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 X04: Polymers and Block copolymers at Interfaces IIFocus Live
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Sponsoring Units: DPOLY DSOFT Chair: Reza Foudazi, New Mexico State University |
Friday, March 19, 2021 8:00AM - 8:12AM Live |
X04.00001: Membrane Binding of poly(butylene oxide)-poly(ethylene oxide) Block Polymers Nicholas Van Zee, Timothy Lodge, Marc Hillmyer Poloxamers are a class of block polymers composed of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) segments. Due to their amphiphilicity, poloxamers can associate to unilamellar liposome membranes and influence properties such as membrane rigidity, fluidity, and permeability. They have also been used pharmaceutically to restore cell membrane integrity and to treat conditions such as Duchenne’s muscular dystrophy and ischemia reperfusion injury. This study investigates the effect of hydrophobicity on polymer/membrane binding. A series of PBO-b-PEO polymers with varying molar masses and compositions were synthesized using anionic polymerization. The critical micelle concentration of each polymer was determined using light scattering and dye solubilization experiments. Additional pulsed-field-gradient NMR and surface plasmon resonance techniques were used to compare the binding affinity of PBO and PPO systems. |
Friday, March 19, 2021 8:12AM - 8:24AM Live |
X04.00002: Tailoring adhesion and wettability of thin polymer films with surface-active bottlebrush polymer additives Travis Laws, Hao Mei, Tanguy Terlier, Rafael Verduzco, Gila E Stein We designed surface-active poly(tert-butyl acrylate-co-styrene) bottlebrush additives for polystyrene films. The additives preferentially enrich the surface and substrate interfaces of the solution-cast film. This behavior is attributed to a combination of effects: an entropic preference for the branched bottlebrush architecture at surfaces and interfaces; the inclusion of low energy tert-butyl acrylate moieties; and unfavorable enthalpic interactions between the bottlebrush additive and the polystyrene host. Subsequent thermal annealing activates a deprotection reaction that converts t-butyl acrylate to acrylic acid, increasing both surface wettability and adhesion to the underlying silicon substrate. This work demonstrates a method to tailor surface properties by using a combination of energetic and entropic effects to drive additives toward interfaces, followed by a simple post-deposition reaction to increase the additive’s polarity and tailor related functions. |
Friday, March 19, 2021 8:24AM - 8:36AM Live |
X04.00003: Large-scale Reversible Domain Restructuring Mechanism between Direct (Solvent) Immersion Annealing and Thermal Annealing in Lamellar Block Copolymer Films Kshitij Sharma, Ali Masud, Guangcui Yuan, Sushil K Satija, Alamgir Karim Thin films of symmetric block-copolymers (L-BCP) like polystyrene-b-polymethyl methacrylate (PS-b-PMMA) assume lamellar microstructure parallel to the Si substrate due to wetting of the Si oxide layer by the PMMA domain. We investigate the origins of drastically different domain spacing achieved in dried L-BCP films after immersion in a mixture of controlled good/intermediate/poor solvent, termed direct immersion annealing (DIA), compared to thermal melt annealing. DIA has been shown to produce microdomains (~Lo/2) that are nearly 50% smaller in size compared to that produced by thermal annealing (Lo, that is also predicted by equilibrium melt theory). We show it is possible to reversibly go from one domain size to the other by switching successive annealing techniques. There is however, asymmetry in the kinetics of the reversibility processes due to the different molecular mechanisms involved in the two techniques. To explore this, in-situ Neutron Reflectivity was performed for DIA from a thermally annealed state. The interesting structural crossover between the two distinct states and the underlying kinetics of the reversibility process will be discussed in terms of chain swelling, chain diffusion and in-plane vs out-of-plane chain junction density evolution. |
Friday, March 19, 2021 8:36AM - 9:12AM Live |
X04.00004: Controlling Block Polymer Interfaces for Next-Generation Membrane Separations Invited Speaker: Bryan Boudouris Designer macromolecules provide a platform by which to generate structured, multifunctional materials with tailored biochemical, redox, and optoelectronic properties. Furthermore, the solution-processable nature of functional polymers allows for device fabrication procedures that are compatible with high-throughput (e.g., roll-to-roll coating) manufacturing processes. Importantly, in many of these applications, block polymer interfaces play crucial roles in the end-use situations. As such, elucidating the underlying physics associated with these multicomponent macromolecules is critical to long-term engineering success. Here, we show that A-B-C triblock polymers and A-B diblock polymers can be used to modify interfacial interactions in designer water purification membranes. By tuning the molecular weight, molecular weight distribution, block polymer chemical composition, and casting techniques employed, we generate mechanically-robust nanoporous thin films that are well-suited for nanofiltration and membrane adsorber applications. In fact, high-flux separations (i.e., at permeabilities equal to or greater than current commercial membranes) of particles down to ~1 nm in diameter are presented. Additionally, we demonstrate that, through the appropriate selection of the block polymer moieties, the physics of the nanopore walls can be controlled in a direct manner. In addition to observing key physical effects that result due to the large grafting density in confined nanopores, these wall chemistries provide unique functionality to the end-use membranes. In this way, we demonstrate that membranes cast from these materials separate ionic species of similar size. Moreover, these membranes remove >99% of myriad heavy metal cations from aqueous solutions in a manner that is independent of the background electrolyte. Therefore, these tailored macromolecules provide an excellent handle by which to control block polymer interfaces in a technologically-relevant platform. