Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B05: Nonequilibrium Structures and Dynamics of Polymeric Materials IFocus
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Sponsoring Units: DPOLY Chair: Antonio Faraone, National Institute of Standards and Technology Room: Room 128 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B05.00001: Investigating microstructure formation in block copolymer membranes with dynamic self-consistent field theory Anthony J Cooper, Douglas Grzetic, Glenn H Fredrickson, Kris T Delaney Block copolymers have garnered much interest as candidate materials for ultrafiltration membranes, due to their ability to self-assemble an isoporous selective layer at the membrane surface. However, the vast number of formulation and processing variables has remained an obstacle for understanding the structural evolution of the surface layer and porous substructure. Here, we employ dynamical self-consistent field theory to investigate the effects of various parameters such as film composition and solvent selectivity on the resulting development of the porous substructure. We discuss the impact of each parameter on pore size distribution and the underlying micellar morphology that is a precursor to the membrane substructure. |
Monday, March 6, 2023 11:42AM - 11:54AM |
B05.00002: Fragmentation Kinetics of Block Copolymer Micelles: Effect of Changing Interfacial Tension Supriya Gupta, Timothy P Lodge Block copolymers offer great potential as drug delivery carriers, functional nanomaterials, and nanoreactors. The spherical micelles attain equilibrium predominantly by micelle fusion, fragmentation, and chain exchange mechanisms. The present study examines the fragmentation kinetics of 1,2-polybutadiene-b-poly(ethylene oxide) block copolymer micelles in 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide-based ionic liquids to comprehend the role of the driving force for fragmentation, represented by the micelle size ratio Q/Qeq. The micelle size ratio Q/Qeq was varied by the strategic mixing of different ionic liquids with varying interfacial tensions. The interfacial tensions for a series of ionic liquids with 1-2-polybutadiene homopolymer were measured using a pendant drop test. Micelles were characterized using in-situ dynamic light scattering, small-angle X-ray scattering, and transmission electron microscopy. Dilution of a micellar solution with a less selective solvent is found to influence the fragmentation kinetics. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B05.00003: Effect of polymer topology on the self-assembly of micellesRaquel Lopez-Rios De Castro*, Robert M. Ziolek & Christian D. LorenzBiological Physics & Soft Matter Research Group, Department of Physics,King’s College London, London, UK WC2R 2LS Raquel Lopez-Rios de Castro The structure of molecules has often been shown to play an important role in the function and properties of the materials that they form at various lengths and time scales. In polymer science, the choice of macromolecular structures historically has been linear and randomly branched. More recently, more controlled polymer topologies have been formulated because of the development of advanced synthetic techniques. As a result, there has been an increased interest in the role that topology plays in a variety of systems. While in all these investigations there are differences observed as a result of the changing topologies, very little is known as to how the molecular scale interactions of these polymers which have the same composition but just different topology result in these differences. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B05.00004: Supersoft, Porous Hydrogels with Structure and Properties Reminiscent of Natural Tissue Elisabeth C Lloyd, Robert J Hickey, Chao Lang While hierarchical ordering is a distinctive feature of natural tissues and responsible for many of their unique properties, replicating such structures in synthetic materials is extremely difficult. Here, we combine the nanoscale micelle network formed from the self-assembly of amphiphilic triblock copolymers in water with the porous microstructure formed during solvent exchange to produce biomimetic hydrogels. Initially, the triblock copolymer is dissolved in an organic solvent common for both blocks and injected into water. The simultaneous solvent exchange and micellation of the polymer in water will produce a porous gel, with micelles forming the pore walls. Here, we show that the micellar nanostructure is largely insensitive to processing conditions but varies with polymer size and composition. In contrast, the porous microstructure is heavily dependent on the processing conditions of the polymer. The gels are extremely soft, but surprisingly these materials can stretch to many times their original length, with strain-hardening behaviors at high strain and no hysteresis upon recovery. This research presents an exciting class of new materials, with diverse applications and an opportunity to probe the mechanisms of non-solvent induced self-assembly. