The droplet evaporation rate was determined as described previously [13]. Briefly, a microbalance (MSE3.6P; Sartorius) was placed inside an environmental chamber to weigh ten 1-μL droplets, which were spotted on a microscope cover glass (12-545-M; Fisher Scientific), over 1 h. Droplet mass was recorded at 1-min intervals. Droplet evaporation rate was calculated as shown in Eq 3. Dropletevaporationrate=dmdt=mtn−mtn−1(3)  Where m is the mass of droplets (mg), and tn is n min after droplets were spotted.