The surface-tension-driven motion of a surfactant-coated liquid thread in inviscid
surroundings is investigated using linear stability theory as well as one-dimensional
nonlinear approximations to the governing Navier–Stokes equations. Examination of
analytic limits of the linear dispersion relationship demonstrates that surfactant acts as
a distinct mechanism for long-wavelength cut-off, instead of inertia, if the surfactant
effects exceed a critical value, β = ½, where β is a dimensionless surface-tension
gradient. Two different long-wavelength regimes can be identified, depending on the
degree of tangential stress, with β = 1 characterizing a transition from extensionally
dominated inertial flow to shear-dominated viscous flow. One-dimensional nonlinear
models are formulated which capture the changes in behaviour with variation of β
by inclusion of the necessary high-order terms. Scaling close to breakup shows that
surfactant is swept away from the pinching region and then has little effect.