Friction-induced energy dissipation is one of the key factors contributing to the unique properties of granular materials, such as the preparation history dependence of the packing structure. However, it remains unclear whether or not more realistic systems that involve two or more types of friction possess unique properties distinct from those that are frictionless or with a single type of friction. Here, we use numerical simulations to investigate the packing structure of binary mixtures of particles with particle type-dependent friction coefficient. Taking single-component systems as reference, we use an effective friction coefficient mu e to represent the overall frictional strength in granular systems prepared via different protocols. Our results demonstrate that mu e exhibits a power-law dependence on the individual friction coefficients. Furthermore, we propose models that accurately predict the packing structure of frictional particle systems across a range of compositions, size ratios, and preparation protocols.

Semi-flexible [2]catenanes with varying ring sizes exhibit tumbling, slip-tumbling and fold-slipping dynamic behaviors under steady shear flow conditions.

We investigate the ring-linear polymer blends under Poiseuille flow across a range of flow intensities. As rings are flexible (K- br = 0), the threading probability gradually increases with an increase in flow field strength. However, as rings are semiflexible (K- br > 0), the threading probability significantly decreases and then significantly increases as the flow field strength increases. Additionally, for different ring rigidity parameters, the critical flow field strength corresponding to the rapid increase in the threading probability is almost the same. When the flow field strength exceeds this critical value, ring-linear polymer blends will aggregate into a cluster due to the combination of entanglement between polymers and the large differences in the velocities of the polymers. The cluster moves along the direction of the flow field and can be bisected by the flow channel's centerplane into two parts, and each part performs the tank-treading motion in opposite directions: one moving counterclockwise and the other moving clockwise. The dynamic movement of the cluster significantly promotes an increase in threading probability. Furthermore, the nonlinear relationship between the characteristic time of tank-treading motion and flow field strength suggests that the structure of the cluster exhibits similar dynamic and structural behaviors over a certain range of flow field strengths. The results could enhance our understanding of the intricate threading properties observed in ring-linear polymer blends upon exposure to external force fields.

The dynamical and conformational properties of the comb polymer with various rigidities of the backbone and arms in steady shear flow are studied by using a hybrid mesoscale simulation approach that combines multiparticle collision dynamics with standard molecular dynamics. First, during the process of the comb polymer undergoing periodic tumbling motion, we find that the rigidity of the arms always promotes the tumbling motion of the comb polymer, but the rigidity of the backbone shifts from hindering to promoting it with increasing the rigidity of the arms. In addition, the comb polymer transitions from vorticity tumbling to gradient tumbling with the increase in shear rate. Second, the range of variation of the end-to-end distance of the backbone and the average end-to-end distance of the arms increases with the increase in the rigidity of the arms and backbone, respectively, and the range of both changes grows with the increase in shear rate. Furthermore, as the rigidity increases, the moldability of the comb polymer decreases and the orientation angle of the comb polymer increases.

The stretching dynamics and dynamical behaviors of individual branched ring polymer (BRP), a coarse-grained model for some types of the starch, in steady shear flow are studied by using a hybrid mesoscale simulation approach that combines multiparticle collision dynamics with standard molecular dynamics. By analyzing the stretched configuration of BRPs, we find the polymer size increases nonmonotonically with increasing branch length. Meanwhile, the decrease of the alignment angle of the stretched configuration of BRPs follows a universal power law during the first downward phase as the shear rate increases. Constructing the three-dimensional surface of the polymer's ring backbone and tracing the temporal fluctuations of the surface's normal vector along the simulation trajectory, the tumbling and tank-treading motion are clearly reflected by periodic and non-periodic changes of the normal vector. Interestingly, these temporal changes are much more regular than that of the gyration tensor. Thus, a novel cross-correlation function, which is the correlation between fluctuations of the normal vector along the flow direction and the velocity-gradient direction, is proposed to analyze the tumbling motion that usually coexists with the tank-treading motion. This function can naturally address the fails of traditional method that analyzing the tumbling motion by determining the correlation of temporal fluctuations of the gyration tensor Gαα. By analyzing the dynamical behaviors of BRPs, diverse dependences of the tumbling frequency ωTB and tank-treading frequency ωTT on the shear rate γ̇ are observed at a wide range of shear rates and polymer sizes. Furthermore, our simulations also reveal that the tank-treading motion is more stable than the tumbling motion for small-branch-size BRPs but the tumbling motion is more stable than the tank-treading motion for large-branch-size BRPs.

Using particle-resolved computer simulations, we investigate the effect of friction on the packing structure of hard-sphere mixtures with two kinds of particles under external compression. We first show that increasing friction between the particles results in a more disordered and less efficient packing of the local structure on the nearest neighbor scale. It is also found that standard two-point correlation functions, i.e., radial distribution function and static structure factor, show basically no detectable changes beyond short-range distances upon varying inter-particle friction. Further analysis of the structure using a four-point correlation method reveals that these systems have on the intermediate-range scale a three-dimensional structure with an icosahedral/dodecahedral symmetry that exhibits a pronounced dependence on friction: small friction gives rise to an orientational order that extends to larger distances. Our results also demonstrate that composition plays a role in that the degree of structural order and the structural correlation length are mainly affected by the friction coefficients associated with the more abundant species.

