Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W19: Nonequilibrium Structures of Polymeric Materials IFocus Recordings Available
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Sponsoring Units: DPOLY GSNP DSOFT Chair: Shiwang Cheng, Michigan State University Room: McCormick Place W-185A |
Thursday, March 17, 2022 3:00PM - 3:12PM |
W19.00001: Anomalous Glass Transition Breadths of Random Ionomers Han Umana, Trung D Nguyen, Jeremy Wang, Monica Olvera De La Cruz, John M Torkelson Efficient control over the thermal behavior of polymeric materials is desired for shape memory and acoustic dampening materials. In this work, we report a simple yet versatile approach to tune the glass transition range of a family of random ionomers via their side-chain structure and charge fraction. We analyze random ionomers of poly (3-sulfopropylmethacrylate-ran-methyl methacrylate) by differential scanning calorimetry (DSC) and find that beyond a critical charge fraction (fq) the glass transition temperature shifts to higher values and the glass transition breadth gets broadened significantly in response to thermal treatment. Non-equilibrium Molecular Dynamics (MD) simulations elucidate the roles of several key design parameters of the ionomers near the glass transitions, specifically the importance of the charged species and the polymer side chain. Analysis of energetics and structural relaxation dynamics reveals the effects of strong ionic correlations in a low dielectric constant medium and the side chain mobility on the transition from liquid to supercooled liquid. As fq increases beyond a critical value, the local ionic concentrations are more heterogeneous, and the distribution of the ionic cluster sizes gets broader at the transition point. The resulting enhanced degree of compositional and dynamic heterogeneity leads to a shift in the supercooled liquid transition towards higher temperatures. |
Thursday, March 17, 2022 3:12PM - 3:24PM |
W19.00002: Decoding the Conditions for Aperiodicity in Complex Diblock Micelle Packings via Breakout Crystallization Andreas J Mueller, Aaron P Lindsay, Ashish Jayaraman, Timothy P Lodge, Mahesh K Mahanthappa, Frank S Bates Over the past decade it has been well documented that bulk particle forming diblock copolymer melts will often self-assemble into a metastable dodecagonal quasicrystal (DDQC), possessing crystallographically forbidden 12-fold rotational symmetry, en route to equilibrium Frank–Kasper phases. The conditions for this behavior, however, remain obscure. To this end we designed a crystalline amorphous poly(ethylene oxide)-block-poly(2-ethyl hexylacrylate) diblock copolymer that undergoes breakout crystallization. Melting the semicrystalline state enabled direct access to a supercooled liquid-like packing (LLP) of particles far below the melt order-disorder transition temperature. Critically, this mode of access to the LLP state purely on heating avoids unwanted phase nucleation associated with traversing higher temperature regions of the phase space. Extensive temperature-dependent synchrotron small angle X-ray scattering demonstrated that this pure LLP state alone gives rise to the DDQC– avoiding any nucleation of the high-temperature body centered cubic particle packing. Accordingly, we cast the DDQC as an Ostwald-step between LLP and the equilibrium Frank-Kasper σ phase, representing the kinetically favored diblock particle packing polymorph when growing σ from LLP. |
Thursday, March 17, 2022 3:24PM - 3:36PM |
W19.00003: Spin-coated mesoporous thin-film quantum materials from block copolymer self-assembly Fei Yu, Randal P Thedford, Ulrich Wiesner Superconducting niobium carbonitride thin films are prepared from the self-assembly of block copolymers (BCPs) and niobia sol nanoparticles. The fabrication pathway starts with spin-coating the hybrid solution of an amphiphilic triblock terpolymer poly(isoprene-b-styrene-b-ethylene oxide) (ISO) with its hydrophilic PEO block swollen by the niobia sol. The mesostructured hybrid film undergoes heat treatment in air to become a mesoporous niobium oxide. Following treat treatments in ammonia and carburizing gas (mixture of methane, hydrogen, and nitrogen) at up to 1000 °C, superconducting niobium carbonitride thin films are obtained, showing a superconducting transition temperature (Tc) at 13 K. Grazing-incidence X-ray scattering at both small and wide angles confirms controllable mesoporosity, nanocrystallinity of the superconducting film. The granular nature of the materials results in a sharp rise in resistivity before superconducting transition, which is associated with a thermally activated conduction mechanism. The upper critical field performance of such BCP-templated mesoporous superconductors exceeds that of bulk materials. For nanofabrication of microelectronic devices, this solution-processable materials system is amenable to patterning through common photolithographic technique. Patterned thin strips are also superconducting, albeit with a lower Tc. The network mesostructure from BCP self-assembly together with patternable dimensions through lithography may lead to discovery of new physics emergent form structural topology, while the large surface area could enjoy potential use in sensing and detection applications. This unique pathway from BCP self-assembly to mesostructured superconductors serves as an emergent technology for novel quantum materials fabrication. |