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X04.00005: Field Theoretic Simulation Study of Order-to-disorder Transition of Block Copolymers Confined within Neutral Surfaces Jaeup Kim, Daeseong Yong In this study, we investigated the order-to-disorder transition (ODT) behavior of multiple-layered cylinder- and lamella-forming block copolymer (BCP) films with neutral boundary conditions. The self-consistent field theory (SCFT) and Langevin field theoretic simulation (L-FTS), which is one of the partial saddle point approximation methods, are used to figure out the influence of wetting condition on the phase transition behavior. The SCFT study showed that (χN)ODT value of lamella-forming BCPs with neutral wetting condition increases as film thickness decreases, and it is consistent with experimental results. However, phase behavior of cylinder-forming BCPs confined within neutral surfaces was unsettled with SCFT which ignores composition fluctuation effect. In order to account for the fluctuation effect, we implemented L-FTS of discrete chain model under confinement. Ultraviolet divergence is eliminated by renormalization and calibration of Flory-Huggins parameters, allowing accurate comparison of (χN)ODT changes. By performing L-FTS with experimentally relevant invariant polymerization index, we showed that (χN)ODT value of cylinder-forming BCPs within neutral interfaces increases as the film thickness decreases, which is a consistent result with experiments. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X04.00006: Effect of Conformational Asymmetry on the Stability of Network Phases in Diblock Copolymer Melts Pengyu Chen, Kevin D Dorfman Despite the great success in understanding the microphase separation and the self-assemblies of periodic microstructures in block copolymer systems, stabilization of exotic ordered co-continuous network structures beyond double-gyroid remains a challenge. Motivated by the ability of conformational asymmetry to stabilize Frank-Kasper phases in sphere forming morphologies, we perform simulations using self-consistent field theory (SCFT) to investigate the influence of conformational asymmetry on the stability of network phases in a diblock copolymer melt. The free energies of nine network structures, as well as competing non-network structures, are analyzed. The free energy comparison indicates O70, which is stable for conformationally symmetric systems, continues to be an equilibrium morphology in a narrow composition window for high conformational asymmetry, while O52 is slightly less stable than O70 throughout the whole phase diagram. More exotic network phases remain metastable in the presence of conformational asymmetry. Nevertheless, conformational asymmetry has a significant influence on the relative stability of the network phases, which may provide insights into how a complex network might be stabilized in more complex systems. |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X04.00007: Predicting excess free energy of mixing for molecular mixtures by inducing phase separation in simulations. Shreya Shetty, Puja Agarwala, Enrique D Gomez, Scott Milner Excess free energy of mixing governs phase behavior of mixtures. We have developed a method that combines molecular dynamic simulations and thermodynamic integration along the path of transformation of molecules to measure the excess free energy of mixing of molecular mixtures. But this method requires the molecules to be structurally related. To overcome this limitation, we have developed a new method to measure the excess mixing free energy, which involves simulations of molecular mixture where we weaken the cross interactions between different species until they phase separate. We measure the thermodynamic work required to modify the interactions and the interfacial energy between the separated phases to compute the excess free energy of mixing. To verify the method, we determine the excess free energy of mixing Lennard Jones (LJ) beads with themselves and the excess free energy of mixing for benzene-pyridine mixture. We find that for LJ beads mixing with themselves, the excess free energy of mixing approaches the expected value of -kT Log(2) per bead. For the benzene-pyridine mixture, simulation results for the excess mixing free energy agree with experiments. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X04.00008: Irreversible Physisorption of PS-b-PMMA for Neutral Layer Wooseop Lee, Yeongsik Kim, Hyungju ahn, Du Yeol Ryu Polymer chains are irreversibly physisorbed onto impenetrable substrates by intermolecular forces (i.e. H bonding, vdW force or dipolar moment), as the chains favor the conformations which maximizes the segmental contact to compensate the conformational entropy loss. In this study, we succeeded in guiding perpendicular microdomains of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) film with the aid of the irreversibly-adsorbed neutral layer made of PS-b-PMMA and evaluated its compositional randomness in terms of the correlation length (ξ). This method is widely applicable to various substrates without any necessity of random copolymer brushes or mats, other than PS-b-PMMA itself. |
