Replace The Preparation Of Nano Air Bubbles And Temperature On The Impact Of Research

The discovery of nanobubbles resulted from research into the long rangehydrophobic attractive force (LRHAF) between hydrophobic bodies in aqueoussolution. Since the first experimental evidence by Blake and Kitchener, the debateover the mechanism of the LRHAF has been active. It is now clear that in many casesthe “hydrophobic” force measured was an artifact due to the presence of gaseousdomains called nanobubbles at the liquid–hydrophobic solid interface. Opticalmethods for observing nanobubbles are unsuitable as the bubbles are smaller than thewavelength of light. AFM is the most powerful device for monitoring the nanobubblesat the solid-liquid interface, but the contact mode AFM (CMAFM) is not effective asthe probing force tends to be too high for the soft nanobubbles. The most directevidence of nanobubbles accumulation at the water–hydrophobic solid interfacecomes from tapping mode AFM (TMAFM) images on a variety of hydrophobicsurfaces. Since then, nanobubbles had attracted increasing attention in various fields.There are many methods to producing nanobubbles including direct immersing,electrolysis, liquid heating and exchange of two solvents. The method of exchangingalcohol-water was used to generate nanobubbles widely and proved to be an effectivemethod that could generate large amount nanobubbles on varied surfaces with highrepeatability. It was also possible to generate nanobubbles by replacing other organicsolvents with water. However, exchange of organic solvents with water has somelimitations. For example, it can not be applied on biomembranes and some organicpollutants maybe introduced by alcohol. So some novel methods should be developed.In this paper, for producing interfacial nanobubbles, a systematic experiment,called temperature difference method, was carried out by replacing low temperaturewater (LTW) with high temperature water (HTW) at the highly oriented pyrolyticgraphite (HOPG)–water interface. The results showed that the temperature differencemethod can produce nanobubbles at the HOPG surface in a certain temperature range.The confirmation of the existence of nanobubbles has been carried out by using phaseimaging of AFM, contact angle and degassing process. When the temperature of HTW lower than37°C, the height, lateral size and number of nanobubbles wereincreased with the temperature. The height and lateral size of nanobubbles reachedtheir maximum at37°C, but the number of nanobubbles reached its summit at38°C.In order to explain the phenomena of nanobubbles, we calculated the total volume ofnanobubbles in an area of1μm2. The results showed that the total volume reached itsmaximum value at37°C, which indicated that this temperature was very suitable forthe gas releasing and the formation of nanobubbles.The results also showed that the contact angles of nanobubbles on hydrophobicHOPG surface in a stable range （160°–170°）. This may be relevant with thecharacters of the substrate. Compared with the method of exchanging alcohol-water,the nanobubbles were smaller than those produced by the temperature differencemethod. The results showed that the radius of curvature of nanobubbles variedbetween200nm and1000nm.Not only nanobubbles but also other gaseous states could be observed throughthe temperature difference method. It was found that various gas accumulation states,including nanobubbles, pancake-like gas layers, and the coexistence of nanobubbleson top of pancake-like gas layers, could be present at the same time. The apparentheight of the pancake-like gas layer was about2.5nm and the diameter was about700nm. The apparent heights of those two layers from the surface were about1.5nm and10nm, respectively. The characteristics and reasons for the formation were consistentwith previous work.We also used Soft X-ray Testing Technology (STXM) to investigate thenanobubbles filled with carbon dioxide which produced by the temperature differencemethod. The results showed that there was a strong absorption peak near the carbondioxide feature absorption peak. This verified the existence of nanobubbles at thesolid-liquid interface. Furthermore, we also obtained the inner composition and otherinformation of nanobubbles by STXM.