Bubble dynamics and atomization in evaporating polymeric droplets

Abstract

We investigate the interaction of an aqueous polymeric droplet with a tuneable continuous laser in an acoustically levitated environment. The effect of laser irradiation intensity and polymeric concentration on various spatio-temporal parameters is unearthed using high-speed shadowgraphy and theoretical scaling analysis. We observe four temporal phases: droplet evaporation, vapour bubble growth followed by membrane inflation, bubble/membrane rupture through hole nucleation and droplet breakup. During the initial droplet evaporation phase, concentration build-up at the droplet surface beyond a critical limit leads to the formation of a skin layer. It is revealed that, at a given location inside the droplet, hot spots occur, and the maximum temperature at the hot spots scales linearly with irradiation intensity until a bubble nucleates. The low-intensity laser interaction leads to symmetric membrane inflation that eventually forms holes at droplet poles and cracks on the shell surface. On the contrary, high intensity causes early bubble nucleation followed by asymmetric membrane inflation that eventually ruptures through multiple hole formation. Furthermore, the growth and rupture of the membrane is followed by a catastrophic breakup of the droplet. Two dominant atomization modes are reported at significantly high irradiation intensities: stable sheet collapse and unstable sheet breakup. The evolution of droplets into a stable/unstable sheet follows universally observed ligament and hole dynamics. A regime map is shown to describe the influence of polymer concentration and irradiation intensity on the strength and mode of droplet atomization.

Bubble dynamics and atomization of acoustically levitated diesel and biodiesel droplets using femtosecond laser pulses

“…The phenomenon of bubble dynamics is nicely explained from the generation of bubbles to its evolution. The use of a femtosecond laser to generate microbubbles allows for exact control and prediction of the size, position, and polydispersity of the generated bubbles, making them useful in applications such as microemulsions 38 , 49 , laser-induce fragmentation of polymers 1 , 64 , and laser induced cavitation in e-fuels 6 , 48 , 51 . Furthemore, the findings could help in understanding the incubation effect and optimizing laser parameters for medical laser and nano/micro-object manipulation applications.…”

“…Atomization of a single droplets of diesel and biodiesel, Rapeseed Methyl Ester (RME) in a quiescent medium is crucial for understanding the fundamental physics of fluid dynamics, droplet breakup and evaporation of fuels in combustion devices. Various methods have been developed to investigate different phenomena associated with individual droplets, including fragmentation, deformation, expansion, bubble dynamics, cavitation, coalescence, and evaporation 1 – 6 . Laser-matter interaction, and in particular laser-induced breakdown (LIB), has emerged as a progressive technique for scrutinizing and analyzing these phenomena.…”

Insights on droplet drift and effective utilization of pesticide in “Third Pole”：Qinghai-Tibet Plateau of China

“…However, droplet distortion, collision, and evaporation between the nozzle and the target are absent. Droplet spatial behavior serves as a transitional link that can both represent the potential process of pesticide deposition and serve as feedback for the management of particle size [ [23] , [24] , [25] ]. The highest peak in the world, located in China's Qinghai-Tibet Plateau, is where the Yellow, Yangtze, and Lancang rivers originate.…”