Macromolecular Theory and Simulations最新文献

In the realm of polymer composites, the research of nanoparticles has risen in prominence. Graphene oxide (GO) is one of the best nanofillers in natural rubber (NR). In this work, GO nanosheets are utilized as reinforcement in an NR composite to anticipate mechanical characteristics. The researchers project the effect of GO sheets in NR with varied volume percentages and defective GO sheet reinforcement in NR composites. When the volume percentage of GO sheet in the NR nanocomposite is 4.6% and 7.2%, respectively, the value of Young's modulus rose by 68.8% and 166.2%. GO/NR with a 7.2% volume fraction has the highest ultimate tensile strength as compared with lower volume fractions of GO/NR nanocomposites. An increase of 63.49% in ultimate tensile strength in GO/NR nanocomposites (7.2% vol fraction) is seen as compared with pristine NR. Creep characteristics of NR nanocomposites are also investigated. The results reveal that the addition of GO sheets considerably increases the creep resistance strength of NR nanocomposites. The zone of secondary creep grows narrower as the continuous stress level increases.

Polydimethylsiloxane (PDMS) membrane in suitable-fluorinated level have excellent pervaporation performance as well as antibiological contamination performance. The pervaporation membranes with different PDMS/fluorosilane mass ratios, the adsorption and dissolution behaviors of acetone molecules on the membrane surface, as well as the diffusion and permeation behaviors in the membranes are studied by all-atom molecular dynamics simulation (AAMDS). The results show that when the mass ratio of PDMS/fluorosilane is 100/20, the surface solubility of acetone is 11.711 (J cm⁻³)^0.5, and the interfacial interaction is −16897.0415 kcal mol⁻¹, both of which are the highest. The results of wide-angle X-ray diffraction (WAXD) showed that there are amorphous regions in the membranes suitable for acetone penetration. The maximum chain spacing of the PDMS/fluorosilane(100/20)_membranes is 10.8482 Å, and the free volume fraction (FFV) is 3.03%, both of which are the largest. The change rate of long-term mean square displacement (MSD) in PDMS/fluorosilane(100/20)_Membrane with time is 0.45269. The Young's modulus E, shear modulus G, volume modulus K, and Poisson's ratio ν of PDMS/fluorosilane(100/20)_Membrane are 0.3249, 0.4061, 0.0492 GPa and -0.5999, respectively. The elasticity of the membrane enhances the diffusion behavior of acetone molecules, and the self-diffusion coefficient of acetone in the membrane is 0.07545 Ų ps⁻¹.

Mean-square radius of gyration Rg² and the graph diameter D of the random crosslinked network polymers are investigated to find a linear relationship, Rg² = a D. The proportionality coefficient, a is dominated by the cycle (circuit) rank, or the number of intramolecular crosslinks k_c, and a convenient equation is proposed for the relationship between a and k_c. This relationship makes it possible to estimate Rg² based on D and k_c, which can reduce the required computational time to determine the Rg²-values greatly. This new method is applied to find that the contraction factor g decreases with k_c, and the differences in the primary chain length distribution that constitute the network polymers vanish for large k_c-values.

Nitrile-butadiene rubber (NBR) has been wildly applied in vibration control technology, it is usually mixed with organic small molecular modifiers and well vulcanized, which can greatly enhance the mechanical and damping properties of the material. This work aims to design the optimum blending ratio of hindered phenol A/B/NBR composite with the best damping property by means of molecular dynamics (MD) simulation, and investigate the mechanical performance from the molecular level. The shear deformation simulation is conducted on pure NBR models to study the impact of rubber crosslink degree (CD) on elasticity and plasticity of NBR. To research the damping mechanism of the material, detailed analyses of the micro molecular structure and reciprocating shear simulation are carried out on NBR composite models with different hindered phenol A/B ratio. The simulation results indicate a strong positive correlation between intermolecular H-bonds and loss factor η, and the NBR composite with hindered phenol A/B per hundred rubber (phr) 30/30 shows the best damping performance.

