Study On Nano - Bubbles Produced By Different Gas - Containing Aqueous Solution Replacement Method And Its Physical Properties

As interfacial phenomenon is closely related to our life, the research on the problem of interface has been a hotspot and difficulty research to scientists. And as the water is one of the most common liquid in our daily life, the research about the nature of water on the interface is more conspicuous. The discovery of nanobubbles resulted from research into the long range hydrophobic attractive force (LRHAF) between hydrophobic bodies in aqueous solution. In the classical thermodynamic theory, the nanobubbles in water at room temperature are considered to be not stable. In recent years, with the deepening of the research on the hydrophobic surface, more and more phenomenon supports strongly the presence of nanobubbles on solid-liquid interface. Recently the existence of nanobubbles has been supported by various results from neutron reflection(NR), surface force apparatus(SFA) and atomic force microscopy(AFM), especially from the studies of direct imaging by AFM which supported strongly the presence of nanobubbles.At present, the most powerful means of direct detection of solid-liquid interface nanobubbles is atomic force microscope (AFM). In order to image nanobubbles by AFM, the flat substrates were usually used, such as highly oriented pyrolytic graphite(HOPG), mica, gold, polystyrene and silicon surfaces hydrophobized by silannation. At present the formation of nanobubbles has been examined in some experiments, some methods have been established to intentionally produce a large number of nanobubbles, such as direct immersing, liquid heating, electrochemical reaction and exchange of two different solvent. The method of exchanging alcohol-water was used to generate nanobubbles widely and proved to be an effective method that could generate large amount nanobubbles on varied surfaces with high repeat ability. It was also possible to generate nanobubbles by replacing other organic solvents with water. However, exchange of organic solvents with water has some defects and limitations. On the one hand, it cannot be applied on some important substrates which are soluble in the organic solvent such as organic coatings or biomembranes. On the other hand, it is easy to introduce contaminations to the system for organic solvents. To overcome these shortages, some novel methods of producing nanobubbles should be proposed. As the put forward of methods by exchanging water with NaCl solution and by changing temperature difference, we can opens up a new way of thinking on nanobubbles generated method.The two methods had no organic solvent, by which organic pollutants cannot be introduced. And they found that these two methods to produce nanobubbles both are using lower dissolved gas solution (respectively, salt water, hot water) to replace higher dissolved gas solution (water respectively, and the cold water). Some recent studies show that the supersaturation of the gas in is not the necessary condition to produce nanobubbles. Two main factors are temperature and the amount of dissolved gas. It follows that for unsaturated system, nanobubbles may also be generated. In this paper, for producing interfacial nanobubbles, a systematic experiment was carried out by replacing water with different amount of dissolved gas at the highly oriented pyrolytic graphite (HOPG)-water interface. The results show that the existence of the dissolved gas difference can produce nanobubbles on the hydrophobic HOPG surface at a certain amount. Through producing the nanobubbles by the dissolved gas difference method at different scanning parameter, different imaging mode, and the influence of tip to bubbles, we confirmed the possible conditions that generate nanobubbles and the existence of nanobubbles. Through the method of replacing water with different dissolved gas to produce nanobubbles, with the increase of dissolved gas different, the number of bubbleshas increased and the particle size of bubbles decreases gradually. In order to describe the properties of nanobubbles easier, we calculated the total volume of nanobubbles per square micron. The results found that with the increase of dissolved gas different, the total volume gas in per square micron has increased, too. Solutions show that, in the replacement process, the amount of gas emitting is bigger in the solution of bigger dissolved gas difference. So the nanobubbles can also generate easier.Under the condition of the same dissolved gas difference, we also studied the influence of nanobubbles in different concentrations of water replacement. Results showed that under the condition of the same dissolved gas difference, with the increase of dissolved gas in water, the number of bubbles has increased and the total volume of nanobubbles per square micron decreases gradually. But its effect is less obvious than the effect of dissolved gas difference.Based on the experimental results, the nanobubbles can produce easier on the hydrophobic HOPG surface than on the hydrophilic mica surface. In addition, we found that the replacement order and basal place time are also related to the amount of nanobubbles. The experiment also found that nanobubbles have the trend of growing easier along the steps on the surface.