Effects of the Laplace number (λ) on the retraction of the interface after the plug rupture for the Laplace number in the range 20 ⩽ λ ⩽ 1500. The solid and dashed lines show the clean and the contaminated cases, respectively. (Lpi = 1.0, h2 = 0.05, Δp = 1, β = 0.7, χ = 0.01, Sc = 10, Scs = 100, Ka = 104, Kd = 100, C0 = 10−4).