The influence of pore wettability on the dynamics of imbibition and drainage

Using large-scale molecular-dynamic (MD) simulations, we have shown previously that the classical Lucas–Washburn equation commonly employed to describe capillary imbibition and drainage should be modified to include dynamic contact-angle effects. In addition, we have demonstrated how these effects can be accounted for using the molecular-kinetic theory of dynamic wetting. In a further publication, we presented theoretical arguments and experimental evidence that the velocity of wetting depends on the intrinsic wettability of the solid surface in such a way that there exists an optimum contact angle at which the velocity of wetting is a maximum. Here, we combine these ideas to show how the maximum speeds of capillary imbibition and drainage are affected both by the pore wettability and the pressures used to drive capillary displacement. In particular, we introduce the concept of dynamic wetting transitions (DWTs) and discuss how these limit displacement efficiency and can be manipulated by controlling pore wettability. The results of this work may be beneficial in optimising the performance of capillary processes such as those involved in oil recovery.