Study On The Property Of Nanobubbles By Advanced Nano-detection Techniques

The study of nanobubbles developed rapidly in the last decade,and it has become a research hotspot in interfacial science nowadays.It was demonstrated that nanobubbles provide an increasing impact on many fields including environment,biology,medicine,medical care etc.The fundamental research on nanobubble presented a guiding effect for its future applications in more fields and directions.Actually,the nanobubble itself has many important scientific questions.Firstly,although many mechanisms were proposed to explain the stability of nanobubble,there were still a lot of arguments on these mechanisms.In addition,there are few studies on the existence and basic properties of bulk nanobubbles,actually,the application value of bulk nanobubble was much higher than interfacial nanobubble.Thus,more convictive experiments were needed in order to prove such theoretical models.Besides,limited by detective method,researches on inside information of nanobubble were also lacking,however,it was the most powerful information to understand and explain the stability of interfacial nanobubble as well as bulk nanobubble.Based on the above issues,this paper proposed a simple approach to discriminate nanobubble from organic nanodroplet by using new atomic force microscopy?AFM?technique combined with Force Volume mode.Using advanced synchrotron radiation techniques including scanning transmission X-ray microscopy?STXM?and hard X-ray fluorescence,combined with nanosight tracking analysis technique,the interfacial behavior,internal information as well as internal gases density of nanobubble were investigated for the first time.According to the research content,this thesis can be divided into the following parts.First,we provide an easy way to distinguish nanobubble from organic nanodroplet.In view of the current debate about the nanobubble is contaminant or not,this paper selected polydimethylsiloxane?PDMS?as the representative contamination.Herein,a systematic measurement and comparison of nanobubble and PDMS nanodroplet was carried out by using PF-QNM mode in AFM.During the experiment,a simple and reproducible method to generate a large number of PDMS nanodroplets was presented firstly.By comparing their size,contact angle,and stiffness,it was found that nanobubbles could not been distinguished from PDMS nanodroplets from these information.Finally,the Force Volume model was used to study the mechanical information of the nanobubble and PDMS nanodroplet,as a peculiar plateau in both the approach and retraction curves was found on nanobubble.However,they were linearly changing on PDMS nanodroplet.In this way,by the featured plateau in the force curve on nanobubbles,we could able to distinguish nanobubbles from PDMS nanodroplets directly in AFM study.Furthermore,as the internal information was crucial to explaining the stability of nanobubble,we investigated and analyzed single nanobubble by using scanning transmission X-ray microscopy?STXM?.In the experiment,electrochemically generated oxygen nanobubbles were measured by STXM for their 2-D images,afterwards they were do stack scanning near the oxygen K edge to obtain their chemical properties.It was confirmed that the component of nanobubble inside are indeed oxygen gas.More importantly,the density of nanobubble inside had been estimated by optical density?OD?calculation and multiple linear least-squares curve fitting method.The result showed that the gas density inside nanobubble was about39.3 times as ambient air.Meanwhile,a high concentration of oxygen was also found dissolving in the water surrounding nanobubble,and its concentration was more than1000 times as normal O₂ solubility.This oversaturation environment should be the key factor to stabilize nanobubble for a long time.In the last,chemical information,number and size as well as the inside density of bulk nanobubbles and microbubbles were studied by using hard X-ray fluorescence and nanosight tracking analysis.Krypton?Kr?nanobubbles and microbubbles were produced by gas compression method.After a micro X-ray mapping,we acquired the2-D images of Kr microbubbles.Next we obtained the absorption density of Kr in water solution by X-ray fluorescence spectra.Combined with the mean concentration and size of nanobubbles in the same system of water solution measured by Nanosight,we showed the calculation process of Kr density inside nanobubble which was existing in water.