The case for managed energetic rinsing in surface finishing operations involving aqueous processes

Water rinsing is an essential process in many surface finishing activities. It facilitates removal of chemical residues from surfaces between active processing steps, so providing a barrier against progressive contamination and any resulting dysfunction of process sequences. However, as 'rinses' in general are not commercial products their management typically becomes the sole responsibility of the finisher who may not have sufficient insight into rinsing technology to be able to optimise their function. Constraints on water usage detract from effective rinsing where solely volume of rinse water is relied upon. If the dynamics of rinsing are fully understood, the focused use of energy can enable improved rinsing action with minimal water use. A critical factor is the relationship between water and micro-rough surfaces. The degree of roughness of a surface has a profound influence on the ability of water to wet its surface whilst displacing air or other liquids already present. Deliberately textured surfaces can be difficult to rinse in this respect by accident of their design. Surfaces apparently smooth to the naked eye may be significantly rough at the micro and 'nano' level and thus be very difficult to rinse in water without some adequate applied force. Referring to classic research on the wettability of structured surfaces by Wenzel and Cassie, and Baxter, energy-based strategies for the optimisation of water rinsing in surface finishing processes are described.