报告名称1：Surface nanobubbles: formation, universality of the contact angle, and stability

报 告 人：Professor Detlef Lohse, University of Twente, Netherland

时　　间：2013年4月28日（星期日）上午10:00

地　　点：张江办公楼101会议室

报告人简介：

Professor Detlef Lohse, Chair of Physics of Fluids, at the Department of Applied Physics, University of Twente, Enschede, the Netherlands. His group works on a variety of aspects in fluid mechanics, in particular on those related to bubbles. The focus of their work is the fundamental understanding the phenomena of the physics of fluids, bubbles and jets, which we undertake by experimental, numerical and theoretical means. They published about 300 publications in refereed scientific journals, including 7 Nature/Science papers, 60 Physical Review Letters, 2 Review of Modern Physics, 1 Annual Review of Fluid Mechanics, and 1 Physics Today cover article.

摘要:

We study surface nanobubbles using molecular dynamics (MD) simulation of ternary (gas, liquid, solid) systems of Lennard-Jones fluids. They form for sufficiently low gas solubility in the liquid, i.e., for large relative gas concentration. For strong enough gas-solid attraction, the surface nanobubble is sitting on a gas layer, which forms in between the liquid and the solid. This gas layer is the reason for the universality of the contact angle, which we calculate from the microscopic parameters. Under the conditions of the MD simulations, the nanobubbles dissolve within less of a microsecond.So why then, under normal experimental conditions,　are surface nanobubbles stable for many hours or even up to days rather than the expected microseconds? We present a theory that the limited gas diffusion through the water in the far field, the cooperative effect of nanobubble clusters, and the pinned contact line of the nanobubbles lead to the very slow dissolution rate.

References:

J. H. Weijs, J. H. Snoeijer, and D. Lohse, Phys. Rev. Lett. 108, 104501 (2012);

J. H. Weis and D. Lohse, Phys. Rev. Lett. 110, 054501 (2013)

报告名称2：Surface Nanobubbles Nucleate Droplets

报 告 人：Dr Xuehua Zhang, University of Melbourne, Austrilia

时　　间：2013年4月29日（星期一）上午11:00

地　　点：张江办公楼101会议室

摘要

When a water-repelling solid is in contact with water, gaseous domains of nanoscale thickness, called surface nanobubbles, often remain on the surface. The presence of such nanobubbles can influence a variety of interfacial processes, such as fluid slippage over a wall, surface forces, biomolecular adsorption, (photo) catalysis and surface corrosion. It is, however, unknown how surface nanobubbles respond to a large temperature increase and whether they can influence interfacial events during boiling, such as surface drying from evaporation and droplet condensation. We show here that surface nanobubbles withstand an increase of temperature up to the boiling point of bulk water. Remarkably, we find that nanobubbles nucleate droplets during the evaporation process and that these droplets grow by condensation. Our results demonstrate the stability of nanobubbles at close-to-boiling temperatures and their persistence even after the bulk water has receded from the surface due to their ability to condense a shielding liquid microdroplet around them. This work is a starting point for studying the impact of nanoscale fluidic domains on the motion of the receding three-phase line and for understanding the phase transition initiated by surface nanobubbles.