Using molecular dynamics simulation, we study the desolvation process of a polymer-loaded droplet after collision with a wall. The energy and time dependence of the process is analyzed for various droplet-polymer combinations. By changing droplet size, polymer size, solvent, and polymer species, separately, we can assess the influence of these factors individually. We find that the polymer is isolated for impact energies E per solvent molecule, which exceed a threshold value E(isol), which is of the order of the cohesive energy E(coh) of the solvent. The influence of the solvent can be quantified by the solute-solvent interaction energy per molecule E(ss). If the same polymer is embedded in solvents with similar E(coh), we find that desolvation proceeds more easily in the solvent with the smaller solute-solvent interaction energy per molecule E(ss). Polymers with high interaction energy need higher impact energies for complete desolvation. This interface energy also characterizes the desolvation of different polymers in the same solvent. E(isol) increases slowly with the size of the droplet and decreases with the size of the polymer. These findings may help to improve the production of intact isolated macromolecules out of their solutions.

Using molecular-dynamics simulation, we investigate the fragmentation behavior of droplets after collision with a wall. We demonstrate that the ratio of the impact to the cohesive energy E(coh) of the droplet is the key quantity characterizing the droplet fragmentation process. To show this both van der Waals-bonded Ar and N(2) droplets and polar H(2)O droplets are studied. If the impact energy per molecule E<(0.35-0.4)E(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 maximum fragment contains only less than 4% of the initial droplet mass and around one-third of the droplet has been shattered into isolated molecules. The disintegration process continuously increases with collision energy. These findings are relevant for the process of droplet fragmentation as used in the method of impact desolvation of electrosprayed microdroplets mass spectrometry.

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