Atomistic Simulation of Nanodroplet Collisions with a Wall: Fragmentation and Impact Desolvation of Macromolecules

Abstract

AbstractImpacts of nanodroplets on a hard wall are studied using molecular-dynamics simulation. We focus on water droplets; both pure solvent droplets and droplets filled with a macromolecule are investigated. By choosing a hydrophilic (polyketone) and a hydrophobic (polyethylene) polymer, the effects of the water–polymer interaction can be studied. The process of droplet fragmentation and the ensuing isolation of the embedded macromolecule are investigated. The energy and time dependence of the process is analyzed for various droplet–polymer combinations. By changing droplet size, polymer size, and polymer species separately, we can assess the influence of these factors individually. We demonstrate that the ratio of the impact energy, E, to the cohesive energy, E coh, of the droplet is the key quantity characterizing the droplet fragmentation process. If the impact energy per molecule \(E < (0.29\text{-}0.4) \cdot E_{\mathrm{coh}}\), the droplet is reflected without fragmenting. Beyond that impact energy fragmentation of the droplet abruptly starts. At E = E coh, the fragmentation process already results in a fine dispersal of the droplet into daughter droplets. The disintegration process continuously increases with collision energy. We find that the polymer is isolated for impact energies E per solvent molecule, which exceed a threshold value of the order of the cohesive energy E coh of the solvent. We find that in this energy regime, the temperature of the isolated polymer increases linearly with E.KeywordsDroplet SizeImpact EnergyCohesive EnergyPolymer TemperatureCentral FragmentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.