发表论文

In this work, by using coarse-grained molecular dynamics simulations, we found that poly(2-methacryloyloxyethyl phosphorylcholine)(PMPC) showed a strong solubility and a so-called antipolyelectrolyte effect(APE) in water. In contrast, obvious aggregations but no APE were found in n-butyl-substituted choline phosphate polymers(PMBP) solutions. The underlying mechanisms for different solution behaviors of PMPC and PMBP were investigated in detail. Our results indicate that the presence of butyl groups in PMBP enhances both the electrostatic interactions and the hydrophobicity of PMBP molecules in the system. Both factors were found to contribute to the formations of aggregates in the PMBP system. Further researches revealed that hydrophobicity arising from the butyl group plays a more important role than electrostatic interactions in inducing the PMBP aggregation. In addition, the strong hydrophobicity in PMBP was found to be responsible for the absence of APE. These results are expected to contribute to a better understanding and a better design of the solution properties of polyzwitt erions.

We numerically investigate the connection between spatial density correlation and dynamical heterogeneity in glass-forming liquids. We demonstrate that the cluster size defined by the spatial aggregation of densely packed particles (DPPs) can better capture the difference between the dynamics of the Lennard-Jones glass model and the Weeks-Chandler-Andersen truncation model than the commonly used pair correlation functions. More interestingly, we compare the mobility of DPPs and loosely packed particles, and we find that high local density correlates well with slow dynamics in systems with relatively hard repulsive interactions but links to mobile ones in the system with soft repulsive interactions at one relaxation time scale. Our results show clear evidence that the above model dependence behavior stems from the hopping motion of DPPs at the end of the caging stage due to the compressive nature of soft repulsive spheres, which activates the dynamics of DPPs in the α relaxation stage.

How to create novel desired structures by rational design of building blocks represents a significant challenge in materials science. Here we report a conceptually new design principle for creating supracolloidal fullerene-like cages through the self-assembly of soft patchy particles interacting via directional nonbonded interactions by mimicking non-planar sp2 hybridized carbon atoms in C60. Our numerical investigations demonstrate that the rational design of patch configuration, size, and interaction can drive soft three-patch particles to reversibly self-assemble into a vast collection of supracolloidal fullerene-like cages. We further elucidate the formation mechanisms of supracolloidal fullerene-like cages by analyzing the structural characteristics and the formation process. Our results provide conceptual and practical guidance towards the experimental realization of supracolloidal fullerene-like cages, as well as a new perspective on understanding the fullerene formation mechanisms.

We propose a kinetic chain growth algorithm for coarse-grained (CG) simulations in this work. By defining the reaction probability, it delivers a description of consecutive polymerization process. This algorithm is validated by modeling the process of individual styrene monomers polymerizing into polystyrene chains, which is proved to correctly reproduce the properties of polymers in experiments. By bridging the relationship between the generic chain growth process in CG simulations and the chemical details, the impediment to reaction can be reflected. Regarding to the kinetics, it models a polymerization process with an Arrhenius-type reaction rate coefficient. Moreover, this algorithm can model both the gradual and jump processes of the bond formation, thus it readily encompasses several kinds of previous CG models of chain growth. With conducting smooth simulations, this algorithm can be potentially applied to describe the variable macroscopic features of polymers with the process of polymerization. The algorithm details and techniques are introduced in this article. © 2016 Wiley Periodicals, Inc.

We present a computer simulation study on the wettability of a hairy surface with different topological structures such as single hairs, hair bundles and network structure. Superficially, for end-tethered rigid hairs or flexible hairs, the nonwettability of the substrate should be analyzed in completely different ways. For rigid hairs, the contact angle is dominantly dependent on the top layer density of hairs. A larger top layer density leads to a larger interaction between droplet and surface, as well as a lower contact angle. For flexible hairs, the nonwettability is determined by the typical properties of hairs right below the droplet, e.g., the chemistry of the surface, the topography and strength of the hair bundle/network or nonwetted area below the projection of the droplet. Nevertheless, it is also possible to generalize these aspects into a uniform procedure, which implies an intrinsic consistent mechanism of the dewetting behavior for droplets on such hairy surfaces. Counterintuitively, we also suggest that the surface which can strongly resist the transition to the Wenzel state does not necessarily lead to a large contact angle, especially in a system where the droplet is treated as liquid bulk. This study helps to build up guidelines for the design of nonwetting surface materials.

