发表论文

Stable and monodisperse phenylboronic acid-functionalized nanoparticles (PBA-NPs) were fabricated using the 3-((acrylamido)methyl)phenylboronic acid homopolymer (PBAH) via the solvent displacement technique. The effect of operating parameters, including stirring time, initial polymer concentration and the proportion of methanol, on the self-assembly process was systematically investigated. The diameters of PBA-NPs were increased by increasing the initial PBAH concentration and the proportion of methanol. Likewise, there was a linear dependence between the size of self-assembled nanoparticles and the polymer concentration. Moreover, the dissipative particle dynamics (DPD) simulation technique was used to investigate the mechanism of self-assembly behavior of the PBAH, which indicated that the interior of PBA-NPs was hydrophobic and compact, and boronic acid groups were displayed on both the exterior and interior of PBA-NPs. The resulting PBA-NPs could successfully encapsulate emodin through PBA–diol interaction and the encapsulation efficiency (EE%) and drug loading content (DLC%) of drug-loaded PBA-NPs were 78% and 2.1%, respectively. Owing to the acid-labile feature of the boronate linkage, a reduction in environmental pH from 7.4 to 5.0 could trigger the disassociation of the boronate ester bonds, which could accelerate the drug release from PBA–emodin-NPs. Besides, PBA–emodin-NPs showed a much higher cytotoxicity to HepG2 cells (cancer cells) than MC-3T3-E1 cells (normal cells). These results imply that PBA-NPs would be a promising scaffold for the delivery of polyphenolic drugs.

It is crucial to understand how much and how far the structure and dynamics properties of the polymer melt can be affected by incorporating nanoparticles (NPs) in the system. Here, we show that in an athermal all-polymer nanocomposites prepared from mixtures of linear polystyrene chains and cross-linked polystyrene NPs, the influence range of the NP on the melt polymer properties, namely interphase thickness, depends on the properties investigated. The local segment conformations can be affected in the range of an NP radius. However, if the interphase thickness is defined by the influence range of the NP on the radius of gyration (Rg) of the melt chain, it can be 1.5Rg for short-chain melts where the chain has a Rg smaller than particle radius Ra. For intermediate chain length polymer melts (Rg > Ra), the influence range of the NP does not change with the chain length. With the chain length further increasing, melt chains cannot feel the existence of the NP; the influence of the NP on the Rg tensors of the melt chain can be negligible. For the dynamics properties, the effects caused by the NP can be differently at different length and time scales. The mobility of the monomers can be slowed down in the vicinity of the NP, but they can have a faster mobility in the tangential direction than in the radial direction of the NP surface. More importantly, the segmental relaxation of the melt chains can be accelerated by the fast thermal deformations of the loose NP surface structures. We demonstrate that the softness of the NP and its deformability are crucial to the dynamics properties of the nanocomposites.

We investigate numerically the relaxation and diffusion dynamics in three-dimensional Kob-Andersen glass-forming liquids in which part of the particles are randomly chosen and pinned permanently. We find that both the relaxation dynamics and diffusion dynamics slow down as increasing the pinning concentration (cpin) at fixed temperatures that we study. For higher temperature and lower cpin, the α relaxation time τ and the diffusion coefficient D have the scaling relationship D ∼ τ−1. However, this coupling behavior breaks down if cpin is further increased, and the scaling relationship is replaced by D ∼ τ−ν with ν < 1. At temperatures around the onset temperature of the bulk system, a transition from ν ∼ 0.75 to ν ∼ 0.61 with increasing cpin is found. However, at lower temperatures, ν ∼ 0.67 holds in the whole studied cpin range. By fitting the relaxation time as a function of cpin with Vogel-Fulcher-Tamman equation, we find that the change of scaling exponent ν is accompanied with the change of fragility parameter K at higher temperatures. However, at lower temperatures, pinning particles have little effect on the system’s qualitative properties. Moreover, we investigate three measures of heterogeneity of dynamics and find that the relaxation and the diffusion motion of particles show different responses to the pinned particles, which may lead to the slower relaxation than diffusion and the decoupling of relaxation and diffusion. The string-like motion is found to saturate at the mode-coupling theory (MCT) crossover point, which indicates that other relaxation modes may exist below the MCT transition point.

We present a molecular dynamics simulation study on the controlling factors that influence the wettability of a hairy surface. By adopting the hairs with appropriate grafting density, hair length, and hair rigidity, the hairy surface shows good performance on droplet repellency. When the droplet sits on the hairy surface, the flexible hairs can spontaneously bundle with the appropriate amount of neighboring hairs to enhance the surface hydrophobicity, thus providing a new possibility to control the surface wettability. The hairy surface with tunable grafting density and hair rigidity, bridges the gap between surfaces with soft polymer brushes and surfaces that are completely hard but porous.

