The Solid Liquid Interface Nano Bubbles Generation And Nature Of Research

he existence of gas nanobubbles in liquids was first inferred from thelong-ranged attractions between hydrophobic solid surfaces immersedin aqueous media. While the first nanobubble images were acquiredowing to the development of in situ scanning probe microscopy (SPM)techniques, namely tapping mode （which consisted of a conventionalAFM probe tip attached to a vibrating cantilever that scanned acrosssamples immersed in water）atomic force microscopy (AFM). Becausecontact mode AFM is not effective, as the probing force tends to betoo high for the soft nanobubbles. Since then, nanobubbles hadattracted increasing attention in various fields.In order to image nanobubbles by AFM, the flat substrates wereusually used, such as highly oriented pyrolytic graphite(HOPG), mica,gold, polystyrene and silicon surfaces hydrophobized by silannation. Forproduce nanobubbles on those surfaces, varied methods have beenintroduced including direct immersing, electrolysis, liquid heating andexchange of two solvents. The method of exchanging alcohol-waterwas used to generate nanobubbles widely and proved to be aneffective method that could generate large amount nanobubbles onvaried surfaces with high repeatability. It was also possible to generatenanobubbles by replacing other organic solvents with water. However,exchange of organic solvents with water has some limitations. Forexample, it can not be applied on some important substrates which aresoluble in the organic solvent such as organic coatings orbiomembranes.How to produce nanobubbles repeatedly on a delete surface withsufficient amount is a key issue in nanobubbles research. Alcohol-waterexchange could generate nanobubbles ascribe greatly alcoholcontains higher concentration of dissolved gas than that in water. However, it is not clear if this mechanism would work when exchangingwater with the relatively low concentrations of dissolved gas such as saltsolutions. In this paper, we employed NaCl solutions with differentconcentrations to replace water on HOPG surface. We found thatnanobubbles could indeed be generated. Nanobubbles could beapparently observed when the NaCl concentration was as low as0.15M and their densities increased with the salt concentrations. When theconcentration of NaCl was higher than2.00M， the number ofnanobubbles increased slowly and nearly kept a constant. Thecharacteristics of nanobubbles merging，with its contact angle round164°were consistent with the results obtained by other scientists. Wealso showed that the dissolved gas played an important role in theformation process of nanobubbles.Based on the experimental results, nanobubbles could be exist inalcohol, which is considered to be rarely happened in water. Inaddition, the period of HOPG surface exposed to the air is related to theamount of nanobubbles. Soft X-ray Testing Technology(STXM) was alsoapplied to investigate the nanobubbles, which proved thatnanobubbles exist in the buck phase.