Thursday, March 17, 2022 3:36PM - 3:48PM |
W19.00004: Phase formation in architecturally asymmetric coil-brush diblock copolymers McKenzie L Coughlin, Lucy Liberman, Jerrick Edmund, Frank S Bates, Timothy P Lodge Diblock copolymers are known to self-assemble into a variety of structures, and the effects of molecular weight, volume fraction, compatibility between the blocks, and block chemistry have been extensively studied. The effect of architectural differences between the blocks on phase behavior are less well understood. In this work, five sets of norbornene-based coil-block-bottlebrush copolymers with high conformational asymmetry were synthesized using grafting-through living ring-opening metathesis polymerization with poly(norbornene-exo,exo-dimethyl ester) as the coil block and bottlebrush blocks containing oligomeric poly(ethylene-alt-propylene) side chains. The consequences of changing the volume fraction of the coil block, and the side chain length in the brush block, were studied as a function of temperature using small-angle X-ray scattering (SAXS). Increasing the side chain length of the brush block shifts the phase diagram towards higher compositions of the coil block, while retaining the classical lamellar, gyroid, and cylindrical morphologies. Small-amplitude oscillatory shear rheology was used to estimate the statistical segment lengths of each block, where the conformational asymmetry increases with increasing side chain length. |
Thursday, March 17, 2022 3:48PM - 4:00PM |
W19.00005: Priming Self-Assembly Pathways by Stacking Individual BCP Layers Sebastian T Russell, Kevin Yager, Masafumi Fukuto, Suwon Bae Block copolymers (BCPs) are a versatile class of macromolecules that spontaneously form well-defined nanostructured arrays that can vary in shape and periodicity. Nonequilibrium assembly strategies hold considerable promise to expand the library of self-assembled nanoscale patterns through exploiting self-assembly’s adaptive nature. We developed a pathway priming strategy where BCP initial configurations (i.e., the initial spatial distribution of chains) are engineered to be structured in nontrivial ways. This is accomplished by sequentially flow coating distinct BCP materials to form layered initial states. Allowing self-assembly to proceed from these non-equilibrium initial states gives rise to a succession of previously inaccessible intermediate states We present a library of exotic motifs non-native to conventional BCP thin-films, including vertical perforated lamellae, aqueduct (lines-on-dots), parapet (dots-on-lines), and criss-cross lamellae networks. Pathway priming leverages self-assembly processes that are manifestly pathway-dependent and expand the accessible range of structures, in turn enabling material properties that surpass their equilibrium analogs. |
Thursday, March 17, 2022 4:00PM - 4:12PM |
W19.00006: Controlling Nano- and Micro-Scale Ordering in Biomimetic Non-Equilibrium Hydrogels Elisabeth C Lloyd Natural materials possess hierarchical ordering on a range of length scales, making these materials highly difficult to mimic. Triblock copolymers composed of hydrophobic end blocks and a hydrophilic midblock will self-assemble on contact with water, but the resulting hydrogel network only possesses nano-scale ordering and is very brittle when produced using processing methods that result in thermodynamic structures. Here, we propose a new, non-equilibrium method where the triblock copolymer is first dissolved in a water-miscible solvent favorable for both polymer blocks, then transferred to a mold and immersed in a water bath. The rapid diffusion of solvent results in hydrogels with porous microstructures, leading to remarkably soft and extensible hydrogels with both nano- and micro-scale structures. The presented work will highlight the impact of block copolymer molecular weight, relative block composition, solvent, and polymer solution concentration on the final structure of the hydrogels. Interestingly, we will demonstrate parameters that influence the porous microstructure without strongly affecting the nanostructure, allowing us to produce hydrogels with tunable properties and a hierarchical microstructure reminiscent of natural tissues. |