Friday, March 19, 2021 10:00AM - 10:12AM Live |
X04.00009: Designing A-b-(B-r-C) block copolymers for lithographic applications Yuba Dahal, Hongbo Feng, Juan De Pablo, Paul F Nealey, R. Joseph Kline, Debra Audus Designing defect-free structures with a specified pitch size for the lithographic applications is a challenging task due to the need to balance both chain interactions and surface interactions. One approach is to decouple the phase separation from the surface interactions through A-b-(B-r-C) polymers where the A is PS and B and C are modified-PGMA. For perpendicular lamellae structures, the surface energy of A should be balanced by the surface energy of B-r-C by varying the relative ratio of B to C. However, the parameter space is large. Having surface energy information of various candidate blocks can be crucial to reduce the parameter space. For perpendicular lamellae structures, surface energy of the A block should be balanced by the surface energies of B and C blocks. Here we perform all atom molecular dynamics simulations to determine the effects of chemistry on the density and surface energy. This information can then be used to reduce the synthetic burden during the design of these block copolymers. |
Friday, March 19, 2021 10:12AM - 10:24AM Live |
X04.00010: Ionic Liquid Enhanced Long-Range Ordering in Lamellar Block Copolymer Films Ali Masud, Jack Douglas, Alamgir Karim Symmetric PS-b-PMMA block copolymers (BCP) films cast on Silicon wafers are known to form a lamellar structures upon annealing, with PMMA and PS block wetting the substrate and air interface respectively. However, attaining complete parallel ordering becomes increasingly difficult as the molecular weight (Mw) and thickness of the BCP films increase, due to meandering of lamellae in the film. In order to enhance the degree of BCP ordering, previous studies have focused on enhancing the thermodynamic driving force, χN, where χ is the Flory-Huggins interaction parameter and N is the number of segments. Increasing χ with decreasing temperature or increasing N, can enhance thermodynamic driving force but slows kinetics drastically and results in higher defect formation due to lower mobility above glass transition temperature Tg and the entanglement of polymers when Mw increase. In this work we use IL to enhance χ, and attain lamellar films with lower defects and enhanced parallel stratification in high Mw and thickness films. Such enhancement occurs due to the enhanced χ, coupled with enhanced mobility due to a lower Tg of the IL/BCP system. These defect free films may be useful in applications such as batteries, solid state dielectric capacitors, barrier materials etc.χ |
Friday, March 19, 2021 10:24AM - 10:36AM On Demand |
X04.00011: Order to Order Transition from Cylindrical to Lamellar Microdomain Upon Heating with Upper Critical Ordering Transition Block Copolymer Seonghyeon Ahn, Yeseong Seo, Chao Duan, Lixun Zhang, Weihua Li, JinKon Kim For upper critical ordering transition (UCOT) block copolymers where χ decreases with increasing temperature, the sequence of order to order transition (OOT) upon heating of AB diblock and A1BA2 triblock copolymers with UCOT is as follows: lamellae to gyroids to cylinders to spheres before order to disorder transition. However, the opposite direction OOT is impossible in UCOT block copolymers. |
Friday, March 19, 2021 10:36AM - 10:48AM On Demand |
X04.00012: Inverted cylindrical microdomains by binary blends of AB/AC block copolymers with hydrogen bonding interactions Sukwon Kang, JinKon Kim AB type block copolymers generally show hexagonally packed cylindrical microdomains at a volume fraction of cylindrical microdomain having 0.2 ~ 0.35. In this study, we obtained inverted cylindrical structures consisting of the major block in the minor matrix by using a binary blend consisting of lamella-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and polystyrene-block-poly(4-hydroxystyrene) (PS-b-PHS), where hydrogen bonding occurs between P2VP and PHS blocks. We found, via transmission electron microscopy and small angle X-ray scattering, inverted HEX cylindrical microdomains having the volume fraction of the cylinders of 0.65. |
Friday, March 19, 2021 10:48AM - 11:00AM On Demand |
X04.00013: End-on orientation of poly(3-alkylthiophene)s by microphase separation of amphiphilic diblock copolymer Philgon Kim, JinKon Kim To fabricate end-on orientation of poly(3-alkylthiophene) (P3AT) where the polymer main chains are vertically oriented on the substrate, we synthesized poly(3-dodecylthiophene)-block-poly(3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methylthiophene) copolymer (P3DDT-b-P3TEGT) using the GRIM method. P3DDT-b-P3TEGT showed lamellar microdomains, confirmed by SAXS. The thin film morphology measured by AFM and GIWAXS showed parallel oriented lamellar microdomains on a substrate, because of a large difference of surface tension between hydrophobic P3DDT and hydrophilic P3TEGT blocks. In this geometry, both P3DDT and P3TEGT backbone chains were oriented perpendicularly to the lamellar layer; thus the end-on orientation of P3DDT chains was obtained. P3DDT-b-P3TEGT film showed much improved hole mobility compared with neat P3DDT film in spite of presence of P3TEGT block with low hole mobility. Once one can design lamellar forming block copolymers having higher mobility than P3DDT and P3TEGT, much higher hole mobility would be expected, which is very useful for designing high performance vertically operating devices. |
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