  While a drop of liquid is placed on another liquid surface, two possible
coalescence outcomes are observed. The parent drop bounces several times,
floats and then disappears within the liquid pool without producing daughter
droplets. This is called complete coalescence. Another outcome is the
generation of secondary droplets from the primary drop itself. This is called
partial coalescence. Repetitions of such phenomenon as a successive
self-similar event is also known as coalescence cascade. In a nutshell,
complete coalescence is governed strongly by swallowing mechanism whereas
partial coalescence is attributed to slippage mechanism and solutal Marangoni
flow. Here we use high speed camera and witness that water drop coalesces
completely after impacting on pool of liquid whereas drop of non-ionic
surfactant (TWEEN 20) coalesces partially. We also observe that number of
daughter droplet generation is a strong function of surfactant concentration.
Here we utilise the images to elaborately explain both the phenomenon in a
sequential event based approach using the basic understanding of physics. We
observe the transient evolution of drop morphology during each stage and find
shape wise resemblances with many common objects. Our study reveals some
interesting insight on the intermediate mechanisms and enlightens distinctive
features of both the phenomena. Here we propose for the first time that
additional instability due to slippage of rising water layer from the
surfactant drop and upward thrust due to Laplace pressure helps in formation of
secondary droplet. Keywords: Partial coalescence, complete coalescence, high
speed camera, drop morphology, slippage, Laplace pressure.
