Adhesion force and the character of surfaces immersed in seawater

Abstract

A new method to measure adhesion force, or that force that holds surfaces in molecular contact, is used to quantify the effect of natural surface films on adhesion between surfaces immersed in seawater. Results of measurements demonstrate that bacterial films significantly modify surface adhesion and that the resulting interfacial force is nearly independent of bulk material composition. Where surfaces are hydrophilic and of similar surface charge, as is typical of surfaces in seawater, formation of bacterial films should cause a marked increase in adhesion force. A reduction in adhesion force observed for surfaces in seawater of low biological activity is attributed to adsorption of a surface active conditioning film, while a further reduction in adhesion force sometimes observed under bloom conditions remains unexplained. A broad range of adhesion forces corresponding to different sites on a surface can be understood in terms of surface microheterogeneity. Adhesion force measurements may be key for understanding steady state aggregate size, the timing of the sinking of blooms, and formation of oxygen-minimum layers. Understanding the nature of surfaces immersed in seawater is essential to understanding particle aggregation and disaggregation and the effects that these processes have on sedimentation of particulate matter in the ocean. The dynamics of particles in seawater has been the subject of many experimental and theoretical treatments in the