Nucleation in sessile saline microdroplets: induction time measurement via deliquescence–recrystallization cycling

Abstract

Induction time, a measure of how long one will wait for nucleation to occur, is an important parameter in quantifying nucle-ation kinetics and its underlying mechanisms. Due to the stochastic...

Evaporation Dynamics of Sessile Saline Microdroplets in Oil

“…In a special case of a long 1D array of monodisperse microdroplets ( N > 60), each droplet tends to evaporate at the same rate (i.e., J n ≈ J m ). This has been experimentally verified in our previous work . With this assumption, we can simplify eq as Indeed, the predictions of the simplified model (eq ) converge to that of the full model (eq ) at large values of N (Figure S4 and section 2.4 of the SI), which justifies our simplification.…”

“…Because of the stochastic nature of nucleation, a large number of independent induction time measurements are necessary to quantify the kinetics. To address this, we have recently developed a method to measure the induction times of hundreds of sessile microdroplets based on images taken from a bottom-view microscope . A schematic diagram of a typical microdroplet configuration (2D matrix) is shown in Figure a, and an example image is shown in Figure b, where the distance between droplet lines is always much greater than the distance between adjacent droplets (i.e., L 2 > L 1 ).…”

“…We measured three characteristic times, namely, the saturation time (droplet is saturated), matching time (the refractive index of the droplet equals that of the oil), and nucleation time. Although the use of the bottom-view microscope gives only the droplet volume and concentration at some specific time points, it allows the simultaneous measurement of hundreds of droplets, which is useful for studying the stochastic nature of nucleation …”

“…This has been experimentally verified in our previous work. 41 With this assumption, we can simplify eq 10 as i k j j j j j j y…”

“…However, in microliter droplets, it has been shown that various internal and Marangoni flows can lead to temperature and concentration gradients. , To address this, we reduce the droplet size down to the picoliter range and reduce the evaporation rate by immersing the droplet in an oil bath. Because water can diffuse into the oil in small amounts, the oil bath is subjected to regulated humidity, with the goal of controlling the diffusion of droplet water into the oil. The oil bath also serves as a thermal buffer which minimizes temperature gradients due to evaporation.…”