Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R63: Self-Assembly in Polymer Blends and NanocompositesFocus Live
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Sponsoring Units: DPOLY Chair: Gregory Doerk, Brookhaven National Laboratory |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R63.00001: Phase behavior of polymeric microemulsion in ternary A+B+AB blends Russell Spencer, Mark W Matsen Ternary blends of AB diblock copolymers with A and B homopolymers microphase segregate into lamellae (LAM) for copolymer-rich blends and macrophase segregate into A- and B-rich regions for homopolymer-rich blends. Mean-field theory predicts that these regions are separated by three-phase coexistence of the LAM, A-rich, and B-rich phases, which terminates at a Lifshitz critical point. Experiments, however, report that the Lifshitz point is destroyed by fluctuations and that the three-phase coexistence is replaced by a channel of bicontinuous microemulsion (BμE). Using field-theoretic simulations, we show that fluctuations do indeed destroy the Lifshitz point, but that three-phase coexistence continues to exist. However, at high temperatures, the LAM+A+B coexistence predicted by mean-field theory is replaced by BμE+A+B coexistence. We speculate that the single-phase BμE observed in experiments is a result of kinetic trapping as the blend is cooled from the mixed state. |
Thursday, March 18, 2021 8:12AM - 8:24AM Live |
R63.00002: Coarse-grained molecular dynamics simulation study of structure and thermodynamics in blends with hydrogen bonding polymers Arjita Kulshreshtha, Ryan Hayward, Arthi Jayaraman Hydrogen bonding (H-bonding) in polymer blends can lead to the formation of supramolecular polymers whose morphology changes with the number and placement of H-bonding groups along the polymers. In this talk, we will present a molecular dynamics (MD) simulation study to understand morphology and phase behavior in blends with varying number and placement of H-bonding groups. We use our recently developed coarse-grained (CG) model for polymers with directional interactions and study a symmetric blend of two polymers, one with H-bonding acceptor groups and one with donor groups. First, we validate our MD simulation results against phase diagrams from past theoretical work of Fredrickson and coworkers on end associating polymers, for varying H-bonding attraction strength and polymer segregation strength. We then present results in polymer blends for varying H-bonding groups composition (i.e., fraction of monomers with H-bonding groups) and placement (e.g., random vs. regular placement of multiple H-bonding groups, center vs. end placement of a single H-bonding group per polymer). We characterize the blend morphology, domain sizes, and placement of H-bonding groups within the domains as a function of varying H-bonding attraction and polymer segregation strength. |
Thursday, March 18, 2021 8:24AM - 8:36AM Live |
R63.00003: Molecular Dynamics Study of Self-assembly Behavior of Block Copolymer Blend Thin Films Suwon Bae, Kevin G. Yager Thin film blends of equal lengths of cylinder- and lamella-forming diblock copolymers, denoted C and L, adopt morphologies depending on fractional composition of the blend constituents. We investigate the behavior of the thin film blends on neutral substrates that promote vertical domain orientation by means of molecular dynamics simulations. Both cylinders and lamellae coexist in separate regions in a single pattern with comparable fractions and either type of structure gradually disappears from the pattern with decreasing fraction of the corresponding type of copolymer, resulting in a spatially uniform, single type of struture. The domain spacing of cylinders increases with increasing fraction of L while that of lamellae does not nearly change with increasing fraction of C. Cylinders swell with more L despite their equal molecular weights and lamellae split into smaller ones with more C. In addition to the patterns, we study the underlying behavior of the constituent copolymer chains in each morphology and energy barriers between cylinders and lamellae. |
Thursday, March 18, 2021 8:36AM - 8:48AM Live |
