Investigating the nano-bubbles aggregation in two-phase systems: A molecular dynamics study.

• The nano-bubbles aggregation in Argon two-phase systems on a Pt substrate have been investigated. • The growth rate of the individual bubbles can be effectively modified with the number or distances of the heat sources. • Whatever the gap between two adjacent heats are smaller, the size, lifespan and stability of the bubbles has increased. • As soon as the existence of a film layer of vapor molecules between two neighboring bubbles, bubbles aggregation phenomena occur. • The spacing between two adjacent heats related to neighboring bubbles aggregation or separation is represented. These days, understanding the nano-bubble aggregation has attracted lot of attentions in various fields from medicine to industries. In the present work, by means of molecular dynamics simulation, effects of surface conditions on nano-bubbles aggregation in two-phase systems have been studied. Hence, in the argon two-phase system, two heat sources have been installed on a Pt substrate and their distance has been changed: From the first to seventh system, the gap between these two surface-mounted heat sources is 46.80, 39.90, 31.20, 24.30, 23.40, 11.70, and 00.00 Å, respectively. Corresponding to the simulation results, the effect of the number of heat sources and their distances on the individual-bubbles growth rate is quite evident: whatever the spacing between two adjacent heats are smaller, the formed nano-bubbles are more stable or larger as well, and have longer lifespan. Besides, according to the calculation of the changes in quantities of the bubble contact angle (CA/deg.), size (H/Å), diameter of the cross-section area (L/Å), and thickness of the outer layer (A/Å), it was observed that each of these nano-bubbles, which have the same formation conditions and exist simultaneously in the equilibrium system, behave differently. Interestingly, by reducing the distance between the two sources in the range of 31.20–11.70 Å, owing to the existence of a film layer of vapor molecules between two neighboring nano-bubbles, the bubbles aggregation phenomena occur. At last, if the gap between the heat two sources becomes zero, an ultra-stable nano-bubble, which will has the largest size, lifetime and stability, is observed. [ABSTRACT FROM AUTHOR]