Macromolecular Theory and Simulations最新文献

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.

Graphyne (GY) is a new carbon material with excellent electrical conductivity and low thermal conductivity (TC). The doping of GY into polymers to improve the thermoelectric properties of the material has become a hot research trend. In this study, molecular dynamics (MD) and nonequilibrium MD are used to study the effect of the number of oxidation units of polyaniline (PANI) on TC and heat transfer of PANI and GY/PANI systems. The geometric structure of polymer, interaction energy, and heat transport of all systems are studied and analyzed. It is found that (1) as the number of oxidation units of PANI increases, the interchain and intrachain heat transfers of PANI are decreased thereby decreasing the heat transfer of the PANI chains; (2) the weak interaction energy at the interface hinders the heat flux transfer, and the phonon vibration of GY and PANI mismatch at the interfaces; eventually the above reasons lead to low interface TC; (3) the doping of GY can effectively reduce the TC of the system. This study provides some research ideas and theoretical exploration for the application of polymer doped with GY composites in the field of thermoelectricity.

The graph diameter D is correlated with the mean-square radius of gyration Rg² and is a useful measure to design and control the network architecture. The fraction d of segments located in the diameter chain, defined by d = D/n_s, where n_s is the total number of segments in the polymer, is investigated for various statistical network polymers. It is found that the relationship between d and the cycle rank r of the well-developed statistical networks follows a master curve. As a convenient measure to define the well-developed networks, the network maturity index (NMI) is proposed. The random crosslinked networks with NMI > 3 are considered well-developed, but a larger value of NMI is required for the nonrandom, heterogeneous networks. With the help of prior knowledge of the relationship between Rg² and D, the master curve for the relationship between the contraction factor g and r can also be determined.

A Monte Carlo model is employed to investigate the grafting of maleic anhydride onto polypropylene using a peroxide initiator. The study aimed to develop a comprehensive model that considered a very detailed kinetic mechanism, including chain transfer to polymer, homopolymerization as well as several copolymer reactions. The relative importance of these reactions is evaluated using a sensitivity analysis, which identified homopolymerization, β-scission, chain grafting, and termination by disproportionation as the most influential reactions. The kinetic constants of these reactions are tuned to fit reported experimental data using the Surface Response Method. The model considers a pseudo-homogeneous reaction medium and predicts average molecular weights, degree of grafting, molecular weight distribution, and grafting distribution. Furthermore, model simulations provided useful information about the impact of initial concentrations of reactants and reaction time on the molecular properties of the grafted polymer.

Molecular dynamics method is employed to characterize the mechanical properties of polydimethylsiloxane (PDMS) materials reinforced by graphene nanoplatelets (GNPs). Modeling results demonstrate that the addition of GNPs to PDMS significantly improves the damping properties of PDMS at high temperatures. The underlying physical mechanism is further investigated, and it is found that the interfacial interactions between the GNPs and PDMS play a crucial role in the energy dissipation capabilities. At elevated temperatures, a decrease in the interaction energy between the GNPs and PDMS matrix is observed, increasing the interfacial shipment, and improving the energy dissipation. In addition, GNPs will reflect more impact energy at a higher temperature. This study provides valuable insights into the use of GNPs for the improvement of the damping performance of PDMS materials at high temperatures.

This study presents a numerical investigation of the dimerization of polyglutamine homo-peptides of varying length. It employs the PRIME20 intermediate resolution protein model and studies it with a flat-histogram type Monte Carlo simulation that gives access to the thermodynamic equilibrium of this model over the complete control parameter range (for the simulations this is temperature). For densities comparable to typical in vitro experimental conditions, this study finds that the aggregation and folding of the polyglutamine chains occur concurrently. However, as a function of chain length the sequence of establishment of intra- and intermolecular hydrogen bonding contacts changes. Chains longer than about N = 24 polyglutamine repeat units fold first and then aggregate. This agrees well with the experimental finding that, beyond N = 24 the single polyglutamine chain is the critical nucleus for the aggregation of amyloid fibrils. A finite size scaling of the ordering temperatures reveals that for this chain length (and longer chains) folding occurs at physiological (respectively larger) temperatures, whereas shorter chains are disordered at physiological conditions.