R63.00004: Phase behavior of diblock copolymer-homopolymer ternary blends with a compositionally asymmetric diblock copolymer Bo Zhang, Shuyi Xie, Timothy Lodge, Frank Bates The phase behavior of ternary polymer blends comprising poly(cyclohexylethylene) (C) and polyethylene (E) homopolymers and a compositionally asymmetric CE diblock copolymer rich in C was investigated. Blend morphologies and phase boundaries were established using a combination of optical transmission, small-angle X-ray scattering, and small-angle neutron scattering measurements. The locations of ordered phases are shifted significantly towards lower fractions of C homopolymer, compared to previous results from ternary blends with a symmetric diblock copolymer. Conversely, the Scott line of critical points remains virtually unchanged, coincident with the binary blend critical composition. A central finding is that the line of nearly congruent order-disorder transitions is decoupled in composition from that of the Scott line of critical points. This study demonstrates that diblock copolymer compositional asymmetry significantly impacts the ordered phase regime, but has a marginal effect on the region displaying macroscopic phase separation. It also provides useful guidance for tuning interfacial curvature, a crucial factor in the formation of bicontinuous microemulsions. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R63.00005: Microphase Separation of Hydrogen-Bonded Polystyrene-Polydimethylsiloxane Copolymer Blends Jaechul Ju, Ryan Hayward Self-assembled morphologies play a pivotal role in developing material’s properties. It would drive innovation if the transition of self-assembled structures is controlled by external stimulus. Hydrogen bonding (H-bonding) as secondary interaction has combined with a polymer blend system. It can be dissociated and re-associated as a function of temperature, developing reversible bonds. In our system, phenol (Ph) and pyridine (Py) are attached in pendent to polystyrene (PS) and polydimethylsiloxane (PDMS), respectively. The tendency for PS-PDMS to phase-separate competes with the H-bonding attraction of Ph-Py. We observed that macrophase- or microphase separation is dictated by the degree to which H-bonding attraction enhances the inherent immiscibility of PS-PDMS. The broad peaks of small-angle X-ray scattering indicate the formation of disordered nanostructures. An increase in domain size (~20 nm to ~60 nm) with increasing temperature (120-160 degree Celcius) was observed due to progressive dissociation of H-bonds, and this is (partially) reversible. The selective PDMS etching test proves the percolation of PDMS, indicating the original co-continuous nanostructures. This opens new possibilities for fine-tuning the domain size of co-continuous polymer nanostructures. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R63.00006: Emergence of Laves Phases in Diblock Copolymer/Homopolymer Blends Andreas Mueller, Aaron Lindsay, Ashish Jayaraman, Timothy Lodge, Mahesh Mahanthappa, Frank Bates Over the past decade, complex particle packings known as Frank-Kasper (FK) phases have been established as fundamental to the phase behavior of compositionally-asymmetric diblock copolymers with low molecular weight and high conformational asymmetry. Laves phases represent a subclass of FK phases, which have only previously been accessed by specific thermal processing protocols. However, recent work with particle-forming surfactant micelles in water indicates that addition of oil to the oleophilic particle cores enables equilibrium Laves phase formation. Inspired by these results, we sought to explore the ability of analogous diblock/core segment homopolymer blends to form similar complex particle packings. Accordingly, we blended a non-FK phase forming polystyrene-block-poly(1,4-butadiene) (SB) diblock copolymer (minority B) with B homopolymers of various molecular weights. Temperature-dependent synchrotron small angle X-ray scattering, and transmission electron microscopy revealed this type of blending indeed breeds complexity in the resulting particle packings, yielding insight into universal geometric principles guiding FK phase formation across soft matter. