RESUMO
The study of the long-term evolution of slow chemical reactions is challenging because quantum-based reactive molecular dynamics simulation times are typically limited to hundreds of picoseconds. Here, the extended Lagrangian Born-Oppenheimer molecular dynamics formalism is used in conjunction with parallel replica dynamics to obtain an accurate tool to describe the long-term chemical dynamics of shock-compressed benzene. Langevin dynamics has been employed at different temperatures to calculate the first reaction times in liquid benzene at pressures and temperatures consistent with its unreacted Hugoniot. Our coupled engine runs for times on the order of nanoseconds (one to two orders of magnitude longer than traditional techniques) and is capable of detecting reactions that are characterized by rates significantly slower than we could study before. At lower pressures and temperatures, we mainly observe Diels-Alder metastable reactions, whereas at higher pressures and temperatures we observe stable polymerization reactions.
RESUMO
We demonstrate how a generalized self-consistent field theory for polymer melts that includes elastic stress and strain fields can be applied to the study of AB diblock copolymers melts. By obtaining the stress distributions for volume conserving strain loadings where lamellar and hexagonal morphologies are stable, we show that the local stress is reduced at the domain interface but slightly enhanced in the immediate vicinity of the interface. The overall stress profile is the result of the combined effects of chain connectivity across the interface, which yields a positive contribution, and the immiscible nature of the monomers, which leads to a stress reduction because of interfacial tension.
