Bulk liquid soluble surfactant induced retardation of the thermocapillary migration of a droplet

摘要

Thermocapillary migration of droplet under earth gravity was successfully demonstrated by using a density matched system (water / n-butyl benzoate) in the application of the Plateau configuration. The thermal coefficient of interfacial tension over a temperature range of 20-50 degrees C was determined for water / n-butyl benzoate, and consequently the theoretical prediction for the motion of water droplet in n-butyl benzoate in the presence of a vertical temperature gradient can then be made. Experimental results of thermocapillary migration for the clean interface were found to be less efficient than the theoretical ones. This is attributable to the thermal convection effect, trace surface active impurities effect and/or wall effect which are neglected in the theory. On the other hand, the experimental results reveal that thermocapillary migration of water droplet is significantly depressed by the deliberately introduced bulk liquid soluble surfactants. Several millimolars of Span 80 and Span 85 were shown to inhibit the thermocapillary effect completely. [References: 16]