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Issue 11, 2018
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Emerging investigator series: determination of biphasic core–shell droplet properties using aerosol optical tweezers

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Abstract

We present a new algorithm for the analysis of whispering gallery modes (WGMs) found in the cavity enhanced Raman spectra retrieved from optically tweezed droplets. Our algorithm improves the computational scaling when analyzing core–shell droplets (i.e. phase-separated or biphasic droplets) in the aerosol optical tweezers (AOT), making it computationally practical to analyze spectra collected at a few Hz over hours-long experiments. This enables the determination of the size and refractive index of both the core and shell phases with high accuracy, at 0.5 Hz time resolution. Phase-separated core–shell droplets are common morphologies in a wide variety of biophysical, colloidal, and aerosolized chemical systems, and have recently become a major focus in understanding the atmospheric chemistry of particulate matter. Our new approach reduces the number of parameters directly searched for, decreasing computational demands. We assess the accuracy of the diameters and refractive indices retrieved from a homogeneous or core–shell droplet. We demonstrate the performance of the new algorithm using experimental data from a droplet of aqueous glycerol coated by squalane. We demonstrate that a shell formation causes adjacent WGMs to split from each other in their wavenumber position through the addition of a secondary organic aerosol shell around a NaCl(aq) droplet. Our new algorithm paves the way for more in-depth physiochemical experiments into liquid–liquid phase separation and their consequences for interfacial chemistry—a topic with growing experimental needs for understanding the dynamics and chemistry of atmospheric aerosol particles, and in biochemical systems.

Graphical abstract: Emerging investigator series: determination of biphasic core–shell droplet properties using aerosol optical tweezers

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Publication details

The article was received on 13 Apr 2018, accepted on 04 Jun 2018 and first published on 05 Jun 2018


Article type: Paper
DOI: 10.1039/C8EM00166A
Citation: Environ. Sci.: Processes Impacts, 2018,20, 1512-1523
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    Emerging investigator series: determination of biphasic core–shell droplet properties using aerosol optical tweezers

    K. Gorkowski, N. M. Donahue and R. C. Sullivan, Environ. Sci.: Processes Impacts, 2018, 20, 1512
    DOI: 10.1039/C8EM00166A

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