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 G04: Beyond Linear: Structure, Dynamics, Response and Unique Properties of Topological Polymers IIFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Ryan Poling-Skutvik, University of Rhode Island Room: Room 127 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G04.00001: Core-Shell Gyroid in ABC Bottlebrush Block Terpolymers Shuquan Cui, Bo Zhang, Liyang Shen, Frank S Bates, Timothy P Lodge Block polymer self-assembly provides a robust toolkit for creating useful materials with 3D periodic network morphologies. However, the network dimensions are limited in linear copolymers due to the coil conformations and the slow self-assembly kinetics at high molecular weights. A block bottlebrush architecture can circumvent both shortcomings owing to extended chain conformations and molecular dynamics substantially free of chain entanglements. However, until now network morphologies have not been reported in bottlebrush block polymers. In this work, we systematically explore the phase behavior of poly(ethylene-alt-propylene)-b-polystyrene (PEP-PS) diblock and PEP-PS-b-poly(ethylene oxide) (PEP-PS-PEO) triblock bottlebrush polymers prepared by ring-opening metathesis polymerization (ROMP). No network phases were found in the diblocks, whereas the addition of minor bottlebrush PEO blocks led to a substantial core-shell double gyroid (GYR) phase window. Encouragingly, the GYR unit cell dimensions increased as d ~ Nbb0.92 with the backbone degree of polymerization Nbb, portending the ability to access larger network dimensions than previously obtained with linear polymers. Besides the GYR network, several new intriguing phases also appeared in triblock bottlebrush terpolymers. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G04.00002: Atomistic Molecular Dynamics Simulations of Cyclic Bottlebrush Polymers Guang Chen, Elena Dormidontova Bottlebrush polymers (BBPs) with cyclic backbones have attracted significant attention due to their unique topological features. Experiments have shown that cyclic BBPs are more compact than their linear counterparts and suppress interpolymer associations. However, they have remained rather unexplored computationally compared to their linear analogs which would otherwise provide molecular details on the morphologies of cyclic BBPs. Using atomistic molecular dynamics simulations we investigate cyclic poly(vinyl alcohol)-graft-poly(ethylene oxide) BBPs (c-PVA-g-PEO) and focus on the side chain length effect. The dependence of the structural properties, shape change, and hydration properties on side chain length are studied. Our results provide scaling laws that describe the dependence of the size of BBPs on graft length in the limit of long and short grafts. We also demonstrate different regimes that determine the stretching of the backbone and the side chains. Moreover, we evaluate the local crowdedness of cyclic BBPs induced by the grafted chains, which affect the loading capacity for cyclic BBPs when used as a carrier. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G04.00003: Diffusion of Linear and Star Polyacids in Solution and Multilayer Assemblies Aliaksei Aliakseyeu, John F Ankner, Svetlana A Sukhishvili We studied diffusion of linear (LPMAA) and 4-, 6- and 8-arm star poly(methacrylic acids) (4PMAA, 6PMAA and 8PMAA, respectively) of matched molecular weights in solution and within electrostatic layer-by-layer (LbL) films. Linear and star PMAA (LPMAA and sPMAA, respectively) exhibited significant differences in mobility that were dependent on pH and salt concentration. Fluorescence correlation spectroscopy (FCS) showed that at high pH star polymers were more compact, with ~15% smaller hydrodynamic radius (Rh) of 8PMAA as compared to its linear counterpart. In contrast, hydrodynamic size of PMAA was independent on molecular architecture at low pHs where molecular conformations were determined by intermolecular hydrogen bonding. In the case of LbL films of the polyacids assembled with a linear polycation, molecular architecture did not impact film growth, but strongly affected PMAA mobility measured by fluorescence recovery after photobleaching (FRAP). For all the films, the dependences of PMAA diffusion coefficients on NaCl concentration were exponential, but sPMAA’s mobility was more responsive to the presence of ions. As a result, two regimes and a crossover salt concentration were identified, with LPMAA diffusing faster than sPMAA at low salt concentrations, and the opposite order of diffusion rates at higher salt contents. Possible contribution of the ionic-bonding-induced entanglements to this phenomenon will be discussed. |
Tuesday, March 7, 2023 12:06PM - 12:42PM |
