deviating from 1-dimensional chain would be a 3-dimensional cluster. We recently study 3D clusters of molecular nanoparticles in bulk state. Such cluster, a giant molecule, is a new class of soft matter having 3D shapes and composed of chemically linked rigid molecular nanoparticles. |
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