Effect of chemical and geometrical parameters influencing the wettability of smectite clay films

•The influence of exchangeable ions and size of particles on the wettability of clay films is presented.•In addition to Atomic Force Microscopy parameters, spatial correlation method used to determine the Hurst exponent and the spatial extension of roughness.•The nature of exchangeable cation influences the roughness of the clay films but it is the hydration energies of the respective cations that mainly control contact angle values.•For a given exchangeable cation, the size of clay particles influences surface roughness of films and hence contact angles.•Wettability of clays due to surface ions: efficiency of low salinity waterflooding.

The wettability of three swelling clays (beidellite, nontronite and montmorillonite) exchanged with different interlayer ions (Li+, Na+, K+ and Ca2+) was investigated by using the static sessile drop method for contact angle measurements. The results show that water contact angles on clay films vary as a function of the nature of the ion with a specific behaviour of K+-exchanged clays. The effect of various parameters influencing contact angle measurements such as relative humidity (RH), particle size and surface roughness has also been examined. RH has only a limited effect on contact angles even if drop stabilisation was observed. As far as the effect of particle size is concerned, the results obtained on montmorillonite of four different sizes show that the smallest angles are obtained on films of particles of the smallest sizes for a given exchangeable ion. This is clearly linked to differences in roughness that were deduced by analysing Atomic Force Microscopy experiments. In contrast, the nature of the exchangeable cation influences roughness in the order Li+ < Na+ < K+ < Ca2+ but this order does not correspond to that deduced from the evolution of contact angles, which confirms the influence of the nature of the cation on wettability.

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