Iterferometry has supplied a plausible explanation of the threshold development of the Marangoni convection - the effect repeatedly observed in experiments but contradictive to the traditional notions of motion initiation in the Newtonian fluids. It has been found that the appearance of a certain surface tension gradient required for initiation and development of the Marangoni convection is related to the formation of the adsorbed layer of uncontrolled impurities at the free surface of the fluid. Deformation of this layer occurs when the difference in the surfactant (surface-active substance) concentration reaches several percents. In this paper, we discuss the results of experimental investigation of the Marangoni convection initiated at the free surface of water by local injection of the aqueous solutions of the surfactants. For a surfactant we used monoatomic alcohols belonging to one homological series. A series of experiments have been carried out to define the threshold values of the concentration difference and the order of magnitude of the critical Marangoni numbers. It has been found that the threshold value decreases with increasing length of the surfactant molecules and characteristic dimensions of the free surface.
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