Macromolecular Theory and Simulations最新文献

Polyhydroxybutyrate (PHB) is a sustainable and compostable polyester, which has great potential for use as food packaging film, having similar barrier properties to conventional plastics. PHB is semi-crystalline and is often copolymerised with polyhydroxyvalerate (PHV) to form poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Molecular dynamics (MD) simulations provide valuable insight into the polymer structure and gas diffusion, but the accuracy of MD simulations depends on the force field. This work presents a modified all-atom General Amber Force Field that enables PHB, PHV and PHVB copolymers to be modelled. The structural properties of crystal and amorphous phases of PHB and PHV were in good agreement with experiment. The diffusion coefficients of water and oxygen in amorphous PHB were also in good agreement with experimental values. The diffusion coefficient of oxygen in PHV was larger than in PHB, mainly due to the lower density of PHV. The diffusion coefficient of water in PHV was similar to PHB as its diffusion is hindered by the interaction of water with the polar ester groups on the polymer chains. This force field can be used to investigate the diffusion of water and oxygen in PHB, PHV and PHBV copolymers, and to optimise the barrier properties of PHBV-based plastic film.

Understanding the ionization behavior of weak polyelectrolytes in aqueous solutions with added salt is crucial for designing advanced materials. Predicting the ionization states of weak polyelectrolyte is challenging due to the interplay between long-range Coulomb interactions, conformational flexibility, and chemical equilibria. Bead-spring models with explicit ion treatment provide accurate results but are computationally expensive. In contrast, Ising-like site-binding models are computationally efficient but neglect conformational flexibility and use an implicit salt description. To assess the validity of these approximations, a site-binding model is compared with bead-spring models that include implicit and explicit ion treatments. These results show that under strong electrostatic coupling, explicit ion treatment is critical for accurately modeling ionization behavior. Both the site-binding and implicit bead-spring models overestimate monomer correlations in this regime, leading to significant deviations from the explicit bead-spring model. Under weak coupling, typical of aqueous environments with monovalent salts, all models give reasonable ionization curves, with slight differences. The implicit bead-spring model shows slightly stronger suppression of ionization, while the site-binding model aligns more closely with the explicit bead-spring model due to compensating errors in ion treatment and flexibility. In conclusion, while all models perform well under weak coupling, explicit ion treatment is essential for accurate ionization under strong coupling.

In this paper, the dynamic deformation of supercritical CO₂ bubbles in the shear flow field of polyethylene terephthalate (PET) is analyzed, and the dynamic continuous extrusion process of PET microcellular foaming is numerically simulated. The extrusion process of PET supercritical CO₂ homogeneous solution is simulated by the user defined function (UDF) program, and the volume of fluid (VOF) method is used to track the gas-liquid interface. The deformation of supercritical CO₂ bubbles in the PET microcellular foaming extrusion process is simulated in FLUENT software. It is found that in the continuous dynamic extrusion process, the bubble moves with the polymer at a certain angle, and there will be an area at the two ends to inhibit the shear thinning of the melt, which affects the movement pattern of the bubble. The increase in shear rate is the main factor causing the increase in the aspect ratio of the bubble. The increase of the rheological index can promote the bubble to maintain the spherical shape by affecting the shear flow field around the bubble. In addition, it is found that the effect of surface tension on bubble morphology in the shear flow field is not as large as that in the static flow field.

A centrifugal technique for separating molten polymer blends is investigated. In a rotating cylinder, the components of mixtures of LDPE (Low-Density Poly(Ethylene)) and PET (Poly(Ethylene) Terephthalate) are separated, which is enabled by the different component densities. The separation quality depends on material and operational parameters. More details can be found in article 2400109 by Günter Brenn and co-workers.

The critical importance of solvent selection in lutein solvation lies in its significant commercial value and health benefits. This study employs molecular dynamics (MD) simulations to elucidate the atomic-level interactions of lutein with 2-methyl tetrahydrofuran (2-MeTHF), a microemulsion system (Tween 80: n-propanol: isoamyl acetate: water), a deep eutectic solvent (DES) (choline chloride: glucose, 1:3 molar ratio), and hexane. This study addresses the gap in atomic-scale understanding of lutein-solvent interactions by providing a comparative analysis. MD simulations offer comprehensive insights into structural properties, such as radial distribution functions (RDF), hydrogen bonding (H-bonding) dynamics, and transport properties like mean square displacement (MSD) within these solvent systems. The analysis reveals that DES exhibits the highest suitability for lutein solvation among the solvents studied, suggesting its potential to enhance extraction efficiency while significantly reducing environmental impact, which is validated by experimental literature. These findings contribute to developing more efficient, sustainable, and environmentally friendly extraction techniques for lutein and similar bioactive compounds, potentially benefiting the extraction of other xanthophylls and structurally related molecules.

The metering section of an industrial-scale single screw extruder is modeled, and two kinds of discontinuous baffles, three rows of plate baffles, and two types of plow-shaped baffles, arranged in staggered or parallel ways, are proposed to improve the distributive and dispersive mixing. Considering the narrow gap between the screw and barrel, the finite element method along with the mesh superposition technique is applied to solve fully 3D isothermal flow fields where the fluid is assumed to obey the Carreau constitutive model. The computation codes are successfully developed to achieve particle tracking using the fourth-order Runge–Kutta scheme. Distributive mixing is evaluated in terms of the evolution of tracer particles and Poincaré sections. Dispersive mixing is then examined in terms of shear rates, mixing index, distribution probability function of mixing index, and its integral function for particles tracking with time. For the same pressure drop and the same screw rotating speed, when compared to the conventional single screw, the numerical simulation results showed that the screw with staggered plow-shaped baffles achieved better distributive mixing with the output nearly unchanged while three rows of plate baffles significantly enhanced both distributive and dispersive mixing at the cost of output reduction by 13.2%.

A general algorithm is introduced to compute single-chain partition functions in field-theoretic simulations of polymers with nested tree-like topologies, including self-consistent field theory simulations that invoke the mean-field approximation. The algorithm is an extension of a method used in a number of recent studies on the phase behavior of bottlebrush block copolymers. In those studies, the computational cost of computing single-chain partition functions is reduced by aggregating the statistical weight of degenerate side arms. By extending this method to chains with arbitrary degrees of branching, the computational cost is reduced to scale with the total length of unique segments in the chain instead of the total length/mass of the entire chain. The method is first validated on a model dendrimer system by comparing results to coarse-grained molecular dynamics simulations and also demonstrate its advantage over more conventional approaches to compute single-chain partition functions. The algorithm is subsequently used to analyze the phase behavior of a molecularly informed field-theoretic model of poly(butyl acrylate)-graft-poly(dodecyl acrylate) (pBA-graft-pDDA) copolymers in a dodecane solvent. The methodology can help advance field-theoretic investigations of branched polymers by leveraging degeneracy in the chain to reduce computational cost and avoid the need to develop architecture-specific algorithms.