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 T15: Block Copolymer Self-Assembly |
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Sponsoring Units: DPOLY Chair: Shuyi Xie, Univ of California, Santa Barbara Room: Room 207 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T15.00001: Coherent States Field Theory for Supramolecular Dendron-like Polymers Dan Sun, Kris T Delaney, Glenn H Fredrickson Supramolecular assembly provides a powerful venue for creating intricate polymer architectures whose direct synthesis would be difficult or impossible. In this study, we explore the use of ABn miktoarm star copolymer and An star homopolymer with terminal functional groups as supramolecular building blocks to construct a range of reversible dendron-like copolymers. To study such systems, we apply the coherent states (CS) field-theoretic representation in tandem with a mean-field approximation. The CS framework is advantaged over the conventional auxiliary field (AF) representation because it eliminates the need for explicit enumeration of all reaction products. We show how the thermally tunable phase behavior is influenced by the placement of reactive groups, their binding strength, and their self vs. hetero-complementary character. In particular, the deflection of phase boundaries and relative stability of complex sphere phases is explored and compared with non-reactive miktoarm stars. |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T15.00002: Effects of dynamic bonds on the kinetic pathways of the disorder-order transition of supramolecular diblock copolymers Xiangyu Zhang, Dong Meng Supramolecular block copolymers (SBC) consist of covalent polymer building blocks that are connected into well-defined architectures via supramolecular bonds. Assisted by the dynamic and reversible supramolecular interactions, it is envisaged that SBC self-assemblies may exhibit more diverse morphologies, stimuli-responsivity and dramatically reduced annealing times/temperatures comparing to their covalent analogues. At the fundamental level, these features are related to the free-energy landscape of self-assemblies. It is therefore of central importance to understand the impact of dynamic/reversible bonds on the free energy landscape during structure transitions. In this study, we first conduct direct dynamics simulations to compare the kinetics of the disorder-order transition (DOT) of supramolecular diblock copolymers (SDBC) to that of covalent diblock copolymers (CDBC). We show that intermediate plateau in the structure order parameter is observed for both systems during the transition, and the length of plateau is shorter for SDBC. The observation indicates the presence of free-energy barriers in DOT, the magnitude of which is affected by the reversible bonds. Next, we apply the string method to construct the minimum free energy path of the transition, from which the transition state and the free energy barrier are evaluated. We show that the transition states are similar between SDBC and CDBC, but the free energy barrier associated with the DOT in SDBC is lower than that in CDBC. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T15.00003: Fluctuation effects on the order-order transitions of a diblock copolymer melt Mark W Matsen, Tom M Beardsley, James D Willis While there are many studies examining fluctuation effects on order-disorder transitions of block copolymer melts, there is relatively little understanding of how fluctuations affect the order-order transitions. This is because of difficulties in comparing the relative stability of ordered phases. The source of the problem is that their periodicities are inevitably different, and thus the phases need to be simulated in boxes of different size. Given recent advances in our understanding of the ultra-violet divergence that occurs in field-theoretic simulations, we are now able to calculate and compare free energies from different size boxes. Using this ability, we calculate fluctuation-corrected phase diagrams. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T15.00004: Is the ODT of diblock copolymers a mean-field transition? Insights from DPD Alfredo Alexander-Katz, Hejin Huang The order-disorder transition (ODT) in diblock copolymers has fascinated scientists for many decades and has inspired multiple theories to explain its origin. After the pioneering work of Leibler, as well as that of Fredrickson and Helfand, (F-H) it was possible to understand within a mean field theory framework how such phases appeared and what the effect of fluctuations on the ODT transition were. Over the last few years, however, several new theories have emerged trying to incorporate fluctuations in different ways to better match experimentally observed temperatures compared to the F-H results. Here, we revisit this problem by using a coarse-grained computational technique called Dissipative Particle Dynamics and explore the mean field limit within this approximation. Our results suggest that the experimentally observed transition can be well explained by the mean-field limit albeit with a different chain model that correctly captures the physics of the problem, as well as reducing some constraints of the theory which also make physical sense. Molecular insights from the simulations will be provided to show the limitations of previous theories and inform new theories and models in this area. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T15.00005: Study of Fluctuation Effect on Diblock Copolymers Blended with Random Copolymers by Using Langevin Field Theoretic Simulation Hyeon U Jeong, Daeseong Yong, Jaeup Kim For the past few decades, self-consistent field theory (SCFT) has been a popular tool for the study of polymeric nanostructures. However, SCFT is intrinsically a mean-fields theory, and there are limitations in applying it for complex nanostructures which are strongly affected by compositional fluctuation. Recently, a few methods have been developed to include fluctuation effects on polymer field theory, and Langevin field theoretic simulation (L-FTS) is one of the front runners. By adopting partial saddle point approximation and Langevin dynamics on polymer field theory, L-FTS has successfully incorporated the fluctuation effect. Even though it is faster than other FTS methods, it still requires heavy computational resource. We recently developed a deep learning approach for the prediction of partial saddle points to enhance the performance of L-FTS. In this presentation, we demonstrate the effect of fluctuation on the diblock copolymer (BCP)-random copolymer (RCP) blend system by comparing L-FTS and SCFT results. Our major focus is on the shift of order-to-disorder transition (ODT) points of Flory-Huggins interaction parameter, χNODT. At low RCP fraction, χNODT predicted by SCFT increases almost linearly as RCP fraction increases. As expected, the χNODT predicted by L-FTS increased faster than that calculated by SCFT, and the degree increases as the fluctuation level goes up. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T15.00006: Langevin Field Theoretic Simulation on the Order-to-disorder Transition of Frank-Kasper Phases Wonjun Kang, Daeseong Yong, Jaeup Kim Frank-Kasper (FK) phases are spherical phases with low symmetry, and their formation is experimentally reported for conformationally asymmetric diblock copolymers. Several theoretical works using self-consistent field theory (SCFT) also predict the emergence of FK phases. However, SCFT does not consider the effect of the compositional fluctuation, which is known to change the nature of the order-to-disorder transition (ODT). Because of this, direct transition from disordered phase to FK phases has not been theoretically predicted, even though it is commonly observed in experiments. In order to understand the nature of ODTs, we perform Langevin field theoretic simulation (L-FTS), which samples the ensemble of polymers so that the effect of compositional fluctuation can be accounted for after enough time steps of simulation. Until now, this method was not feasible to study FK phases due to the large unit cell size and high computational cost. With recently developed L-FTS library accelerated by deep learning, we examine the ODT positions of σ, A15, C15 and C14 phases at various parameter values. We find that direct ODT from disordered phase to some FK phases are possible at high enough fluctuation level, which was reported in recent experiments. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T15.00007: Topological Effect on Order-Disorder Transition of Self-Assembled High-χ Block Copolymers Cheng-Yen Chang, Gkreti-Maria Manesi, Apostolos Avgeropoulos, Rong-Ming Ho This work aims to systematically examine the topological effect on the self-assembly of high-χ block copolymers. Symmetric polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymers (BCPs) with different topologies including diblock, 3-arm star-block, and 4-arm star-block possessing various molecular weights are synthesized to investigate the topological effect on the temperature of order-disorder transition (TODT) through temperature-resolved small-angle X-ray scattering experiments. Apparent increase on the TODT can be identified with the increase of arm number of the BCPs with equivalent arm length. On the basis of self-consistent field theory, the Flory-Huggins interaction parameters (χ) can be determined from the regression of the measured TODT. With the invariant of the enthalpic contribution of interaction parameter (χH) for the block copolymers, there is a significant variation on the entropic contribution of interaction parameter (χS) as the arm number increases, reflecting the topology effect on the entropic penalty of chain packings. Accordingly, the topology might effectively alter the χ value due to the dependence of χS on the arm number, in line with the theoretical prediction. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T15.00008: Alternating Gyroid Stabilized by Surfactant-Like Triblock Copolymers in SI/SO/ISO Ternary Blends Pengyu Chen, Kevin D Dorfman Block copolymers self-assembled into chiral alternating-gyroid (AG) morphologies are desirable templates for fabricating photonic materials. Recent self-consistent field theory (SCFT) calculations on a model system predicted that adding a minuscule amount of ABC triblock into a blend of double-gyroid-forming AB and BC diblocks with immiscible A and C blocks stabilizes AG. Here, we use SCFT to investigate the feasibility of this method in practice by computing the phase behaviors of ternary mixtures of poly(styrene-block-isoprene) (SI), poly(styrene-block-ethylene oxide) (SO), and poly(isoprene-block-styrene-block-ethylene oxide) (ISO). The addition of ISO successfully stabilizes AG, however, the phase window is relatively narrow, due to the packing frustration induced by the mismatch in preferred domain sizes between SI and SO diblock copolymers. Designing the system to have comparable diblock domain sizes significantly enhances the relative stability of AG against the competing alternating lamellae. Moreover, the stabilization of alternating morphologies is sensitive to temperature, and less ISO is needed at lower temperatures. The effect of other design parameters, such as diblock volume fraction, will be provided. These computational results provide insights into possible experimental strategies for producing AG. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T15.00009: Ordered microphases in binary blends of AB and ABC block polymers SoJung Park, Frank S Bates, Kevin D Dorfman Blending block polymers with different block lengths is a well-established strategy for producing new ordered nanostructures that are difficult to realize in neat block copolymer melts. In this study, we investigate the phase behavior of binary blends of AB diblock copolymer and ABC triblock terpolymer, using self-consistent field theory (SCFT). We present phase diagrams of the blend systems as functions of segregation strength and blend composition, which exhibit a rich phase behavior due to an expansive parameter space with eight independent parameters (three Flory–Huggins interaction parameters, three block compositions, one overall molecular weight ratio, and one blend composition). Changing just one parameter, blend composition, produces complexity in phase behavior with the emergence of unusual core-shell network phases with asymmetric core and shell volume fractions and a new cylinder-in-O70 hybrid network phase. Our SCFT calculations suggest that the nonclassical nanostructures are stabilized via interfacial modification induced by preferential localization of blocks of different lengths in the same domain. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T15.00010: Synthesis and Phase Behavior of PS-(PS-b-P2VP)3 Miktoarm Star Block Copolymer Dokyung Woo, Yeseong Seo, Luyang Li, Weihua Li Gyroid nanostructures have received much attention because of potential applications for next-generation storage devices and membranes. However, to maximize its structural advantages, gyroid nanostructures with larger channel volumes are needed. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T15.00011: Topological effect on the phase behaviour of Triblock Copolymer and Homopolymer Blends Jiayu Xie, Anchang Shi The phase behaviour of binary blends composed of linear symmetric AB-type triblock copolymers and A-homopolymers is examined using the self-consistent field theory, focusing on the occurrence of the Frank-Kasper (FK) phases. Previous studies showed that several FK phases (σ, C14 and C15) could be stabilized by adding A-homopolymers to AB-diblock copolymers. Because diblock copolymers and homologous triblock copolymers exhibit qualitatively similar phase diagrams, it is expected that the addition of A-homopolymers into AB-type triblock copolymers would result in similar phase behaviour. For a given composition, linear symmetric AB-type triblock copolymers can assume two, ABA and BAB, topologies. A naturally arising question is how such a topological difference affects the phase behaviour of the blends. In order to answer this question, two phase diagrams corresponding to BAB/A and ABA/A blends are constructed. A surprisingly large difference between the phase diagrams of ABA/A and BAB/A blends is observed. The small difference between the phase diagrams of neat BAB and ABA melts is amplified by the addition of a homopolymer compatible with their minority block. Further analyses on the density profiles suggest different distributions of A-homopolymers in the BAB/A and ABA/A blends, which is responsible to the very different behaviours of the two systems. The results of our study shed light to the topological effect of block copolymers on the formation of ordered phases in more complex polymeric blends. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T15.00012: Stabilizing network morphologies of block copolymers by end-group chemistry Hojun Lee, Moon Jeong Park Network morphologies in block copolymers have been in the spotlight for nanotechnologies owing to the unique interconnected nanodomains. However, achieving thermodynamically stable network morphologies from block copolymers has not been trivial because of high packing frustration at the interconnected junctions. In this study, we report a simple but powerful method to lower the packing frustration of network morphologies of block copolymers. A set of polystyrene-b-poly(ethylene oxide) (SEO) block copolymers were synthesized and various end-functional groups were introduced via different synthetic routes. This allowed the simultaneous control of junction molecules for end-functionalized SEO block copolymers. Notably, despite the symmetric block compositions, thermodynamically stable network morphologies of gyroid (Ia3d), orthorhombic network (Fddd), and double primitive cubic structure (Im3m) were obtained for SEOs upon attaching di-end-functional moieties. A fine-tuning of the packing frustration of network morphologies was enabled by controlling the type of junction molecule, which modulated the PEO chain conformation and the strength of end-end interactions. Our work established configurable packing frustration of network morphologies for block copolymers through the tailored end groups and junction molecules, which will be a platform of block copolymer self-assembly. |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T15.00013: Order-to-order transitions in architecturally asymmetric linear-block-bottlebrush copolymers using ionic liquids as selective solvents. Camila Perales Microphase separated block copolymers (BCPs) form technologically useful 3D networks (NETs) that find applications arising from their bicontinuous nature which enables orthogonal tunability of the properties of each domain, e.g., mechanically tough yet highly ion conductive materials. However, the the phase space over which NETs stably form is limited to small composition windows due in large part to the packing frustration associated with the nodes connecting NETs. Here, we explore how the addition of block selective solvents to an architecturally asymmetric linear-block-bottlebrush BCP induces order-to-order transitions. Six different ionic liquids with varying alkyl chain lengths are used in order to control the selectivity of the solvent for the minority linear segments. In situ small angle X-ray scattering is used to characterize the solvent-induced order-to-order transitions and to quantify the solvent selectivity. We show that the addition of ionic liquid allows for the formation of a variety of coexisting morphologies regardless of the selectivity of the solvent. |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T15.00014: Role of solvent quality on the morphology of concentrated block copolymer thin films Abdol Hadi Mokarizadeh, Mesfin Tsige In the last two decades, self-assembled block copolymer (BCP) thin films have received major interest as they have found applications in nanoelectronics, batteries, membrane filtration and drug delivery. There are experimental methods for tuning phase behavior of self-assembled block copolymer as each one brings some advantage into the way of controlling the self-assembly process. While solvent vapor annealing has been found to be very useful, there is no clear framework on how to control the different parameters such as solvent quality, temperature, and annealing vapor pressure for achieving a desired morphology in copolymers. Moreover, for the case of symmetric triblock or higher block copolymers, the formation of loop/bridge conformation can have a significant impact on the morphology and mechanical properties of the material where experimental limitations still exist in characterizations of loop/bridge conformations. In the present work, we employed a coarse-grained molecular dynamics simulation to investigate the effects of solvent quality and chain stiffness on the phase behavior of symmetric ABA triblock copolymer focusing on loop/bridge conformations for different morphologies. The results demonstrate the correlation between the solvent quality, chain conformations and phase behavior of the ABA copolymer. |
Thursday, March 9, 2023 2:18PM - 2:30PM |
T15.00015: Using fluorinated junctions to bias orientation of block copolymers Mingqiu Hu, Xindi Li, Javid Rzayev, Thomas P Russell We synthesized hydrophobic-hydrophobic block copolymers (BCPs) of poly(solketal methacrylate)-block-polystyrene, PSM-b-PS, with various volume ratios of the two blocks, with and without a fluorinated junction point. After hydrolysis of the PSM block into poly(glycerol monomethacrylate), the hydrophilic-hydrophobic block copolymers are within their strong segregation limit. In the BCPs with fluorinated junctions, the junctions have lower surface energy than both blocks. The fluorinated junctions tend to segregate to the polymer-air and polymer-substrate interfaces, promoting the orientation of the microdomain normal to the surface. For the BCPs with fluorinated junctions, we observed a mixture of perpendicular and parallel lamellae. When the thickness of the film is commensurate with the full pitch of the lamellae, the lamellae will tend to form a parallel orientation. Otherwise, when the film thickness is not commensurate with the full pitch, the lamellae are oriented normal to the interface. This perpendicular orientation is driven by the enthalpic gain of placing the fluorinated junctions at the interface. The lamellae are parallel to the substrate for BCPs without the fluorinated junctions for the same molecular weight. With the island-hole morphologies, a transition from parallel to perpendicular lamellae was observed at the edge of the islands. The transition is caused by the gradual change in film thickness at the edge of the islands, where the film thickness is no longer commensurate with the full pitch of the lamellae. The self-assembled morphologies were characterized by atomic force microscopy and grazing-incidence small-angle x-ray scattering. |
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