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R63.00007: Decoupling the Surface Energy and Thermodynamic Contributions to Nanoparticle Surface Enrichment in Polymer Nanocomposite Films Russell John Composto, Shawn Maguire, Michael J. Boyle, John Derek Demaree, Connor R Bilchak, Nadia Krook, Austin Wesley Keller, Andreea-Maria Pana, Kohji Ohno, Manuel Maréchal, Patrice Rannou The surface composition of a polymer nanocomposite (PNC) is often different from the bulk due to surface energy and thermodynamic forces. Here, we probe these two contributions in a model system of PMMA grafted silica nanoparticles (PMMA-NP) in a poly(styrene-ran-acrylonitrile) (SAN) matrix using Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) as a function of thermal annealing temperature and time. Studies are performed above and below the lower critical solution temperature (LCST) of this system to decouple the two contributions. With increasing annealing time at temperatures below the LCST, a monotonic increase in surface excess of PMMA-NPs is observed, which is attributed to the difference in surface energies between the constituents. Upon quenching the film into the two-phase region, a much larger increase in PMMA-NP surface coverage is observed, attributed to a stronger thermodynamic driving force for phase separation, namely the Flory-Huggins interaction parameter. Using the measured surface excess values of PMMA-NPs at multiple annealing times and temperatures, the diffusion coefficients of the grafted nanoparticles are extracted and compared to prevailing theoretical models. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R63.00008: Thermodynamics and Kinetics of Polymer Grafted Nanoparticle Composites Shawn Maguire, Russell John Composto In this work, model binary and ternary polymer nanocomposites (PNCs) of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NP), poly(styrene-ran-acrylonitrile) (SAN), and PMMA homopolymers are examined to probe thermodynamic and kinetic parameters underlying phase behavior and nanoparticle assembly. Using complimentary techniques, the addition of PMMA to PMMA-NP/SAN is observed to increase the miscibility in off-critical compositions. This compatibilization is attributed to interfacial segregation of PMMA and supported by molecular dynamics simulations. Knowing the phase diagram, the interplay between phase separation and wetting is then studied by quenching binary PNC films into the two phase region. The morphology exhibits wetting layers of PMMA-NPs at the surface and substrate separated by “pillars” of PMMA-NPs that span the thickness. These “pillars” enhance the film modulus and hardness as measured by nanoindentation. PMMA-NP surface excess increases rapidly with time and reaches a plateau that is dependent on quench depth. The diffusion coefficients of PMMA-NPs are measured and compared with prevailing models. Overall, these results highlight the complex parameter space in PNCs and provide new insights and control over bulk and surface morphologies of PNCs. |
Thursday, March 18, 2021 9:36AM - 10:12AM Live |
R63.00009: Tuning Nanostructure and Mechanical Properties in Polymer Materials via Reaction-Induced Phase Transitions Invited Speaker: Robert Hickey Material structure is the intersection between chemistry and property. An exciting way to control polymer material nanostructure is to drive macromolecular transformations via reaction-induced phase transitions. Recently, our group has shown how in situ polymer grafting strategies transform linear diblock copolymers into multi-graft copolymers, inducing order-order and disorder-order structural transitions. In the reported approach, a poly(styrene)-block-poly(butadiene) (PS-PBD) diblock copolymer swollen with styrene monomer will undergo lamellar-to-hexagonally-packed cylinder or a disordered-to-hexagonally-packed cylinder transition during the polymerization of styrene, which is a result of PS grafting from the PBD block. Here, the presentation will demonstrate how the in situ polymer grafting process previously used for diblock copolymers is easily applied to PS-PBD-PS triblock copolymers and hybrid polymer/inorganic nanoparticle systems, resulting in materials with enhanced mechanical properties or controlled nanoparticle dispersions, respectively. The work presented here emphasizes how in situ grafting strategies drive macromolecular transformations, leading to materials with controllable nanoscale morphologies and physical properties. |
Thursday, March 18, 2021 10:12AM - 10:24AM Live |
