The dynamics of thin liquid films in the presence of surface‐tension gradients

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Abstract
The climbing of Marangoni films up vertical solid surfaces was investigated experimentally and theoretically. The system considered was a nonisothermal plate with its warm end partially immersed in a nonvolatile liquid. Observed film thicknesses and rates of climb were in agreement with an approximate hydrodynamic model obtained by assuming the supply capacity of the film to be rate limiting.The results of this study confirm the hypothesis is that previously observed liquid films formed against gravitational forces above equilibrium menisci are produced by surface‐tension inequalities. It is pointed out that hydrodynamic processes cannot allow for the advancement of the leading edge of Marangoni films and a separate physicochemical process is required to explain spontaneous spreading of these films. Evidence is presented for the formation of much thinner primary films ahead of the secondary bulk films described by hydrodynamics. These primary films appear to be produced by a combination of multilayer adsorption and/or surface diffusion. The kinetics of these diffusional processes may limit spreading rates when surface‐tension gradients become sufficiently large.Finally, the Marangoni films were found to be unstable in a manner hithertonot considered.

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