Adhesion under water: surface energy considerations

Contact angles for a set of probe liquids on solid surfaces have been used to determine the components of the solid surface energies. By the use of suitable combining rules, such data have then been used to calculate the work of adhesion of oil onto various solid surfaces under water. A surprising outcome of such studies is that the order of strengths of adhesion of ‘liquid’ to solid surfaces under water is opposite to that for adhesion in air. For example, oily materials do not adhere well to ‘non-stick’ surfaces such as PTFE in air but adhere strongly under water. Such considerations are extended to the adhesion of bacteria to solid surfaces under water and the possible role of adsorbed protein layers in the adhesion process. In these systems, the predictions are born out by direct observations of bacterial fouling taken from the recent literature.