Coalescence is the process by which two different fluid droplets join to form one larger droplet (or one larger droplet and one smaller droplet, in the case of partial coalescence). The dynamics of this process has been studied using a variety of means, including optical microscopy, ultra-fast x-ray phase imaging, resistance measurements, and confocal microscopy of colloids; these investigations have revealed interesting scaling behavior in the dynamics of fluid droplet coalescence.
Coalescence is often undesirable (for example, in emulsions and foams). A good deal of work focuses on controlling this process: this can be by preventing direct contact between the two droplet interfaces using adsorbed species at the droplet-external fluid interface (such as particles or surfactants), or by using charge.
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