Cleaning solid surfaces with liquid interfaces and foams: From theory to applications

Abstract

All personal and industrial cleaning sectors search for environmentally friendly methods to clean contaminated solid surfaces. Having relied for a long time on chemical and physico-chemical means with non-negligible environmental impact, these sectors are increasingly exploring the use of physical phenomena to improve cleaning efficiency. We summarise here recent progress in the area of cleaning methods that exploit the physical properties of liquid interfaces created by liquid menisci, bubbles, drops or foams. The high energy of these interfaces leads to a complex interplay between (1) interfacial forces, (2) viscous stresses created by flow fields under confinement, and (3) the capacity to adsorb solid and liquid contaminations. In appropriately designed cleaning processes, this interplay can reach an astounding efficiency, in many cases even with pure water, i.e. in the absence of any detergent. We will also show that whilst foams have always been assumed to be a mere side product of cleaning processes, recent research puts in evidence that they can actually be highly efficient cleaning agents, provided that their physical properties are properly chosen. We discuss a wide range of examples in which different interface-based cleaning methods have been investigated, including solid and liquid contaminations, or biological contaminations (bacteria, biofilms and biofouling).