Effect of surface curvature and wettability on the shape of nanobubble and hollow structure of gold nanoparticles

This report discusses how the shape of the heterogeneous nucleation surface affects the formation of hydrogen nanobubbles, which are used in fabricating the hollow structure of gold nanoparticles. The hydrogen nanobubbles nucleate and grow through a supersaturation mechanism where hydrogen atoms are generated during the electrochemical process. The concave surface of a cylindrical anodic aluminum oxide (AAO) pore facilitates the homogeneous nucleation of hydrogen nanobubbles without the need for a three-phase contact line. This makes AAO pores useful as templates for synthesizing spherical hollow gold structures (HAuNPs) via a disproportionation reaction and electro less process. In contrast, the flat surface of polydimethylsiloxane (PDMS) on the electrochemical chip can be utilized to produce spherical caps of hydrogen nanobubbles and bowl-shaped gold nanoparticles (BAuNPs) due to its low interaction energy. Additionally, the shape of BAuNPs can be adjusted by modifying the surface wettability, which is related to the water contact angle. A hydrophobic substrate produces a smaller contact angle for hydrogen nanobubbles compared to hydrophilic substrates. However, the variation in the contact angle of hydrogen nanobubbles is much less than the change in the water contact angle of the substrate. Furthermore, as the water contact angle of the substrate increases, the size of the hydrogen nanobubbles decreases.