A multi-scale approach to electrospray ion source modeling has been developed. The evolution of a single-emitter electrospray plume in a pure ionic regime is simulated with a combination of electrohydrodynamic fluids and n-body particle modeling. Simulations are performed for the ionic liquid, EMI-BF4, firing in a positive pure-ion mode. The metastable nature of ion clusters is captured using an ion fragmentation model informed by molecular dynamics simulations and experimental data. Results are generated for three operating points (120, 324, and 440 nA) and are used to predict performance relevant properties, such as the divergence angle and the extractor surface impingement rate. Comparisons to experimental data recorded at similar operating points are provided.

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The angular distribution of emitted species in electrospray ion beams is not well characterized and can have negative effects on propulsive performance and emitter lifetime. We present an experimental characterization of the angular distribution of emitted species in a single electrospray ion beam as a function of firing voltage using time of flight mass spectrometry. Angular current distributions indicate the central axis of emission varies up to 10 • from the central axis of the emitter tip. Variation in the ion species as a function of angle depends on the firing voltage. Simulations of single particle trajectories indicate that fragmentation of ion clusters results in ion products moving closer to the center of the beam and neutral products spreading up to 47 • depending on how rapid fragmentation occurs. Experimental results are compared to multiscale full-beam simulations of electrospray emission and future use of these simulations to explain angular beam behavior is discussed.

UNSTRUCTURED The opioid crisis is ravaging economies and communities across the United States. Technology has the potential to end this crisis. Digital health offers new ways to reach, diagnose, and treat individuals with opioid use disorders. Federal research funding tends to reflect the nation’s research priorities and shape the direction of innovation. We reviewed funded projects by the National Institute on Drug Abuse (NIDA) from 2013 to 2017, a period leading to the substantial increase in federal funding and the launch of the HEAL (Helping End Addiction Long-TermSM) initiative in 2018. We presented our viewpoint of the research landscape of the digital health development for the opioid crisis. Overall, there was a gradual increase in NIDA grant funding for technology in the opioid crisis and the percentage of NIDA technology awards funding new projects has nearly doubled. More specifically, we discuss the types of applications and potential challenges in five emerging technology categories: electronic health, mobile health, virtual reality, artificial intelligence, and biosensor. Diversification of funding in these categories offers the promise of more innovation in new technologies to combat the opioid epidemic.

In this work, we present coordinated molecular dynamics, ion cluster acceleration, and retarding potential analysis simulations to determine cluster fragmentation behavior in a realistic emitter geometry for electrosprays operating in the pure ionic regime. Molecular dynamics simulations are used to determine the fragmentation rates of ionic liquid clusters as a function of internal energy, electric field strength, and cluster size. A simplified model of electrospray cluster acceleration is developed from previous electrohydrodynamic emission models and used to simulate retarding potential analysis curves. Fragmentation rates and beam composition are inferred for experimental data based on the molecular dynamics and cluster acceleration simulations. We find that for these experimental data, temperatures of EMI-BF4 dimers likely range between 590 and 687 K while trimer temperatures are larger between 989 and 1092 K. The percentage of monomers, dimers, and trimers in the beam is approximately 45%, 30%–43%, and 13%–25%, respectively. Both ionic liquid cluster temperatures and beam composition agree with previous analysis of this experimental work, supporting the use of coordinated molecular dynamics and retarding potential analysis as a method of inferring electrospray beam parameters. Insights gained from this simulation process are discussed in the context of currently unexplained electrospray emitter behavior and experimental results including the presence of tetramers and trimers in the beam and fragmentation rates in high electric field regions.

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