Nanojets: Electrification, Energetics, Dynamics, Stability and Breakup

Abstract : Simulation methodologies, algorithms, and computer codes allowing molecular dynamics simulations of formation, propagation, and breakup processes of nanojets, generated either through the application of pressure or through the action of an electric field to liquids containing solvated charges, were developed. Particular emphasize was placed on simulations of electrically driven nanojets of liquid formamide solutions with dissolved NAI, and on investigations of the behavior and response of nanoscale drops of such solutions as well as of pure formamide, when placed in strong electric fields. The simulations, and coordinated electrospray experiments at the AFRL, Hanscom AFB, demonstrated a mixed charge emission regime exhibiting field-induced cluster ion evaporation and ejection of charged droplets. The simulation average mass-to-charge ratios and maximal surface fields of about 1V/nm agree with the experimental results and with electrohydrodynamic theory of cone-jets. The measured solvated ion distributions are also correctly reproduced by the simulations. Emission of charged particles is found in the simulations to occur predominantly from the tip of the nanojet, rather then from the neck between the Taylor cone and the nanojet. The MD simulations revealed novel field-induced structural ordering processes and electro-crystallization of pure formamide drops. The microscopic results obtained through the atomic-scale simulations were analyzed and compared to the predictions of a continuum formulation.