We perform all-atom molecular dynamics simulations of lithium triflate in 1,2-dimethoxyethane using six different literature force fields. This system is representative of many experimental studies ...of lithium salts in solvents and polymers. We show that multiple historically common force fields for lithium ions give qualitatively incorrect results when compared with those from experiments and quantum chemistry calculations. We illustrate the importance of correctly selecting force field parameters and give recommendations on the force field choice for lithium electrolyte applications.
We study a binary blend of telechelic homopolymers that can form reversible AB-type bonds at the chain ends. Reversibly bonding polymers display novel material properties, including thermal ...tunability and self-healing, that are not found in conventional covalently bonded polymers. Previous studies of reversibly bonding polymer systems have been limited by the computational demand of accounting for an infinite number of possible reaction products in a spatially inhomogeneous, self-assembled structure. We demonstrate that newly developed theoretical models and numerical methods enable the simultaneous computation of phase equilibrium, reaction equilibrium, and self-assembly via self-consistent field theory. Phase diagrams are computed at a variety of physically relevant conditions and are compared with nonreactive analogues as well as previous experimental studies of telechelic polymer blends.
A wide range of field-update algorithms for polymer self-consistent field theory (SCFT) and field theoretic simulations (FTSs) are analyzed. We provide the first direct comparison between Anderson ...mixing and fictitious relaxational dynamics for SCFT and find nearly equivalent performance when both schemes are properly tuned. We also show that predictor–corrector algorithms are the most efficient among fictitious dynamics approaches despite increased costs per step. For FTS, adaptive time stepping is found to dramatically improve algorithm stability for inhomogeneous systems and enable simulation at much lower chain length and density than was previously achievable.
The hexagonally close-packed (HCP) sphere phase is predicted to be stable across a narrow region of linear block copolymer phase space, but the small free energy difference separating it from ...face-centered cubic spheres usually results in phase coexistence. Here, we report the discovery of pure HCP spheres in linear block copolymer melts with A = poly(2,2,2-trifluoroethyl acrylate) (“F”) and B = poly(2-dodecyl acrylate) (“2D”) or poly(4-dodecyl acrylate) (“4D”). In 4DF diblocks and F4DF triblocks, the HCP phase emerges across a substantial range of A-block volume fractions (circa f A = 0.25–0.30), and in F4DF, it forms reversibly when subjected to various processing conditions which suggests an equilibrium state. The time scale associated with forming pure HCP upon quenching from a disordered liquid is intermediate to the ordering kinetics of the Frank–Kasper σ and A15 phases. However, unlike σ and A15, HCP nucleates directly from a supercooled liquid or soft solid without proceeding through an intermediate quasicrystal. Self-consistent field theory calculations indicate the stability of HCP is intimately tied to small amounts of molar mass dispersity (Đ); for example, an HCP-forming F4DF sample with f A = 0.27 has an experimentally measured Đ = 1.04. These insights challenge the conventional wisdom that pure HCP is difficult to access in linear block copolymer melts without the use of blending or other complex processing techniques.
The distinctiveness of nonconcatenated ring polymers, as manifested in their fractal globular conformations and self-similar dynamics with no long-lived entanglement network, propels the idea of ...using ring topology to transform the phase behavior of block copolymers. With limited experimental studies of high-molecular-weight diblock ring polymers, large-scale molecular simulations of symmetric diblock copolymers are used to investigate the effects of nonconcatenated ring topology on their phase behavior. The absence of an entanglement network facilitates the phase-separation kinetics, suggesting relative ease in processing diblock ring polymers. The more compact globular conformations of ring polymers with respect to the Gaussian random-walk conformations require a higher enthalpic repulsion to drive the lamellar phase separation. Compared with the mean-field theory for the order–disorder transition in Gaussian diblock ring polymers, the simulations demonstrate the necessity for a new theory incorporating both the effects of fluctuations and the topological invariance of nonconcatenation. In the strong segregation regime, diblock ring polymers are stretched near the lamellar interface but with the globular conformational statistics preserved at larger length scales. The lamellar spacing d increases with enthalpic repulsion between the two blocks as well as the molecular weight of the diblock ring. The scaling argument for d of diblock linear polymers is modified by accounting for the globular conformations and predicts well the dependencies of d on the enthalpic repulsion and molecular weight. The lamellar interface becomes sharper as the enthalpic repulsion increases. While the theory predicts that the intrinsic interfacial width does not depend on the polymer molecular weight or topology, the apparent interfacial width w, which is broadened by the capillary wave, exhibits slight variation with the molecular weight and topology.
