Study On Preparation Of Nano - Bubbles By Open Temperature Difference Method And Its Influencing Factors

Now, the human life is closely linked with interface phenomenon, because it is ubiquitous in various kinds of chemical, biological and colloidal systems. So, the research on interface problem has been a hot and difficulty research to scientists. Water is a common material in our daily life, and relate to interface phenomenon, the research about interface water is more conspicuous. On solid-liquid interface have a strong mutual attraction and it is called as long-ranged attractions between hydrophobic(LRHAF). According to research LRHAF, the solid-liquid interface nanobubbles are put forward by the researches. However, in the classical thermodynamic theory, the nanobubbles are considered to be unstable at room temperature in water. For the past few years, with the more research on hydrophobic surface, many phenomenons support the presence of nanobubbles on solid-liquid interface. The existence of nanobubbles has been proved by neutron reflection(NR) and atomic force microscope(AFM), especially imaging by AFM, confirm the existence of nanobubbles effectively.So far, the most powerful means of imaging solid-liquid interface nanobubbles is atomic force microscope(AFM). In order to image nanobubbles by AFM, the flat substrates are usually used, such as highly oriented pyrolytic graphite(HOPG), mica, gold, polystyrene and so on. Besides, the formation of nanobubbles methods are also researched, such as exchange of two different solvent, direct immersing, electrochemical method and so on. The method of exchanging alcohol-water was used to generate nanobubbles widely and proved to be an effective method that can generate large amount nanobubbles on varied surfaces with high repetitively. However, some important substrates which are soluble in the organic solvent or easy to introduce organic contamination to the system. To overcome these shortages, some new methods of generating nanobubbles should be found. Temperature difference methods and different dissolved gas change method open a new way on production of nanobubbles.For the analysis of the two methods, we know that using lower dissolved gas solution to replace higher dissolved gas solution will generate nanobubbles. Some recent studies have shown that nanobubble formation is affected by temperature and the amount of dissolved gas. So, we establish a new method to generate nanobubbles in opening system. The result show that nanobubbles are generated when LTDW touched the HOPG. Through producing the nanobubbles by this 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. In order to describe the properties of nanobubbles easier, we have studied the effect of dissolved gas and substrate temperature. When the dissolved oxygen is higher, it is easier to generate nanobubbles on HOPG surface. Also, the number of nanobubbles increases with HOPG temperature and reaches its maximum at 42℃. When the temperature of HOPG continues to increase, the number of nanobubbles will decrease.In the experiment we also explore the effects of contaminant on nanobubbles, when the probe, water and substrate are polluted, the imaging and production of nanobubbles will be effected. In addition, the conclusion is obtained that nanobubbles are not contaminant by Raman scattering spectroscopy.