Thursday, March 17, 2022 4:12PM - 4:24PM |
W19.00007: Melt-processed polyethylene nanofilms via layer multiplying coextrusion: Exploring scaling laws relating tensile properties to intrinsic and extrinsic factors Dayne A Plemmons Polymer nanofibers typically show a sharp rise in moduli and strength below some critical diameter (~100nm to 10µm). It has been hypothesized that a combination of increased molecular orientation and decreased surface flaws contribute to the observed scaling laws. However, relations for polymer nanofibers have come primarily from electrospun fibers where the diameters of the fibers are directly linked to chain orientation via extensional flow parameters. Thus, surface effects impacting deformation in the confined state may be difficult to fully decouple. Here, we use an alternative approach to produce nanofilms of high-density polyethylene (HDPE) of varying thickness and crystalline morphology. The melt-based process relies on coextrusion of HDPE with a sacrificial layer, ethylene vinyl alcohol (EVOH). Layers of varying dimension are achieved using a series of layer multiplying (LM) dies which split and stack the melt flows. After solid-state uniaxial orientation of the extruded composite, the EVOH layers are selectively dissolved to yield HDPE nanolayers. Independent control of the molecular orientation (via extent of uniaxial orientation) and layer dimension (via number of LM dies) allows a platform to study the intrinisic and extrinsic factors dictating tensile properties. |
Thursday, March 17, 2022 4:24PM - 5:00PM |
W19.00008: Entropic partitioning and entropy-enthalpy compensation (EEC) effect in relaxation of nanopatterned polymer blend and nanocomposite films Invited Speaker: Alamgir Karim Surface textured polymer nanocomposite films are utilized in many device applications, therefore understanding the relaxation behavior of such films is important. By imprinting methods, we are able to create nanopatterns of different polymer mixtures and polymer nanocomposite (PNC) films with entropy driven differential segregation of components into patterned regions characterized by a partition coefficient, K and associated free energy of mixing gain or loss. We study slumping of imprinted polymer grafted nanoparticle (PGNP) systems, high molecular weight, block copolymer systems under direct immersion annealing (DIA) in solvent mixture, and cyclic polymer systems compared to linear ones. These differential partitioning results are also extended to polymeric blend systems of disparate molecular weight. By extending an in-situ wrinkle relaxation method, we observe that the thermal stability of wrinkled PNC films, both above and below the glass transition temperature (Tg) is proportional to film’s NP (polymer grafted and bare) concentration, with a slope that changes sign at a compensation temperature (Tcomp), determined to be in the vicinity of the film’s Tg. This provides unambiguous confirmation of entropy-enthalpy compensation (EEC) as a general feature of PNC films, implying that the stability of PNC films changes from being enhanced to becoming diminished by simply passing through this characteristic temperature, a phenomenon having evident practical ramifications. We suggest EEC will also arise in films where residual stresses are associated with the film fabrication process, relevant to nanotech device applications. |
Thursday, March 17, 2022 5:00PM - 5:12PM |
W19.00009: Supramolecular structures of alternative polymer-nanoparticle hybrids Shalin Patil, Ruikun Sun, Shiwang Cheng, Xiaobing Zuo, Xuehui Dong, Dongdong Zhou Through covalently bonding polymer blocks with small-size nanoparticles, the alternative polymer-nanoparticle hybrids can assemble into unprecedented supramolecular nanostructures due to the interparticle interactions. In this contribution, we investigate the formation of the supramolecular structure of linear alternating polystyrene (PS)-polyhedral oligomeric silsesquioxane (POSS) polymer hybrids (LAPH), through a combination of small-angle x-ray scattering (SAXS) and rheology. Clear clustering with average sizes of 2-8 POSS particles is observed through SAXS, confirming the strong tendency for nanoparticle aggregation. The linear rheology shows a very weak modulus plateau at the intermediate time scale and clear evidence of gelation at the long-time limit. Importantly, the modulus plateau is much smaller than the prediction of intra-chain nanoparticle association, implying the formation of inter-connected flower-like supramolecular structures of LAPH. These observations highlight nanoparticle-nanoparticle association as an alternative way to control the nanostructure formation. |
