Static and dynamic properties of grafted ring polymer: Molecular dynamics simulation

The static and dynamic properties of a system of end-grafted flexible ring polymer chains grafted to a flat substrate and exposed to a good solvent are studied by using a molecular dynamics method. The monomers are described by a coarse-grained bead-spring model. Varying the grafting density p and the degree of polymerization or chain length N, we obtain the density profiles of monomers, study the structural properties of the chain （radius of gyration, bond orientational parameters, etc.）, and also present the dynamic characteristics such as chain energy and bond force. Compared with a linear polymer brush, the ring polymer brush exhibits different static and dynamic properties for moderate or short chain length, while it behaves like linear polymer brush in the regime of long chain length.

Quartic coupling and its effect on wetting behaviors in nematic liquid crystals

Based on the fact that rubbed groove patterns also affect the anchoring of liquid crystals at substrates,a quartic coupling is included in constructing the surface energy for a liquid crystal cell.The phase diagram and the wetting behaviors of the liquid crystal cell,bounded by surfactant-laden interfaces in a magnetic field perpendicular to the substrate are discussed by taking the quartic coupling into account.The nematic order increases at the surface while it decreases in the bulk as a result of the introduction of quartic substrate-liquid crystal coupling,indicating that the groove anchoring makes the liquid crystal molecules align more orderly near the substrate than away from it.This causes a different wetting behavior：complete wetting.

Aggregation of fullerene (C_(60)) nanoparticle:A molecular-dynamic study

We present the results of molecular dynamics simulations of net positively charged fullerene nanoparticles in salt- free and salt-added solution. The aggregation of fullerene （C60）-like nanoparticle and counterion are studied in detail as a function of temperatures and a finite salt concentration. Our simulations show that the strong conformation changes as temperature changes. The net positively-charged nanoparticles do not repel each other but are condensed under proper temperatures. If salts are added, the aggregated nanoparticles will be disaggregated due to the Debye screening effect.

Entropy dominated behaviors of confined polymer-nanoparticle composites

Stretched polymers will lose their possible configurations if they are mixed with nanoparticles or touch a hard wall, which leads to a strong depletion attraction responsible for the enrichment of nanoparticles near substrates. Moreover, it is found that there exists a sacrifice mechanism in confined pure polymer samples or polymer-nanoparticle mixtures, that part of the polymers, in order to reach a minimum free energy for the total system, are adsorbed on hard walls even though they lose their conformation. The current study provides a simple yet effective approach for the design of thin polymer composites.

Biaxiality of Liquid Crystal Formed by Bent-Core Molecules with a Transverse Dipole Moment Deviating from their Angular Bisector

Monte Carlo simulations are performed to study the phase diagram of liquid crystals formed by bent-core molecules with a strong transverse dipole moment deviating from their angular bisector.The results show that the strong dipolar interaction,after suppressing uniaxial phases,encourages biaxiality,which leads to a Landau point or even to a Landau line in the phase diagram,inducing a more stable biaxial nematic phase.It is also found that a deviation of dipole moment from the angular bisector also suppresses uniaxiality in the small bend-angle regime.

The Phase Transition of Nematic Liquid Crystal Cells Bounded by Surfactant-Laden Interfaces

Taking into account the surface-coupling strength effect,we discuss the phase transitions of a finite thickness cell bounded by surfactant-laden interfaces in a magnetic field perpendicular to the substrate and it is compared with that of a semi-infinite system.It is found that the larger the thickness,the closer the three-dimensional phase transition surface of the finite system to that of the semi-infinite one.The simulation also shows that when a magnetic field is applied to a nematic semi-infinite sample,an orientational phase transition first takes place close to the interface and then extends to the inner space as the temperature increases.