Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P54: Tuning Polymer Sequence and ArchitectureFocus
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Sponsoring Units: DPOLY DBIO Chair: Charles Sing Room: BCEC 254A |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P54.00001: Polymer chain sequence effects on the glass transition William Drayer, David Simmons Progress in synthetic chemistry over the last 20 years has opened the door to synthesis of polymers with an increasing spectrum of monomer sequence control, ranging from gradient copolymers to peptoids. In many of these polymers as in sequence non-controlled polymers, the glass transition plays a central role in dynamic, mechanical, and transport properties. However, the effect of sequence on the glass transition remains poorly understood. Here we employ molecular dynamics simulations of sequence controlled glass-forming liquids to quantify the effect of sequence on glass transition behavior. Results indicate that sequence can have a profound impact on Tg. Ultimately, we explore the transition from sequence effects to interface effects on Tg as monomer block size increases to the phase-separating limit. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P54.00002: Investigation of Monomer Segment and Salt Distributions in Self-Assembled, Tapered Block Polymer Electrolytes Priyanka Ketkar, Thomas H Epps Tapered block polymers (TBPs) contain modified monomer segment distributions (e.g., gradient or random copolymer regions) at the junction between two homogeneous blocks. Nanostructured polystyrene-block-poly(oligo-oxyethylene methacrylate) TBP electrolytes recently have been shown to exhibit improved ionic conductivities, shear moduli, and processibilities in comparison to their conventional block polymer analogues; however, the microscopic characteristics of TBPs that impart these enhanced properties are unknown. We are studying the nanoscale distribution of monomer segments and lithium salts in normal-, inverse-, and random-tapered TBPs via X-ray and neutron reflectivity, and we are correlating these distributions to the ionic conductivity (via AC impedance spectroscopy) and glass transition temperature (via differential scanning calorimetry) of the materials. By probing the effects of the tapered architecture on ion transport, we can guide the rational design of higher-performance polymer electrolytes. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P54.00003: Coherent States Field Theory Simulations for Supramolecular Multiblock Copolymers Daniel Vigil, Kris T Delaney, Glenn Fredrickson We present simulation results for a binary mixture of telechelic polymers that can reversibly bond to the opposite species to form multi-block copolymers. Traditional auxiliary-field (AF) polymer field theory can neither accurately nor efficiently simulate the telechelic system because of the challenges of counting an infinite number of possible reaction products. Instead, we extend a “coherent states” framework (CS), originally due to Edwards and Freed, to a form that automatically accounts for all reaction products. A previously reported algorithm for simulating CS theories did not converge in ordered block copolymer microphases, so new algorithms were developed for this work. We verify our methods against the classic diblock copolymer system and present new results for the phase behavior of binary telechelic polymer mixtures. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P54.00004: Miscibility Enhancement in Polyisoprene-Polyolefin Block Copolymers Sravya Jangareddy, Richard Alan Register Polydienes and polyolefins generally show limited compatibility (high interaction energy density, X). We investigate the thermodynamic interactions in symmetric amorphous polydiene-polyolefin block copolymers composed of polyisoprene (PI) and hydrogenated medium-vinyl polybutadiene (hPB). The regular solution model suggests that styrene units (S), given the higher solubility parameter of polystyrene, can boost inter-block miscibility when incorporated in small amounts into the hPB block via random copolymerization (hSBR). Block and “block-random” copolymers were prepared by anionic polymerization, followed by selective saturation of the butadiene units. Diblock copolymers with no S (PI-hPBs) exhibited an interaction energy density of 0.81 MPa, after correcting the measured value of X for the imperfect selectivity of the hydrogenation catalyst. A selectively saturated block-random copolymer with ~10 wt% styrene in the random block (PI-hSBR10) exhibited a measured X of 0.30 MPa, which is lower than the measured X (uncorrected) of a PI-hPB diblock copolymer (0.52 MPa) with identical levels of block saturation, indicating a strong enhancement in compatibility. Further work delineating the effect of S content on inter-block miscibility is underway. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P54.00005: Theory of interchain packing and dynamics in associating copolymer liquids Ashesh Ghosh, Kenneth S. Schweizer We employ liquid state theory to explore the role of attractive groups regularly co-polymerized in a chain backbone on the structure and dynamics of unentangled polymer liquids that can form thermoreversible bonds. Significant progress has been made by others using coarse-grained polymer physics models based on phenomenological input parameters that quantify the sticker association energy and bond dissociation lifetime. However, these approaches are not force-based, and do not include molecular-scale information about packing correlations and its consequences on sticker clustering, dynamic bond formation and dissociation events. Based on the microscopic forces and single chain structure as input, we combine equilibrium integral equation theory and generalized Rouse models that capture local caging and physical bond formation to study the latter aspects and related issues such as emergent elasticity. The timescale for stickers and non-stickers that define the coupled activated bond breakage and local cage reorganization processes, and the correlation between structure and dynamics, are studied as a function of experimentally controllable variables such as polymer volume fraction, fraction of stickers, strength and spatial range of the attractive interaction, and chain length. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P54.00006: Morphology Transitions of Linear S1I1S2I2 Tetrablock Copolymers at the Symmetric Overall Volume Fraction. Seonghyeon Ahn, Bin Zhao, Chao Duan, Weihua Li, Jin Kim Block copolymers have been extensively investigated because of their various nanostructures. For a simple diblock copolymer, hexagonally packed cylindrical microdomains have been found with volume fractions of one block (fA) having 0.2~0.35, while gyroid microdomains were observed at fA having ~0.35. So, gyroid and cylindrical microdomain could not prepare pore volume larger than this value (~0.35) in diblock copolymers, because lamellar microdomains are expected. Here, we investigated morphology transitions of linear tetrablock copolymers of polystyrene-block-polyisoprene-block-polystyrene-block-polyisoprene (S1I1S2I2) by varying volume fraction of PI1 block (fPI1), while maintaining the symmetric volume fraction of total PS blocks and PI blocks (fPS1+fPS2: fPI1+fPI2 = 1:1). An interesting sequence of morphology transitions was observed as fPI1 was increased: lamellae→asymmetric lamellae→hexagonally packed PI-cylinders→double gyroid with PI-network domains→short-period lamellae. It is particularly interesting that cylindrical and gyroid morphologies were observed in linear block copolymers with symmetric overall volume fraction. |
Wednesday, March 6, 2019 3:42PM - 4:18PM |
P54.00007: Genetically encoded biomaterials that self-assemble across multiple length scales Invited Speaker: Ashutosh Chilkoti Elastin like polypeptides (ELPs), composed of repeats of VPGXG pentapeptides that recur in all tropoelastin sequences, are the best studied class of peptide polymers that exhibit lower critical solution temperature (LCST) phase behavior in water, and these polymers have enabled innovative approaches to nanoparticle self-assembly, cancer therapy, regenerative medicine and protein purification. I will discuss how this class of intrinsically disordered polypeptides is an enormously mutable model system that has allowed us to probe the sequence origins of aqueous phase behavior in polypeptides, leading to the identification of sequence heuristics for the de novo design of peptide polymers that exhibit aqueous phase behavior. I will also discuss how we have used ELPs as a template to encode higher order, hierarchical self-assembly into macroscopic biomaterials by modulating the degree of order in these intrinsically disordered polymers, and by genetically encoding a post-translational modification into an ELP. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P54.00008: Multicompartment Copolymer Micelles: effects of chain architecture, composition and interaction strength Boyuan Yu, Abelardo Ramirez-Hernandez, Juan De Pablo Controlling the self-assembly of block copolymers in solution will enable engineering of multicompartment micelles (MCMs), with target structures for applications including drug delivery, or stimuli-responsive carriers. While extensive research has been carried out on amphiphilic di-block copolymers, little is known about the phase behavior of multiblock polymers in solution. In this work, a mesoscopic approach is used to explore the self-assembly behavior of tetrablock copolymers with varying architectures, block sequences, compositions, and interaction strengths. Our results are summarized in phase diagrams that reveal the influence of different parameters on the morphologies of MCMs. The results presented in this work could provide a useful guide for the synthesis of new MCMs. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P54.00009: Interpreting the hierarchical morphology of ABC miktoarm terpolymers using self-consistent field theory Jyoti Mahalik, Hyeyoung Kim, Matthias ML Arras, Weiyu Wang, Sergey Chernyy, Kunlun Hong, Gregory S Smith, Bobby G Sumpter, Thomas Russell, Rajeev Kumar Miktoarm stars based on poly(cis 1,4-isoprene), poly(styrene) and poly(2-vinylpyridine) (ISV) were studied using small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), transmission electron microscopy (TEM) and self-consistent field theory (SCFT). Array of morphologies are observed for different composition of ISV-x (where x is the volume ratio of V:I and I:S are kept fixed at 1:1). Typically, TEM and SAXS are sufficient to characterize the bulk morphology of diblock copolymers. But for ABC miktoarms additional characterization tools are necessary. Picking one system from the array of samples, we have demonstrated how self-consistent field theory (SCFT) can guide the interpretation of hierarchical morphology. The SCFT studies also provides guidelines for deuterating the correct arm prior to SANS investigation. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P54.00010: Miktoarm Stars via Grafting-Through Copolymerization: Self-Assembly and the Star-to-Bottlebrush Transition Joshua Lequieu, Adam E Levi, Christopher M Bates, Glenn Fredrickson The grafting-through copolymerization of two distinct macromonomers via ring-opening metathesis polymerization is typically used to form random or diblock bottlebrush polymers with large total backbone degrees of polymerization (NBB) relative to that of the side-chains (NSC). Here, we demonstrate that Grubbs-type chemistry in the opposite limit, namely NBB << NSC, produces well-defined materials with excellent control over ensemble-averaged properties, including molar mass, dispersity, composition, and number of branch points. The dependence of self-assembly on these molecular design parameters was systematically probed using small angle X-ray scattering and self-consistent field theoretic simulations. Our analysis reveals that two-component bottlebrush copolymers with small NBB behave like miktoarm star polymers. The star-to-bottlebrush transition is quantifiable for both random and diblock sequences by unique signatures in the experimental scaling of domain spacing and simulated distribution of backbone/side-chain density within lamellar unit cells. These findings represent a conceptual framework that simplifies the synthesis of miktoarm star polymers when dispersity in molar mass and composition can be tolerated. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P54.00011: Exploring the Phase Behavior of Poly(styrene)-block-Poly(dimethylsiloxane) Brush Block Copolymers Huafeng Fei, Benjamin M Yavitt, Xiyu Hu, Gayathri Kopanati, Alexander Ribbe, James J Watkins We report the experimental phase behavior of a family of poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) bottlebrush block copolymers (BBCPs). The BBCPs rapidly self-assemble into microphase separated morphologies after mild thermal annealing. By systematically tuning architectural parameters such as volume fraction (fPS), side chain length (Nsc), and overall backbone length (Nbb), a diverse array of morphologies were resolved and a phase map was constructed. We identify ordered lamellar, cylindrical, and deformed spherical morphologies. The lamellar window spans a wide range of fPS from 0.40 – 0.75 when Nbb is short and Nsc of PS and PDMS are equal. However, order-order transitions to cylindrical and spherical morphology are observed as Nbb increases and Nsc becomes asymmetric. The self-assembly and phase transitions are described by a contrast between both the backbone and side chain flexibility of the PDMS and PS blocks. These findings provide an insight into the rich phase behavior of this architecturally complex class of macromolecules and provide direction towards the future fabrication and design of BBCP templated functional materials. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P54.00012: Molecular Architecture Driven Self-Assembly of Block Copolymers Shifeng Nian, Zihao Gong, Liheng Cai Block copolymers composed of immiscible polymeric blocks self-assemble to a rich variety of ordered nanostructures that find applications in many technologically important realms. Among different types of block copolymers, linear-bottlebrush-linear (LBBL) triblock copolymers present an emerging platform for creating multifunctional nanostructures. However, little is known about the fundamental mechanism of their self-assembly. We synthesize a series of LBBL polymers with precisely controlled anisotropy of bottlebrush block and weight fraction of the linear block. Characterizing morphology and microphase separation of the self-assembled nanostructures, we find that the molecular anisotropy of bottlebrush is sufficient to drivee LBBL polymers self-assemble to long range ordered nanostructures with exceptionally large domain sizes inaccessible by existing copolymer systems. Our results suggest that the self-assembly of LBBL polymers is driven by their molecular architecture rather than detailed chemistry. Such understanding may enable discovery of polymeric nanostructures with unpreceded properties and multifunction. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P54.00013: Strong Induced Chiroptical Effects in Light Emitting Polymer Blends Jessica Wade, L Wan Current OLED displays rely on a circularly polarised (CP) filter to enhance contrast by |
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