Single-walled carbon nanotubes (SCWNTs) have outstanding properties that depend on structural features such as their chirality. Thus, developing a strategy to control chirality during SWCNT synthesis is critical for the exploitation of nanotube-based technologies in fields such as electronics and biomedicine. In response to this need, tuning the nanocatalyst structure has been envisioned as a means to control the nanotube structure. We use reactive classical molecular dynamics to simulate nanotube growth on supported Ni(32), Ni(80), and Ni(160) nanoparticles at various metal/support interaction strengths (E(adh)). The initial carbon ring formation is shown to correlate to the nanoparticle surface structure, demonstrating the existence of a "template effect" through a dominant occupation of hollow sites. The E(adh) strength alters the dynamic/structural behavior of the nanoparticle, in turn influencing the interplay between nanotube and nanoparticle structures. For example, the contact region between the nanoparticle surface and the growing nanotube decreases as E(adh) increases because capillary forces that raise the metal into the nanotube are counteracted by the strong metal/support interaction. The nanoparticle mobility decreases as E(adh) increases, eliminating a possible inverse template effect but hindering defect annealing in detriment of the nanotube/nanoparticle structural correlation. On the other hand, the contact between the nanoparticle and the nanotube increases with nanoparticle size. However, the heterogeneity of the nanoparticle structure increases with size, reducing the structural correlation. These results suggest that an appropriate combination of nanoparticle size and strength of the catalyst/support interaction may enhance the desired template effect and bias formation of specific nanotube chiralities.

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A mathematical model for free-radical copolymerization kinetics with cross linking of vinyl/divinyl monomers in carbon dioxide at supercritical conditions was developed. The copolymerization of styrene and divinylbenzene is analyzed as a case study. The effects of the kinetic and physical parameters on monomer conversion, molecular-weight development, copolymer composition, appearance of the gelation point, gel fraction, and average cross-link density are studied. Model predictions show the expected trends, although the system is quite sensitive to pressure, which provides an interesting and promising way to tailor some of the polymer properties.

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