Macromolecular Theory and Simulations最新文献

Brownian Dynamics is used to investigate the scattering functions of ideal and excluded volume linear polymers in two to seven spatial dimensions. The scattering functions for ideal and excluded volume polymers examined are in agreement with theoretical predictions in all dimensions. As the dimension is increased, the scattering functions for the excluded volume chains converge toward the ideal results. These findings indicate that excluded volume chains behave more and more as ideal ones as the dimension gets larger.

Front Cover: In article number 2200076, Tiancheng Chen and Yuci Xu study the self-assembly of A(BC)₂B multiblock copolymer in a nanopore using the self-consistent field theory. Obtain the hierarchical concentric ring (HC_k), hierarchical perforated cylinder (HP_k), hierarchical helix (HH_k), and hierarchical disk (HD_k) in research. Then discuss the stability of hierarchical structures by exploring the influence of pore size and χ_AB on k.

Droplet coalescence is ubiquitous in nature and, at the same time key to various technologies, such as inkjet printing. Herein, this study reports on the coalescence of polymer droplets with different chain lengths coalescing on substrates of different wettability. By means of molecular dynamics simulations of a coarse-grained model, it is found that the rate of bridge growth is higher in the case of droplets with smaller contact angles (more wettable substrates) and decreases with the increase of the chain length of the polymers. Different behavior is also identified in the dynamics of the approach of the two droplets during coalescence with the substrate wettability playing a more important role compared to the chain length of the polymers. While the dynamics of the droplet are greatly affected by the latter parameters, the density profile and flow patterns remain the same for the different cases. Thus, this study anticipates that it provides further insights into the coalescence of liquid polymer droplets on solid substrates with implications for relevant technologies.

The renormalized bond lifetime model (RBLM) is a popular scaling theory for the effective lifetime of reversible bonds in transient networks. It recognizes that stickers connected by a reversible bond undergo many (J) cycles of dissociation and reassociation. After finally separating, one of these stickers finds a new open partner in time τ_open via a subdiffusive process whose mean-squared displacement is proportional to t^α, where t is the time elapsed, and α is the subdiffusion exponent. The RBLM makes convenient mathematical approximations to obtain analytical expressions for J and τ_open. The consequences of relaxing these approximations is investigated by performing fractional Brownian motion (FBM) simulations. It is found that the scaling relations developed in the RBLM hold surprisingly well. However, RBLM overestimates both τ_open and J, especially at lower values of α. For α = 0.5, corresponding to the Rouse limit, it is found that τ_open is overestimated by a factor of approximately 4x, while the approximation for J is nearly exact. The degree of overestimation worsens as α decreases, and increases to 1–2 orders of magnitude at α = 0.25, corresponding to the reptation limit. This has important ramifications for experimental studies that use RBLM to interpret rheology and dielectric spectroscopy observations.

Metropolis Monte–Carlo simulation is carried out for microphase-separated bulk state of AB diblock copolymers with various compositions. The distribution probability of end segments in long B-block chain are explored to determine the Wigner–Seitz(WS) cells as primitive cells for four known periodic structures, lamellar-, Gyroid-, cylindrical-, and spherical ones. The end segments are commonly turned to be localized at the several distinct far sites from the lattice points of WS cells for all morphologies investigated. Among them, when the fraction of A segments is 0.25, a hexagonal prism type column appears as a WS, while when the fraction is much lower at 0.1, body-centered cubic(BCC) lattice is formed and its end segments are found to be localized at hexagonal frames and also on the six square faces of truncated octahedron or Kelvin's Tetrakaidecahedron(KT), which has rarely been found in real soft material ever. This achievement is strongly pointing that each micelle formed by self-assembled diblock coplymers in bulk have essentially the framework of equivolume KT in real material systems.

High-temperature butyl acrylate polymerizations in bulk and in solution are investigated experimentally and by kinetic Monte Carlo (kMC) simulations. The experimental data comprise conversion-time data, molar mass distributions, and branching levels per polymer chain derived from size-exclusion chromatography with a multiangle laser light scattering detector. A kMC model is established, which allows for the description of the impact of solvent and temperature on molar mass distribution as well as type and content of macromonomers. Within the study kinetic coefficients for transfer to solvent and the thermal self-initiation of the monomer are determined according to the Metropolis Hastings algorithm. The kMC simulations provide information, which are otherwise not accessible, for example, the number of branch points per molecule as a function of molar mass or the molar mass distribution of various macromonomer species. Moreover, molar ratios of mid-chain and chain-end radicals are at hand for temperatures up to 160°C, which are important for the interpretation of the experimentally and via simulation-derived polymer topology as a function of molar masses.

Mean-square radius of gyration Rg² and the graph diameter D, which describe the dimensions of polymers, are investigated for the network polymers. Both for the random and nonrandom statistical networks whose cycle rank is r, a linear relationship Rg² = a_r D applies. The ratio ϕ of a_r against the corresponding ring-free architecture a₀, ϕ_r = a_r/a₀ has a universal relationship applicable both for the random and nonrandom networks with ϕ_r∝r^−0.25 for large r’s, and an empirical relationship, ϕ_r = [(1 + r)^−2/3 + r/2]^−0.25 is proposed. For the polymer fraction having a given number of r, the nonrandom nature of crosslinking tends to make both Rg² and D larger compared with the corresponding random networks, except for the limited cases with small values of r’s.

Given the importance of preserving the mechanical properties of recycled isotactic polypropylene (iPP) during its processing, this work provides an improved understanding of the contribution of introducing physical or chemical crosslinks using the dissipative particle dynamics (DPD) method, which makes it possible to model iPP structures with a realistic range of crosslink densities. First, the protocol to build a coarse-grained model of iPP from an all-atom expression by Bayesian optimization is described. A Bayesian optimization procedure employing two different cutoff distances successfully provides optimal DPD parameters reproducing iPP's properties compared to the all-atom system. Then, the coarse-grained iPP model with optimal DPD parameters is applied to study structures containing a realistic range of crosslink densities to evaluate their mechanical properties. These calculations demonstrate that the mechanical properties such as the Young's modulus and ultimate strength increase while the fracture strain decreases with an increase in the crosslink density, which is consistent with experimental observations. The results also show that there is a critical crosslink density above which these properties start to be improved due to the introduction of crosslinks. These findings can help us to obtain targeted properties of recycled iPP by introducing physical or chemical crosslinks.