We study the self-assembly behaviour of two-patch particles with D1h symmetry by using Brownian dynamics simulations. The self-assembly process of two-patch particles with diverse patch coverage in two selective solvent conditions is investigated. The patchy particles in a solvent that is bad for patches but good for matrix form linear thread-like structures with low patch coverage, whereas they form 3D network structures with relatively high patch coverage on surface. For patchy particles in a solvent which is good for patches but bad for body, monolayer structures are obtained at high patch coverage, and some cluster structures emerge when surface patch coverage is low.

Coarse-grained models for β-cyclodextrin (β-CD) and adamantane (ADA) are proposed by fitting to their experimental host−guest complex equilibrium constant in solution. By using Brownian dynamics simulations, we suggest a simple supramolecular route for synthesizing multiblock copolymers (MBCs) via forming complexes between β-CD and ADA groups terminated at the chain ends of diblock copolymers (DBCs). The chain length distribution of the resulted MBC is found to follow the statistics of Flory formula for typical linear condensation polymerization process. Therefore, the proposed supramolecular route can be viewed as a novel linear condensation polymerization process with DBCs as reactive monomers. Due to the complex formations between head and tail (β-CD and ADA), ringshaped MBCs are also observed in our simulations, which will reduce the yield of the MBC. Because we are using a generic model for DBC, the proposed route of building MBCs are applicable for all synthetic DBCs with two ends terminated by either β-CD or ADA groups.

GALAMOST [graphics processing unit (GPU)-accelerated large-scale molecular simulation toolkit] is a molecular simulation package designed to utilize the computational power of GPUs. Besides the common features of molecular dynamics (MD) packages, it is developed specially for the studies of self-assembly, phase transition, and other properties of polymeric systems at mesoscopic scale by using some lately developed simulation techniques. To accelerate the simulations, GALAMOST contains a hybrid particle-field MD technique where particle–particle interactions are replaced by interactions of particles with density fields. Moreover, the numerical potential obtained by bottom-up coarse-graining methods can be implemented in simulations with GALAMOST. By combining these force fields and particle-density coupling method in GALAMOST, the simulations for polymers can be performed with very large system sizes over long simulation time. In addition, GALAMOST encompasses two specific models, that is, a soft anisotropic particle model and a chain-growth polymerization model, by which the hierarchical self-assembly of soft anisotropic particles and the problems related to polymerization can be studied, respectively. The optimized algorithms implemented on the GPU, package characteristics, and benchmarks of GALAMOST are reported in detail. © 2013 Wiley Periodicals, Inc.

The polymer-grafted nanoparticles prepared by the surface-initiated polymerization induced from the spherical surface is studied by coarse-grained molecular dynamics simulations combined with the stochastic reaction model. The coupling effect of the initiator density and the grafting surface curvature is mainly investigated. The confinement degree greatly changes with the grafting surface curvature, thus the initiation efficiency, the grafted chain polydispersity, as well as the chain mass distribution show great dependence on the surface curvature. The results reveal that preparing the nanoparticle with desired size (i.e., grafting surface curvature) is crucial for control of the grafted chain polydispersity and even its dispersion in the polymer matrix. Our studies shed light on better design of grafted nanoparticles and better control of dispersion in polymer matrices for improving the performance of polymer nanocomposite materials.

利用耗散粒子动力学模拟方法, 研究了杂臂星型嵌段共聚物 Am( Bn )2 在溶液中自组装形成囊泡的行为. 主要分析了自组装过程、 亲水分枝和疏水分枝的长度及分子构型对组装结构的影响. 结果表明, 杂臂星型聚合物在溶液中会自组装形成碟状胶束, 之后弯曲闭合形成囊泡. 当亲水部分的分枝较短时, 易于形成囊泡结构; 在可形成囊泡结构的条件下, 双分子层囊泡膜的厚度随分枝长度的增加而增加. 与构成相近的线型 嵌段共聚物相比, 杂臂星型嵌段共聚物更易形成囊泡结构, 且形成的囊泡结构较薄.

利用粗粒化分子动力学( CGMD) 方法研究了两亲性接枝共聚物在不同选择性溶剂中的自组装行为. 分析了主链刚性及链长对自组装结构的影响. 研究结果表明, 当溶剂对主链为良溶剂而对支链为不良溶剂 时, 两亲性接枝共聚物随主链刚性的增加自组装形成花状胶束、 花桥状胶束及桥状胶束, 并且组分比例对自 组装结构影响很大; 随着链长的增加, 柔性链出现单花状胶束到多花状胶束的转化. 当溶剂对主链为不良溶 剂而对支链为良溶剂时, 可得到近球形或椭球形核壳状胶束及束状结构; 不同链长时, 柔性接枝共聚物链均 只能得到近球形的单核壳状胶束.