A novel kind of dual-speed corotating non-twin kneading elements with a zero stagger angle is designed to improve mixing ability. The physical model considering several narrow gaps is developed where the inlet and outlet transition sections are also included. Finite element method associated with the mesh superposition technique is further applied to solve the time-dependent flow field where fluid is assumed to obey the Carreau constitutive model. The tracers initially from different locations are tracked using a self-developed fourth-order Runge–Kutta scheme. Distributive mixing is evaluated through evolution of tracer droplets and decaying of variance index with time. In addition, a Lagrangian statistics method is used to characterize the dispersive mixing in terms of the statistical distributions of mixing index and their integration areas within the range of mixing index larger than 0.5. In contrast, the kneading elements of a conventional twin screw configuration are also modeled to show the mixing difference.

Front Cover: Phase behavior of symmetric ABCBD pentablock quarterpolymers has been investigated by Monte-Carlo simulation. Two alternating helices of red(A) and blue(B)) domains are trapped in {100} large homochiral holes of the level surface for the Schoen's Gyroid surface indicated in green. The red and blue helices are naturally packed tetragonally with the same helical sense, i.e., they keep homochirality. This is reported by Jiro Suzuki, Atsushi Takano, and Yushu Matsushita in article number 2200015.

The structure of model compounds for the amphiphilic copolymer poly(diisobutylene-alt-maleic acid), DIBMA, is investigated with (gas phase) B3LYP/6-31G** and PM7 calculations. It is found that in the monoprotonated state of the repeating unit strong (about 70 kJ mol⁻¹) ionic hydrogen bonds are formed within the hydrogen succinate rings, which impart partial structural rigidity on the backbone of the copolymer. Based on literature pK_a values of the first and second deprotonation step of the succinic acid units, it is argued that the ionic hydrogen bonds are likely to be present in aqueous solution as well. The main chain conformation depends strongly on the stereochemical configuration of the carbon atoms in the hydrogen succinate rings. The possible consequences of the hydrogen bonding for the mechanism of membrane solubilization by maleic acid-based amphiphilic copolymers are discussed.

The effects of the primary structure of multifunctional reactive polymers on the network structure and the mechanical properties of gels formed by crosslinking the reactive polymers with crosslinkers are studied by a coarse-grained molecular dynamics simulation. When functional groups are randomly arranged on the polymers, the network structure, such as the number densities of elastically effective chains and entanglements, and the mechanical properties depend on the number average molecular weight of the polymers; however, these properties are almost independent of the molecular weight distribution and the functional group number distribution of the polymers. The control of the arrangement of functional groups on the polymers improves the uniformity and the mechanical properties. By changing the arrangement from a random one to a periodic one, the number of elastically effective chains and the shear modulus increase, and the occurrence of entanglement is suppressed. The detailed analysis of the network structure reveals that the improvement of the mechanical properties is mainly due to the reduction of intramolecular crosslinking.

In this work the role of spherical confinement combined with single and block mutations in small peptides on the onset of specific conformational states is analyzed. An intramolecular potential for the polypeptide chain, composed by a bending term plus a Lennard-Jones type long range potential is proposed. For the intermolecular interaction with the sphere an integrated Lennard-Jones (LJ) type potential is used between monomers and the sphere surface. To compute the set of minima values for the total intra and intermolecular potential a combination of a multi-population genetic algorithm and an hybridized Nelder—Mead simplex algorithm are used, that yield to a larger degree of precision in the prediction of the set of minima potential energy values. To characterize the conformational states of the peptides the gyration tensor, radius of gyration, the asphericity, and the linear anisotropy are computed, and the influence of single-point and block mutations on the most energetically stable conformations are assed. Results suggest that the spherical confinement does have a significant influence of the polymer conformations; and single-point mutations introduced along the chain also have a prominent role on peptide's folded states. This opens up the possibility to targeted-designed peptides with particular and desired properties upon folding.