Investigating the influence of cationic surfactants with varied alkyl chain lengths on nanobubble characteristics

Abstract

Nanobubbles in pure water have a negative charge, leading to strong electrostatic repulsion, contributing to their remarkable stability. However, introducing cationic surfactants can alter this charge to a positive one, affecting the nanobubble properties. This study investigates the influence of cationic surfactants with varying alkyl chain lengths on the properties of nanobubbles generated by ultrasonic cavitation. The results showed each surfactant addition significantly affects nanobubble size, concentration, and zeta potential. The nanobubbles became smaller and exhibited an increasing magnitude of zeta potential as the alkyl chain length increased, approaching the critical micelle concentration (CMC). The nanobubble concentration increased until it reached the CMC of the surfactants. Zeta potential values were in the range of −22.81 – 61.84 mV, with an average diameter of 171.5 – 275 nm and a concentration of 9.22 × 108 – 2.91 × 109 bubbles/mL. The Gibbs adsorption equation was applied to study the adsorption dynamics of the cationic surfactant molecules. Furthermore, the stability of the nanobubbles in the presence of these surfactants was investigated based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. This study provides a comprehensive understanding of how the alkyl chain length of cationic surfactants affects the nanobubble properties, paving the way for future research and applications. © 2025