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The present work aims at studying the nonlinear breakup mechanism for Taylor bubble in a T-junction with a square cross-section of 400×400 μm by using a high-speed digital camera.During the nonlinear collapse process,the variation of the minimum radius of bubble neck (r0) with the remaining time until pinch-off (τ) could be scaled by a power-law relationship: r0 ∝ τα,though the collapse rate is diverse surrounding the asymmetric neck.Under the confinement of the wall,the nonlinear collapse process could be divided into two stages: liquid filling stage and free surface stage.The critical radius rc of the asymmetric neck at the transition of the stages reduces with the increase of the flow rate and viscosity of the liquid phase,but increases with the surface tension.In the liquid filling stage,the gaseous neck collapses under the squeezing of the liquid and the exponent α approaches to 0.33.In the free surface stage,the exponent increases with the increase of liquid viscosity: from α = 0.5 for 1 mPa.s to α =1 for 100 mPa.s.In addition,little surfactant of SDS (sodium dodecyl sulfate) in deionized water enlarges the exponent α to 0.7 and induces the gaseous neck to pinch-off at the end,and then the isolated neck evolves to satellite bubbles.