An Atomic Force Microscope (AFM), Asylum MFP-3D (Asylum Research, Santa Barbara, CA) and the AC260T probes (Olympus, Tokyo, Japan) were used to measure the size and lifetime of EWNS. The AFM scan rate was 1 Hz and the scanned area 5 μm × 5 μm with 256 scan lines. All images were subjected to 1st order image flattening with the Asylum Software (range of 100 nm and threshold of 100 pm for the mask).
The sampling funnel was removed and the mica surface was placed at a 2.0 cm distance from the counter electrode for an average time of 120s to avoid particle coalescence and the formation of irregular shaped droplets on the mica surface. The EWNS were directly sprayed on a freshly cleaved mica surface (Ted Pella, Redding, CA). The mica surface was imaged immediately after the spray using AFM. The contact angle of a freshly cleaved, unmodified, mica surface is close to 0° so the EWNS were spread on the mica surface adopting a dome like shape20 (link). The diameter (a) and the height (h) of the spread droplet were measured directly from the AFM topography and used to calculate the volume of the dome-like spread of EWNS with our previously validated methodology8 (link). Assuming that airborne EWNS have the same volume, an equivalent diameter can be calculated with equation(2) :
where a is the radius of the spread droplet and h the height.
The sampling funnel was removed and the mica surface was placed at a 2.0 cm distance from the counter electrode for an average time of 120s to avoid particle coalescence and the formation of irregular shaped droplets on the mica surface. The EWNS were directly sprayed on a freshly cleaved mica surface (Ted Pella, Redding, CA). The mica surface was imaged immediately after the spray using AFM. The contact angle of a freshly cleaved, unmodified, mica surface is close to 0° so the EWNS were spread on the mica surface adopting a dome like shape20 (link). The diameter (a) and the height (h) of the spread droplet were measured directly from the AFM topography and used to calculate the volume of the dome-like spread of EWNS with our previously validated methodology8 (link). Assuming that airborne EWNS have the same volume, an equivalent diameter can be calculated with equation
where a is the radius of the spread droplet and h the height.
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