Siphon-type Washing Technique with Liquids Containing Microbubbles for Removing Soiled Models from Solid Surfaces

This study investigated the synergistic effect of dispersed microbubble (MB) liquids and siphon-type washing on the removal of starch paste, a model food soil, from five substrate materials with different surface properties: polytetrafluoroethylene, acrylic resin, glass, aluminum, and stainless steel. The cleaning performance was quantitatively evaluated through mass loss measurements and washing rate calculations. The influence of MB size distribution, stability, and surfactant type (anionic, cationic, and nonionic) on the detergency mechanism was systematically investigated. MB dispersions in tap water achieved a maximum washing rate enhancement ratio of 1.56 across all substrates. However, surfactant addition exhibited divergent effects on MB-enhanced cleaning: anionic surfactants [linear alkylbenzene sulfonate] significantly improved detergency, nonionic surfactants [polyoxyethylene (23) lauryl ether] showed moderate enhancement, whereas cationic surfactants [benzalkonium chloride] resulted in diminished or negligible cleaning performance on specific substrates. Characterization of MB dynamics revealed that surfactant-containing systems generated smaller bubbles with reduced stability and increased susceptibility to collapse, while MBs in tap water exhibited superior size retention and longevity. A positive correlation between washing rate enhancement and static contact angle reduction indicated that interfacial wettability modification is a critical factor in MB-assisted cleaning. The proposed detergency mechanism involves electrostatic interaction between negatively charged MB interfaces and soil particles, modulated by surfactant adsorption behavior at the gas-liquid interface. The vertical upward flow pattern characteristic of siphon-type washing was found to synergistically exploit MB buoyancy, resulting in enhanced soil detachment compared to conventional horizontal flow systems. These findings demonstrate that optimizing MB generation conditions, surfactant selection, and hydrodynamic flow configurations can significantly enhance cleaning efficiency for soil removal applications.