| Description |
Understanding how ultrathin liquid polymer films spread on the nanoscale is of critical importance to numerous physical phenomena and engineering applications. However, although crucial to the design and application of such ultrathin polymer films, the physical mechanisms that govern spreading on the nanoscale are not well-understood. We use molecular dynamics simulations to shed light on the nanoscale phenomena underlying ultrathin liquid polymer film spreading and show how various environmental and design parameters affect nanoscale spreading. In addition, we investigate the physical mechanisms that drive terraced polymer spreading, quantify the speed at which the edge of a polymer droplet advances on a flat substrate, and study how surface wettability can be altered through modification of a nanoscale substrate texture. We find that the functional end groups of the polymer molecule play a critical role in ultrathin polymer film spreading such that spreading increases with increasing molecule length for polymer molecules with functional end groups but decreases with increasing molecule length for polymer molecules without functional end groups. The presence of functional polymer end groups also determines if layer and terrace formations occur. For both polymer molecules with and without functional end groups, spreading is inhibited by molecule entanglement beyond a critical molecule length, such that spreading becomes independent of polymer functional end groups and molecule weight. The edge of a liquid polymer droplet spreads according to a power law with two distinct regimes, which we iv attribute to competing physical mechanisms: a pressure difference in the liquid droplet and molecule entanglement. For polymer spreading on substrates with a nanoscale texture, we find that texture groove shape is the primary factor that modifies polymer spreading because the texture groove shape determines the minimum potential energy of a substrate and polymer molecules spread along the groove to minimize their energy state. |