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B05.00005: Kinetically-Arrested Nanostructures from Amphiphilic Mikto-Grafted Molecular Brush Polymers in Solution Abelardo Ramirez-Hernandez The solution self-assembly of heterografted molecular brush polymers offers a rich platform to create functional organic nanostructures. In recent years, it has become evident that kinetics, not just thermodynamics, plays an important role in defining the self-assembled structures that can be created. In this work, we present results from extensive molecular dynamics simulations that explore the self-assembly behavior of amphiphilic mikto-grafted brush polymers as the solvent quality for one of the side blocks is changed by a rapid quench. We have performed a systematic study of the effect of different architectural parameters and the degree of incompatibility between side chains on the final self-assembled nanostructures. Our simulation results indicate that kinetically-trapped complex nanostructures are prevalent as the number of macromonomers increases. A quantitative analysis on the structure of the self-assembled morphologies was performed by computing the gyration tensor and relative shape anisotropy as the different relevant architectural parameters were varied. Our results are summarized in terms of non-equilibrium morphology diagrams. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B05.00006: Are Water Swollen Sulfonated Polystyrene Polyelectrolytes Slurries in Equilibrium?Molecular Dynamics Simulations Study Shalika D Meedin, Bryce A Thurston, Gary S Grest, Dvora Perahia Ionic aggregates affect the mechanical and transport properties of ionizable polymers and are strongly influenced by changes in their electrostatic environment that occur either in direct exposure to electric fields, or exposure to ions and solvents. With the complex nature of ionizable polymers, any electrostatic perturbation drives the system out of equilibrium. Here, we follow water-sulfonated polystyrene (SPS) complexes using atomistic molecular dynamics simulations. Water swollen SPS in the polyelectrolyte regime at sulfonation levels f=0.55-1.00 are followed as a function of time and their structure and dynamics and the characteristics of the ionic assemblies are calculated. Addition of water breaks the percolating ionic clusters and concurrently enhances polymer mobility. S(q) consists of an intense broad signature, which shifts to larger dimensions for f ≥ 0.75. This behavior is attributed to formation of macro aggregates with long-lived domains bordered by water. g(r) shows that the S-S distance increases with time indicative of slow water penetration. With increasing f, for all water concentration, the mobility of the polymers increases, though all components are dynamic and remain far from equilibrium. |
Monday, March 6, 2023 12:42PM - 1:18PM |
B05.00007: Flow-induced Nematic Alignment and Nucleation Acceleration in Polymer Melts Invited Speaker: Ralph H Colby Using rheo-optical methods we show that poly(ether ether ketone) melts of various chain lengths begin to exhibit a sudden nematic alignment at the critical shear rate beyond which shear flow accelerates nucleation. The shear-induced isotropic-to-nematic (I-N) transition manifests in the shear rate dependence of viscosity with three regimes: I) An isotropic response with no measurable birefringence at low shear rates, with zero-shear-rate viscosity 0~Mw6, predicted for isotropic melts of rodlike polymers by Doi. II) An I-N transition with an isotropic-nematic biphase, two steady state values of apparent viscosity and measurable birefringence at intermediate shear rates. III) A fully nematic alignment with strong birefringence at high shear rates with shear thinning viscosity η~-1/2, predicted by Marrucci and observed for all nematic polymers. We find that other aromatic backbone polymers exhibit similar features, even ones that never crystallize. We also study the effects of shear flow on nucleation acceleration of more flexible polymers to determine which aspects of these flow effects are universal to all semicrystalline polymers. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B05.00008: Flow-induced configuration microphase separation and crystallization of entangled polyethylene under uniaxial extensional flows Mohammad Hadi Nafar Sefiddashti, Brian J Edwards, Bamin Khomami Recent nonequilibrium molecular dynamics (NEMD) simulations of planar extensional flows (PEF) of a linear C1000H2002 melt demonstrated that entangled polymer melts can undergo a coil-stretch transition and configurational microphase separation within an intermediate range of extension rate, where the coil and stretched molecules coexist in separate domains. PEF is, however, hard to reproduce in experimental settings, and hence most of the extensional flow experiments of polymeric liquids have been performed in uniaxial extension flow (UEF) geometries. This makes the comparison of PEF simulation findings and experimental observations difficult and debatable. |
Monday, March 6, 2023 1:30PM - 1:42PM Author not Attending |