G04.00004: Dynamics of Circular Macromolecules: Evidence of Rubber-like Behavior at High Z-numbers Invited Speaker: Gregory B McKenna It is "known" that macromolecular rings of modest molecular weight show no rubbery plateau. It is also known that addition of relatively small amounts of linear chain can lead to the development of a rubbery plateau, but one that is lower than that of the linear counterpart. In the present work, we explore this phenomenon in two series of experiments. First we examine solutions of mixtures of circular DNA with the linear analog to investigate the rubbery plateau and viscosity behavior. In this case, while the DNA is a very large molecule, the value of Zw varies from 2.6 to 8.4. We find that the rubbery plateau GN0 varies with linear chain content in a fashion similar to that reported in the synthetic polymer literature. At the same time, we also find a very large viscosity enhancement relative to the pure linear material for blends of 15% and 50% linear chains in the rings, the enhancements being greater than found in synthetic polymer investigations, thus suggesting that linear chain threading has a different impact on the rubbery response and the dynamics themselves. Second, we examine the behavior of circular poly(3,6-dioxa-1,8-octanedithiol) (polyDODT) synthesized by reversible radical recombination polymerization (R3P) that has molecular weights Mw from approximately 43 kg/mol to over 550 kg/mol, which corresponds to an entanglement number Zw from approximately 23 to over 300 if the chains were linear. We find that these systems exhibit a GN0 that is the same as that of the linear counterpart. However, upon diluting the systems to control the value of Zw, that GN0 scales similarly to the linear polymer except that the plateau disappears for Zw<15, i.e., a much higher nominal entanglement number. We also find that the circular macromolecules, below a critical value of Zw follow the same linear dependence of viscosity on Zw as do Rouse-like linear chains, but to much higher values of Zw. Furthermore, when the value of Zw exceeds 15 in the rings, the viscosity follows Zw5.8 whereas in the linear chains the viscosity turns to a Zw3.4 power dependence at approximately Zw=2. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G04.00005: Can linear block copolymers stabilize perpendicular lamellae in linear-cyclic block copolymer blend films? Rahul Kumar, Wenqi Yang, Julie N Albert, Henry Ashbaugh Block copolymer (BCP) thin films with lamellar nanostructures oriented perpendicular to the substrate surface are a potential alternative to photolithography for patterning nanoscale features. Molecular cyclization has been shown to reduce BCP feature size and improve thin film stability, but orientation control also is needed for lithography. Here, we use dissipative particle dynamics (DPD) simulations to study the relative stability of perpendicular (vs. parallel or mixed) lamellae of cyclic and linear BCPs. To mimic experiments, BCP chains are confined between a substrate (2D lattice of DPD beads), and a “gas” (bath of DPD beads). With non-selective surface interactions, both linear and cyclic BCPs form perpendicular lamellae as expected. To test relative stability, we increased the substrate surface preference for one of the blocks until lamellae oriented parallel to the substrate and found that perpendicular lamellae are more stable for linear BCPs than for cyclic BCPs. Moreover, adding 10% linear chains enhances perpendicular lamellae stability in majority-cyclic BCP blends without changing feature size. We seek to understand the thermodynamics behind these differences based on near-surface chain orientations and free energy calculations. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G04.00006: Investigation of the Self-Assembly Behavior of Statistical Bottlebrush Copolymers via Self-Consistent Field Theory Simulations Duyu Chen, Timothy Quah, Kris T Delaney, Glenn H Fredrickson In this work, we employ self-consistent field theory (SCFT) simulations to systematically investigate the phase behavior of statistical bottlebrush copolymers A-stat-B, an intriguing subclass of bottlebrush copolymers with random or alternating sequences of A and B side chains. We find that a broader variety of ordered mesophases can be stabilized in the melts of these copolymers relative to the more extensively studied bottlebrush block copolymers. In particular, we observe that these statistical copolymers can stabilize sphere phases over a larger range of species volume fractions than their diblock and tetrablock counterparts, but require much higher segregation strength to achieve this. The sphere and hexagonally-packed cylinder phases formed by conformationally symmetric statistical bottlebrush copolymers, possess interesting discrete core-shell structures with the backbone and lower volume fraction side-chain species forming shells and cores, respectively. Moreover, we uncover a new strategy of stabilizing the Frank-Kasper phase A15 by introducing conformational asymmetry through different side-chain lengths, and also observe deflection of order-order phase boundaries and significant mixing between the backbones and short side chains as conformational asymmetry is introduced. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G04.00007: Coarse-grained models and interactions of bottlebrush polymers Tianyuan Pan, Charles E Sing Bottlebrush polymers are a class of highly-branched macromolecules that have potential in self-assembled photonic materials applications. Despite the advancement in experimental techniques, computational studies of bottlebrush polymer solutions and melts remain challenging due to the high computational cost involved in explicitly accounting for the presence of side chains. In this work we consider a coarse-grained molecular model of bottlebrush polymers where the side chains are modeled implicitly, with the aim of expediting simulations by accessing longer length and time scales. The key ingredients of this model are the size of a coarse-grained segment and a suitably coarse-grained interaction potential between the non-bonded segments. We start from using finer grained explicit side chain models, with data obtained from Monte Carlo and Brownian Dynamics simulations. Then we incorporate the molecular information (size, stiffness, etc.) into an implicit side chain model. Finally we develop a workflow to extract the coarse-grained interactions from potential of mean force calculations, and achieve good agreements between the fine-grained and coarse-grained models. Though developed in the context of homopolymer bottlebrushes in athermal solvents, our proposed method can be extended to other solvent conditions as well as to different monomer chemistries. We expect our implicit side chain model will prove useful for accelerating large-scale simulations of bottlebrush solutions and assembly. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G04.00008: Co-continuous Nanostructure Formation by Randomly-Branched Copolymers of Polystyrene and Poly(D,L-lactide) Jaechul Ju, Ryan C Hayward Co-continuous polymer nanostructures (CPNs) have drawn much attention due to their synergistic combination of the properties of constituting polymers in three dimensions. While CPNs have been found to form robustly across a wide composition window of ~ 30 wt. % within randomly linked copolymer networks, these systems do not easily allow the formation of thin membranes due to their covalent network architectures. As a solution-processible alternative, we selected randomly-branched block copolymers, with the expectation that thin-films of CPNs could be fabricated while maintaining wide co-continuous composition windows. Mono- and di-azido-terminated polystyrene (PS) and poly(D,L-lactide) (PLA) were chosen as starting blocks due to their incompatibility, and they were coupled with multi-alkynes by copper-catalyzed azide-alkyne cycloaddition. To prevent gelation, the average polymer functionality (fp) was tuned by the ratio of mono- and di-azido terminated polymers, and crosslinker functionality (fc) was controlled by selecting one of three multi-functional alkynes. For each system, the composition of PS and PLA was varied and the window of co-continuity was determined by gravimetry and small-angle X-ray scattering. We found that the breadth of the co-continuous window widened upon increasing fp from unity toward the gel point for each value of fc, and that systems with fc = 4 could achieve a co-continuous window as wide as the previous network architectures, while maintaining the ability to form thin films by solution processing. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G04.00009: Exploring Conformations of Comb-like Polymers with Varying Grafting Density in Dilute Solutions Using Dissipative Particle Dynamics Carlos A Salinas Soto, Abelardo Ramirez-Hernandez, Su-Mi Hur Comb and bottlebrush polymers have shown potential as advanced materials for applications in polymer science due to the tunability of the polymer architecture. Tunable architectural parameters include: the density of grafted sidechains into the polymer backbone, σ , the backbone length, Nbb, and the sidechain length, Nsc. Grafting density has a strong effect on polymer conformations: as it varies from values characteristic of a linear polymer with no grafted chains (σ=0) to those of a bottlebrush (σ=1), comb-like polymers adopt stiffer conformations and the overall size of polymer increases. To predict the effect of the different molecular parameters on the conformations of comb-like polymers, scaling theories have been used. A free energy model in terms