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Controlling and characterizing the coagulation of liquid aerosol droplets
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) A CERS spectrum from a single aqueous aerosol droplet, radius of . The inset image and intensity profile illustrate the approach for determining the droplet size from the image. (b) Comparison of the droplet size estimated from the image with that determined from CERS. The error bars are substantially larger in the size estimation from the image, with the errors from the CERS measurements smaller than the symbol size. The dotted line represents an independent calibration predicted from a ruled micrometer scale.

Image of FIG. 2.
FIG. 2.

(a) The particle trajectory during the time the optical trap is turned off for a droplet of in radius. The gray circle indicates the trap position. (b) Variation in the mean displacement with the time the optical trap is turned off (dashed line is to guide the eyes).

Image of FIG. 3.
FIG. 3.

By equally sharing the trapping laser beam over four trapping sites using rapid beam steering with an AOM, four droplets can be simultaneously trapped. The droplet radii can be determined from the CERS fingerprints as 3.944, 4.352, 4.488, and , left to right, respectively.

Image of FIG. 4.
FIG. 4.

A demonstration of the simultaneous manipulation and coagulation of two aqueous aerosol droplets, frames (a)–(c) in sequence. CERS fingerprints of (a) left droplet (modes identified by circles) (b) left and right (modes identified by crosses) droplets, and (c) droplet after coagulation.

Image of FIG. 5.
FIG. 5.

Correlation of the combined volume of two trapped droplets and their coagulated volume. The dotted line illustrates the result expected when the combined volume is equal to the coagulated volume. The correlation coefficient between the combined volume and coagulated volume is 0.9933, with a standard deviation of the combined volume from the coagulated volume of .

Image of FIG. 6.
FIG. 6.

(a) Schematic illustrating the processes of particle sedimentation and recapture following trap translation. (b) The maximum distance between traps that a droplet can be recaptured with variation in droplet diameter and trapping laser power (, , and ). The lines are shown as a guide.

Image of FIG. 7.
FIG. 7.

The identity of the final trap in which the coagulated droplet resides can be controlled by varying the relative trap strengths. At low trapping power ratios, the left trap is stronger [scheme (a)], while at high trapping power ratios the right trap is stronger [scheme (c)]. The probability that the coagulated droplet resides in the left trap is shown by the filled circles and the probability that it resides in the right trap is shown by the diamonds.

Image of FIG. 8.
FIG. 8.

Investigation of the dependence of the distance at which coagulation occurs on the summed radii of the two droplets. The dotted line represents the expected coagulation distance if the two droplets were to coagulate at the point of physical contact. (a) An example of an expected coagulation event at a separation just prior to coagulation. (b) An example of a coagulation event occurring for a large combined droplet radius, where the smaller droplet appears to be displaced in the vertical plane.

Image of FIG. 9.
FIG. 9.

Comparison of the spectra and images of the single trapped aqueous sodium chloride aerosol droplet prior to coagulation and after coagulation with droplets of (a) aqueous sodium chloride aerosol, (b) ethanol, and (c) decane. In (b), the gray lines indicate the extension of the mode progression over both the OH and CH stretching vibrations.

Image of FIG. 10.
FIG. 10.

Variation in the difference between spectral spacings of the TE and TM modes with change in core and shell thicknesses for a layered ethanol/sodium chloride/water droplet (open circles). The variation with change in droplet size for a homogeneous droplet of 40% volume of ethanol/water/sodium chloride is shown for comparison (filled gray squares) and for a sodium chloride/water droplet (open squares). The mean experimental difference for the spectrum shown in Fig. 9 is shown by the dotted line, with the shaded gray box equivalent to one standard deviation.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Controlling and characterizing the coagulation of liquid aerosol droplets