Impact Desolvation of Polymers Embedded in Nanodroplets

Abstract

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.

Surface Impact Simulations of Helium Nanodroplets

“…Classical molecular dynamics simulations are a mature computational workhorse for studying real-time chemical dynamics in large systems (with more than a dozen or so atoms). The molecular dynamics approach has recently been applied to study the desolvation of species embedded in nanodroplets by colliding the droplet with a solid surface [22]. In these simulations, droplets containing as many as 6000 particles (typically water molecules or argon atoms) are studied for periods of time as long as 300 picoseconds.…”

“…One of these is zero-point averaged dynamics (ZPAD), which incorporates the effects of atomic delocalization by treating individual atoms as smeared-out probability distributions that move along classical trajectories. ZPAD simulations have recently been used, for example, to carry out 30-ps molecular dynamics simulations of doped He N droplets with N ≈ 100 [22][23][24].…”

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

“…A prime reason for the increased energy loss to larger droplets is the increased time scale of isolation. 13 The delayed isolation will give the polymer more time to relax its energy to the solvent. In addition, the increased heat capacity of the surrounding water shell will more efficiently cool the polymer.…”

“…Recently, the desolvation process of polymers 13 and of proteins 14 caused by collisions with a wall has been studied using the technique of molecular-dynamics simulation. The dependence on polymer species (hydrophilic or hydrophobic) and size, and on the solvent species and droplet size was systematically investigated.…”

“…In addition, the fragmentation dynamics and the resulting fragmentation patterns of pure droplets (without embedded macromolecules) have been studied for droplets composed of van-der-Waals bonded atoms [15][16][17][18] and molecules, 19,20 and in particular also for water. 13,21,22 In the present study, we investigate the fate of the embedded polymer after the desolvation process using molecular-dynamics simulations. Of particular interest is its temperature, and how it is related to impact velocity, and droplet and polymer size.…”