以梳形高分子为纽带, 基于粗粒化分子动力学模拟方法, 研究了线形、 梳形和星形拓扑结构高分子的 静态和动态性质, 以揭示稀溶液中高分子链行为与链拓扑结构依赖关系的一般性规律. 研究结果表明, 随着 线形鄄梳形鄄星形的链拓扑结构转变, 回转半径的标度关系由仅依赖分子聚合度转变为同时依赖链聚合度与臂 数或侧链数. 分析了星形高分子和梳形高分子的静态和动态性质的特征规律. 星形高分子的臂数增加使其 尺寸迅速减小, 形状则由长椭球形转变为类球形, 且扩散系数也随之增加.

Gay-Berne (GB) potential is regarded as an accurate model in the simulation of anisotropic particles, especially for liquid crystal (LC) mesogens. However, its computational complexity leads to an extremely time-consuming process for large systems. Here, we developed a GPU-accelerated molecular dynamics (MD) simulation with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions for mesogens in small molecules, main-chain or side-chain polymers. For identical mesogens in three different molecules, on cooling from fully isotropic melts, the small molecules form a singledomain smectic-B phase, while the main-chain LC polymers prefer a single-domain nematic phase as a result of connective restraints in neighboring mesogens. The phase transition of side-chain LC polymers undergoes a two-step process:nucleation of nematic islands and formation of multi-domain nematic texture. The particular behavior originates in the fact that the rotational orientation of the mesogenes is hindered by the polymer backbones. Both the global distribution and the local orientation of mesogens are critical for the phase transition of anisotropic particles. Furthermore, compared with the MD simulation in LAMMPS, our GPU-accelerated code is about 4 times faster than the GPU version of LAMMPS and at least 200 times faster than the CPU version of LAMMPS. This study clearly shows that GPU-accelerated MD simulation with GB potential in GALAMOST can efficiently handle systems with anisotropic particles and interactions, and accurately explore phase differences originated from molecular structures.

We propose a facile inverse design strategy to generate three-dimensional (3D) nanopatterns by using either block copolymers or a binary homopolymer blend via dissipative particle dynamics simulations. We find that the composition window of block copolymers to form a specific 3D morphology can be expanded when the self-assembly of block copolymers is directed by templates. We also find that a binary homopolymer blend can serve as a better candidate in the inverse templating design, since they have similar performances on recovering the target pattern, with much lower cost. This strategy is proved efficient for fabricating templates with desired topographical configuration, and the inverse design idea sheds lights on better control and design of materials with complex nanopatterns.

Although multiple overstretched DNA states were identified in experiments, the mechanism of the emergence of distinct states is still unclear. Molecular dynamics simulation is an ideal tool to clarify the mechanism, but the force loading rates in stretching achieved by conventional all-atom DNA models are much faster, which essentially affect overstretching states. We employed a modified coarse-grained DNA model with an unprecedented low loading rate in simulations to study the overstretching transitions of end-opened double-stranded DNA. We observed two-strand peeling off for DNA with low stability and the S-DNA with high stability under tension. By introducing a melting-forbidden model which prevents base-pair breaking, we still observed the overstretching transition induced by the formation of S-DNA due to the change of dihedral angle. Hence, we confirmed that the competition between the two strain-softening manners, i.e., base-pair breaking and dihedral angle variation, results in the emergence of distinct overstretched DNA states.

We propose a simple and general mesoscale soft patchy particle model, which can felicitously describe the deformable and surface-anisotropic characteristics of soft patchy particles. This model can be used in dynamics simulations to investigate the aggregation behavior and mechanism of various types of soft patchy particles with tunable number, size, direction, and geometrical arrangement of the patches. To improve the computational efficiency of this mesoscale model in dynamics simulations, we give the simulation algorithm that fits the compute unified device architecture (CUDA) framework of NVIDIA graphics processing units (GPUs). The validation of the model and the performance of the simulations using GPUs are demonstrated by simulating several benchmark systems of soft patchy particles with 1 to 4 patches in a regular geometrical arrangement. Because of its simplicity and computational efficiency, the soft patchy particle model will provide a powerful tool to investigate the aggregation behavior of soft patchy particles, such as patchy micelles, patchy microgels, and patchy dendrimers, over larger spatial and temporal scales.