Radially Ejected Bubbles Driven by Thermocapillarity in Equilibrated Vapor-Liquid Mixtures

We report a novel nucleation method that exploits thermocapillary forces in binary fluids to generate a cloud of bubbles ejected radially from a thermally pulsed wire. The bubbles are nucleated within milliseconds of the extinction of the microsecond pulse and are ejected outward from the wire surface due to the thermocapillary force created by the radial temperature gradient. At low temperatures the surface tension of the vapor-liquid mixture, consisting of ethane-n-octane, increases with increasing temperature, ejecting the bubbles away from the heated wire. By proper choice of fluid composition, temperature, or pressure, the sign of the surface tension gradient can be inverted such that nucleated bubbles are attracted to the wire. As opposed to water-alcohol mixtures that have a surface tension minimum, we show that this mixture-which we refer to as an equilibrated vapor-liquid mixture-exhibits a surface tension maximum, creating a unique set of behaviors which have not yet been fully examined in the literature.