Thursday, March 17, 2022 5:12PM - 5:24PM |
W19.00010: A Meso-scale Simulation Study of Short-range Morphologies and Properties of Thermoplastic Polyurethane Affected by Graphene Nano-fillers under External Flow Sunsheng Zhu, Shaghayegh Khani, Joao M Maia Embedding nanofillers into polymers is crucial to improving the engineering properties of these materials. Recent computational approaches have paved the way for bridging the gap between the microstructure and macroscopic properties of materials. Our group has performed mesoscale Dissipative Particle Dynamics simulations to investigate the effect of incorporation of Graphene Nanosheets (GNs) on morphologies and mechanical properties of Thermoplastic Polyurethane (TPU). In particular, we have investigated the effects of local interactions, compositions, and chemistry of components on the final morphologies of materials. Our observations show that GNs can potentially act as a nucleating agent leading to crystallization of TPU at nanosheet surface. These crystalline domains connected with regions of soft segments are speculated to be the morphological origin of experimentally observed enhancements in mechanical properties. Under quiescent conditions, Flory-Huggins χ parameters between hard-soft segments, TPU compositions, and surface chemistry of GNs are critical factors dictating final morphologies. Additionally, the simple shear flow is applied to investigate the effect of shear rate on final morphologies. Our findings can benefit the design and fabrication of TPU nanocomposites. |
Thursday, March 17, 2022 5:24PM - 5:36PM |
W19.00011: Non-diffusing melts of 3-dimensional architectured polymers: giant molecules and soft-nanoparticles, and the boundary of the liquid-solid transition Gengxin Liu The extreme architecture deviating from the 1-dimensional chain would be a 3-dimensional soft-cluster. Two experimental cases, giant molecules and soft-nanoparticles, as well as coarse-grained soft-clusters by molecular dynamics simulation. Giant molecules have been precisely synthesized, having 16 or 24 POSS building blocks chemically linked by short, flexible chains. Of 25 and 38 kg/mol respectively, they show different dynamics above Tg: one is liquid while the other is solid-like. We also use microemulsion polymerization to synthesize series of nanogels to act as soft-nanoparticles. We propose an equation to describe their relaxation time as a function of diameter and crosslinking degree. It can describe the critical diameter, ranging from 5 to 21 nm, as a function of crosslinking degree. Soft-nanoparticles smaller than this critical diameter can relax in melt, while larger than it cannot relax. The critical diameters may serve as the boundary between thermal molecular or macromolecular domains and athermal colloidal domain, and can be unified as the number of basic moving units in the 3-dimensional architectured polymers. Recent molecular dynamics study further confirms this and suggests its connection to the concept of cooperation during glass transition. |
Thursday, March 17, 2022 5:36PM - 5:48PM |
W19.00012: Memory effect in simulations of asymmetric diblock copolymers under thermal processing Yang Yang, Robert A Wickham, Anchang Shi Recent experiments [Kim et al. Science 356,520(2017); PNAS 115,847(2018)] observed that the temperature protocol used to heat and cool an asymmetric diblock copolymer from its disordered micelle liquid state to its ordered micelle crystal phase, and back, can influence which ordered phase is found. This suggests some memory of the initial ordered micelle phase is preserved in the disordered micelle state. To develop an understanding of this memory effect, we perform simulations of a time-dependent Landau-Brazovskii model, which has stability regions for disorder, BCC, FCC, as well as Frank-Kasper phases. Our protocol is to equilibrate a low-temperature ordered micelle phase, rapidly heat to just above the order-disorder transition, anneal for a time tH, then quench back to the low temperature and observe the time, tL, it takes for the ordered phase to (re-)form. For small tH, we find that the ordered phase re-forms quickly (tL is small), regardless of whether the original ordered phase is stable or metastable. We measure tL as a function of tH and find a threshold tH above which the system remains in the disordered micelle liquid over our (long) simulation time. We examine trends of this memory effect as we move around the low temperature region of the phase diagram. |
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