Figure 7. Impact of disjoining pressure on water film thickness and wettability.

(a) Schematic of the various contributions of van der Waals (dashed line), structural (dotted line) and electrostatic (solid and dot-dash lines) on the disjoining pressure (modified from ref. 57). When the oil-water and mineral-water interfaces have the same polarity, the contribution of electrostatic forces is positive; when they have opposing polarity, the contribution is negative. The contribution of electrostatic forces is larger at low ionic strength (IS) than at high IS. (b) Total disjoining pressure corresponding to (a). Solid and dot-dash lines in show the disjoining pressure at low and high IS respectively when the interfaces have the same polarity; dot and dash lines show the disjoining pressure at low and high IS when the interfaces have opposing polarity. The labels c-e correspond to figures (c–e) which show schematically the water film on a rough mineral surface (sketched based on images from ref. 61 and insight from refs ⁶² and ⁶³). The mineral surfaces are water-wet where the film is stable, but can become oil-wet where the film has collapsed.