We present a new methodology for polymer self-consistent field theory (SCFT) that has spectral accuracy in the contour dimension while retaining linear scaling of computational effort with system ...size. In contrast, traditional linear-scaling algorithms only have polynomial order accuracy. The improved accuracy allows for faster simulations and lower memory costs compared to traditional algorithms. The new spectral methods are enabled by converting from an auxiliary field representation to a recently developed “polymer coherent states” framework.
The small specific entropy of mixing of high molecular weight polymers implies that most blends of dissimilar polymers are immiscible with poor physical properties. Historically, a wide range of ...compatibilization strategies have been pursued, including the addition of copolymers or emulsifiers or installing complementary reactive groups that can promote the in situ formation of block or graft copolymers during blending operations. Typically, such reactive blending exploits reversible or irreversible covalent or hydrogen bonds to produce the desired copolymer, but there are other options. Here, we argue that ionic bonds and electrostatic correlations represent an underutilized tool for polymer compatibilization and in tailoring materials for applications ranging from sustainable polymer alloys to organic electronics and solid polymer electrolytes. The theoretical basis for ionic compatibilization is surveyed and placed in the context of existing experimental literature and emerging classes of functional polymer materials. We conclude with a perspective on how electrostatic interactions might be exploited in plastic waste upcycling.
We use self-consistent field theory (SCFT) to map phase boundaries between periodic microphases for linear, comb-like, and bottlebrush diblock copolymers with continuous Gaussian, discrete Gaussian, ...and freely jointed chain statistics. By using a properly defined asymmetry parameter, composed of a variety of architectural parameters including side-chain length and segment length, we obtain a universal phase diagram for sphere phases that include A15 and σ phases. We do not observe a transition from comb-like to bottlebrush scaling with architectural parameter variation, which we attribute to the mean field approximation of SCFT.
Polymers are an effective test-bed for studying topological constraints in condensed matter due to a wide array of synthetically-available chain topologies. When linear and ring polymers are blended ...together, emergent rheological properties are observed as the blend can be more viscous than either of the individual components. This emergent behavior arises since ring-linear blends can form long-lived topological constraints as the linear polymers thread the ring polymers. Here, we demonstrate how the Gauss linking integral can be used to efficiently evaluate the relaxation of topological constraints in ring-linear polymer blends. For majority-linear blends, the relaxation rate of topological constraints depends primarily on reptation of the linear polymers, resulting in the diffusive time \(\tau_{d,R}\) for rings of length \(N_R\) blended with linear chains of length \(N_l\) to scale as \(\tau_{d,R}\sim N_R^2N_L^{3.4}\).
Acylsugars are polyesters of short-to medium-length acyl chains on sucrose or glucose backbones that are produced in secretory glandular trichomes of many solanaceous plants, including cultivated ...tomato (Solanum lycopersicum). Despite their roles in biotic stress adaptation and their wide taxonomic distribution, there is relatively little information about the diversity of these compounds and the genes responsible for their biosynthesis. In this study, acylsugar diversity was assessed for 80 accessions of the wild tomato species Solanum habrochaites from throughout the Andes Mountains. Trichome metabolites were analyzed by liquid chromatography-time of flight-mass spectrometry, revealing the presence of at least 34 structurally diverse acylsucroses and two acylglucoses. Distinct phenotypic classes were discovered that varied based on the presence of glucose or sucrose, the numbers and lengths of acyl chains, and the relative total amounts of acylsugars. The presence or absence of an acetyl chain on the acylsucrose hexose ring caused clustering of the accessions into two main groups. Analysis of the Acyltransferase2 gene (the apparent ortholog of Solyc01g105580) revealed differences in enzyme activity and gene expression correlated with polymorphism in S. habrochaites accessions that varied in acylsucrose acetylation. These results are consistent with the hypothesis that glandular trichome acylsugar acetylation is under selective pressure in some populations of S. habrochaites and that the gene mutates to inactivity in the absence of selection.
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