of exclude volume interactions and backbone’s elastic entropy has been proposed and used to describe experimental data, however the full validity of such free energy is still lacking. In this work, we have performed extensive simulations using Dissipative Particle Dynamics (DPD) and focused on two backbone lengths, Nbb=50, 100, and three sidechain lengths, Nsc=5, 10, 20, the grafting density was also varied from σ=0 to σ=1 . To quantify the effect of the different architectural parameters on polymer conformations we computed the gyration tensor, GM, to obtain the relative shape anisotropy parameter A3 , the asphericity, b, and the radius of gyration Rg. In addition, the backbone and sidechains end-to-end distances, the bond-bond correlation function, G(l) , and the Kuhn length were computed. Our results were compared to the scaling prediction (Rg/Rg,0)5∼(1+A0σ+A1σ2) proposed by Morozova and Lodge (2017)1 for the experimental conformations of methylcellulose grafted with polyethylene glycol (PEG); our data was also compared to the scaling relation (Rg/Rg,0)-1∼(σNsc)0.66 obtained by Tang et al. (2022)2 from Brownian Dynamics simulations. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G04.00010: Mesogen alignment in liquid crystal elastomer (LCE) microparticles under mechanical stress: experiments and simulations Chuqiao Chen, Viviana Palacio-Betancur, Annie Zhi, Stuart J Rowan, Juan J De Pablo When subjected to mechanical stress, liquid crystal elastomers (LCEs) undergo semi-soft deformations and the director field aligns in the direction of strain. The optical morphology gives distinct patterns corresponding to the stress field, thereby offering potential applications as stress-sensing devices. While the strategy can be employed at the microscopic scale, investigations to date have almost exclusively focused on LCEs in bulk, and the effect of geometric confinement has received little attention. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G04.00011: Effect of the mesogenic type of attachment and composition on the structural and viscoelastic behavior of side-chain liquid crystal polymer systems Diego Becerra, Lisa M Hall Side-chain liquid crystal polymers (SCLCPs) consist of a flexible backbone with mesogenic units attached in an end-on or a side-on configuration as pendant groups via flexible spacers. These molecules have potential applications in areas requiring controllable deformations. At high enough temperatures, entropic effects dominate, and the polymer chains approach a random walk configuration. In contrast, at lower temperatures, the liquid crystal (LC) groups can form ordered phases. We conduct coarse-grained molecular dynamics simulations of SCLCP systems with purely end-on and purely side-on groups, and also copolymers with both LC types at a variety of compositions. For some compositions, the transition temperature of copolymers lies below that of both respective SCLCPs with only one LC type, which we attribute to the disruption of the orientational and positional order of the crystalline mesophases when two different LC types are attached to the same polymer backbone. Also, we have observed that this non-monotonic behavior for the transition temperature is extended to the relaxation dynamics of the systems. This work provides molecular insights into the origin and mechanisms behind the non-monotonic trends observed in the structural and viscoelastic behavior of the SCLCP systems. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G04.00012: Synthesis and characterization of monodisperse liquid crystalline oligomers: Mapping the evolution of phase behavior from monomer to polymer Chun Lam Clement Chan, Shawn M Maguire, Callie W Zheng, Kirstin S Bode, Emily C Davidson The thermo-induced actuation and soft elastic behavior of liquid crystal (LC) polymers have led to their interest for a wide variety of applications, from soft robotics to elastocaloric devices. However, our current understanding of LC polymeric phase transitions is incomplete due to a number of competing variables, including molecular weight dispersity. Notably, the behavior of an LC polymer differs markedly from that of its constituent monomer; the effects of transitioning from monomer to polymer remains relatively unexplored. Here, we apply a new LC synthetic strategy to prepare a series of monodisperse LC oligomers of controlled lengths. We map the effects of increasing molecular weight on the thermal transitions of these LC materials. These results are contrasted with the behavior of comparable species prepared via conventional step-growth polymerization. These studies highlight important factors affecting LC transitions, allowing for the design of more tailored and precise LC behaviors. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700