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. 2020 Oct 29;3(5):1791–1810. doi: 10.1016/j.matt.2020.10.012

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Colorimetric Visualization of Modified Droplets

(A–C) (A) Unmodified, nearly neutral droplets leave drying stains made of polymer and salts that are highly visible under (B) the reflection mode of imaging, but not under (C) the transmission mode.

(D) In contrast, since modified droplets contain acid and can dope polyaniline, they leave green stains that are visible under both modes of imaging.

(E–H) (E and F) and (G and H) are representative images of stains of droplets passing through a gauze cloth and a lint-free wipe, respectively. Note that not all the droplets observed under the reflection mode (E and G) can be seen under the transmission mode, due to insufficient level of acid modification. All scale bars represent 200 μm.