A Monte Carlo simulation model for the random packing of unequal spherical particles is presented in this paper. With this model, the particle radii obeying a given distribution are generated and randomly placed within a cubic packing domain with high packing density and many overlaps. Then a relaxation iteration is applied to reduce or eliminate the overlaps, while the packing space is gradually expanded. The simulation is completed once the mean overlap value falls below a preset value. To simulate the random close packing, a "vibration" process is applied after the relaxation iteration. For log-normal distributed particles, the effect of particle size standard deviation, and for bidisperse particles, the effects of particle size ratio and the volume fraction of large particles on packing density and on coordination number are investigated. Simulation results show good agreement with that obtained by experiments and by other simulations. The randomness, homogeneity, and isotropy, which have not been evaluated before for packing of distributed particles, are also examined using statistical measures.
Abstract. By mixing macromolecular blowing agent grafted nano-SiO2 with polypropylene (PP) melt, the nanoparticle agglomerates can be pulled apart due to the in-situ bubble-stretching resulting from gasification of the side foaming groups on the grafted polymer. The present work evaluated the interfacial effect in the PP based nanocomposites prepared using the aforesaid technique through introducing rubbery components to the backbone of the grafted polymer chains. The results indicated that deagglomeration of the nanoparticles was not bound to yield the highest properties of the composites. The positive effect of the nanoparticles was brought into full play because of the joint contributions of particles dispersion status and interfacial interaction. An interlayer with proper flexibility ensured an overall enhancement of mechanical properties, especially impact strength, of the nanocomposites. : nanomaterials, processing technologies, nanoparticles, nanocomposites, interfacial effect eXPRESS Polymer Letters Vol.1, No.1 (2007) [2][3][4][5][6][7] Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2007.2 defoaming of the compounds was not necessary prior to injection molding. It implies that this technique could lead to deagglomeration of the nanoparticles when nanocomposites are being manufactured, without side effect that might deteriorate performance. For polymer-based nanocomposites, an appropriate surface treatment of inorganic nanoparticles should not only improve dispersion of the fillers, but also bring about notable influence on the interfacial characteristics, and subsequently enhance the mechanical properties of the ultimate composites [6]. Considering that graft treatment of nanoparticles leads to specific interfacial structures that can be tailored by changing graft monomers and graft conditions [7], the authors of the present work planned to introduce polymer chain units with relatively higher molecular mobility (i.e., poly(butyl acrylate)) into the aforesaid grafted polymeric foaming agent poly(p-vinylphenylsulfonylhydrazide) through copolymerization. It is hoped that the stiffness of the interlayer in the nanocomposites originally constructed by the grafted poly(p-vinylphenylsulfonylhydrazide) containing rigid phenyl groups can be somewhat balanced. In accordance with this idea, poly(p-vinylphenylsulfonylhydrazide-co-butyl acrylate) grafted nanosilica was synthesized. Afterwards, the treated nanoparticles were melt compounded with PP. With the help of in-situ bubble-stretching effect and the flexible interphase, agglomerated silica nanoparticles should be disconnected from each other and adhered to the matrix polymer via the grafted copolymer chains (Figure 1). In this paper, the feasibility of this technical route was analyzed by characterizing the grafted nano-silica and their influence on the structure and properties of PP based composites. Keywords Experimental MaterialsSilica (Aerosil 200) was supplied by Degussa Co., Germany with an average diameter of 12 nm and ...
In this paper we study the short-range correlated percolation and the cluster structure of two-dimensional (2D) random packing of binary disks with size ratio lambda in the range of 1-5. A Monte Carlo simulation model is used to generate the configuration of random packing first. Then a from-neighbor-to-neighbor propagation method is used to identify the number and sizes of the clusters. Results show that for lambda=1 the percolation threshold p(c) lies between the square and triangular site percolation thresholds. As lambda increases the percolation threshold p(c) (the area fraction of small disks) decreases. To characterize the cluster structure at the percolation threshold, we scale the cluster size s(c) with the cluster radius R as s(c) proportional, variant R(D). The fractal dimension D obtained lies between 1.86 and 1.88 and is independent of the size ratio lambda. This value is in good agreement with the 2D theoretical fractal dimension which is equal to 91/48.
Abstract.To promote dispersion of nano-silica in monomer casting nylon6 (MC nylon6), nano-silica was dispersed in melted caprolactam with the assistance of ultrasound, anionic polymerization was then initiated to form silica/MC nylon6 in-situ nanocomposites. It was found that hydrogen bonds were formed between nano-silica and caprolactam, in the meantime, ultrasound helped to break the nanoparticles aggregations into smaller ones or even mono-dispersing particles. Therefore, the agglomerated nanoparticles were pulled apart and stabilized by caprolactam. Additionally, the rapid anionic polymerization of caprolactam also contributed to the avoidance of re-agglomeration and deposition of nanoparticles during the polymerization process, leading to the uniform distribution of nanoparticles in the polymer matrix. Mechanical tests indicated that the silica/MC nylon6 in-situ nanocomposites prepared according to the above strategy were simultaneously toughened, strengthened and stiffened. Thermogravimetric analysis (TGA) results showed that thermal stability of nanocomposites was notably improved compared to neat MC nylon6.
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