Micellization Transformations of Sodium Oleate Induced by Gas Nucleation

Enhancing ultrasound applications through shell-less nanobubbles: A study on acoustic and optical properties

Histotripsy employs acoustic inertial cavitation to mechanically destroy tissue, producing acellular debris. While introducing bubbles can lower the cavitation threshold and enhance treatment efficiency, micrometer-scale bubbles struggle to penetrate tissues effectively. Shell-less nanobubbles, with their high internal pressure, stability, negatively charged surfaces, and unique lifetimes ranging from weeks to months, offer a promising alternative. However, their interactions with ultrasound remain unexplored. This study used a claw-type pump nanobubble generator to produce nanobubbles and employed acoustic and optical methods to observe their behavior under high-intensity ultrasound exposure. The results demonstrated that the device generated nanobubble solutions with an average particle size of 107 nm, a concentration of 1.94 × 109 particles/mL, a lifetime exceeding one week, and a zeta potential of -21.2 mV. Acoustic and optical observations further revealed that nanobubble solutions reduced the inertial cavitation threshold of the liquid from 26.5 MPa to 10.3 MPa. These findings suggest a potential strategy to enhance the efficiency of ultrasound histotripsy treatments.

Monitoring effects of hydrodynamic cavitation pretreatment of sodium oleate on the aggregation of fine diaspore particles through small-angle laser scattering

Hydrodynamic cavitation (HC) enhanced fine particle aggregation could be largely due to the generation of tiny bubbles and their role in bridging particles. However, the lack of adequate characterizations of aggregates severally limits our further understanding of the associated aggregation behaviors. In this study, the aggregation of fine diaspore particles was comparatively investigated in sodium oleate (NaOl) solutions with and without HC pretreatment through the small-angle laser scattering (SALS) technique in a shear-induced aggregation (SIA) system. Results showed that HC pretreatment caused the formation of bulk nanobubbles (BNBs), which significantly modified the particle interactions and thereby modified the size and mass fractal dimension (Df) of aggregates under different SIA conditions. Although HC pretreatment did not noticeably alter the gradual change trend of aggregate size and structure characteristics under specific variables, BNBs bridging facilitated the aggregation process towards the diffusion-limited cluster aggregation model, resulting in the formation of larger but looser aggregates. This effect was more pronounced under relatively high NaOl concentrations. Apart from BNBs, the aggregation was also affected by cavitation bubbles formed during shear cavitation, which was more significant under high stirring intensity conditions (i.e., 1800 rpm) than the low stirring intensity conditions (i.e., 600 rpm).

The effect of preparation time and aeration rate on the properties of bulk micro-nanobubble water using hydrodynamic cavitation

Fundamental research on bulk micro-nanobubbles (BMNBs) has grown rapidly due to the demand for their industrial applications and potential role in interfacial sciences. This work focuses on examining properties of such bubbles, including the number, concentration, zeta potential, and surface tension in water. For this purpose, BMNBs were generated by the hydrodynamic cavitation (HC) mechanism. Distilled water and air in the experiments were the liquid and gas phases, respectively. The characterization of bulk microbubbles (BMBs) and bulk nanobubbles (BNBs) were performed through focused beam reflectance measurement (FBRM) and nanoparticle tracking analysis (NTA) techniques, respectively. Zeta potential and surface tension of aqueous solutions were measured at different time and aeration rates. The results showed that aeration rate and preparation time had an important role in the properties of BNBs (concentration, bubble size, and surface charge) and BMBs (number, and bubble size). The instability of BMBs led to the rapid changes in the dissolved oxygen (DO) content in the water. The number of BMBs decreased when preparation time and aeration rate increased, but their size remained constant. By enhancing the preparation time and aeration rate, the concentration of BNBs improved first and then reduced. Additionally, the surface tension of an aqueous solution containing BNBs was significantly lower than that of pure water.