Using hybrid multi-particle collision dynamics (MPCD) and a molecular dynamics (MD) method, we investigate the effect of arms and shear flow on dynamical and structural properties of the comb long-chain branched (LCB) polymer with dense arms. Firstly, we analyze dynamical properties of the LCB polymer by tracking the temporal changes on the end-to-end distance of both backbones and arms as well as the orientations of the backbone in the flow-gradient plane. Simultaneously, the rotation and tumbling behaviors with stable frequencies are observed. In other words, the LCB polymer undergoes a process of periodic stretched–folded–stretched state transition and rotation, whose period is obtained by fitting temporal changes on the orientation to a periodic function. In addition, the impact induced by random and fast motions of arms and the backbone will descend as the shear rate increases. By analyzing the period of rotation behavior of LCB polymers, we find that arms have a function in keeping the LCB polymer’s motion stable. Meanwhile, we find that the rotation period of the LCB polymer is mainly determined by the conformational distribution and the non-shrinkable state of the structure along the velocity-gradient direction. Secondly, structural properties are numerically characterized by the average gyration tensor of the LCB polymer. The changes in gyration are in accordance with the LCB polymer rolling when varying the shear rate. By analyzing the alignment of the LCB polymer and comparing with its linear and star counterparts, we find that the LCB polymer with very long arms, like the corresponding linear chain, has a high speed to reach its configuration expansion limit in the flow direction. However, the comb polymer with shorter arms has stronger resistance on configuration expansion against the imposed flow field. Moreover, with increasing arm length, the comb polymer in shear flow follows change from linear-polymer-like to capsule-like behavior.

Self-assembly behavior of semiflexible polymers on rigid spherical shell is investigated using the molecular dynamics (MD) simulation method. We find that the conformation of semiflexible polymers depends on the length of polymers and bending energy of polymer chains. For moderate adhesive strength and bending energy, the polymers aggregate into multiple clusters, each of which contains several parallel chains. Simultaneously, the self-assembly conformations, volley-ball, helical and tennis-ball state, form on spherical shell depend on the number of clusters. We quantify the self-assembly conformation and analysis its physical mechanics of formation. This work may provide a theoretical foundation for the future theories of conformation prediction and material fabrication.

With combining multi-particle collision dynamics (MPCD) for the solvent and molecular dynamics (MD) for the polymer chains, we have studied the conformation and untying behaviors of a trefoil knot polymer chain translocated through a confined funnel-like channel. For the trefoil knot chain, we found that the untying knot behavior mostly happens during the translocation process, and the translocation behavior of linear chains is also simulated as a comparison. Some characteristics of the trefoil knot chain during translocation process, such as average gyration radius and the average end-to-end distances are discussed, and we statistic the scale relations of the translocation time versus the chain length, and that of the chain rigidity. This study may help to understand translocation behaviors of the knotted linear polymer chain in the capillary flow field.

Molecular dynamics method is used to study the conformation behavior of a semi-flexible polymer chain confined in a cylinder channel.A novel helix-like structure is found to form during the simulation.Moreover,the detailed characteristic parameters and formation probability of these helix-like structures under moderate conditions are investigated.We find that the structure is not a perfect helix,but a bundle of elliptical turns.In addition,we conduct a statistical analysis for the chain monomer distribution along the radial direction.This research contributes to our understanding of the microscopic conformation of polymer chains in confined environments filled with a solvent.

The aggregation behaviors and phase separation of binary nanoparticles immersed in semiflexible polymer brushes are explored using molecular dynamics simulations. The conformations of the binary nanoparticle-brush mixtures are very sensitive to the size ratio q = sigma(l)/sigma(s) where sigma(l) and sigma(s) are the diameters for large and small nanoparticles, respectively, and the attractive interactions epsilon(M) between the nanoparticles and polymer brushes. The phase separation of the binary nanoparticles is observed at a relatively strong attractive interaction under the effects of inter-nanoparticle depletion attractions provided by polymer brushes. Furthermore, the crystallization of small nanoparticles occurs at a strong interaction and a hexagonal close-packed-like (hcp-like) ordered structure is formed. The present results may promise a new approach for controlling the self-assembling behavior of nanoparticles and constructing a better macroscopic performance of the material.

We use molecular dynamics method (MD) combined with multi-particle collision dynamics (MPCD) method to investigate the effects of poiseuille flow on the conformations and migration behaviors of semiflexible chains confined in two infinite flat planes. At low shear rates, the semiflexible chain keeps semirigid conformation in the plane parallel to the infinite flat wall. At high shear rates, the semiflexible chain extends in the flow direction, and it migrates away from the two plat planes with considering hydrodynamic interactions between polymers and solvent molecules. Comparisons with flexible chains are also made, and this study can help us to understand the biological process under confined microfluidic devices.