B05.00009: Phase separation in structured fluids Gabriel I Vega Bellido Trapped structures formed during the phase separation of fluids are used in a variety of engineering applications from polymer membranes for gas separations to bicontinuous structures in which the phases have complimentary properties. However, in nearly all these applications the two individual phases tend to be amorphous with no large-scale internal structure, for which the dynamics of phase separation are relatively well understood. When one of the phases is ordered, such as in a liquid crystal, the kinetics of phase separation and predictions of the structures that form are comparatively poorly understood. In this work, we introduce a computationally inexpensive coarse-grained molecular model of a liquid crystal that can form both nematic and smectic phases, allowing for the study of intermediate out of equilibrium states as the system goes through a phase separation process. By varying the volume fraction, the phase formed by the liquid crystal, and the depth of the quench into the two-phase region, we observe a variety of structures as the system undergoes phase separation. We characterize both the coarsening dynamics and the geometry of the structures formed, showcasing the development of various novel features compared to phase separation in isotropic fluids. We hope the improved understanding of this system will lead to novel materials for use in membrane technologies. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B05.00010: Sequential Thermal and Solvent Immersion Annealing for Self-Assembly of Block Copolymer Films: Hiking the Free Energy Landscape Kshitij Sharma, Aman Agrawal, Ali Masud, John F Ankner, Sushil K Satija, Jack F Douglas, Alamgir Karim The kinetics and morphology of block copolymer (BCP) assembly in films are highly dependent on processing pathways that may include thermal annealing (TA), solvent vapor annealing (SVA), and direct immersion annealing (DIA). Thus, it is only to be expected that sequential/parallel annealing of the same BCP film by two or more techniques can produce unique synergies of ordering kinetics, morphology evolution, and asymmetry in reversibility mechanisms. Here we demonstrate a combinatorial DIA and TA method, where an instantaneous DIA rapidly induces weak parallel lamellar ordering with highly reduced domain sizes that rapidly transform into standard TA equilibrium domain structures when subjected to TA. Overall, the DIA plus TA shows much faster processing kinetics than TA alone for a similar degree of ordering. We then explored the reverse ordering process of TA followed by DIA and observed very different kinetics and morphology evolution, with highly irregular intermediate structures but with the same final state of DIA metastable structure. Considering the structural crossovers observed, a chain rearrangement mechanism for transition between the two distinct morphologies is proposed, and the underlying dynamics of this reversibility process are analyzed in terms of chain swelling, diffusion, and in-plane vs. out-of-plane interfacial evolution. The transitions are plotted on a free-energy diagram to elaborate on the asymmetry in processing kinetics. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B05.00011: Enzyme-induced kinetic control over self-assembly of amphiphilic surfactants Qinyu Zhu, Douglas R Tree, Nicholas Bair, Walter F Paxton One of the main challenges with many pharmaceutical products is the severe side effects caused by the toxicity of drugs to the non-targeted parts of human bodies. Developing an effective controlled release approach would be a potential solution since it minimizes the interaction between the drug and the non-targeted sites. pH responsive micellar structures are heavily researched as drug delivery cargos as they undergo shape and permeability transitions in response to pH changes. However, the knowledge of such systems is imperfect regarding how dynamic changes in pH affect the immediate structures and sizes, which is a quite common scenario in biological organisms. Inspired by some recent experimental observations, we modeled a pH responsive system of O-methyl-serine-dodecylamide hydrochloride (MSDH) solution with urea/urease catalytic reaction as the pH controller. We first used coarse-grained molecular dynamics (CGMD) to simulate the morphologies of MSDH at different pH conditions. Having established the equilibrium self-assembly behavior, we performed a series of in silico tests of pseudo-reaction by applying step-wise perturbations in pH, where we observe qualitatively different structures due to kinetic effects. Finally, we compared several time scales involved in the self-assembly process and discussed possible mechanisms of forming kinetically driven structures. The results could be potentially helpful in developing state-of-art drug delivery systems. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B05.00012: Coaxial Conjugated Polymer/Quantum Rod Nanowires with Preferred Quantum Rod Orientation Eunji Lee One-dimensional crystalline fibrillar assemblies of poly(3-hexylthiophene) (P3HT)-based materials |
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