R63.00010: Co-assembly of nonspherical and heterogeneous nanoparticles in block copolymers Javier Diaz, Marco Pinna, Andrei Zvelindovsky, Ignacio Pagonabarraga Nonspherical nanoparticles and heterogeneous can self-assemble into a microphase-separated block copolymer matrix creating complex structures, thanks to the colloidal orientational degrees of freedom, in addition to the inherent ordering of block copolymer melts. This can result in highly ordered materials where nanoparticles do not act as mere fillers but are decisive in the overall phase behaviour of the system. 2D and 3D mesoscopic simulations show the emergence of complex structures which can be radically different from the neat block copolymer. |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R63.00011: Stabilizing Complex Spherical Phases via Local Segregation in Polymer Blends Jiayu Xie, Chi Lai, Anchang Shi Complex spherical phases have been observed in a variety of soft matter systems, which attracts tremendous attention in the last decade. Interestingly, a number of Frank-Kasper phases including A15, σ, C14 and C15 phases emerged and stabilized in various blending systems, such as AB-diblock-copolymer/A-homopolymer blends, binary mixtures of AB/AB diblock copolymers and lyotropic surfactants mixed with water and oil, etc. These informative experimental observations indicate that blending different components together dramatically enhances the stability of those complex spherical phases. Theoretical works revealed that local segregation of distinct components promotes the formation of spherical domains with different sizes, which is essential to the complex packing of spheres. In this presentation, we summarize in details the mechanisms to stabilize complex spherical packing phases through local segregation in various blending systems containing diblock copolymers based on our recent self-consistent field theory (SCFT) study. We believe that these universal principles could guide the design of other soft matter systems to get access to the novel complex spherical phases. |
Thursday, March 18, 2021 10:36AM - 10:48AM Live |
R63.00012: Stability of the Alternating Gyroid Morphology Formed By a Triblock Copolymer Increases By Adding Homopolymer Natalie Buchanan, Krysia Browka, Lianna Ketcham, Hillary Le, Poornima Padmanabhan Triblock copolymers can self-assemble into the alternating gyroid network which is of interest for various application due to its novel optical properties, high surface area, and structural chirality. However, the morphology is only stable in a narrow volume fraction region in the phase diagram for a non-frustrated triblock copolymer (characterized by repulsive end-blocks), as shown in the literature by theory and experiment. We hypothesized that the addition of selective homopolymers will expand and fill the network and adding conformational entropy, thereby increasing the region of stability. Using coarse-grained molecular simulation, homopolymers of three different lengths were tested across a volume fraction range. The lengths were chosen to sample the dry brush and wet brush regimes. With the addition of homopolymer, alternating gyroids were found throughout this extended region of the phase diagram. By analyzing end-to-end distances against the block’s distance from the interface, it was found that the homopolymers fill the middle of the network while maintaining average bulk conformations, confirming our hypothesis. |
Thursday, March 18, 2021 10:48AM - 11:00AM On Demand |
R63.00013: Entropy-Driven Assembly Behavior of Polymer-Grafted Nanoparticles in 3D Confined Block Copolymers Meng Xu, Hongseok Yun, Kin Liao, Bumjoon Kim Generating organic/inorganic hybrid materials with well-defined morphologies is of great importance as spatial alignments highly affect the integrated properties of hybrid nanomaterials. Herein, we investigated the assemblies of polystyrene-grafted Au nanoparticles (Au@PS) within onion-like polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) particles depending on four parameters: 1) molecular weight (Mn) of PS ligands (N), 2) core size of Au@PS (r), 3) grafting density of PS ligands (σ), and 4) Mn of PS-b-P4VP matrix (P). Change in any of these parameters drives dramatic morphological transitions of BCP/Au@PS hybrid particles. Au@PS having low interfacial interactions with BCP chains were excluded from the BCP domains and formed hexagonal packing on the particle surface. In contrast, high interfacial interactions between Au@PS and BCP chains allowed the formation of Au@PS arrays between PS blocks. The effects of four parameters were concluded in two aspects: N, r, and σ affect the penetrability directed by the ligand architecture of Au@PS whereas P/N determines the swelling behavior of polymer blends. In addition, we introduced the “effective softness (λeff)” model to integrate the effects of N, r, and σ on the penetrability of Au@PS. |
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