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Bulk nanobubbles are a novel nanoscale bubble system with unusual properties which challenge our understanding of bubble behavior. Because of their extraordinary longevity, their existence is still not widely accepted as they are often attributed to the presence of supramolecular structures or contaminants. Nonetheless, bulk nanobubbles are attracting increasing attention in the literature, but reports generally lack objective evidence that the observed nano-entities are indeed nanobubbles. In this paper, we use various physical and chemical analytical techniques to provide multiple evidence that the nano-entities produced mechanically in pure water by a continuous high-shear rotor-stator device or acoustic cavitation and spontaneously by water−ethanol mixing are indeed gas-filled domains. We estimate that the results presented here combined provide conclusive proof that bulk nanobubbles do exist and they are stable. This paper should help close the debate about the existence of bulk nanobubbles and, hence, enable the scientific community to rather focus on developing the missing fundamental science in this area.

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A new technique for generating bulk nanobubble suspensions has been developed based on Henry's law which states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.

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The purpose of this work was to understand the effect of the acoustic cavitation on the alkaline hydrolysis of wool and compare it with a conventional method of steam based alkaline hydrolysis. In acoustic cavitation assisted alkaline hydrolysis, the effect of concentration of solid (wool) and alkali on the properties of wool were also investigated. In conventional alkaline hydrolysis, the experiments were carried in a laboratory scale autoclave at temperature of 120 °C and pressure of 2 bar for 15 min. While acoustic cavitation assisted hydrolysis was carried out using the untreated and treated wool, hydrolyzed samples were characterized using FTIR, TGA and DSC to find out the extent of structural degradation occurring as a result of the treatment. It was observed that both the processes resulted in to a cleavage of disulfide bonds in wool, which cross-link the protein chains and are responsible for the higher stability and lower solubility of wool. However, the acoustic assisted alkaline hydrolysis is an environmentally friendly and less energy intensive process as it was performed at room temperature. The wool hydrolysates produced using acoustic assisted alkaline hydrolysis could find a potential application in agricultural fields such as fertilizer, soil improvement additive, etc.

Bacterial biofilms are a cause of contamination in a wide range of medical and biological areas. Ultrasound is a mechanical energy that can remove these biofilms using cavitation and acoustic streaming, which generates shear forces to disrupt biofilm from its surface. The aim of this narrative review is to investigate the literature on the mechanical removal of biofilm using acoustic cavitation to identify the different operating parameters affecting its removal using this method. The properties of the liquid and the properties of the ultrasound have a large impact on the type of cavitation generated. These include gas content, temperature, surface tension, frequency of ultrasound and acoustic pressure. Many of these parameters require more research to understand their mechanisms in the area of ultrasonic biofilm removal and further research will help to optimise this method for effective removal of biofilms from different surfaces.