Macromolecular Theory and Simulations最新文献

In the present work, a phenomenological model built to represent the suspension polymerization of vinyl chloride in a continuous oscillatory baffled reactor is presented for the first time. Following a previous work (Silva et al., Chemical Engineering Science, 288, 119845, 2024), a tanks-in-series model is employed to represent the reactor and a backflow stream is also considered to simulate backmixing. The intrinsic heterogeneous behavior of vinyl chloride polymerization adds model complexity in comparison to vinyl acetate polymerization reported in the literature. Moreover, the stronger gel effect also makes the temperature control difficult since a higher number of cooling jackets is required to keep a uniform temperature profile. The influence of residence time on reactor operation is investigated. Furthermore, the effects of initiator type and injection points on the polymerization rates and polymer properties are evaluated and shown to influence the process operation significantly.

Utilizing ionic liquids in proton exchange membranes can greatly enhance the performance of fuel cells, enabling their application in high-temperature and dry conditions. Further advancements in this field depend on a fundamental comprehension of their structural characteristics. This study focuses on the sulfonated poly(ether ether ketone) (SPEEK)-1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIm][OTf] composite membrane system. Effects of sulfonation degree, ionic liquid content, and temperature on the structure and conductivity of the composite membrane are investigated by dissipative particle dynamics (DPD) and molecular dynamics (MD) simulations. Results show that [BMIm][OTf] is predominantly distributed around the sulfonic acid groups of SPEEK. At an optimal sulfonation degree and ionic liquid content, interconnected ionic liquid channels can be formed. Nevertheless, an excessively high sulfonation degree may jeopardize the stability of the membrane structure. Moreover, the aggregation of ionic liquid occurs at a high level of ionic liquid content, which hinders the efficient transfer of protons. Generally, increasing the temperature is more conducive to the formation of monodisperse ionic liquid channels within the SPEEK-[BMIm][OTf] composite membrane; however, overhigh temperature may compromise the integrity of the composite membrane structure. The findings of this study offer molecular insights for the development of high-temperature proton exchange membrane fuel cell systems.

This study presents an experimental measurement of interfacial thermal resistance (ITR) at polymer–polymer interfaces using a multi-layered bulk sample approach. ITR is commonly measured using thin-film techniques, but new advancements enable testing in bulk materials with multilayered structures. However, traditional multilayer fabrication is often resource-intensive and lacks consistency. This study introduces a simple rotational overlapping method for fabricating multi-layered polymer samples for bulk ITR measurement. Combining numerical simulations with experimental validation, researchers optimize layer overlapping conditions using measured viscosity data of high-density polyethylene (HDPE), polypropylene (PP), and polylactic acid (PLA). Samples are fabricated at viscosity-matching temperatures, and shear forces from stirring disks create uniform layer patterns. Computational fluid dynamics (CFD) simulations elucidate the layer formation mechanism, enabling the fabrication of samples with over 112 layers within a 4.6 mm thickness. ITR testing reveals a direct correlation between layer number and thermal resistance. PE-PP samples exhibit an average ITR of 9.58 × 10⁻⁶ K m² W⁻¹, with a 10.32% increase in resistance from 38 to 112 layers. Similarly, PE-PLA samples with an ITR of 1.31 × 10⁻⁵ K m² W⁻¹ show a 2.8% increase from 5 to 23 layers. Overall, The experimental procedure provides valuable data to advance the understanding of ITR in polymer–polymer interfaces.

The recent paper by Y. V. Kudryavtsev (Macromol. Theory Simul., https://doi.org/10.1002/mats.202400072) describes steady state conditions and kinetics of randomization in homopolymer/copolymer melts undergoing interchain exchange. By focusing on the analysis of the model equations, the author applies pseudo-first order rate coefficients, which can potentially lead to misleading conclusions, especially concerning kinetics of randomization. In this note, an extended approach, accounting for the second order of the exchange reactions and making the model applicable to polymer solutions, is proposed.

The theory of Odle et al. for the z-average of branched polycondensates is extended to the general case of co-cross-linking of primary chains with different functionalities. Examples are given for free radical and step growth polymerization. For polycondensates, assuming surplus of one functionality and complete conversion, a simple formula for the degree of polymerization DP_z for functional groups is derived:

This study integrates numerical simulations and tribological experiments using a plate-on-disc tribometer to examine the tribological behavior and wear mechanisms of cellulose materials in the solid transport screw of a parallel co-rotating twin-screw extruder. EDEM simulation results indicate that wear on the left screw primarily occurs on the screw threads while wear on the right screw is concentrated at the junction between the screw threads and the bottom of the screw groove. The meshing region experiences the most severe wear due to the combined effects of shear forces and contact stress. Tribological experiments with a plate-on-disc tribometer reveal that adding cellulose with higher aspect ratios reduces friction coefficients. When cellulose has a high aspect ratio, it improves the alignment of wear scar cracks and cellulose molecular chains on the friction contact surface. This results in a gradual alignment of rod-shaped structural cellulose in the direction of frictional sliding, which reduces impact-spalling wear, micro-cutting wear, and scratching abrasion wear. Additionally, cellulose with higher aspect ratios can withstand higher rotational friction speeds during high-speed friction, forming an orientation transfer layer on the friction contact surface. This enhances surface lubrication and reduces abrasive wear and adhesive wear.

The chain dynamics and the rheological property of the polymer solution in the microscale confined space (e.g., microchannel) are complex and still unclear. In this paper, based on the prior research work, a dissipative particle dynamics (DPD) method is established to systematically simulate the dynamic behavior of polymer chains and the properties of the polymer solution in microchannels by combining the modified FENE chain model and a new boundary condition setting, especially for the gradually contracted microchannel. It is found that the concentration of the polymer chain, the degree of constraint, and the Reynolds number influence the dynamic behavior of the polymer chain by changing the constraint effect or the hydrodynamic effect. In addition, the geometrical structure of the microchannel significantly changes the dynamic behavior of the polymer chain. The chain dynamics in the gradually contracted microchannel are quite different from that in the straight microchannel. Finally, the rheological characteristics of the power-law fluid and the lateral migration of the solid particle in the viscoelastic fluid in the microchannel are also simulated, and the simulation results are in good agreement with the result reported in the literature, which further verifies the accuracy of the present simulation method.

An isoconversional state diagram (ISD) method is a graphical representation of the commonly used model free kinetics (MFK) method. An ISD state curve describes the relationship between 1/T and lnβ at a certain conversion degree, where T is the temperature and β is the heating rate. The ISD tangent rule describes the pattern of intersection of two tangents to two adjacent state curves at given points having the same temperature, which can be used for the correction of random error in the experimental thermal analysis data. The comparison of kinetic predictions between the ISD and MFK methods shows that the corrective effect is evident and the prediction quality can be improved in the predictable heating rate and temperature ranges. Furthermore, the proposed implicit method simplifies the ISD construction procedure compared to the previous explicit method.