Ion-Induced Nucleationin Solution:  Promotion of Solute Nucleation in Charged Levitated Droplets

Abstract

We have investigated the nucleation and growth of sodium chloride in both single quiescent charged droplets and charged droplet populations that were levitated in an electrodynamic levitation trap (EDLT). In both cases, the magnitude of a droplet's net excess charge (ions(DNEC)) influenced NaCl nucleation and growth, albeit in different capacities. We have termed the phenomenon ion-induced nucleation in solution. For single quiescent levitated droplets, an increase in ions(DNEC) resulted in a significant promotion of NaCl nucleation, as determined by the number of crystals observed. For levitated droplet populations, a change in NaCl crystal habit, from regular cubic shapes to dome-shaped dendrites, was observed once a surface charge density threshold of -9 x 10(-4) e.nm(-2) was surpassed. Although promotion of NaCl nucleation was observed for droplet population experiments, this can be attributed in part to the increased rate of solvent evaporation observed for levitated droplet populations having a high net charge. Promotion of nucleation was also observed for two organic acids, 2,4,6-trihydroxyacetophenone monohydrate (THAP) and alpha-cyano-4-hydroxycinnamic acid (CHCA). These results are of direct relevance to processes that occur in both soft-ionization techniques for mass spectrometry and to a variety of industrial processes. To this end, we have demonstrated the use of ion-induced nucleation in solution to form ammonium nitrate particles from levitated droplets to be used in in vitro toxicology studies of ambient particle types.

Nucleation of Organic Crystals—A Molecular Perspective

“…The attachment frequency f* can then be determined, and the effect of a particular parameter, for example, the solvent, on the attachment frequency f* can be analyzed. [35,36] However, the interface of the small volume may itself act as a heterogeneous surface that promotes heterogeneous nucleation. It might be possible to eliminate heterogeneous nucleation in sufficiently small volumes by the use of emulsions, [31] in microfluidic devices, [32] and perhaps also at planar liquid-liquid interfaces [33,34] and in levitated droplets.…”

“…It might be possible to eliminate heterogeneous nucleation in sufficiently small volumes by the use of emulsions, [31] in microfluidic devices, [32] and perhaps also at planar liquid-liquid interfaces [33,34] and in levitated droplets. [35,36] However, the interface of the small volume may itself act as a heterogeneous surface that promotes heterogeneous nucleation. Table 1 gives some typical measured values of A, B, and g for a number of small molecules and the protein lysozyme.…”

Accounting for Changes in Particle Charge, Dry Mass and Composition Occurring During Studies of Single Levitated Particles

“…The measured net charge per droplet was in line with similar measurements by other groups. 9,23 The apparent drift in the GF observed in various particle types when the RH was held constant over a long period of time at a given RH are shown in Figure 3. This change is referred to as "apparent" simply because this is how the change might be attributed, even though the RH is invariant in these measurements and, thus, the mass of the particle is not changing.…”

“…Although the net charge found on the droplet in an EDB is relatively low, on the fC scale, 9,23 the density of the charge on the droplet is not equally distributed. Charge−charge repulsion dictates that all of the excess charge on a droplet will be located at or near the surface, creating a microenvironment in the droplet at the surface of high charge imbalance.…”

Keimbildung organischer Kristalle aus molekularer Sichtweise

“…Dann kann die Anlagerungsfrequenz f * bestimmt und der Einfluss beispielsweise des Lösungsmittels auf die Anlagerungsfrequenz f * analysiert werden. Alternativ dazu kann versucht werden, heterogene Keimbildung insgesamt zu vermeiden, was in ausreichend kleinen Volumen unter Verwendung von Emulsionen,31 in Mikrofluidikvorrichtungen32 und möglicherweise an planaren Flüssig‐flüssig‐Grenzflächen33, 34 und in frei schwebenden Tröpfchen35, 36 möglich sein könnte. Dabei ist aber anzumerken, dass die Grenzfläche eines kleinen Volumens ebenfalls als heterogene Grenzfläche wirken kann, die heterogene Keimbildung fördert.…”