A History of Nanobubbles

Abstract

We follow the history of nanobubbles from the earliest experiments pointing to their existence to recent years. We cover the effect of Laplace pressure on the thermodynamic stability of nanobubbles and why this implies that nanobubbles are thermodynamically never stable. Therefore, understanding bubble stability becomes a consideration of the rate of bubble dissolution, so the dominant approach to understanding this is discussed. Bulk nanobubbles (or fine bubbles) are treated separately from surface nanobubbles as this reflects their separate histories. For each class of nanobubbles, we look at the early evidence for their existence, methods for the production and characterization of nanobubbles, evidence that they are indeed gaseous, or otherwise, and theories for their stability. We also look at applications of both surface and bulk nanobubbles.

Surface nanobubbles: Theory, simulation, and experiment. A review

“…Before considering surface NBs, it is worthwhile to briefly discuss the stability of free (bulk) NBs [3]. In fact, much literature refers to bulk NBs, which can form spontaneously under different salt concentration and pH [86].…”

“…water) and a solid substrate, which is usually hydrophobic (see Fig. 1) [1][2][3][4]. The existence of NBs was speculated about 25 years ago by Parker et al as they attempted to estimate the forces between two neutral hydrophobic surfaces immersed in water [5].…”

Electrically controlled cloud of bulk nanobubbles in water solutions

“…They attracted significant attention in the last decade [1–3] due to their long-time stability and high potential for applications. The NBs can be applied for nanocsopic cleaning [4–7], for control of boundary slip in microfluidics [8, 9], for wastewater treatment [10, 11], for heterocoagulation [12, 13], and for medical applications [14, 15].…”

Breaking free from vascular confinement: status and prospects for submicron ultrasound contrast agents

“…Epstein and Plesset theoretically predicted that unencapsulated bubbles smaller than 1 μm should dissipate in less than 0.02 seconds—before they can be detected or characterized, and long before passing from a peripheral vein to the end organ 12 seconds later . The presence of an encapsulating shell reduces this surface tension and inhibits diffusion thereby prolonging circulation times, and there is evidence that with the appropriate shell material selection, persistence in circulation can be considerable enough to permit practical applications .…”