A study of retardation of the thermocapillary flow caused by surfactant addition

Surfactant effect on thermocapillary flow that artificially provoked by a steady point heat source at an air/liquid interface was studied. The experimentally measured surface velocity and temperature profiles reveal that small amounts of SDS in ethylene glycol retard significantly the thermocapillary flow. A dimensionless elasticity number E, which is a ratio of the surfactant-induced restoring force to the thermocapillary force that triggers the flow, is proposed to express the interplay of concentration and temperature effects on interfacial turbulence. The data of this highly viscous liquid together with those of water in a previous work were examined and shown to be satisfactorily correlated by an equation developed in terms of the elasticity number.