  The breakup of liquid threads into droplets is crucial in various
applications, such as nanoprinting, nanomanufacturing, and inkjet printing,
where a detailed understanding of the thinning neck dynamics allows for a
precise droplet control. Here, the role of surfactant in the breakup process is
studied by many-body dissipative particle dynamics, in particular, the various
regime transitions and thread profiles, shedding light on molecular-level
intricacies of this process hitherto inaccessible to continuum theory and
experiments. Moreover, the role of surfactant in the most unstable
perturbation, the formed droplet size, and surfactant distributions have been
unraveled. As surfactant concentration rises, both the wavelength and time to
breakup steadily increase due to the lowering of surface tension below the
critical micelle concentration (CMC) and viscous effects introduced by micelles
above the CMC. These changes prior to the breakup lead to larger droplets being
formed in cases with higher surfactant concentration. We also compared the
thinning dynamics to existing theoretical predictions, revealing that the
surfactant-laden breakup starts at the inertial regime and transitions into the
thermal fluctuation regime when the concentration is increased. Thus, we
illuminate the hitherto poorly investigated and intricate breakup process of
surfactant-laden liquid threads driven by thermal fluctuations, contributing to
a deeper understanding of this process at molecular scales.
