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International audienc

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Clarifying heterogeneous nucleation process on fractal surfaces is an important issue to understand its thermodynamic principles and forward the engineering aspects. We developed a thermodynamic model to capture the process of forming a crystal or drop embryo on fractal surfaces and the corresponding characteristic parameters. We showed that the differences between the critical size of the embryos on the fractal surfaces and those on the flat surfaces are negligible for the hydrophobic nuclei, but become significant for the hydrophilic nuclei. We reported the available domains of forming the critical embryos and obtained the shape function for the first time. The results also recover the data reported in the literature. Finally, we present the possible mechanisms of vanishing of the energy barriers against forming the critical embryos on the fractal surfaces as the apparent contact angle is relatively small. The obtained results may help to engineer the nucleation process by designing substrate surfaces in a fractal structure.

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ABSTRACT:The melt rheological analysis of high-density polyethylene reinforced with vapor-grown carbon nanofibers (VGCNFs) was performed on an oscillatory rheometer. The influence of frequency, temperature, and nanofiber concentration (up to 30 wt %) on the rheological properties of composites was investigated. Specifically, the viscosity increase is accompanied by an increase in the elastic melt properties, represented by the storage modulus GЈ, which is much higher than the increase in the loss modulus GЉ. The composites and pure PE exhibit a typical shear thinning behavior as complex viscosity decreases rapidly with the increase of shearing frequency. The shear thinning behavior is much more pronounced for the composites with high fiber concentration. The rheological threshold value for this system was found to be around 10 wt % of VGCNF. The damping factor was reduced significantly by the inclusion of nanofibers into the matrix.