We investigate the fragmentation dynamics of acoustically levitated microemulsion droplets subjected to laser irradiation. The influence of irradiation intensity and emulsion composition on bubble dynamics and subsequent breakup characteristics is investigated. Our findings demonstrate an inverse relationship between irradiation intensity and the onset of vapor bubble nucleation, which is consistent with theory. Depending on the composition and irradiation intensity, distinct regimes of bubble growth are revealed. The growth and collapse of these bubbles result in droplet fragmentation via ligament-mediated breakup and sheet breakup. These breakup modes are governed by interfacial instabilities, including Faraday, Rayleigh-Taylor, and Plateau-Rayleigh mechanisms. The bubble growth and collapse events are quantified using a breakup impact parameter ($\beta$), which, in turn, reveals the onset of instability triggering droplet breakup. Consequently, the variations in ligament dynamics [using Weber number (We)] are explained and correlated to the respective bubble growth and collapse events. In particular, our experimental data show that small-sized bubbles (lower value of $\beta$) typically result in the ejection of high-momentum ligaments (larger We). Finally, we report the growth and collapse dynamics of a highly viscous bubble that forms toward the end of the droplet lifetime due to the high concentration of nonvolatile surfactant.

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• Atomization
• Bubble dynamics
• Drop breakup
• Surface instabilities
• Drops & bubbles
• Emulsions