Response of polymer molecules embedded in a nanodroplet to collisions with a wall

Abstract

Using molecular-dynamics simulation, we study the collision of polymer-filled water droplets with a wall. We are interested in impact velocities which lead to polymer isolation after the collision. This occurs if the impact energy per solvent molecule, E, exceeds roughly the cohesive energy of the solvent. We find that in this energy regime, the polymer temperature increases linearly with E. The dependence on polymer size and on droplet size is investigated. In addition, we present an extension of the principal-component analysis which can be used on molecular-dynamics trajectories to consider the time evolution of internal degrees of freedom in polymers. This allows us to study in detail the energy transfer between polymer and solvent, and the internal energy redistribution within the polymer. Potential and kinetic energy of the polymer have equilibrated after around 100 ps, while almost no energy is conveyed to polymer translational motion. Since the polymer temperature increases linearly with E, at too high impact energies, the polymer is subject to unimolecular decay. This allows us to predict the impact energy window for successful polymer isolation. PACS numbers: 36.20.Ey, 36.40.Qv, 82.80.Ms, 79.20.Ap