A many-body dissipative particle dynamics study of fluid-fluid spontaneous capillary displacement

The fluid-fluid spontaneous capillary displacement is a model related to many important natural processes and industrial applications, such as groundwater remediation and oil recovery. To study the displacement process in microscale where experimental observations are hard to perform, computational simulations are an adequate approach. In the present work, we report a many-body dissipative particle dynamics (MDPD) simulation study on the fluid-fluid spontaneous capillary displacement. System parameters such as the wetting property of both fluids, the miscibility between them, and the capillary radius, can be adjusted independently and separately in the simulation, thus their influences on the spontaneous capillary displacement process can be observed individually. Based on our previous study of MDPD simulations on fluid imbibition, we are able to monitor the motion of the fluid-fluid interface in this spontaneous capillary displacement simulation accurately. Combined with the new method for three-phase contact angle calculation proposed in the present study, the displacement curve obtained is in good accordance with the theoretical description even in the very beginning of the spontaneous capillary displacement motion. Our findings provide microscopic information about the fluid-fluid spontaneous displacement process, and lay a basis for further studies on more complex systems.