The dynamics of retraction of an initially highly slender liquid sheet of an incompressible Newtonian fluid the surface of which is covered with a monolayer of insoluble surfactant and that is surrounded by a passive gas is analyzed in the Stokes limit. In this limit, the sheets retract without the formation of a rim or capillary waves along the liquid-gas (L-G) interface. The dynamics of retraction is studied in situations in which surface rheological effects are absent as well as when they are present. Initially, the cross sections of liquid sheets are rectangular in shape albeit with semicircular caps at both ends, i.e. the cross sections resemble elongated two-dimensional (2D) drops. The 2D drops begin to retract due to the capillary pressure difference between their tips and their rectangularly shaped interiors. The free surface flow within the 2D drop is governed by the continuity and the Stokes equations which determine the flow, i.e. the velocity and pressure fields, and the convection-diffusion equation which governs surfactant transport, and hence surfactant concentration, along the L-G interface. Surface tension is related to surfactant concentration by the Szyskowski equation and the surface rheology is described by the Boussinesq-Scriven constitutive equation which involves surface shear and dilatational viscosities that are both functions of surfactant concentration. The dynamics is governed by five dimensionless groups: initial aspect ratio $L_0$, initial surfactant concentration ${\mathrm{\Gamma }}_0$, surfactant strength parameter $\beta$, surface Peclet number $\mathrm{Pe}$ (the dimensionless ratio of surface convection to diffusion of a surfactant), and reference Boussinesq-Scriven number $B_0$ which measures the relative importance of surface to bulk viscous stresses. Taking advantage of sheet slenderness, a set of one-dimensional (1D) slender-sheet equations is derived using a control volume analysis. The 1D equations are solved numerically by a finite-element-based method and predictions made with the 1D algorithm are shown to accord well with ones in which the 2D free surface flow within the 2D drop is solved numerically without invoking slenderness. The results reveal that the early time retraction dynamics far from the two tips are nearly independent of $\mathrm{Pe}$. Moreover, since the two surfaces of the sheet in this region remain planar for long times after the initiation of retraction, a control volume analysis is used to analytically calculate the maximum film thickness and retraction velocity that are likewise independent of $\mathrm{Pe}$. In the theoretical analysis, advantage is taken of the fact that away from the tips, surfactant concentration and sheet half-thickness are simply functions of time and proportional to one another. The analytical results are expressed as implicit functions of time in terms of the exponential integral function and explicitly if surface tension varies slightly during retraction. It is shown that sheets with $B_0\ne 0$ retract slower than ones with $B_0=0$, which in turn retract slower than ones with clean interfaces. The role of finite inertia is also investigated briefly and it is demonstrated that rim formation is suppressed so long as $\mathrm{Oh}(1+B_0{\mathrm{\Gamma }}_0)\gg L_0$ where $\mathrm{Oh}$ is the Ohnesorge number $[\text{viscous}\text{force}/\sqrt{\text{(inertia)(surface}\text{tension}\text{force)}}]$.

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• Interfacial flows
• Thin fluid films
• Drops & bubbles