Surface and colloidal mechanisms of surfactant free cleaning

Due to growing concerns about the environmental effects of detergents, research has shifted toward eco-friendly cleaning methods, including the use of purified water. This study aims to increase our understanding of how the properties of purified water can be used to achieve effective washing with minimal surfactant use. We investigated the removal of common soils, such as olive oil, from hydrophilic and hydrophobic surfaces and examined interactions among olive oil, water, and fabric. To further examine the broader impact of purified water, bacterial viability after treatment with different purified grades was investigated. For hydrophilic surfaces, thin vaseline and thick oil films were washed at varying temperatures and washing cycles. Quartz Crystal Microbalance with Dissipation Monitoring data showed that most thin films were removed within two cycles, while higher temperatures improved efficiency. For thicker films, we were able to divide the washing process into two regimes (exponential and linear), where each one is governed by different washing mechanisms and stability principles. For hydrophobic surfaces, two approaches were tested. First, the pH of purified water was increased with traces of NaOH, and second, small amounts of lipase were added. Both methods significantly enhance cleaning efficiency. The pH-adjusted pure water promotes deprotonation of fatty acids in olive oil and facilitates oil removal from surfaces through roll-up and interfacial tension reduction mechanisms. The added lipase can hydrolyse olive oil into more water-soluble products, which can act as natural surfactants. For interactions between cotton, olive oil, and water, spatially resolved SAXS data revealed that water and oil interact with cotton at different length scales, and that washing partially redistributes and removes oil. Finally, we showed that isothermal calorimetry is an excellent method for assessing bacterial viability and that multiple washing cycles and prolonged incubation can reduce bacterial survival.