The self-assembly behavior of nanorods (NRs) on soft elastic shells is investigated using the molecular dynamics (MD) simulation method. The self-assembly structures of the adsorbed nanorods depend on the length of the nanorods as well as the bending energy of the soft elastic shells. For short nanorods, the aggregates consist of regular pentagons around the gibbosity at low bending energies, and the ordered structures are gradually broken when the bending energy increases. In the meantime, the adsorption ability of the nanorods on the elastic shells decreases when the binding energy increases. For long nanorods, the binding energy can induce the nanorods to aggregate in clusters on shells with low or moderate bending energy, and each cluster is formed by several parallel long nanorods. However, the self-assembly structures of long nanorods disappear for shells with high bending energy because the adsorption becomes isotropic for nanorods on a rigid shell. Meanwhile, the adsorption of nanorods on the shell can also affect the shape of the soft elastic shell, especially for long nanorods. This investigation can help us understand the complexity of the self-assembly of nanorods on an elastic shell.

Coarse-grained molecular dynamics simulations are used to explore the spatial orientations and conformational transitions of nanorods (NRs) within semiflexible polymer brushes. The orientations of the NR clusters are controlled by the competition between the entropy cost for NRs infiltrated into the polymer brushes and the attractive energy between NRs and polymer brushes. By reducing the grafting density or enhancing the number of NRs, the NR cluster experiences an orientation transition from the vertical direction to the horizontal direction. The semiflexible polymer brushes are regarded as the soft confinements for the NRs, and the soft confinements can induce the formation of the NR aggregation under the effect of the depletion attractions. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

A coarse-grained model for an elastic shell grafted with polymer chains is investigated by molecular dynamics methods. With increasing the number of grafted polymer chains (GPCs), it is found that the conformation of the shell undergoes from expansion to collapse and back to the expansion. By varying the density of the GPCs, the phase transition of the elastic shell can be successfully controlled at moderate bending energy of the shell and at moderate binding energy between the shell and GPCs. Furthermore, the self-assembly structures of the GPCs are also affected by the elastic shell in certain conditions. In the case of a few GPCs on the shell, the chains tend to be adsorbed on the shell surface unfolded at high value of bending energy. However, when the bending energy is small, the chains can be folded several times easily. This may be an important step toward a deeper understanding of how to control the microstructure in the production of biocomposites. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Statistical properties and phase transitions of semiflexible polymers on a soft elastic shell are investigated by using a molecular dynamics (MD) simulation method. The phase diagram of adsorbed semiflexible polymers depends on the bending energy of the elastic shell and the binding energy between polymers and the elastic shell. The ordered regular pentagons of polymers are observed at a moderate adhesive strength and bending energy. At the same time, the shape of the soft elastic shell can be controlled easily by adjusting the chain length of adsorbed polymers, which is helpful for the regulation and reshaping of membranes in the micrometre range or smaller sizes.

The phase behaviour of polyethylene knotted ring chains is investigated by using molecular dynamics simulations. In this paper,we focus on the collapse of the polyethylene knotted ring chain,and also present the results of linear and ring chains for comparison. At high temperatures,a fully extensive knot structure is observed. The mean-square radius of gyration per bond S 2/（Nb2） and the shape factor δ depend on not only the chain length but also the knot type. With temperature decreasing,chain collapse is observed,and the collapse temperature decreases with the chain length increasing. The actual collapse transition can be determined by the specific heat capacity C v ,and the knotted ring chain undergoes gas-liquid-solid-like transition directly. The phase transition of a knotted ring chain is only one-stage collapse,which is different from the polyethylene linear and ring chains. This investigation can provide some insights into the statistical properties of knotted polymer chains.

An off-lattice Monte Carlo method was used to study the conformational properties of semiflexible chains confined between two concentric cylinders. The conformations of confined semiflexible chains depend on the bending energy as well as the size of confinement, and the semiflexible chains with particular rigidities confined in the appropriate spaces can form helical structures under entropically driven. The inner cylinder plays a key role in the formation of helical conformations, whereas the outer cylinder affects the size of confinement. Furthermore, the helical structures keep fluctuating like a harmonic oscillation, and the clockwise or counterclockwise helical conformations will appear with the same possibility in the processes of relaxation-helix transitions. This study can help us understand the conformational behaviors of biological macromolecules in confined space.

A knotted polymer chain passing through a pore is investigated by molecule dynamics method. In this paper, we take 31 knot as an example. It is found that, during the process of translocation, the size of the knot fluctuates until the knot is unknotted. In addition, the effect of the knot on the translocation velocity of the knotted chain is also discussed. For the given external force, the average translocation time τ satisfies the scaling relation:τ～N α, and the scaling exponent α increases with the external force f. For short knotted polymer chains, the average translocation time τ decreases when the external force f increases. However, for very long knotted polymer chains, the average translocation time τ increases when the external force f increases. In the meantime, the position of knot in a knotted polymer chain also affects the average translocation time τ strongly. The closer the knot approaches the first translocated monomer, the longer the average translocation time. This investigation can provide some insights into the translocation of knotted polymer chains (especially knotted DNA) through the nanopore, and help us understand the translocation behavior of biomacromolecules.