Macromolecular Theory and Simulations最新文献

The entanglement length plays a key role in deciding many important properties of thermoplastics. A number of computational techniques exist for the determination of entanglement length. In Ahmad et al.,^[1] a method is proposed that treats a macromolecular chain as a 1D open curve and identifies entanglements by computing the linking number between two such interacting curves. If the curves wind around each other, a topological entanglement is detected. However, the entanglement length that is measured in experiments is assumed to be between rheological entanglements, which are clusters of such topological entanglements that collectively anchor the interacting chains strongly. In this article, the method of clustering topological entanglements into rheological ones is further elaborated and the robustness of the method is assessed. It is shown that this method estimates an entanglement length that depends on the forcefield chosen and is reasonably constant for chain lengths longer than the entanglement length. For shorter chain lengths, the method returns an infinite value of entanglement length indicating that the sample is unentangled. Moreover, in spite of using a geometry-based algorithm for clustering topological entanglements, the estimated entanglement length retains known empirical connections with physical attributes associated with the ensemble.

Step-growth polymerized systems of type “A3 + A1” are considered. The monomers bear, respectively, 3 or 1 reactive A group. During the reaction, an A group on one monomeric unit might react with an A group on another such unit, thus chemically coupling the two units involved. Complexly structured polymeric molecules are formed. The A3's act as branching points; the A1's as end cappers. At the end of the reaction, the population of molecules present in the reactor vessel varies in size and branching structure. A method is presented to calculate the bivariate (molecular size) × (square radius of gyration) number distribution. It is shown that within the class of molecules of the same size, their square radius of gyration follows a shifted gamma distribution. Two new molecular parameters are introduced: the D index and the G index. The method uses bivariate generating functions.

A time–temperature-transformation diagram is created for the curing reaction of a diglycidylether bisphenol A (DGEBA)-based epoxy resin. It results from a kinetic analysis performed by means of dynamical differential scanning calorimetry (DSC) measurements; a gelation curve determined with isothermal and dynamical rheological tests; and a vitrification curve obtained from temperature-modulated dynamic DSC measurements. The resulting diagram is validated by comparison of isothermal measurements with the corresponding calculated curves.

Lignin, a renewable aromatic polymer, has great potential as a synthetic building block for functional materials. The effects of quaternary ammonic methylation of alkali lignin (AL) on the morphologies and ofloxacin antibiotic (OA) removal application from water are investigated by using the dissipative particle dynamics (DPD) simulation method. Untreated AL can form spherical aggregates, but the phenylpropane units of untreated AL and loaded broad-spectrum OA molecules are randomly distributed in aggregates. However, if quaternary ammonic groups are grafted onto all orthopositions of the phenolic hydroxyl groups (100-QAMAL), then multilamellar spherical aggregates are obtained and OA molecules are entrapped in the aggregates. To prepare multilamellar spherical aggregates with an ordered and regular layered structure, <15 v% of 100-QAMAL and low molecular weights of AL (≈4700–9400 Da) are suggested to be used. Lignin-based multilamellar spherical aggregates can be adopted as potential functional carriers for removing pollutant OA from water.

Solid polymer electrolytes are being explored as replacements for organic electrolytes in lithium-ion batteries due to their less flammable nature and high mechanical strength. However, challenges remain, such as low ionic conductivity, and significant interfacial impedance with electrodes. Understanding the structure and dynamics of ions within polymer electrolytes and near the anode is crucial for enhancing battery performance and safety. In this study, the structural and dynamic properties of lithium cation (Li⁺) and bis(trifluoromethane sulfonyl)imide anion (TFSI⁻) in poly(ethylene oxide) matrix are examined in bulk PEO-LiTFSI electrolyte and in the presence of a graphite surface using molecular dynamics simulations. The findings suggest that the presence of graphite surface does not affect the coordination of oxygen atoms around the Li⁺ ions. Results also show that the dynamics of the ions and ether oxygen is hindered near the graphite surface compared to the region away from the graphite surface.

In order to investigate the effect of rheological parameter of blends on mixing performance of dynamic mixers, the flow of virtual material (VM)/thermoplastic polyurethanes (TPU) with high and low viscosities in it are simulated. The effect of rheological parameter ratios, including zero shear viscosity ratio (η_0VM/η_0TPU), relaxation time ratio (λ_VM/λ_TPU) and non-Newtonian index ratio (N_VM/N_TPU) on pressure drop (Δp), segregation scale (S), and power consumption (P) are analyzed using Taguchi Orthogonal Method, and the effects of rotation speed (n) of the rotor and flow rate ratio (Q_VM/Q_TPU) are studied using single factor method. The results indicate η_0VM/η_0TPU is the most significant factor affecting Δp, S, and P. When η_0VM/η_0TPU = 1, λ_VM/λ_TPU = 1, N_VM/N_TPU = 1, S of blends reach the minimum value. With n increasing, the influences of Q_VM/Q_TPU and viscosity of TPU on S are reduced.

An improved viscoelastic spring lattice model is used to analyze the mechanical properties of polymer composites containing different microstructures, as exemplified by hydroxyl-terminated polybutadiene-based solid propellants. A drop-on-demand structural model is programmed using the C language to simulate the real solid propellant microstructure. The results show that increasing the particle content has a positive effect on the tensile strength of the propellant, but is detrimental to the ductility. The increase in particle size decreases the maximum tensile strength of the material, reflecting the importance of the dewetting process in the microstructure analysis. Finally, the model accurately predicts that initial defects have a destructive effect on the mechanical properties of the material.