Macromolecular Theory and Simulations最新文献

Robust mathematical treatment of the Ozawa/Flynn/Wall isoconversion method is conducted to determine the value and uncertainty of the activation energy and pre-exponential factor for the degradation of polypropylene in thermogravimetric analysis experiments at constant heating rates. The present work employs mathematical models and uncertainty propagation techniques based on the Guide to the Expression of Uncertainty in Measurement to estimate the Arrhenius activation energy and pre-exponential factor due to the uncertainty of the integration constant b, both in a linear and a third-degree reciprocal polynomial model with respect to x. The error arising from Doyle's linear approximation in the improper integral of temperature in the Arrhenius equation is examined, and an alternative method is proposed to correct this error, reducing it to 0.032% in the working interval of −200 ≤ x ≤ −15, where x = −E/RT. Given the increased sensitivity of modern thermogravimetric analysis equipment, these improvements are considered essential for obtaining reliable results that align with experimental precision limits compared to previous works. Thus, this allows for the development of an enhanced quality assurance framework by providing more robust uncertainty estimation and a better understanding of the method. Moreover, this approach can be applied to other similar polymer system.

Front Cover: Visualizing higher probability sites for end segments forming a matrix phase formed by B-component in a BCC lattice structure from an AB diblock copolymer. The red surfaces are the A/B interfaces, and the higher probability isosurface of end B-segments is displayed in green. The end segments are localized on the frame of the Kelvin's tetrakaidecahedron, truncated octahedron. This is reported by Jiro Suzuki and Yushu Matsushita in article number 2300016.

The structure of a thin film of symmetric ABA triblock copolymer melts in an external in-plane DC or AC electric field is studied theoretically. The situation is considered when the triblock copolymer forms a hexagonal morphology of standing cylinders in bulk in the absence of an external field. Self-consistent field theory calculations are carried out to determine the most thermodynamically favorable thin film structure among the cylindrical phases perpendicular and parallel to the substrate and the lamellar phase perpendicular to the substrate. The results are presented as phase diagrams with the film thickness and electric field energy on the axes and as distributions of the local composition, which serve as an order parameter in the system. It is confirmed that electric fields only weakly affect the spinodal curves of block copolymers but they can reorient or markedly modify microphase-separated morphologies in those systems. Such restructuring is consistent with a considerable modulation of the free surface of a copolymer film and it can lead to the coexistence of different phases that appear in the film areas with different local thicknesses.

The suitability of dissipative particle dynamics simulations is investigated to predict the dynamics of polymer chains in dilute polymer solutions. The authors find that the predictions depend on the value of the repulsive parameter for bead-bead pairwise interactions used in the DPD simulations (a_ij). For all systems, the chain sizes and the relaxation time spectrum are analyzed. For a_ij = 0, theta solvent behaviour is obtained, whereas the dynamics at equilibrium agrees well with the predictions of the Zimm model. For higher values of aij, the static properties of the chain show good solvent behaviour. However, the scaling laws for the chain dynamics at equilibrium show wide variations, with consistent results obtained only at an intermediate value of a_ij = 25. At higher values of the repulsive parameter (a_ij ⩾ 25), the simulations are also able to predict the abrupt cut-off in the relaxation spectrum, which has been observed earlier in experiments of dilute solutions. To verify further, the chain dynamics in shear flow using DPD simulations is studied. Specifically, the variation of the chain is analysed stretch and end-over-end tumbling with shear rates. Overall, the trends obtained from DPD simulations agree well with those observed in earlier BD simulations.

Monte Carlo simulations that examine the partitioning of dilute solutions of ring or linear chains into a slit pore using two chain models, the random-walk (RW) model and the self-avoiding walk (SAW) model are presented. The partitioning coefficients K for the ring and the linear chains at the surface interaction both under the critical adsorption point (CAP) and above the CAP are compared. In both chain models, K for the ring remains larger than K for the linear chains. The ring chain crosses over the point K = 1 at a weaker surface interaction than the linear chain. When extrapolated to infinite chain length, the cross-over point for the ring and linear chain becomes the same (within statistical errors) for the RW model but remains different for the SAW model. The density profiles of the ring within the pore reveal the development of humps near the wall as the surface interaction crosses over the CAP. The excluded volume interaction in the SAW model additionally impacts the partitioning of chains in a solution consisting of a binary mixture of ring and linear chains and makes the K values in a binary mixture differ from the monodispersed solutions.

Poly(aryl ether sulfone ketone) (PPESK) is an engineering plastic with high strength, good heat resistance, insulation, and chemical corrosion resistance. The properties of PPESK fiber prepared by centrifugal melt electrospinning can be improved, and the method is efficient and environmentally friendly. This article employs a systematic analysis to investigate the impact of process parameters on the jet formation process, jet motion, fiber diameter, fiber yield, and changes in molecular chain orientation of PPESK. The analysis uses dissipative particle dynamics simulation to reveal that PPESK fibers can attain a certain degree of refinement, and fiber yield can be increased with an appropriate increase in rotational speed, temperature, and electric field force. Moreover, for PPESK with different chain lengths, longer molecular chains impede the untwisting of the molecular chains within the fiber, weakening the fiber orientation, increasing fiber diameter, and resulting in a slower fiber yield increase. These simulation results provide theoretical guidance for preparing PPESK ultrafine fibers with the required performance, shortening the exploration process of actual spinning, and saving time and labor.

This study investigates the marginal distributions of grafted stiff polymer tips in a 2D embedding space using both analytical methods and Monte Carlo simulations. By mapping active Brownian particle (ABP) trajectories in the short-time regime, analytical expressions for the elongation of the free end of the polymer under horizontal and vertical forces are derived and these expressions are validated using Monte Carlo simulations. These results indicate that the theoretical predictions match well with the simulation results when the chain length is short or the force is large. However, a slight discrepancy is observed between the theoretical and simulation results when the chain is extremely long, although the qualitative asymptotic results remain valid. Additionally, expressions are provided for the horizontal and vertical force versus displacement for the wormlike chain under the weakly bending approximation. This research provides insights into how the trajectories of an ABP correspond to the equilibrium configuration of a semiflexible polymer. These findings have potential applications in various fields, including biophysics and materials science, where understanding the behavior of grafted polymers is crucial.

Front Cover: In article number 2300014, Yoshitake Suganuma and James A. Elliott investigate the effect of crosslink density on mechanical properties of isotactic polypropylene (iPP) by the dissipative particle dynamics (DPD) method. Coarse-grained structures of iPP (blue chains) with different numbers of crosslinks (magenta spheres) are developed from an all-atom model of iPP by Bayesian optimization, and their tensile tests are performed in DPD simulations.