Figure 23.

A cylindrical disk translating within an insoluble surfactant monolayer atop a bulk fluid layer of finite depth H. Also shown is the resistance coefficient |F|/4πηR|U| as a function of both sublayer thickness and Boussinesq number. The gray dash-dot lines are the numerical calculations of Stone & Ajdari (1998) at specified Bq, and the solid lines are asymptotic values for small and large H/R. The bottom-most solid lines represent the Bq → 0 limit (table 4). The dashed asymptotes correspond to a clean interface, from (4.158) and (4.162), and highlights the fact that even an inviscid surfactant increases drag on a translating probe as compared to a surfactant-free surface.