THE ROLE OF WATER PURITY IN EMULSIFICATION AND REMOVAL OF OIL FROM SOLID SURFACES

Sammanfattning: Detergents are broadly used in our everyday life for cleaning and washing procedures. They are however, a source of water pollution and can have a negative effect on human health and the environment. To reduce their negative impact, a new trend of using only pure water for washing and cleaning applications is being implemented. However, a scientific basis needs to be established first, as the mechanisms and the effectiveness of this method are not fully understood. In this work, we aim to investigate the effect of water purity on the removal of oil from surfaces and the stability of colloidal systems. To do that, two purified water grades are compared with non-purified tap water and 10 mM NaCl solution. Results from measurement of oil film mass before and after water contact and Quartz Crystal Microbalance with Dissipation (QCM-D) indicate that purified water grades can wash a surface more efficiently than non-purified water grades. Contact angle measurements show that pure water facilitates the cleaning process while spreading of oil on plastic surfaces indicates that electrostatic interactions have an important role in the system. Visual observations of o/w emulsions, show that purified water grades redisperse the oil better. We hypothesize that the mechanism behind the cleaning and washing without detergents relies on the electrostatic interactions. To further investigate the effect of salt on cleaning mechanisms, we performed zeta potential measurements. Results indicate that salt has a negative effect on the stability of the particles.